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Sample records for break galaxy close

  1. Record-breaking ancient galaxy clusters

    NASA Astrophysics Data System (ADS)

    2003-12-01

    A tale of two record-breaking clusters hi-res Size hi-res: 768 kb Credits: for RDCS1252: NASA, ESA, J.Blakeslee (Johns Hopkins Univ.), M.Postman (Space Telescope Science Inst.) and P.Rosati, Chris Lidman & Ricardo Demarco (European Southern Observ.) for TNJ1338: NASA, ESA, G.Miley (Leiden Observ.) and R.Overzier (Leiden Obs) A tale of two record-breaking clusters Looking back in time to when the universe was in its formative youth, the Advanced Camera for Surveys (ACS) aboard the NASA/ESA Hubble Space Telescope captured these revealing images of two galaxy clusters. The image at left, which is made with an additional infrared exposure taken with the European Southern Observatory’s Very Large Telescope, shows mature galaxies in a massive cluster that existed when the cosmos was 5000 million years old. The cluster, called RDCS1252.9-2927, is as massive as ‘300 trillion’ suns and is the most massive known cluster for its epoch. The image reveals the core of the cluster and is part of a much larger mosaic of the entire cluster. Dominating the core are a pair of large, reddish elliptical galaxies [near centre of image]. Their red colour indicates an older population of stars. Most of the stars are at least 1000 million years old. The two galaxies appear to be interacting and may eventually merge to form a larger galaxy that is comparable to the brightest galaxies seen in present-day clusters. The red galaxies surrounding the central pair are also cluster members. The cluster probably contains many thousands of galaxies, but only about 50 can be seen in this image. The full mosaic (heic0313d) reveals several hundred cluster members. Many of the other galaxies in the image, including several of the blue galaxies, are foreground or background galaxies. The colour-composite image was assembled from two observations (through i and z filters) taken between May and June 2002 by the ACS Wide Field Camera, and one image with the ISAAC instrument on the VLT taken in 2002

  2. Dust Attenuation in Lyman Break Galaxies

    NASA Astrophysics Data System (ADS)

    Vijh, U. P.; Witt, A. N.; Gordon, K. D.

    2002-05-01

    In order to determine the star formation history of the universe from deep surveys at UV/optical rest frame wavelengths, one must have a reliable estimate of the attenuation factor for galaxies at high redshifts. That star formation is heavily enshrouded in dust is no longer in doubt. The exact nature, geometry and the amount of this dust/attenuation needs to be known out to high redshifts. We present an analysis of UV attenuation of a large (N=906) sample of Lyman Break Galaxies (LBGs) (data provided by Charles C. Steidel, Caltech) by internal dust. Using spectral energy distributions (SEDs) from the PEGASE stellar evolutionary synthesis model we apply dust corrections to the G - R colours using the Witt & Gordon (2000) dust attenuation models, to arrive at the UV attenuation factors. We show that the dust in the LBG sample exhibits SMC-like characteristics rather than MW type, and that the dust geometry is best represented by a clumpy shell configuration. The dust attenuation in individual LBGs is found to be proportional to their rest frame UV luminosities, i.e. their current star formation rate. We find that the average luminosity-weighted dust attenuation factor at 1600 Å is in the range 10-40 which agrees with the upper limit set by the FIR background. We also find that most of the star formation at 2 < z < 4 occurs in galaxies with luminosity ~ 1011-1012Lsun, equivalent to of the present day Luminous Infra-Red Galaxies and the Ultra Luminous Infra-Red Galaxies. This work has been supported by NASA grants NAG5-9376 and NAG5-9202, which we acknowledge with gratitude.

  3. The submillimeter spectral break in Seyfert galaxies

    NASA Technical Reports Server (NTRS)

    Engargiola, G.; Harper, D. A.; Elvis, Martin; Willner, S. P.

    1988-01-01

    Observations have been made of four Seyfert 1 galaxies at 155 microns and three at 370 microns. Two of the galaxies were detected at 155 microns, but none was detected at 370 microns. The 155 microns data and the strong upper limits at 370 microns show that the infrared continua decrease sharply beyond 100-155 microns. These observations depict a clear spectral difference between radio-loud and radio-quiet active galactic nuclei. The limits on the 100-370 microns spectral slope are consistent either with synchrotron self-absorption of a nonthermal source or with thermal dust emission similar to that arising from the disks of normal galaxies. The 155 microns flux from NGC 4151 is spatially extended through a radius of at least 48 arcsec, arguing for substantial dust emission at wavelengths greater than 80 microns and an even shorter cutoff wavelength for nonthermal emission from the active nucleus. The spectral breaks implied by our data suggest that the nuclear nonthermal sources must be smaller than about 10 light hours.

  4. SIZING UP Ly{alpha} AND LYMAN BREAK GALAXIES

    SciTech Connect

    Malhotra, Sangeeta; Rhoads, James E.; McLinden, Emily; Finkelstein, Steven L.; Hathi, Nimish; Nilsson, Kim; Pirzkal, Norbert

    2012-05-10

    We measure the sizes for a sample of 174 Ly{alpha}-selected galaxies with broadband imaging with the Hubble Space Telescope. Over the redshift range 2.25 < z < 6, Ly{alpha}-selected galaxies have a characteristic, constant, small size in rest-frame ultraviolet (UV) light. Coupled with a characteristic star formation intensity (i.e., UV luminosity per unit area), this can explain their non-evolving ultraviolet continuum luminosity function. This is in contrast to Lyman break galaxies (LBGs) over the same redshift range, which have been previously shown to increase in linear size as H(z){sup -1}. The compact physical size seems to be a critical determining factor in whether a galaxy will show Ly{alpha} emission or not. The L{sub *} of LBGs and its evolution with redshift can be derived from a simple model where the star formation intensity has an upper limit set by feedback processes, independent of redshift. The increase in L{sub *} of LBGs is mainly driven by the increase in linear size over redshifts for z = 2-7. Since Ly{alpha} galaxies do not grow in linear size, they do not show an increase in L{sub *}.

  5. Symmetry Breaking and Optical Negative Index of Closed Nanorings

    NASA Astrophysics Data System (ADS)

    Kante, Boubacar; Park, Yong-Shik; O'Brien, Kevin; Shuldman, Daniel; Lanzillotti-Kimura, Norberto; Wong, Zi; Yin, Xiaobo; Zhang, Xiang; UC Berkeley Team

    2013-03-01

    We report the first experimental demonstration of broadband negative-index metamaterial made solely of closed metallic nanorings. Using symmetry breaking that negatively couples the discrete nanorings, we measured negative phase delay in our composite chess metamaterial. Our approach open avenues towards topological nanophotonics with on demand linear and non-linear responses.

  6. Nonlinear Scattering by a Partially Closed Surface Breaking Crack

    NASA Astrophysics Data System (ADS)

    Poznić, M.; Pecorari, C.

    2005-04-01

    Nonlinear scattering from a partially closed, two dimensional, surface-breaking crack in a homogenous linear elastic half-space is considered. The boundary conditions along the crack are described in terms of the mechanics of two distributions of nonlinear springs. Both the linear and the nonlinear acoustic response of the crack shows to be highest when the surface breaking crack is insonified by a shear vertical wave at the longitudinal critical angle. The increased efficiency of generation of higher harmonics under the above circumstances suggests a means of localizing the nonlinear crack. Finally, the model provides a simple interpretation of the highly localized nonlinear response of delaminations observed in thin composites.

  7. X-Ray Emission from Ultraviolet Luminous Galaxies and Lyman Break Galaxies

    NASA Technical Reports Server (NTRS)

    Hornschemeier, Ann; Ptak, A. F.; Salim, S.; Heckman, T. P.; Overzier, R.; Mallery, R.; Rich, M.; Strickland, D.; Grimes, J.

    2009-01-01

    We present results from an XMM mini-survey of GALEX-selected Ultraviolet-Luminous Galaxies (UVLGs) that appear to include an interesting subset that are analogs to the distant (3Break Galaxies (LBGs). The 2-10 kev X-ray emission of LBGs appear to be broadly similar to that of galaxies in the local Universe, possibly indicating similarity in the production of accreting binaries over large evolutionary timescales in the Universe. We have detected luminous X-ray emission from one UVLG that permits basic X-ray spectroscopic analysis, and have direct X-ray constraints on a total of 6 UVLGs. We find evidence for likely large scatter in the assumed X-ray/star-formation rate relation for LBGs.

  8. Symmetry breaking and optical negative index of closed nanorings

    NASA Astrophysics Data System (ADS)

    Kanté, Boubacar; Park, Yong-Shik; O'Brien, Kevin; Shuldman, Daniel; Lanzillotti-Kimura, Norberto D.; Jing Wong, Zi; Yin, Xiaobo; Zhang, Xiang

    2012-11-01

    Metamaterials have extraordinary abilities, such as imaging beyond the diffraction limit and invisibility. Many metamaterials are based on split-ring structures, however, like atomic orbital currents, it has long been believed that closed rings cannot produce negative refractive index. Here we report a low-loss and polarization-independent negative-index metamaterial made solely of closed metallic nanorings. Using symmetry breaking that negatively couples the discrete nanorings, we measured negative phase delay in our composite ‘chess metamaterial’. The formation of an ultra-broad Fano-resonance-induced optical negative-index band, spanning wavelengths from 1.3 to 2.3 μm, is experimentally observed in this structure. This discrete and mono-particle negative-index approach opens exciting avenues towards symmetry-controlled topological nanophotonics with on-demand linear and nonlinear responses.

  9. The Stellar Populations of Lyman Break Galaxies at z ~ 5

    NASA Astrophysics Data System (ADS)

    Yabe, Kiyoto; Ohta, Kouji; Iwata, Ikuru; Sawicki, Marcin; Tamura, Naoyuki; Akiyama, Masayuki; Aoki, Kentaro

    2009-03-01

    We present the results of spectral energy distribution (SED) fitting analysis for Lyman break galaxies (LBGs) at z ~ 5 in the Great Observatories Origins Deep Survey North (GOODS-N) and its flanking fields (the GOODS-FF). With the publicly available Infrared Array Camera (IRAC) images in the GOODS-N and IRAC data in the GOODS-FF, we constructed the rest-frame UV to optical SEDs for a large sample (~100) of UV-selected galaxies at z ~ 5. Comparing the observed SEDs with model SEDs generated with a population synthesis code, we derived a best-fit set of parameters (stellar mass, age, color excess, and star formation rate) for each of the sample LBGs. The derived stellar masses range from 108 to 1011 M sun with a median value of 4.1 × 109 M sun. Comparison with z = 2-3 LBGs shows that the stellar masses of z ~ 5 LBGs are systematically smaller by a factor of 3-4 than those of z = 2-3 LBGs in a similar rest-frame UV luminosity range. The star formation ages are relatively younger than those of the z = 2-3 LBGs. We also compared the results for our sample with other studies for the z = 5-6 galaxies. Although there seem to be similarities and differences in the properties, we could not conclude its significance. We also derived a stellar mass function of our sample by correcting for incompletenesses. Although the number densities in the massive end are comparable to the theoretical predictions from semianalytic models involving active galactic nucleus feedback, the number densities in the low-mass part are smaller than the model predictions. By integrating the stellar mass function down to 108 M sun, the stellar mass density at z ~ 5 is calculated to be (0.7-2.4) ×107 M sun Mpc-3. The stellar mass density at z ~ 5 is dominated by the massive part of the stellar mass function. Compared with other observational studies and the model predictions, the mass density of our sample is consistent with general trend of the increase of the stellar mass density with time.

  10. Dust properties of Lyman-break galaxies at z ~ 3

    NASA Astrophysics Data System (ADS)

    Álvarez-Márquez, J.; Burgarella, D.; Heinis, S.; Buat, V.; Lo Faro, B.; Béthermin, M.; López-Fortín, C. E.; Cooray, A.; Farrah, D.; Hurley, P.; Ibar, E.; Ilbert, O.; Koekemoer, A. M.; Lemaux, B. C.; Pérez-Fournon, I.; Rodighiero, G.; Salvato, M.; Scott, D.; Taniguchi, Y.; Vieira, J. D.; Wang, L.

    2016-03-01

    Context. Since the mid-1990s, the sample of Lyman-break galaxies (LBGs) has been growing thanks to the increasing sensitivities in the optical and in near-infrared telescopes for objects at z> 2.5. However, the dust properties of the LBGs are poorly known because the samples are small and/or biased against far-infrared (far-IR) or submillimeter (submm) observations. Aims: This work explores from a statistical point of view the far-IR and submm properties of a large sample of LBGs at z ~ 3 that cannot be individually detected from current far-IR observations. Methods: We select a sample of 22, 000 LBGs at 2.5 galaxies included in the sample allows us to split it into several bins as a function of UV luminosity (LFUV), UV continuum slope (βUV), and stellar mass (M∗) to better sample their variety. We stack in PACS (100 and 160 μm) images from PACS Evolution Probe survey (PEP), SPIRE (250, 350 and 500 μm) images from the Herschel Multi-tied Extragalactic Survey (HerMES) programs, and AzTEC (1.1 mm) images from the Atacama Submillimeter Telescope Experiment (ASTE). Our stacking procedure corrects the biases induced by galaxy clustering and incompleteness of our input catalogue in dense regions. Results: We obtain the full infrared spectral energy distributions (SED) of subsamples of LBGs and derive the mean IR luminosity as a function of LFUV, βUV, and M∗. The average IRX (or dust attenuation) is roughly constant over the LFUV range, with a mean of 7.9 (1.8 mag). However, it is correlated with βUV, AFUV = (3.15 ± 0.12) + (1.47 ± 0.14) βUV, and stellar mass, log (IRX) = (0.84 ± 0.11)log (M∗/ 1010.35) + 1.17 ± 0.05. We investigate using a statistically controlled stacking analysis as a function of (M∗, βUV), the dispersion of the IRX-βUV and IRX-M∗ plane. On the one hand, the dust attenuation shows a departure of up to 2.8 mag above the mean IRX-βUV relation when log (M

  11. Starbursts: From 30 Doradus to Lyman Break Galaxies

    NASA Astrophysics Data System (ADS)

    de Grijs, R.; González Delgado, R. M.

    2005-05-01

    Starbursts are important features of early galaxy evolution. Many of the distant, high-redshift galaxies we are able to detect are in a starbursting phase, often apparently provoked by a violent gravitational interaction with another galaxy. In fact, if we did not know that major starbursts existed, these conference proceedings testify that we would indeed have difficulties explaining the key properties of the Universe! The enhanced synergy facilitated by the collaboration among observers using cutting-edge ground and space-based facilities, theorists and modellers has made these proceedings into a true reflection of the state of the art in this very rapidly evolving field.

  12. Electrons in a closed galaxy model of cosmic rays

    NASA Technical Reports Server (NTRS)

    Ramaty, R.; Westergaard, N. J.

    1976-01-01

    The consistency of positrons and electrons was studied using a propagation model in which the cosmic rays are stopped by nuclear collisions or energy losses before they can escape from the galaxy (the closed-galaxy model). The fact that no inconsistency was found between the predictions and the data implies that the protons which produce the positrons by nuclear reactions could have their origin in a large number of distant sources, as opposed to the heavier nuclei which in this model come from a more limited set of sources. The closed-galaxy model predicts steep electron and positron spectra at high energies. None of these are inconsistent with present measurements; but future measurements of the spectrum of high-energy positrons could provide a definite test for the model. The closed-galaxy model also predicts that the interstellar electron intensity below a few GeV is larger than that implied by other models. The consequence of this result is that electron bremsstrahlung is responsible for about 50% of the galactic gamma-ray emission at photon energies greater than 100 MeV.

  13. Comparing Local Starbursts to High-Redshift Galaxies: A Search for Lyman-Break Analogs

    NASA Technical Reports Server (NTRS)

    Petty, Sara M.; de Mello, Duila F.; Gallagher III, John S.; Gardner, Jonathan; Lotz, Jennifer M.; Mountain, C. Matt; Smith, Linda J.

    2008-01-01

    We compare the restframe far-ultraviolet (FUV) morphologies of 8 nearby interacting and starburst galaxies (Arp 269, M 82, Mrk 08, NGC 0520, NGC 1068, NGC 3079, NGC 3310, NGC 7673) with 54 galaxies at z approx.1.5 and 46 galaxies at z approx.4 in the Great Observatories Origins Deep Survey (GOODS) images taken with the Advanced Camera for Surveys onboard the Hubble Space Telescope. We calculate the Gini coefficient (G), the second order moment of 20% of the brightest pixels (M20), and the S ersic index (n). We find that 20% (11/54) of z approx.1.5 and 37% (17/46) of z approx.4 galaxies are bulge-like, using G and M20. We also find approx.70% of the z approx.1.5 and z approx.4 galaxies have exponential disks with n > 0.8. The 2D profile combined with the nonparametric methods provides more detail, concerning the nature of disturbed systems, such as merger and post-merger types. We also provide qualitative descriptions of each galaxy system and at each redshift. We conclude that Mrk 08, NGC 3079, and NGC 7673 have similar morphologies as the starburst FUV restframe galaxies and Lyman-break galaxies at z approx.1.5 and 4, and determine that they are Lyman-break analogs.

  14. Dark matter distribution in the Coma cluster from galaxy kinematics: breaking the mass-anisotropy degeneracy

    NASA Astrophysics Data System (ADS)

    Łokas, Ewa L.; Mamon, Gary A.

    2003-08-01

    We study velocity moments of elliptical galaxies in the Coma cluster using Jeans equations. The dark matter distribution in the cluster is modelled by a generalized formula based upon the results of cosmological N-body simulations. Its inner slope (cuspy or flat), concentration and mass within the virial radius are kept as free parameters, as well as the velocity anisotropy, assumed independent of position. We show that the study of line-of-sight velocity dispersion alone does not allow us to constrain the parameters. By a joint analysis of the observed profiles of velocity dispersion and kurtosis, we are able to break the degeneracy between the mass distribution and velocity anisotropy. We determine the dark matter distribution at radial distances larger than 3 per cent of the virial radius and we find that the galaxy orbits are close to isotropic. Due to limited resolution, different inner slopes are found to be consistent with the data and we observe a strong degeneracy between the inner slope α and concentration c; the best-fitting profiles have the two parameters related with c= 19-9.6α. Our best-fitting Navarro-Frenk-White profile has concentration c= 9, which is 50 per cent higher than standard values found in cosmological simulations for objects of similar mass. The total mass within the virial radius of 2.9h-170 Mpc is 1.4 × 1015h-170 Msolar (with 30 per cent accuracy), 85 per cent of which is dark. At this distance from the cluster centre, the mass-to-light ratio in the blue band is 351h70 solar units. The total mass within the virial radius leads to estimates of the density parameter of the Universe, assuming that clusters trace the mass-to-light ratio and baryonic fraction of the Universe, with Ω0= 0.29 +/- 0.1.

  15. CAN AGN FEEDBACK BREAK THE SELF-SIMILARITY OF GALAXIES, GROUPS, AND CLUSTERS?

    SciTech Connect

    Gaspari, M.; Brighenti, F.; Temi, P.

    2014-03-01

    It is commonly thought that active galactic nucleus (AGN) feedback can break the self-similar scaling relations of galaxies, groups, and clusters. Using high-resolution three-dimensional hydrodynamic simulations, we isolate the impact of AGN feedback on the L {sub x}-T {sub x} relation, testing the two archetypal and common regimes, self-regulated mechanical feedback and a quasar thermal blast. We find that AGN feedback has severe difficulty in breaking the relation in a consistent way. The similarity breaking is directly linked to the gas evacuation within R {sub 500}, while the central cooling times are inversely proportional to the core density. Breaking self-similarity thus implies breaking the cool core, morphing all systems to non-cool-core objects, which is in clear contradiction with the observed data populated by several cool-core systems. Self-regulated feedback, which quenches cooling flows and preserves cool cores, prevents dramatic evacuation and similarity breaking at any scale; the relation scatter is also limited. The impulsive thermal blast can break the core-included L {sub x}-T {sub x} at T {sub 500} ≲ 1 keV, but substantially empties and overheats the halo, generating a perennial non-cool-core group, as experienced by cosmological simulations. Even with partial evacuation, massive systems remain overheated. We show that the action of purely AGN feedback is to lower the luminosity and heat the gas, perpendicular to the fit.

  16. Physical properties of local star-forming analogues to z ˜ 5 Lyman-break galaxies

    NASA Astrophysics Data System (ADS)

    Greis, Stephanie M. L.; Stanway, Elizabeth R.; Davies, Luke J. M.; Levan, Andrew J.

    2016-07-01

    Intense, compact, star-forming galaxies are rare in the local Universe but ubiquitous at high redshift. We interpret the 0.1-22 μm spectral energy distributions of a sample of 180 galaxies at 0.05 < z < 0.25 selected for extremely high surface densities of inferred star formation in the ultraviolet. By comparison with well-established stellar population synthesis models, we find that our sample comprises young (˜60-400 Myr), moderate mass (˜6 × 109 M⊙) star-forming galaxies with little dust extinction (mean stellar continuum extinction Econt(B - V) ˜ 0.1) and find star formation rates of a few tens of solar masses per year. We use our inferred masses to determine a mean specific star formation rate for this sample of ˜10-9 yr-1, and compare this to the specific star formation rates in distant Lyman-break galaxies (LBGs), and in other low-redshift populations. We conclude that our sample's characteristics overlap significantly with those of the z ˜ 5 LBG population, making ours the first local analogue population well tuned to match those high-redshift galaxies. We consider implications for the origin and evolution of early galaxies.

  17. Indirect Evidence for Escaping Lyman Continuum Photons in Local Lyman Break Galaxy Analogs

    NASA Astrophysics Data System (ADS)

    Alexandroff, Rachael; Heckman, Timothy M.; Borthakur, Sanchayeeta; Overzier, Roderik

    2015-01-01

    A population of early star-forming galaxies is the leading candidate for the re-ionization of the universe. It is still unclear, however, what conditions and physical processes would enable a significant fraction of the ionizing photons to escape from these gas-rich galaxies. In addition, studies of high redshift galaxies have yet to uncover a large sample of galaxies with the required high escape fraction of ionizing photons.We have uncovered a sample of local analogs to high-redshift, star-forming Lyman Break Galaxies (LBGs) called Lyman Break Analogs (LBAs) by matching the Sloan Digital Sky Survey (SDSS) and Galaxy Evolution Explorer (GALEX) catalogs. These galaxies are remarkably similar to LBGs in their properties-- morphology, size, UV luminosity, SFR, mass, velocity dispersion, metallicity and dust content. We obtained HST COS far-UV spectroscopy plus ancillary multi-waveband data of a sample of 22 LBAs to look for indirect evidence of escaping ionizing radiation (leakiness).We measure three parameters: (1) the residual intensity in the cores of saturated interstellar low-ionization absorption-lines, which indicates incomplete covering by that gas in the galaxy. (2) The relative amount of blue-shifted Lyman alpha line emission, which can indicate the existence of holes in the neutral hydrogen on the front-side of the galaxy outflow, and (3) the relative weakness of the [SII] optical emission lines that trace matter-bounded HII regions. We find all three diagnostics agree well with one another. Finally, we find the strongest correlation between these leakiness indicators and both the compactness of the galactic star-forming region (size and star formation rate/area) and the speed of the galactic outflow. This suggests that extreme feedback- a high intensity of ionizing radiation and strong pressure from both radiation and a hot galactic wind- combines to create significant holes in the neutral gas. These results not only shed new light on the physical

  18. A Resolved Map of the Infrared Excess in a Lyman Break Galaxy at z = 3

    NASA Astrophysics Data System (ADS)

    Koprowski, M. P.; Coppin, K. E. K.; Geach, J. E.; Hine, N. K.; Bremer, M.; Chapman, S.; Davies, L. J. M.; Hayashino, T.; Knudsen, K. K.; Kubo, M.; Lehmer, B. D.; Matsuda, Y.; Smith, D. J. B.; van der Werf, P. P.; Violino, G.; Yamada, T.

    2016-09-01

    We have observed the dust continuum of 10 z = 3.1 Lyman break galaxies with the Atacama Large Millimeter/submillimeter Array at ˜450 mas resolution in Band 7. We detect and resolve the 870 μm emission in one of the targets with a flux density of S 870 = 192 ± 57 μJy, and measure a stacked 3σ signal of S 870 = 67 ± 23 μJy for the remaining nine. The total infrared luminosities are L 8-1000 = (8.4 ± 2.3) × 1010 L ⊙ for the detection and L 8-1000 = (2.9 ± 0.9) × 1010 L ⊙ for the stack. With Hubble Space Telescope Advanced Camera for Surveys I-band imaging we map the rest-frame UV emission on the same scale as the dust, effectively resolving the “infrared excess” (IRX = L FIR/L UV) in a normal galaxy at z = 3. Integrated over the galaxy we measure IRX = 0.56 ± 0.15, and the galaxy-averaged UV slope is β = -1.25 ± 0.03. This puts the galaxy a factor of ˜10 below the IRX-β relation for local starburst nuclei of Meurer et al. However, IRX varies by more than a factor of 3 across the galaxy, and we conclude that the complex relative morphology of the dust relative to UV emission is largely responsible for the scatter in the IRX-β relation at high-z. A naive application of a Meurer-like dust correction based on the UV slope would dramatically overestimate the total star formation rate, and our results support growing evidence that when integrated over the galaxy, the typical conditions in high-z star-forming galaxies are not analogous to those in the local starburst nuclei used to establish the Meurer relation.

  19. A Resolved Map of the Infrared Excess in a Lyman Break Galaxy at z = 3

    NASA Astrophysics Data System (ADS)

    Koprowski, M. P.; Coppin, K. E. K.; Geach, J. E.; Hine, N. K.; Bremer, M.; Chapman, S.; Davies, L. J. M.; Hayashino, T.; Knudsen, K. K.; Kubo, M.; Lehmer, B. D.; Matsuda, Y.; Smith, D. J. B.; van der Werf, P. P.; Violino, G.; Yamada, T.

    2016-09-01

    We have observed the dust continuum of 10 z = 3.1 Lyman break galaxies with the Atacama Large Millimeter/submillimeter Array at ∼450 mas resolution in Band 7. We detect and resolve the 870 μm emission in one of the targets with a flux density of S 870 = 192 ± 57 μJy, and measure a stacked 3σ signal of S 870 = 67 ± 23 μJy for the remaining nine. The total infrared luminosities are L 8–1000 = (8.4 ± 2.3) × 1010 L ⊙ for the detection and L 8–1000 = (2.9 ± 0.9) × 1010 L ⊙ for the stack. With Hubble Space Telescope Advanced Camera for Surveys I-band imaging we map the rest-frame UV emission on the same scale as the dust, effectively resolving the “infrared excess” (IRX = L FIR/L UV) in a normal galaxy at z = 3. Integrated over the galaxy we measure IRX = 0.56 ± 0.15, and the galaxy-averaged UV slope is β = ‑1.25 ± 0.03. This puts the galaxy a factor of ∼10 below the IRX–β relation for local starburst nuclei of Meurer et al. However, IRX varies by more than a factor of 3 across the galaxy, and we conclude that the complex relative morphology of the dust relative to UV emission is largely responsible for the scatter in the IRX–β relation at high-z. A naive application of a Meurer-like dust correction based on the UV slope would dramatically overestimate the total star formation rate, and our results support growing evidence that when integrated over the galaxy, the typical conditions in high-z star-forming galaxies are not analogous to those in the local starburst nuclei used to establish the Meurer relation.

  20. Unveiling the Structure of Barred Galaxies at 3.6 μm with the Spitzer Survey of Stellar Structure in Galaxies (S4G). I. Disk Breaks

    NASA Astrophysics Data System (ADS)

    Kim, Taehyun; Gadotti, Dimitri A.; Sheth, Kartik; Athanassoula, E.; Bosma, Albert; Lee, Myung Gyoon; Madore, Barry F.; Elmegreen, Bruce; Knapen, Johan H.; Zaritsky, Dennis; Ho, Luis C.; Comerón, Sébastien; Holwerda, Benne; Hinz, Joannah L.; Muñoz-Mateos, Juan-Carlos; Cisternas, Mauricio; Erroz-Ferrer, Santiago; Buta, Ron; Laurikainen, Eija; Salo, Heikki; Laine, Jarkko; Menéndez-Delmestre, Karín; Regan, Michael W.; de Swardt, Bonita; Gil de Paz, Armando; Seibert, Mark; Mizusawa, Trisha

    2014-02-01

    We have performed two-dimensional multicomponent decomposition of 144 local barred spiral galaxies using 3.6 μm images from the Spitzer Survey of Stellar Structure in Galaxies. Our model fit includes up to four components (bulge, disk, bar, and a point source) and, most importantly, takes into account disk breaks. We find that ignoring the disk break and using a single disk scale length in the model fit for Type II (down-bending) disk galaxies can lead to differences of 40% in the disk scale length, 10% in bulge-to-total luminosity ratio (B/T), and 25% in bar-to-total luminosity ratios. We find that for galaxies with B/T >= 0.1, the break radius to bar radius, r br/R bar, varies between 1 and 3, but as a function of B/T the ratio remains roughly constant. This suggests that in bulge-dominated galaxies the disk break is likely related to the outer Lindblad resonance of the bar and thus moves outward as the bar grows. For galaxies with small bulges, B/T < 0.1, r br/R bar spans a wide range from 1 to 6. This suggests that the mechanism that produces the break in these galaxies may be different from that in galaxies with more massive bulges. Consistent with previous studies, we conclude that disk breaks in galaxies with small bulges may originate from bar resonances that may be also coupled with the spiral arms, or be related to star formation thresholds.

  1. X-Ray Properties of Lyman Break Galaxies in the Hubble Deep Field North Region

    NASA Technical Reports Server (NTRS)

    Nandra, K.; Mushotzky, R. F.; Arnaud, K.; Steidel, C. C.; Adelberger, K. L.; Gardner, J. P.; Teplitz, H. I.; Windhorst, R. A.; White, Nicholas E. (Technical Monitor)

    2002-01-01

    We describe the X-ray properties of a large sample of z approximately 3 Lyman Break Galaxies (LBGs) in the region of the Hubble Deep Field North, derived from the 1 Ms public Chandra observation. Of our sample of 148 LBGs, four are detected individually. This immediately gives a measure of the bright AGN (active galactic nuclei) fraction in these galaxies of approximately 3 per cent, which is in agreement with that derived from the UV (ultraviolet) spectra. The X-ray color of the detected sources indicates that they are probably moderately obscured. Stacking of the remainder shows a significant detection (6 sigma) with an average luminosity of 3.5 x 10(exp 41) erg/s per galaxy in the rest frame 2-10 keV band. We have also studied a comparison sample of 95 z approximately 1 "Balmer Break" galaxies. Eight of these are detected directly, with at least two clear AGN based on their high X-ray luminosity and very hard X-ray spectra respectively. The remainder are of relatively low luminosity (< 10(exp 42) erg/s, and the X-rays could arise from either AGN or rapid star-formation. The X-ray colors and evidence from other wavebands favor the latter interpretation. Excluding the clear AGN, we deduce a mean X-ray luminosity of 6.6 x 10(exp 40) erg/s, a factor approximately 5 lower than the LBGs. The average ratio of the UV and X-ray luminosities of these star forming galaxies L(sub UV)/L (sub X), however, is approximately the same at z = 1 as it is at z = 3. This scaling implies that the X-ray emission follows the current star formation rate, as measured by the UV luminosity. We use our results to constrain the star formation rate at z approximately 3 from an X-ray perspective. Assuming the locally established correlation between X-ray and far-IR (infrared) luminosity, the average inferred star formation rate in each Lyman break galaxy is found to be approximately 60 solar mass/yr, in excellent agreement with the extinction-corrected UV estimates. This provides an external

  2. DISCOVERY OF LYMAN BREAK GALAXIES AT z {approx} 7 FROM THE zFourGE SURVEY

    SciTech Connect

    Tilvi, V.; Papovich, C.; Tran, K.-V. H.; Labbe, I.; Straatman, C. M. S.; Spitler, L. R.; Glazebrook, K.; Kacprzak, G. G.; Persson, S. E.; Monson, A.; Quadri, R. F.; Kelson, D. D.; Van Dokkum, P.; Ashby, M. L. N.; Fazio, G. G.; Faber, S. M.; Ferguson, H. C.; Grogin, N. A.; Koekemoer, A. M.; and others

    2013-05-01

    Star-forming galaxies at redshifts z > 6 are likely responsible for the reionization of the universe, and it is important to study the nature of these galaxies. We present three candidates for z {approx} 7 Lyman break galaxies (LBGs) from a 155 arcmin{sup 2} area in the CANDELS/COSMOS field imaged by the deep FourStar Galaxy Evolution (zFourGE) survey. The FourStar medium-band filters provide the equivalent of R {approx} 10 spectroscopy, which cleanly distinguishes between z {approx} 7 LBGs and brown dwarf stars. The distinction between stars and galaxies based on an object's angular size can become unreliable even when using Hubble Space Telescope imaging; there exists at least one very compact z {approx} 7 candidate (FWHM {approx} 0.5-1 kpc) that is indistinguishable from a point source. The medium-band filters provide narrower redshift distributions compared with broadband-derived redshifts. The UV luminosity function derived using the three z {approx} 7 candidates is consistent with previous studies, suggesting an evolution at the bright end (M{sub UV} {approx} -21.6 mag) from z {approx} 7 to z {approx} 5. Fitting the galaxies' spectral energy distributions, we predict Ly{alpha} equivalent widths for the two brightest LBGs, and find that the presence of a Ly{alpha} line affects the medium-band flux thereby changing the constraints on stellar masses and UV spectral slopes. This illustrates the limitations of deriving LBG properties using only broadband photometry. The derived specific star-formation rates for the bright LBGs are {approx}13 Gyr{sup -1}, slightly higher than the lower-luminosity LBGs, implying that the star-formation rate increases with stellar mass for these galaxies.

  3. Optical-to-IR Photometric Properties of Lyman Break Galaxies in the HDF-North

    NASA Astrophysics Data System (ADS)

    Papovich, C.; Dickinson, M.; Ferguson, H.; NICMOS HDF--N GO Team

    1999-12-01

    We present the photometric properties of Lyman Break Galaxies (LBGs) in the Hubble Deep Field North (HDF--N) using deep seven--band photometry from WFPC2 (UBVI, Williams et al. 1996), NICMOS (JH, Dickinson et al. 2000), and newly derived Ks--band photometry from ground--based KPNO data (Dickinson 1997; Papovich & Dickinson 2000). For the 27 HDF galaxies with spectroscopic redshifts 2.0 ≲ z ≲ 3.5, our photometry spans rest frame wavelengths extending from the Lyman limit through rest--frame λ 0 ≳ 5000 Angstroms. In this poster, we compare the spectral energy distributions (SEDs) of the LBGs to empirical spectral templates from Kinney et al. (1996) and Coleman, Wu, & Weedman (1980), and to population synthesis models from Bruzual & Charlot (1996). We consider general constraints on galaxy ages, star formation histories, and extinction. By selection, the LBGs contain strong, blue UV continua. In general, they are well fit by local starburst templates. To fit the SEDs of specific galaxies, most require modest but non--zero reddening. At rest--frame optical wavelengths, many galaxies show evidence for significant contributions from longer lived (A and later) stars, but none appear to be dominated by old (red) stellar populations. In some cases, there may be significant broad band flux contributions from strong nebular emission lines ([N 2]+Hα , [O 3]+Hβ , [O 2]). We discuss the implications for the evolutionary history of these galaxies using these empirical results. Support for this work is provided by NASA through grant GO-07817.01-96A.

  4. Dust emission from the lensed Lyman break galaxy cB58

    NASA Astrophysics Data System (ADS)

    Baker, A. J.; Lutz, D.; Genzel, R.; Tacconi, L. J.; Lehnert, M. D.

    2001-06-01

    We detect 1.2 mm continuum emission from dust in the gravitationally lensed Lyman break galaxy MS 1512+36-cB58. Our detected flux is surprisingly low: relative to local starburst galaxies, cB58 appears to produce somewhat less far-IR emission than its UV reddening predicts. After comparing several different estimates of the source's dust content, we conclude that the apparent discrepancy is most likely related to uncertainty in its UV spectral slope. Alternate scenarios to account for a far-IR ``deficit'' which rely on a high dust temperature or differential magnification are less satisfactory. Our result underscores one of the risks inherent in characterizing the cosmic star formation history from rest-UV data alone.

  5. A Lyman Break Galaxy in the Epoch of Reionization from Hubble Space Telescope (HST) Grism Spectroscopy

    NASA Technical Reports Server (NTRS)

    Rhoads, James E.; Malhotra, Sangeeta; Stern, Daniel K.; Gardner, Jonathan P.; Dickinson, Mark; Pirzkal, Norbert; Spinrad, Hyron; Reddy, Naveen; Dey, Arjun; Hathi, Nimish; Grogin, Norman; Koekemoer, Anton; Peth, Michael A.; Cohen, Seth; Budavari, Tamas; Ferreras, Ignacio; Gronwall, Caryl; Haiman, Zoltan; Meurer, Gernhardt; Straughn, Amber N.

    2013-01-01

    Slitless grism spectroscopy from space offers dramatic advantages for studying high redshift galaxies: high spatial resolution to match the compact sizes of the targets, a dark and uniform sky background, and simultaneous observation over fields ranging from five square arcminutes (HST) to over 1000 square arcminutes (Euclid). Here we present observations of a galaxy at z = 6.57 the end of the reioinization epoch identified using slitless HST grism spectra from the PEARS survey (Probing Evolution And Reionization Spectroscopically) and reconfirmed with Keck + DEIMOS. This high redshift identification is enabled by the depth of the PEARS survey. Substantially higher redshifts are precluded for PEARS data by the declining sensitivity of the ACS grism at greater than lambda 0.95 micrometers. Spectra of Lyman breaks at yet higher redshifts will be possible using comparably deep observations with IR-sensitive grisms.

  6. SPECTROSCOPIC CONFIRMATION OF z {approx} 7 LYMAN BREAK GALAXIES: PROBING THE EARLIEST GALAXIES AND THE EPOCH OF REIONIZATION

    SciTech Connect

    Pentericci, L.; Fontana, A.; Castellano, M.; Grazian, A.; Boutsia, K.; Giallongo, E.; Maiolino, R.; Paris, D.; Santini, P.; Vanzella, E.; Cristiani, S.; Dijkstra, M.; Dickinson, M.; Giavalisco, M.; Moorwood, A.

    2011-12-20

    We present the final results from our ultra-deep spectroscopic campaign with FORS2 at the ESO Very Large Telescope (VLT) for the confirmation of z {approx_equal} 7 'z-band dropout' candidates selected from our VLT/Hawk-I imaging survey over three independent fields. In particular, we report on two newly discovered galaxies at redshift {approx}6.7 in the New Technology Telescope Deep Field. Both galaxies show an Ly{alpha} emission line with rest-frame equivalent widths (EWs) of the order of 15-20 A and luminosities of (2-4) Multiplication-Sign 10{sup 42} erg s{sup -1}. We also present the results of ultra-deep observations of a sample of i-dropout galaxies, from which we set a solid upper limit on the fraction of interlopers. Out of the 20 z-dropouts observed we confirm 5 galaxies at 6.6 < z < 7.1. This is systematically below the expectations drawn on the basis of lower redshift observations: in particular, there is a significant lack of objects with intermediate Ly{alpha} EWs (between 20 and 55 A). We conclude that the observed trend for the rising fraction of Ly{alpha} emission in Lyman break galaxies from z {approx} 3 to z {approx} 6 is most probably reversed from z {approx} 6 to z {approx} 7. Explaining the observed rapid change in the Ly{alpha} emitter fraction among the dropout population with reionization requires a fast evolution of the neutral fraction of hydrogen in the universe. Assuming that the universe is completely ionized at z = 6 and adopting a set of semi-analytical models, we find that our data require a change of the neutral hydrogen fraction of the order of {Delta}{chi}{sub H{sub i}}{approx}0.6 in a time {Delta}z {approx} 1, provided that the escape fraction does not increase dramatically over the same redshift interval.

  7. FAR-INFRARED PROPERTIES OF LYMAN BREAK GALAXIES FROM COSMOLOGICAL SIMULATIONS

    SciTech Connect

    Cen Renyue

    2011-12-15

    Utilizing state-of-the-art adaptive mesh refinement cosmological hydrodynamic simulations with ultra-high resolution (114 h{sup -1} pc) and a large sample size ({>=}3300 galaxies of stellar mass {>=}10{sup 9} M{sub Sun }), we show how the stellar light of Lyman break galaxies at z = 2 is distributed between optical/ultraviolet (UV) and far-infrared (FIR) bands. With a single scalar parameter for dust obscuration we can simultaneously reproduce the observed UV luminosity function for the entire range (3-100 M{sub Sun} yr{sup -1}) and extant FIR luminosity function at the bright end ({>=}20 M{sub Sun} yr{sup -1}). We quantify that galaxies more massive or having higher star formation rate (SFR) tend to have larger amounts of dust obscuration mostly due to a trend in column density and in a minor part due to a mass (or SFR)-metallicity relation. It is predicted that the FIR luminosity function in the range SFR = 1-100 M{sub Sun} yr{sup -1} is a power law with a slope of about -1.7. We further predict that there is a 'galaxy desert' at SFR{sub FIR} < 0.02(SFR{sub UV}/10 M{sub Sun} yr{sup -1}){sup 2.1} M{sub Sun} yr{sup -1} in the SFR{sub UV} - SFR{sub FIR} plane. Detailed distributions of SFR{sub FIR} at a fixed SFR{sub UV} are presented. Upcoming observations by the Atacama Large Millimeter Array should test this model. If confirmed, it validates the predictions of the standard cold dark matter model and has important implications on the intrinsic SFR function of galaxies at high redshift.

  8. SPECTROSCOPIC CONFIRMATION OF FAINT LYMAN BREAK GALAXIES NEAR REDSHIFT FIVE IN THE HUBBLE ULTRA DEEP FIELD

    SciTech Connect

    Rhoads, James E.; Malhotra, Sangeeta; Cohen, Seth; Grogin, Norman; Hathi, Nimish; Ryan, Russell; Straughn, Amber; Windhorst, Rogier A. Pirzkal, Norbert; Xu Chun; Koekemoer, Anton; Panagia, Nino; Dickinson, Mark; Ferreras, Ignacio; Gronwall, Caryl; Kuemmel, Martin; Walsh, Jeremy; Meurer, Gerhardt; Pasquali, Anna; Yan, H.-J.

    2009-05-20

    We present the faintest spectroscopically confirmed sample of z {approx} 5 Lyman break galaxies (LBGs) to date. The sample is based on slitless grism spectra of the Hubble Ultra Deep Field region from the Grism ACS Program for Extragalactic Science (GRAPES) and Probing Evolution and Reionization Spectroscopically (PEARS) projects, using the G800L grism on the Hubble Space Telescope Advanced Camera for Surveys. We report here confirmations of 39 galaxies, preselected as candidate LBGs using photometric selection criteria. We compare a 'traditional' V-dropout selection, based on the work of Giavalisco et al., to a more liberal one (with V - i > 0.9), and find that the traditional criteria are about 64% complete and 81% reliable. We also study the Ly{alpha} emission properties of our sample. We find that Ly{alpha} emission is detected in {approx}1/4 of the sample, and that the liberal V-dropout color selection includes {approx}55% of previously published line-selected Ly{alpha} sources. Finally, we examine our stacked two-dimensional spectra. We demonstrate that strong, spatially extended ({approx}1'') Ly{alpha} emission is not a generic property of these LBGs, but that a modest extension of the Ly{alpha} photosphere (compared to the starlight) may be present in those galaxies with prominent Ly{alpha} emission.

  9. The clustering and halo occupation distribution of Lyman-break galaxies at z ˜ 4

    NASA Astrophysics Data System (ADS)

    Park, Jaehong; Kim, Han-Seek; Wyithe, J. Stuart B.; Lacey, C. G.; Baugh, C. M.; Barone-Nugent, R. L.; Trenti, M.; Bouwens, R. J.

    2016-09-01

    We investigate the clustering of Lyman-break galaxies (LBGs) at z ˜ 4. Using the hierarchical galaxy formation model GALFORM, we predict, for the first time using a semi-analytical model with feedback from active galactic nuclei (AGN), the angular correlation function (ACF) of LBGs and find agreement within 3σ with new measurements of the ACF from surveys including the Hubble eXtreme Deep Field (XDF) and Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) field. Our simulations confirm the conclusion reached using independent models that although the predicted ACFs reproduce the trend of increased clustering with luminosity, the dependence is less strong than observed. We find that for the detection limits of the XDF field, central LBGs at z ˜ 4 predominantly reside in haloes of mass ˜1011-1012 h-1 M⊙ and that satellites reside in larger haloes of mass ˜1012-1013 h-1 M⊙. The model predicts fewer bright satellite LBGs at z ˜ 4 than is inferred from measurements of the ACF at small scales. By analysing the halo occupation distribution (HOD) predicted by the model, we find evidence that AGN feedback affects the HOD of central LBGs in massive haloes. This is a new high-redshift test of this important feedback mechanism. We investigate the effect of photometric errors in the observations on the ACF predictions. We find that the observational uncertainty in the galaxy luminosity reduces the clustering amplitude and that this effect increases towards faint galaxies, particularly on small scales. To compare properties of model with observed LBGs, this uncertainty must be considered.

  10. Evidence for Black Hole Growth in Local Analogs to Lyman Break Galaxies

    NASA Technical Reports Server (NTRS)

    Jia, Jianjun; Ptak, Andrew; Heckman, Timothy M.; Overzier, Roderik A.; Hornschemeier, Ann; LaMassa, Stephanie M.

    2011-01-01

    We have used XMM-Newton to observe six Lyman break analogs (LBAs): members of the rare population of local galaxies that have properties that are very similar to distant Lyman break galaxies. Our six targets were specifically selected because they have optical emission-line properties that are intermediate between starbursts and Type 2 (obscured) active galactic nuclei (AGNs). Our new X-ray data provide an important diagnostic of the presence of an AGN. We find X-ray luminosities of order 10(sup 42) erg per second and ratios of X-ray to far-IR lummositles that are higher than values in pure starburst galaxies by factors ranging from approximately 3 to 30. This strongly suggests the presence of an AGN in at least some of the galaxies. The ratios of the luminosities of the hard (2-10 keV) X-ray to [O III] emission line are low by about an order of magnitude compared with Type 1 AGN, but are consistent with the broad range seen in Type 2 AGN. Either the AGN hard X-rays are significantly obscured or the [O III] emission is dominated by the starburst. We searched for an iron emission line at approximately 6.4 ke V, which is a key feature of obscured AGNs, but only detected emission at the approximately 2sigma level. Finally, we find that the ratios of the mid-infrared (24 micrometer) continuum to [O III]lambda 5007 luminosities in these LBAs are higher than the values for Type 2 AGN by an average of 0.8 dex. Combining all these clues, we conclude that an AGN is likely to be present, but that the bolometric luminosity is produced primarily by an intense starburst. If these black holes are radiating at the Eddington limit, their masses would lie in the range of 10(sup 5) - 10(sup 6) solar mass. These objects may offer ideal local laboratories to investigate the processes by which black holes grew in the early universe.

  11. BREAKS IN THIN AND THICK DISKS OF EDGE-ON GALAXIES IMAGED IN THE SPITZER SURVEY OF STELLAR STRUCTURE IN GALAXIES (S{sup 4}G)

    SciTech Connect

    Comeron, Sebastien; Salo, Heikki; Laurikainen, Eija; Laine, Jarkko; Elmegreen, Bruce G.; Athanassoula, E.; Bosma, Albert; Knapen, Johan H.; Gadotti, Dimitri A.; Sheth, Kartik; Munoz-Mateos, Juan Carlos; Kim, Taehyun; Hinz, Joannah L.; Regan, Michael W.; Gil de Paz, Armando; Menendez-Delmestre, Karin; Seibert, Mark; Ho, Luis C.; Mizusawa, Trisha; Holwerda, Benne

    2012-11-10

    Breaks in the radial luminosity profiles of galaxies have until now been mostly studied averaged over disks. Here, we study separately breaks in thin and thick disks in 70 edge-on galaxies using imaging from the Spitzer Survey of Stellar Structure in Galaxies. We built luminosity profiles of the thin and thick disks parallel to midplanes and we found that thin disks often truncate (77%). Thick disks truncate less often (31%), but when they do, their break radius is comparable with that in the thin disk. This suggests either two different truncation mechanisms-one of dynamical origin affecting both disks simultaneously and another one only affecting the thin disk-or a single mechanism that creates a truncation in one disk or in both depending on some galaxy property. Thin disks apparently antitruncate in around 40% of galaxies. However, in many cases, these antitruncations are an artifact caused by the superposition of a thin disk and a thick disk, with the latter having a longer scale length. We estimate the real thin disk antitruncation fraction to be less than 15%. We found that the ratio of the thick and thin stellar disk mass is roughly constant (0.2 < M{sub T} /M{sub t} < 0.7) for circular velocities v{sub c} > 120 km s{sup -1}, but becomes much larger at smaller velocities. We hypothesize that this is due to a combination of a high efficiency of supernova feedback and a slower dynamical evolution in lower-mass galaxies causing stellar thin disks to be younger and less massive than in higher-mass galaxies.

  12. LATE-TIME OBSERVATIONS OF GRB 080319B: JET BREAK, HOST GALAXY, AND ACCOMPANYING SUPERNOVA

    SciTech Connect

    Tanvir, N. R.; O'Brien, P. T.; Wiersema, K.; Starling, R. L. C.; Rol, E.; Levan, A. J.; Svensson, K.; Fruchter, A. S.; Granot, J.; Jakobsson, P.; Fynbo, J.; Hjorth, J.; Curran, P. A.; Burrows, D. N.; Genet, F.

    2010-12-10

    The Swift-discovered GRB 080319B was by far the most distant source ever observed at naked-eye brightness, reaching a peak apparent magnitude of 5.3 at a redshift of z = 0.937. We present our late-time optical (Hubble Space Telescope, Gemini, and Very Large Telescope) and X-ray (Chandra) observations, which confirm that an achromatic break occurred in the power-law afterglow light curve at {approx}11 days post-burst. This most likely indicates that the gamma-ray burst (GRB) outflow was collimated, which for a uniform jet would imply a total energy in the jet E{sub jet} {approx}> 10{sup 52} erg. Our observations also show a late-time excess of red light, which is well explained if the GRB was accompanied by a supernova (SN), similar to those seen in some other long-duration GRBs. The latest observations are dominated by light from the host and show that the GRB took place in a faint dwarf galaxy (r(AB) {approx} 27.0, rest frame M{sub B} {approx} -17.2). This galaxy is small even by the standards of other GRB hosts, which is suggestive of a low-metallicity environment. Intriguingly, the properties of this extreme event-a small host and bright SN-are entirely typical of the very low luminosity bursts such as GRB 980425 and GRB 060218.

  13. Late-time Observations of GRB 080319B: Jet Break, Host Galaxy, and Accompanying Supernova

    NASA Astrophysics Data System (ADS)

    Tanvir, N. R.; Rol, E.; Levan, A. J.; Svensson, K.; Fruchter, A. S.; Granot, J.; O'Brien, P. T.; Wiersema, K.; Starling, R. L. C.; Jakobsson, P.; Fynbo, J.; Hjorth, J.; Curran, P. A.; van der Horst, A. J.; Kouveliotou, C.; Racusin, J. L.; Burrows, D. N.; Genet, F.

    2010-12-01

    The Swift-discovered GRB 080319B was by far the most distant source ever observed at naked-eye brightness, reaching a peak apparent magnitude of 5.3 at a redshift of z = 0.937. We present our late-time optical (Hubble Space Telescope, Gemini, and Very Large Telescope) and X-ray (Chandra) observations, which confirm that an achromatic break occurred in the power-law afterglow light curve at ~11 days post-burst. This most likely indicates that the gamma-ray burst (GRB) outflow was collimated, which for a uniform jet would imply a total energy in the jet E jet >~ 1052 erg. Our observations also show a late-time excess of red light, which is well explained if the GRB was accompanied by a supernova (SN), similar to those seen in some other long-duration GRBs. The latest observations are dominated by light from the host and show that the GRB took place in a faint dwarf galaxy (r(AB) ≈ 27.0, rest frame MB ≈ -17.2). This galaxy is small even by the standards of other GRB hosts, which is suggestive of a low-metallicity environment. Intriguingly, the properties of this extreme event—a small host and bright SN—are entirely typical of the very low luminosity bursts such as GRB 980425 and GRB 060218.

  14. A physical model for the redshift evolution of high-z Lyman-break galaxies

    NASA Astrophysics Data System (ADS)

    Jose, Charles; Srianand, Raghunathan; Subramanian, Kandaswamy

    2014-10-01

    We present a galaxy formation model to understand the evolution of stellar mass (M*)-UV luminosity relations, stellar mass functions and specific star formation rate (sSFR) of Lyman-break galaxies (LBGs) along with their UV luminosity functions (LFs) in the redshift range 3 ≤ z ≤ 8. Our models assume a physically motivated form for star formation in galaxies and model parameters are calibrated by fitting the observed UV LFs of LBGs. We find the fraction of baryons that gets converted into stars remains nearly constant for z ≥ 4 but shows an increase for z < 4. However, the rate of converting baryons into stars does not evolve significantly in the redshift range 3 ≤ z ≤ 8. Our model further successfully explains the M*-UV luminosity (MAB) correlations of LBGs. While our model predictions of stellar mass functions compare well with the inferred data from observations at the low-mass end, we need to invoke the Eddington bias to fit the high-mass end. At any given redshift, we find the sSFR to be constant over the stellar mass range 5 × 108-5 × 109 M⊙ and the redshift evolution of sSFR is well approximated by a form (1 + z)2.4 for 3 ≤ z ≤ 8 which is consistent with observations. Thus, we find that dark matter halo buildup in the ΛCDM model is sufficient to explain the evolution of UV LFs of LBGs along with their M*-MAB relations, the stellar mass functions and the sSFR for 3 ≤ z ≤ 8.

  15. Rest-Frame Mid-Infrared Detection of an Extremely Luminous Lyman Break Galaxy with the Spitzer Infrared Spectrograph (IRS)

    NASA Technical Reports Server (NTRS)

    Teplitz, H. I.; Charmandaris, V.; Armus, L.; Appleton, P. N.; Houck, J. R.; Soifer, B. T.; Weedman, D.; Brandl, B. R.; vanCleve, J.; Grillmair, C.; Uchid, K. I.

    2004-01-01

    We present the first rest-frame of approximately 4 microns detection of a Lyman break galaxy. The data were obtained using the 16 microns imaging capability of the Spitzer Infrared Spectrograph. The target object, J134026.44+634433.2, is an extremely luminous Lyman break galaxy at z=2.79, first identified in Sloan Digital Sky Survey (SDSS) spectra (as reported by Bentz et al.). The source is strongly detected with a flux of 0.94 +/- 0.02 mJy. Combining Spitzer and SDSS photometry with supporting ground-based J- and K-band data, we show that the spectral energy distribution is consistent with an actively star-forming galaxy. We also detect other objects in the Spitzer field of view, including a very red mid-infrared source. We find no evidence of a strong lens among the mid-infrared sources.

  16. A LYMAN BREAK GALAXY IN THE EPOCH OF REIONIZATION FROM HUBBLE SPACE TELESCOPE GRISM SPECTROSCOPY

    SciTech Connect

    Rhoads, James E.; Malhotra, Sangeeta; Cohen, Seth; Zheng Zhenya; Stern, Daniel; Dickinson, Mark; Pirzkal, Norbert; Grogin, Norman; Koekemoer, Anton; Peth, Michael A.; Spinrad, Hyron; Reddy, Naveen; Hathi, Nimish; Budavari, Tamas; Ferreras, Ignacio; Gardner, Jonathan P.; Gronwall, Caryl; Haiman, Zoltan; Kuemmel, Martin; Meurer, Gerhardt; and others

    2013-08-10

    We present observations of a luminous galaxy at z = 6.573-the end of the reionization epoch-which has been spectroscopically confirmed twice. The first spectroscopic confirmation comes from slitless Hubble Space Telescope Advanced Camera for Surveys grism spectra from the PEARS survey (Probing Evolution And Reionization Spectroscopically), which show a dramatic continuum break in the spectrum at rest frame 1216 A. The second confirmation is done with Keck + DEIMOS. The continuum is not clearly detected with ground-based spectra, but high wavelength resolution enables the Ly{alpha} emission line profile to be determined. We compare the line profile to composite line profiles at z = 4.5. The Ly{alpha} line profile shows no signature of a damping wing attenuation, confirming that the intergalactic gas is ionized at z = 6.57. Spectra of Lyman breaks at yet higher redshifts will be possible using comparably deep observations with IR-sensitive grisms, even at redshifts where Ly{alpha} is too attenuated by the neutral intergalactic medium to be detectable using traditional spectroscopy from the ground.

  17. INDECENT EXPOSURE IN SEYFERT 2 GALAXIES: A CLOSE LOOK

    SciTech Connect

    Tran, Hien D.; Lyke, J. E.; Mader, Jeff A.

    2011-01-10

    NGC 3147, NGC 4698, and 1ES 1927+654 are active galaxies that are classified as Seyfert 2s, based on the line ratios of strong narrow emission lines in their optical spectra. However, they exhibit rapid X-ray spectral variability and/or little indication of obscuration in X-ray spectral fitting, contrary to expectation from the active galactic nucleus (AGN) unification model. Using optical spectropolarimetry with LRIS and near-infrared spectroscopy with NIRSPEC at the W. M. Keck Observatory, we conducted a deep search for hidden polarized broad H{alpha} and direct broad Pa{beta} or Br{gamma} emission lines in these objects. We found no evidence for any broad emission lines from the active nuclei of these galaxies, suggesting that they are unobscured, completely 'naked' AGNs that intrinsically lack broad-line regions.

  18. PHYSICAL PROPERTIES, STAR FORMATION, AND ACTIVE GALACTIC NUCLEUS ACTIVITY IN BALMER BREAK GALAXIES AT 0 < z < 1

    SciTech Connect

    Diaz Tello, J.; Donzelli, C.; Padilla, N.; Fujishiro, N.; Yoshikawa, T.; Hanami, H.; Hatsukade, B.

    2013-07-01

    We present a spectroscopic study with the derivation of the physical properties of 37 Balmer break galaxies, which have the necessary lines to locate them in star-forming-active galactic nuclei (AGNs) diagnostic diagrams. These galaxies span a redshift range from 0.045 to 0.93 and are somewhat less massive than similar samples of previous works. The studied sample has multiwavelength photometric data coverage from the ultraviolet to mid-infrared (MIR) Spitzer bands. We investigate the connection between star formation and AGN activity via optical, mass-excitation (MEx), and MIR diagnostic diagrams. Through optical diagrams, 31 (84%) star-forming galaxies, two (5%) composite galaxies, and three (8%) AGNs were classified, whereas from the MEx diagram only one galaxy was classified as AGN. A total of 19 galaxies have photometry available in all the IRAC/Spitzer bands. Of these, three AGN candidates were not classified as AGN in the optical diagrams, suggesting they are dusty/obscured AGNs, or that nuclear star formation has diluted their contributions. By fitting the spectral energy distribution of the galaxies, we derived the stellar masses, dust reddening E(B - V), ages, and UV star formation rates (SFRs). Furthermore, the relationship between SFR surface density ({Sigma}{sub SFR}) and stellar mass surface density per time unit ({Sigma}{sub M{sub */{tau}}}) as a function of redshift was investigated using the [O II] {lambda}3727, 3729, H{alpha} {lambda}6563 luminosities, which revealed that both quantities are larger for higher redshift galaxies. We also studied the SFR and specific SFR (SSFR) versus stellar mass and color relations, with the more massive galaxies having higher SFR values but lower SSFR values than less massive galaxies. These results are consistent with previous ones showing that, at a given mass, high-redshift galaxies have on average larger SFR and SSFR values than low-redshift galaxies. Finally, bluer galaxies have larger SSFR values than redder

  19. Star Formation in Damped Lyman-alpha systems and the Outskirts of Lyman Break Galaxies

    NASA Astrophysics Data System (ADS)

    Rafelski, Marc Alexander

    In this thesis we begin to unify two pictures of the high redshift universe: absorption line systems such as damped Lyman alpha systems (DLAs) that provide the fuel for star formation, and compact star forming regions such as Lyman break galaxies (LBGs) which form the majority of stars. Wolfe & Chen (2006) find that the in situ star formation in DLAs is less than 5% of what is expected from the Kennicutt-Schmidt (KS) relation, but they do not constrain DLAs associated with bright star-forming regions such as LBGs. In this work we search for spatially-extended star formation in the outskirts of LBGs at z ∼3. To this end, we create a sample of z ∼3 LBGs in the Hubble Ultra Deep Field (UDF) by using photometric redshifts enabled by the introduction of an extremely deep u -band image. By stacking these galaxies, we find spatially extended low surface brightness emission around LBGs in the V -band image of the UDF, corresponding to the z ∼3 rest-frame far-ultraviolet light, which is a sensitive measure of star formation rates (SFRs). We connect this emission around LBGs to the expected emission from DLAs, and the results suggest that the SFR efficiency in such gas at z ∼3 is between factors of 10 and 50 lower than predictions based on the KS relation. This decreased efficiency is likely due to the lower metallicity of DLA gas. In addition, we measure the metallicity evolution of DLAs out to z ∼5, and find a continued decrease of metallicity with increasing redshift and a metallicity "floor"' around one thousandth of the solar value. We also compare the metallicity distribution and chemistry of DLAs and halo stars, and find that they are not inconsistent. Lastly, we study the photometric variability of stars in the Galactic center in order to further our understanding of the massive young stars forming in the presence of a super massive black hole. All together, these results improve our understanding of star formation and provide constraints for models and

  20. VizieR Online Data Catalog: Lyman break galaxies (LBG) at z~1 (Chen+, 2013)

    NASA Astrophysics Data System (ADS)

    Chen, Z.; Shu, C. G.; Burgarella, D.; Buat, V.; Huang, J.-S.; Luo, Z. J.

    2014-06-01

    After carefully cross-identifying previously discovered - and selected by the Galaxy Evolution Explorer (GALEX) - Lyman break galaxy (LBG) candidates one-to-one with their optical counterparts in the field of the Chandra Deep Field South (CDF-S), we re-estimate their photometric redshifts using multiwavelength data from ultraviolet and optical to near-infrared. Considering their re-estimated photometric redshifts and spectral energy distributions, we refine a new updated sample of 383 LBGs at 0.7<~z<~1.4, with two confirmed active galactic nuclei being excluded. There are 260 and 111 LBGs classified as starburst and irregular types, respectively. The ages of the LBGs span from several Myr to 1.5Gyr with a median of ~50Myr. Their dust-corrected star formation rates (SFRs) and stellar masses (M*) are 4-220M⊙/yr and from 2.3x108 to 4x1011M⊙, with median values of ~25M⊙/yr and ~1010M⊙. The rest-frame far-ultraviolet luminosity function of the LBGs is presented with the best-fitting Schechter parameters of α=-1.61+/-0.40, M*=-20.40+/-0.22 and φ*=(0.89+/-0.30)x10-3/Mpc3/dex. LBGs of irregular types are mainly distributed along the main sequence of star-forming galaxies, while most LBGs of starburst types are located in the starburst region. Together with previous studies, we suggest that the star formation mode for LBGs at z>3 is mainly starburst, and that it evolves to be more significant to the quenching mode after z~3. A downsizing effect is clearly found, and we discuss the physical implications and comparisons with previous studies in detail. LBGs with larger SFRs are, on average, more compact. In the rest-frame colour (U-B)-M* diagram, LBGs are distributed in the `blue' cloud. We suggest that LBGs might evolve along the blue cloud from later to earlier types. The Hubble Space Telescope images in F606W (V band) and F850LP (z band) are taken from the Galaxy Evolution from Morphology and SEDs (GEMS) survey and the Great Observatories Origins Deep Survey

  1. Low-redshift quasars in the SDSS Stripe 82. Host galaxy colours and close environment

    NASA Astrophysics Data System (ADS)

    Bettoni, D.; Falomo, R.; Kotilainen, J. K.; Karhunen, K.; Uslenghi, M.

    2015-12-01

    We present a photometrical and morphological multicolour study of the properties of low-redshift (z < 0.3) quasar hosts based on a large and homogeneous data set of quasars derived from the Sloan Digital Sky Survey (DR7). We used quasars that were imaged in the SDSS Stripe82 that is up to 2 mag deeper than standard Sloan images. This sample is part of a larger data set of ˜400 quasars at z < 0.5 for which both the host galaxies and their galaxy environments were studied. For 52 quasars, we undertake a study of the colour of the host galaxies and of their close environments in the u, g, r, i and z bands. We are able to resolve almost all the quasars in the sample in the filters g, r, i and z and also in u for about 50 per cent of the targets. We found that the mean colours of the QSO host galaxy (g - i = 0.82 ± 0.26; r - i = 0.26 ± 0.16 and u - g = 1.32 ± 0.25) are very similar to the values of a sample of inactive galaxies matched in terms of redshift and galaxy luminosity with the quasar sample. There is a suggestion that the most massive QSO hosts have bluer colours. Both quasar hosts and the comparison sample of inactive galaxies have candidates of close (<50 kpc) companion galaxies for ˜30 per cent of the sources with no significant difference between active and inactive galaxies. We do not find significant correlation between the central black hole (BH) mass and the quasar host luminosity that appears to be extra luminous at a given BH mass with respect to the local relation (MBH - Mhost) for inactive galaxies. This confirms previous suggestion that a substantial disc component, not correlated with the BH mass, is present in the galaxies hosting low-z quasars. These results support a scenario where the activation of the nucleus has negligible effects on the global structural and photometrical properties of the hosting galaxies.

  2. A close nuclear black-hole pair in the spiral galaxy NGC 3393.

    PubMed

    Fabbiano, G; Wang, Junfeng; Elvis, M; Risaliti, G

    2011-09-22

    The current picture of galaxy evolution advocates co-evolution of galaxies and their nuclear massive black holes, through accretion and galactic merging. Pairs of quasars, each with a massive black hole at the centre of its galaxy, have separations of 6,000 to 300,000 light years (refs 2 and 3; 1 parsec = 3.26 light years) and exemplify the first stages of this gravitational interaction. The final stages of the black-hole merging process, through binary black holes and final collapse into a single black hole with gravitational wave emission, are consistent with the sub-light-year separation inferred from the optical spectra and light-variability of two such quasars. The double active nuclei of a few nearby galaxies with disrupted morphology and intense star formation (such as NGC 6240 with a separation of about 2,600 light years and Mrk 463 with a separation of about 13,000 light years between the nuclei) demonstrate the importance of major mergers of equal-mass spiral galaxies in this evolution; such mergers lead to an elliptical galaxy, as in the case of the double-radio-nucleus elliptical galaxy 0402+379 (with a separation of about 24 light years between the nuclei). Minor mergers of a spiral galaxy with a smaller companion should be a more common occurrence, evolving into spiral galaxies with active massive black-hole pairs, but have hitherto not been seen. Here we report the presence of two active massive black holes, separated by about 490 light years, in the Seyfert galaxy NGC 3393 (50 Mpc, about 160 million light years). The regular spiral morphology and predominantly old circum-nuclear stellar population of this galaxy, and the closeness of the black holes embedded in the bulge, provide a hitherto missing observational point to the study of galaxy/black hole evolution. Comparison of our observations with current theoretical models of mergers suggests that they are the result of minor merger evolution. PMID:21881560

  3. A close nuclear black-hole pair in the spiral galaxy NGC 3393.

    PubMed

    Fabbiano, G; Wang, Junfeng; Elvis, M; Risaliti, G

    2011-08-31

    The current picture of galaxy evolution advocates co-evolution of galaxies and their nuclear massive black holes, through accretion and galactic merging. Pairs of quasars, each with a massive black hole at the centre of its galaxy, have separations of 6,000 to 300,000 light years (refs 2 and 3; 1 parsec = 3.26 light years) and exemplify the first stages of this gravitational interaction. The final stages of the black-hole merging process, through binary black holes and final collapse into a single black hole with gravitational wave emission, are consistent with the sub-light-year separation inferred from the optical spectra and light-variability of two such quasars. The double active nuclei of a few nearby galaxies with disrupted morphology and intense star formation (such as NGC 6240 with a separation of about 2,600 light years and Mrk 463 with a separation of about 13,000 light years between the nuclei) demonstrate the importance of major mergers of equal-mass spiral galaxies in this evolution; such mergers lead to an elliptical galaxy, as in the case of the double-radio-nucleus elliptical galaxy 0402+379 (with a separation of about 24 light years between the nuclei). Minor mergers of a spiral galaxy with a smaller companion should be a more common occurrence, evolving into spiral galaxies with active massive black-hole pairs, but have hitherto not been seen. Here we report the presence of two active massive black holes, separated by about 490 light years, in the Seyfert galaxy NGC 3393 (50 Mpc, about 160 million light years). The regular spiral morphology and predominantly old circum-nuclear stellar population of this galaxy, and the closeness of the black holes embedded in the bulge, provide a hitherto missing observational point to the study of galaxy/black hole evolution. Comparison of our observations with current theoretical models of mergers suggests that they are the result of minor merger evolution.

  4. LSD: Lyman-break galaxies Stellar populations and Dynamics - I. Mass, metallicity and gas at z ~ 3.1

    NASA Astrophysics Data System (ADS)

    Mannucci, F.; Cresci, G.; Maiolino, R.; Marconi, A.; Pastorini, G.; Pozzetti, L.; Gnerucci, A.; Risaliti, G.; Schneider, R.; Lehnert, M.; Salvati, M.

    2009-10-01

    We present the first results of a project, Lyman-break galaxies Stellar populations and Dynamics (LSD), aimed at obtaining spatially resolved, near-infrared (IR) spectroscopy of a complete sample of Lyman-break galaxies at z ~ 3. Deep observations with adaptive optics resulted in the detection of the main optical lines, such as [OII] λ3727, Hβ and [OIII] λ5007, which are used to study sizes, star formation rates (SFRs), morphologies, gas-phase metallicities, gas fractions and effective yields. Optical, near-IR and Spitzer/Infrared Array Camera photometry are used to measure stellar mass. We obtain that morphologies are usually complex, with the presence of several peaks of emissions and companions that are not detected in broad-band images. Typical metallicities are 10-50 per cent solar, with a strong evolution of the mass-metallicity relation from lower redshifts. Stellar masses, gas fraction and evolutionary stages vary significantly among the galaxies, with less massive galaxies showing larger fractions of gas. In contrast with observations in the local universe, effective yields decrease with stellar mass and reach solar values at the low-mass end of the sample. This effect can be reproduced by gas infall with rates of the order of the SFRs. Outflows are present but are not needed to explain the mass-metallicity relation. We conclude that a large fraction of these galaxies is actively creating stars after major episodes of gas infall or merging. Based on observations collected with European Southern Observatory/Very Large Telescope (ESO/VLT) (proposals 075.A-0300 and 076.A-0711), with the Italian TNG, operated by FGG (INAF) at the Spanish Observatorio del Roque de los Muchachos, and with the Spitzer Space Telescope, operated by JPL (Caltech) under a contract with NASA.

  5. IRAS high resolution studies and modeling of closely interacting galaxies. Galaxy collisions: Infrared observations and analysis of numerical models. UV spectroscopy of massive young stellar populations in interacting galaxies

    NASA Technical Reports Server (NTRS)

    Lamb, Susan A.

    1993-01-01

    The Final Technical Report covering the period from 15 Aug. 1989 to 14 Aug. 1991 is presented. Areas of research included Infrared Astronomy Satellite (IRAS) high resolution studies and modeling of closely interacting galaxies; galaxy collisions: infrared observations and analysis of numerical models; and UV spectroscopy of massive young stellar populations in interacting galaxies. Both observational studies and theoretical modelling of interacting galaxies are covered. As a consequence the report is divided into two parts, one on each aspect of the overall project.

  6. Unveiling the structure of barred galaxies at 3.6 μm with the Spitzer survey of stellar structure in galaxies (S{sup 4}G). I. Disk breaks

    SciTech Connect

    Kim, Taehyun; Lee, Myung Gyoon; Gadotti, Dimitri A.; Muñoz-Mateos, Juan-Carlos; Sheth, Kartik; Madore, Barry F.; Ho, Luis C.; Elmegreen, Bruce; Knapen, Johan H.; Cisternas, Mauricio; Erroz-Ferrer, Santiago; Zaritsky, Dennis; Comerón, Sébastien; Laurikainen, Eija; Salo, Heikki; Holwerda, Benne; Hinz, Joannah L.; Buta, Ron; and others

    2014-02-20

    We have performed two-dimensional multicomponent decomposition of 144 local barred spiral galaxies using 3.6 μm images from the Spitzer Survey of Stellar Structure in Galaxies. Our model fit includes up to four components (bulge, disk, bar, and a point source) and, most importantly, takes into account disk breaks. We find that ignoring the disk break and using a single disk scale length in the model fit for Type II (down-bending) disk galaxies can lead to differences of 40% in the disk scale length, 10% in bulge-to-total luminosity ratio (B/T), and 25% in bar-to-total luminosity ratios. We find that for galaxies with B/T ≥ 0.1, the break radius to bar radius, r {sub br}/R {sub bar}, varies between 1 and 3, but as a function of B/T the ratio remains roughly constant. This suggests that in bulge-dominated galaxies the disk break is likely related to the outer Lindblad resonance of the bar and thus moves outward as the bar grows. For galaxies with small bulges, B/T < 0.1, r {sub br}/R {sub bar} spans a wide range from 1 to 6. This suggests that the mechanism that produces the break in these galaxies may be different from that in galaxies with more massive bulges. Consistent with previous studies, we conclude that disk breaks in galaxies with small bulges may originate from bar resonances that may be also coupled with the spiral arms, or be related to star formation thresholds.

  7. TESTING THE EVOLUTIONARY SEQUENCE BETWEEN HIDDEN BROAD-LINE REGION (HBLR) AND NON-HBLR SEYFERT 2 GALAXIES WITH THE 4000 A BREAK STRENGTHS

    SciTech Connect

    Yu, Po-Chieh; Hwang, Chorng-Yuan; Huang, Kui-Yun; Ohyama, Youichi E-mail: hwangcy@astro.ncu.edu.tw E-mail: ohyama@asiaa.sinica.edu.tw

    2013-05-01

    We compare the 4000 A break (D{sub n} (4000)) strength in the central kpc of hidden broad-line region (HBLR) and non-HBLR Seyfert 2 galaxies to investigate the origin of these galaxies. Our results show that the D{sub n} (4000) strengths in the nuclear regions of the non-HBLR Seyfert 2 galaxies are larger than those in the HBLR galaxies. We also show that the D{sub n} (4000) strength is not related to the morphology of host galaxies. These results imply that the non-HBLR Seyfert 2 galaxies have an older stellar population in nuclear regions than the HBLR galaxies. This suggests that an evolutionary connection might exist between non-HBLR and HBLR Seyfert 2 galaxies. We propose a potential evolutionary scenario and a modified unification model for Seyfert galaxies. In this scheme, Seyfert 1 and HBLR Seyfert 2 galaxies evolve into unabsorbed and absorbed non-HBLR Seyfert 2 galaxies. We also discuss the implications of our results in the hydrogen column density distribution of the non-HBLR Seyfert 2 galaxies.

  8. VizieR Online Data Catalog: Balmer break galaxies at z<1.5 star formation (Diaz Tello+, 2016)

    NASA Astrophysics Data System (ADS)

    Diaz Tello, J.; Donzelli, C.; Padilla, N.; Akiyama, M.; Fujishiro, N.; Yoshikawa, T.; Hanami, H.

    2016-05-01

    The galaxies presented in this article come from a sample constructed to study star formation activity of massive galaxies in the redshift range z=0.1-3.0 (Diaz Tello et al., 2013ApJ...771....7D; hereafter D13). The chosen field, the SXDF (RA=02:18:00, DE=-05:00:00; Furusawa et al., 2008, Cat. J/ApJS/176/1) has the advantage that deep photometric data is available in the bands u, B, R, i, z (Subaru), J, H, K (UKIRT), and in all MIR Spitzer bands. The parent sample was selected using the λ3646 Balmer and λ4000 break features as tracers of redshift, as described by Daddi et al. (2004ApJ...617..746D), utilizing the BzK color-color diagram to select star-forming galaxies in a particular redshift range. Furthermore, we used two color-color diagrams to select star-forming galaxies in a lower redshift range than the BzK diagram; these diagrams were presented in Hanami et al. (2012PASJ...64...70H; uVi and uRJ diagrams). (1 data file).

  9. Star formation rate and extinction in faint z ∼ 4 Lyman break galaxies

    SciTech Connect

    To, Chun-Hao; Wang, Wei-Hao; Owen, Frazer N.

    2014-09-10

    We present a statistical detection of 1.5 GHz radio continuum emission from a sample of faint z ∼ 4 Lyman break galaxies (LBGs). To constrain their extinction and intrinsic star formation rate (SFR), we combine the latest ultradeep Very Large Array 1.5 GHz radio image and the Hubble Space Telescope Advanced Camera for Surveys (ACS) optical images in the GOODS-N. We select a large sample of 1771 z ∼ 4 LBGs from the ACS catalog using B {sub F435W}-dropout color criteria. Our LBG samples have I {sub F775W} ∼ 25-28 (AB), ∼0-3 mag fainter than M{sub UV}{sup ⋆} at z ∼ 4. In our stacked radio images, we find the LBGs to be point-like under our 2'' angular resolution. We measure their mean 1.5 GHz flux by stacking the measurements on the individual objects. We achieve a statistical detection of S {sub 1.5} {sub GHz} = 0.210 ± 0.075 μJy at ∼3σ for the first time on such a faint LBG population at z ∼ 4. The measurement takes into account the effects of source size and blending of multiple objects. The detection is visually confirmed by stacking the radio images of the LBGs, and the uncertainty is quantified with Monte Carlo simulations on the radio image. The stacked radio flux corresponds to an obscured SFR of 16.0 ± 5.7 M {sub ☉} yr{sup –1}, and implies a rest-frame UV extinction correction factor of 3.8. This extinction correction is in excellent agreement with that derived from the observed UV continuum spectral slope, using the local calibration of Meurer et al. This result supports the use of the local calibration on high-redshift LBGs to derive the extinction correction and SFR, and also disfavors a steep reddening curve such as that of the Small Magellanic Cloud.

  10. THE MOLECULAR GAS CONTENT OF z = 3 LYMAN BREAK GALAXIES: EVIDENCE OF A NON-EVOLVING GAS FRACTION IN MAIN-SEQUENCE GALAXIES AT z > 2

    SciTech Connect

    Magdis, Georgios E.; Rigopoulou, D.; Daddi, E.; Sargent, M.; Elbaz, D.; Gobat, R.; Tan, Q.; Aussel, H.; Feruglio, C.; Charmandaris, V.; Dickinson, M.; Reddy, N.

    2012-10-10

    We present observations of the CO[J = 3 {yields} 2] emission toward two massive and infrared luminous Lyman break galaxies (LBGs) at z = 3.21 and z = 2.92, using the IRAM Plateau de Bure Interferometer, placing first constraints on the molecular gas masses (M{sub gas}) of non-lensed LBGs. Their overall properties are consistent with those of typical (main-sequence) galaxies at their redshifts, with specific star formation rates {approx}1.6 and {approx}2.2 Gyr{sup -1}, despite their large infrared luminosities (L{sub IR} Almost-Equal-To (2-3) Multiplication-Sign 10{sup 12} L{sub Sun }) derived from Herschel. With one plausible CO detection (spurious detection probability of 10{sup -3}) and one upper limit, we investigate the evolution of the molecular gas-to-stellar mass ratio (M{sub gas}/M{sub *}) with redshift. Our data suggest that the steep evolution of M{sub gas}/M{sub *} of normal galaxies up to z {approx} 2 is followed by a flattening at higher redshifts, providing supporting evidence for the existence of a plateau in the evolution of the specific star formation rate at z > 2.5.

  11. KECK SPECTROSCOPY OF FAINT 3>z>7 LYMAN BREAK GALAXIES: A HIGH FRACTION OF LINE EMITTERS AT REDSHIFT SIX

    SciTech Connect

    Stark, Daniel P.; Ellis, Richard S.; Ouchi, Masami

    2011-02-10

    As Ly{alpha} photons are scattered by neutral hydrogen, a change with redshift in the Ly{alpha} equivalent width (EW) distribution of distant galaxies offers a promising probe of the degree of ionization in the intergalactic medium and hence when cosmic reionization ended. This simple test is complicated by the fact that Ly{alpha} emission can also be affected by variations in the kinematics and dust content of the host galaxies. In the first paper in this series, we demonstrated both a luminosity- and redshift-dependent trend in the fraction of Ly{alpha} emitters seen within color-selected 'Lyman break' galaxies (LBGs) over the range 3 < z < 6; lower luminosity galaxies and those at higher redshift show an increased likelihood of strong emission. Here, we present the results from 12.5 hr exposures with the Keck DEIMOS spectrograph focused primarily on LBGs at z {approx_equal} 6 which enable us to confirm the redshift dependence of line emission more robustly and to higher redshift than was hitherto possible. We find that 54% {+-} 11% of faint z {approx_equal} 6 LBGs show strong (W{sub Ly{alpha},0}>25 A) emission, an increase of 55% from a sample of similarly luminous z {approx_equal} 4 galaxies. With a total sample of 74 z {approx_equal} 6 LBGs, we determine the luminosity-dependent Ly{alpha} EW distribution. Assuming continuity in these trends to the new population of z {approx_equal} 7 sources located with the Hubble WFC3/IR camera, we predict that unless the neutral fraction rises in the intervening 200 Myr, the success rate for spectroscopic confirmation using Ly{alpha} emission should be high.

  12. The {open_quotes}leak-before-break{close_quotes} applicability in decision support system {open_quotes}strength{close_quotes}

    SciTech Connect

    Torop, V.M.; Orynyak, I.V.; Kutovoy, O.L.

    1997-04-01

    A software decision support system, STRENGTH, for application of leak before break analysis, is described. The background methodology and sample application are outlined. The program allows multioptional computation of loading parameters for different types of defects, and variable properties for metals and welded joints. Structural strength is assessed, and service life predictions are made. The program is used to analyze specific defects identified by nondestructive testing.

  13. Maximal breaking of symmetry at critical angles and a closed-form expression for angular deviations of the Snell law

    NASA Astrophysics Data System (ADS)

    Araújo, Manoel P.; Carvalho, Silvânia A.; De Leo, Stefano

    2014-09-01

    A detailed analysis of the propagation of laser Gaussian beams at critical angles shows under which conditions it is possible to maximize the breaking of symmetry in the angular distribution and for which values of the laser wavelength and beam waist it is possible to find an analytic formula for the maximal angular deviation from the optical path predicted by the Snell law. For beam propagation through N dielectric blocks and for a maximal breaking of symmetry, a closed expression for the Goos-Hänchen shift is obtained. The multiple-peak phenomenon clearly represents additional evidence of the breaking of symmetry in the angular distribution of optical beams. Finally, the laser wavelength and beam-waist conditions to produce focal effects in the outgoing beam are also briefly discussed.

  14. Possible breaking of the FIR-radio correlation in tidally interacting galaxies

    NASA Astrophysics Data System (ADS)

    Donevski, D.; Prodanović, T.

    2015-10-01

    Far-infrared (FIR)-radio correlation is a well-established empirical connection between continuum radio and dust emission of star-forming galaxies, often used as a tool in determining star formation rates. Here we expand the point made by Murphy that in the case of some interacting star-forming galaxies there is a non-thermal emission from the gas bridge in between them, which might cause a dispersion in this correlation. Galactic interactions and mergers have been known to give rise to tidal shocks and disrupt morphologies especially in the smaller of the interacting components. Here we point out that these shocks can also heat the gas and dust and will inevitably accelerate particles and result in a tidal cosmic ray population in addition to standard galactic cosmic rays in the galaxy itself. This would result in a non-thermal emission not only from the gas bridges of interacting systems, but from interacting galaxies as a whole in general. Thus both tidal heating and additional non-thermal radiation will obviously affect the FIR-radio correlation of these systems, the only question is how much. In this scenario the FIR-radio correlation is not stable in interacting galaxies, but rather evolves as the interaction/merger progresses. To test this hypothesis and probe the possible impact of tidal cosmic ray population, we have analysed a sample of 43 infrared-bright star-forming interacting galaxies at different merger stages. We have found that their FIR-radio correlation parameter and radio emission spectral index vary noticeably over different merger stages and behave as it would be expected from our tidal-shock scenario. Important implications of departure of interacting galaxies from the FIR-radio correlation are discussed.

  15. Images From Hubbles's ACS Tell A Tale Of Two Record-Breaking Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    2004-01-01

    Looking back in time nearly 9 billion years, an international team of astronomers found mature galaxies in a young universe. The galaxies are members of a cluster of galaxies that existed when the universe was only 5 billion years old, or about 35 percent of its present age. This compelling evidence that galaxies must have started forming just after the big bang was bolstered by observations made by the same team of astronomers when they peered even farther back in time. The team found embryonic galaxies a mere 1.5 billion years after the birth of the cosmos, or 10 percent of the universe's present age. The "baby galaxies" reside in a still-developing cluster, the most distant proto-cluster ever found. The Advanced Camera for Surveys (ACS) aboard NASA's Hubble Space Telescope was used to make observations of the massive cluster, RDCS 1252.9-2927, and the proto-cluster, TN J1338-1942. Observations by NASA's Chandra X-ray Observatory yielded the mass and heavy element content of RDCS 1252, the most massive known cluster for that epoch. These observations are part of a coordinated effort by the ACS science team to track the formation and evolution of clusters of galaxies over a broad range of cosmic time. The ACS was built especially for studies of such distant objects. These findings further support observations and theories that galaxies formed relatively early in the history of the cosmos. The existence of such massive clusters in the early universe agrees with a cosmological model wherein clusters form from the merger of many sub-clusters in a universe dominated by cold dark matter. The precise nature of cold dark matter, however, is still not known. The first Hubble study estimated that galaxies in RDCS 1252 formed the bulk of their stars more than 11 billion years ago (at redshifts greater than 3). The results were published in the Oct. 20, 2003 issue of the Astrophysical Journal. The paper's lead author is John Blakeslee of the Johns Hopkins University in

  16. Indirect Evidence for Escaping Ionizing Photons in Local Lyman Break Galaxy Analogs

    NASA Astrophysics Data System (ADS)

    Alexandroff, Rachael M.; Heckman, Timothy M.; Borthakur, Sanchayeeta; Overzier, Roderik; Leitherer, Claus

    2015-09-01

    A population of early star-forming galaxies is the leading candidate for the re-ionization of the universe. It is still unclear, however, what conditions and physical processes would enable a significant fraction of the ionizing (Lyman continuum) photons to escape from these gas-rich galaxies. In this paper we present the results of the analysis of Hubble Space Telescope Cosmic Origins Spectrograph far-UV (FUV) spectroscopy plus ancillary multi-waveband data of a sample of 22 low-redshift galaxies that are good analogs to typical star-forming galaxies at high redshift. We measure three parameters that provide indirect evidence of the escape of ionizing radiation (leakiness): (1) the residual intensity in the cores of saturated interstellar low-ionization absorption lines, which indicates incomplete covering by that gas in the galaxy; (2) the relative amount of blueshifted Lyα line emission, which can indicate the existence of holes in the neutral hydrogen on the front-side of the galaxy outflow, and (3) the relative weakness of the [S ii] optical emission lines that trace matter-bounded H ii regions. We show that our residual intensity measures are only negligibly affected by infilling from resonance emission lines. We find all three diagnostics agree well with one another. We use these diagnostics to rank-order our sample in terms of likely leakiness, noting that a direct measure of escaping Lyman continuum has recently been made for one of the leakiest members of our sample. We then examine the correlations between our ranking and other proposed diagnostics of leakiness. We find a good correlation with the equivalent width of the Lyα emission line, but no significant correlations with either the flux ratio of the [O iii]/[O ii] emission lines or the ratio of star-formation rates derived from the (dust-corrected) FUV and Hα luminosities. Turning to galaxy properties, we find the strongest correlations with leakiness are with the compactness of the star

  17. Images From Hubbles's ACS Tell A Tale Of Two Record-Breaking Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    2004-01-01

    Looking back in time nearly 9 billion years, an international team of astronomers found mature galaxies in a young universe. The galaxies are members of a cluster of galaxies that existed when the universe was only 5 billion years old, or about 35 percent of its present age. This compelling evidence that galaxies must have started forming just after the big bang was bolstered by observations made by the same team of astronomers when they peered even farther back in time. The team found embryonic galaxies a mere 1.5 billion years after the birth of the cosmos, or 10 percent of the universe's present age. The "baby galaxies" reside in a still-developing cluster, the most distant proto-cluster ever found. The Advanced Camera for Surveys (ACS) aboard NASA's Hubble Space Telescope was used to make observations of the massive cluster, RDCS 1252.9-2927, and the proto-cluster, TN J1338-1942. Observations by NASA's Chandra X-ray Observatory yielded the mass and heavy element content of RDCS 1252, the most massive known cluster for that epoch. These observations are part of a coordinated effort by the ACS science team to track the formation and evolution of clusters of galaxies over a broad range of cosmic time. The ACS was built especially for studies of such distant objects. These findings further support observations and theories that galaxies formed relatively early in the history of the cosmos. The existence of such massive clusters in the early universe agrees with a cosmological model wherein clusters form from the merger of many sub-clusters in a universe dominated by cold dark matter. The precise nature of cold dark matter, however, is still not known. The first Hubble study estimated that galaxies in RDCS 1252 formed the bulk of their stars more than 11 billion years ago (at redshifts greater than 3). The results were published in the Oct. 20, 2003 issue of the Astrophysical Journal. The paper's lead author is John Blakeslee of the Johns Hopkins University in

  18. A generation-dispersion model of ambient and transient bubbles in the close vicinity of breaking waves

    NASA Astrophysics Data System (ADS)

    Baldy, Serge

    1993-10-01

    Bubble models are necessary to ascertain bubble contribution to ocean-atmosphere fluxes of gas, aerosols, humidity, and latent heat. Previous theories flatten the wave breaking layer to a theoretical boundary from which bubbles are dispersed by turbulence working against buoyancy lift. As a consequence, bubble population characteristics next to the surface are not derived from these models but depend on empirical or semiempirical assumptions made at this boundary. By considering bubble injection with puffs of intense turbulence, specifying how bubbles are first created by a small-scale similarity reasoning, and using a wavy interface, the present bubble theory expands this layer to a more physical breaking layer. Bubble concentration density as a function of bubble diameter, depth, and sea state parameters is obtained through explicit integrals. The model is found to be consistent with the previous bubble theories: the back flattening of the model breaking layer indeed results in equations compatible with these theories. The model variations in bubble concentration density with different parameters is coherent with experimental laws: the dominant bubble concentration is found to vary as about d-4 with bubble diameter and u*3 with wind friction velocity, but because of breaking patches, a d-2 bubble distribution is obtained very close to the surface. The concordance of the model with experimental data in the recent and classic bubble literature is quite good.

  19. Galaxies

    SciTech Connect

    Not Available

    1981-01-01

    Normal galaxies, radio galaxies, and Seyfert galaxies are considered. The large magellanic cloud and the great galaxy in Andromedia are highlighted. Quasars and BL lacertae objects are also discussed and a review of the spectral observations of all of these galaxies and celestial objects is presented.

  20. On breaking the age-metallicity degeneracy in early-type galaxies: outflows versus star formation efficiency

    NASA Astrophysics Data System (ADS)

    Ferreras, Ignacio; Silk, Joseph

    2000-08-01

    A simple model of chemical enrichment in cluster early-type galaxies is presented where the main parameters driving the formation of the stellar component are reduced to four: the infall time-scale (τf), the formation epoch (zF), the star formation efficiency (Ceff) and the fraction of gas ejected in outflows (Bout). We find that only variations in Bout or Ceff can account for the colour-magnitude relation, so that the most luminous galaxies had low values of ejected gas and high efficiencies. Less massive galaxies can be related either to a lower star formation efficiency (Ceff sequence) or to an increased outflow rate (Bout sequence). The combination of chemical enrichment tracks with population synthesis models is used to explore the correlation between mass-to-light ratios and masses. A significant slope mismatch is found between stellar and total ML ratios, which cannot be explained by an age spread and implies a non-linear correlation between total and stellar mass: MTOT ∝ M1.2ST. The sequences driven by star formation efficiency (Ceff) and outflows (Bout) are shown to predict different trends at high redshift. The variation with redshift of the slope of the fundamental plane will increase significantly in the efficiency sequence - driven by age - and will slightly decrease in the outflow sequence - driven by metallicity. The evolution of the zero-point is similar in both cases and within the observational errors of current observations. Measurement of the dependence of the tilt of the fundamental plane on redshift will break the degeneracy between outflows and star formation efficiency, which will enable us to determine whether the colour-magnitude relation is controlled by age or metallicity.

  1. Spectral breaks as a signature of cosmic ray induced turbulence in the Galaxy.

    PubMed

    Blasi, Pasquale; Amato, Elena; Serpico, Pasquale D

    2012-08-10

    We show that the complex shape of the cosmic ray (CR) spectrum, as recently measured by PAMELA and inferred from Fermi-LAT γ-ray observations of molecular clouds in the Gould belt, can be naturally understood in terms of basic plasma astrophysics phenomena. A break from a harder to a softer spectrum at rigidity R is approximately equal to 10 GV follows from a transition from transport dominated by advection of particles with Alfvén waves to a regime where diffusion in the turbulence generated by the same CRs is dominant. A second break at R is approximately equal to 200 GV happens when the diffusive propagation is no longer determined by the self-generated turbulence, but rather by the cascading of externally generated turbulence (for instance due to supernova bubbles) from large spatial scales to smaller scales where CRs can resonate. Implications of this scenario for the cosmic ray spectrum, grammage, and anisotropy are discussed.

  2. Properties of z ~ 3-6 Lyman break galaxies. II. Impact of nebular emission at high redshift

    NASA Astrophysics Data System (ADS)

    de Barros, S.; Schaerer, D.; Stark, D. P.

    2014-03-01

    Context. To gain insight on the mass assembly and place constraints on the star formation history (SFH) of Lyman break galaxies (LBGs), it is important to accurately determine their properties. Aims: We estimate how nebular emission and different SFHs affect parameter estimation of LBGs. Methods: We present a homogeneous, detailed analysis of the spectral energy distribution (SED) of ~1700 LBGs from the GOODS-MUSIC catalogue with deep multi-wavelength photometry from the U band to 8 μm to determine stellar mass, age, dust attenuation, and star formation rate. Using our SED fitting tool, which takes into account nebular emission, we explore a wide parameter space. We also explore a set of different star formation histories. Results: Nebular emission is found to significantly affect the determination of the physical parameters for the majority of z ~ 3-6 LBGs. We identify two populations of galaxies by determining the importance of the contribution of emission lines to broadband fluxes. We find that ~65% of LBGs show detectable signs of emission lines, whereas ~35% show weak or no emission lines. This distribution is found over the entire redshift range. We interpret these groups as actively star-forming and more quiescent LBGs, respectively. We find that it is necessary to considerer SED fits with very young ages (<50 Myr) to reproduce some colours affected by strong emission lines. Other arguments favouring episodic star formation and relatively short star formation timescales are also discussed. Considering nebular emission generally leads to a younger age, lower stellar mass, higher dust attenuation, higher star formation rate, and a large scatter in the SFR-M⋆ relation. Our analysis yields a trend of increasing specific star formation rate with redshift, as predicted by recent galaxy evolution models. Conclusions: The physical parameters of approximately two thirds of high redshift galaxies are significantly modified when we account for nebular emission. The

  3. GRB 051008: a long, spectrally hard dust-obscured GRB in a Lyman-break galaxy at z ≈ 2.8

    NASA Astrophysics Data System (ADS)

    Volnova, A. A.; Pozanenko, A. S.; Gorosabel, J.; Perley, D. A.; Frederiks, D. D.; Kann, D. A.; Rumyantsev, V. V.; Biryukov, V. V.; Burkhonov, O.; Castro-Tirado, A. J.; Ferrero, P.; Golenetskii, S. V.; Klose, S.; Loznikov, V. M.; Minaev, P. Yu.; Stecklum, B.; Svinkin, D. S.; Tsvetkova, A. E.; de Ugarte Postigo, A.; Ulanov, M. V.

    2014-08-01

    We present observations of the dark gamma-ray burst GRB 051008 provided by Swift/BAT, Swift/XRT, Konus-WIND, INTEGRAL/SPI-ACS in the high-energy domain and the Shajn, Swift/UVOT, Tautenburg, NOT, Gemini and Keck I telescopes in the optical and near-infrared bands. The burst was detected only in gamma- and X-rays and neither a prompt optical nor a radio afterglow was detected down to deep limits. We identified the host galaxy of the burst, which is a typical Lyman-break galaxy (LBG) with R-magnitude of 24.06 ± 0.10 mag. A redshift of the galaxy of z = 2.77_{-0.20}^{+0.15} is measured photometrically due to the presence of a clear, strong Lyman-break feature. The host galaxy is a small starburst galaxy with moderate intrinsic extinction (AV = 0.3) and has a star formation rate of ˜60 M⊙ yr-1 typical for LBGs. It is one of the few cases where a GRB host has been found to be a classical LBG. Using the redshift we estimate the isotropic-equivalent radiated energy of the burst to be Eiso = (1.15 ± 0.20) × 1054 erg. We also provide evidence in favour of the hypothesis that the darkness of GRB 051008 is due to local absorption resulting from a dense circumburst medium.

  4. Belgian experience in applying the {open_quotes}leak-before-break{close_quotes} concept to the primary loop piping

    SciTech Connect

    Gerard, R.; Malekian, C.; Meessen, O.

    1997-04-01

    The Leak Before Break (LBB) concept allows to eliminate from the design basis the double-ended guillotine break of the primary loop piping, provided it can be demonstrated by a fracture mechanics analysis that a through-wall flaw, of a size giving rise to a leakage still well detectable by the plant leak detection systems, remains stable even under accident conditions (including the Safe Shutdown Earthquake (SSE)). This concept was successfully applied to the primary loop piping of several Belgian Pressurized Water Reactor (PWR) units, operated by the Utility Electrabel. One of the main benefits is to permit justification of supports in the primary loop and justification of the integrity of the reactor pressure vessel and internals in case of a Loss Of Coolant Accident (LOCA) in stretch-out conditions. For two of the Belgian PWR units, the LBB approach also made it possible to reduce the number of large hydraulic snubbers installed on the primary coolant pumps. Last but not least, the LBB concept also facilitates the steam generator replacement operations, by eliminating the need for some pipe whip restraints located close to the steam generator. In addition to the U.S. regulatory requirements, the Belgian safety authorities impose additional requirements which are described in details in a separate paper. An novel aspect of the studies performed in Belgium is the way in which residual loads in the primary loop are taken into account. Such loads may result from displacements imposed to close the primary loop in a steam generator replacement operation, especially when it is performed using the {open_quote}two cuts{close_quotes} technique. The influence of such residual loads on the LBB margins is discussed in details and typical results are presented.

  5. Cross-correlating 21cm intensity maps with Lyman Break Galaxies in the post-reionization era

    SciTech Connect

    Villaescusa-Navarro, Francisco; Viel, Matteo; Alonso, David; Datta, Kanan K.; Santos, Mário G. E-mail: viel@oats.inaf.it E-mail: kanan@ncra.tifr.res.in E-mail: mgrsantos@uwc.ac.za

    2015-03-01

    We investigate the cross-correlation between the spatial distribution of Lyman Break Galaxies (LBGs) and the 21cm intensity mapping signal at z∼[3–5]. At these redshifts, galactic feedback is supposed to only marginally affect the matter power spectrum, and the neutral hydrogen distribution is independently constrained by quasar spectra. Using a high resolution N-body simulation, populated with neutral hydrogen a posteriori, we forecast for the expected LBG-21cm cross-spectrum and its error for a 21cm field observed by the Square Kilometre Array (SKA1-LOW and SKA1-MID), combined with a spectroscopic LBG survey with the same volume. The cross power can be detected with a signal-to-noise ratio (SNR) up to ∼10 times higher (and down to ∼ 4 times smaller scales) than the 21cm auto-spectrum for this set-up, with the SNR depending only very weakly on redshift and the LBG population. We also show that while both the 21cm auto- and LBG-21cm cross-spectra can be reliably recovered after the cleaning of smooth-spectrum foreground contamination, only the cross-power is robust to problematic non-smooth foregrounds like polarized synchrotron emission.

  6. Lopsidedness of cluster galaxies in modified gravity

    SciTech Connect

    Wu, Xufen; Zhao, HongSheng; Famaey, Benoit E-mail: hz4@st-andrews.ac.uk

    2010-06-01

    We point out an interesting theoretical prediction for elliptical galaxies residing inside galaxy clusters in the framework of modified Newtonian dynamics (MOND), that could be used to test this paradigm. Apart from the central brightest cluster galaxy, other galaxies close enough to the centre experience a strong gravitational influence from the other galaxies of the cluster. This influence manifests itself only as tides in standard Newtonian gravity, meaning that the systematic acceleration of the centre of mass of the galaxy has no consequence. However, in the context of MOND, a consequence of the breaking of the strong equivalence principle is that the systematic acceleration changes the own self-gravity of the galaxy. We show here that, in this framework, initially axisymmetric elliptical galaxies become lopsided along the external field's direction, and that the centroid of the galaxy, defined by the outer density contours, is shifted by a few hundreds parsecs with respect to the densest point.

  7. Extended LY alpha emission from a damped LY alpha absorber at z=1.93, and the relation between damped LY alpha absorbers and Lyman-break galaxies

    NASA Astrophysics Data System (ADS)

    Fynbo, J. U.; Møller, P.; Warren, S. J.

    1999-05-01

    The number of damped Lyalpha absorbers (DLAs) currently known is about 100, but our knowledge of their sizes and morphologies is still very sparse, as very few have been detected in emission. Here we present narrow-band and broad-band observations of a DLA in the field of the quasar pair Q0151+048A (qA) and Q0151+048B (qB). These two quasars have very similar redshifts, z_em=1.922 and 1.937 respectively, and an angular separation of 3.27 arcsec. The spectrum of qA contains a DLA at z_abs = 1.9342 (close to the emission redshift) which shows an emission line in the trough, detected at 4sigma. Our narrow-band image confirms this detection, and we find Lyalpha emission from an extended area covering 6 x 3 arcsec^2, corresponding to 25 x 12 h^-2 kpc^2 (q_0=0.5, H_0 = 100 h km s^-1). The total Lyalpha luminosity from the DLA is 1.2 x 10^43 h^-2 erg s^-1, which is several times higher than the Lyalpha luminosity found from other DLAs. The narrow-band image also indicates that qB is not covered by the DLA. This fact, together with the large equivalent width of the emission line from the Lyalpha cloud, the large luminosity, and the ~ 300 km s^-1 blueshift relative to the DLA, can plausibly be explained if qB is the source of ionizing photons, lying to the near side of the DLA at a distance from the DLA of <20 h^-1 kpc. In this case the size of the emission-line region corresponds to the area over which the cloud is optically thick, i.e., is indicative of the size of a Lyman-limit system. We also consider the relation between DLAs and Lyman-break galaxies (LBGs). If DLAs are gaseous discs surrounding LBGs, and if the apparent brightnesses and impact parameters of the few identified DLAs are representative of the brighter members of the population, then the luminosity distribution of DLAs is nearly flat, and we would expect that some 70 per cent of the galaxy counterparts to DLAs at z ~ 3 are fainter than m_R=28.

  8. A DEEP SEARCH FOR MOLECULAR GAS IN TWO MASSIVE LYMAN BREAK GALAXIES AT z = 3 AND 4: VANISHING CO-EMISSION DUE TO LOW METALLICITY?

    SciTech Connect

    Tan, Q.; Gao, Y.; Daddi, E.; Sargent, M.; Béthermin, M.; Bournaud, F.; Elbaz, D.; Pannella, M.; Hodge, J.; Walter, F.; Carilli, C.; Owen, F.; Dannerbauer, H.; Dickinson, M.; Morrison, G.; Riechers, D.

    2013-10-20

    We present deep IRAM Plateau de Bure Interferometer observations, searching for CO-emission toward two massive, non-lensed Lyman break galaxies at z = 3.216 and 4.058. With one low significance CO detection (3.5σ) and one sensitive upper limit, we find that the CO lines are ∼>3-4 times weaker than expected based on the relation between IR and CO luminosities followed by similarly massive galaxies at z = 0-2.5. This is consistent with a scenario in which these galaxies have low metallicity, causing an increased CO-to-H{sub 2} conversion factor, i.e., weaker CO-emission for a given molecular (H{sub 2}) mass. The required metallicities at z > 3 are lower than predicted by the fundamental metallicity relation at these redshifts, consistent with independent evidence. Unless our galaxies are atypical in this respect, detecting molecular gas in normal galaxies at z > 3 may thus remain challenging even with ALMA.

  9. Spitzer UltRa Faint SUrvey Program (SURFS UP). II. IRAC-detected Lyman-Break Galaxies at 6 ≲ z ≲ 10 behind Strong-lensing Clusters

    NASA Astrophysics Data System (ADS)

    Huang, Kuang-Han; Bradač, Maruša; Lemaux, Brian C.; Ryan, R. E., Jr.; Hoag, Austin; Castellano, Marco; Amorín, Ricardo; Fontana, Adriano; Brammer, Gabriel B.; Cain, Benjamin; Lubin, L. M.; Merlin, Emiliano; Schmidt, Kasper B.; Schrabback, Tim; Treu, Tommaso; Gonzalez, Anthony H.; von der Linden, Anja; Knight, Robert I.

    2016-01-01

    We study the stellar population properties of the IRAC-detected 6 ≲ z ≲ 10 galaxy candidates from the Spitzer UltRa Faint SUrvey Program. Using the Lyman Break selection technique, we find a total of 17 galaxy candidates at 6 ≲ z ≲ 10 from Hubble Space Telescope images (including the full-depth images from the Hubble Frontier Fields program for MACS 1149 and MACS 0717) that have detections at signal-to-noise ratios ≥ 3 in at least one of the IRAC 3.6 and 4.5 μm channels. According to the best mass models available for the surveyed galaxy clusters, these IRAC-detected galaxy candidates are magnified by factors of ˜1.2-5.5. Due to the magnification of the foreground galaxy clusters, the rest-frame UV absolute magnitudes M1600 are between -21.2 and -18.9 mag, while their intrinsic stellar masses are between 2 × 108M⊙ and 2.9 × 109M⊙. We identify two Lyα emitters in our sample from the Keck DEIMOS spectra, one at zLyα = 6.76 (in RXJ 1347) and one at zLyα = 6.32 (in MACS 0454). We find that 4 out of 17 z ≳ 6 galaxy candidates are favored by z ≲ 1 solutions when IRAC fluxes are included in photometric redshift fitting. We also show that IRAC [3.6]-[4.5] color, when combined with photometric redshift, can be used to identify galaxies which likely have strong nebular emission lines or obscured active galactic nucleus contributions within certain redshift windows.

  10. Nonequilibrium evolution of a {open_quotes}tsunami,{close_quotes} a high multiplicity initial quantum state: Dynamical symmetry breaking

    SciTech Connect

    Boyanovsky, D.; de Vega, H.J.; Holman, R.; Kumar, S.P.; Pisarski, R.D.

    1998-03-01

    We propose to study the nonequilibrium features of heavy-ion collisions by following the evolution of an initial state with a large number of quanta with a distribution around a momentum {vert_bar}{rvec k}{sub 0}{vert_bar} corresponding to a {ital thin spherical shell} in momentum space, a {open_quotes}tsunami.{close_quotes} An O(N)({rvec {Phi}}{sup 2}){sup 2} model field theory in the large N limit is used as a framework to study the nonperturbative aspects of the nonequilibrium dynamics including a resummation of the effects of the medium (the initial particle distribution). In a theory where the symmetry is spontaneously broken in the absence of the medium, when the initial number of particles per correlation volume is chosen to be larger than a critical value the medium effects can restore the symmetry of the initial state. We show that if one begins with such a symmetry-restored, nonthermal, initial state, nonperturbative effects automatically induce spinodal instabilities leading to a {ital dynamical} breaking of the symmetry. As a result there is explosive particle production and a redistribution of the particles towards low momentum due to the nonlinearity of the dynamics. The asymptotic behavior displays the onset of Bose condensation of pions and the equation of state at long times is that of an ultrarelativistic gas although the momentum distribution is {ital nonthermal}. {copyright} {ital 1998} {ital The American Physical Society}

  11. MS 1512 cB58: A case study of star formation, metal enrichment and superwinds in Lyman break galaxies

    NASA Astrophysics Data System (ADS)

    Pettini, Max; Rix, Samantha A.; Steidel, Chuck C.; Hunt, Matthew P.; Shapley, Alice E.; Adelberger, Kurt L.

    2002-07-01

    Recent advances in instrumentation and observing techniques have made it possible to begin to study in detail the stellar populations and the interstellar media of galaxies at redshift z = 3, when the universe was still in its ‘teen years’. I illustrate recent progress in this field with the latest observations of the gravitationally lensed galaxy MS 1512- cB58.

  12. Medium-resolution spectroscopy of FORJ0332-3557: probing the interstellar medium and stellar populations of a lensed Lyman-break galaxy at z = 3.77

    NASA Astrophysics Data System (ADS)

    Cabanac, Rémi A.; Valls-Gabaud, David; Lidman, Chris

    2008-06-01

    We recently reported the discovery of FORJ0332-3557, a lensed Lyman-break galaxy at z = 3.77 in a remarkable example of strong galaxy-galaxy gravitational lensing. We present here a medium-resolution rest-frame ultraviolet (UV) spectrum of the source, which appears to be similar to the well-known Lyman-break galaxy MS1512-cB58 at z = 2.73. The spectral energy distribution is consistent with a stellar population of less than 30Ma, with an extinction of Av = 0.5 mag and an extinction-corrected star formation rate SFRUV of 200-300h-170Msolara-1. The Lyα line exhibits a damped profile in absorption produced by a column density of about NHI = (2.5 +/- 1.0) × 1021cm-2, superimposed on an emission line shifted both spatially (0.5 arcsec with respect to the UV continuum source) and in velocity space (+830kms-1 with respect to the low-ionization absorption lines from its interstellar medium), a clear signature of outflows with an expansion velocity of about 270kms-1. A strong emission line from HeII λ164.04 nm indicates the presence of Wolf-Rayet stars and reinforces the interpretation of a very young starburst. The metallic lines indicate subsolar abundances of elements Si, Al and C in the ionized gas phase. Based on observations made at the ESO VLT under programmes 74.A-0536 and 78.A-0240. E-mail: remi.cabanac@ast.obs-mip.fr (RAC); david.valls-gabaud@obspm.fr (DV-G); clidman@eso.org (CL)

  13. KECK SPECTROSCOPY OF FAINT 3 < z < 7 LYMAN BREAK GALAXIES. III. THE MEAN ULTRAVIOLET SPECTRUM AT z {approx_equal} 4

    SciTech Connect

    Jones, Tucker; Ellis, Richard S.; Stark, Daniel P.

    2012-05-20

    We present and discuss the mean rest-frame ultraviolet spectrum for a sample of 81 Lyman break galaxies (LBGs) selected to be B-band dropouts at z {approx_equal} 4. The sample is mostly drawn from our ongoing Keck/DEIMOS survey in the GOODS fields and augmented with archival Very Large Telescope data. In general, we find similar spectroscopic trends to those found in earlier surveys of LBGs at z = 3. Specifically, low-ionization absorption lines which trace neutral outflowing gas are weaker in galaxies with stronger Ly{alpha} emission, bluer UV spectral slopes, lower stellar masses, lower UV luminosities, and smaller half-light radii. This is consistent with a physical picture whereby star formation drives outflows of neutral gas which scatter Ly{alpha} and produce strong low-ionization absorption lines, while increasing galaxy stellar mass, size, metallicity, and dust content. Typical galaxies are thus expected to have stronger Ly{alpha} emission and weaker low-ionization absorption at earlier times, and we indeed find somewhat weaker low-ionization absorption at higher redshifts. In conjunction with earlier results from our survey, we argue that the reduced low-ionization absorption is likely caused by lower covering fraction and/or velocity range of outflowing neutral gas at earlier epochs. Although low-ionization absorption decreases at higher redshift, fine-structure emission lines are stronger, suggesting a greater concentration of neutral gas at small galactocentric radius ({approx}< 5 kpc). Our continuing survey will enable us to extend these diagnostics more reliably to higher redshift and determine the implications for the escape fraction of ionizing photons which governs the role of early galaxies in cosmic reionization.

  14. First Results from the Faint Infrared Grism Survey (FIGS): First Simultaneous Detection of Lyα Emission and Lyman Break from a Galaxy at z = 7.51

    NASA Astrophysics Data System (ADS)

    Tilvi, V.; Pirzkal, N.; Malhotra, S.; Finkelstein, S. L.; Rhoads, J. E.; Windhorst, R.; Grogin, N. A.; Koekemoer, A.; Zakamska, N. L.; Ryan, R.; Christensen, L.; Hathi, N.; Pharo, J.; Joshi, B.; Yang, H.; Gronwall, C.; Cimatti, A.; Walsh, J.; O'Connell, R.; Straughn, A.; Ostlin, G.; Rothberg, B.; Livermore, R. C.; Hibon, P.; Gardner, Jonathan P.

    2016-08-01

    Galaxies at high redshifts are a valuable tool for studying cosmic dawn, therefore it is crucial to reliably identify these galaxies. Here, we present an unambiguous and first simultaneous detection of both the Lyα emission and the Lyman break from a z=7.512 +/- 0.004 galaxy, observed in the Faint Infrared Grism Survey (FIGS). These spectra, taken with the G102 grism on the Hubble Space Telescope (HST), show a significant emission line detection (6σ ) in two observational position angles (PAs), with Lyα line flux of 1.06+/- 0.19× {10}-17 {erg} {{{s}}}-1 {{cm}}-2. The line flux is nearly a factor of four higher than that in the archival MOSFIRE spectroscopic observations. This is consistent with other recent observations, implying that ground-based near-infrared spectroscopy underestimates the total emission line fluxes, and if confirmed, can have strong implications for reionization studies that are based on ground-based Lyα measurements. A 4σ detection of the NV line in one PA also suggests a weak active galactic nucleus (AGN), and if confirmed, would make this source the highest-redshift AGN yet found. These observations from HST thus clearly demonstrate the sensitivity of the FIGS survey, and the capability of grism spectroscopy for studying the epoch of reionization.

  15. Stellar Populations of Lyman Break Galaxies at z approx. to 1-3 in the HST/WFC3 Early Release Science Observations

    NASA Technical Reports Server (NTRS)

    Hathi, N. P.; Cohen, S. H.; Ryan, R. E., Jr.; Finkelstein, S. L.; McCarthy, P. J.; Windhorst, R. A.; Yan, H.; Koekemoer, A. M.; Rutkowski, M. J.; OConnell, R. W.; Straughn, A. N.; Balick, B.; Bond, H. E.; Calzetti, D.; Disney, M. J.; Dopita, M. A.; Frogel, Jay A.; Hall, D. N. B.; Holtzman, J. A.; Kimble, R. A.; Paresce, F.; Saha, A.; Silk, J. I.; Tauger, J. T.; Young, E. T.

    2012-01-01

    We analyze the spectral energy distributions (SEDs) of Lyman break galaxies . (LBGs) at z approx = 1-3 selected using the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) UVIS channel filters. These HST /WFC3 obse,rvations cover about 50 arcmin2 in the GOODS-South field as a part of the WFC3 Early Release Science program. These LBGs at z approx = 1-3 are selected using dropout selection criteria similar to high redshift LBGs. The deep multi-band photometry in this field is used to identify best-fit SED models, from which we infer the following results: (1) the photometric redshift estimate of these dropout selected LBGs is accurate to within few percent; (2) the UV spectral slope f3 is redder than at high redshift (z > 3), where LBGs are less dusty; (3) on average, LBGs at .z approx = 1-3 are massive, dustier and more highly star-forming, compared to LBGs at higher redshifts with similar luminosities, though their median values are similar within 1a uncertainties. This could imply that identical dropout selection technique, at all. redshifts, find physically similar galaxies; and (4) the stellar masses of these LBGs are directly proportional to their UV luminosities with a logarithmic slope of approx 0.46, and star-formation rates are proportional to their stellar masses with a logarithmic slope of approx 0.90. These relations hold true - within luminosities probed in this study - for LBGs from z approx = 1.5 to 5. The star-forming galaxies selected using other color-based techniques show similar correlations at z approx = 2, but to avoid any selection biases, and for direct comparison with LBGs at z > 3, a true Lyman break selection at z approx = 2 is essential. The future HST UV surveys,. both wider and deeper, covering a large luminosity range are important to better understand LBG properties, and their evolution.

  16. A XMM-Newton observation of a sample of four close dwarf spheroidal galaxies

    NASA Astrophysics Data System (ADS)

    Manni, L.; Nucita, A. A.; De Paolis, F.; Testa, V.; Ingrosso, G.

    2015-08-01

    We present the results of the analysis of deep archival XMM-Newton observations towards the dwarf spheroidal galaxies Draco, Leo I, Ursa Major II (UMa II) and Ursa Minor (UMi) in the Milky Way neighbourhood. The X-ray source population is characterized and cross-correlated with available databases to infer their nature. We also investigate if intermediate-mass black holes are hosted in the centre of these galaxies. For Draco, we detect 96 high-energy sources, two of them possibly being local stars, while no evidence for any X-ray emitting central compact object is found. Towards the Leo I and UMa II fields of view, we reveal 116 and 49 X-ray sources, respectively. None of them correlates with the putative central black holes and only one is likely associated with a UMa II local source. The study of the UMi dwarf galaxy found 54 high-energy sources and a possible association with a source at the dwarf spheroidal galaxy centre. We put an upper limit on the luminosity of the central compact object of 4.02 × 1033 erg s-1. Furthermore, via the correlation with a radio source near the galactic centre, the putative black hole should have a mass of (2.76^{+32.00}_{-2.54})× 10^6 M_{{{⊙}}} and be radiatively inefficient. This confirms a previous result obtained using Chandra data alone.

  17. A Study of the Contribution of the Damped Lyman α Systems and Lyman Break Galaxies to the Metal Content of the High-Redshift Universe

    NASA Astrophysics Data System (ADS)

    Lanfranchi, Gustavo; Friaça, Amancio C. S.

    We investigate the evolutionary history of the Universe's metal content through chemical abundances, taken from the literature, and predictions from chemical evolution models. The estimated abundances of several elements (C, N, O, S, Si, Fe, Cr, Zn) were taken from observations of QSOs absorption line systems over a wide range of redshift ( z ˜ 0.5 - 4.5). First, the observational data is analysed with robust statistical methods, which reveals important features: the metallicity of the QSOs absorption line systems increases with N(HI) until it reaches a peak at log(N(HI)) ˜ 20 - 20.5, and then declines suggesting a selection effect; there is an underabundance of Fe and Cr with respect to Zn in Damped Lyman α Systems (DLAS); the [α/Fe] ratio in DLAs is suprasolar; there is a trend of decreasing abundance with increasing N(HI) for Fe, Cr, Zn, Si and S in DLAs. After the statistical analysis, the observational data is compared with predictions of chemical evolution models. We apply different models to these systems due to the uncertainties about the nature of the QSOs absorption line systems. The DLAs are investigated with one zone models describing: a) dwarf galaxies with galactic winds and b) disk galaxies with infall. A chemodynamical model for spheroids is used to study the Lyman Break Galaxies (LBGs). In order to compare the observational data with the models, we use the ratios [N/α] and [α/Fe]. These ratios in DLAs are only partially reproduced by the disk and dwarf galaxy models suggesting that the DLAs come from a variety of morphological types of galaxies and not only one (Lanfranchi & Friaça, in preparation). They also imply a typically long timescale for the star formation in these systems. In contrast, the observational constraints for the LBGs are met by models for spheroid formation with typically short timescales for star formation ( ≈ 10 Gyr^{-1}), giving support to a scenario for galaxy formation in which there is a dichotomy between the

  18. KECK SPECTROSCOPY OF FAINT 3 < z < 8 LYMAN BREAK GALAXIES: EVIDENCE FOR A DECLINING FRACTION OF EMISSION LINE SOURCES IN THE REDSHIFT RANGE 6 < z < 8

    SciTech Connect

    Schenker, Matthew A.; Ellis, Richard S.; Robertson, Brant E.; Stark, Daniel P.; Dunlop, James S.; McLure, Ross J.; Kneib, Jean-Paul; Richard, Johan

    2012-01-10

    Using deep Keck spectroscopy of Lyman break galaxies selected from infrared imaging data taken with the Wide Field Camera 3 on board the Hubble Space Telescope, we present new evidence for a reversal in the redshift-dependent fraction of star-forming galaxies with detectable Lyman alpha (Ly{alpha}) emission in the redshift range 6.3 < z < 8.8. Our earlier surveys with the DEIMOS spectrograph demonstrated a significant increase with redshift in the fraction of line emitting galaxies over the interval 4 < z < 6, particularly for intrinsically faint systems which dominate the luminosity density. Using the longer wavelength sensitivities of Low Resolution Imaging Spectrometer and NIRSPEC, we have targeted 19 Lyman break galaxies selected using recent WFC3/IR data whose photometric redshifts are in the range 6.3 < z < 8.8 and which span a wide range of intrinsic luminosities. Our spectroscopic exposures typically reach a 5{sigma} sensitivity of <50 A for the rest-frame equivalent width (EW) of Ly{alpha} emission. Despite the high fraction of emitters seen only a few hundred million years later, we find only two convincing and one possible line emitter in our more distant sample. Combining with published data on a further seven sources obtained using FORS2 on the ESO Very Large Telescope, and assuming continuity in the trends found at lower redshift, we discuss the significance of this apparent reversal in the redshift-dependent Ly{alpha} fraction in the context of our range in continuum luminosity. Assuming all the targeted sources are at their photometric redshift and our assumptions about the Ly{alpha} EW distribution are correct, we would expect to find so few emitters in less than 1% of the realizations drawn from our lower redshift samples. Our new results provide further support for the suggestion that, at the redshifts now being probed spectroscopically, we are entering the era where the intergalactic medium is partially neutral. With the arrival of more

  19. AN ULTRAVIOLET ULTRA-LUMINOUS LYMAN BREAK GALAXY AT Z = 2.78 IN NDWFS BOOeTES FIELD {sup ,} {sup ,}

    SciTech Connect

    Bian Fuyan; Fan Xiaohui; Jiang Linhua; McGreer, Ian; Wang Ran; Dey, Arjun; Green, Richard F.; Maiolino, Roberto; Walter, Fabian; Lin, Yen-Ting

    2012-10-01

    We present one of the most ultraviolet (UV) luminous Lyman break galaxies (LBGs; J1432+3358) at z = 2.78, discovered in the NOAO Deep Wide-Field Survey Booetes field. The R-band magnitude of J1432+3358 is 22.29 AB, more than two magnitudes brighter than typical L* LBGs at this redshift. The deep z-band image reveals two components of J1432+3358 separated by 1.''0 with a flux ratio of 3:1. The high signal-to-noise ratio rest-frame UV spectrum shows Ly{alpha} emission line and interstellar medium absorption lines. The absence of N V and C IV emission lines, and the non-detection in X-ray and radio wavelengths and mid-infrared (MIR) colors indicates weak or no active galactic nuclei (<10%) in this galaxy. The galaxy shows a broader line profile, with a FWHM of about 1000 km s{sup -1} and a larger outflow velocity ( Almost-Equal-To 500 km s{sup -1}) than those of typical z {approx} 3 LBGs. The physical properties are derived by fitting the spectral energy distribution (SED) with stellar synthesis models. The dust extinction, E(B - V) = 0.12, is similar to that in normal LBGs. The star formation rates (SFRs) derived from the SED fitting and the dust-corrected UV flux are consistent with each other, {approx}300 M{sub Sun} yr{sup -1}, and the stellar mass is (1.3 {+-} 0.3) Multiplication-Sign 10{sup 11} M{sub Sun }. The SFR and stellar mass in J1432+3358 are about an order of magnitude higher than those in normal LBGs. The SED-fitting results support that J1432+3358 has a continuous star formation history, with a star formation episode of 6.3 Multiplication-Sign 10{sup 8} yr. The morphology of J1432+3358 and its physical properties suggest that J1432+3358 is in an early phase of a 3:1 merger process. The unique properties and the low space number density ({approx}10{sup -7} Mpc{sup -3}) are consistent with the interpretation that such galaxies are either found in a short unobscured phase of the star formation or that a small fraction of intensive star-forming galaxies are

  20. DISCOVERY OF A CLOSE PAIR OF FAINT DWARF GALAXIES IN THE HALO OF CENTAURUS A

    SciTech Connect

    Crnojević, D.; Sand, D. J.; Caldwell, N.; McLeod, B.; Guhathakurta, P.; Toloba, E.; Simon, J. D.; Strader, J.

    2014-11-10

    As part of the Panoramic Imaging Survey of Centaurus and Sculptor (PISCeS), we report the discovery of a pair of faint dwarf galaxies (CenA-MM-Dw1 and CenA-MM-Dw2) at a projected distance of ∼90 kpc from the nearby elliptical galaxy NGC 5128 (CenA). We measure a tip of the red giant branch distance to each dwarf, finding D = 3.63 ± 0.41 Mpc for CenA-MM-Dw1 and D = 3.60 ± 0.41 Mpc for CenA-MM-Dw2, both of which are consistent with the distance to NGC 5128. A qualitative analysis of the color-magnitude diagrams indicates stellar populations consisting of an old, metal-poor red giant branch (≳12 Gyr, [Fe/H] ∼ –1.7 to –1.9). In addition, CenA-MM-Dw1 seems to host an intermediate-age population as indicated by its candidate asymptotic giant branch stars. The derived luminosities (M{sub V} = –10.9 ± 0.3 for CenA-MM-Dw1 and –8.4 ± 0.6 for CenA-MM-Dw2) and half-light radii (r{sub h} = 1.4 ± 0.04 kpc for CenA-MM-Dw1 and 0.36 ± 0.08 kpc for CenA-MM-Dw2) are consistent with those of Local Group dwarfs. CenA-MM-Dw1's low central surface brightness (μ {sub V,} {sub 0} = 27.3 ± 0.1 mag arcsec{sup –2}) places it among the faintest and most extended M31 satellites. Most intriguingly, CenA-MM-Dw1 and CenA-MM-Dw2 have a projected separation of only 3 arcmin (∼3 kpc): we are possibly observing the first, faint satellite of a satellite in an external group of galaxies.

  1. STELLAR POPULATIONS OF LYMAN BREAK GALAXIES AT z {approx_equal} 1-3 IN THE HST/WFC3 EARLY RELEASE SCIENCE OBSERVATIONS

    SciTech Connect

    Hathi, N. P.; McCarthy, P. J.; Cohen, S. H.; Windhorst, R. A.; Rutkowski, M. J.; Ryan, R. E. Jr.; Koekemoer, A. M.; Bond, H. E.; Finkelstein, S. L.; Yan, H.; O'Connell, R. W.; Straughn, A. N.; Kimble, R. A.; Balick, B.; Calzetti, D.; Disney, M. J.; Dopita, M. A.; Frogel, Jay A.; Hall, D. N. B.; Holtzman, J. A.; and others

    2013-03-10

    We analyze the spectral energy distributions (SEDs) of Lyman break galaxies (LBGs) at z {approx_equal} 1-3 selected using the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) UVIS channel filters. These HST/WFC3 observations cover about 50 arcmin{sup 2} in the GOODS-South field as a part of the WFC3 Early Release Science program. These LBGs at z {approx_equal} 1-3 are selected using dropout selection criteria similar to high-redshift LBGs. The deep multi-band photometry in this field is used to identify best-fit SED models, from which we infer the following results: (1) the photometric redshift estimate of these dropout-selected LBGs is accurate to within few percent; (2) the UV spectral slope {beta} is redder than at high redshift (z > 3), where LBGs are less dusty; (3) on average, LBGs at z {approx_equal} 1-3 are massive, dustier, and more highly star forming, compared to LBGs at higher redshifts with similar luminosities (0.1L* {approx}< L {approx}< 2.5L*), though their median values are similar within 1{sigma} uncertainties. This could imply that identical dropout selection technique, at all redshifts, finds physically similar galaxies; and (4) the stellar masses of these LBGs are directly proportional to their UV luminosities with a logarithmic slope of {approx}0.46, and star formation rates are proportional to their stellar masses with a logarithmic slope of {approx}0.90. These relations hold true-within luminosities probed in this study-for LBGs from z {approx_equal} 1.5 to 5. The star-forming galaxies selected using other color-based techniques show similar correlations at z {approx_equal} 2, but to avoid any selection biases, and for direct comparison with LBGs at z > 3, a true Lyman break selection at z {approx_equal} 2 is essential. The future HST UV surveys, both wider and deeper, covering a large luminosity range are important to better understand LBG properties and their evolution.

  2. A massive dense gas cloud close to the nucleus of the Seyfert galaxy NGC 1068

    NASA Astrophysics Data System (ADS)

    Furuya, Ray S.; Taniguchi, Yoshiaki

    2016-10-01

    Using the ALMA archival data of both 12CO (6-5) line and 689-GHz continuum emission towards the archetypical Seyfert galaxy, NGC 1068, we identified a distinct continuum peak separated by 15 pc from the nuclear radio component S1 in projection. The continuum flux gives a gas mass of ˜2 × 105 M⊙ and bolometric luminosity of ˜108 L⊙, leading to a star formation rate of ˜0.1 M⊙ yr-1. Subsequent analysis on the line data suggest that the gas cloud has a size of ˜10 pc, yielding to a mean H2 number density of ˜105 cm-3. We therefore refer to the gas as a "massive dense gas cloud": the gas density is high enough to form a "protostar cluster" with a stellar mass of ˜104 M⊙. We found that the gas stands at a unique position between galactic and extraglactic clouds in the diagrams of start formation rate (SFR) vs. gas mass proposed by Lada et al. (2012, ApJ, 745, 190) and surface density of gas vs. SFR density by Krumholz and McKee (2005, ApJ, 630, 250). All the gaseous and star-formation properties may be understood in terms of the turbulence-regulated star formation scenario. Since there are two stellar populations with ages of 300 Myr and 30 Myr in the 100 pc scale circumnulear region, we discuss that NGC 1068 has experienced at least three episodic star-formation events with the likelihood that the inner star-forming region is the younger. Together with several lines of evidence that the dynamics of the nuclear region is decoupled from that of the entire galactic disk, we discuss that the gas inflow towards the nuclear region of NGC 1068 may be driven by a past minor merger.

  3. A VERY CLOSE BINARY BLACK HOLE IN A GIANT ELLIPTICAL GALAXY 3C 66B AND ITS BLACK HOLE MERGER

    SciTech Connect

    Iguchi, Satoru; Okuda, Takeshi; Sudou, Hiroshi E-mail: okuda@a.phys.nagoya-u.ac.j

    2010-12-01

    Recent observational results provide possible evidence that binary black holes (BBHs) exist in the center of giant galaxies and may merge to form a supermassive black hole in the process of their evolution. We first detected a periodic flux variation on a cycle of 93 {+-} 1 days from the 3 mm monitor observations of a giant elliptical galaxy 3C 66B for which an orbital motion with a period of 1.05 {+-} 0.03 yr had been already observed. The detected signal period being shorter than the orbital period can be explained by taking into consideration the Doppler-shifted modulation due to the orbital motion of a BBH. Assuming that the BBH has a circular orbit and that the jet axis is parallel to the binary angular momentum, our observational results demonstrate the presence of a very close BBH that has a binary orbit with an orbital period of 1.05 {+-} 0.03 yr, an orbital radius of (3.9 {+-} 1.0) x 10{sup -3} pc, an orbital separation of (6.1{sup +1.0} {sub -0.9}) x 10{sup -3} pc, a larger black hole mass of (1.2{sup +0.5} {sub -0.2}) x 10{sup 9} M {sub sun}, and a smaller black hole mass of (7.0{sup +4.7} {sub -6.4}) x 10{sup 8} M {sub sun}. The BBH decay time of (5.1{sup +60.5} {sub -2.5}) x 10{sup 2} yr provides evidence for the occurrence of black hole mergers. This Letter will demonstrate the interesting possibility of black hole collisions to form a supermassive black hole in the process of evolution, one of the most spectacular natural phenomena in the universe.

  4. Inhibition of RNA silencing by the coat protein of Pelargonium flower break virus: distinctions from closely related suppressors.

    PubMed

    Martínez-Turiño, Sandra; Hernández, Carmen

    2009-02-01

    Viral-derived double-stranded RNAs (dsRNAs) activate RNA silencing, generating small interfering RNAs (siRNAs) which are incorporated into an RNA-induced silencing complex (RISC) that promotes homology-dependent degradation of cognate RNAs. To counteract this, plant viruses express RNA silencing suppressors. Here, we show that the coat protein (CP) of Pelargonium flower break virus (PFBV), a member of the genus Carmovirus, is able to efficiently inhibit RNA silencing. Interestingly, PFBV CP blocked both sense RNA- and dsRNA-triggered RNA silencing and did not preclude generation of siRNAs, which is in contrast with the abilities that have been reported for other carmoviral CPs. We have also found that PFBV CP can bind siRNAs and that this ability correlates with silencing suppression activity and enhancement of potato virus X pathogenicity. Collectively, the results indicate that PFBV CP inhibits RNA silencing by sequestering siRNAs and preventing their incorporation into a RISC, thus behaving similarly to unrelated viral suppressors but dissimilarly to orthologous ones.

  5. The UDF05 Follow-up of the HUDF: I. The Faint-End Slope of the Lyman-Break Galaxy Population at zeta approx. 5

    NASA Technical Reports Server (NTRS)

    Oesch, P. A.; Stiavelli, M.; Carollo, C. M.; Bergeron, L. E.; Koekemoer, A.; Lucas, R. A.; Pavlovsky, C. M.; Trenti, M.; Lilly, S. J.; Beckwith, S. V. W.; Dahlen, T.; Ferguson, H. C.; Gardner, J. P.; Lacey, C.; Mobasher, B.; Panagia, N.; Rix, H.-W.

    2007-01-01

    We present the UDF05 project, a HST Large Program of deep ACS (F606W, F775W, F850LP, and NICMOS (Fll0W, Fl60W) imaging of three fields, two of which coincide with the NICP1-4 NICMOS parallel observations of the Hubble Ultra Deep Field (HUDF). In this first paper we use the ACS data for the NICP12 field, as well as the original HUDF ACS data, to measure the UV Luminosity Function (LF) of z approximately 5 Lyman Break Galaxies (LBGs) down to very faint levels. Specifically, based on a V - i, i - z selection criterion, we identify a sample of 101 and 133 candidate z approximately 5 galaxies down to z(sub 850) = 28.5 and 29.25 magnitudes in the NICP12 field and in the HUDF, respectively. Using an extensive set of Monte Carlo simulations we derive corrections for observational biases and selection effects, and construct the rest-frame 1400 Angstroms LBG LF over the range M(sub 1400) = [-22.2, -17.1], i.e. down to approximately 0.04 L(sub *) at z = 5. We show that: (i) Different assumptions for the SED distribution of the LBG population, dust properties and intergalactic absorption result in a 25% variation in the number density of LBGs at z = 5 (ii) Under consistent assumptions for dust properties and intergalactic absorption, the HUDF is about 30% under-dense in z = 5 LBGs relative to the NICP12 field, a variation which is well explained by cosmic variance; (iii) The faint-end slope of the LF is independent of the specific assumptions for the input physical parameters, and has a value of alpha approximately -1.6, similar to the faint-end slope of the LF that has been measured for LBGs at z = 3 and z = 6. Our study therefore supports no variation in the faint-end of the LBG LF over the whole redshift range z = 3 to z = 6. The comparison with theoretical predictions suggests that (a,) the majority of the stars in the z = 5 LBG population are produced with a Top-Heavy IMF in merger-driven starbursts, and that (b) possibly, either the fraction of stellar mass produced in

  6. Breaking The Quasar L-z Degeneracy Using PDF-weighted Quasar-galaxy Cross-correlations In Deep, Wide NASA Fields

    NASA Astrophysics Data System (ADS)

    Ball, Nicholas M.; Myers, A. D.; White, M.; Hickox, R. C.; Brunner, R. J.

    2010-01-01

    We present a new method for measuring the two-point correlation function, as described by Myers, White, and Ball (2009). The method is an augmentation of previous techniques that use a heterogeneous set of spectroscopic objects to anchor the distance scale, and a well-controlled set of photometric detections to reduce noise. Our new approach weights by the information present in the full photometric redshift probability density function (PDF) to dramatically improve the clustering signal. For instance, an initial test yielded a factor of 5 improvement for quasar clustering in the Sloan Digital Sky Survey. The extra signal arises because we neither express the photometric redshift as a single value nor assign a simplified PDF functional form such as a single Gaussian. Our technique is generally applicable and should be particularly useful where complex spectroscopic data sets (e.g., BOSS) are overlapped by deep photometry (e.g., Pan-STARRS, DES, or LSST). Our method depends only on photometric detections in a single survey, but additional multi-wavelength data can be used to refine the information in the PDF weighting. This makes our approach also highly suited to regions of the sky where deep, multiwavelength space surveys overlap ground-based spectroscopy (e.g., COSMOS or the Bootes Survey). We assign photometric redshift PDFs to photometrically classified galaxies detected in the optical component of COSMOS, and use PDF weights to cross-correlate them against a spectroscopically confirmed AGN sample. We also report on similar results in the Bootes Survey. The deep spectroscopy and photometry in fields such as COSMOS and Bootes will allow new investigations of how AGN cluster as a function of luminosity and type, potentially breaking the so-called L-z degeneracy. Finally, we address the often computationally intensive requirements of utilizing full PDFs. This research was funded in part by NASA ADP grant NNX08AJ28G.

  7. Rest-frame Optical Emission Lines in z ˜ 3.5 Lyman-break-selected Galaxies: The Ubiquity of Unusually High [OIII]/Hβ Ratios at 2 Gyr

    NASA Astrophysics Data System (ADS)

    Holden, B. P.; Oesch, P. A.; González, V. G.; Illingworth, G. D.; Labbé, I.; Bouwens, R.; Franx, M.; van Dokkum, P.; Spitler, L.

    2016-03-01

    We present K-band spectra of rest-frame optical emission lines for 24 star-forming galaxies at z ˜ 3.2-3.7 using MOSFIRE on the Keck I telescope. Strong rest-frame optical [O iii] and Hβ emission lines were detected in 18 Lyman break galaxies (LBGs). The median flux ratio of [O iii]λ5007 to Hβ is {5.1}-0.5+0.5. This is a factor of 5-10 times higher than in local galaxies with similar stellar masses. None of our sources are detected in deep X-ray stacks, ruling out significant contamination by active galactic nuclei. Combining our sample with a variety of LBGs from the literature, including 49 galaxies selected in a very similar manner, we find a high median ratio of [O iii]/Hβ = {4.8}-1.7+0.8. This high ratio seems to be a ubiquitous feature of z ˜ 3-4 LBGs, very different from typical local star-forming galaxies at similar stellar masses. The only comparable systems at z ˜ 0 are those with similarly high specific star formation rates (SSFRs), though ˜5 times lower stellar masses. High SSFRs may result in a higher ionization parameter, higher electron density, or harder ionizing radiation, which, combined different elemental abundances, result in a much higher [O iii]/Hβ line ratio. This implies a strong relation between a global property of a galaxy, the SSFR, and the local conditions of ISM in star-forming regions. Partially based on data obtained with the Hubble Space Telescope operated by AURA, Inc. for NASA under contract NAS5-26555. Partially based on observations with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407.

  8. STELLAR POPULATIONS OF Ly{alpha} EMITTERS AT z = 4.86: A COMPARISON TO z {approx} 5 LYMAN BREAK GALAXIES

    SciTech Connect

    Yuma, Suraphong; Ohta, Kouji; Yabe, Kiyoto; Shimasaku, Kazuhiro; Yoshida, Makiko; Ouchi, Masami; Iwata, Ikuru; Sawicki, Marcin

    2010-09-10

    We present a study of a stellar population of Ly{alpha} emitters (LAEs) at z = 4.86 in the Great Observatories Origins Deep Survey North (GOODS-N) field and its flanking field. The LAEs are selected based on optical narrowband (NB711) and broadband (V, I{sub c} , and z') observations by the Suprime-Cam attached to the Subaru Telescope. With the publicly available Infrared Array Camera (IRAC) data in GOODS-N and further IRAC observations in the flanking fields, we select five LAEs that are not contaminated by neighboring objects in IRAC images and construct their observed spectral energy distributions (SEDs) with I{sub c} , z', IRAC 3.6 {mu}m, and 4.5 {mu}m band photometries. The SEDs cover the rest-frame UV-to-optical wavelengths. We derive the stellar masses, ages, color excesses, and star formation rates (SFRs) of the five LAEs using an SED fitting method. Assuming a constant star formation history, we find that the stellar masses range from 10{sup 8} to 10{sup 10} M {sub sun} with the median value of 2.5 x 10{sup 9} M{sub sun}. The derived ages range from very young (7.4 Myr) to 437 Myr, with a median age of 25 Myr. The color excess E(B - V) is between 0.1and0.4 mag. SFRs are 55-209 M{sub sun} yr{sup -1}. A comparison of the stellar populations is made between 3 LAEs and 88 Lyman break galaxies (LBGs) selected at the same redshift, in the same observed field, and down to the same limit of the rest-frame UV luminosity. These three LAEs are the brightest and reddest samples of all the LAE samples at z = 4.86. The LAEs are distributed at the relatively faint part of the UV-luminosity distribution of LBGs. Deriving the stellar properties of the LBGs by fitting their SEDs with the same model ensures that model difference does not affect the comparison. It is found that the stellar properties of the LAEs are located in the region where the properties of LBGs are distributed. On average, the LAEs show less dust extinction and lower SFRs than LBGs, while the stellar

  9. Oxygen abundance maps of CALIFA galaxies

    NASA Astrophysics Data System (ADS)

    Zinchenko, I. A.; Pilyugin, L. S.; Grebel, E. K.; Sánchez, S. F.; Vílchez, J. M.

    2016-11-01

    We construct maps of the oxygen abundance distribution across the discs of 88 galaxies using Calar Alto Legacy Integral Field Area survey (CALIFA) Data Release 2 (DR2) spectra. The position of the centre of a galaxy (coordinates on the plate) was also taken from the CALIFA DR2. The galaxy inclination, the position angle of the major axis, and the optical radius were determined from the analysis of the surface brightnesses in the Sloan Digital Sky Survey (SDSS) g and r bands of the photometric maps of SDSS Data Release 9. We explore the global azimuthal abundance asymmetry in the discs of the CALIFA galaxies and the presence of a break in the radial oxygen abundance distribution. We found that there is no significant global azimuthal asymmetry for our sample of galaxies, i.e. the asymmetry is small, usually lower than 0.05 dex. The scatter in oxygen abundances around the abundance gradient has a comparable value, ≲0.05 dex. A significant (possibly dominant) fraction of the asymmetry can be attributed to the uncertainties in the geometrical parameters of these galaxies. There is evidence for a flattening of the radial abundance gradient in the central part of 18 galaxies. We also estimated the geometric parameters (coordinates of the centre, the galaxy inclination and the position angle of the major axis) of our galaxies from the analysis of the abundance map. The photometry-map-based and the abundance-map-based geometrical parameters are relatively close to each other for the majority of the galaxies but the discrepancy is large for a few galaxies with a flat radial abundance gradient.

  10. Interaction effects on galaxy pairs with Gemini/GMOS - II: oxygen abundance gradients

    NASA Astrophysics Data System (ADS)

    Rosa, D. A.; Dors, O. L.; Krabbe, A. C.; Hägele, G. F.; Cardaci, M. V.; Pastoriza, M. G.; Rodrigues, I.; Winge, C.

    2014-11-01

    In this paper, we derive oxygen abundance gradients from H II regions located in 11 galaxies in eight systems of close pairs. Long-slit spectra in the range 4400-7300 Å were obtained with the Gemini Multi-Object Spectrograph at Gemini South (GMOS-S). Spatial profiles of oxygen abundance in the gaseous phase along galaxy discs were obtained using calibrations based on strong emission lines (N2 and O3N2). We found oxygen gradients to be significantly flatter for all the studied galaxies than those in typical isolated spiral galaxies. Four objects in our sample, AM 1219A, AM 1256B, AM 2030A and AM 2030B, show a clear break in the oxygen abundance at galactocentric radius R/R25 between 0.2 and 0.5. For AM 1219A and AM 1256B, we found negative slopes for the inner gradients, and for AM 2030B, we found a positive slope. All three cases show a flatter behaviour to the outskirts of the galaxies. For AM 2030A, we found a positive slope for the outer gradient, while the inner gradient is almost compatible with a flat behaviour. We found a decrease of star formation efficiency in the zone that corresponds to the oxygen abundance gradient break for AM 1219A and AM 2030B. For the former, a minimum in the estimated metallicities was found very close to the break zone, which could be associated with a corotation radius. However, AM 1256B and AM 2030A, present a star formation rate maximum but not an extreme oxygen abundance value. All four interacting systems that show oxygen gradient breaks have extreme SFR values located very close to break zones.The H II regions located in close pairs of galaxies follow the same relation between the ionization parameter and the oxygen abundance as those regions in isolated galaxies.

  11. First Results from the Faint Infrared Grism Survey (FIGS): First Simultaneous Detection of Lyα Emission and Lyman Break from a Galaxy at z = 7.51

    NASA Astrophysics Data System (ADS)

    Tilvi, V.; Pirzkal, N.; Malhotra, S.; Finkelstein, S. L.; Rhoads, J. E.; Windhorst, R.; Grogin, N. A.; Koekemoer, A.; Zakamska, N. L.; Ryan, R.; Christensen, L.; Hathi, N.; Pharo, J.; Joshi, B.; Yang, H.; Gronwall, C.; Cimatti, A.; Walsh, J.; O’Connell, R.; Straughn, A.; Ostlin, G.; Rothberg, B.; Livermore, R. C.; Hibon, P.; Gardner, Jonathan P.

    2016-08-01

    Galaxies at high redshifts are a valuable tool for studying cosmic dawn, therefore it is crucial to reliably identify these galaxies. Here, we present an unambiguous and first simultaneous detection of both the Lyα emission and the Lyman break from a z=7.512 +/- 0.004 galaxy, observed in the Faint Infrared Grism Survey (FIGS). These spectra, taken with the G102 grism on the Hubble Space Telescope (HST), show a significant emission line detection (6σ ) in two observational position angles (PAs), with Lyα line flux of 1.06+/- 0.19× {10}-17 {erg} {{{s}}}-1 {{cm}}-2. The line flux is nearly a factor of four higher than that in the archival MOSFIRE spectroscopic observations. This is consistent with other recent observations, implying that ground-based near-infrared spectroscopy underestimates the total emission line fluxes, and if confirmed, can have strong implications for reionization studies that are based on ground-based Lyα measurements. A 4σ detection of the NV line in one PA also suggests a weak active galactic nucleus (AGN), and if confirmed, would make this source the highest-redshift AGN yet found. These observations from HST thus clearly demonstrate the sensitivity of the FIGS survey, and the capability of grism spectroscopy for studying the epoch of reionization.

  12. Cosmological parameter constraints from galaxy-galaxy lensing and galaxy clustering with the SDSS DR7

    NASA Astrophysics Data System (ADS)

    Mandelbaum, Rachel; Slosar, Anže; Baldauf, Tobias; Seljak, Uroš; Hirata, Christopher M.; Nakajima, Reiko; Reyes, Reinabelle; Smith, Robert E.

    2013-06-01

    Recent studies have shown that the cross-correlation coefficient between galaxies and dark matter is very close to unity on scales outside a few virial radii of galaxy haloes, independent of the details of how galaxies populate dark matter haloes. This finding makes it possible to determine the dark matter clustering from measurements of galaxy-galaxy weak lensing and galaxy clustering. We present new cosmological parameter constraints based on large-scale measurements of spectroscopic galaxy samples from the Sloan Digital Sky Survey (SDSS) data release 7. We generalize the approach of Baldauf et al. to remove small-scale information (below 2 and 4 h-1 Mpc for lensing and clustering measurements, respectively), where the cross-correlation coefficient differs from unity. We derive constraints for three galaxy samples covering 7131 deg2, containing 69 150, 62 150 and 35 088 galaxies with mean redshifts of 0.11, 0.28 and 0.40. We clearly detect scale-dependent galaxy bias for the more luminous galaxy samples, at a level consistent with theoretical expectations. When we vary both σ8 and Ωm (and marginalize over non-linear galaxy bias) in a flat Λ cold dark matter model, the best-constrained quantity is σ8(Ωm/0.25)0.57 = 0.80 ± 0.05 (1σ, stat. + sys.), where statistical and systematic errors (photometric redshift and shear calibration) have comparable contributions, and we have fixed ns = 0.96 and h = 0.7. These strong constraints on the matter clustering suggest that this method is competitive with cosmic shear in current data, while having very complementary and in some ways less serious systematics. We therefore expect that this method will play a prominent role in future weak lensing surveys. When we combine these data with Wilkinson Microwave Anisotropy Probe 7-year (WMAP7) cosmic microwave background (CMB) data, constraints on σ8, Ωm, H0, wde and ∑mν become 30-80 per cent tighter than with CMB data alone, since our data break several parameter

  13. TOTAL MOLECULAR GAS MASSES OF z {approx} 3 LYMAN- BREAK GALAXIES: CO(J = 1 {yields} 0) EMISSION IN MS 1512-cB58 AND THE COSMIC EYE

    SciTech Connect

    Riechers, Dominik A.; Carilli, Christopher L.; Momjian, Emmanuel; Walter, Fabian

    2010-12-01

    We report the detection of CO(J = 1 {yields} 0) emission toward the lensed L {sup *} {sub UV} Lyman-break galaxies (LBGs) MS 1512-cB58 (z = 2.73) and the Cosmic Eye (z = 3.07), using the Expanded Very Large Array. The strength of the CO line emission reveals molecular gas reservoirs with masses of (4.6 {+-} 1.1) x 10{sup 8} ({mu}{sub L}/32){sup -1} ({alpha}{sub CO}/0.8) M {sub sun} and (9.3 {+-} 1.6) x 10{sup 8} ({mu}{sub L}/28){sup -1} ({alpha}{sub CO}/0.8) M {sub sun}, respectively. These observations suggest {approx}30%-40% larger gas reservoirs than previously estimated based on CO(J = 3 {yields} 2) observations due to subthermal excitation of the J = 3 line. These observations also suggest gas mass fractions of 0.46 {+-} 0.17 and 0.16 {+-} 0.06. The CO(J = 1 {yields} 0) emission in the Cosmic Eye is slightly resolved on scales of 4.''5 {+-} 1.''5, consistent with previous studies of nebular emission lines. This suggests that the molecular gas is associated with the most intensely star-forming regions seen in the ultraviolet (UV). We do not resolve the CO(J = 1 {yields} 0) emission in cB58 at {approx}2'' resolution, but find that the CO(J = 1 {yields} 0) emission is also consistent with the position of the UV-brightest emission peak. The gas masses, gas fractions, moderate CO line excitation, and star formation efficiencies in these galaxies are consistent with what is found in nearby luminous infrared galaxies. These observations thus currently represent the best constraints on the molecular gas content of 'ordinary' (i.e., {approx}L* {sub UV}) z {approx} 3 star-forming galaxies. Despite comparable star formation rates, the gas properties of these young LBGs seem to be different from the recently identified optical/infrared-selected high-z massive, gas-rich star-forming galaxies, which are more gas-rich and massive, but have lower star formation efficiencies, and presumably trace a different galaxy population.

  14. Breaking Bat

    ERIC Educational Resources Information Center

    Aguilar, Isaac-Cesar; Kagan, David

    2013-01-01

    The sight of a broken bat in Major League Baseball can produce anything from a humorous dribbler in the infield to a frightening pointed projectile headed for the stands. Bats usually break at the weakest point, typically in the handle. Breaking happens because the wood gets bent beyond the breaking point due to the wave sent down the bat created…

  15. Normal and Starburst Galaxies in Deep X-ray Surveys

    NASA Technical Reports Server (NTRS)

    Hornschemeier, Ann

    2006-01-01

    This talk will cover progress of the last several years in unraveling the nature of normal and starburst galaxies in deep X-ray surveys. This includes discussion of the normal galaxy X-ray Luminosity Function in deep field and cluster surveys and what it tells us about the binary populations in galaxies. The utility of broad band X-ray emission, especially as compared to other multiwavelength measurements of current/recent star formation, will be reviewed. These broad band X-ray measurements of star formation are based upon X-ray/Star Formation Rate correlations that span the currently available redshift range (0 < z < 1). I will also discuss new efforts underway to systematically characterize the X-ray emission from galaxies in group and cluster environments, including a new effort underway in the Coma cluster of galaxies. I will finish with discussion of the redshift frontier for studies of X-ray star formation, currently 2 approx.4, where the UV-selected Lyman Break galaxies are the best glimpse we have into X-ray emission from star formation in the early Universe. Lyman Break galaxies are of particular interest due to the overlap in basic properties with starburst galaxies in the more local Universe. Understanding the outflows in such starburst galaxies is of critical importance to constraining the "stellar" portion of cosmic feedback. The talk will close with a brief discussion of distant normal galaxy science with future X-ray observatories such as the upcoming Con-X/XEUS mission(s).

  16. The multifrequency parsec-scale structure of PKS 2254-367 (IC 1459): a luminosity-dependent break in morphology for the precursors of radio galaxies?

    NASA Astrophysics Data System (ADS)

    Tingay, S. J.; Edwards, P. G.

    2015-03-01

    We present the first multifrequency very long baseline interferometry (VLBI) images of PKS 2254-367, a gigahertz-peaked spectrum (GPS) radio source hosted by the nearby galaxy IC 1459 (D = 20.5 Mpc). PKS 2254-367 and the radio source in NGC 1052 (PKS 0238-084; D = 17.2 Mpc) are the two closest GPS radio sources to us, far closer than the next closest example, PKS 1718-649 (D = 59 Mpc). As such, IC 1459 and NGC 1052 offer opportunities to study the details of the parsec-scale radio sources as well as the environments that the radio sources inhabit, across the electromagnetic spectrum. Given that some models for the origin and evolution of GPS radio sources require a strong connection between the radio source morphology and the gaseous nuclear environment, such opportunities for detailed study are important. Our VLBI images of PKS 2254-367 show that the previously identified similarities between IC 1459 and NGC 1052 continue on to the parsec-scale. Both compact radio sources appear to have symmetric jets of approximately the same luminosity, much lower than typically noted in compact double GPS sources. Similarities between PKS 2254-367 and NGC 1052, and differences with respect to other GPS galaxies, lead us to speculate that a sub-class of GPS radio sources, with low luminosity and with jet-dominated morphologies, exists and would be largely absent from radio source surveys with ˜1 Jy flux density cut-offs. We suggest that this possible low-luminosity, jet-dominated population of GPS sources could be an analogue of the Fanaroff-Riley type I (FR I) radio galaxies, with the higher luminosity lobe-dominated GPS sources being the analogue of the FR II radio galaxies.

  17. THE LBT BOOeTES FIELD SURVEY. I. THE REST-FRAME ULTRAVIOLET AND NEAR-INFRARED LUMINOSITY FUNCTIONS AND CLUSTERING OF BRIGHT LYMAN BREAK GALAXIES AT Z {approx} 3

    SciTech Connect

    Bian Fuyan; Fan Xiaohui; Jiang Linhua; McGreer, Ian; Dave, Romeel; Dey, Arjun; Green, Richard F.; Maiolino, Roberto; Walter, Fabian; Lee, Kyoung-Soo

    2013-09-01

    We present a deep LBT/LBC U{sub spec}-band imaging survey (9 deg{sup 2}) covering the NOAO Booetes field. A total of 14,485 Lyman break galaxies (LBGs) at z {approx} 3 are selected, which are used to measure the rest-frame UV luminosity function (LF). The large sample size and survey area reduce the LF uncertainties due to Poisson statistics and cosmic variance by {>=}3 compared to previous studies. At the bright end, the LF shows excess power compared to the best-fit Schechter function, which can be attributed to the contribution of z {approx} 3 quasars. We compute the rest-frame near-infrared LF and stellar mass function (SMF) of z {approx} 3 LBGs based on the R-band and [4.5 {mu}m]-band flux relation. We investigate the evolution of the UV LFs and SMFs between z {approx} 7 and z {approx} 3, which supports a rising star formation history in the LBGs. We study the spatial correlation function of two bright LBG samples and estimate their average host halo mass. We find a tight relation between the host halo mass and the galaxy star formation rate (SFR), which follows the trend predicted by the baryonic accretion rate onto the halo, suggesting that the star formation in LBGs is fueled by baryonic accretion through the cosmic web. By comparing the SFRs with the total baryonic accretion rates, we find that cosmic star formation efficiency is about 5%-20% and it does not evolve significantly with redshift, halo mass, or galaxy luminosity.

  18. Closing in on a Short-Hard Burst Progenitor: Constraints From Early-Time Optical Imaging and Spectroscopy of a Possible Host Galaxy of GRB 050509b

    SciTech Connect

    Bloom, Joshua S.; Prochaska, J.X.; Pooley, D.; Blake, C.W.; Foley, R.J.; Jha, S.; Ramirez-Ruiz, E.; Granot, J.; Filippenko, A.V.; Sigurdsson, S.; Barth, A.J.; Chen, H.-W.; Cooper, M.C.; Falco, E.E.; Gal, R.R.; Gerke, B.F.; Gladders, M.D.; Greene, J.E.; Hennanwi, J.; Ho, L.C.; Hurley, K.; /UC, Berkeley, Astron. Dept. /Lick Observ. /Harvard-Smithsonian Ctr. Astrophys. /Princeton, Inst. Advanced Study /KIPAC, Menlo Park /Penn State U., Astron. Astrophys. /UC, Irvine /MIT, MKI /UC, Davis /UC, Berkeley /Carnegie Inst. Observ. /UC, Berkeley, Space Sci. Dept. /Michigan U. /LBL, Berkeley /Spitzer Space Telescope

    2005-06-07

    The localization of the short-duration, hard-spectrum gamma-ray burst GRB050509b by the Swift satellite was a watershed event. Never before had a member of this mysterious subclass of classic GRBs been rapidly and precisely positioned in a sky accessible to the bevy of ground-based follow-up facilities. Thanks to the nearly immediate relay of the GRB position by Swift, we began imaging the GRB field 8 minutes after the burst and have continued during the 8 days since. Though the Swift X-ray Telescope (XRT) discovered an X-ray afterglow of GRB050509b, the first ever of a short-hard burst, thus far no convincing optical/infrared candidate afterglow or supernova has been found for the object. We present a re-analysis of the XRT afterglow and find an absolute position of R.A. = 12h36m13.59s, Decl. = +28{sup o}59'04.9'' (J2000), with a 1{sigma} uncertainty of 3.68'' in R.A., 3.52'' in Decl.; this is about 4'' to the west of the XRT position reported previously. Close to this position is a bright elliptical galaxy with redshift z = 0.2248 {+-} 0.0002, about 1' from the center of a rich cluster of galaxies. This cluster has detectable diffuse emission, with a temperature of kT = 5.25{sub -1.68}{sup +3.36} keV. We also find several ({approx}11) much fainter galaxies consistent with the XRT position from deep Keck imaging and have obtained Gemini spectra of several of these sources. Nevertheless we argue, based on positional coincidences, that the GRB and the bright elliptical are likely to be physically related. We thus have discovered reasonable evidence that at least some short-duration, hard-spectra GRBs are at cosmological distances. We also explore the connection of the properties of the burst and the afterglow, finding that GRB050509b was underluminous in both of these relative to long-duration GRBs. However, we also demonstrate that the ratio of the blast-wave energy to the {gamma}-ray energy is consistent with that of long-duration GRBs. We thus find plausible

  19. Breaking Bat

    NASA Astrophysics Data System (ADS)

    Aguilar, Isaac-Cesar; Kagan, David

    2013-02-01

    The sight of a broken bat in Major League Baseball can produce anything from a humorous dribbler in the infield to a frightening pointed projectile headed for the stands. Bats usually break at the weakest point, typically in the handle. Breaking happens because the wood gets bent beyond the breaking point due to the wave sent down the bat created by the collision with the ball. The kind of wood that is used plays a role in the manner in which the bat breaks—-its "failure mode." We report on a simple experiment to compare the breaking strength and failure modes of ash and maple dowels. The results illustrate some of the features of breaking bats under game conditions.

  20. The LBT Boötes Field Survey. I. The Rest-frame Ultraviolet and Near-infrared Luminosity Functions and Clustering of Bright Lyman Break Galaxies at Z ~ 3

    NASA Astrophysics Data System (ADS)

    Bian, Fuyan; Fan, Xiaohui; Jiang, Linhua; McGreer, Ian; Dey, Arjun; Green, Richard F.; Maiolino, Roberto; Walter, Fabian; Lee, Kyoung-Soo; Davé, Romeel

    2013-09-01

    We present a deep LBT/LBC U spec-band imaging survey (9 deg2) covering the NOAO Boötes field. A total of 14,485 Lyman break galaxies (LBGs) at z ~ 3 are selected, which are used to measure the rest-frame UV luminosity function (LF). The large sample size and survey area reduce the LF uncertainties due to Poisson statistics and cosmic variance by >=3 compared to previous studies. At the bright end, the LF shows excess power compared to the best-fit Schechter function, which can be attributed to the contribution of z ~ 3 quasars. We compute the rest-frame near-infrared LF and stellar mass function (SMF) of z ~ 3 LBGs based on the R-band and [4.5 μm]-band flux relation. We investigate the evolution of the UV LFs and SMFs between z ~ 7 and z ~ 3, which supports a rising star formation history in the LBGs. We study the spatial correlation function of two bright LBG samples and estimate their average host halo mass. We find a tight relation between the host halo mass and the galaxy star formation rate (SFR), which follows the trend predicted by the baryonic accretion rate onto the halo, suggesting that the star formation in LBGs is fueled by baryonic accretion through the cosmic web. By comparing the SFRs with the total baryonic accretion rates, we find that cosmic star formation efficiency is about 5%-20% and it does not evolve significantly with redshift, halo mass, or galaxy luminosity. Based on data acquired using the Large Binocular Telescope (LBT). The LBT is an international collaboration among institutions in the United States, Italy, and Germany. LBT Corporation partners are: The University of Arizona on behalf of the Arizona university system; Istituto Nazionale di Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max-Planck Society, the Astrophysical Institute Potsdam, and Heidelberg University; The Ohio State University, and The Research Corporation, on behalf of The University of Notre Dame, University of Minnesota, and University

  1. A SIMPLE TECHNIQUE FOR PREDICTING HIGH-REDSHIFT GALAXY EVOLUTION

    SciTech Connect

    Behroozi, Peter S.; Silk, Joseph

    2015-01-20

    We show that the ratio of galaxies' specific star formation rates (SSFRs) to their host halos' specific mass accretion rates (SMARs) strongly constrains how the galaxies' stellar masses, SSFRs, and host halo masses evolve over cosmic time. This evolutionary constraint provides a simple way to probe z > 8 galaxy populations without direct observations. Tests of the method with galaxy properties at z = 4 successfully reproduce the known evolution of the stellar mass-halo mass (SMHM) relation, galaxy SSFRs, and the cosmic star formation rate (CSFR) for 5 < z < 8. We then predict the continued evolution of these properties for 8 < z < 15. In contrast to the nonevolution in the SMHM relation at z < 4, the median galaxy mass at fixed halo mass increases strongly at z > 4. We show that this result is closely linked to the flattening in galaxy SSFRs at z > 2 compared to halo SMARs; we expect that average galaxy SSFRs at fixed stellar mass will continue their mild evolution to z ∼ 15. The expected CSFR shows no breaks or features at z > 8.5; this constrains both reionization and the possibility of a steep falloff in the CSFR at z = 9-10. Finally, we make predictions for stellar mass and luminosity functions for the James Webb Space Telescope, which should be able to observe one galaxy with M {sub *} ≳ 10{sup 8} M {sub ☉} per 10{sup 3} Mpc{sup 3} at z = 9.6 and one such galaxy per 10{sup 4} Mpc{sup 3} at z = 15.

  2. Using Galaxy Winds to Constrain Galaxy Evolution

    NASA Astrophysics Data System (ADS)

    Churchill, Christopher W.; Klypin, A.; Ceverino, D.; Kacprzak, G.; Klimek, E.

    2010-01-01

    Analysis of mock quasar spectra of metal absorption lines in the proximity of formed galaxies in cosmological simulation is a highly promising for understanding the role of galaxies in IGM physics, or IGM physics in the role of galaxy formation in context of the cosmic web. Such analysis using neutral hydrogen in the cosmic web has literally revolutionized our understanding of the Lyman alpha forest. We are undertaking a wholesale approach to use powerful Lambda-CDM simulations to interpret absorption line data from redshift 1-3 starbursting galaxies e.g. Lyman break galaxies, etc) The data with which direct quantitative comparison is made are from the DEEP survey (Weiner et al.) and the collective work of Steidel et al. and collaborators. The simulations are performed using the Eulerian Gasdynamics plus N-body Adaptive Refinement Tree (ART) code, which has gas cell resolutions of 20-50 pc. Physical processes implemented in the code include realistic radiative cooling, star formation, metal enrichment and thermal feedback due to type II and type Ia supernovae. We quantitatively compare the spatial and kinematic distribution of HI, MgII, CIV, and OVI of absorption lines over a range of impact parameters for various simulated galaxies as a function of redshift, and discuss key insights for interpreting the underlying temperature, density, and ionization structure of the halo/cosmic-web interface, and the influence of galaxies on its chemical enrichment.

  3. Whirlpool Galaxy

    NASA Technical Reports Server (NTRS)

    1999-01-01

    Scientists are seeing unprecedented detail of the spiral arms and dust clouds in the nearby Whirlpool galaxy, thanks to a new Hubble Space Telescope image, available at http://www.jpl.nasa.gov/pictures/wfpc/wfpc.html. The image uses data collected January 15 and 24, 1995, and July 21, 1999, by Hubble's Wide Field and Planetary Camera 2, designed and built by JPL. Using the image, a research group led by Dr. Nick Scoville of the California Institute of Technology, Pasadena, clearly defined the structure of the galaxy's cold dust clouds and hot hydrogen, and they linked star clusters within the galaxy to their parent dust clouds.

    The Whirlpool galaxy is one of the most photogenic galaxies. This celestial beauty is easily seen and photographed with smaller telescopes and studied extensively from large ground- and space-based observatories. The new composite image shows visible starlight and light from the emission of glowing hydrogen, which is associated with the most luminous young stars in the spiral arms.

    The galaxy is having a close encounter with a nearby companion galaxy, NGC 5195, just off the upper edge of the image. The companion's gravitational pull is triggering star formation in the main galaxy, lit up by numerous clusters of young and energetic stars in brilliant detail. Luminous clusters are highlighted in red by their associated emission from glowing hydrogen gas.

    This image was composed by the Hubble Heritage Team from Hubble archive data and was superimposed onto data taken by Dr. Travis Rector of the National Optical Astronomy Observatory at the .9-meter (35-inch) telescope at the National Science Foundation's Kitt Peak National Observatory, Tucson, Ariz. Scoville's team includes M. Polletta of the University of Geneva, Switzerland; S. Ewald and S. Stolovy of Caltech; and R. Thompson and M. Rieke of the University of Arizona, Tucson.

    The Space Telescope Science Institute, Baltimore, Md., manages space operations for the Hubble Space

  4. Radio Galaxies.

    ERIC Educational Resources Information Center

    Downes, Ann

    1986-01-01

    Provides background information on radio galaxies. Topic areas addressed include: what produces the radio emission; radio telescopes; locating radio galaxies; how distances to radio galaxies are found; physics of radio galaxies; computer simulations of radio galaxies; and the evolution of radio galaxies with cosmic time. (JN)

  5. MCG+00-32-16: An Irregular Galaxy Close to the Lowest Redshift Absorber on the 3C 273 Line of Sight

    NASA Technical Reports Server (NTRS)

    Hoffman, G. L.; Lu, N. Y.; Salpeter, E. E.; Connell, B. M.; Fromhold-Treu, R.

    1998-01-01

    We present H I synthesis array mapping and CCD photometry in B and R for MCG+00-32-16. The H I disk is rotating in such a way that the side of the galaxy closer to the sight-line to the quasar has the larger velocity difference from the absorber.

  6. A dusty, normal galaxy in the epoch of reionization.

    PubMed

    Watson, Darach; Christensen, Lise; Knudsen, Kirsten Kraiberg; Richard, Johan; Gallazzi, Anna; Michałowski, Michał Jerzy

    2015-03-19

    Candidates for the modest galaxies that formed most of the stars in the early Universe, at redshifts z > 7, have been found in large numbers with extremely deep restframe-ultraviolet imaging. But it has proved difficult for existing spectrographs to characterize them using their ultraviolet light. The detailed properties of these galaxies could be measured from dust and cool gas emission at far-infrared wavelengths if the galaxies have become sufficiently enriched in dust and metals. So far, however, the most distant galaxy discovered via its ultraviolet emission and subsequently detected in dust emission is only at z = 3.2 (ref. 5), and recent results have cast doubt on whether dust and molecules can be found in typical galaxies at z ≥ 7. Here we report thermal dust emission from an archetypal early Universe star-forming galaxy, A1689-zD1. We detect its stellar continuum in spectroscopy and determine its redshift to be z = 7.5 ± 0.2 from a spectroscopic detection of the Lyman-α break. A1689-zD1 is representative of the star-forming population during the epoch of reionization, with a total star-formation rate of about 12 solar masses per year. The galaxy is highly evolved: it has a large stellar mass and is heavily enriched in dust, with a dust-to-gas ratio close to that of the Milky Way. Dusty, evolved galaxies are thus present among the fainter star-forming population at z > 7.

  7. A dusty, normal galaxy in the epoch of reionization.

    PubMed

    Watson, Darach; Christensen, Lise; Knudsen, Kirsten Kraiberg; Richard, Johan; Gallazzi, Anna; Michałowski, Michał Jerzy

    2015-03-19

    Candidates for the modest galaxies that formed most of the stars in the early Universe, at redshifts z > 7, have been found in large numbers with extremely deep restframe-ultraviolet imaging. But it has proved difficult for existing spectrographs to characterize them using their ultraviolet light. The detailed properties of these galaxies could be measured from dust and cool gas emission at far-infrared wavelengths if the galaxies have become sufficiently enriched in dust and metals. So far, however, the most distant galaxy discovered via its ultraviolet emission and subsequently detected in dust emission is only at z = 3.2 (ref. 5), and recent results have cast doubt on whether dust and molecules can be found in typical galaxies at z ≥ 7. Here we report thermal dust emission from an archetypal early Universe star-forming galaxy, A1689-zD1. We detect its stellar continuum in spectroscopy and determine its redshift to be z = 7.5 ± 0.2 from a spectroscopic detection of the Lyman-α break. A1689-zD1 is representative of the star-forming population during the epoch of reionization, with a total star-formation rate of about 12 solar masses per year. The galaxy is highly evolved: it has a large stellar mass and is heavily enriched in dust, with a dust-to-gas ratio close to that of the Milky Way. Dusty, evolved galaxies are thus present among the fainter star-forming population at z > 7. PMID:25731171

  8. Galaxies at High Redshift

    NASA Astrophysics Data System (ADS)

    Bauer, F. E.

    2014-10-01

    Recent years have seen tremendous progress in finding and charactering star-forming galaxies at high redshifts across the electromagnetic spectrum, giving us a more complete picture of how galaxies evolve, both in terms of their stellar and gas content, as well as the growth of their central supermassive black holes. A wealth of studies now demonstrate that star formation peaked at roughly half the age of the Universe and drops precariously as we look back to very early times, and that their central monsters apparently growth with them. At the highest-redshifts, we are pushing the boundaries via deep surveys at optical, X-ray, radio wavelengths, and more recently using gamma-ray bursts. I will review some of our accomplishments and failures. Telescope have enabled Lyman break galaxies to be robustly identified, but the UV luminosity function and star formation rate density of this population at z = 6 - 8 seems to be much lower than at z = 2 - 4. High escape fractions and a large contribution from faint galaxies below our current detection limits would be required for star-forming galaxies to reionize the Universe. We have also found that these galaxies have blue rest-frame UV colours, which might indicate lower dust extinction at z > 5. There has been some spectroscopic confirmation of these Lyman break galaxies through Lyman-α emission, but the fraction of galaxies where we see this line drops at z > 7, perhaps due to the onset of the Gunn-Peterson effect (where the IGM is opaque to Lyman-α).

  9. PKS 2349-014: A Luminous Quasar With Thin Wisps, A Large Off-Center Nebulosity, and A Close Companion Galaxy

    NASA Technical Reports Server (NTRS)

    Bahcall, John N.; Kirhakos, Sofia; Schneider, Donald P.

    1995-01-01

    Hubble Space Telescope (HST) images (WFC2) of PKS 2349-014 show that this luminous nearby quasar is interacting with diffuse (presumably galactic) material. Two thin wisps that have a total extent of about 20 kpc (for H0 = 100 km s(exp -1) and Omega0 = 1.0) are observed to approximately surround the quasar. One of the wisps appears to pass through a companion galaxy that is located at a projected distance of 3 kpc from the center of the quasar light. The companion galaxy, if located at the distance of PKS 2349-014, has an intrinsic size and luminosity similar to the Large Magellanic Cloud. A faint extended nebulosity, which is detected over a region of 35 kpc x 50 kpc and is centered about 5 kpc from the quasar nucleus, overlaps the wisps. The immediate environment of PKS 2349-014 is different from the environments of the other eight luminous quasars that we have studied previously with the HST. If the multiple light components of the HST images are fit to a single de Vaucouleurs profile, as was done in previous analyses of ground-based data, then the results obtained for the total luminosity of the model galaxy is in agreement with the earlier ground-based studies.

  10. The evolution of galaxies from primeval irregulars to present-day ellipticals.

    PubMed

    Mori, Masao; Umemura, Masayuki

    2006-03-30

    Galaxy formation is believed to proceed in a 'bottom up' manner, starting with the formation of small clumps of gas and stars that then merge hierarchically into giant systems. The baryonic gas loses thermal energy by radiative cooling and falls towards the centres of the new galaxies, while supernovae blow gas out. Any realistic model therefore requires a proper treatment of these processes, but hitherto this has been far from satisfactory. Here we report a simulation that follows evolution from the earliest stages of galaxy formation through the period of dynamical relaxation, at which point the resulting galaxy is in its final form. The bubble structures of gas revealed in our simulation (for times of less than 3 x 10(8) years) resemble closely high-redshift Lyman-alpha emitters. After 10(9) years, these bodies are dominated by stellar continuum radiation and then resemble the Lyman break galaxies, which are high-redshift star-forming galaxies. At this point, the abundance of elements heavier than helium ('metallicity') appears to be solar. After 1.3 x 10(10) years, these galaxies resemble present-day ellipticals.

  11. STUDYING LARGE- AND SMALL-SCALE ENVIRONMENTS OF ULTRAVIOLET LUMINOUS GALAXIES

    SciTech Connect

    Basu-Zych, Antara R.; Schiminovich, David; Heinis, Sebastien; Heckman, Tim; Bianchi, Luciana; Overzier, Roderik; Zamojski, Michel; Barlow, Tom A.; Conrow, Tim; Forster, Karl G.; Friedman, Peter G.; Martin, D. Christopher; Morrissey, Patrick; Ilbert, Olivier; Koekemoer, Anton M.; Donas, Jose; Milliard, Bruno; Lee, Young-Wook; Madore, Barry F.; Neff, Susan G.

    2009-07-10

    Studying the environments of 0.4 < z < 1.2 ultraviolet (UV)-selected galaxies, as examples of extreme star-forming galaxies (with star formation rates (SFRs) in the range of 3-30 M{sub sun} yr{sup -1}), we explore the relationship between high rates of star formation, host halo mass, and pair fractions. We study the large- and small-scale environments of local ultraviolet luminous galaxies (UVLGs) by measuring angular correlation functions. We cross-correlate these systems with other galaxy samples: a volume-limited sample (ALL), a blue luminous galaxy sample, and a luminous red galaxy (LRG) sample. We determine the UVLG comoving correlation length to be r{sub 0} = 4.8{sup +11.6}{sub -2.4} h {sup -1} Mpc at (z) = 1.0, which is unable to constrain the halo mass for this sample. However, we find that UVLGs form close (separation <30 kpc) pairs with the ALL sample, but do not frequently form pairs with LRGs. A rare subset of UVLGs, those with the highest FUV surface brightnesses, are believed to be local analogs of high-redshift Lyman break galaxies (LBGs) and are called Lyman break analogs (LBAs). LBGs and LBAs share similar characteristics (i.e., color, size, surface brightness, specific SFRs, metallicities, and dust content). Recent Hubble Space Telescope images of z {approx} 0.2 LBAs show disturbed morphologies, signs of mergers and interactions. UVLGs may be influenced by interactions with other galaxies and we discuss this result in terms of other high star-forming, merging systems.

  12. Constraining inflation with future galaxy redshift surveys

    SciTech Connect

    Huang, Zhiqi; Vernizzi, Filippo; Verde, Licia E-mail: liciaverde@icc.ub.edu

    2012-04-01

    With future galaxy surveys, a huge number of Fourier modes of the distribution of the large scale structures in the Universe will become available. These modes are complementary to those of the CMB and can be used to set constraints on models of the early universe, such as inflation. Using a MCMC analysis, we compare the power of the CMB with that of the combination of CMB and galaxy survey data, to constrain the power spectrum of primordial fluctuations generated during inflation. We base our analysis on the Planck satellite and a spectroscopic redshift survey with configuration parameters close to those of the Euclid mission as examples. We first consider models of slow-roll inflation, and show that the inclusion of large scale structure data improves the constraints by nearly halving the error bars on the scalar spectral index and its running. If we attempt to reconstruct the inflationary single-field potential, a similar conclusion can be reached on the parameters characterizing the potential. We then study models with features in the power spectrum. In particular, we consider ringing features produced by a break in the potential and oscillations such as in axion monodromy. Adding large scale structures improves the constraints on features by more than a factor of two. In axion monodromy we show that there are oscillations with small amplitude and frequency in momentum space that are undetected by CMB alone but can be measured by including galaxy surveys in the analysis.

  13. Gas in void galaxies

    NASA Astrophysics Data System (ADS)

    Kreckel, Kathryn Joyce

    . We find that the void galaxies are ! generally gas rich, low luminosity, blue disk galaxies, but identify three as early type galaxies. The void galaxy optical and H I properties are not unusual for their luminosity and morphology. The small scale clustering in the void is similar to that in higher density regions, and we identify 18 H I rich neighboring galaxies in the voids. Two of these are systems of three galaxies linearly aligned and joined by a H I bridge, suggestive of filamentary formation within the void. We find no population of H I rich low luminosity galaxies within the observed voids that are not close companions of the targeted sample. Finally, to put these observations in a theoretical context, we analyze a (120 h^-1 Mpc)^3 adaptive mesh refinement hydrodynamic simulation that contains a high resolution subvolume centered on a ~30 Mpc diameter void. We construct mock observations with ~1 kpc resolution of the stellar and gas properties of these systems which reproduce the range of colors and luminosities observed in the SDSS for nearby galaxies, however we find no strong trends with density. We also make predictions for a significant population of low luminosity (M_r = -14) dwarf galaxies that is preferentially located in low density regions and specifically in the void center.

  14. 76 FR 61760 - Post Office Closing

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-10-05

    ...: Notice. SUMMARY: This document informs the public that an appeal of the closing of the Breaks, Virginia... received a petition for review of the Postal Service's determination to close the Breaks post office in Breaks, Virginia. The petition was filed by Keith Mullins (Petitioner) and is postmarked September...

  15. Beyond the Break: Observational Evidence of Stellar Migration

    NASA Astrophysics Data System (ADS)

    Yoachim, Peter; Roškar, R.; Debattista, V. P.

    2012-01-01

    We use the VIRUS-P IFU spectrograph to observe 6 nearby disk galaxies. In three cases (NGC 2684, NGC 6155, and NGC 7437), we find that a downward break in the disk surface brightness profile corresponds with a change in the dominant stellar population with the interior being dominated by active star formation and the exterior having older stellar populations. This is similar to theoretical models that predict surface brightness breaks are caused by stellar migration, with the outer disk being populated from scattered old interior stars. In three more cases (IC 1132, NGC 4904, and NGC 6691), we find no significant change in the stellar population as one crosses the break radius. In these galaxies, both the inner and outer disks are dominated by active star formation and younger stellar populations. While radial migration can contribute to radial profile breaks, it appears multiple mechanisms are required to explain all of our observed stellar profile breaks.

  16. JSPAM: Interacting galaxies modeller

    NASA Astrophysics Data System (ADS)

    Wallin, John F.; Holincheck, Anthony; Harvey, Allen

    2015-11-01

    JSPAM models galaxy collisions using a restricted n-body approach to speed up computation. Instead of using a softened point-mass potential, the software supports a modified version of the three component potential created by Hernquist (1994, ApJS 86, 389). Although spherically symmetric gravitationally potentials and a Gaussian model for the bulge are used to increase computational efficiency, the potential mimics that of a fully consistent n-body model of a galaxy. Dynamical friction has been implemented in the code to improve the accuracy of close approaches between galaxies. Simulations using this code using thousands of particles over the typical interaction times of a galaxy interaction take a few seconds on modern desktop workstations, making it ideal for rapidly prototyping the dynamics of colliding galaxies. Extensive testing of the code has shown that it produces nearly identical tidal features to those from hierarchical tree codes such as Gadget but using a fraction of the computational resources. This code was used in the Galaxy Zoo: Mergers project and is very well suited for automated fitting of galaxy mergers with automated pattern fitting approaches such as genetic algorithms. Java and Fortran versions of the code are available.

  17. Closing the loop: a self-consistent model of optical, X-ray and Sunyaev-Zel'dovich scaling relations for clusters of Galaxies

    NASA Astrophysics Data System (ADS)

    Rozo, E.; Bartlett, J. G.; Evrard, A. E.; Rykoff, E. S.

    2014-02-01

    We demonstrate that optical data from Sloan Digital Sky Survey, X-ray data from ROSAT and Chandra, and Sunyaev-Zel'dovich (SZ) data from Planck can be modelled in a fully self-consistent manner. After accounting for systematic errors and allowing for property covariance, we find that scaling relations derived from optical and X-ray selected cluster samples are consistent with one another. Moreover, these cluster scaling relations satisfy several non-trivial spatial abundance constraints and closure relations. Given the good agreement between optical and X-ray samples, we combine the two and derive a joint set of LX-M and YSZ-M relations. Our best-fitting YSZ-M relation is in good agreement with the observed amplitude of the thermal SZ power spectrum for a Wilkinson Microwave Anisotropy Probe 7 cosmology, and is consistent with the masses for the two CLASH galaxy clusters published thus far. We predict the halo masses of the remaining z ≤ 0.4 CLASH clusters, and use our scaling relations to compare our results with a variety of X-ray and weak lensing cluster masses from the literature.

  18. Percolation and galaxies.

    PubMed

    Schulman, L S; Seiden, P E

    1986-07-25

    A theory is presented in which much of the structure of spiral galaxies arises from a percolation phase transition that underlies the phenomenon of propagating star formation. According to this view, the appearance of spiral arms is a consequence of the differential rotation of the galaxy and the characteristic divergence of correlation lengths for continuous phase transitions. Other structural properties of spiral galaxies, such as the distribution of the gaseous components and the luminosity, arise directly from a feedback mechanism that pins the star formation rate close to the critical point of the phase transition. The approach taken in this article differs from traditional dynamical views. The argument is presented that, at least for some galaxies, morphological and other features are already fixed by general properties of phase transitions, irrespective of detailed dynamic or other considerations. PMID:17794566

  19. Local starburst galaxies and their descendants. Statistics from the Sloan Digital Sky Survey

    NASA Astrophysics Data System (ADS)

    Bergvall, Nils; Marquart, Thomas; Way, Michael J.; Blomqvist, Anna; Holst, Emma; Östlin, Göran; Zackrisson, Erik

    2016-03-01

    Aims: Despite strong interest in the starburst phenomenon in extragalactic astronomy, the concept remains ill-defined. Here we use a strict definition of starburst to examine the statistical properties of starburst galaxies in the local universe. We also seek to establish links between starburst galaxies, post-starburst (hereafter postburst) galaxies, and active galaxies. Methods: Data were selected from the Sloan Digital Sky Survey DR7. We applied a novel method of treating dust attenuation and derive star formation rates, ages, and stellar masses assuming a two-component stellar population model. Dynamical masses are calculated from the width of the Hα line. These masses agree excellently with the photometric masses. The mass (gas+stars) range is ~109-1011.5ℳ⊙. As a selection criterion for starburst galaxies, we use, the birthrate parameter, b = SFR/ ⟨ SFR ⟩, requiring that b ≥ 3. For postburst galaxies, we use, the equivalent width of Hδ in absorption with the criterion EWHδ,abs ≥ 6 Å. Results: We find that only 1% of star-forming galaxies are starburst galaxies. They contribute 3-6% to the stellar production and are therefore unimportant for the local star formation activity. The median starburst age is 70 Myr roughly independent of mass, indicating that star formation is mainly regulated by local feedback processes. The b-parameter strongly depends on burst age. Values close to b = 60 are found at ages ~10 Myr, while almost no starbursts are found at ages >1 Gyr. The median baryonic burst mass fraction of sub-L∗ galaxies is 5% and decreases slowly towards high masses. The median mass fraction of the recent burst in the postburst sample is 5-10%. A smaller fraction of the postburst galaxies, however, originates in non-bursting galaxies. The age-mass distribution of the postburst progenitors (with mass fractions >3%) is bimodal with a break at logℳ(ℳ⊙) ~ 10.6, above which the ages are doubled. The starburst and postburst luminosity

  20. EXTREME GAS FRACTIONS IN CLUMPY, TURBULENT DISK GALAXIES AT z ∼ 0.1

    SciTech Connect

    Fisher, David B.; Glazebrook, Karl; Bassett, Robert; Bolatto, Alberto; Obreschkow, Danail; Cooper, Erin Mentuch; Wisnioski, Emily; Abraham, Roberto G.; Damjanov, Ivana; Green, Andy; McGregor, Peter

    2014-08-01

    In this Letter, we report the discovery of CO fluxes, suggesting very high gas fractions in three disk galaxies seen in the nearby universe (z ∼ 0.1). These galaxies were investigated as part of the DYnamics of Newly Assembled Massive Objects (DYNAMO) survey. High-resolution Hubble Space Telescope imaging of these objects reveals the presence of large star forming clumps in the bodies of the galaxies, while spatially resolved spectroscopy of redshifted Hα reveals the presence of high dispersion rotating disks. The internal dynamical state of these galaxies resembles that of disk systems seen at much higher redshifts (1 < z < 3). Using CO(1-0) observations made with the Plateau de Bure Interferometer, we find gas fractions of 20%-30% and depletion times of t {sub dep} ∼ 0.5 Gyr (assuming a Milky-Way-like α{sub CO}). These properties are unlike those expected for low-redshift galaxies of comparable specific star formation rate, but they are normal for their high-z counterparts. DYNAMO galaxies break the degeneracy between gas fraction and redshift, and we show that the depletion time per specific star formation rate for galaxies is closely tied to gas fraction, independent of redshift. We also show that the gas dynamics of two of our local targets corresponds to those expected from unstable disks, again resembling the dynamics of high-z disks. These results provide evidence that DYNAMO galaxies are local analogs to the clumpy, turbulent disks, which are often found at high redshift.

  1. Triple Scoop from Galaxy Hunter

    NASA Technical Reports Server (NTRS)

    2006-01-01

    [figure removed for brevity, see original site] [figure removed for brevity, see original site] [figure removed for brevity, see original site] Figure 1Figure 2Figure 3

    Silver Dollar Galaxy: NGC 253 (figure 1) Located 10 million light-years away in the southern constellation Sculptor, the Silver Dollar galaxy, or NGC 253, is one of the brightest spiral galaxies in the night sky. In this edge-on view from NASA's Galaxy Evolution Explorer, the wisps of blue represent relatively dustless areas of the galaxy that are actively forming stars. Areas of the galaxy with a soft golden glow indicate regions where the far-ultraviolet is heavily obscured by dust particles.

    Gravitational Dance: NGC 1512 and NGC 1510 (figure 2) In this image, the wide ultraviolet eyes of NASA's Galaxy Evolution Explorer show spiral galaxy NGC 1512 sitting slightly northwest of elliptical galaxy NGC 1510. The two galaxies are currently separated by a mere 68,000 light-years, leading many astronomers to suspect that a close encounter is currently in progress.

    The overlapping of two tightly wound spiral arm segments makes up the light blue inner ring of NGC 1512. Meanwhile, the galaxy's outer spiral arm is being distorted by strong gravitational interactions with NGC 1510.

    Galaxy Trio: NGC 5566, NGC 5560, and NGC 5569 (figure 3) NASA's Galaxy Evolution Explorer shows a triplet of galaxies in the Virgo cluster: NGC 5560 (top galaxy), NGC 5566 (middle galaxy), and NGC 5569 (bottom galaxy).

    The inner ring in NGC 5566 is formed by two nearly overlapping bright arms, which themselves spring from the ends of a central bar. The bar is not visible in ultraviolet because it consists of older stars or low mass stars that do not emit energy at ultraviolet wavelengths. The outer disk of NGC 5566 appears warped, and the disk of NGC 5560 is clearly disturbed. Unlike its galactic neighbors, the disk of NGC 5569 does not appear to have been distorted by any passing

  2. Growing Galaxies Gently

    NASA Astrophysics Data System (ADS)

    2010-10-01

    of the flow of pristine gas from the surrounding space and the associated formation of new stars. They were very careful to make sure that their specimen galaxies had not been disturbed by interactions with other galaxies. The selected galaxies were very regular, smoothly rotating discs, similar to the Milky Way, and they were seen about two billion years after the Big Bang (at a redshift of around three). In galaxies in the modern Universe the heavy elements [1] are more abundant close to the centre. But when Cresci's team mapped their selected distant galaxies with the SINFONI spectrograph on the VLT [2] they were excited to see that in all three cases there was a patch of the galaxy, close to the centre, with fewer heavy elements, but hosting vigorously forming stars, suggesting that the material to fuel the star formation was coming from the surrounding pristine gas that is low in heavy elements. This was the smoking gun that provided the best evidence yet of young galaxies accreting primitive gas and using it to form new generations of stars. As Cresci concludes: "This study has only been possible because of the outstanding performance of the SINFONI instrument on the VLT. It has opened a new window for studying the chemical properties of very distant galaxies. SINFONI provides information not only in two spatial dimensions, but also in a third, spectral dimension, which allows us to see the internal motions inside galaxies and study the chemical composition of the interstellar gas." Notes [1] The gas filling the early Universe was almost all hydrogen and helium. The first generations of stars processed this primitive material to create heavier elements such as oxygen, nitrogen and carbon by nuclear fusion. When this material was subsequently spewed back into space by intense particle winds from massive young stars and supernova explosions the amounts of heavy elements in the galaxy gradually increased. Astronomers refer to elements other than hydrogen and

  3. First Observational Support for Overlapping Reionized Bubbles Generated by a Galaxy Overdensity

    NASA Astrophysics Data System (ADS)

    Castellano, M.; Dayal, P.; Pentericci, L.; Fontana, A.; Hutter, A.; Brammer, G.; Merlin, E.; Grazian, A.; Pilo, S.; Amorin, R.; Cristiani, S.; Dickinson, M.; Ferrara, A.; Gallerani, S.; Giallongo, E.; Giavalisco, M.; Guaita, L.; Koekemoer, A.; Maiolino, R.; Paris, D.; Santini, P.; Vallini, L.; Vanzella, E.; Wagg, J.

    2016-02-01

    We present an analysis of deep Hubble Space Telescope (HST) multi-band imaging of the BDF field specifically designed to identify faint companions around two of the few Lyα emitting galaxies spectroscopically confirmed at z ∼ 7. Although separated by only 4.4 proper Mpc these galaxies cannot generate H ii regions large enough to explain the visibility of their Lyα lines, thus requiring a population of fainter ionizing sources in their vicinity. We use deep HST and VLT-Hawk-I data to select z ∼ 7 Lyman break galaxies around the emitters. We select six new robust z ∼ 7 LBGs at Y ∼ 26.5–27.5 whose average spectral energy distribution is consistent with the objects being at the redshift of the close-by Lyα emitters. The resulting number density of z ∼ 7 LBGs in the BDF field is a factor of approximately three to four higher than expected in random pointings of the same size. We compare these findings with cosmological hydrodynamic plus radiative transfer simulations of a universe with a half neutral IGM: we find that indeed Lyα emitter pairs are only found in completely ionized regions characterized by significant LBG overdensities. Our findings match the theoretical prediction that the first ionization fronts are generated within significant galaxy overdensities and support a scenario where faint, “normal” star-forming galaxies are responsible for reionization.

  4. Interacting galaxies resolved by IRAS

    NASA Technical Reports Server (NTRS)

    Mazzarella, Joseph M.; Surace, Jason A.

    1994-01-01

    We discuss procedures, limitations and results of high resolution processing of interacting galaxies observed by the Infrared Astronomical Satellite (IRAS). Among 56 potentially resolvable interacting groups selected from the IRAS Bright Galaxy Sample, 22 systems have been resolved yielding fluxes for a total of 51 galaxies. In about 2/3 of the resolved pairs, both galaxies were detected in the far-infrared. A set of isolated non-interacting galaxies was chosen from the Bright Galaxy Sample for comparison with the interacting galaxies. For the current sample, which naturally excludes close pairs and ultraluminous merging systems, the primary conclusions are: (1) It is not possible to distinguish individual interacting galaxies from isolated galaxies of similar luminosity on the basis of infrared properties alone. (2) No direct correlation was found between measures of interaction strength and indicators of enhanced star formation within the resolved systems. (3) Comparison of the interacting and isolated samples indicates statistically significant differences between their distributions of far-infrared color ratios, luminosities, and surface brightnesses. Even during the early stages of interaction spanned by these systems, in a statistical sense, tidal perturbations substantially boost far-infrared indicators of star formation compared to non-interacting systems. We also briefly discuss future prospects for pushing the IRAS data to its limits for additional interacting systems.

  5. Galaxy and Mass Assembly (GAMA): merging galaxies and their properties

    NASA Astrophysics Data System (ADS)

    De Propris, Roberto; Baldry, Ivan K.; Bland-Hawthorn, Joss; Brough, Sarah; Driver, Simon P.; Hopkins, Andrew M.; Kelvin, Lee; Loveday, Jon; Phillipps, Steve; Robotham, Aaron S. G.

    2014-11-01

    We derive the close pair fractions and volume merger rates for galaxies in the Galaxy and Mass Assembly (GAMA) survey with -23 < Mr < -17 (ΩM = 0.27, ΩΛ = 0.73, H0 = 100 km s-1 Mpc-1) at 0.01 < z < 0.22 (look-back time of <2 Gyr). The merger fraction is approximately 1.5 per cent Gyr-1 at all luminosities (assuming 50 per cent of pairs merge) and the volume merger rate is ≈3.5 × 10-4 Mpc-3 Gyr-1. We examine how the merger rate varies by luminosity and morphology. Dry mergers (between red/spheroidal galaxies) are found to be uncommon and to decrease with decreasing luminosity. Fainter mergers are wet, between blue/discy galaxies. Damp mergers (one of each type) follow the average of dry and wet mergers. In the brighter luminosity bin (-23 < Mr < -20), the merger rate evolution is flat, irrespective of colour or morphology, out to z ˜ 0.2. The makeup of the merging population does not appear to change over this redshift range. Galaxy growth by major mergers appears comparatively unimportant and dry mergers are unlikely to be significant in the buildup of the red sequence over the past 2 Gyr. We compare the colour, morphology, environmental density and degree of activity (BPT class, Baldwin, Phillips & Terlevich) of galaxies in pairs to those of more isolated objects in the same volume. Galaxies in close pairs tend to be both redder and slightly more spheroid dominated than the comparison sample. We suggest that this may be due to `harassment' in multiple previous passes prior to the current close interaction. Galaxy pairs do not appear to prefer significantly denser environments. There is no evidence of an enhancement in the AGN fraction in pairs, compared to other galaxies in the same volume.

  6. Ring Around a Galaxy

    NASA Technical Reports Server (NTRS)

    1999-01-01

    Space Telescope Science Institute astronomers are giving the public chances to decide where to aim NASA's Hubble Space Telescope. Guided by 8,000 Internet voters, Hubble has already been used to take a close-up, multi-color picture of the most popular object from a list of candidates, the extraordinary 'polar-ring' galaxy NGC 4650A. Located about 130 million light-years away, NGC 4650A is one of only 100 known polar-ring galaxies. Their unusual disk-ring structure is not yet understood fully. One possibility is that polar rings are the remnants of colossal collisions between two galaxies sometime in the distant past, probably at least 1 billion years ago. What is left of one galaxy has become the rotating inner disk of old red stars in the center. Meanwhile, another smaller galaxy which ventured too close was probably severely damaged or destroyed. The bright bluish clumps, which are especially prominent in the outer parts of the ring, are regions containing luminous young stars, examples of stellar rebirth from the remnants of an ancient galactic disaster. The polar ring appears to be highly distorted. No regular spiral pattern stands out in the main part of the ring, and the presence of young stars below the main ring on one side and above on the other shows that the ring is warped and does not lie in one plane. Determining the typical ages of the stars in the polar ring is an initial goal of our Polar Ring Science Team that can provide a clue to the evolution of this unusual galaxy. The HST exposures were acquired by the Hubble Heritage Team, consisting of Keith Noll, Howard Bond, Carol Christian, Jayanne English, Lisa Frattare, Forrest Hamilton, Anne Kinney and Zolt Levay, and guest collaborators Jay Gallagher (University of Wisconsin-Madison), Lynn Matthews (National Radio Astronomy Observatory-Charlottesville), and Linda Sparke (University of Wisconsin-Madison).

  7. A photometrically and spectroscopically confirmed population of passive spiral galaxies

    NASA Astrophysics Data System (ADS)

    Fraser-McKelvie, Amelia; Brown, Michael J. I.; Pimbblet, Kevin A.; Dolley, Tim; Crossett, Jacob P.; Bonne, Nicolas J.

    2016-10-01

    We have identified a population of passive spiral galaxies from photometry and integral field spectroscopy. We selected z < 0.035 spiral galaxies that have WISE colours consistent with little mid-infrared emission from warm dust. Matched aperture photometry of 51 spiral galaxies in ultraviolet, optical and mid-infrared show these galaxies have colours consistent with passive galaxies. Six galaxies form a spectroscopic pilot study and were observed using the Wide-Field Spectrograph to check for signs of nebular emission from star formation. We see no evidence of substantial nebular emission found in previous red spiral samples. These six galaxies possess absorption-line spectra with 4000 Å breaks consistent with an average luminosity-weighted age of 2.3 Gyr. Our photometric and integral field spectroscopic observations confirm the existence of a population of local passive spiral galaxies, implying that transformation into early-type morphologies is not required for the quenching of star formation.

  8. SHELS: OPTICAL SPECTRAL PROPERTIES OF WISE 22 {mu}m SELECTED GALAXIES

    SciTech Connect

    Hwang, Ho Seong; Geller, Margaret J.; Kurtz, Michael J.; Fabricant, Daniel G.; Dell'Antonio, Ian P. E-mail: mgeller@cfa.harvard.edu E-mail: dfabricant@cfa.harvard.edu

    2012-10-10

    We use a dense, complete redshift survey, the Smithsonian Hectospec Lensing Survey (SHELS), covering a 4 deg{sup 2} region of a deep imaging survey, the Deep Lens Survey (DLS), to study the optical spectral properties of Wide-field Infrared Survey Explorer (WISE) 22 {mu}m selected galaxies. Among 507 WISE 22 {mu}m selected sources with (S/N){sub 22{mu}m} {>=} 3 ( Almost-Equal-To S{sub 22{mu}m} {approx}> 2.5 mJy), we identify the optical counterparts of 481 sources ({approx}98%) at R < 25.2 in the very deep, DLS R-band source catalog. Among them, 337 galaxies at R < 21 have SHELS spectroscopic data. Most of these objects are at z < 0.8. The infrared (IR) luminosities are in the range 4.5 Multiplication-Sign 10{sup 8}(L{sub Sun }) {approx}< L{sub IR} {approx}< 5.4 Multiplication-Sign 10{sup 12}(L{sub Sun }). Most 22 {mu}m selected galaxies are dusty star-forming galaxies with a small (<1.5) 4000 A break. The stacked spectra of the 22 {mu}m selected galaxies binned in IR luminosity show that the strength of the [O III] line relative to H{beta} grows with increasing IR luminosity. The optical spectra of the 22 {mu}m selected galaxies also show that there are some ({approx}2.8%) unusual galaxies with very strong [Ne III] {lambda}3869, 3968 emission lines that require hard ionizing radiation such as active galactic nuclei (AGNs) or extremely young massive stars. The specific star formation rates (sSFRs) derived from the 3.6 and 22 {mu}m flux densities are enhanced if the 22 {mu}m selected galaxies have close late-type neighbors. The sSFR distribution of the 22 {mu}m selected galaxies containing AGNs is similar to the distribution for star-forming galaxies without AGNs. We identify 48 dust-obscured galaxy candidates with large ({approx}> 1000) mid-IR to optical flux density ratio. The combination of deep photometric and spectroscopic data with WISE data suggests that WISE can probe the universe to z {approx} 2.

  9. The Environment of Barred Galaxies Revisited

    NASA Astrophysics Data System (ADS)

    Cervantes Sodi, B.; Li, C.; Park, C.; Wang, L.

    We present a study of the environment of barred galaxies using galaxies drawn from the SDSS. We use several different statistics to quantify the environment: the projected two-point cross-correlation function, the background-subtracted number counts of neighbor galaxies, the overdensity of the local environment, the membership of our galaxies to galaxy groups to segregate central and satellite systems, and, for central galaxies, the stellar to halo mass ratio (M∗/Mh). When we split our sample into early- and late-type galaxies, we see a weak but significant trend for early-type galaxies with a bar to be more strongly clustered on scales from a few 100 kpc to 1 Mpc when compared to unbarred early-type galaxies. This indicates that the presence of a bar in early-type galaxies depends on the location within their host dark matter halos. This is confirmed by the group catalog in the sense that for early-types, the fraction of central galaxies is smaller if they have a bar. For late-type galaxies, we find fewer neighbors within ˜ 50 kpc around the barred galaxies when compared to unbarred galaxies from the control sample, suggesting that tidal forces from close companions suppress the formation/growth of bars. For central late-type galaxies, bars are more common on galaxies with high M∗/Mh values, as expected from early theoretical works which showed that systems with massive dark matter halos are more stable against bar instabilities. Finally, we find no obvious correlation between overdensity and the bars in our sample, showing that galactic bars are not obviously linked to the large-scale structure of the universe.

  10. Globular Clusters, Ultracompact Dwarfs, and Dwarf Galaxies in Abell 2744 at a Redshift of 0.308

    NASA Astrophysics Data System (ADS)

    Lee, Myung Gyoon; Jang, In Sung

    2016-11-01

    We report a photometric study of globular clusters (GCs), ultracompact dwarfs (UCDs), and dwarf galaxies in the giant merging galaxy cluster Abell 2744 at z = 0.308. Color–magnitude diagrams of the point sources derived from deep F814W (rest frame r‧) and F105W (rest frame I) images of Abell 2744 in the Hubble Space Telescope Frontier Field show a rich population of point sources, which have colors that are similar to those of typical GCs. These sources are as bright as -14.9\\lt {M}r\\prime ≤slant -11.4 (26.0 < F814W(Vega) ≤ 29.5) mag, being mostly UCDs and bright GCs in Abell 2744. The luminosity function (LF) of these sources shows a break at {M}r\\prime ≈ -12.9 (F814W ≈ 28.0) mag, indicating a boundary between UCDs and bright GCs. The numbers of GCs and UCDs are estimated to be 1,711,640+589,760 ‑430,500 and 147 ± 26, respectively. The clustercentric radial number density profiles of the UCDs and bright GCs show similar slopes, but these profiles are much steeper than those of the dwarf galaxies and the mass density profile based on gravitational lensing analysis. We derive an LF of the red sequence galaxies for -22.9\\lt {M}r\\prime ≤slant -13.9 mag. The faint end of this LF is fit well by a flat power law with α =-1.14+/- 0.08, showing no faint upturn. These results support the galaxy-origin scenario for bright UCDs: they are the nuclei of dwarf galaxies that are stripped when they pass close to the center of massive galaxies or a galaxy cluster, while some of the faint UCDs are at the bright end of the GCs.

  11. Deficiency of "Thin" Stellar Bars in Seyfert Host Galaxies.

    PubMed

    Shlosman; Peletier; Knapen

    2000-06-01

    Using all available major samples of Seyfert galaxies and their corresponding closely matched control samples of nonactive galaxies, we find that the bar ellipticities (or axial ratios) in Seyfert galaxies are systematically different from those in nonactive galaxies. Overall, there is a deficiency of bars with large ellipticities (i.e., "thin" or "strong" bars) in Seyfert galaxies compared to nonactive galaxies. Accompanied with a large dispersion due to small number statistics, this effect is strictly speaking at the 2 sigma level. To obtain this result, the active galaxy samples of near-infrared surface photometry were matched to those of normal galaxies in type, host galaxy ellipticity, absolute magnitude, and, to some extent, redshift. We discuss possible theoretical explanations of this phenomenon within the framework of galactic evolution, and, in particular, of radial gas redistribution in barred galaxies. Our conclusions provide further evidence that Seyfert hosts differ systematically from their nonactive counterparts on scales of a few kiloparsecs.

  12. A MINUET OF GALAXIES

    NASA Technical Reports Server (NTRS)

    2002-01-01

    This troupe of four galaxies, known as Hickson Compact Group 87 (HCG 87), is performing an intricate dance orchestrated by the mutual gravitational forces acting between them. The dance is a slow, graceful minuet, occurring over a time span of hundreds of millions of years. The Wide Field and Planetary Camera 2 on NASA's Hubble Space Telescope (HST) provides a striking improvement in resolution over previous ground-based imaging. In particular, this image reveals complex details in the dust lanes of the group's largest galaxy member (HCG 87a), which is actually disk-shaped, but tilted so that we see it nearly edge-on. Both 87a and its elliptically shaped nearest neighbor (87b) have active galactic nuclei which are believed to harbor black holes that are consuming gas. A third group member, the nearby spiral galaxy 87c, may be undergoing a burst of active star formation. Gas flows within galaxies can be intensified by the gravitational tidal forces between interacting galaxies. So interactions can provide fresh fuel for both active nuclei and starburst phenomena. These three galaxies are so close to each other that gravitational forces disrupt their structure and alter their evolution. From the analysis of its spectra, the small spiral near the center of the group could either be a fourth member or perhaps an unrelated background object. The HST image was made by combining images taken in four different color filters in order to create a three-color picture. Regions of active star formation are blue (hot stars) and also pinkish if hot hydrogen gas is present. The complex dark bands across the large edge-on disk galaxy are due to interstellar dust silhouetted against the galaxy's background starlight. A faint tidal bridge of stars can be seen between the edge-on and elliptical galaxies. HCG 87 was selected for Hubble imaging by members of the public who visited the Hubble Heritage website (http://heritage.stsci.edu) during the month of May and registered their votes

  13. Les galaxies

    NASA Astrophysics Data System (ADS)

    Combes, Francoise

    2016-08-01

    Considerable progress has been made on galaxy formation and evolution in recent years, and new issues. The old Hubble classification according to the tuning fork of spirals, lenticulars and ellipticals, is still useful but has given place to the red sequence, the blue cloud and the green valley, showing a real bimodality of types between star forming galaxies (blue) and quenched ones (red). Large surveys have shown that stellar mass and environment density are the two main factors of the evolution from blue to red sequences. Evolution is followed directly with redshift through a look-back time of more than 12 billion years. The most distant galaxy at z=11. has already a stellar mass of a billion suns. In an apparent anti-hierarchical scenario, the most massive galaxies form stars early on, while essentially dwarf galaxies are actively star-formers now. This downsizing feature also applies to the growth of super-massive black holes at the heart of each bulgy galaxy. The feedback from active nuclei is essential to explain the distribution of mass in galaxies, and in particular to explain why the fraction of baryonic matter is so low, lower by more than a factor 5 than the baryonic fraction of the Universe. New instruments just entering in operation, like MUSE and ALMA, provide a new and rich data flow, which is developed in this series of articles.

  14. Disrupted Stars in Unusual Galaxies

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-03-01

    Tidal disruption events (TDEs) occur when a star passes a little too close to a supermassive black hole at the center of a galaxy. Tidal forces from the black hole cause the passing star to be torn apart, resulting in a brief flare of radiation as the stars material accretes onto the black hole. A recent study asks the following question: do TDEs occur most frequently in an unusual type of galaxy?A Trend in DisruptionsSo far, we have data from eight candidate TDEs that peaked in optical and ultraviolet wavelengths. The spectra from these observations have shown an intriguing trend: many of these TDEs host galaxies exhibit weak line emission (indicating little or no current star-formation activity), and yet they show strong Balmer absorption lines (indicating star formation activity occurred within the last Gyr). These quiescent, Balmer-strong galaxies likely underwent a period of intense star formation that recently ended.To determine if TDEs are overrepresented in such galaxies, a team of scientists led by Decker French (Steward Observatory, University of Arizona) has quantified the fraction of galaxies in the Sloan Digital Sky Survey (SDSS) that exhibit similar properties to those of TDE hosts.Quantifying OverrepresentationSpectral characteristics of SDSS galaxies (gray) and TDE candidate host galaxies (colored points): line emission vs. Balmer absorption. The lower right-hand box identifies thequiescent, Balmer-strong galaxies which contain most TDE events, yet are uncommon among the galaxy sample as a whole. Click for a better look! [French et al. 2016]French and collaborators compare the optical spectra of the TDE host galaxies to those of nearly 600,000 SDSS galaxies, using two different cutoffs for the Balmer absorption the indicator of past star formation. Their strictest cut, filtering for very high Balmer absorption, selected only 0.2% of the SDSS galaxies, yet 38% of the TDEs are hosted in such galaxies. Using a more relaxed cutoff selects 2.3% of

  15. Midsummer's Dream Galaxies

    NASA Astrophysics Data System (ADS)

    2005-08-01

    -years away in the constellation Coma Berenices (Berenice's Hair). It displays a bright yellowish central bulge that juts out above most impressive dust lanes. Because it is relatively close (it is only 12 times farther away than Messier 31, the Andromeda galaxy, which is the major galaxy closest to us) and relatively large (roughly one third larger than the Milky Way), it does not fit entirely into the field of view of the FORS instrument (about 7 x 7 arcmin2). Many background galaxies are also visible in this FORS image, giving full meaning to their nickname of "island universes". Messier 83 If our Milky Way were to resemble this one, we certainly would be proud of our home! The beautiful spiral galaxy Messier 83 [4] is located in the southern constellation Hydra (the Water Snake) and is also known as NGC 5236 and as the Southern Pinwheel galaxy. Its distance is about 15 million light-years. Being about twice as small as the Milky Way, its size on the sky is 11x10 arcmin2. The image show clumpy, well-defined spiral arms that are rich in young stars, while the disc reveals a complex system of intricate dust lanes. This galaxy is known to be a site of vigorous star formation.

  16. DEEP NEAR-INFRARED SPECTROSCOPY OF PASSIVELY EVOLVING GALAXIES AT z {approx}> 1.4

    SciTech Connect

    Onodera, M.; Carollo, M.; Lilly, S.; Renzini, A.; Mancini, C.; Cappellari, M.; Strazzullo, V.; Daddi, E.; Gobat, R.; McCracken, H. J.; Ilbert, O.; Capak, P.; Cimatti, A.; Giavalisco, M.; Koekemoer, A. M.; Kong, X.; Motohara, K.; Ohta, K.; and others

    2012-08-10

    We present the results of new near-IR spectroscopic observations of passive galaxies at z {approx}> 1.4 in a concentration of BzK-selected galaxies in the COSMOS field. The observations have been conducted with Subaru/MOIRCS, and have resulted in absorption lines and/or continuum detection for 18 out of 34 objects. This allows us to measure spectroscopic redshifts for a sample that is almost complete to K{sub AB} = 21. COSMOS photometric redshifts are found in fair agreement overall with the spectroscopic redshifts, with a standard deviation of {approx}0.05; however, {approx}30% of objects have photometric redshifts systematically underestimated by up to {approx}25%. We show that these systematic offsets in photometric redshifts can be removed by using these objects as a training set. All galaxies fall in four distinct redshift spikes at z = 1.43, 1.53, 1.67, and 1.82, with this latter one including seven galaxies. SED fits to broadband fluxes indicate stellar masses in the range of {approx}4-40 Multiplication-Sign 10{sup 10} M{sub Sun} and that star formation was quenched {approx}1 Gyr before the cosmic epoch at which they are observed. The spectra of several individual galaxies have allowed us to measure their H{delta}{sub F} indices and the strengths of the 4000 A break, which confirms their identification as passive galaxies, as does a composite spectrum resulting from the co-addition of 17 individual spectra. The effective radii of the galaxies have been measured on the COSMOS HST/ACS i{sub F814W}-band image, confirming the coexistence at these redshifts of passive galaxies, which are substantially more compact than their local counterparts with others that follow the local effective radius-stellar mass relation. For the galaxy with the best signal-to-noise spectrum we were able to measure a velocity dispersion of 270 {+-} 105 km s{sup -1} (error bar including systematic errors), indicating that this galaxy lies closely on the virial relation given its stellar

  17. ROSAT HRI Observations of the Starburst Galaxy M82

    NASA Astrophysics Data System (ADS)

    Schulman, E.; Bregman, J. N.

    1992-12-01

    Gas-dynamical models of starburst galaxies predict that supernova heating creates a bubble of hot gas which breaks out of the disk. Some models predict a polar outflow in which the hot gas escapes along an edge-brightened chimney-like structure, while others predict spherical galactic winds. In order to test these models we have obtained a 25 ksec ROSAT HRI image of the starburst galaxy M82. Our HRI image has a resolution of about 5''(70 pc) and a field of view of about 30' (20 kpc). The image includes photons with energies between 0.2 and 1.5 keV and is almost an order of magnitude more sensitive than previous images. The X-ray emission extends perpendicular to the disk 3-4 kpc which is comparable to the extent of the emission detected with the Einstein IPC, although our resolution is more than a factor of 10 better. The emission is neither collimated nor spherically distributed, but has a conical distribution in which the emission close to the center of the galaxy is more compact than the emission farther away from the disk. The X-ray emission is not edge-brightened and decreases in hardness with distance from the center of the galaxy. The mean energy in the core is about 0.85 keV, while the mean energy a few kpc from the disk is about 0.25 keV. The shape, temperature, and lack of edge-brightening of the emission is in conflict with some starburst models. ES wishes to acknowledge support from a NASA Graduate Student Research Program Fellowship.

  18. Gas dynamics in interacting and merging galaxies

    SciTech Connect

    Olson, K.M.

    1990-01-01

    A three dimensional model of the dynamics of gas clouds in interacting galaxies is developed. The gas clouds move under the combined gravitational influence of two galaxies passing close to each other. By performing a multipole expansion of the gravitational field the effects of self-gravity within a galaxy are included. This allows the case to be modeled in which the two galaxies merge. The gas clouds are allowed to interact with one another by colliding. They either coalesce to form a larger cloud or are disrupted, depending on their relative kinetic energy as compared to the total gravitational binding energy of the two-cloud system. Various cases are considered by varying such parameters as impact parameter, inclination of the gaseous disk of a galaxy to the orbital plane of the two, interacting galaxies, relative velocity of the galaxies, the mass ratio of the galaxies, and the presence of gas in the second galaxy. As the strength of the interaction increases the more disturbed the interstellar medium becomes. The clouds collide at an increased rate and with larger velocities so that the fraction of collisions which disrupt the clouds rises as the strength of the interaction increases. Since interacting galaxies are observed to have elevated star formation rates, it is concluded that the star formation induced by the interaction of two galaxies is related to the high velocity, disruptive cloud-cloud collisions.

  19. Galaxy Clustering Around Nearby Luminous Quasars

    NASA Technical Reports Server (NTRS)

    Fisher, Karl B.; Bahcall, John N.; Kirhakos, Sofia; Schneider, Donald P.

    1996-01-01

    We examine the clustering of galaxies around a sample of 20 luminous low redshift (z approx. less than 0.30) quasars observed with the Wide Field Camera-2 on the Hubble Space Telescope (HST). The HST resolution makes possible galaxy identification brighter than V = 24.5 and as close as 1 min or 2 min to the quasar. We find a significant enhancement of galaxies within a projected separation of approx. less than 100 1/h kpc of the quasars. If we model the QSO/galaxy correlation function as a power law with a slope given by the galaxy/galaxy correlation function, we find that the ratio of the QSO/galaxy to galaxy/galaxy correlation functions is 3.8 +/- 0.8. The galaxy counts within r less than 15 1/h kpc of the quasars are too high for the density profile to have an appreciable core radius (approx. greater than 100 1/h kpc). Our results reinforce the idea that low redshift quasars are located preferentially in groups of 10-20 galaxies rather than in rich clusters. We see no significant difference in the clustering amplitudes derived from radio-loud and radio-quiet subsamples.

  20. Local Group dwarf galaxies: nature and nurture

    NASA Astrophysics Data System (ADS)

    Sawala, Till; Scannapieco, Cecilia; White, Simon

    2012-02-01

    We investigate the formation and evolution of dwarf galaxies in a high-resolution, hydrodynamical cosmological simulation of a Milky Way sized halo and its environment. Our simulation includes gas cooling, star formation, supernova feedback, metal enrichment and ultraviolet heating. In total, 90 satellites and more than 400 isolated dwarf galaxies are formed in the simulation, allowing a systematic study of the internal and environmental processes that determine their evolution. We find that 95 per cent of satellite galaxies are gas free at z= 0, and identify three mechanisms for gas loss: supernova feedback, tidal stripping and photoevaporation due to re-ionization. Gas-rich satellite galaxies are only found with total masses above ˜5 × 109 M⊙. In contrast, for isolated dwarf galaxies, a total mass of ˜109 M⊙ constitutes a sharp transition; less massive galaxies are predominantly gas free at z= 0, more massive, isolated dwarf galaxies are often able to retain their gas. In general, we find that the total mass of a dwarf galaxy is the main factor which determines its star formation, metal enrichment and its gas content, but that stripping may explain the observed difference in gas content between field dwarf galaxies and satellites with total masses close to 109 M⊙. We also find that a morphological transformation via tidal stripping of infalling, luminous dwarf galaxies whose dark matter is less concentrated than their stars cannot explain the high total mass-to-light ratios of the faint dwarf spheroidal galaxies.

  1. HUBBLE'S INFRARED GALAXY GALLERY

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Astronomers have used the NASA Hubble Space Telescope to produce an infrared 'photo essay' of spiral galaxies. By penetrating the dust clouds swirling around the centers of these galaxies, the telescope's infrared vision is offering fresh views of star birth. These six images, taken with the Near Infrared Camera and Multi-Object Spectrometer, showcase different views of spiral galaxies, from a face-on image of an entire galaxy to a close-up of a core. The top row shows spirals at diverse angles, from face-on, (left); to slightly tilted, (center); to edge-on, (right). The bottom row shows close-ups of the hubs of three galaxies. In these images, red corresponds to glowing hydrogen, the raw material for star birth. The red knots outlining the curving spiral arms in NGC 5653 and NGC 3593, for example, pinpoint rich star-forming regions where the surrounding hydrogen gas is heated by intense ultraviolet radiation from young, massive stars. In visible light, many of these regions can be hidden from view by the clouds of gas and dust in which they were born. The glowing hydrogen found inside the cores of these galaxies, as in NGC 6946, may be due to star birth; radiation from active galactic nuclei (AGN), which are powered by massive black holes; or a combination of both. White is light from middle-age stars. Clusters of stars appear as white dots, as in NGC 2903. The galaxy cores are mostly white because of their dense concentration of stars. The dark material seen in these images is dust. These galaxies are part of a Hubble census of about 100 spiral galaxies. Astronomers at Space Telescope Science Institute took these images to fill gaps in the scheduling of a campaign using the NICMOS-3 camera. The data were non-proprietary, and were made available to the entire astronomical community. Filters: Three filters were used: red, blue, and green. Red represents emission at the Paschen Alpha line (light from glowing hydrogen) at a wavelength of 1.87 microns. Blue shows the

  2. Breaking the Hermetic Seal.

    ERIC Educational Resources Information Center

    Hill, Paul

    2001-01-01

    The key to handling persistent challenges (increased accountability demands, unstable superintendencies, educator shortages, minority underachievement, and resistant high schools) is breaking down institutional barriers separating today's schools from their surrounding communities. Tapping human and cultural resources and offering better…

  3. Stellar populations in spiral galaxies: broadband versus spectroscopic viewpoints

    NASA Astrophysics Data System (ADS)

    MacArthur, Lauren Anne

    2006-06-01

    This thesis addresses the stellar population content in the bulges and disks of spiral galaxies using broad-band and spectroscopic data. The results can be used to constrain models of galaxy formation in addition to establishing a comprehensive, model-independent, picture of colour and line-index gradients in spiral galaxies. Building upon my Masters study of structural parameters in spiral galaxies, I use the largest collection of multi-band (optical and IR) surface brightness profiles for face-on and moderately-tilted galaxies to extract radial colour profiles. The colour gradients are then translated into age and metallicity gradients by comparison with stellar population synthesis (SPS) models considering a range of star formation histories, including recent bursts. Based on their integrated light, we find that high surface brightness (SB) regions of galaxies formed their stars earlier than lower SB ones, or at a similar epoch but on shorter timescale. At a given SB level, the star formation histories are modulated by the overall potential of the galaxy such that brighter/higher rotational velocity galaxies formed earlier. This formation "down-sizing" implied by our results is inconsistent with current implementations of semi-analytic structure formation models. In order to alleviate concerns that our colour gradients could be affected by dust reddening, we designed a similar spectroscopic investigation and explored the dust sensitivity of absorption-line indices. The latter test makes use of the latest SPS, models incorporating a multi-component model for the line and continuum attenuation due to dust. For quiescent stellar populations (e.g. spheroids and globular clusters), dust extinction effects are small for most indices with the exception of the 4000 Å break. For models with current star formation, many indices may suffer from dust reddening and any departures depend on age, dust distribution, and the effective optical depth. However, a number of useful

  4. Stellar populations in spiral galaxies: Broadband versus spectroscopic viewpoints

    NASA Astrophysics Data System (ADS)

    MacArthur, Lauren Anne

    This thesis addresses the stellar population content in the bulges and disks of spiral galaxies using broad-band and spectroscopic data. The results can be used to constrain models of galaxy formation in addition to establishing a comprehensive, model-independent, picture of colour and line-index gradients in spiral galaxies. Building upon my Masters study of structural parameters in spiral galaxies, I use the largest collection of multi-band (optical and IR) surface brightness profiles for face-on and moderately-tilted galaxies to extract radial colour profiles. The colour gradients are then translated into age and metallicity gradients by comparison with stellar population synthesis (SPS) models considering a range of star formation histories, including recent bursts. Based on their integrated light, we find that high surface brightness (SB) regions of galaxies formed their stars earlier than lower SB ones, or at a similar epoch but on shorter timescale. At a given SB level, the star formation histories are modulated by the overall potential of the galaxy such that brighter/higher rotational velocity galaxies formed earlier. This formation "down-sizing" implied by our results is inconsistent with current implementations of semi-analytic structure formation models. In order to alleviate concerns that our colour gradients could be affected by dust reddening, we designed a similar spectroscopic investigation and explored the dust sensitivity of absorption-line indices. The latter test makes use of the latest SPS, models incorporating a multi-component model for the line and continuum attenuation due to dust. For quiescent stellar populations (e.g. spheroids and globular clusters), dust extinction effects are small for most indices with the exception of the 4000 Å break. For models with current star formation, many indices may suffer from dust reddening and any departures depend on age, dust distribution, and the effective optical depth. However, a number of useful

  5. CS (5-4) survey towards nearby infrared bright galaxies

    NASA Astrophysics Data System (ADS)

    Wang, Junzhi; Zhang, Zhiyu; Shi, Yong

    2011-09-01

    With the observations of the CS (5-4) line towards a sample of 24 infrared bright galaxies using Heinrich Hertz Submillimeter Telescope (HHSMT), we detected CS (5-4) emission in 14 galaxies, including 12 ultraluminous infrared galaxies (ULIRGs)/luminous infrared galaxies (LIRGs) and two nearby normal galaxies. As a good dense gas tracer, which has been well used for studying star formation in the Milky Way, CS (5-4) can trace the active star-forming gas in galaxies. The correlation between CS (5-4) luminosity, which is estimated with detected CS (5-4) line emission, and the infrared luminosity in these 14 galaxies, is fitted with a correlation coefficient of 0.939 and a slope close to unity. This correlation confirms that dense gas, which is closely linked to star formation, is very important for understanding star formation in galaxies.

  6. DISTANT CLUSTER OF GALAXIES [left

    NASA Technical Reports Server (NTRS)

    2002-01-01

    One of the deepest images to date of the universe, taken with NASA's Hubble Space Telescope (HST), reveals thousands of faint galaxies at the detection limit of present day telescopes. Peering across a large volume of the observable cosmos, Hubble resolves thousands of galaxies from five to twelve billion light-years away. The light from these remote objects has taken billions of years to cross the expanding universe, making these distant galaxies fossil evidence' of events that happened when the universe was one-third its present age. A fraction of the galaxies in this image belong to a cluster located nine billion light-years away. Though the field of view (at the cluster's distance) is only two million light-years across, it contains a multitude of fragmentary objects. (By comparison, the two million light-years between our Milky Way galaxy and its nearest large companion galaxy, in the constellation Andromeda, is essentially empty space!) Very few of the cluster's members are recognizable as normal spiral galaxies (like our Milky Way), although some elongated members might be edge-on disks. Among this zoo of odd galaxies are ``tadpole-like'' objects, disturbed and apparently merging systems dubbed 'train-wrecks,' and a multitude of faint, tiny shards and fragments, dwarf galaxies or possibly an unknown population of objects. However, the cluster also contains red galaxies that resemble mature examples of today's elliptical galaxies. Their red color comes from older stars that must have formed shortly after the Big Bang. The image is the full field view of the Wide Field and Planetary Camera-2. The picture was taken in intervals between May 11 and June 15, 1994 and required an 18-hour long exposure, over 32 orbits of HST, to reveal objects down to 29th magnitude. [bottom right] A close up view of the peculiar radio galaxy 3C324 used to locate the cluster. The galaxy is nine billion light-years away as measured by its spectral redshift (z=1.2), and located in the

  7. Exploring galaxy environments on large and small scales

    NASA Astrophysics Data System (ADS)

    Berrier, Heather Danae

    I examine galaxy environments and galaxy interactions using LCDM N-body simulations, redshift surveys, and a sample of 77 galaxies in close pairs and groups. I show that some simulations and models for assigning luminosities to dark matter halos reproduce the observed counts-in-cylinders statistic distribution quite well, except for very isolated galaxies. I also find that the close-pair fraction from a LCDM simulation matches both the observed close- pair count at z=0 and the pair fraction evolution. Finally, I use U and V photometry of a sample of previously-studied galaxies to support results suggesting a relationship between galaxy separation and starburst strength, and confirm that U-B colors are a sensitive indicator of burst strength. This will be useful in studies of high redshift galaxies.

  8. The Hooked Galaxy

    NASA Astrophysics Data System (ADS)

    2006-06-01

    Life is not easy, even for galaxies. Some indeed get so close to their neighbours that they get rather distorted. But such encounters between galaxies have another effect: they spawn new generations of stars, some of which explode. ESO's VLT has obtained a unique vista of a pair of entangled galaxies, in which a star exploded. Because of the importance of exploding stars, and particularly of supernovae of Type Ia [1], for cosmological studies (e.g. relating to claims of an accelerated cosmic expansion and the existence of a new, unknown, constituent of the universe - the so called 'Dark Energy'), they are a preferred target of study for astronomers. Thus, on several occasions, they pointed ESO's Very Large Telescope (VLT) towards a region of the sky that portrays a trio of amazing galaxies. MCG-01-39-003 (bottom right) is a peculiar spiral galaxy, with a telephone number name, that presents a hook at one side, most probably due to the interaction with its neighbour, the spiral galaxy NGC 5917 (upper right). In fact, further enhancement of the image reveals that matter is pulled off MCG-01-39-003 by NGC 5917. Both these galaxies are located at similar distances, about 87 million light-years away, towards the constellation of Libra (The Balance). ESO PR Photo 22/06 ESO PR Photo 22/06 The Hooked Galaxy and its Companion NGC 5917 (also known as Arp 254 and MCG-01-39-002) is about 750 times fainter than can be seen by the unaided eye and is about 40,000 light-years across. It was discovered in 1835 by William Herschel, who strangely enough, seems to have missed its hooked companion, only 2.5 times fainter. As seen at the bottom left of this exceptional VLT image, a still fainter and nameless, but intricately beautiful, barred spiral galaxy looks from a distance the entangled pair, while many 'island universes' perform a cosmic dance in the background. But this is not the reason why astronomers look at this region. Last year, a star exploded in the vicinity of the hook

  9. On Galaxies with UV Excess from Kazarian Lists

    NASA Astrophysics Data System (ADS)

    Yeghiazaryan, A. A.

    2016-09-01

    Presented are the results of a statistical study of galaxies with UV excess from six Kazarian lists. Morphology, activity, heliocentric redshift and the magnitude of 502 out of 702 galaxies from Kazarian lists were considered. It is shown that these galaxies have different morphological types, different degrees of activity, and often contain condensations and double nuclei. It is also shown that most of the closely located Kazarian galaxies form physical systems.

  10. Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Miller, Christopher J. Miller

    2012-03-01

    There are many examples of clustering in astronomy. Stars in our own galaxy are often seen as being gravitationally bound into tight globular or open clusters. The Solar System's Trojan asteroids cluster at the gravitational Langrangian in front of Jupiter’s orbit. On the largest of scales, we find gravitationally bound clusters of galaxies, the Virgo cluster (in the constellation of Virgo at a distance of ˜50 million light years) being a prime nearby example. The Virgo cluster subtends an angle of nearly 8◦ on the sky and is known to contain over a thousand member galaxies. Galaxy clusters play an important role in our understanding of theUniverse. Clusters exist at peaks in the three-dimensional large-scale matter density field. Their sky (2D) locations are easy to detect in astronomical imaging data and their mean galaxy redshifts (redshift is related to the third spatial dimension: distance) are often better (spectroscopically) and cheaper (photometrically) when compared with the entire galaxy population in large sky surveys. Photometric redshift (z) [Photometric techniques use the broad band filter magnitudes of a galaxy to estimate the redshift. Spectroscopic techniques use the galaxy spectra and emission/absorption line features to measure the redshift] determinations of galaxies within clusters are accurate to better than delta_z = 0.05 [7] and when studied as a cluster population, the central galaxies form a line in color-magnitude space (called the the E/S0 ridgeline and visible in Figure 16.3) that contains galaxies with similar stellar populations [15]. The shape of this E/S0 ridgeline enables astronomers to measure the cluster redshift to within delta_z = 0.01 [23]. The most accurate cluster redshift determinations come from spectroscopy of the member galaxies, where only a fraction of the members need to be spectroscopically observed [25,42] to get an accurate redshift to the whole system. If light traces mass in the Universe, then the locations

  11. Nature of multiple-nucleus cluster galaxies

    SciTech Connect

    Merritt, D.

    1984-05-01

    In models for the evolution of galaxy clusters which include dynamical friction with the dark binding matter, the distribution of galaxies becomes more concentrated to the cluster center with time. In a cluster like Coma, this evolution could increase by a factor of approximately 3 the probability of finding a galaxy very close to the cluster center, without decreasing the typical velocity of such a galaxy significantly below the cluster mean. Such an enhancement is roughly what is needed to explain the large number of first-ranked cluster galaxies which are observed to have extra ''nuclei''; it is also consistent with the high velocities typically measured for these ''nuclei.'' Unlike the cannibalism model, this model predicts that the majority of multiple-nucleus systems are transient phenomena, and not galaxies in the process of merging.

  12. Extended Source/Galaxy All Sky 2

    NASA Technical Reports Server (NTRS)

    2003-01-01

    This panoramic view encompasses the entire sky and reveals the distribution of galaxies beyond the Milky Way galaxy, which astronomers call extended sources, as observed by Two Micron All-Sky Survey. The image is assembled from a database of over 1.6 million galaxies listed in the survey's All-Sky Survey Extended Source Catalog,; more than half of the galaxies have never before been catalogued. The colors represent how the many galaxies appear at three distinct wavelengths of infrared light (blue at 1.2 microns, green at 1.6 microns, and red at 2.2 microns). Quite evident are the many galactic clusters and superclusters, as well as some streamers composing the large-scale structure of the nearby universe. The blue overlay represents the very close and bright stars from our own Milky Way galaxy. In this projection, the bluish Milky Way lies predominantly toward the upper middle and edges of the image.

  13. Luminosities of Barred and Unbarred S0 Galaxies

    NASA Astrophysics Data System (ADS)

    van den Bergh, Sidney

    2012-07-01

    Lenticular galaxies with MB < -21.5 are almost exclusively unbarred, whereas both barred and unbarred objects occur at fainter luminosity levels. This effect is observed both for objects classified in blue light, and for those that were classified in the infrared. This result suggests that the most luminous (massive) S0 galaxies find it difficult to form bars. As a result, the mean luminosity of unbarred lenticular galaxies in both B and IR light is observed to be ~0.4 mag brighter than that of barred lenticulars. A small contribution to the observed luminosity difference that is found between SA0 and SB0 galaxies may also be due to the fact that there is an asymmetry between the effects of small classification errors on SA0 and SB0 galaxies. An elliptical (E) galaxy might be misclassified as a lenticular (S0) or an S0 as an E. However, an E will never be misclassified as an SB0, nor will an SB0 ever be called an E. This asymmetry is important because E galaxies are typically twice as luminous as S0 galaxies. The present results suggest that the evolution of luminous lenticular galaxies may be closely linked to that of elliptical galaxies, whereas fainter lenticulars might be more closely associated with ram-pressure stripped spiral galaxies. Finally, it is pointed out that fine details of the galaxy formation process might account for some of the differences between the classifications of the same galaxy by individual competent morphologists.

  14. Baby Galaxies in the Adult Universe

    NASA Technical Reports Server (NTRS)

    2004-01-01

    [figure removed for brevity, see original site] Figure 1

    This artist's conception illustrates the decline in our universe's 'birth-rate' over time. When the universe was young, massive galaxies were forming regularly, like baby bees in a bustling hive. In time, the universe bore fewer and fewer 'offspring,' and newborn galaxies (white circles) matured into older ones more like our own Milky Way (spirals).

    Previously, astronomers thought that the universe had ceased to give rise to massive, young galaxies, but findings from NASA's Galaxy Evolution Explorer suggest that may not be the case. Surveying thousands of nearby galaxies with its highly sensitive ultraviolet eyes, the telescope spotted three dozen that greatly resemble youthful galaxies from billions of years ago. In this illustration, those galaxies are represented as white circles on the right, or 'today' side of the timeline.

    The discovery not only suggests that our universe may still be alive with youth, but also offers astronomers their first close-up look at what appear to be baby galaxies. Prior to the new result, astronomers had to peer about 11 billion light-years into the distant universe to see newborn galaxies. The newfound galaxies are only about 2 to 4 billion light-years away.

  15. Galaxy Mergers and Dark Matter Halo Mergers in LCDM: Mass, Redshift, and Mass-Ratio Dependence

    SciTech Connect

    Stewart, Kyle R.; Bullock, James S.; Barton, Elizabeth J.; Wechsler, Risa H.; /KIPAC, Menlo Park /SLAC

    2009-08-03

    We employ a high-resolution LCDM N-body simulation to present merger rate predictions for dark matter halos and investigate how common merger-related observables for galaxies - such as close pair counts, starburst counts, and the morphologically disturbed fraction - likely scale with luminosity, stellar mass, merger mass ratio, and redshift from z = 0 to z = 4. We provide a simple 'universal' fitting formula that describes our derived merger rates for dark matter halos a function of dark halo mass, merger mass ratio, and redshift, and go on to predict galaxy merger rates using number density-matching to associate halos with galaxies. For example, we find that the instantaneous merger rate of m/M > 0.3 mass ratio events into typical L {approx}> fL{sub *} galaxies follows the simple relation dN/dt {approx_equal} 0.03(1+f)Gyr{sup -1} (1+z){sup 2.1}. Despite the rapid increase in merger rate with redshift, only a small fraction of > 0.4L{sub *} high-redshift galaxies ({approx} 3% at z = 2) should have experienced a major merger (m/M > 0.3) in the very recent past (t < 100 Myr). This suggests that short-lived, merger-induced bursts of star formation should not contribute significantly to the global star formation rate at early times, in agreement with observational indications. In contrast, a fairly high fraction ({approx} 20%) of those z = 2 galaxies should have experienced a morphologically transformative merger within a virial dynamical time. We compare our results to observational merger rate estimates from both morphological indicators and pair-fraction based determinations between z = 0-2 and show that they are consistent with our predictions. However, we emphasize that great care must be made in these comparisons because the predicted observables depend very sensitively on galaxy luminosity, redshift, overall mass ratio, and uncertain relaxation timescales for merger remnants. We show that the majority of bright galaxies at z = 3 should have undergone a major

  16. Electroweak symmetry breaking

    SciTech Connect

    Chanowitz, M.S.

    1990-09-01

    The Higgs mechanism is reviewed in its most general form, requiring the existence of a new symmetry-breaking force and associated particles, which need not however be Higgs bosons. The first lecture reviews the essential elements of the Higgs mechanism, which suffice to establish low energy theorems for the scattering of longitudinally polarized W and Z gauge bosons. An upper bound on the scale of the symmetry-breaking physics then follows from the low energy theorems and partial wave unitarity. The second lecture reviews particular models, with and without Higgs bosons, paying special attention to how the general features discussed in lecture 1 are realized in each model. The third lecture focuses on the experimental signals of strong WW scattering that can be observed at the SSC above 1 TeV in the WW subenergy, which will allow direct measurement of the strength of the symmetry-breaking force. 52 refs., 10 figs.

  17. STELLAR POPULATIONS AND RADIAL MIGRATIONS IN VIRGO DISK GALAXIES

    SciTech Connect

    Roediger, Joel C.; Courteau, Stephane; Sanchez-Blazquez, Patricia; McDonald, Michael E-mail: courteau@astro.queensu.ca E-mail: mcdonald@space.mit.edu

    2012-10-10

    We present new stellar age profiles, derived from well-resolved optical and near-infrared images of 64 Virgo cluster disk galaxies, whose analysis poses a challenge for current disk galaxy formation models. Our ability to break the age-metallicity degeneracy and the significant size of our sample represent key improvements over complementary studies of field disk galaxies. Our results can be summarized as follows: first, and contrary to observations of disk galaxies in the field, these cluster galaxies are distributed almost equally amongst the three main types of disk galaxy luminosity profiles (I/II/III), indicating that the formation and/or survival of Type II breaks is suppressed within the cluster environment. Second, we find examples of statistically significant inversions ({sup U}-shapes{sup )} in the age profiles of all three disk galaxy types, reminiscent of predictions from high-resolution simulations of classically truncated Type II disks in the field. These features characterize the age profiles for only about a third ({<=}36%) of each disk galaxy type in our sample. An even smaller fraction of cluster disks ({approx}11% of the total sample) exhibit age profiles that decrease outward (i.e., negative age gradients). Instead, flat and/or positive age gradients prevail ({>=}50%) within our Type I, II, and III subsamples. These observations thus suggest that while stellar migrations and inside-out growth can play a significant role in the evolution of all disk galaxy types, other factors contributing to the evolution of galaxies can overwhelm the predicted signatures of these processes. We interpret our observations through a scenario whereby Virgo cluster disk galaxies formed initially like their brethren in the field but which, upon falling into the cluster, were transformed into their present state through external processes linked to the environment (e.g., ram-pressure stripping and harassment). Current disk galaxy formation models, which have largely

  18. Bar Formation from Galaxy Flybys

    NASA Astrophysics Data System (ADS)

    Holley-Bockelmann, Kelly; Lang, Meagan; Sinha, Manodeep

    2016-05-01

    Both simulations and observations reveal that flybys—fast, one-time interactions between two galaxy halos—are surprisingly common, comparable to galaxy mergers. Since these are rapid, transient events with the closest approach well outside the galaxy disk, it is unclear if flybys can transform the galaxy in a lasting way. We conduct collisionless N-body simulations of three coplanar flyby interactions between pure-disk galaxies to take a first look at the effects flybys have on disk structure, with particular focus on stellar bar formation. We find that some flybys are capable of inciting a bar; bars form in both galaxies during our 1:1 interaction and in the secondary during our 10:1 interaction. The bars formed have ellipticities >0.5, sizes on the order of the scale length of the disk, and persist to the end of our simulations, ~5 Gyr after pericenter. The ability of flybys to incite bar formation implies that many processes associated with secular bar evolution may be more closely tied with flyby interactions than previously thought.

  19. BAR FORMATION FROM GALAXY FLYBYS

    SciTech Connect

    Lang, Meagan; Holley-Bockelmann, Kelly; Sinha, Manodeep E-mail: k.holley@vanderbilt.edu

    2014-08-01

    Recently, both simulations and observations have revealed that flybys—fast, one-time interactions between two galaxy halos—are surprisingly common, nearing/comparable to galaxy mergers. Since these are rapid, transient events with the closest approach well outside the galaxy disk, it is unclear if flybys can transform the galaxy in a lasting way. We conduct collisionless N-body simulations of three coplanar flyby interactions between pure-disk galaxies to take a first look at the effects flybys have on disk structure, with particular focus on stellar bar formation. We find that some flybys are capable of inciting a bar with bars forming in both galaxies during our 1:1 interaction and in the secondary during our 10:1 interaction. The bars formed have ellipticities ≳ 0.5, sizes on the order of the host disk's scale length, and persist to the end of our simulations, ∼5 Gyr after pericenter. The ability of flybys to incite bar formation implies that many processes associated with secular bar evolution may be more closely tied with interactions than previously thought.

  20. Discovering Teenage Galaxies

    NASA Astrophysics Data System (ADS)

    2007-11-01

    Staring for the equivalent of every night for two weeks at the same little patch of sky with ESO's Very Large Telescope, an international team of astronomers has found the extremely faint light from teenage galaxies billions of light years away. These galaxies, which the research team believes are the building blocks of normal galaxies like our Milky Way, had eluded detection for three decades, despite intensive searches. ESO PR Photo 52/07 ESO PR Photo 52/07 A 92-hour long spectrum Two-dimensional spectrum obtained in 92 hours of exposure time, showing the line emitter candidates. The quasar absorption lines are visible close to the centre of the image. The team, led by Martin Haehnelt of the University of Cambridge, UK, Michael Rauch and George Becker of the Observatories of the Carnegie Institution, USA, and Andy Bunker of the Anglo-Australian Observatory, reports their results in the 1 March 2008 issue of the Astrophysical Journal. "This is the first time that the sky has been searched to this depth and the unrivalled sensitivity of the picture taken with the VLT was key to succeeding," says Haehnelt. Experts have long speculated that galaxies like ours were created by the amalgamation of proto-galaxies early in the history of the Universe, but the light from these fragments was so faint that astronomers had struggled to prove they were there at all. Astronomers thought that the teenage galaxies must be out there because they were blocking part of the light from objects even further away in space. "Previous attempts have usually been frustrated by the difficulty of detecting extremely faint objects: the amount of time required even with an 8-metre class telescope like the VLT considerably exceeds typical observing time awards. We have thus exploited the periods of less good weather with the FORS2 spectrograph at the VLT, taking advantage of the service observing mode," says Becker. In service mode, ESO staff astronomers at Paranal are responsible for carrying

  1. "Galaxy," Defined

    NASA Astrophysics Data System (ADS)

    Willman, B.; Strader, J.

    2012-09-01

    A growing number of low luminosity and low surface brightness astronomical objects challenge traditional notions of both galaxies and star clusters. To address this challenge, we propose a definition of galaxy that does not depend on a cold dark matter model of the universe: a galaxy is a gravitationally bound collection of stars whose properties cannot be explained by a combination of baryons and Newton's laws of gravity. After exploring several possible observational diagnostics of this definition, we critically examine the classification of ultra-faint dwarfs, globular clusters, ultra-compact dwarfs, and tidal dwarfs. While kinematic studies provide an effective diagnostic of the definition in many regimes, they can be less useful for compact or very faint systems. To explore the utility of using the [Fe/H] spread as a complementary diagnostic, we use published spectroscopic [Fe/H] measurements of 16 Milky Way dwarfs and 24 globular clusters to uniformly calculate their [Fe/H] spreads and associated uncertainties. Our principal results are (1) no known, old star cluster less luminous than MV = -10 has a significant (gsim0.1 dex) spread in its iron abundance; (2) known ultra-faint dwarf galaxies can be unambiguously classified with a combination of kinematic and [Fe/H] observations; (3) the observed [Fe/H] spreads in massive (gsim 106 M ⊙) globular clusters do not necessarily imply that they are the stripped nuclei of dwarfs, nor a need for dark matter; and (4) if ultra-compact dwarf galaxies reside in dark matter halos akin to those of ultra-faint dwarfs of the same half-light radii, then they will show no clear dynamical signature of dark matter. We suggest several measurements that may assist the future classification of massive globular clusters, ultra-compact dwarfs, and ultra-faint galaxies. Our galaxy definition is designed to be independent of the details of current observations and models, while our proposed diagnostics can be refined or replaced as

  2. Comparing Stellar Populations of Galaxies across the Hubble Sequence

    NASA Astrophysics Data System (ADS)

    Kaleida, Catherine C.; Parkash, Vaishali; Jansen, Rolf

    2014-02-01

    We propose to investigate the spatial distributions of stellar populations within a statistically significant set of galaxies, representing the full range of luminosity and morphological type. By obtaining new, near-infrared images of these galaxies to complement existing optical and near-UV data, we can self-consistently probe the older stellar populations, dust extinction, and metallicity, and ultimately determine ages of and age variations within the stellar components of these galaxies. This information can then be used to compare stellar populations between luminous and faint galaxies of the same Hubble type, and between similar luminosity galaxies of different types. Galaxy candidates for this study were drawn from the Nearby Field Galaxy Survey (Jansen 2000), which provides U, B, and R optical images and both nuclear and globally integrated spectra. Near- infrared J, H, and K_s surface photometry can break the age-dust- metallicity degeneracy in galaxy spectral energy distributions (SEDs), but existing 2MASS image data is not sufficiently deep for this purpose. We therefore request observing time on the Infrared Side Port Imager (ISPI) on the CTIO 4-m Blanco telescope to secure J, H, and K_s images reaching out to the optical radius for 12 NFGS galaxies observable from Cerro Tololo in 2014A. Specific results expected from this sample are the distributions of age, dust, and metallicity across galaxies of differing type and luminosity. These distributions will allow us to address systematic trends in assembly history that can confront simulations of hierarchical galaxy formation.

  3. Comparing Stellar Populations of Galaxies across the Hubble Sequence

    NASA Astrophysics Data System (ADS)

    Kaleida, Catherine C.; Parkash, Vaishali; Jansen, Rolf

    2014-08-01

    We propose to investigate the spatial distributions of stellar populations within a statistically significant set of galaxies, representing the full range of luminosity and morphological type. By obtaining new, near-infrared images of these galaxies to complement existing optical and near-UV data, we can self-consistently probe the older stellar populations, dust extinction, and metallicity, and ultimately determine ages of and age variations within the stellar components of these galaxies. This information can then be used to compare stellar populations between luminous and faint galaxies of the same Hubble type, and between similar luminosity galaxies of different types. Galaxy candidates for this study were drawn from the Nearby Field Galaxy Survey (Jansen 2000), which provides U, B, and R optical images and both nuclear and globally integrated spectra. Near- infrared J, H, and K_s surface photometry can break the age-dust- metallicity degeneracy in galaxy spectral energy distributions (SEDs), but existing 2MASS image data is not sufficiently deep for this purpose. We therefore request observing time on the Infrared Side Port Imager (ISPI) on the CTIO 4-m Blanco telescope to secure J, H, and K_s images reaching out to the optical radius for 19 NFGS galaxies observable from Cerro Tololo in 2014B. Specific results expected from this sample are the distributions of age, dust, and metallicity across galaxies of differing type and luminosity. These distributions will allow us to address systematic trends in assembly history that can confront simulations of hierarchical galaxy formation.

  4. Cosmology with equivalence principle breaking in the dark sector

    SciTech Connect

    Keselman, Jose Ariel; Nusser, Adi; Peebles, P. J. E.

    2010-03-15

    A long-range force acting only between nonbaryonic particles would be associated with a large violation of the weak equivalence principle. We explore cosmological consequences of this idea, which we label ReBEL (daRk Breaking Equivalence principLe). A high resolution hydrodynamical simulation of the distributions of baryons and dark matter confirms our previous findings that a ReBEL force of comparable strength to gravity on comoving scales of about 1 h{sup -1} Mpc causes voids between the concentrations of large galaxies to be more nearly empty, suppresses accretion of intergalactic matter onto galaxies at low redshift, and produces an early generation of dense dark-matter halos. A preliminary analysis indicates the ReBEL scenario is consistent with the one-dimensional power spectrum of the Lyman-Alpha forest and the three-dimensional galaxy autocorrelation function. Segregation of baryons and DM in galaxies and systems of galaxies is a strong prediction of ReBEL. ReBEL naturally correlates the baryon mass fraction in groups and clusters of galaxies with the system mass, in agreement with recent measurements.

  5. Model Breaking Points Conceptualized

    ERIC Educational Resources Information Center

    Vig, Rozy; Murray, Eileen; Star, Jon R.

    2014-01-01

    Current curriculum initiatives (e.g., National Governors Association Center for Best Practices and Council of Chief State School Officers 2010) advocate that models be used in the mathematics classroom. However, despite their apparent promise, there comes a point when models break, a point in the mathematical problem space where the model cannot,…

  6. The Breaking Broomstick Demonstration.

    ERIC Educational Resources Information Center

    Mamola, Karl C.; Pollock, Joseph T.

    1993-01-01

    Describes and explains the breaking broomstick demonstration first reported in 1532. A needle is fixed at each end of the broomstick, and these needles are made to rest on two glasses, placed on chairs. If the broomstick is struck violently with another stout stick, the former will be broken, but the glasses will remain intact. (PR)

  7. Extragalatic zoo. I. [New galaxies

    SciTech Connect

    Schorn, R.A.

    1988-01-01

    The characteristics of various types of extragalactic objects are described. Consideration is given to cD galaxies, D galaxies, N galaxies, Markarian galaxies, liners, starburst galaxies, and megamasers. Emphasis is also placed on the isolated extragalatic H I region; the isolated extragalatic H II region; primeval galaxies or photogalaxies; peculiar galaxies; Arp galaxies; interacting galaxies; ring galaxies; and polar-ring galaxies. Diagrams of these objects are provided.

  8. The afterglow and the host galaxy of GRB 011211

    NASA Astrophysics Data System (ADS)

    Jakobsson, P.; Hjorth, J.; Fynbo, J. P. U.; Gorosabel, J.; Pedersen, K.; Burud, I.; Levan, A.; Kouveliotou, C.; Tanvir, N.; Fruchter, A.; Rhoads, J.; Grav, T.; Hansen, M. W.; Michelsen, R.; Andersen, M. I.; Jensen, B. L.; Pedersen, H.; Thomsen, B.; Weidinger, M.; Bhargavi, S. G.; Cowsik, R.; Pandey, S. B.

    2003-09-01

    We present optical, near-infrared, and X-ray observations of the optical afterglow (OA) of the X-ray rich, long-duration gamma-ray burst GRB 011211. Hubble Space Telescope (HST) data obtained 14, 26, 32, and 59 days after the burst, show the host galaxy to have a morphology that is fairly typical of blue galaxies at high redshift. We measure its magnitude to be R = 24.95 +/- 0.11. We detect a break in the OA R-band light curve which is naturally accounted for by a collimated outflow geometry. By fitting a broken power-law to the data we find a best fit with a break 1.56 +/- 0.02 days after the burst, a pre-break slope of alpha1 = -0.95 +/- 0.02, and a post-break slope of alpha2 = -2.11 +/- 0.07. The UV-optical spectral energy distribution (SED) around 14 hours after the burst is best fit with a power-law with index beta = -0.56 +/- 0.19 reddened by an SMC-like extinction law with a modest AV = 0.08 +/- 0.08 mag. By comparison, from the XMM-Newton X-ray data at around the same time, we find a decay index of alphaX = -1.62 +/- 0.36 and a spectral index of betaX = -1.21+0.10-0.15. Interpolating between the UV-optical and X-ray implies that the cooling frequency is located close to ~ 1016 Hz in the observer frame at the time of the observations. We argue, using the various temporal and spectral indices above, that the most likely afterglow model is that of a jet expanding into an external environment that has a constant mean density rather than a wind-fed density structure. We estimate the electron energy index for this burst to be p ~ 2.3. Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden. Based on observations made with ESO Telescopes at the Paranal Observatory by GRACE under programme ID 69.D-0701. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the

  9. Secular Evolution in Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Kormendy, John

    2013-10-01

    Self-gravitating systems evolve toward the most tightly bound configuration that is reachable via the evolution processes that are available to them. They do this by spreading -- the inner parts shrink while the outer parts expand -- provided that some physical process efficiently transports energy or angular momentum outward. The reason is that self-gravitating systems have negative specific heats. As a result, the evolution of stars, star clusters, protostellar and protoplanetary disks, black hole accretion disks and galaxy disks are fundamentally similar. How evolution proceeds then depends on the evolution processes that are available to each kind of self-gravitating system. These processes and their consequences for galaxy disks are the subjects of my lectures and of this Canary Islands Winter School. I begin with a review of the formation, growth and death of bars. Then I review the slow (`secular') rearrangement of energy, angular momentum, and mass that results from interactions between stars or gas clouds and collective phenomena such as bars, oval disks, spiral structure and triaxial dark haloes. The `existence-proof' phase of this work is largely over: we have a good heuristic understanding of how nonaxisymmetric structures rearrange disk gas into outer rings, inner rings and stuff dumped onto the centre. The results of simulations correspond closely to the morphology of barred and oval galaxies. Gas that is transported to small radii reaches high densities. Observations confirm that many barred and oval galaxies have dense central concentrations of gas and star formation. The result is to grow, on timescales of a few Gyr, dense central components that are frequently mistaken for classical (elliptical-galaxy-like) bulges but that were grown slowly out of the disk (not made rapidly by major mergers). The resulting picture of secular galaxy evolution accounts for the richness observed in galaxy structure. We can distinguish between classical and pseudo

  10. Crashing galaxies, cosmic fireworks

    SciTech Connect

    Keel, W.C.

    1989-01-01

    The study of binary systems is reviewed. The history of the study of interacting galaxies, the behavior of gas in binary systems, studies to identify the processes that occur when galaxies interact, and the relationship of Seyfert galaxies and quasars to binary systems are discussed. The development of an atlas of peculiar galaxies (Arp, 1966) and methods for modeling galaxy interactions are examined.

  11. A Chandra View of the Normal S0 Galaxy NGC 1332. I. An Unbroken, Steep Power-Law Luminosity Function for the Low-Mass X-Ray Binary Population

    NASA Astrophysics Data System (ADS)

    Humphrey, Philip J.; Buote, David A.

    2004-09-01

    Chandra ACIS -S3 observations of the nearby S0 galaxy NGC 1332 resolve much of the X-ray emission into 73 point sources, of which 37 lie within the D25 isophote. The remaining galaxy emission comprises hot, diffuse gas and unresolved sources and is discussed in two companion papers. The point-source X-ray luminosity function (XLF) shows the characteristic break seen in other early-type galaxies at ~2×1038 ergs s-1. After applying corrections for detection incompleteness at low luminosities due to source confusion and contamination from diffuse galactic emission, the break vanishes and the data are well described as a single power law. This result casts further doubt on there being a ``universal'' XLF break in early-type galaxies, marking the division between neutron star and black hole systems. The logarithmic slope of the differential XLF (dN/dL), β=2.7+/-0.5, is marginally (~2.5 σ) steeper than has been found for analogous completeness-corrected fits of other early-type galaxies but closely matches the behavior seen at high luminosities in these systems. Two of the sources within D25 are ultraluminous X-ray sources (ULXs), although neither have LX>2×1039 ergs s-1. The absence of very luminous ULXs in early-type galaxies suggests a break in the XLF slope at ~(1-2)×1039 ergs s-1, although the data were not of sufficient quality to constrain such a feature in NGC 1332. The sources have a spatial distribution consistent with the optical light and display a range of characteristics that are consistent with an LMXB population. The general spectral characteristics of the individual sources, as well as the composite source spectra, are in good agreement with observations of other early-type galaxies, although a small number of highly absorbed sources are seen. Two sources have very soft spectra, two show strong variability, indicating compact binary nature, and one source shows evidence of an extended radial profile. We do not detect a central source in NGC 1332

  12. A catalog of low surface brightness galaxies - List II

    NASA Technical Reports Server (NTRS)

    Schombert, James M.; Bothun, Gregory D.; Schneider, Stephen E.; Mcgaugh, Stacy S.

    1992-01-01

    A list of galaxies characterized by low surface brightness (LSB) is presented which facilitates the recognition of galaxies with brightnesses close to that of the sky. A total of 198 objects and 140 objects are listed in the primary and secondary catalogs respectively, and LSB galaxies are examined by means of H I redshift distributions. LSB disk galaxies are shown to have similar sizes and masses as the high-surface-brightness counterparts, and ellipticals and SOs are rarely encountered. Many LSB spirals have stellarlike nuclei, and most of the galaxies in the present catalog are late-type galaxies in the Sc, Sm, and Im classes. The LSB region of observational parameter space is shown to encompass a spectrum of types as full as that of the Hubble sequence. It is suggested that studies of LSB galaxies can provide important data regarding the formation and star-formation history of all galaxies.

  13. REEXAMINATION OF THE RADIAL ABUNDANCE GRADIENT BREAK IN NGC 3359

    SciTech Connect

    Zahid, H. J.; Bresolin, F.

    2011-06-15

    In this contribution, we reexamine the radial oxygen abundance gradient in the strongly barred spiral galaxy NGC 3359, for which, using an imaging spectrophotometric technique, Martin and Roy detected a break near the effective radius of the galaxy. We have new emission line flux measurements of H II regions in NGC 3359 from spectra obtained with the Subaru telescope to further investigate this claim. We find that there are small systematic variations in the line ratios determined from narrowband imaging as compared to our spectroscopic measurements. We derive and apply a correction to the line ratios found by Martin and Roy and statistically examine the validity of the gradient break proposed for NGC 3359 using recently developed metallicity diagnostics. We find that, with a high degree of confidence, a model with a break fits the data significantly better than one without it. This suggests that the presence of a strong bar in spiral galaxies can generate measurable changes in the radial distribution of metals.

  14. EXPLORING THE z = 3-4 MASSIVE GALAXY POPULATION WITH ZFOURGE: THE PREVALENCE OF DUSTY AND QUIESCENT GALAXIES

    SciTech Connect

    Spitler, Lee R.; Rees, Glen; Straatman, Caroline M. S.; Labbé, Ivo; Glazebrook, Karl; Kacprzak, Glenn G.; Nanayakkara, Themiya; Tran, Kim-Vy H.; Papovich, Casey; Kawinwanichakij, Lalitwadee; Mehrtens, Nicola; Tilvi, Vithal; Tomczak, Adam R.; Quadri, Ryan F.; Persson, S. Eric; Kelson, Daniel D.; McCarthy, Patrick J.; Monson, Andrew J.; Van Dokkum, Pieter; Allen, Rebecca

    2014-06-01

    Our understanding of the redshift z > 3 galaxy population relies largely on samples selected using the popular ''dropout'' technique, typically consisting of UV-bright galaxies with blue colors and prominent Lyman breaks. As it is currently unknown if these galaxies are representative of the massive galaxy population, we here use the FOURSTAR Galaxy Evolution (ZFOURGE) survey to create a stellar mass-limited sample at z = 3-4. Uniquely, ZFOURGE uses deep near-infrared medium-bandwidth filters to derive accurate photometric redshifts and stellar population properties. The mass-complete sample consists of 57 galaxies with log M >10.6, reaching below M {sup *} at z = 3-4. On average, the massive z = 3-4 galaxies are extremely faint in the observed optical with median R{sub tot}{sup AB}=27.48±0.41 (rest-frame M {sub 1700} = –18.05 ± 0.37). They lie far below the UV luminosity-stellar mass relation for Lyman break galaxies and are about ∼100 × fainter at the same mass. The massive galaxies are red (R – K {sub s} {sub AB} = 3.9 ± 0.2; rest-frame UV-slope β = –0.2 ± 0.3) likely from dust or old stellar ages. We classify the galaxy spectral energy distributions by their rest-frame U–V and V–J colors and find a diverse population: 46{sub −6−17}{sup +6+10}% of the massive galaxies are quiescent, 40{sub −6−5}{sup +6+7}% are dusty star-forming galaxies, and only 14{sub −3−4}{sup +3+10}% resemble luminous blue star-forming Lyman break galaxies. This study clearly demonstrates an inherent diversity among massive galaxies at higher redshift than previously known. Furthermore, we uncover a reservoir of dusty star-forming galaxies with 4 × lower specific star-formation rates compared to submillimeter-selected starbursts at z > 3. With 5 × higher numbers, the dusty galaxies may represent a more typical mode of star formation compared to submillimeter-bright starbursts.

  15. Galaxy-galaxy(-galaxy) lensing as a sensitive probe of galaxy evolution

    NASA Astrophysics Data System (ADS)

    Saghiha, H.; Hilbert, S.; Schneider, P.; Simon, P.

    2012-11-01

    Context. The gravitational lensing effect provides various ways to study the mass environment of galaxies. Aims: We investigate how galaxy-galaxy(-galaxy) lensing can be used to test models of galaxy formation and evolution. Methods: We consider two semi-analytic galaxy formation models based on the Millennium Run N-body simulation: the Durham model by Bower et al. (2006, MNRAS, 370, 645) and the Garching model by Guo et al. (2011, MNRAS, 413, 101). We generate mock lensing observations for the two models, and then employ Fast Fourier Transform methods to compute second- and third-order aperture statistics in the simulated fields for various galaxy samples. Results: We find that both models predict qualitatively similar aperture signals, but there are large quantitative differences. The Durham model predicts larger amplitudes in general. In both models, red galaxies exhibit stronger aperture signals than blue galaxies. Using these aperture measurements and assuming a linear deterministic bias model, we measure relative bias ratios of red and blue galaxy samples. We find that a linear deterministic bias is insufficient to describe the relative clustering of model galaxies below ten arcmin angular scales. Dividing galaxies into luminosity bins, the aperture signals decrease with decreasing luminosity for brighter galaxies, but increase again for fainter galaxies. This increase is likely an artifact due to too many faint satellite galaxies in massive group and cluster halos predicted by the models. Conclusions: Our study shows that galaxy-galaxy(-galaxy) lensing is a sensitive probe of galaxy evolution.

  16. Galaxy formation.

    PubMed

    Peebles, P J

    1998-01-01

    It is argued that within the standard Big Bang cosmological model the bulk of the mass of the luminous parts of the large galaxies likely had been assembled by redshift z approximately 10. Galaxy assembly this early would be difficult to fit in the widely discussed adiabatic cold dark matter model for structure formation, but it could agree with an isocurvature version in which the cold dark matter is the remnant of a massive scalar field frozen (or squeezed) from quantum fluctuations during inflation. The squeezed field fluctuations would be Gaussian with zero mean, and the distribution of the field mass therefore would be the square of a random Gaussian process. This offers a possibly interesting new direction for the numerical exploration of models for cosmic structure formation.

  17. Galaxy formation

    PubMed Central

    Peebles, P. J. E.

    1998-01-01

    It is argued that within the standard Big Bang cosmological model the bulk of the mass of the luminous parts of the large galaxies likely had been assembled by redshift z ∼ 10. Galaxy assembly this early would be difficult to fit in the widely discussed adiabatic cold dark matter model for structure formation, but it could agree with an isocurvature version in which the cold dark matter is the remnant of a massive scalar field frozen (or squeezed) from quantum fluctuations during inflation. The squeezed field fluctuations would be Gaussian with zero mean, and the distribution of the field mass therefore would be the square of a random Gaussian process. This offers a possibly interesting new direction for the numerical exploration of models for cosmic structure formation. PMID:9419326

  18. Shaping galaxy evolution with galaxy structure

    NASA Astrophysics Data System (ADS)

    Cheung, Edmond

    A fundamental pursuit of astronomy is to understand galaxy evolution. The enormous scales and complex physics involved in this endeavor guarantees a never-ending journey that has enamored both astronomers and laymen alike. But despite the difficulty of this task, astronomers have still attempted to further this goal. Among of these astronomers is Edwin Hubble. His work, which includes the famous Hubble sequence, has immeasurably influenced our understanding of galaxy evolution. In this thesis, we present three works that continues Hubble's line of study by using galaxy structure to learn about galaxy evolution. First, we examine the dependence of galaxy quiescence on inner galactic structure with the AEGIS/ DEEP2 survey at 0.5In this thesis, we present three works that continues Hubble's line of study by using galaxy structure to learn about galaxy evolution. First, we examine the dependence of galaxy quiescence on inner galactic structure with the AEGIS/ DEEP2 survey at 0.5galaxies from quiescent galaxies. Our method indicates that the inner stellar mass is the most correlated parameter of quenching, implying that the process that quenches galaxies must also buildup their inner structure. Second, we explore the relationship between galactic bars and their host galaxies with Galaxy Zoo 2 at z˜0. The correlations of bar properties and galaxy properties are consistent with simulations of bar formation and evolution, indicating that bars affect their host galaxies. Finally, we investigate whether bars can drive supermassive black hole growth with data from Chandra and Galaxy Zoo: Hubble at 0.2galaxies to a matched sample of inactive, control galaxies shows that there is no statistically significant excess of bars in active hosts. Our result shows that bars are not the primary fueling mechanism of supermassive black hole

  19. Local starburst galaxies and their descendants. Statistics from the Sloan Digital Sky Survey

    NASA Technical Reports Server (NTRS)

    Bergvall, Nils; Marquart, Thomas; Way, Michael J.; Blomqvist, Anna; Holst, Emma; Ostlin, Goran; Zackrisson, Erik

    2016-01-01

    Despite strong interest in the starburst phenomenon in extragalactic astronomy, the concept remains ill-defined. Here we use a strict definition of starburst to examine the statistical properties of starburst galaxies in the local universe. We also seek to establish links between starburst galaxies, post-starburst (hereafter postburst) galaxies, and active galaxies. Data were selected from the Sloan Digital Sky Survey DR7. We applied a novel method of treating dust attenuation and derive star formation rates, ages, and stellar masses assuming a two-component stellar population model. Dynamical masses are calculated from the width of the H-alpha line. These masses agree excellently with the photometric masses. The mass (gas+stars) range is approximately 10( exp 9) - 10(exp 11.5) solar mass. As a selection criterion for starburst galaxies, we use, the birthrate parameter, b = SFR/SFR, requiring that b is greater than 3. For postburst galaxies, we use, the equivalent width of Hdelta in absorption with the criterion EW (sub Hdelta_abs) is greater than 6 A. Results. We find that only 1% of star-forming galaxies are starburst galaxies. They contribute 3-6% to the stellar production and are therefore unimportant for the local star formation activity. The median starburst age is 70 Myr roughly independent of mass, indicating that star formation is mainly regulated by local feedback processes. The b-parameter strongly depends on burst age. Values close to b = 60 are found at ages approximately 10 Myr, while almost no starbursts are found at ages greater than 1 Gyr. The median baryonic burst mass fraction of sub-L galaxies is 5% and decreases slowly towards high masses. The median mass fraction of the recent burst in the postburst sample is 5-10%. A smaller fraction of the postburst galaxies, however, originates in non-bursting galaxies. The age-mass distribution of the postburst progenitors (with mass fractions is greater than 3%) is bimodal with a break at logM(solar mass

  20. Which String Breaks? Revisited

    NASA Astrophysics Data System (ADS)

    Frye, Christopher

    2011-03-01

    Many have seen the common introductory physics demonstration in which a heavy ball hangs from a string, with another identical string hanging freely from the ball. When the instructor pulls the bottom string slowly, the top string breaks. However, when the instructor pulls the bottom string very rapidly, the bottom string breaks. This simple experiment is used to demonstrate inertia and Newton's laws. In The Physics Teacher of November 1996, there is an article in which the authors create a model of this problem in an attempt to explain the outcomes quantitatively. However, their analysis gave strange results. Using an improved model, I will show that the results of this demonstration can be obtained using only simple calculations. This work was funded by a RAMP grant from the University of Central Florida.

  1. Dwarf spheroidal galaxies: Keystones of galaxy evolution

    NASA Technical Reports Server (NTRS)

    Gallagher, John S., III; Wyse, Rosemary F. G.

    1994-01-01

    Dwarf spheroidal galaxies are the most insignificant extragalactic stellar systems in terms of their visibility, but potentially very significant in terms of their role in the formation and evolution of much more luminous galaxies. We discuss the present observational data and their implications for theories of the formation and evolution of both dwarf and giant galaxies. The putative dark-matter content of these low-surface-brightness systems is of particular interest, as is their chemical evolution. Surveys for new dwarf spheroidals hidden behind the stars of our Galaxy and those which are not bound to giant galaxies may give new clues as to the origins of this unique class of galaxy.

  2. Predicting appointment breaking.

    PubMed

    Bean, A G; Talaga, J

    1995-01-01

    The goal of physician referral services is to schedule appointments, but if too many patients fail to show up, the value of the service will be compromised. The authors found that appointment breaking can be predicted by the number of days to the scheduled appointment, the doctor's specialty, and the patient's age and gender. They also offer specific suggestions for modifying the marketing mix to reduce the incidence of no-shows. PMID:10142384

  3. Galaxies at High Redshift

    NASA Astrophysics Data System (ADS)

    Pérez-Fournon, I.; Balcells, M.; Moreno-Insertis, F.; Sánchez, F.

    2010-08-01

    Participants; Group photograph; Preface; Acknowledgements; 1. Galaxy formation and evolution: recent progress R. Ellis; 2. Galaxies at high redshift M. Dickinson; 3. High-redshift galaxies: the far-infrared and sub-millimeter view A. Franceschini; 4. Quasar absorption lines J. Bechtold; 5. Stellar population synthesis models at low and high redshift G. Bruzual A.; 6. Elliptical galaxies K. C. Freeman; 7. Disk galaxies K. C. Freeman; 8. Dark matter in disk galaxies K. C. Freeman.

  4. A study of massive and evolved galaxies at high redshift

    SciTech Connect

    Nayyeri, H.; Mobasher, B.; Hemmati, S.; De Barros, S.; Ferguson, H. C.; Wiklind, T.; Dahlen, T.; Kassin, S.; Koekemoer, A.; Dickinson, M.; Giavalisco, M.; Fontana, A.; Paris, D.; Ashby, M.; Willner, S.; Barro, G.; Guo, Y.; Hathi, N. P.; Dunlop, J. S.; Targett, T. A.

    2014-10-10

    We use data taken as part of Hubble Space Telescope (HST)/Wide Field Camera 3 (WFC3) observations of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) to identify massive and evolved galaxies at 3 < z < 4.5. This is performed using the strength of the Balmer break feature at rest-frame 3648 Å, which is a diagnostic of the age of the stellar population in galaxies. Using the WFC3 H-band-selected catalog for the CANDELS GOODS-S field and deep multi-waveband photometry from optical (HST) to mid-infrared (Spitzer) wavelengths, we identify a population of old and evolved post-starburst galaxies based on the strength of their Balmer breaks (Balmer break galaxies, BBGs). The galaxies are also selected to be bright in rest-frame near-IR wavelengths and hence massive. We identify a total of 16 BBGs. Fitting the spectral energy distribution of the BBGs shows that the candidate galaxies have average estimated ages of ∼800 Myr and average stellar masses of ∼5 × 10{sup 10} M {sub ☉}, consistent with being old and massive systems. Two of our BBG candidates are also identified by the criteria that are sensitive to star-forming galaxies (Lyman break galaxy selection). We find a number density of ∼3.2 × 10{sup –5} Mpc{sup –3} for the BBGs, corresponding to a mass density of ∼2.0 × 10{sup 6} M {sub ☉} Mpc{sup –3} in the redshift range covering the survey. Given the old age and the passive evolution, it is argued that some of these objects formed the bulk of their mass only a few hundred million years after the big bang.

  5. Secular Evolution in Disk Galaxies

    NASA Astrophysics Data System (ADS)

    Kormendy, John

    2013-10-01

    Self-gravitating systems evolve toward the most tightly bound configuration that is reachable via the evolution processes that are available to them. They do this by spreading -- the inner parts shrink while the outer parts expand -- provided that some physical process efficiently transports energy or angular momentum outward. The reason is that self-gravitating systems have negative specific heats. As a result, the evolution of stars, star clusters, protostellar and protoplanetary disks, black hole accretion disks and galaxy disks are fundamentally similar. How evolution proceeds then depends on the evolution processes that are available to each kind of self-gravitating system. These processes and their consequences for galaxy disks are the subjects of my lectures and of this Canary Islands Winter School. I begin with a review of the formation, growth and death of bars. Then I review the slow (`secular') rearrangement of energy, angular momentum, and mass that results from interactions between stars or gas clouds and collective phenomena such as bars, oval disks, spiral structure and triaxial dark haloes. The `existence-proof' phase of this work is largely over: we have a good heuristic understanding of how nonaxisymmetric structures rearrange disk gas into outer rings, inner rings and stuff dumped onto the centre. The results of simulations correspond closely to the morphology of barred and oval galaxies. Gas that is transported to small radii reaches high densities. Observations confirm that many barred and oval galaxies have dense central concentrations of gas and star formation. The result is to grow, on timescales of a few Gyr, dense central components that are frequently mistaken for classical (elliptical-galaxy-like) bulges but that were grown slowly out of the disk (not made rapidly by major mergers). The resulting picture of secular galaxy evolution accounts for the richness observed in galaxy structure. We can distinguish between classical and pseudo

  6. Local Analogs for High-redshift Galaxies: Resembling the Physical Conditions of the Interstellar Medium in High-redshift Galaxies

    NASA Astrophysics Data System (ADS)

    Bian, Fuyan; Kewley, Lisa J.; Dopita, Michael A.; Juneau, Stephanie

    2016-05-01

    We present a sample of local analogs for high-redshift galaxies selected in the Sloan Digital Sky Survey (SDSS). The physical conditions of the interstellar medium (ISM) in these local analogs resemble those in high-redshift galaxies. These galaxies are selected based on their positions in the [O iii]/Hβ versus [N ii]/Hα nebular emission-line diagnostic diagram. We show that these local analogs share similar physical properties with high-redshift galaxies, including high specific star formation rates (sSFRs), flat UV continuums, and compact galaxy sizes. In particular, the ionization parameters and electron densities in these analogs are comparable to those in z ≃ 2–3 galaxies, but higher than those in normal SDSS galaxies by ≃0.6 dex and ≃0.9 dex, respectively. The mass–metallicity relation (MZR) in these local analogs shows ‑0.2 dex offset from that in SDSS star-forming galaxies at the low-mass end, which is consistent with the MZR of the z˜ 2{--}3 galaxies. We compare the local analogs in this study with those in other studies, including Lyman break analogs (LBA) and green pea (GP) galaxies. The analogs in this study share a similar star formation surface density with LBAs, but the ionization parameters and electron density in our analogs are higher than those in LBAs by factors of 1.5 and 3, respectively. The analogs in this study have comparable ionization parameters and electron densities to the GP galaxies, but our method can select galaxies in a wider redshift range. We find the high sSFR and SFR surface density can increase the electron density and ionization parameters, but still cannot fully explain the difference in ISM condition between nearby galaxies and the local analogs/high-redshift galaxies.

  7. Local Analogs for High-redshift Galaxies: Resembling the Physical Conditions of the Interstellar Medium in High-redshift Galaxies

    NASA Astrophysics Data System (ADS)

    Bian, Fuyan; Kewley, Lisa J.; Dopita, Michael A.; Juneau, Stephanie

    2016-05-01

    We present a sample of local analogs for high-redshift galaxies selected in the Sloan Digital Sky Survey (SDSS). The physical conditions of the interstellar medium (ISM) in these local analogs resemble those in high-redshift galaxies. These galaxies are selected based on their positions in the [O iii]/Hβ versus [N ii]/Hα nebular emission-line diagnostic diagram. We show that these local analogs share similar physical properties with high-redshift galaxies, including high specific star formation rates (sSFRs), flat UV continuums, and compact galaxy sizes. In particular, the ionization parameters and electron densities in these analogs are comparable to those in z ≃ 2-3 galaxies, but higher than those in normal SDSS galaxies by ≃0.6 dex and ≃0.9 dex, respectively. The mass-metallicity relation (MZR) in these local analogs shows -0.2 dex offset from that in SDSS star-forming galaxies at the low-mass end, which is consistent with the MZR of the z˜ 2{--}3 galaxies. We compare the local analogs in this study with those in other studies, including Lyman break analogs (LBA) and green pea (GP) galaxies. The analogs in this study share a similar star formation surface density with LBAs, but the ionization parameters and electron density in our analogs are higher than those in LBAs by factors of 1.5 and 3, respectively. The analogs in this study have comparable ionization parameters and electron densities to the GP galaxies, but our method can select galaxies in a wider redshift range. We find the high sSFR and SFR surface density can increase the electron density and ionization parameters, but still cannot fully explain the difference in ISM condition between nearby galaxies and the local analogs/high-redshift galaxies.

  8. Galaxies Collide to Create Hot, Huge Galaxy

    NASA Technical Reports Server (NTRS)

    2009-01-01

    This image of a pair of colliding galaxies called NGC 6240 shows them in a rare, short-lived phase of their evolution just before they merge into a single, larger galaxy. The prolonged, violent collision has drastically altered the appearance of both galaxies and created huge amounts of heat turning NGC 6240 into an 'infrared luminous' active galaxy.

    A rich variety of active galaxies, with different shapes, luminosities and radiation profiles exist. These galaxies may be related astronomers have suspected that they may represent an evolutionary sequence. By catching different galaxies in different stages of merging, a story emerges as one type of active galaxy changes into another. NGC 6240 provides an important 'missing link' in this process.

    This image was created from combined data from the infrared array camera of NASA's Spitzer Space Telescope at 3.6 and 8.0 microns (red) and visible light from NASA's Hubble Space Telescope (green and blue).

  9. BOOK REVIEW: Symmetry Breaking

    NASA Astrophysics Data System (ADS)

    Ryder, L. H.

    2005-11-01

    One of the most fruitful and enduring advances in theoretical physics during the last half century has been the development of the role played by symmetries. One needs only to consider SU(3) and the classification of elementary particles, the Yang Mills enlargement of Maxwell's electrodynamics to the symmetry group SU(2), and indeed the tremendous activity surrounding the discovery of parity violation in the weak interactions in the late 1950s. This last example is one of a broken symmetry, though the symmetry in question is a discrete one. It was clear to Gell-Mann, who first clarified the role of SU(3) in particle physics, that this symmetry was not exact. If it had been, it would have been much easier to discover; for example, the proton, neutron, Σ, Λ and Ξ particles would all have had the same mass. For many years the SU(3) symmetry breaking was assigned a mathematical form, but the importance of this formulation fell away when the quark model began to be taken seriously; the reason the SU(3) symmetry was not exact was simply that the (three, in those days) quarks had different masses. At the same time, and in a different context, symmetry breaking of a different type was being investigated. This went by the name of `spontaneous symmetry breaking' and its characteristic was that the ground state of a given system was not invariant under the symmetry transformation, though the interactions (the Hamiltonian, in effect) was. A classic example is ferromagnetism. In a ferromagnet the atomic spins are aligned in one direction only—this is the ground state of the system. It is clearly not invariant under a rotation, for that would change the ground state into a (similar but) different one, with the spins aligned in a different direction; this is the phenomenon of a degenerate vacuum. The contribution of the spin interaction, s1.s2, to the Hamiltonian, however, is actually invariant under rotations. As Coleman remarked, a little man living in a ferromagnet would

  10. Galaxy NGC 55

    NASA Technical Reports Server (NTRS)

    2003-01-01

    This image of the nearby edge-on spiral galaxy NGC 55 was taken by Galaxy Evolution Explorer on September 14, 2003, during 2 orbits. This galaxy lies 5.4 million light years from our Milky Way galaxy and is a member of the 'local group' of galaxies that also includes the Andromeda galaxy (M31), the Magellanic clouds, and 40 other galaxies. The spiral disk of NGC 55 is inclined to our line of sight by approximately 80 degrees and so this galaxy looks cigar-shaped. This picture is a combination of Galaxy Evolution Explorer images taken with the far ultraviolet (colored blue) and near ultraviolet detectors, (colored red). The bright blue regions in this image are areas of active star formation detected in the ultraviolet by Galaxy Evolution Explorer. The red stars in this image are foreground stars in our own Milky Way galaxy.

  11. Multicolor surface photometry of powerful radio galaxies

    SciTech Connect

    Smith, E.P.

    1988-01-01

    CCD images of 72 powerful radio galaxies have been obtained with the KPNO 2.1m, 4m and CTIO 4m telescopes utilizing B, V, and R filters to study the colors and other photometric properties of these large systems. The GASP software package was used for the data reduction and detailed 2-d surface photometry. In addition, image modeling techniques were employed to investigate the contributions to galaxy properties by point-like nuclear sources seen in some of these galaxies. It was found that powerful radio galaxies show a much higher frequency than normal bright ellipticals of having optical morphologies which deviate from elliptical symmetry. Approximately 50% of the sample exhibit non-elliptically symmetric isophotes. These prominent distortions are present at surface brightness levels of {le} 25 V mag/(arc sec){sup 2}. In addition, a large fraction ({approximately}50%) of the remaining radio galaxies without the aforementioned morphological peculiarities have large isophotal twists ({Delta}P.A. {ge} 10{degree}) or ellipticity gradients. Significantly {approximately}50% of the galaxies with strong optical emission lines in their spectra display optically peculiar structures very similar to those found by Toomre and Toomre (1972) in their simulations of interacting disk galaxies. The galaxies with weak emission lines in their spectra are less frequently ({approximately}10%) distorted from elliptical shape. Those that are exhibit features like isophote twists, double nuclei and close companion galaxies embedded in the radio galaxy optical isophotes. The (B-V) colors of many of the powerful radio galaxies with strong emission lines are blue relative to normal giant ellipticals at the same redshift.

  12. Breaking a vicious cycle.

    PubMed

    Hayes, Daniel F; Allen, Jeff; Compton, Carolyn; Gustavsen, Gary; Leonard, Debra G B; McCormack, Robert; Newcomer, Lee; Pothier, Kristin; Ransohoff, David; Schilsky, Richard L; Sigal, Ellen; Taube, Sheila E; Tunis, Sean R

    2013-07-31

    Despite prodigious advances in tumor biology research, few tumor-biomarker tests have been adopted as standard clinical practice. This lack of reliable tests stems from a vicious cycle of undervaluation, resulting from inconsistent regulatory standards and reimbursement, as well as insufficient investment in research and development, scrutiny of biomarker publications by journals, and evidence of analytical validity and clinical utility. We offer recommendations designed to serve as a roadmap to break this vicious cycle and call for a national dialogue, as changes in regulation, reimbursement, investment, peer review, and guidelines development require the participation of all stakeholders. PMID:23903752

  13. Ion wave breaking acceleration

    NASA Astrophysics Data System (ADS)

    Liu, B.; Meyer-ter-Vehn, J.; Bamberg, K.-U.; Ma, W. J.; Liu, J.; He, X. T.; Yan, X. Q.; Ruhl, H.

    2016-07-01

    Laser driven ion wave breaking acceleration (IWBA) in plasma wakefields is investigated by means of a one-dimensional (1D) model and 1D/3D particle-in-cell (PIC) simulations. IWBA operates in relativistic transparent plasma for laser intensities in the range of 1020- 1023 W /cm2 . The threshold for IWBA is identified in the plane of plasma density and laser amplitude. In the region just beyond the threshold, self-injection takes place only for a fraction of ions and in a limited time period. This leads to well collimated ion pulses with peaked energy spectra, in particular for 3D geometry.

  14. Spontaneous Symmetry Breaking

    NASA Astrophysics Data System (ADS)

    Strocchi, Franco

    One of the most powerful ideas of modern theoretical physics is the mechanism of spontaneous symmetry breaking. It is at the basis of most of the recent achievements in the description of phase transitions in Statistical Mechanics as well as of collective phenomena in solid state physics. It has also made possible the unification of weak, electromagnetic and strong interactions in elementary particle physics. Philosophically, the idea is very deep and subtle (this is probably why its exploitation is a rather recent achievement) and the popular accounts do not fully do justice to it.

  15. Atmospheric noise of a breaking tidal bore.

    PubMed

    Chanson, Hubert

    2016-01-01

    A tidal bore is a surge of waters propagating upstream in an estuary as the tidal flow turns to rising and the flood tide propagates into a funnel-shaped system. Large tidal bores have a marked breaking roller. The sounds generated by breaking tidal bores were herein investigated in the field (Qiantang River) and in laboratory. The sound pressure record showed two dominant periods, with some similarity with an earlier study [Chanson (2009). J. Acoust. Soc. Am. 125(6), 3561-3568]. The two distinct phases were the incoming tidal bore when the sound amplitude increased with the approaching bore, and the passage of the tidal bore in front of the microphone when loud and powerful noises were heard. The dominant frequency ranged from 57 to 131 Hz in the Qiantang River bore. A comparison between laboratory and prototype tidal bores illustrated both common features and differences. The low pitch sound of the breaking bore had a dominant frequency close to the collective oscillations of bubble clouds, which could be modeled with a bubble cloud model using a transverse dimension of the bore roller. The findings suggest that this model might be over simplistic in the case of a powerful breaking bore, like that of the Qiantang River.

  16. THE STRUCTURE AND KINEMATICS OF THE CIRCUMGALACTIC MEDIUM FROM FAR-ULTRAVIOLET SPECTRA OF z {approx_equal} 2-3 GALAXIES

    SciTech Connect

    Steidel, Charles C.; Bogosavljevic, Milan; Rudie, Gwen C.; Erb, Dawn K.; Shapley, Alice E.; Pettini, Max; Reddy, Naveen; Rakic, Olivera

    2010-07-01

    We present new results on the kinematics and spatial distribution of metal-enriched gas within {approx}125 kpc of star-forming ('Lyman break') galaxies at redshifts 2 {approx_lt} z {approx_lt} 3. In particular, we focus on constraints provided by the rest-frame far-ultraviolet (far-UV) spectra of faint galaxies, and demonstrate how galaxy spectra can be used to obtain key spatial and spectral information more efficiently than possible with QSO sightlines. Using a sample of 89 galaxies with (z) = 2.3 {+-} 0.3 and with both rest-frame far-UV and H{alpha} spectra, we re-calibrate the measurement of accurate galaxy systemic redshifts using only survey-quality rest-UV spectra. We use the velocity-calibrated sample to investigate the kinematics of the galaxy-scale outflows via the strong interstellar (IS) absorption lines and Ly{alpha} emission (when present), as well as their dependence on other physical properties of the galaxies. We construct a sample of 512 close (1''-15'') angular pairs of z {approx} 2-3 galaxies with redshift differences indicating a lack of physical association. Sightlines to the background galaxies provide new information on the spatial distribution of circumgalactic gas surrounding the foreground galaxies. The close pairs sample galactocentric impact parameters 3-125 kpc (physical) at (z) = 2.2, providing for the first time a robust map of cool gas as a function of galactocentric distance for a well-characterized population of galaxies. We propose a simple model of circumgalactic gas that simultaneously matches the kinematics, depth, and profile shape of IS absorption and Ly{alpha} emission lines, as well as the observed variation of absorption line strength (H I and several metallic species) versus galactocentric impact parameter. Within the model, cool gas is distributed symmetrically around every galaxy, accelerating radially outward with v{sub out}(r) increasing with r (i.e., the highest velocities are located at the largest galactocentric

  17. SAMI Galaxy Survey: Spectrally Dissecting 3400 Galaxies By the Dozen

    NASA Astrophysics Data System (ADS)

    Cecil, Gerald N.; Croom, S.; The SAMI Galaxy Survey Team

    2014-01-01

    More than 440 mapped, less than 3000 to go in the Sydney-AAO Multi-object IFU (SAMI) Galaxy Survey! SAMI uses novel, photonic fused-optical fiber “hexabundles” that were developed successfully at The University of Sydney and the Australian Astronomical Observatory AAO), with support from the Australian Research Council Centre of Excellence for All-Sky Astrophysics (CAASTRO). The SAMI Galaxy Survey, led by Assoc. Prof. Croom, is backed by an international team. This spectro-bolometric survey mitigates against “aperture effects” that may mislead when stacking single-fiber galaxy spectra. We seek to answer questions such as “what is the physical role of environment in galaxy evolution? How is stellar mass growth and angular momentum development related in galaxies? How does gas get into and out of galaxies, and how do such flows drive star formation?” SAMI maps stellar and gas properties with 13 integral-field units (IFU) plugged onto a dozen galaxies over the 1° field of the AAT prime-focus corrector. 78% of each bundle's area is filled by sixty-one 1.6-arcsec diameter fibers that are packed closely into concentric circles then their etched, thinned cladding is fused without deforming their cores. The fiber hexabundles route to the bench-mounted AAOmega double-beam spectrograph to cover simultaneously 373-570 nm at R=1730 and 620-735 nm at R=4500. Full spatial resolution of the observing site is recovered by dithered exposures totaling 3.5 hours per field. Target stellar masses generally exceed 108 M⊙, and span a range of environments: ˜650 are within clusters of virial mass 1014-15 M⊙ at 0.03 < z < 0.06, the rest are in the z < 0.1 field with extensive frequency data ancillary to the GAMA Survey. We display some key early results of major science themes being addressed by the SAMI survey team, from rotation curve dependence on group halo mass, through galaxy winds and AGN feedback mechanisms, to oxygen abundance gradients, kinematic decomposition

  18. The structure and evolution of galaxies

    NASA Astrophysics Data System (ADS)

    Martini, Paul

    -infrared and visible-wavelength data combined provide essentially complete wavelength coverage over the 0.3mum--2.5mum range in 9 filters, the equivalent of a low resolution spectrum of each galaxy in this survey. This database includes a relatively large number of Extremely Red Objects, which have spectral energy distributions suggestive of galaxies at z ˜ 1. Galaxy template fits to these objects suggest an equal mix of old elliptical galaxies and young, dusty starbusts. This number of ellipticals provides further support of passive galaxy evolution since z ˜ 1. However the presence of so many dusty starburst galaxies, several with close companions, also shows that many galaxies were still assembling and forming large numbers of stars at this epoch. Recent studies have shown that nearly all galaxies today, including our own, have supermassive black holes at their center that are proportional in mass to the host galaxy spheroid. This result suggests an intimate relationship between the formation and evolution of galaxies and their central black holes. I have derived how upcoming measurements of quasar clustering can determine the characteristic lifetime of quasars, and therefore a timescale for the optically-luminous phase of black hole growth. The quasar lifetime will show if black holes acquired most of their mass during an optically bright quasar phase, or if most of the growth of supermassive black holes occurred during more quiescent, steady accretion over the lifetime of the universe.

  19. Galaxy groups

    SciTech Connect

    Brent Tully, R.

    2015-02-01

    Galaxy groups can be characterized by the radius of decoupling from cosmic expansion, the radius of the caustic of second turnaround, and the velocity dispersion of galaxies within this latter radius. These parameters can be a challenge to measure, especially for small groups with few members. In this study, results are gathered pertaining to particularly well-studied groups over four decades in group mass. Scaling relations anticipated from theory are demonstrated and coefficients of the relationships are specified. There is an update of the relationship between light and mass for groups, confirming that groups with mass of a few times 10{sup 12}M{sub ⊙} are the most lit up while groups with more and less mass are darker. It is demonstrated that there is an interesting one-to-one correlation between the number of dwarf satellites in a group and the group mass. There is the suggestion that small variations in the slope of the luminosity function in groups are caused by the degree of depletion of intermediate luminosity systems rather than variations in the number per unit mass of dwarfs. Finally, returning to the characteristic radii of groups, the ratio of first to second turnaround depends on the dark matter and dark energy content of the universe and a crude estimate can be made from the current observations of Ω{sub matter}∼0.15 in a flat topology, with a 68% probability of being less than 0.44.

  20. The origin of galaxies and clusters of galaxies.

    PubMed

    Peebles, P J

    1984-06-29

    Debate on how galaxies and clusters of galaxies formed has reached an interesting stage at which one can find arguments for quite different scenarios. The galaxy distribution has a complex "frothy" character that could be the fossil of a network of protoclusters or pancakes that produced galaxies. However, there are galaxies like our own that seem never to have been in a protocluster but are physically similar to the galaxies in dense clusters. Some clues to be assessed in resolving this dilemma are the possible existence of galaxy filaments, the relative ages of galaxies and clusters of galaxies, and the continuity between cluster and field galaxies and between galaxies and clusters of galaxies.

  1. Spontaneous breaking of supersymmetry

    SciTech Connect

    Zumino, B.

    1981-12-01

    There has been recently a revival of interest in supersymmetric gauge theories, stimulated by the hope that supersymmetry might help in clarifying some of the questions which remain unanswered in the so called Grand Unified Theories and in particular the gauge hierarchy problem. In a Grand Unified Theory one has two widely different mass scales: the unification mass M approx. = 10/sup 15/GeV at which the unification group (e.g. SU(5)) breaks down to SU(3) x SU(2) x U(1) and the mass ..mu.. approx. = 100 GeV at which SU(2) x U(1) is broken down to the U(1) of electromagnetism. There is at present no theoretical understanding of the extreme smallness of the ratio ..mu../M of these two numbers. This is the gauge hierarchy problem. This lecture attempts to review the various mechanisms for spontaneous supersymmetry breaking in gauge theories. Most of the discussions are concerned with the tree approximation, but what is presently known about radiative correction is also reviewed.

  2. [Closing diastemas].

    PubMed

    Vieira, L C; Pereira, J C; Coradazzi, J L; Francischone, C E

    1990-01-01

    The authors describe a clinical case of closing upper central incisives diastema, reconstructiva of a conoid upper lateral and the rechaping of an upper canine to a lateral incisive. The material used was composite resin.

  3. Interpreting the Clustering of Distant Red Galaxies

    SciTech Connect

    Tinker, Jeremy L.; Wechsler, Risa H.; Zheng, Zheng; /Princeton, Inst. Advanced Study

    2009-08-03

    We analyze the angular clustering of z {approx} 2.3 distant red galaxies (DRGs) measured by Quadri et al. (2008). We find that, with robust estimates of the measurement errors and realistic halo occupation distribution modeling, the measured clustering can be well fit within standard halo occupation models, in contrast to previous results. However, in order to fit the strong break in w({theta}) at {theta} = 10{double_prime}, nearly all satellite galaxies in the DRG luminosity range are required to be DRGs. Within this luminosity-threshold sample, the fraction of galaxies that are DRGs is {approx} 44%, implying that the formation of DRGs is more efficient for satellite galaxies than for central galaxies. Despite the evolved stellar populations contained within DRGs at z = 2.3, 90% of satellite galaxies in the DRG luminosity range have been accreted within 500 Myr. Thus, satellite DRGs must have known they would become satellites well before the time of their accretion. This implies that the formation of DRGs correlates with large-scale environment at fixed halo mass, although the large-scale bias of DRGs can be well fit without such assumptions. Further data are required to resolve this issue. Using the observational estimate that {approx} 30% of DRGs have no ongoing star formation, we infer a timescale for star formation quenching for satellite galaxies of 450 Myr, although the uncertainty on this number is large. However, unless all non-star forming satellite DRGs were quenched before accretion, the quenching timescale is significantly shorter than z {approx} 0 estimates. Down to the completeness limit of the Quadri et al sample, we find that the halo masses of central DRGs are {approx} 50% higher than non-DRGs in the same luminosity range, but at the highest halo masses the central galaxies are DRGs only {approx} 2/3 of the time.

  4. STRUCTURES OF LOCAL GALAXIES COMPARED TO HIGH-REDSHIFT STAR-FORMING GALAXIES

    SciTech Connect

    Petty, Sara M.; De Mello, DuIlia F.; Gallagher, John S.; Gardner, Jonathan P.; Lotz, Jennifer M.; Matt Mountain, C.; Smith, Linda J.

    2009-08-15

    The rest-frame far-ultraviolet morphologies of eight nearby interacting and starburst galaxies (Arp 269, M 82, Mrk 8, NGC 520, NGC 1068, NGC 3079, NGC 3310, and NGC 7673) are compared with 54 galaxies at z {approx} 1.5 and 46 galaxies at z {approx} 4 observed in the Great Observatories Origins Deep Survey (GOODS) taken with the Advanced Camera for Surveys onboard the Hubble Space Telescope. The nearby sample is artificially redshifted to z {approx} 1.5 and 4 by applying luminosity and size scaling. We compare the simulated galaxy morphologies to real z {approx} 1.5 and 4 UV-bright galaxy morphologies. We calculate the Gini coefficient (G), the second-order moment of the brightest 20% of the galaxy's flux (M {sub 20}), and the Sersic index (n). We explore the use of nonparametric methods with two-dimensional profile fitting and find the combination of M {sub 20} with n an efficient method to classify galaxies as having merger, exponential disk, or bulge-like morphologies. When classified according to G and M {sub 20} 20/30% of real/simulated galaxies at z {approx} 1.5 and 37/12% at z {approx} 4 have bulge-like morphologies. The rest have merger-like or intermediate distributions. Alternatively, when classified according to the Sersic index, 70% of the z {approx} 1.5 and z {approx} 4 real galaxies are exponential disks or bulge-like with n>0.8, and {approx} 30% of the real galaxies are classified as mergers. The artificially redshifted galaxies have n values with {approx} 35% bulge or exponential at z {approx} 1.5 and 4. Therefore, {approx} 20%-30% of Lyman-break galaxies have structures similar to local starburst mergers, and may be driven by similar processes. We assume merger-like or clumpy star-forming galaxies in the GOODS field have morphological structure with values n < 0.8 and M {sub 20}> - 1.7. We conclude that Mrk 8, NGC 3079, and NGC 7673 have structures similar to those of merger-like and clumpy star-forming galaxies observed at z {approx} 1.5 and 4.

  5. APEX Snaps First Close-up of Star Factories in Distant Universe

    NASA Astrophysics Data System (ADS)

    2010-03-01

    For the first time, astronomers have made direct measurements of the size and brightness of regions of star-birth in a very distant galaxy, thanks to a chance discovery with the APEX telescope. The galaxy is so distant, and its light has taken so long to reach us, that we see it as it was 10 billion years ago. A cosmic "gravitational lens" is magnifying the galaxy, giving us a close-up view that would otherwise be impossible. This lucky break reveals a hectic and vigorous star-forming life for galaxies in the early Universe, with stellar nurseries forming one hundred times faster than in more recent galaxies. The research is published online today in the journal Nature. Astronomers were observing a massive galaxy cluster [1] with the Atacama Pathfinder Experiment (APEX) telescope, using submillimetre wavelengths of light, when they found a new and uniquely bright galaxy, more distant than the cluster and the brightest very distant galaxy ever seen at submillimetre wavelengths. It is so bright because the cosmic dust grains in the galaxy are glowing after being heated by starlight. The new galaxy has been given the name SMM J2135-0102. "We were stunned to find a surprisingly bright object that wasn't at the expected position. We soon realised it was a previously unknown and more distant galaxy being magnified by the closer galaxy cluster," says Carlos De Breuck from ESO, a member of the team. De Breuck was making the observations at the APEX telescope on the plateau of Chajnantor at an altitude of 5000 m in the Chilean Andes. The new galaxy SMM J2135-0102 is so bright because of the massive galaxy cluster that lies in the foreground. The vast mass of this cluster bends the light of the more distant galaxy, acting as a gravitational lens [2]. As with a telescope, it magnifies and brightens our view of the distant galaxy. Thanks to a fortuitous alignment between the cluster and the distant galaxy, the latter is strongly magnified by a factor of 32. "The magnification

  6. SURFACE BRIGHTNESS PROFILES OF DWARF GALAXIES. I. PROFILES AND STATISTICS

    SciTech Connect

    Herrmann, Kimberly A.; Hunter, Deidre A.; Elmegreen, Bruce G. E-mail: dah@lowell.edu

    2013-11-01

    Radial surface brightness profiles of spiral galaxies are classified into three types: (I) single exponential, or the light falls off with one exponential to a break before falling off (II) more steeply, or (III) less steeply. Profile breaks are also found in dwarf disks, but some dwarf Type IIs are flat or increasing out to a break before falling off. Here we re-examine the stellar disk profiles of 141 dwarfs: 96 dwarf irregulars (dIms), 26 Blue Compact Dwarfs (BCDs), and 19 Magellanic-type spirals (Sms). We fit single, double, or even triple exponential profiles in up to 11 passbands: GALEX FUV and NUV, ground-based UBVJHK and Hα, and Spitzer 3.6 and 4.5 μm. We find that more luminous galaxies have brighter centers, larger inner and outer scale lengths, and breaks at larger radii; dwarf trends with M{sub B} extend to spirals. However, the V-band break surface brightness is independent of break type, M{sub B} , and Hubble type. Dwarf Type II and III profiles fall off similarly beyond the breaks but have different interiors and IIs break ∼twice as far as IIIs. Outer Type II and III scale lengths may have weak trends with wavelength, but pure Type II inner scale lengths clearly decrease from the FUV to visible bands whereas Type III inner scale lengths increase with redder bands. This suggests the influence of different star formation histories on profile type, but nonetheless the break location is approximately the same in all passbands. Dwarfs continue trends between profile and Hubble types such that later-type galaxies have more Type II but fewer Type I and III profiles than early-type spirals. BCDs and Sms are over-represented as Types III and II, respectively, compared to dIms.

  7. Merging Galaxies Create a Binary Quasar

    NASA Astrophysics Data System (ADS)

    2010-02-01

    Observatory in California indicated that the object was likely a binary quasar in the midst of a galaxy merger. Carnegie's Mulchaey then used the 6.5 meter Baade-Magellan telescope at the Las Campanas observatory in Chile to obtain deeper images and more detailed spectroscopy of the merging galaxies. "Just because you see two galaxies that are close to each other in the sky doesn't mean they are merging," says Mulchaey. "But from the Magellan images we can actually see tidal tails, one from each galaxy, which suggests that the galaxies are in fact interacting and are in the process of merging." Thomas Cox, now a fellow at the Carnegie Observatories, corroborated this conclusion using computer simulations of the merging galaxies. When Cox's model galaxies merged, they showed features remarkably similar to what Mulchaey observed in the Magellan images. "The model verifies the merger origin for this binary quasar system," he says. "It also hints that this kind of galaxy interaction is a key component of the growth of black holes and production of quasars throughout our universe." * The authors of the paper published in the Astrophysical Journal are Paul J. Green of the Harvard-Smithsonian Center for Astrophysics, Adam D. Myers of the University of Illinois at Urbana-Champaign, Wayne A. Barkhouse of the University of North Dakota, John S. Mulchaey of the Observatories of the Carnegie Institution for Science, Vardha N. Bennert of the Department of Physics, University of California, Santa Barbara, Thomas J. Cox of the Observatories of the Carnegie Institution for Science, Thomas L. Aldcroft of the Harvard-Smithsonian Center for Astrophysics, and Joan M. Wrobel of National Radio Astronomy Observatory, Socorro, NM. More information, including images and other multimedia, can be found at: http://chandra.harvard.edu and http://chandra.nasa.gov

  8. GALAXY GROWTH BY MERGING IN THE NEARBY UNIVERSE

    SciTech Connect

    Jiang Tao; Hogg, David W.; Blanton, Michael R.

    2012-11-10

    We measure the mass growth rate by merging for a wide range of galaxy types. We present the small-scale (0.014 h {sup -1} {sub 70} Mpc < r < 11 h {sub 70} {sup -1} Mpc) projected cross-correlation functions w(r {sub p}) of galaxy subsamples from the spectroscopic sample of the NYU Value-Added Galaxy Catalog (5 Multiplication-Sign 10{sup 5} galaxies of redshifts 0.03 < z < 0.15) with galaxy subsamples from the Sloan Digital Sky Survey imaging (4 Multiplication-Sign 10{sup 7} galaxies). We use smooth fits to de-project the two-dimensional functions w(r {sub p}) to obtain smooth three-dimensional real-space cross-correlation functions {xi}(r) for each of several spectroscopic subsamples with each of several imaging subsamples. Because close pairs are expected to merge, the three-space functions and dynamical evolution time estimates provide galaxy accretion rates. We find that the accretion onto massive blue galaxies and onto red galaxies is dominated by red companions, and that onto small-mass blue galaxies, red and blue galaxies make comparable contributions. We integrate over all types of companions and find that at fixed stellar mass, the total fractional accretion rates onto red galaxies ({approx}3 h {sub 70} percent per Gyr) are greater than that onto blue galaxies ({approx}1 h {sub 70} percent per Gyr). These rates are almost certainly overestimates because we have assumed that all close pairs merge as quickly as the merger time that we used. One conclusion of this work is that if the total growth of red galaxies from z = 1 to z = 0 is mainly due to merging, the merger rates must have been higher in the past.

  9. Application of break preclusion concept in German nuclear power plants

    SciTech Connect

    Roos, E.; Maier, V.; Nagel, G.

    1997-04-01

    The break preclusion concept is based on {open_quotes}KTA rules{close_quotes}, {open_quotes}RSK guidelines{close_quotes} and {open_quotes}Rahmenspeziflkation Basissicherheit{close_quotes}. These fundamental rules containing for example requirements on material, design, calculation, manufacturing and testing procedures are explained and the technical realisation is shown by means of examples. The proof of the quality of these piping systems can be executed by means of fracture mechanics calculations by showing that in every case the leakage monitoring system already detect cracks which are clearly smaller than the critical crack. Thus the leak before break behavior and the break preclusion concept is implicitly affirmed. In order to further diminish conservativities in the fracture mechanics procedures, specific research projects are executed which are explained in this contribution.

  10. Galaxy-galaxy lensing by non-spherical haloes - I. Theoretical considerations

    NASA Astrophysics Data System (ADS)

    Howell, Paul J.; Brainerd, Tereasa G.

    2010-09-01

    We use a series of Monte Carlo simulations to investigate the theory of galaxy-galaxy lensing by non-spherical dark matter haloes. The simulations include a careful accounting of the effects of multiple deflections on the galaxy-galaxy lensing signal. In a typical observational data set where the mean tangential shear of sources with redshifts zs ~= 0.6 is measured with respect to the observed symmetry axes of foreground galaxies with redshifts zl ~= 0.3, we find that the signature of anisotropic galaxy-galaxy lensing differs substantially from the simple expectation that one would have in the absence of multiple deflections. In general, the observed ratio of the mean tangential shears, γ+(θ)/γ-(θ), is strongly suppressed compared to the function that one would measure if the intrinsic symmetry axes of the foreground galaxies were known. Depending upon the characteristic masses of the lenses, the observed ratio of the mean tangential shears may be consistent with an isotropic signal (despite the fact that the lenses are non-spherical), or it may even be reversed from the expected signal (i.e. the mean tangential shear for sources close to the observed minor axes of the lenses may exceed the mean tangential shear for sources close to the observed major axes of the lenses). These effects are caused primarily by the fact that the images of the lens galaxies have, themselves, been lensed and therefore the observed symmetry axes of the lens galaxies differ from their intrinsic symmetry axes. We show that the effects of lensing of the foreground galaxies on the observed function γ+(θ)/γ-(θ) cannot be eliminated simply by the rejection of foreground galaxies with very small image ellipticities nor by simply focusing the analysis on sources that are located very close to the observed symmetry axes of the foreground galaxies. We conclude that any attempt to use a measurement of γ+(θ)/γ-(θ) to constrain the shapes of dark matter galaxy haloes must include Monte

  11. Ergodicity breaking and localization

    NASA Astrophysics Data System (ADS)

    Geneston, Elvis; Tuladhar, Rohisha; Beig, M. T.; Bologna, Mauro; Grigolini, Paolo

    2016-07-01

    We study the joint action of the non-Poisson renewal events (NPR) yielding Continuous-time random walk (CTRW) with index α <1 and two different generators of Hurst coefficient H ≠0.5 , one generating fractional Brownian motion (FBM) and another scaled Brownian motion (SBM). We discuss the ergodicity breaking emerging from these joint actions and we find that in both cases the adoption of time averages leads to localization. In the case of the joint action of NPR and SBM, localization occurs when SBM would produce subdiffusion. The joint action of NPR and FBM, on the contrary, may lead to localization when FBM is a source of superdiffusion. The joint action of NPR and FBM is equivalent to extending the CTRW to the case where the jumps of the runner are correlated and we argue that the the memory-induced localization requires a refinement of the theoretical perspective about determinism and randomness.

  12. Ergodicity breaking and localization.

    PubMed

    Geneston, Elvis; Tuladhar, Rohisha; Beig, M T; Bologna, Mauro; Grigolini, Paolo

    2016-07-01

    We study the joint action of the non-Poisson renewal events (NPR) yielding Continuous-time random walk (CTRW) with index α<1 and two different generators of Hurst coefficient H≠0.5, one generating fractional Brownian motion (FBM) and another scaled Brownian motion (SBM). We discuss the ergodicity breaking emerging from these joint actions and we find that in both cases the adoption of time averages leads to localization. In the case of the joint action of NPR and SBM, localization occurs when SBM would produce subdiffusion. The joint action of NPR and FBM, on the contrary, may lead to localization when FBM is a source of superdiffusion. The joint action of NPR and FBM is equivalent to extending the CTRW to the case where the jumps of the runner are correlated and we argue that the the memory-induced localization requires a refinement of the theoretical perspective about determinism and randomness. PMID:27575105

  13. Star-formation rates, molecular clouds, and the origin of the far-infrared luminosity of isolated and interacting galaxies

    NASA Technical Reports Server (NTRS)

    Solomon, P. M.; Sage, L. J.

    1988-01-01

    The CO luminosities of 93 galaxies have been determined and are compared with their IRAS FIR luminosities. Strongly interacting/merging galaxies have L(FIR)/L(CO) substantially higher than that of isolated galaxies or galactic giant molecular clouds (GMCs). Galaxies with tidal tails/bridges are the most extreme type with L(FIR)/L(CO) nine times as high as isolated galaxies. Interactions between close pairs of galaxies do not have much effect on the molecular content and global star-formation rate. If the high ratio L(FIR)/L(CO) in strongly interacting galaxies is due to star formation then the efficiency of this process is higher than that of any galactic GMC. Isolated galaxies, distant pairs, and close pairs have an FIR/CO luminosity ratio which is within a factor of two of galactic GMCs with H II regions. The CO luminosities of FIR-luminous galaxies are among the highest observed for any spiral galaxies.

  14. THE STRUCTURE OF 2MASS GALAXY CLUSTERS

    SciTech Connect

    Blackburne, Jeffrey A.; Kochanek, Christopher S.

    2012-01-01

    We use a sample of galaxies from the Two Micron All Sky Survey Extended Source Catalog to refine a matched filter method of finding galaxy clusters that takes into account each galaxy's position, magnitude, and redshift if available. The matched filter postulates a radial density profile, luminosity function, and line-of-sight velocity distribution for cluster galaxies. We use this method to search for clusters in the galaxy catalog, which is complete to an extinction-corrected K-band magnitude of 13.25 and has spectroscopic redshifts for roughly 40% of the galaxies, including nearly all brighter than K = 11.25. We then use a stacking analysis to determine the average luminosity function, radial distribution, and velocity distribution of cluster galaxies in several richness classes, and use the results to update the parameters of the matched filter before repeating the cluster search. We also investigate the correlations between a cluster's richness and its velocity dispersion and core radius using these relations to refine priors that are applied during the cluster search process. After the second cluster search iteration, we repeat the stacking analysis. We find a cluster galaxy luminosity function that fits a Schechter form, with parameters M{sub K*} - 5log h = -23.64 {+-} 0.04 and {alpha} = -1.07 {+-} 0.03. We can achieve a slightly better fit to our luminosity function by adding a Gaussian component on the bright end to represent the brightest cluster galaxy population. The radial number density profile of galaxies closely matches a projected Navarro-Frenk-White profile at intermediate radii, with deviations at small radii due to well-known cluster centering issues and outside the virial radius due to correlated structure. The velocity distributions are Gaussian in shape, with velocity dispersions that correlate strongly with richness.

  15. The environments of poor clusters of galaxies

    NASA Astrophysics Data System (ADS)

    Bliton, Mark Alan

    Poor clusters of galaxies are fundamental cosmological structures, but have received relatively little attention compared to rich, Abell clusters. In order to fully understand galaxy clustering, we must examine galaxy associations of all masses and richness levels. We have therefore undertaken an X-ray, optical, and radio investigation of the environments of poor clusters, in order to understand how their galaxies, radio sources, and intracluster media influence and interact with one another. To examine the global properties of poor clusters as observed in these three wavelength regimes, we have utilized three major sky surveys: the ROSAT All-Sky Survey, the Digitized Sky Survey, and the NRAO VLA Sky Survey. For the purposes of this study, we construct a complete, volume-limited sample of 306 poor clusters in the redshift range 0.01--0.03. We compute the X-ray luminosity function (XLF) of poor clusters and compare to XLFs of nearby, rich, Abell clusters. We also compute the bivariate radio luminosity function (BRLF), which is the fraction of radio-loud galaxies of a given optical magnitude. Higher richness clusters produce increased AGN activity in M* galaxies. We find that only clusters with an elliptical as their dominant galaxy possess an ICM. This implies that the presence of a dominant elliptical at the center of a poor cluster is more closely linked to the presence of an ICM than the overall morphological mix of the cluster galaxies. We also find a strong anti-correlation between richness and the fraction of starburst radio galaxies in poor clusters. There may be two factors which contribute to this anti-correlation. For richer clusters, the ICM density may be sufficiently strong that it can strip gas from starforming galaxies, thereby reducing the level of star formation in richer systems. Conversely, the poorest clusters contain higher galaxy compactness, which results in smaller nearest-neighbor distances between galaxies. These smaller galaxy separations

  16. THE ACS NEARBY GALAXY SURVEY TREASURY. XI. THE REMARKABLY UNDISTURBED NGC 2403 DISK

    SciTech Connect

    Williams, Benjamin F.; Dalcanton, Julianne J.; Stilp, Adrienne; Radburn-Smith, David; Dolphin, Andrew; Skillman, Evan D. E-mail: jd@astro.washington.edu E-mail: dolphin@raytheon.com

    2013-03-10

    We present detailed analysis of color-magnitude diagrams of NGC 2403, obtained from a deep (m {approx}< 28) Hubble Space Telescope (HST) Wide Field Planetary Camera 2 observation of the outer disk of NGC 2403, supplemented by several shallow (m {approx}< 26) HST Advanced Camera for Surveys fields. We derive the spatially resolved star formation history of NGC 2403 out to 11 disk scale lengths. In the inner portions of the galaxy, we compare the recent star formation rates (SFRs) we derive from the resolved stars with those measured using GALEX FUV + Spitzer 24{mu} fluxes, finding excellent agreement between the methods. Our measurements also show that the radial gradient in recent SFR mirrors the disk exponential profile to 11 scale lengths with no break, extending to SFR densities a factor of {approx}100 lower than those that can be measured with GALEX and Spitzer ({approx}2 Multiplication-Sign 10{sup -6} M{sub Sun} yr{sup -1} kpc{sup -2}). Furthermore, we find that the cumulative stellar mass of the disk was formed at similar times at all radii. We compare these characteristics of NGC 2403 to those of its ''morphological twins'', NGC 300 and M 33, showing that the structure and age distributions of the NGC 2403 disk are more similar to those of the relatively isolated system NGC 300 than to those of the Local Group analog M 33. We also discuss the environments and HI morphologies of these three nearby galaxies, comparing them to integrated light studies of larger samples of more distant galaxy disks. Taken together, the physical properties and evolutionary history of NGC 2403 suggest that the galaxy has had no close encounters with other M 81 group members and may be falling into the group for the first time.

  17. Star Formation in Irregular Galaxies.

    ERIC Educational Resources Information Center

    Hunter, Deidre; Wolff, Sidney

    1985-01-01

    Examines mechanisms of how stars are formed in irregular galaxies. Formation in giant irregular galaxies, formation in dwarf irregular galaxies, and comparisons with larger star-forming regions found in spiral galaxies are considered separately. (JN)

  18. Combining Galaxy-Galaxy Lensing and Galaxy Clustering

    SciTech Connect

    Park, Youngsoo; Krause, Elisabeth; Dodelson, Scott; Jain, Bhuvnesh; Amara, Adam; Becker, Matt; Bridle, Sarah; Clampitt, Joseph; Crocce, Martin; Honscheid, Klaus; Gaztanaga, Enrique; Sanchez, Carles; Wechsler, Risa

    2015-01-01

    Combining galaxy-galaxy lensing and galaxy clustering is a promising method for inferring the growth rate of large scale structure, a quantity that will shed light on the mechanism driving the acceleration of the Universe. The Dark Energy Survey (DES) is a prime candidate for such an analysis, with its measurements of both the distribution of galaxies on the sky and the tangential shears of background galaxies induced by these foreground lenses. By constructing an end-to-end analysis that combines large-scale galaxy clustering and small-scale galaxy-galaxy lensing, we also forecast the potential of a combined probes analysis on DES datasets. In particular, we develop a practical approach to a DES combined probes analysis by jointly modeling the assumptions and systematics affecting the different components of the data vector, employing a shared halo model, HOD parametrization, photometric redshift errors, and shear measurement errors. Furthermore, we study the effect of external priors on different subsets of these parameters. We conclude that DES data will provide powerful constraints on the evolution of structure growth in the universe, conservatively/ optimistically constraining the growth function to 8%/4.9% with its first-year data covering 1000 square degrees, and to 4%/2.3% with its full five-year data covering 5000 square degrees.

  19. Revealing the nature of star forming blue early-type galaxies at low redshift

    NASA Astrophysics Data System (ADS)

    George, Koshy; Zingade, Kshama

    2015-11-01

    Context. Star forming early-type galaxies with blue optical colours at low redshift can be used to test our current understanding of galaxy formation and evolution. Aims: We want to reveal the fuel and triggering mechanism for star formation in these otherwise passively evolving red and dead stellar systems. Methods: We undertook an optical and ultraviolet study of 55 star forming blue early-type galaxies, searching for signatures of recent interactions that could be driving the molecular gas into the galaxy and potentially triggering the star formation. Results: We report here our results on star forming blue early-type galaxies with tidal trails and in close proximity to neighbouring galaxies that are evidence of ongoing or recent interactions between galaxies. There are 12 galaxies with close companions with similar redshifts, among which two galaxies are having ongoing interactions that potentially trigger the star formation. Two galaxies show a jet feature that could be due to the complete tidal disruption of the companion galaxy. The interacting galaxies have high star formation rates and very blue optical colours. Galaxies with no companion could have undergone a minor merger in the recent past. Conclusions: The recent or ongoing interaction with a gas-rich neighbouring galaxy could be responsible for bringing cold gas to an otherwise passively evolving early-type galaxy. The sudden gas supply could trigger the star formation, eventually creating a blue early-type galaxy. The galaxies with ongoing tidal interaction are blue and star forming, thereby implying that blue early-type galaxies can exist even when the companion is on flyby so does not end up in a merger. Based on data compiled from Galaxy Zoo project, and the volunteers contribution are acknowledged at http://www.galaxyzoo.org/Volunteers.aspx

  20. Galaxies as gravitational lenses.

    PubMed

    Barnothy, J; Barnothy, M F

    1968-10-18

    Of all the galaxies in the visible part of the universe, 500 million are seen through intervening galaxies. In some instances the foreground galaxy will act as a gravitational lens and produce distorted and (in brightness) greatly amplified images of the galaxy behind it; such images may simulate starlike superluminous objects such as quasars (quasi-stellar objects). The number of gravitational lenses is several times greater than the number of quasars yet observed. In other instances the superposition of the image upon a visible foreground galaxy may simulate morphological configurations resembling N-type, dumbbell, spiral, or barred-spiral galaxies. PMID:17836654

  1. The AMIGA sample of isolated galaxies. X. A first look at isolated galaxy colors

    NASA Astrophysics Data System (ADS)

    Fernández Lorenzo, M.; Sulentic, J.; Verdes-Montenegro, L.; Ruiz, J. E.; Sabater, J.; Sánchez, S.

    2012-04-01

    Context. The basic properties of galaxies can be affected by both nature (internal processes) or nurture (interactions and effects of environment). Deconvolving the two effects is an important current effort in astrophysics. Observed properties of a sample of isolated galaxies should be mainly the result of internal (natural) evolution. It follows that nurture-induced galaxy evolution can only be understood through a comparative study of galaxies in different environments. Aims: We take a first look at SDSS (g - r) colors of galaxies in the AMIGA sample, which consists of many of the most isolated galaxies in the local Universe. This alerted us at the same time to the pitfalls of using automated SDSS colors. Methods: We focused on median values for the principal morphological subtypes found in the AMIGA sample (E/S0 and Sb-Sc) and compared them with equivalent measures obtained for galaxies in denser environments. Results: We find a weak tendency for AMIGA spiral galaxies to be redder than objects in close pairs. We find no clear difference when we compared this with galaxies in other (e.g. group) environments. However, the (g - r) color of isolated galaxies shows a Gaussian distribution, as might be expected assuming nurture-free evolution. We find a smaller median absolute deviation in colors for isolated galaxies compared to both wide and close pairs. The majority of the deviation on median colors for spiral subtypes is caused by a color-luminosity correlation. Surprisingly, isolated and non-isolated early-type galaxies show similar (g - r). We see little evidence for a green valley in our sample because most spirals redder than (g - r) = 0.7 have spurious colors. Conclusions: The redder colors of AMIGA spirals and lower color dispersions for AMIGA subtypes - compared with close pairs - are likely caused by a more passive star formation in very isolated galaxies. Full Tables 1 and 2 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130

  2. X-ray Emission from Early Universe Analog Galaxies

    NASA Astrophysics Data System (ADS)

    Brorby, Matthew; Kaaret, Philip; Prestwich, Andrea H.; Mirabel, I. Felix; Feng, Hua

    2016-01-01

    Around 300,000 years after the Big Bang, the Universe had cooled enough to combine and form neutral atoms. This signified the beginning of a time known as the Dark Ages. Neutral matter began to fall into the dark matter gravitational wells that were seeded after the initial moments of the Big Bang. As the first stars and galaxies formed within these gravitational wells, the surrounding baryonic matter was heated and started to ionize. The source of energetic photons that heated and reionized the early Universe remains uncertain. Early galaxies had low metallicity and recent population synthesis calculations suggest that the number and luminosity of high-mass X-ray binaries are enhanced in star-forming galaxies with low metallicity, offering a potentially important and previously overlooked source of heating and reionization. Here we examine two types of local galaxies that have been shown to be good analogs to the early galaxies in the Universe: Blue compact dwarf galaxies (BCDs) and Lyman Break Analogs (LBAs).A BCD is defined by its blue optical colors, low metallicities, and physically small size. This makes BCDs the best available local analogs for early star formation. We analyzed data from a sample of 25 metal-poor BCDs and compared our results with those of near-solar metallicity galaxies. Using a Bayesian approach, we showed that the X-ray luminosity function for the low-metallicity BCDs is significantly elevated relative to the XLF for near-solar metallicity galaxies.Larger, gas-rich galaxies may have formed shortly after these first galaxies. These larger galaxies would be similar in their properties to the high-redshift Lyman break galaxies (LBGs). LBAs provide the best local comparison to the LBGs. We studied a sample of 10 LBAs in order to measure the relation between star formation rate and X-ray luminosity for these galaxies. We found that for LBAs with intermediate sub-solar metallicities, there is enhanced X-ray emission relative to the expected

  3. Mapping the Milky Way Galaxy with LISA

    NASA Technical Reports Server (NTRS)

    McKinnon, Jose A.; Littenberg, Tyson

    2012-01-01

    Gravitational wave detectors in the mHz band (such as the Laser Interferometer Space Antenna, or LISA) will observe thousands of compact binaries in the galaxy which can be used to better understand the structure of the Milky Way. To test the effectiveness of LISA to measure the distribution of the galaxy, we simulated the Close White Dwarf Binary (CWDB) gravitational wave sky using different models for the Milky Way. To do so, we have developed a galaxy density distribution modeling code based on the Markov Chain Monte Carlo method. The code uses different distributions to construct realizations of the galaxy. We then use the Fisher Information Matrix to estimate the variance and covariance of the recovered parameters for each detected CWDB. This is the first step toward characterizing the capabilities of space-based gravitational wave detectors to constrain models for galactic structure, such as the size and orientation of the bar in the center of the Milky Way

  4. Core break-off mechanism

    NASA Technical Reports Server (NTRS)

    Myrick, Thomas M. (Inventor)

    2003-01-01

    A mechanism for breaking off and retaining a core sample of a drill drilled into a ground substrate has an outer drill tube and an inner core break-off tube sleeved inside the drill tube. The break-off tube breaks off and retains the core sample by a varying geometric relationship of inner and outer diameters with the drill tube. The inside diameter (ID) of the drill tube is offset by a given amount with respect to its outer diameter (OD). Similarly, the outside diameter (OD) of the break-off tube is offset by the same amount with respect to its inner diameter (ID). When the break-off tube and drill tube are in one rotational alignment, the two offsets cancel each other such that the drill can operate the two tubes together in alignment with the drill axis. When the tubes are rotated 180 degrees to another positional alignment, the two offsets add together causing the core sample in the break-off tube to be displaced from the drill axis and applying shear forces to break off the core sample.

  5. Simple stringy dynamical supersymmetry breaking

    SciTech Connect

    Aharony, Ofer; Kachru, Shamit; Silverstein, Eva

    2007-12-15

    We present simple string models which dynamically break supersymmetry without non-Abelian gauge dynamics. The Fayet model, the Polonyi model, and the O'Raifeartaigh model each arise from D-branes at a specific type of singularity. D-brane instanton effects generate the requisite exponentially small scale of supersymmetry breaking.

  6. Simple Stringy Dynamical SUSY Breaking

    SciTech Connect

    Aharony, Ofer; Kachru, Shamit; Silverstein, Eva; /Stanford U., Phys. Dept. /SLAC

    2007-08-08

    We present simple string models which dynamically break supersymmetry without non-Abelian gauge dynamics. The Fayet model, the Polonyi model, and the O'Raifeartaigh model each arise from D-branes at a specific type of singularity. D-brane instanton effects generate the requisite exponentially small scale of supersymmetry breaking.

  7. Entanglement–breaking indices

    SciTech Connect

    Lami, L.; Giovannetti, V.

    2015-09-15

    We study a set of new functionals (called entanglement–breaking indices) which characterize how many local iterations of a given (local) quantum channel are needed in order to completely destroy the entanglement between the system of interest over which the transformation is defined and an external ancilla. The possibility of contrasting the noisy effects introduced by the channel iterations via the action of intermediate (filtering) transformations is analyzed. We provide some examples in which our functionals can be exactly calculated. The differences between unitary and non-unitary filtering operations are analyzed showing that, at least for systems of dimension d larger than or equal to 3, the non-unitary choice is preferable (the gap between the performances of the two cases being divergent in some cases). For d = 2 (qubit case), on the contrary, no evidences of the presence of such gap is revealed: we conjecture that for this special case unitary filtering transformations are optimal. The scenario in which more general filtering protocols are allowed is also discussed in some detail. The case of a depolarizing noise acting on a two–qubit system is exactly solved in a general case.

  8. A Zoo of Galaxies

    NASA Astrophysics Data System (ADS)

    Masters, Karen L.

    2015-03-01

    We live in a universe filled with galaxies with an amazing variety of sizes and shapes. One of the biggest challenges for astronomers working in this field is to understand how all these types relate to each other in the background of an expanding universe. Modern astronomical surveys (like the Sloan Digital Sky Survey) have revolutionised this field of astronomy, by providing vast numbers of galaxies to study. The sheer size of the these databases made traditional visual classification of the types galaxies impossible and in 2007 inspired the Galaxy Zoo project (www.galaxyzoo.org); starting the largest ever scientific collaboration by asking members of the public to help classify galaxies by type and shape. Galaxy Zoo has since shown itself, in a series of now more than 30 scientific papers, to be a fantastic database for the study of galaxy evolution. In this Invited Discourse I spoke a little about the historical background of our understanding of what galaxies are, of galaxy classification, about our modern view of galaxies in the era of large surveys. I finish with showcasing some of the contributions galaxy classifications from the Galaxy Zoo project are making to our understanding of galaxy evolution.

  9. Breaking down barriers

    SciTech Connect

    Anderson, J.

    1996-03-01

    This article is a review of the financing of international power projects. Within the past 15 months, a number of deals have been closed, teaching the industry several important lessons about financing projects in emerging markets. As a result, new models are being developed for financing projects, and it is estimated that 50 deals with a total dollar value of $20B could close in 1996. Two recent closures, in Indonesia and in India, are reviewed. The global outlook is discussed, especially from the financing side. More transparency in the markets, reform of regulations, increased local capital, government backing, and continued persistence by developers and their financiers is expected to make for a smoother future in project financing.

  10. Recovering dark-matter clustering from galaxies with Gaussianization

    NASA Astrophysics Data System (ADS)

    McCullagh, Nuala; Neyrinck, Mark; Norberg, Peder; Cole, Shaun

    2016-04-01

    The Gaussianization transform has been proposed as a method to remove the issues of scale-dependent galaxy bias and non-linearity from galaxy clustering statistics, but these benefits have yet to be thoroughly tested for realistic galaxy samples. In this paper, we test the effectiveness of the Gaussianization transform for different galaxy types by applying it to realistic simulated blue and red galaxy samples. We show that in real space, the shapes of the Gaussianized power spectra of both red and blue galaxies agree with that of the underlying dark matter, with the initial power spectrum, and with each other to smaller scales than do the statistics of the usual (untransformed) density field. However, we find that the agreement in the Gaussianized statistics breaks down in redshift space. We attribute this to the fact that red and blue galaxies exhibit very different fingers of god in redshift space. After applying a finger-of-god compression, the agreement on small scales between the Gaussianized power spectra is restored. We also compare the Gaussianization transform to the clipped galaxy density field and find that while both methods are effective in real space, they have more complicated behaviour in redshift space. Overall, we find that Gaussianization can be useful in recovering the shape of the underlying dark-matter power spectrum to k ˜ 0.5 h Mpc-1 and of the initial power spectrum to k ˜ 0.4 h Mpc-1 in certain cases at z = 0.

  11. The Unexpected Past of a Dwarf Galaxy

    NASA Astrophysics Data System (ADS)

    1996-08-01

    in this way effectively `eats' the smaller one. Thus the Milky Way may contain the remains of many smaller galaxies it has met and consumed in the past. A natural consequence of this theory is that the Milky Way halo may at least partially consist of stars which originally belonged to these smaller galaxies. However, it is also possible that some of the halo stars formed during the early collapse of the gas cloud from which the Milky Way formed. Like the Milky Way, the two nearest, large spiral galaxies (the Andromeda nebula and M33 in the neighbouring Triangulum constellation) are also surrounded by halos of old stars. Contrarily, investigations of the smaller galaxies in the Local Group have until now not shown that they possess such halos. These dwarf galaxies greatly outnumber the large spiral galaxies - to date about two dozen are known - and they are considered to be the last survivors of the earlier cannibalism phase. The nearest are the well-known Magellanic Clouds, about 170,000 (Large Cloud) and 250,000 light years distant (Small Cloud). They can be seen with the unaided eye from the Southern hemisphere. Recent studies indicate that they orbit the Milky Way and that they may eventually fall prey to our galaxy in a future round of cannibalism. So far, no evidence has been found of an old halo around the Magellanic Clouds. This does not necessarily imply that all dwarf galaxies must likewise lack halos: it is also possible that the halos of the Magellanic Clouds were stripped away when they came too close to the Milky Way sometime in the past. The isolated WLM dwarf galaxy Down in the southern sky, in the constellation of Cetus (the Whale or the Sea Monster), lies a relative faint and distant, small galaxy which astronomers normally refer to as the WLM dwarf galaxy . It was first seen in 1909 by the famous astrophotographer Max Wolf on photographic plates obtained at the Heidelberg Observatory (Germany), but it was only in 1926 that its true nature was

  12. Faint Lyα Emitters, Star-forming Galaxies, and Damped Lyα Systems

    NASA Astrophysics Data System (ADS)

    Rauch, M.; Haehnelt, M.; Bunker, A.; Becker, G.; Marleau, F.; Graham, J.; Cristiani, S.; Jarvis, M.; Lacey, C.; Morris, S.; Peroux, C.; Roettgering, H.; Theuns, T.

    2008-10-01

    We have discovered a population of faint single line emitters, likely to be identified with faint z˜ 3 Lyα emitters and with the host galaxies of damped Lyman alpha systems. The objects appear to constitute the bulk of the star-forming galaxies detected so far from the ground, and are likely to provide the gaseous reservoir from which present-day Milky way type galaxies have formed. Unlike color-selected (yman break galaxies, these objects appear to have low star-formation rates, relatively strong Lyalpha emission, and low masses, metallicities, and dust content (s.a. arXiv:0711.1354).

  13. Star Formation in Galaxies

    NASA Technical Reports Server (NTRS)

    1987-01-01

    Topics addressed include: star formation; galactic infrared emission; molecular clouds; OB star luminosity; dust grains; IRAS observations; galactic disks; stellar formation in Magellanic clouds; irregular galaxies; spiral galaxies; starbursts; morphology of galactic centers; and far-infrared observations.

  14. Galaxy NGC 300

    NASA Technical Reports Server (NTRS)

    2003-01-01

    This image of the nearby spiral galaxy NGC 300 was taken by Galaxy Evolution Explorer in a single orbit exposure of 27 minutes on October 10, 2003. NGC 300 lies 7 million light years from our Milky Way galaxy and is one of a group of galaxies in the constellation Sculptor. NGC 300 is often used as a prototype of a spiral galaxy because in optical images it displays flowing spiral arms and a bright central region of older (and thus redder) stars. The Galaxy Evolution Explorer image taken in ultraviolet light shows us that NGC 300 is an efficient star-forming galaxy. The bright blue regions in the Galaxy Evolution Explorer image reveal new stars forming all the way into the nucleus of NGC 300.

  15. Internal kinematics of modelled interacting disc galaxies

    NASA Astrophysics Data System (ADS)

    Kronberger, T.; Kapferer, W.; Schindler, S.; Böhm, A.; Kutdemir, E.; Ziegler, B. L.

    2006-10-01

    We present an investigation of galaxy-galaxy interactions and their effects on the velocity fields of disc galaxies in combined N-body/hydrodynamic simulations, which include cooling, star formation with feedback, and galactic winds. Rotation curves (RCs) of the gas are extracted from these simulations in a way that follows the procedure applied to observations of distant, small, and faint galaxies as closely as possible. We show that galaxy-galaxy mergers and fly-bys disturb the velocity fields significantly and hence the RCs of the interacting galaxies, leading to asymmetries and distortions in the RCs. Typical features of disturbed kinematics are significantly rising or falling profiles in the direction of the companion galaxy and pronounced bumps in the RCs. In addition, tidal tails can leave strong imprints on the rotation curve. All these features are observable for intermediate redshift galaxies, on which we focus our investigations. We use a quantitative measure for the asymmetry of rotation curves to show that the appearance of these distortions strongly depends on the viewing angle. We also find in this way that the velocity fields settle back into relatively undisturbed equilibrium states after unequal mass mergers and fly-bys. About 1 Gyr after the first encounter, the RCs show no severe distortions anymore. These results are consistent with previous theoretical and observational studies. As an illustration of our results, we compare our simulated velocity fields and direct images with rotation curves from VLT/FORS spectroscopy and ACS images of a cluster at z=0.53 and find remarkable similarities.

  16. Are dusty galaxies blue? Insights on UV attenuation from dust-selected galaxies

    SciTech Connect

    Casey, C. M.; Cooray, A.; Scoville, N. Z.; Sanders, D. B.; Lee, N.; Finkelstein, S. L.; Capak, P.; Conley, A.; De Zotti, G.; Farrah, D.; Fu, H.; Le Floc'h, E.; Ilbert, O.; Ivison, R. J.; Takeuchi, T. T.

    2014-12-01

    Galaxies' rest-frame ultraviolet (UV) properties are often used to directly infer the degree to which dust obscuration affects the measurement of star formation rates (SFRs). While much recent work has focused on calibrating dust attenuation in galaxies selected at rest-frame ultraviolet wavelengths, locally and at high-z, here we investigate attenuation in dusty, star forming galaxies (DSFGs) selected at far-infrared wavelengths. By combining multiwavelength coverage across 0.15-500 μm in the COSMOS field, in particular making use of Herschel imaging, and a rich data set on local galaxies, we find an empirical variation in the relationship between the rest-frame UV slope (β) and the ratio of infrared-to-ultraviolet emission (L {sub IR}/L {sub UV} ≡ IRX) as a function of infrared luminosity, or total SFR. Both locally and at high-z, galaxies above SFR ≳ 50 M {sub ☉} yr{sup –1} deviate from the nominal IRX-β relation toward bluer colors by a factor proportional to their increasing IR luminosity. We also estimate contamination rates of DSFGs on high-z dropout searches of <<1% at z ≲ 4-10, providing independent verification that contamination from very dusty foreground galaxies is low in Lyman-break galaxy searches. Overall, our results are consistent with the physical interpretation that DSFGs, e.g., galaxies with >50 M {sub ☉} yr{sup –1}, are dominated at all epochs by short-lived, extreme burst events, producing many young O and B stars that are primarily, yet not entirely, enshrouded in thick dust cocoons. The blue rest-frame UV slopes of DSFGs are inconsistent with the suggestion that most DSFGs at z ∼ 2 exhibit steady-state star formation in secular disks.

  17. Experimenting with galaxies

    NASA Technical Reports Server (NTRS)

    Miller, Richard H.

    1992-01-01

    A study to demonstrate how the dynamics of galaxies may be investigated through the creation of galaxies within a computer model is presented. The numerical technique for simulating galaxies is shown to be both highly efficient and highly robust. Consideration is given to the anatomy of a galaxy, the gravitational N-body problem, numerical approaches to the N-body problem, use of the Poisson equation, and the symplectic integrator.

  18. The rate of gravitational galaxy clustering

    NASA Astrophysics Data System (ADS)

    Saslaw, William C.

    1992-06-01

    The rate of gravitational galaxy clustering is considered within the framework of the simple but fundamental case when the initial distribution of galaxy positions is close to Poisson and most of the matter is closely associated with the galaxies. Simple gravitational clustering in an expanding universe is found to evolve along an adiabat of the equation of state which includes gravitational interactions. The faster the universe expands relative to its gravitational clustering time scale, the better this adiabatic approximation becomes. This generalizes the well-known result that a homogeneous unclustered perfect gas in an expanding universe evolves along an adiabat of the perfect gas equation of state. The evolving clustering is characterized. There is a critical value of 0.8604 at which clustering dominates the equation of state and the specific heat at constant volume becomes negative. Subsequent growth of clustering slows appreciably. Numerical N-body experiments are consistent with these properties.

  19. Galaxy Cluster Smashes Distance Record

    NASA Astrophysics Data System (ADS)

    2009-10-01

    he most distant galaxy cluster yet has been discovered by combining data from NASA's Chandra X-ray Observatory and optical and infrared telescopes. The cluster is located about 10.2 billion light years away, and is observed as it was when the Universe was only about a quarter of its present age. The galaxy cluster, known as JKCS041, beats the previous record holder by about a billion light years. Galaxy clusters are the largest gravitationally bound objects in the Universe. Finding such a large structure at this very early epoch can reveal important information about how the Universe evolved at this crucial stage. JKCS041 is found at the cusp of when scientists think galaxy clusters can exist in the early Universe based on how long it should take for them to assemble. Therefore, studying its characteristics - such as composition, mass, and temperature - will reveal more about how the Universe took shape. "This object is close to the distance limit expected for a galaxy cluster," said Stefano Andreon of the National Institute for Astrophysics (INAF) in Milan, Italy. "We don't think gravity can work fast enough to make galaxy clusters much earlier." Distant galaxy clusters are often detected first with optical and infrared observations that reveal their component galaxies dominated by old, red stars. JKCS041 was originally detected in 2006 in a survey from the United Kingdom Infrared Telescope (UKIRT). The distance to the cluster was then determined from optical and infrared observations from UKIRT, the Canada-France-Hawaii telescope in Hawaii and NASA's Spitzer Space Telescope. Infrared observations are important because the optical light from the galaxies at large distances is shifted into infrared wavelengths because of the expansion of the universe. The Chandra data were the final - but crucial - piece of evidence as they showed that JKCS041 was, indeed, a genuine galaxy cluster. The extended X-ray emission seen by Chandra shows that hot gas has been detected

  20. 3D structure of nearby groups of galaxies

    NASA Astrophysics Data System (ADS)

    Makarova, L.; Makarov, D.; Klypin, A.; Gottlöber, S.

    2016-10-01

    Using high accuracy distance estimates, we study the three-dimensional distribution of galaxies in five galaxy groups at a distance less than 5 Mpc from the Milky Way. Due to proximity of these groups our sample of galaxies is nearly complete down to extremely small dwarf galaxies with absolute magnitudes M B = -12. We find that the average number-density profile of the groups shows a steep power-law decline dn/dV ˜ R-3 at distances R=(100-500) kpc consistent with predictions of the standard cosmological model. We also find that there is no indication of a truncation or a cutoff in the density at the expected virial radius: the density profile extends at least to 1.5 Mpc. Vast majority of galaxies within 1.5 Mpc radius around group centres are gas-rich star-forming galaxies. Early-type galaxies are found only in the central ˜ 300 kpc region. Lack of dwarf spheroidal and dwarf elliptical galaxies in the field and in the outskirts of large groups is a clear indication that these galaxies experienced morphological transformation when they came close to the central region of forming galaxy group.

  1. Far Away Galaxy Under The Microscope

    NASA Astrophysics Data System (ADS)

    2006-08-01

    An international group of astronomers have discovered large disc galaxies akin to our Milky Way that must have formed on a rapid time scale, only 3 billion years after the Big Bang. In one of these systems, the combination of adaptive optics techniques with the new SINFONI spectrograph on ESO's Very Large Telescope (VLT) resulted in a record-breaking resolution of a mere 0.15 arcsecond, giving an unprecedented detailed view of the anatomy of such a distant proto-disc galaxy. "We have been able, for the first time, to obtain well resolved, two dimensional images of the gas motions in distant star forming galaxies, whose light has traveled more than 11 billion years to the Earth," said Reinhard Genzel, lead author of a paper in this week's issue of Nature in which these results are presented. This tells the story how galaxies looked like a mere 3 billion years after the Big Bang. ESO PR Photo 31a/06 ESO PR Photo 31a/06 emission of the galaxy BzK-15504 (SINFONI/VLT) Over the past decade astronomers have established a global framework of how galaxies formed and evolved when the Universe was only a few billion years old. Gas of ordinary matter cooled and collected in concentrations of the mysterious 'dark' matter (so called dark matter halos). Since that time and up to the present epoch collisions and mergers of galaxies subsequently led to the hierarchical build-up of galaxy mass. This general picture leaves open, however, on what timescales galaxies were assembled and when and how bulges and discs, the primary components of present day galaxies, were formed. A major study of distant, luminous star forming galaxies at ESO's VLT, the 'SINS' (Spectroscopic Imaging Survey in the Near-Infrared with SINFONI) survey, has now resulted in a major break-through on these questions. This study exploited SINFONI [1], a novel infrared 'integral field spectrometer' that simultaneously delivers sharp images, with adaptive optics, and highly resolved colour information (spectra) of an

  2. Enhanced X-ray Emission from Early Universe Analog Galaxies

    NASA Astrophysics Data System (ADS)

    Brorby, Matthew; Kaaret, Philip; Prestwich, Andrea H.; Mirabel, I. Felix; Feng, Hua

    2016-04-01

    X-rays from binaries containing compact objects may have played an important role in heating the early Universe. Here we discuss our findings from X-ray studies of blue compact dwarf galaxies (BCDs), Lyman break analogs (LBAs), and Green Pea galaxies (GP), all of which are considered local analogs to high redshift galaxies. We find enhanced X-ray emission per unit star-formation rate which strongly correlates with decreasing metallicity. We find evidence for the existence of a L_X-SFR-Metallicity plane for star-forming galaxies. The exact properties of X-ray emission in the early Universe affects the timing and morphology of reionization, both being observable properties of current and future radio observations of the redshifted 21cm signal from neutral hydrogen.

  3. Low surface brightness galaxies

    NASA Technical Reports Server (NTRS)

    Vanderhulst, J. M.; Deblok, W. J. G.; Mcgaugh, S. S.; Bothun, G. D.

    1993-01-01

    A program to investigate the properties of low surface brightness (LSB) galaxies involving surface photometry in U, B, V, R, I, and H-alpha, HI imaging with the Westerbork Synthesis Radio Telescope (WSRT) and the very large array (VLA) and spectrophotometry of H2 regions in LSB galaxies is underway. The goal is to verify the idea that LSB galaxies have low star formation rates because the local gas density falls below the critical density for star formation, and to study the stellar population and abundances in LSB galaxies. Such information should help understanding the evolutionary history of LSB galaxies. Some preliminary results are reported.

  4. Segregation properties of galaxies

    SciTech Connect

    Santiago, B.X.; Da Costa, L.N. )

    1990-10-01

    Using the recently completed Southern Sky Redshift Survey, in conjunction with measurements of the central surface brightness, the existence of segregation in the way galaxies of different morphology and surface brightness are distributed in space is investigated. Results indicate that there is some evidence that low surface brightness galaxies are more randomly distributed than brighter ones and that this effect is independent of the well-known tendency of early-type galaxies to cluster more strongly than spirals. Presuming that the observed clustering was established at the epoch of galaxy formation, it may provide circumstantial evidence for biased galaxy formation. 24 refs.

  5. DISK GALAXIES WITH BROKEN LUMINOSITY PROFILES FROM COSMOLOGICAL SIMULATIONS

    SciTech Connect

    Martinez-Serrano, F. J.; Serna, A.; Domenech-Moral, M.; Dominguez-Tenreiro, R.

    2009-11-10

    We present smoothed particle hydrodynamics cosmological simulations of the formation of three disk galaxies with a detailed treatment of chemical evolution and cooling. The resulting galaxies have properties compatible with observations: relatively high disk-to-total ratios, thin stellar disks, and good agreement with the Tully-Fisher and the luminosity-size relations. They present a break in the luminosity profile at 3.0 +- 0.5 disk scale lengths while showing an exponential mass profile without any apparent breaks, which is in line with recent observational results. Since the stellar mass profile is exponential, only differences in the stellar populations can be the cause of the luminosity break. Although we find a cutoff for the star formation rate (SFR) imposed by a density threshold in our star formation model, it does not coincide with the luminosity break and is located at 4.3 +- 0.4 disk scale lengths, with star formation going on between both radii. The color profiles and the age profiles are 'U-shaped', with the minimum for both profiles located approximately at the break radius. The SFR to stellar mass ratio increases until the break, explaining the coincidence of the break with the minimum of the age profile. Beyond the break, we find a steep decline in the gas density and, consequently, a decline in the SFR and redder colors. We show that most stars (64%-78%) in the outer disk originate in the inner disk and afterward migrate there. Such stellar migrations are likely the main origin of the U-shaped age profile and, therefore, of the luminosity break.

  6. Galaxy NGC 3079

    NASA Technical Reports Server (NTRS)

    1999-01-01

    A lumpy bubble of hot gas rises from a cauldron of glowing matter in a distant galaxy, as seen by NASA's Hubble Space Telescope.

    The new images, taken by Hubble's Wide Field and Planetary Camera 2, are online at http://oposite.stsci.edu/pubinfo/pr/2001/28 and http://www.jpl.nasa.gov/images/wfpc. The camera was designed and built by NASA's Jet Propulsion Laboratory, Pasadena, Calif.

    Galaxy NGC 3079, located 50 million light-years from Earth in the constellation Ursa Major, has a huge bubble in the center of its disc, as seen in the image on the left. The smaller photo at right shows a close-up of the bubble. The two white dots are stars.

    Astronomers suspect the bubble is being blown by 'winds,' or high-speed streams of particles, released during a burst of star formation. The bubble's lumpy surface has four columns of gaseous filaments towering above the galaxy's disc. The filaments whirl around in a vortex and are expelled into space. Eventually, this gas will rain down on the disc and may collide with gas clouds, compress them and form a new generation of stars.

    Theoretical models indicate the bubble formed when winds from hot stars mixed with small bubbles of hot gas from supernova explosions. Radio telescope observations indicate those processes are still active. Eventually, the hot stars will die, and the bubble's energy source will fade away.

    The images, taken in 1998, show glowing gas as red and starlight as blue/green. Results appear in the July 1, 2001 issue of the Astrophysical Journal. More information about the Hubble Space Telescope is at http://www.stsci.edu. More information about the Wide Field and Planetary Camera 2 is at http://wfpc2.jpl.nasa.gov.

    The Space Telescope Science Institute, Baltimore, Md., manages space operations for Hubble for NASA's Office of Space Science, Washington, D.C. The institute is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract with the Goddard

  7. The host galaxy and Fermi-LAT counterpart of HESS J1943+213

    NASA Astrophysics Data System (ADS)

    Peter, D.; Domainko, W.; Sanchez, D. A.; van der Wel, A.; Gässler, W.

    2014-11-01

    Context. The very-high energy (VHE, E> 100 GeV) gamma-ray sky shows diverse Galactic and extragalactic source populations. For some sources the astrophysical object class could not be identified so far. Aims: The nature (Galactic or extragalactic) of the VHE gamma-ray source HESS J1943+213 is explored. We specifically investigate the proposed near-infrared counterpart 2MASS J19435624+2118233 of HESS J1943+213 and investigate the implications of a physical association. Methods: We present K-band imaging from the 3.5 m CAHA telescope of 2MASS J19435624+2118233. Furthermore, 5 years of Fermi-LAT data were analyzed to search for a high-energy (HE, 100 MeV galaxy, and thus point toward an extragalactic scenario for the VHE gamma-ray source, assuming that the near-infrared source is the counterpart of HESS J1943+213. A high-Sérsic index profile provides a better fit than an exponential profile, indicating that the surface brightness profile of 2MASS J19435624+2118233 follows that of a typical, massive elliptical galaxy more closely than that of a disk galaxy. With Fermi-LAT a HE counterpart is found with a power-law spectrum above 1 GeV, with a normalization of (3.0 ± 0.8stat ± 0.6sys) × 10-15 cm-2 s-1 MeV-1 at the decorrelation energy Edec = 15.1 GeV and a spectral index of Γ = 1.59 ± 0.19stat ± 0.13sys. This gamma-ray spectrum shows a rather sharp break between the HE and VHE regimes of ΔΓ = 1.47 ± 0.36. Conclusions: The infrared and HE data strongly favor an extragalactic origin of HESS J1943+213, where the infrared counterpart traces the host galaxy of an extreme blazar and where the rather sharp spectral break between the HE and VHE regime indicates attenuation on extragalactic background light. The

  8. Galaxies as gravitational lenses.

    PubMed

    Sadeh, D

    1967-12-01

    The probability that a galaxy gathers light from another remote galaxy, and deflects and focuses it toward an observer on Earth, is calculated according to various cosmologic models. I pose the question of whether an object called a quasar is a single, intrinsically luminous entity or the result of accidental alignment, along the line of sight, of two normal galaxies, the more distant of which has its light amplified by the gravitational-lens effect of the nearer galaxy. If galaxies are distributed at random in the universe, the former alternative is true. But, if we assume that most galaxies exist in pairs, we can find about 30 galaxies occurring exactly one behind the other in such a way as to enable amplification of the order of 50. This model explains also the variations in intensity in quasars, but fails to explain others of their observed properties. PMID:17734305

  9. How Do Galaxies Grow?

    NASA Astrophysics Data System (ADS)

    2008-08-01

    Astronomers have caught multiple massive galaxies in the act of merging about 4 billion years ago. This discovery, made possible by combining the power of the best ground- and space-based telescopes, uniquely supports the favoured theory of how galaxies form. ESO PR Photo 24/08 ESO PR Photo 24/08 Merging Galaxies in Groups How do galaxies form? The most widely accepted answer to this fundamental question is the model of 'hierarchical formation', a step-wise process in which small galaxies merge to build larger ones. One can think of the galaxies forming in a similar way to how streams merge to form rivers, and how these rivers, in turn, merge to form an even larger river. This theoretical model predicts that massive galaxies grow through many merging events in their lifetime. But when did their cosmological growth spurts finish? When did the most massive galaxies get most of their mass? To answer these questions, astronomers study massive galaxies in clusters, the cosmological equivalent of cities filled with galaxies. "Whether the brightest galaxies in clusters grew substantially in the last few billion years is intensely debated. Our observations show that in this time, these galaxies have increased their mass by 50%," says Kim-Vy Tran from the University of Zürich, Switzerland, who led the research. The astronomers made use of a large ensemble of telescopes and instruments, including ESO's Very Large Telescope (VLT) and the Hubble Space Telescope, to study in great detail galaxies located 4 billion light-years away. These galaxies lie in an extraordinary system made of four galaxy groups that will assemble into a cluster. In particular, the team took images with VIMOS and spectra with FORS2, both instruments on the VLT. From these and other observations, the astronomers could identify a total of 198 galaxies belonging to these four groups. The brightest galaxies in each group contain between 100 and 1000 billion of stars, a property that makes them comparable

  10. Tidal Disruption Events Prefer Unusual Host Galaxies

    NASA Astrophysics Data System (ADS)

    Arcavi, Iair; French, K. Decker; Zabludoff, Ann I.

    2016-06-01

    A star passing close to a supermassive black hole (SMBH) can be torn apart in a Tidal Disruption Events (TDE). TDEs that are accompanied by observable flares are now being discovered in transient surveys and are revealing the presence and the properties of otherwise-quiescent SMBHs. Recently, it was discovered that TDEs show a strong preference for rare post-starburst galaxies, (i.e. galaxies that have undergone intense star formation but are no longer forming stars today). We quantify this preference and find that TDEs are approximately 30-200 times more likely to occur in post-starburst hosts (compared to the general SDSS galaxy population), with the enhancement factor depending on the star formation history of the galaxy. This surprising host-galaxy preference connects the until-now disparate TDE subclasses of UV/optical-dominated TDEs and X-ray-dominated TDEs, and serves as the basis for TDE-targeted transient surveys. Post-starburst galaxies may be post-mergers, with binary SMBH systems that are still spiraling in. Such systems could enhance the TDE rate, but it is not yet clear if models can quantitatively reproduce the observed enhancement. Alternative explanations for enhanced TDE rate in post-starbursts include non-spherical post-merger central potentials and enhanced rates of giant stars.

  11. THE ORIENTATION OF GALAXIES IN GALAXY CLUSTERS

    SciTech Connect

    Godlowski, Wlodzimierz; Piwowarska, Paulina; Panko, Elena; Flin, Piotr E-mail: paoletta@interia.p E-mail: sfflin@cyf-kr.edu.p

    2010-11-10

    We present an analysis of the spatial orientations of galaxies in 247 optically selected rich Abell clusters which have at least 100 members in the considered area. We investigated the relation between angles that give information about galaxy angular momenta and the number of members in each structure. The position angles of the galaxies' major axes, as well as two angles describing the spatial orientation of the galaxy plane, were tested for isotropy by applying three different statistical tests. It is found that the values of the statistics increase with the amount of the galaxies' members, which is equivalent to the existence of a relation between anisotropy and the number of galaxies in a cluster. The search for connection between the galaxies' alignments and Bautz-Morgan (BM) morphological types of examined clusters showed a weak dependence. A statistically marginal relation between velocity dispersion and cluster richness was observed. In addition, it was found that the velocity dispersion decreases with BM type at almost 3{sigma} level. These results show the dependence of alignments with respect to clusters' richness, which can be regarded as an environmental effect.

  12. The Physical Origin of Galaxy Morphologies and Scaling Laws

    NASA Technical Reports Server (NTRS)

    Steinmetz, Matthias; Navarro, Julio F.

    2002-01-01

    We propose a numerical study designed to interpret the origin and evolution of galaxy properties revealed by space- and ground-based imaging and spectroscopical surveys. Our aim is to unravel the physical processes responsible for the development of different galaxy morphologies and for the establishment of scaling laws such as the Tully-Fisher relation for spirals and the Fundamental Plane of ellipticals. In particular, we plan to address the following major topics: (1) The morphology and observability of protogalaxies, and in particular the relationship between primordial galaxies and the z approximately 3 'Ly-break' systems identified in the Hubble Deep Field and in ground-based searches; (2) The origin of the disk and spheroidal components in galaxies, the timing and mode of their assembly, the corresponding evolution in galaxy morphologies and its sensitivity to cosmological parameters; (3) The origin and redshift evolution of the scaling laws that link the mass, luminosity size, stellar content, and metal abundances of galaxies of different morphological types. This investigation will use state-of-the-art N-body/gasdynamical codes to provide a spatially resolved description of the galaxy formation process in hierarchically clustering universes. Coupled with population synthesis techniques. our models can be used to provide synthetic 'observations' that can be compared directly with observations of galaxies both nearby and at cosmologically significant distances. This study will thus provide insight into the nature of protogalaxies and into the formation process of galaxies like our own Milky Way. It will also help us to assess the cosmological significance of these observations within the context of hierarchical theories of galaxy formation and will supply a theoretical context within which current and future observations can be interpreted.

  13. Transformations in our Understanding of Galaxy Evolution

    NASA Astrophysics Data System (ADS)

    Bershady, M. A.

    2016-10-01

    A new generation of instruments has launched large surveys now mapping galaxy evolution with single- and multi-object integral-field spectrographs (IFS). These surveys form counterpoints to the mapping of the Milky Way with multi-object stellar spectroscopy and the Gaia satellite. Combined, they allow us to better place the Milky Way in context of the galaxy population at z˜0; to understand if the Milky Way is indeed a normal spiral; and to leverage its unique archaeological record against observations of distant galaxies. These studies illustrate opportunities awaiting next-generation instruments and surveys that push to higher spectral resolution, lower surface-brightness, and into the near and even mid-infrared. Here we focus on the advantages of higher spectral resolution IFS, as enabled by WEAVE. Ground-breaking science opportunities include characterizing and kinematically resolving the ionized gas and stars in dynamically cold galaxies. Such studies will benefit from increased sensitivity both in S/N and line-diagnostics, pushing extragalactic observations in integrated light much closer to where our understanding of Milky Way chemo-dynamics is today.

  14. Probing primordial features with future galaxy surveys

    NASA Astrophysics Data System (ADS)

    Ballardini, M.; Finelli, F.; Fedeli, C.; Moscardini, L.

    2016-10-01

    We study the capability of future measurements of the galaxy clustering power spectrum to probe departures from a power-law spectrum for primordial fluctuations. On considering the information from the galaxy clustering power spectrum up to quasi-linear scales, i.e. k < 0.1 h Mpc‑1, we present forecasts for DESI, Euclid and SPHEREx in combination with CMB measurements. As examples of departures in the primordial power spectrum from a simple power-law, we consider four Planck 2015 best-fits motivated by inflationary models with different breaking of the slow-roll approximation. At present, these four representative models provide an improved fit to CMB temperature anisotropies, although not at statistical significant level. As for other extensions in the matter content of the simplest ΛCDM model, the complementarity of the information in the resulting matter power spectrum expected from these galaxy surveys and in the primordial power spectrum from CMB anisotropies can be effective in constraining cosmological models. We find that the three galaxy surveys can add significant information to CMB to better constrain the extra parameters of the four models considered.

  15. Measuring neutrino masses with a future galaxy survey

    SciTech Connect

    Hamann, Jan; Hannestad, Steen; Wong, Yvonne Y.Y. E-mail: sth@phys.au.dk

    2012-11-01

    We perform a detailed forecast on how well a EUCLID-like photometric galaxy and cosmic shear survey will be able to constrain the absolute neutrino mass scale. Adopting conservative assumptions about the survey specifications and assuming complete ignorance of the galaxy bias, we estimate that the minimum mass sum of Σm{sub ν} ≅ 0.06 eV in the normal hierarchy can be detected at 1.5σ to 2.5σ significance, depending on the model complexity, using a combination of galaxy and cosmic shear power spectrum measurements in conjunction with CMB temperature and polarisation observations from PLANCK. With better knowledge of the galaxy bias, the significance of the detection could potentially reach 5.4σ. Interestingly, neither PLANCK+shear nor PLANCK+galaxy alone can achieve this level of sensitivity; it is the combined effect of galaxy and cosmic shear power spectrum measurements that breaks the persistent degeneracies between the neutrino mass, the physical matter density, and the Hubble parameter. Notwithstanding this remarkable sensitivity to Σm{sub ν}, EUCLID-like shear and galaxy data will not be sensitive to the exact mass spectrum of the neutrino sector; no significant bias ( < 1σ) in the parameter estimation is induced by fitting inaccurate models of the neutrino mass splittings to the mock data, nor does the goodness-of-fit of these models suffer any significant degradation relative to the true one (Δχ{sub eff}{sup 2} < 1)

  16. THE KINEMATICS OF IONIZED GAS IN LYMAN-BREAK ANALOGS AT z {approx} 0.2

    SciTech Connect

    Goncalves, Thiago S.; Martin, D. Christopher; Wyder, Ted K.; Basu-Zych, Antara; Overzier, Roderik; Law, David R.; Mallery, Ryan; Rich, R. Michael; Schiminovich, David; Heckman, Timothy H.

    2010-12-01

    We present results for 19 'Lyman-break analogs' observed with Keck/OSIRIS with an adaptive-optics-assisted spatial resolution of less than 200 pc. We detect satellites/companions, diffuse emission, and velocity shear, all with high signal-to-noise ratios. These galaxies present remarkably high velocity dispersion along the line of sight ({approx}70 km s{sup -1}), much higher than standard star-forming spirals in the low-redshift universe. We artificially redshift our data to z {approx} 2.2 to allow for a direct comparison with observations of high-z Lyman-break galaxies and find striking similarities between both samples. This suggests that either similar physical processes are responsible for their observed properties, or, alternatively, that it is very difficult to distinguish between different mechanisms operating in the low- versus high-redshift starburst galaxies based on the available data. The comparison between morphologies in the UV/optical continuum and our kinemetry analysis often shows that neither is by itself sufficient to confirm or completely rule out the contribution from recent merger events. We find a correlation between the kinematic properties and stellar mass, in that more massive galaxies show stronger evidence for a disk-like structure. This suggests a co-evolutionary process between the stellar mass buildup and the formation of morphological and dynamical substructure within the galaxy.

  17. Lyman Break Analogs: Constraints on the Formation of Extreme Starbursts at Low and High Redshift

    NASA Technical Reports Server (NTRS)

    Goncalves, Thiago S.; Overzier, Roderik; Basu-Zych, Antara; Martin, D. Christopher

    2011-01-01

    Lyman Break Analogs (LBAs), characterized by high far-UV luminosities and surface brightnesses as detected by GALEX, are intensely star-forming galaxies in the low-redshift universe (z approximately equal to 0.2), with star formation rates reaching up to 50 times that of the Milky Way. These objects present metallicities, morphologies and other physical properties similar to higher redshift Lyman Break Galaxies (LBGs), motivating the detailed study of LBAs as local laboratories of this high-redshift galaxy population. We present results from our recent integral-field spectroscopy survey of LBAs with Keck/OSIRIS, which shows that these galaxies have the same nebular gas kinematic properties as high-redshift LBGs. We argue that such kinematic studies alone are not an appropriate diagnostic to rule out merger events as the trigger for the observed starburst. Comparison between the kinematic analysis and morphological indices from HST imaging illustrates the difficulties of properly identifying (minor or major) merger events, with no clear correlation between the results using either of the two methods. Artificial redshifting of our data indicates that this problem becomes even worse at high redshift due to surface brightness dimming and resolution loss. Whether mergers could generate the observed kinematic properties is strongly dependent on gas fractions in these galaxies. We present preliminary results of a CARMA survey for LBAs and discuss the implications of the inferred molecular gas masses for formation models.

  18. The LMT Galaxies' 3 mm Spectroscopic Survey: First Results

    NASA Astrophysics Data System (ADS)

    Rosa González, D.; Schloerb, P.; Vega, O.; Hunt, L.; Narayanan, G.; Calzetti, D.; Yun, M.; Terlevich, E.; Terlevich, R.; Mayya, Y. D.; Chávez, M.; Montaña, A.; Pérez García, A. M.

    2014-09-01

    The molecular phase of the interstellar medium (ISM) in galaxies offers fundamental insight for understanding star-formation processes and how stellar feedback affects the nuclear activity of certain galaxies. We present here Large Millimeter Telescope spectra obtained with the Redshift Search Receiver, a spectrograph that covers simultaneously the 3 mm band from 74 to 111 GHz with a spectral resolution of around 100 km/s. Our selected galaxies, have been detected previously in HCN, and have different degrees of nuclear activity — one normal galaxy (NGC 6946), the starburst prototype (M82) and two %ultraluminous infrared galaxies (ULIRGs, IRAS 17208-0014 and Mrk 231). We plotted our data in the HCO+/HCN vs. HCN/13CO diagnostic diagram finding that NGC 6946 and M82 are located close to other normal galaxies; and that both IRAS 17208-0014 and Mrk 231 are close to the position of the well known ULIRG Arp 220 reported by Snell et al. (2011). We found that in Mrk 231 - a galaxy with a well known active galactic nucleus - the HCO+/HCN ratio is similar to the ratio observed in normal galaxies.

  19. Measuring the neutrino mass from future wide galaxy cluster catalogues

    SciTech Connect

    Carbone, Carmelita; Moscardini, Lauro; Cimatti, Andrea; Fedeli, Cosimo E-mail: cosimo.fedeli@astro.ufl.edu E-mail: a.cimatti@unibo.it

    2012-03-01

    We present forecast errors on a wide range of cosmological parameters obtained from a photometric cluster catalogue of a future wide-field Euclid-like survey. We focus in particular on the total neutrino mass as constrained by a combination of the galaxy cluster number counts and correlation function. For the latter we consider only the shape information and the Baryon Acoustic Oscillations (BAO), while marginalising over the spectral amplitude and the redshift space distortions. In addition to the cosmological parameters of the standard ΛCDM+ν model we also consider a non-vanishing curvature, and two parameters describing a redshift evolution for the dark energy equation of state. For completeness, we also marginalise over a set of ''nuisance'' parameters, representing the uncertainties on the cluster mass determination. We find that combining cluster counts with power spectrum information greatly improves the constraining power of each probe taken individually, with errors on cosmological parameters being reduced by up to an order of magnitude. In particular, the best improvements are for the parameters defining the dynamical evolution of dark energy, where cluster counts break degeneracies. Moreover, the resulting error on neutrino mass is at the level of σ(M{sub ν}) ∼ 0.9 eV, comparable with that derived from present Lyα forest measurements and Cosmic Microwave background (CMB) data in the framework of a non-flat Universe. Further adopting Planck priors and reducing the number of free parameters to a ΛCDM+ν cosmology allows to place constraints on the total neutrino mass of σ(M{sub ν}) ∼ 0.08 eV, close to the lower bound enforced by neutrino oscillation experiments. Finally, in the optimistic case where uncertainties in the calibration of the mass-observable relation were so small to be neglected, the combination of Planck priors with cluster counts and power spectrum would constrain the total neutrino mass down to σ(M{sub ν}) ∼ 0.034 eV, i

  20. Galaxy NGC 247

    NASA Technical Reports Server (NTRS)

    2003-01-01

    This image of the dwarf spiral galaxy NGC 247 was taken by Galaxy Evolution Explorer on October 13, 2003, in a single orbit exposure of 1600 seconds. The region that looks like a 'hole' in the upper part of the galaxy is a location with a deficit of gas and therefore a lower star formation rate and ultraviolet brightness. Optical images of this galaxy show a bright star on the southern edge. This star is faint and red in the Galaxy Evolution Explorer ultraviolet image, revealing that it is a foreground star in our Milky Way galaxy. The string of background galaxies to the North-East (upper left) of NGC 247 is 355 million light years from our Milky Way galaxy whereas NGC 247 is a mere 9 million light years away. The faint blue light that can be seen in the Galaxy Evolution Explorer image of the upper two of these background galaxies may indicate that they are in the process of merging together.

  1. MODELING THE ALIGNMENT PROFILE OF SATELLITE GALAXIES IN CLUSTERS

    SciTech Connect

    Song, Hyunmi; Lee, Jounghun E-mail: jounghun@astro.snu.ac.kr

    2012-04-01

    Analyzing the halo and galaxy catalogs from the Millennium Simulations at redshifts z = 0, 0.5, 1, we determine the alignment profiles of cluster galaxies by measuring the average alignments between the major axes of the pseudo inertia tensors from all satellites within a cluster's virial radius and from only those satellites within some smaller radius as a function of the top-hat scale difference. The alignment profiles quantify how well the satellite galaxies retain the memory of the external tidal fields after merging into their host clusters and how fast they lose the initial alignment tendency as the cluster's relaxation proceeds. It is found that the alignment profile drops faster at higher redshifts and on smaller mass scales. This result is consistent with the picture that the faster merging of the satellites and earlier onset of the nonlinear effect inside clusters tend to break the preferential alignments of the satellites with the external tidal fields. Modeling the alignment profile of cluster galaxies as a power law of the density correlation coefficient that is independent of the power spectrum normalization ({sigma}{sub 8}) and demonstrating that the density correlation coefficient varies sensitively with the density parameter ({Omega}{sub m}) and neutrino mass fraction (f{sub {nu}}), we suggest that the alignment profile of cluster galaxies might be useful for breaking the {Omega}{sub m}-{sigma}{sub 8} and f{sub {nu}}-{sigma}{sub 8} degeneracies.

  2. Suites of dwarfs around Nearby giant galaxies

    SciTech Connect

    Karachentsev, Igor D.; Kaisina, Elena I.; Makarov, Dmitry I. E-mail: kei@sao.ru

    2014-01-01

    The Updated Nearby Galaxy Catalog (UNGC) contains the most comprehensive summary of distances, radial velocities, and luminosities for 800 galaxies located within 11 Mpc from us. The high density of observables in the UNGC makes this sample indispensable for checking results of N-body simulations of cosmic structures on a ∼1 Mpc scale. The environment of each galaxy in the UNGC was characterized by a tidal index Θ{sub 1}, depending on the separation and mass of the galaxy's main disturber (MD). We grouped UNGC galaxies with a common MD in suites, and ranked suite members according to their Θ{sub 1}. All suite members with positive Θ{sub 1} are assumed to be physical companions of the MD. About 58% of the sample are members of physical groups. The distribution of suites by the number of members, n, follows a relation N(n) ∼ n {sup –2}. The 20 most populated suites contain 468 galaxies, i.e., 59% of the UNGC sample. The fraction of MDs among the brightest galaxies is almost 100% and drops to 50% at M{sub B} = –18{sup m}. We discuss various properties of MDs, as well as galaxies belonging to their suites. The suite abundance practically does not depend on the morphological type, linear diameter, or hydrogen mass of the MD, the tightest correlation being with the MD dynamical mass. Dwarf galaxies around MDs exhibit well-known segregation effects: the population of the outskirts has later morphological types, richer H I contents, and higher rates of star formation activity. Nevertheless, there are some intriguing cases where dwarf spheroidal galaxies occur at the far periphery of the suites, as well as some late-type dwarfs residing close to MDs. Comparing simulation results with galaxy groups, most studies assume the Local Group is fairly typical. However, we recognize that the nearby groups significantly differ from each other and there is considerable variation in their properties. The suites of companions around the Milky Way and M31, consisting of the

  3. The connection between galaxy environment and the luminosity function slopes of star-forming regions

    NASA Astrophysics Data System (ADS)

    Cook, David O.; Dale, Daniel A.; Lee, Janice C.; Thilker, David; Calzetti, Daniela; Kennicutt, Robert C.

    2016-11-01

    We present the first study of GALEX far-ultraviolet (FUV) luminosity functions of individual star-forming regions within a sample of 258 nearby galaxies spanning a large range in total stellar mass and star formation properties. We identify ˜65 000 star-forming regions (i.e. FUV sources), measure each galaxy's luminosity function, and characterize the relationships between the luminosity function slope (α) and several global galaxy properties. A final sample of 82 galaxies with reliable luminosity functions are used to define these relationships and represent the largest sample of galaxies with the largest range of galaxy properties used to study the connection between luminosity function properties and galaxy environment. We find that α correlates with global star formation properties, where galaxies with higher star formation rates and star formation rate densities (ΣSFR) tend to have flatter luminosity function slopes. In addition, we find that neither stochastic sampling of the luminosity function in galaxies with low-number statistics nor the effects of blending due to distance can fully account for these trends. We hypothesize that the flatter slopes in high ΣSFR galaxies is due to higher gas densities and higher star formation efficiencies which result in proportionally greater numbers of bright star-forming regions. Finally, we create a composite luminosity function composed of star-forming regions from many galaxies and find a break in the luminosity function at brighter luminosities. However, we find that this break is an artefact of varying detection limits for galaxies at different distances.

  4. Understanding the physical processes driving galaxy evolution in clusters : a case study of two z~0.5 galaxy clusters

    NASA Astrophysics Data System (ADS)

    Moran, Sean M.

    for Cl 0024 early types. Near the Virial radius of Cl 0024, we observe a number of compact, intermediate-mass ellipticals undergoing a burst of star formation or weak AGN activity, indicated by strong [O II] emission; their locations may mark the minimum radius at which merging is effective in each cluster.While E+S0 galaxies do prove to be sensitive indicators of environmental interaction, it is the spiral galaxies that, of course, host the bulk of star formation within and around these clusters. We therefore probe for kinematic disturbances in spiral disks by measuring resolved rotation curves from optical emission lines, and constructing the Tully-Fisher relation for spirals across Cl 0024 and MS 0451. We find that the cluster Tully-Fisher relation exhibits significantly higher scatter than the field relation. In probing for the origin of this difference, we find that the central mass densities of star-forming spirals exhibit a sharp break near the cluster Virial radius, with spirals in the cluster outskirts exhibiting significantly lower densities. We argue that these results considered together demonstrate that cluster spirals are kinematically disturbed by their environment, likely due to galaxy-galaxy interactions (harassment).We then discuss our most powerful method of tracking galaxy evolution across Cl 0024 and MS 0451: identifying and studying "transition galaxies"-galaxies whose stellar populations or dynamical states indicate a recent or ongoing change in morphology or star formation rate. Such galaxies are often revealed by star formation histories that seem to be at odds with the galaxy morphologies: for example, spiral galaxies with no signs of star formation, or elliptical galaxies that do show signs of star formation.We identify and study one such class of objects, the "passive spirals" in Cl 0024. These objects exhibit no emission lines in their spectra, suggesting a lack of star formation, yet are surprisingly detected in the UV, revealing the

  5. Galaxies Gather at Great Distances

    NASA Technical Reports Server (NTRS)

    2006-01-01

    [figure removed for brevity, see original site] Distant Galaxy Cluster Infrared Survey Poster [figure removed for brevity, see original site] [figure removed for brevity, see original site] Bird's Eye View Mosaic Bird's Eye View Mosaic with Clusters [figure removed for brevity, see original site] [figure removed for brevity, see original site] [figure removed for brevity, see original site] 9.1 Billion Light-Years 8.7 Billion Light-Years 8.6 Billion Light-Years

    Astronomers have discovered nearly 300 galaxy clusters and groups, including almost 100 located 8 to 10 billion light-years away, using the space-based Spitzer Space Telescope and the ground-based Mayall 4-meter telescope at Kitt Peak National Observatory in Tucson, Ariz. The new sample represents a six-fold increase in the number of known galaxy clusters and groups at such extreme distances, and will allow astronomers to systematically study massive galaxies two-thirds of the way back to the Big Bang.

    A mosaic portraying a bird's eye view of the field in which the distant clusters were found is shown at upper left. It spans a region of sky 40 times larger than that covered by the full moon as seen from Earth. Thousands of individual images from Spitzer's infrared array camera instrument were stitched together to create this mosaic. The distant clusters are marked with orange dots.

    Close-up images of three of the distant galaxy clusters are shown in the adjoining panels. The clusters appear as a concentration of red dots near the center of each image. These images reveal the galaxies as they were over 8 billion years ago, since that's how long their light took to reach Earth and Spitzer's infrared eyes.

    These pictures are false-color composites, combining ground-based optical images captured by the Mosaic-I camera on the Mayall 4-meter telescope at Kitt Peak, with infrared pictures taken by Spitzer's infrared array camera. Blue and green represent visible light at wavelengths of 0

  6. The Hawaii K-band galaxy survey. 3: Spectroscopy of K less than 20 galaxies

    NASA Technical Reports Server (NTRS)

    Songaila, A.; Cowie, L. L.; Hu, E. M.; Gardner, J. P.

    1994-01-01

    We present spectra and multicolor (B, I, K) data for near-infrared (K) selected spatially complete magnitude limited (K is less than 20) galaxy samples from the Hawaii Survey. The redshift indentification of the sample of 298 galaxies is substantially complete to a B magnitude of 26 and an I magnitude of 22.5, and identification of observed galaxies ranges from nearly 100% completeness at K is less than 18 to approximately 70% completeness at K = 19-20. We note that many of the unidentified objects appear to be red (I-K) objects which are flat in the optical and spectroscopically featureless. Strengths of spectral-line features and breaks are tabulated for the 262 galaxies with reasonably secure redshifts. The measured redshifts may nearly all fall at z is less than or approximately 1, with the exception of a compact absorption-line object at z = 2.35. At K is less than or equal to 18, the redshift distribution is well fitted by a model with no luminosity evolution, implying that from the K-band Hubble diagram, the Hubble constant can vary at most by 10% over the redshift range from z approximately 0.025 to 0.25, and that positive luminosity evolution at any significant level between z = 0 and z = 1 is ruled out. However, the evolution of both the emission-line strengths and the 4000 A break indicates that galaxies were undergoing significantly more star formation at z = 1 than at the present time.

  7. Deficiency of ''Thin'' Stellar Bars in Seyfert Host Galaxies

    NASA Technical Reports Server (NTRS)

    Shlosman, Isaac; Peletier, Reynier F.; Knapen, Johan

    1999-01-01

    Using all available major samples of Seyfert galaxies and their corresponding control samples of closely matched non-active galaxies, we find that the bar ellipticities (or axial ratios) in Seyfert galaxies are systematically different from those in non-active galaxies. Overall, there is a deficiency of bars with large ellipticities (i.e., 'fat' or 'weak' bars) in Seyferts, compared to non-active galaxies. Accompanied with a large dispersion due to small number statistics, this effect is strictly speaking at the 2 sigma level. To obtain this result, the active galaxy samples of near-infrared surface photometry were matched to those of normal galaxies in type, host galaxy ellipticity, absolute magnitude, and, to some extent, in redshift. We discuss possible theoretical explanations of this phenomenon within the framework of galactic evolution, and, in particular, of radial gas redistribution in barred galaxies. Our conclusions provide further evidence that Seyfert hosts differ systematically from their non-active counterparts on scales of a few kpc.

  8. The Unexpected Past of a Dwarf Galaxy

    NASA Astrophysics Data System (ADS)

    1996-08-01

    in this way effectively `eats' the smaller one. Thus the Milky Way may contain the remains of many smaller galaxies it has met and consumed in the past. A natural consequence of this theory is that the Milky Way halo may at least partially consist of stars which originally belonged to these smaller galaxies. However, it is also possible that some of the halo stars formed during the early collapse of the gas cloud from which the Milky Way formed. Like the Milky Way, the two nearest, large spiral galaxies (the Andromeda nebula and M33 in the neighbouring Triangulum constellation) are also surrounded by halos of old stars. Contrarily, investigations of the smaller galaxies in the Local Group have until now not shown that they possess such halos. These dwarf galaxies greatly outnumber the large spiral galaxies - to date about two dozen are known - and they are considered to be the last survivors of the earlier cannibalism phase. The nearest are the well-known Magellanic Clouds, about 170,000 (Large Cloud) and 250,000 light years distant (Small Cloud). They can be seen with the unaided eye from the Southern hemisphere. Recent studies indicate that they orbit the Milky Way and that they may eventually fall prey to our galaxy in a future round of cannibalism. So far, no evidence has been found of an old halo around the Magellanic Clouds. This does not necessarily imply that all dwarf galaxies must likewise lack halos: it is also possible that the halos of the Magellanic Clouds were stripped away when they came too close to the Milky Way sometime in the past. The isolated WLM dwarf galaxy Down in the southern sky, in the constellation of Cetus (the Whale or the Sea Monster), lies a relative faint and distant, small galaxy which astronomers normally refer to as the WLM dwarf galaxy . It was first seen in 1909 by the famous astrophotographer Max Wolf on photographic plates obtained at the Heidelberg Observatory (Germany), but it was only in 1926 that its true nature was

  9. A Cluster and a Sea of Galaxies

    NASA Astrophysics Data System (ADS)

    2010-05-01

    A new wide-field image released today by ESO displays many thousands of distant galaxies, and more particularly a large group belonging to the massive galaxy cluster known as Abell 315. As crowded as it may appear, this assembly of galaxies is only the proverbial "tip of the iceberg", as Abell 315 - like most galaxy clusters - is dominated by dark matter. The huge mass of this cluster deflects light from background galaxies, distorting their observed shapes slightly. When looking at the sky with the unaided eye, we mostly only see stars within our Milky Way galaxy and some of its closest neighbours. More distant galaxies are just too faint to be perceived by the human eye, but if we could see them, they would literally cover the sky. This new image released by ESO is both a wide-field and long-exposure one, and reveals thousands of galaxies crowding an area on the sky roughly as large as the full Moon. These galaxies span a vast range of distances from us. Some are relatively close, as it is possible to distinguish their spiral arms or elliptical halos, especially in the upper part of the image. The more distant appear just like the faintest of blobs - their light has travelled through the Universe for eight billion years or more before reaching Earth. Beginning in the centre of the image and extending below and to the left, a concentration of about a hundred yellowish galaxies identifies a massive galaxy cluster, designated with the number 315 in the catalogue compiled by the American astronomer George Abell in 1958 [1]. The cluster is located between the faint, red and blue galaxies and the Earth, about two billion light-years away from us. It lies in the constellation of Cetus (the Whale). Galaxy clusters are some of the largest structures in the Universe held together by gravity. But there is more in these structures than the many galaxies we can see. Galaxies in these giants contribute to only ten percent of the mass, with hot gas in between galaxies

  10. Strongly time-variable ultraviolet metal-line emission from the circum-galactic medium of high-redshift galaxies

    NASA Astrophysics Data System (ADS)

    Sravan, Niharika; Faucher-Giguère, Claude-André; van de Voort, Freeke; Kereš, Dušan; Muratov, Alexander L.; Hopkins, Philip F.; Feldmann, Robert; Quataert, Eliot; Murray, Norman

    2016-11-01

    We use cosmological simulations from the Feedback In Realistic Environments project, which implement a comprehensive set of stellar feedback processes, to study ultraviolet (UV) metal-line emission from the circum-galactic medium of high-redshift (z = 2-4) galaxies. Our simulations cover the halo mass range Mh ˜ 2 × 1011-8.5 × 1012 M⊙ at z = 2, representative of Lyman break galaxies. Of the transitions we analyse, the low-ionization C III (977 Å) and Si III (1207 Å) emission lines are the most luminous, with C IV (1548 Å) and Si IV (1394 Å) also showing interesting spatially extended structures. The more massive haloes are on average more UV-luminous. The UV metal-line emission from galactic haloes in our simulations arises primarily from collisionally ionized gas and is strongly time variable, with peak-to-trough variations of up to ˜2 dex. The peaks of UV metal-line luminosity correspond closely to massive and energetic mass outflow events, which follow bursts of star formation and inject sufficient energy into galactic haloes to power the metal-line emission. The strong time variability implies that even some relatively low-mass haloes may be detectable. Conversely, flux-limited samples will be biased towards haloes whose central galaxy has recently experienced a strong burst of star formation. Spatially extended UV metal-line emission around high-redshift galaxies should be detectable by current and upcoming integral field spectrographs such as the Multi Unit Spectroscopic Explorer on the Very Large Telescope and Keck Cosmic Web Imager.

  11. Lens galaxies in the Illustris simulation: power-law models and the bias of the Hubble constant from time delays

    NASA Astrophysics Data System (ADS)

    Xu, Dandan; Sluse, Dominique; Schneider, Peter; Springel, Volker; Vogelsberger, Mark; Nelson, Dylan; Hernquist, Lars

    2016-02-01

    A power-law density model, i.e. ρ (r) ∝ r^{-γ ^' }}, has been commonly employed in strong gravitational lensing studies, including the so-called time-delay technique used to infer the Hubble constant H0. However, since the radial scale at which strong lensing features are formed corresponds to the transition from the dominance of baryonic matter to dark matter, there is no known reason why galaxies should follow a power law in density. The assumption of a power law artificially breaks the mass-sheet degeneracy, a well-known invariance transformation in gravitational lensing which affects the product of Hubble constant and time delay and can therefore cause a bias in the determination of H0 from the time-delay technique. In this paper, we use the Illustris hydrodynamical simulations to estimate the amplitude of this bias, and to understand how it is related to observational properties of galaxies. Investigating a large sample of Illustris galaxies that have velocity dispersion σSIE ≥ 160 km s-1 at redshifts below z = 1, we find that the bias on H0 introduced by the power-law assumption can reach 20-50 per cent, with a scatter of 10-30 per cent (rms). However, we find that by selecting galaxies with an inferred power-law model slope close to isothermal, it is possible to reduce the bias on H0 to ≲ 5 per cent and the scatter to ≲ 10 per cent. This could potentially be used to form less biased statistical samples for H0 measurements in the upcoming large survey era.

  12. Lyman continuum galaxies: Observed Lyman continuum flux measurements at z ~ 3-4 and mechanisms behind the escape

    NASA Astrophysics Data System (ADS)

    Cooke, Jeff; Ryan-Weber, Emma; Garel, Thibault; Gonzalo Diaz, C.

    2016-06-01

    Measuring the surviving Lyman continuum (LyC) flux and inferred ionizing photon escape fraction (f_esc) of Lyman break galaxies has proved challenging, in part due to the historical selection criteria based on a Lyman continuum break. A few galaxies, largely serendipitous, have been detected with measurable LyC flux but have colors inconsistent with Lyman break galaxy expectations for their specific redshifts. I will discuss our physically motivated technique that provides an accurate measure of the average f_esc for the z ~ 3 Lyman break galaxy population that has also identified a population of galaxies, termed Lyman continuum galaxies (LCGs) with high expected levels of surviving LyC flux. I will present the results of our program that uses 30-band photometry, HST imaging, and deep medium-band IR imaging from the ZFOURGE survey to select z ~ 3-4 LCGs. We obtained very deep Keck spectroscopy that has confirmed the LCG population and has directly measured the predicted level of LyC flux. In addition, our program has obtained deep Keck infrared spectroscopy to calibrate restframe optical nebular emission-line models used to predict the LyC escape fraction, with the aim to measure the f_esc of galaxies at the Epoch of Reionization where direct LyC flux detection is not possible.

  13. The Superwind Galaxy NGC 4666

    NASA Astrophysics Data System (ADS)

    2010-09-01

    The galaxy NGC 4666 takes pride of place at the centre of this new image, made in visible light with the Wide Field Imager on the MPG/ESO 2.2-metre telescope at the La Silla Observatory in Chile. NGC 4666 is a remarkable galaxy with very vigorous star formation and an unusual "superwind" of out-flowing gas. It had previously been observed in X-rays by the ESA XMM-Newton space telescope, and the image presented here was taken to allow further study of other objects detected in the earlier X-ray observations. The prominent galaxy NGC 4666 in the centre of the picture is a starburst galaxy, about 80 million light-years from Earth, in which particularly intense star formation is taking place. The starburst is thought to be caused by gravitational interactions between NGC 4666 and its neighbouring galaxies, including NGC 4668, visible to the lower left. These interactions often spark vigorous star-formation in the galaxies involved. A combination of supernova explosions and strong winds from massive stars in the starburst region drives a vast flow of gas from the galaxy into space - a so-called "superwind". The superwind is huge in scale, coming from the bright central region of the galaxy and extending for tens of thousands of light-years. As the superwind gas is very hot it emits radiation mostly as X-rays and in the radio part of the spectrum and cannot be seen in visible light images such as the one presented here. This image was made as part of a follow-up to observations made with the ESA XMM-Newton space telescope in X-rays. NGC 4666 was the target of the original XMM-Newton observations, but thanks to the telescope's wide field-of-view many other X-ray sources were also seen in the background. One such serendipitous detection is a faint galaxy cluster seen close to the bottom edge of the image, right of centre. This cluster is much further away from us than NGC 4666, at a distance of about three billion light-years. In order to fully understand the nature of

  14. Close supermassive binary black holes.

    PubMed

    Gaskell, C Martin

    2010-01-01

    It has been proposed that when the peaks of the broad emission lines in active galactic nuclei (AGNs) are significantly blueshifted or redshifted from the systemic velocity of the host galaxy, this could be a consequence of orbital motion of a supermassive black-hole binary (SMBB). The AGN J1536+0441 ( = SDSS J153636.22+044127.0) has recently been proposed as an example of this phenomenon. It is proposed here instead that J1536+0441 is an example of line emission from a disk. If this is correct, the lack of clear optical spectral evidence for close SMBBs is significant, and argues either that the merging of close SMBBs is much faster than has generally been hitherto thought, or if the approach is slow, that when the separation of the binary is comparable to the size of the torus and broad-line region, the feeding of the black holes is disrupted. PMID:20054358

  15. Close supermassive binary black holes

    NASA Astrophysics Data System (ADS)

    Gaskell, C. Martin

    2010-01-01

    It has been proposed that when the peaks of the broad emission lines in active galactic nuclei (AGNs) are significantly blueshifted or redshifted from the systemic velocity of the host galaxy, this could be a consequence of orbital motion of a supermassive blackhole binary (SMB). The AGN J1536+0441 (=SDSS J153636.22+044127.0) has recently been proposed as an example of this phenomenon. It is proposed here instead that 1536+044 is an example of line emission from a disc. If this is correct, the lack of clear optical spectral evidence for close SMBs is significant and argues either that the merging of close SMBs is much faster than has generally been hitherto thought, or if the approach is slow, that when the separation of the binary is comparable to the size of the torus and broad-line region, the feeding of the black holes is disrupted.

  16. Galaxy NGC5474

    NASA Technical Reports Server (NTRS)

    2003-01-01

    NASA's Galaxy Evolution Explorer took this ultraviolet color image of the galaxy NGC5474 on June 7, 2003. NGC5474 is located 20 million light-years from Earth and is within a group of galaxies dominated by the Messier 101 galaxy. Star formation in this galaxy shows some evidence of a disturbed spiral pattern, which may have been induced by tidal interactions with Messier 101.

    The Galaxy Evolution Explorer mission is led by the California Institute of Technology, which is also responsible for the science operations and data analysis. NASA's Jet Propulsion Laboratory, Pasadena, Calif., a division of Caltech, manages the mission and built the science instrument. The mission was developed under NASA's Explorers Program, managed by the Goddard Space Flight Center, Greenbelt, Md. The mission's international partners include South Korea and France.

  17. Deep infrared galaxies

    NASA Technical Reports Server (NTRS)

    Ashby, Matthew; Houck, J. R.; Hacking, Perry B.

    1992-01-01

    High signal-to-noise ratio optical spectra of 17 infrared-bright emission-line galaxies near the north ecliptic pole are presented. Reddening-corrected line ratios forbidden O III 5007/H-beta, N II 6583/H-alpha, S II (6716 + 6731)/H-alpha, and O I 6300/H-alpha are used to discriminate between candidate energy generation mechanisms in each galaxy. These criteria have frequently been applied to optically selected samples of galaxies in the past, but this is the first time they have been applied to a set of faint flux-limited infrared-selected objects. The analysis indicates the sample contains seven starburst galaxies and three (AGN). However, seven galaxies in the present sample elude the classification scheme based on these line ratios. It is concluded that a two-component (starburst plus AGN) model for energy generation is inadequate for infrared galaxies.

  18. Classic Galaxy with Glamour

    NASA Technical Reports Server (NTRS)

    2005-01-01

    This color composite image of nearby NGC 300 combines the visible-light pictures from Carnegie Institution of Washington's 100-inch telescope at Las Campanas Observatory (colored red and yellow), with ultraviolet views from NASA's Galaxy Evolution Explorer. Galaxy Evolution Explorer detectors image far ultraviolet light (colored blue).

    This composite image traces star formation in progress. Young hot blue stars dominate the outer spiral arms of the galaxy, while the older stars congregate in the nuclear regions which appear yellow-green. Gases heated by hot young stars and shocks due to winds from massive stars and supernova explosions appear in pink, as revealed by the visible-light image of the galaxy.

    Located nearly 7 million light years away, NGC 300 is a member of a nearby group of galaxies known as the Sculptor Group. It is a spiral galaxy like our own Milky Way.

  19. Tidal Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Duc, P.-A.; Mirabel, I. F.; Brinks, E.

    The life and evolution of galaxies are dramatically affected by environmental effects. Interactions with the intergalactic medium and collisions with companions cause major perturbations in the morphology and contents of galaxies: in particular stars and gas clouds may be gravitationally pulled out from their parent galaxies during tidal encounters, forming rings, tails and bridges. This debris of collisions lies at the origin of a new generation of small galaxies, the so-called "tidal dwarf galaxies" (TDGs). The authors have carried out multi-wavelength observations of some 20 TDGs. These systems are made of two stellar components: young stars, formed from the recent collapse of expelled H I clouds, and an older stellar population, tidally pulled out from the disks of their interacting parent galaxies. In the observed TDGs, the current star formation episode is fuelled by a large reservoir of H I gas and is younger than 10 Myr.

  20. Finding the First Galaxies

    NASA Technical Reports Server (NTRS)

    Gardner, Jonathan P.

    2009-01-01

    Astronomers study distant galaxies by taking long exposures in deep survey fields. They choose fields that are empty of known sources, so that they are statistically representative of the Universe as a whole. Astronomers can compare the distribution of the detected galaxies in brightness, color, morphology and redshift to theoretical models, in order to puzzle out the processes of galaxy evolution. In 2004, the Hubble Space Telescope was pointed at a small, deep-survey field in the southern constellation Fornax for more than 500 hours of exposure time. The resulting Hubble Ultra-Deep Field could see the faintest and most distant galaxies that the telescope is capable of viewing. These galaxies emitted their light less than 1 billion years after the Big Bang. From the Ultra Deep Field and other galaxy surveys, astronomers have built up a history of star formation in the universe. the peak occurred about7 billion years ago, about half of the age of the current universe, then the number of stars that were forming was about 15 time the rate today. Going backward in time to when the very first starts and galaxies formed, the average star-formation rate should drop to zero. but when looking at the most distant galaxies in the Ultra Deep field, the star formation rate is still higher than it is today. The faintest galaxies seen by Hubble are not the first galaxies that formed in the early universe. To detect these galaxies NASA is planning the James Webb Space Telescope for launch in 2013. Webb will have a 6.5-meter diameter primary mirror, much bigger than Hubble's 2.4-meter primary, and will be optimized for infrared observations to see the highly redshifted galaxies.

  1. Amazing Andromeda Galaxy

    NASA Technical Reports Server (NTRS)

    2006-01-01

    The many 'personalities' of our great galactic neighbor, the Andromeda galaxy, are exposed in this new composite image from NASA's Galaxy Evolution Explorer and the Spitzer Space Telescope.

    The wide, ultraviolet eyes of Galaxy Evolution Explorer reveal Andromeda's 'fiery' nature -- hotter regions brimming with young and old stars. In contrast, Spitzer's super-sensitive infrared eyes show Andromeda's relatively 'cool' side, which includes embryonic stars hidden in their dusty cocoons.

    Galaxy Evolution Explorer detected young, hot, high-mass stars, which are represented in blue, while populations of relatively older stars are shown as green dots. The bright yellow spot at the galaxy's center depicts a particularly dense population of old stars.

    Swaths of red in the galaxy's disk indicate areas where Spitzer found cool, dusty regions where stars are forming. These stars are still shrouded by the cosmic clouds of dust and gas that collapsed to form them.

    Together, Galaxy Evolution Explorer and Spitzer complete the picture of Andromeda's swirling spiral arms. Hints of pinkish purple depict regions where the galaxy's populations of hot, high-mass stars and cooler, dust-enshrouded stars co-exist.

    Located 2.5 million light-years away, the Andromeda is our largest nearby galactic neighbor. The galaxy's entire disk spans about 260,000 light-years, which means that a light beam would take 260,000 years to travel from one end of the galaxy to the other. By comparison, our Milky Way galaxy's disk is about 100,000 light-years across.

    This image is a false color composite comprised of data from Galaxy Evolution Explorer's far-ultraviolet detector (blue), near-ultraviolet detector (green), and Spitzer's multiband imaging photometer at 24 microns (red).

  2. Galaxy evolution. Galactic paleontology.

    PubMed

    Tolstoy, Eline

    2011-07-01

    Individual low-mass stars have very long lives, comparable to the age of the universe, and can thus be used to probe ancient star formation. At present, such stars can be identified and studied only in the Milky Way and in the very closest of our neighboring galaxies, which are predominantly small dwarf galaxies. These nearby ancient stars are a fossil record that can provide detailed information about the physical processes that dominated the epoch of galaxy formation and subsequent evolution.

  3. Singularities and Closed String Tachyons

    SciTech Connect

    Silverstein, Eva; /SLAC /Stanford U., Phys. Dept.

    2006-03-17

    A basic problem in gravitational physics is the resolution of spacetime singularities where general relativity breaks down. The simplest such singularities are conical singularities arising from orbifold identifications of flat space, and the most challenging are spacelike singularities inside black holes (and in cosmology). Topology changing processes also require evolution through classically singular spacetimes. I briefly review how a phase of closed string tachyon condensate replaces, and helps to resolve, basic singularities of each of these types. Finally I discuss some interesting features of singularities arising in the small volume limit of compact negatively curved spaces and the emerging zoology of spacelike singularities.

  4. A time domain experiment with Swift: monitoring of seven nearby galaxies

    NASA Astrophysics Data System (ADS)

    Andreoni, I.; D'Avanzo, P.; Campana, S.; Branchesi, M.; Bernardini, M. G.; Della Valle, M.; Mannucci, F.; Melandri, A.; Tagliaferri, G.

    2016-03-01

    Context. Focused on the study of transient sources, time domain astronomy today is one of the most active and growing areas of research in astronomy. Most of the present and planned surveys aimed at carrying out time domain studies work in the optical band and founded their searching strategies on fixed cadences. Although nothing similar currently exists in the X-ray and ultraviolet (UV) bands, the Swift satellite is certainly the most appropriate available instrument to carry out such surveys. Aims: We aimed to detect a supernova (SN) shock breakout (SBO) in nearby galaxies. The SBO marks the first escape of radiation from the blast wave that breaks through the photosphere of the star and launches the SN ejecta. The detection of an SBO is a diagnostic for the radius of the progenitor star and the ratio of explosion energy to ejecta mass. It also allows us to determine the onset of the explosion with an accuracy of a few hours to a few seconds. Methods: Using the XRT and UVOT instruments onboard the Swift satellite, we carried out a weekly cadenced, six-month monitoring of seven nearby galaxies: NGC 1084, NGC 2207/IC 2163, NGC 2770, NGC 4303/M 61, NGC 3147, NGC 3690, and NGC 6754. We searched for variable or transient sources in the collected data. These galaxies were selected because they are close (distance ≤50 Mpc), small enough to fit in the Swift/UVOT field of view, and are hosts of at least three SNe in the past 20 yr. Results: We found no evidence for an SN SBO event. Five objects located within the light of the sample galaxies were found to be variable in the X-ray and/or in the UV. These include mainly background active galactic nucleus and unresolved ULX in NGC 3690. In addition to these objects, we found two variable Galactic sources: the known nova CP Draconis (which experienced an outburst during our monitoring) and an uncatalogued eclipsing binary. Conclusions: Despite the lack of SBO detections, the results of our explorative study encourage the

  5. Galaxy UGC10445

    NASA Technical Reports Server (NTRS)

    2003-01-01

    This ultraviolet color image of the galaxy UGC10445 was taken by NASA's Galaxy Evolution Explorer on June 7 and June 14, 2003. UGC10445 is a spiral galaxy located 40 million light-years from Earth.

    The Galaxy Evolution Explorer mission is led by the California Institute of Technology, which is also responsible for the science operations and data analysis. NASA's Jet Propulsion Laboratory, Pasadena, Calif., a division of Caltech, manages the mission and built the science instrument. The mission was developed under NASA's Explorers Program, managed by the Goddard Space Flight Center, Greenbelt, Md. The mission's international partners include South Korea and France.

  6. Galaxy NGC5962

    NASA Technical Reports Server (NTRS)

    2003-01-01

    NASA's Galaxy Evolution Explorer took this ultraviolet color image of the galaxy NGC5962 on June 7, 2003. This spiral galaxy is located 90 million light-years from Earth.

    The Galaxy Evolution Explorer mission is led by the California Institute of Technology, which is also responsible for the science operations and data analysis. NASA's Jet Propulsion Laboratory, Pasadena, Calif., a division of Caltech, manages the mission and built the science instrument. The mission was developed under NASA's Explorers Program, managed by the Goddard Space Flight Center, Greenbelt, Md. The mission's international partners include South Korea and France.

  7. Multiple Core Galaxies

    NASA Technical Reports Server (NTRS)

    Miller, R.H.; Morrison, David (Technical Monitor)

    1994-01-01

    Nuclei of galaxies often show complicated density structures and perplexing kinematic signatures. In the past we have reported numerical experiments indicating a natural tendency for galaxies to show nuclei offset with respect to nearby isophotes and for the nucleus to have a radial velocity different from the galaxy's systemic velocity. Other experiments show normal mode oscillations in galaxies with large amplitudes. These oscillations do not damp appreciably over a Hubble time. The common thread running through all these is that galaxies often show evidence of ringing, bouncing, or sloshing around in unexpected ways, even though they have not been disturbed by any external event. Recent observational evidence shows yet another phenomenon indicating the dynamical complexity of central regions of galaxies: multiple cores (M31, Markarian 315 and 463 for example). These systems can hardly be static. We noted long-lived multiple core systems in galaxies in numerical experiments some years ago, and we have more recently followed up with a series of experiments on multiple core galaxies, starting with two cores. The relevant parameters are the energy in the orbiting clumps, their relative.masses, the (local) strength of the potential well representing the parent galaxy, and the number of cores. We have studied the dependence of the merger rates and the nature of the final merger product on these parameters. Individual cores survive much longer in stronger background potentials. Cores can survive for a substantial fraction of a Hubble time if they travel on reasonable orbits.

  8. Extremely Isolated Elliptical Galaxies

    NASA Astrophysics Data System (ADS)

    Fuse, Christopher R.; Marcum, P.; Fanelli, M.; Aars, C.

    2006-06-01

    Isolated galaxies provide a means of assessing the evolution of galactic systems. Extremely isolated galaxies define a zero-interaction baseline for comparative studies of galaxy evolution. We present results of a search for isolated elliptical galaxies (IEGs). We utilize the optical imaging data produced by the Sloan Digital Sky Survey (SDSS) to identify candidate galaxies from Release 1-4 of the SDSS. Candidate IEGs meet strict isolation criteria: Any IEG must be separated by at least 2.5 Mpc from any neighboring non-dwarf galaxy having a MV fainter than -16.5 mag. The candidate isolated systems have no non-dwarf neighbors within a distance such that we can insure that the IEGs have never interacted with another existing galaxy since formation.In order to increase the signal-to-noise ratio, we have used the SDSS images in the u,g,r filters to create combined sets of images for each IEG. The stacked images permit a more robust determination of the morphology of the candidate galaxies. Verification that these are spheroidal systems is achieved through a bulge/disk decomposition technique using standard surface photometry. Our preliminary sample of 51 isolated systems defines a complete volume-limited population of extremely isolated early-type galaxies within a distance of 72Mpc

  9. CORE SHAPES AND ORIENTATIONS OF CORE-SÉRSIC GALAXIES

    SciTech Connect

    Dullo, Bililign T.; Graham, Alister W.

    2015-01-01

    The inner and outer shapes and orientations of core-Sérsic galaxies may hold important clues to their formation and evolution. We have therefore measured the central and outer ellipticities and position angles for a sample of 24 core-Sérsic galaxies using archival Hubble Space Telescope (HST) images and data. By selecting galaxies with core-Sérsic break radii R{sub b} —a measure of the size of their partially depleted core—that are ≳ 0.''2, we find that the ellipticities and position angles are quite robust against HST seeing. For the bulk of the galaxies, there is a good agreement between the ellipticities and position angles at the break radii and the average outer ellipticities and position angles determined over R {sub e}/2 < R < R {sub e}, where R {sub e} is the spheroids' effective half light radius. However there are some interesting differences. We find a median ''inner'' ellipticity at R{sub b} of ε{sub med} = 0.13 ± 0.01, rounder than the median ellipticity of the ''outer'' regions ε{sub med} = 0.20 ± 0.01, which is thought to reflect the influence of the central supermassive black hole at small radii. In addition, for the first time we find a trend, albeit weak (2σ significance), such that galaxies with larger (stellar deficit-to-supermassive black hole) mass ratios—thought to be a measure of the number of major dry merger events—tend to have rounder inner and outer isophotes, suggesting a connection between the galaxy shapes and their merger histories. We show that this finding is not simply reflecting the well known result that more luminous galaxies are rounder, but it is no doubt related.

  10. Core Shapes and Orientations of Core-Sérsic Galaxies

    NASA Astrophysics Data System (ADS)

    Dullo, Bililign T.; Graham, Alister W.

    2015-01-01

    The inner and outer shapes and orientations of core-Sérsic galaxies may hold important clues to their formation and evolution. We have therefore measured the central and outer ellipticities and position angles for a sample of 24 core-Sérsic galaxies using archival Hubble Space Telescope (HST) images and data. By selecting galaxies with core-Sérsic break radii Rb —a measure of the size of their partially depleted core—that are >~ 0.''2, we find that the ellipticities and position angles are quite robust against HST seeing. For the bulk of the galaxies, there is a good agreement between the ellipticities and position angles at the break radii and the average outer ellipticities and position angles determined over R e/2 < R < R e, where R e is the spheroids' effective half light radius. However there are some interesting differences. We find a median "inner" ellipticity at Rb of epsilonmed = 0.13 ± 0.01, rounder than the median ellipticity of the "outer" regions epsilonmed = 0.20 ± 0.01, which is thought to reflect the influence of the central supermassive black hole at small radii. In addition, for the first time we find a trend, albeit weak (2σ significance), such that galaxies with larger (stellar deficit-to-supermassive black hole) mass ratios—thought to be a measure of the number of major dry merger events—tend to have rounder inner and outer isophotes, suggesting a connection between the galaxy shapes and their merger histories. We show that this finding is not simply reflecting the well known result that more luminous galaxies are rounder, but it is no doubt related.

  11. Hubble Team Breaks Cosmic Distance Record

    NASA Video Gallery

    This animation shows the location of galaxy GN-z11, which is the farthest galaxy ever seen. The video begins by locating the Big Dipper, then showing the constellation Ursa Major. It then zooms int...

  12. Stellar halos around Local Group galaxies

    NASA Astrophysics Data System (ADS)

    McConnachie, Alan W.

    2016-08-01

    The Local Group is now home to 102 known galaxies and candidates, with many new faint galaxies continuing to be discovered. The total stellar mass range spanned by this population covers a factor of close to a billion, from the faintest systems with stellar masses of order a few thousand to the Milky Way and Andromeda, with stellar masses of order 1011 M ⊙. Here, I discuss the evidence for stellar halos surrounding Local Group galaxies spanning from dwarf scales (with the case of the Andromeda II dwarf spheroidal), though to intermediate mass systems (M33) and finishing with M31. Evidence of extended stellar populations and merging is seen across the luminosity function, indicating that the processes that lead to halo formation are common at all mass scales.

  13. When did Round Disk Galaxies Form?

    NASA Astrophysics Data System (ADS)

    Takeuchi, T. M.; Ohta, K.; Yuma, S.; Yabe, K.

    2015-03-01

    When and how galaxy morphology, such as the disk and bulge seen in the present-day universe, emerged is still not clear. In the universe at z >~ 2, galaxies with various morphologies are seen, and star-forming galaxies at z ~ 2 show the intrinsic shape of bar-like structures. Then, when did the round disk structure form? Here we take a simple and straightforward approach to see the epoch when a round disk galaxy population emerged by constraining the intrinsic shape statistically based on the apparent axial ratio distribution of galaxies. We derived the distributions of the apparent axial ratios in the rest-frame optical light (~5000 Å) of star-forming main-sequence galaxies at 2.5 > z > 1.4, 1.4 > z > 0.85, and 0.85 > z > 0.5, and found that their apparent axial ratios show peaky distributions at z >~ 0.85, while a rather flat distribution at the lower redshift. By using a tri-axial model (A > B > C) for the intrinsic shape, we found that the best-fit models give the peaks of the B/A distribution of 0.81 ± 0.04, 0.84 ± 0.04, and 0.92 ± 0.05 at 2.5 > z > 1.4, 1.4 > z > 0.85, and 0.85 > z > 0.5, respectively. The last value is close to the local value of 0.95. Thickness (C/A) is ~0.25 at all the redshifts and is close to the local value (0.21). The results indicate that the shape of the star-forming galaxies in the main sequence changes gradually, and that the round disk is established at around z ~ 0.9. The establishment of the round disk may be due to the cessation of a violent interaction between galaxies or the growth of a bulge and/or a supermassive black hole residing at the center of a galaxy that dissolves the bar structure.

  14. WHEN DID ROUND DISK GALAXIES FORM?

    SciTech Connect

    Takeuchi, T. M.; Ohta, K.; Yuma, S.; Yabe, K.

    2015-03-01

    When and how galaxy morphology, such as the disk and bulge seen in the present-day universe, emerged is still not clear. In the universe at z ≳ 2, galaxies with various morphologies are seen, and star-forming galaxies at z ∼ 2 show the intrinsic shape of bar-like structures. Then, when did the round disk structure form? Here we take a simple and straightforward approach to see the epoch when a round disk galaxy population emerged by constraining the intrinsic shape statistically based on the apparent axial ratio distribution of galaxies. We derived the distributions of the apparent axial ratios in the rest-frame optical light (∼5000 Å) of star-forming main-sequence galaxies at 2.5 > z > 1.4, 1.4 > z > 0.85, and 0.85 > z > 0.5, and found that their apparent axial ratios show peaky distributions at z ≳ 0.85, while a rather flat distribution at the lower redshift. By using a tri-axial model (A > B > C) for the intrinsic shape, we found that the best-fit models give the peaks of the B/A distribution of 0.81 ± 0.04, 0.84 ± 0.04, and 0.92 ± 0.05 at 2.5 > z > 1.4, 1.4 > z > 0.85, and 0.85 > z > 0.5, respectively. The last value is close to the local value of 0.95. Thickness (C/A) is ∼0.25 at all the redshifts and is close to the local value (0.21). The results indicate that the shape of the star-forming galaxies in the main sequence changes gradually, and that the round disk is established at around z ∼ 0.9. The establishment of the round disk may be due to the cessation of a violent interaction between galaxies or the growth of a bulge and/or a supermassive black hole residing at the center of a galaxy that dissolves the bar structure.

  15. The Violent Interstellar Medium in Dwarf Galaxies: Atomic Gas

    NASA Astrophysics Data System (ADS)

    Brinks, E.; Walter, F.

    1998-12-01

    We review the morphology of the warm, neutral ISM as observed in the 21 cm line of neutral hydrogen (H I) of several nearby, gas-rich (dIrr) galaxies. The H I emission is dominated by shell-like structures, most likely superbubbles produced by the combined effects of strong stellar winds followed by supernova explosions of stars more massive than M > 8 M-sun within a region of massive star formation, an OB association. Somewhat counter-intuitively, H I superbubbles grow to larger dimensions in dwarf galaxies than in large spiral galaxies like our own or M 31. This can be explained as follows. In dwarf galaxies, the gravitational potential is lower than in spirals. Hence, for similar H I velocity dispersions, the scaleheight of the H I layer will be larger. Then, for comparable H I surface densities, the volume density will be lower. Both effects facilitate the growth to large dimensions of shells in dwarf galaxies and explains why such shells are much less likely to break through the H I layer into the halo. Moreover, dwarf galaxies lack density waves and tend to be dominated by solid-body rotation. As a result, shells will persist much longer than in spirals. A comparison with other galaxies shows that the energies needed to create H I supershells are the same for all types of galaxies, the energy output of a typical star-forming region therefore not being related to its galactic environment, at least to first order. The overall statistical properties of the H I holes and shells in galaxies show clear trends with Hubble type (or rather mass), such as in their diameter distribution, expansion velocities and ages.

  16. Precision measurement of cosmic magnification from 21 cm emitting galaxies

    SciTech Connect

    Zhang, Pengjie; Pen, Ue-Li; /Canadian Inst. Theor. Astrophys.

    2005-04-01

    We show how precision lensing measurements can be obtained through the lensing magnification effect in high redshift 21cm emission from galaxies. Normally, cosmic magnification measurements have been seriously complicated by galaxy clustering. With precise redshifts obtained from 21cm emission line wavelength, one can correlate galaxies at different source planes, or exclude close pairs to eliminate such contaminations. We provide forecasts for future surveys, specifically the SKA and CLAR. SKA can achieve percent precision on the dark matter power spectrum and the galaxy dark matter cross correlation power spectrum, while CLAR can measure an accurate cross correlation power spectrum. The neutral hydrogen fraction was most likely significantly higher at high redshifts, which improves the number of observed galaxies significantly, such that also CLAR can measure the dark matter lensing power spectrum. SKA can also allow precise measurement of lensing bispectrum.

  17. Breaking scale invariance with quantum gravity

    SciTech Connect

    Amendola, L.; Occhionero, F.; Saez, D. )

    1990-02-01

    It is argued that the closed, nonsingular cosmological model of Starobinsky (1980) allows a self-consistent, albeit schematic, description of the history of the universe from its beginning to now and even provides, given a suitable scenario, the possibility of breaking in a natural way the scale invariance of the perturbation spectrum. A double inflationary scenario is specified in detail to explain the anomalous power observed in the large-scale astronomical structures by assuming that the first inflation is driven by quantum gravity and that the second inflation is driven by the usual inflation. An example of a power spectrum where the scale invariance has been broken and extra power is put above 10 Mpc is presented. The model is now compatible with the observed upper limits from the large angular scale isotropy of the microwave background. 52 refs.

  18. Viscoelasticity Breaks the Symmetry of Impacting Jets

    NASA Astrophysics Data System (ADS)

    Lhuissier, H.; Néel, B.; Limat, L.

    2014-11-01

    A jet of a Newtonian liquid impacting on a wall at right angle spreads as a thin liquid sheet which preserves the radial symmetry of the jet. We report that for a viscoelastic jet (solution of polyethylene glycol in water) this symmetry can break; close to the wall, the jet cross section becomes faceted and radial steady liquid films (wings) form, which connect the cross-section vertices to the sheet. The number of wings increases with increasing the viscoelastic relaxation time of the solution, but also with increasing jet velocity and decreasing distance from the jet nozzle to the wall. We propose a mechanism for this surprising destabilization of the jet shape, which develops perpendicularly to the direction expected for a buckling mechanism, and explain these dependencies. We also discuss the large-scale consequences of the jet destabilization on the sheet spreading and fragmentation, which show through the faceting of hydraulic jumps and of suspended (Savart) sheets.

  19. The Topsy-Turvy Galaxy

    NASA Astrophysics Data System (ADS)

    2006-11-01

    The captivating appearance of this image of the starburst galaxy NGC 1313, taken with the FORS instrument at ESO's Very Large Telescope, belies its inner turmoil. The dense clustering of bright stars and gas in its arms, a sign of an ongoing boom of star births, shows a mere glimpse of the rough times it has seen. Probing ever deeper into the heart of the galaxy, astronomers have revealed many enigmas that continue to defy our understanding. ESO PR Photo 43a/06 ESO PR Photo 43a/06 The Topsy-Turvy Galaxy NGC 1313 This FORS image of the central parts of NGC 1313 shows a stunning natural beauty. The galaxy bears some resemblance to some of the Milky Way's closest neighbours, the Magellanic Clouds. NGC 1313 has a barred spiral shape, with the arms emanating outwards in a loose twist from the ends of the bar. The galaxy lies just 15 million light-years away from the Milky Way - a mere skip on cosmological scales. The spiral arms are a hotbed of star-forming activity, with numerous young clusters of hot stars being born continuously at a staggering rate out of the dense clouds of gas and dust. Their light blasts through the surrounding gas, creating an intricately beautiful pattern of light and dark nebulosity. But NGC 1313 is not just a pretty picture. A mere scratch beneath the elegant surface reveals evidence of some of the most puzzling problems facing astronomers in the science of stars and galaxies. Starburst galaxies are fascinating objects to study in their own right; in neighbouring galaxies, around one quarter of all massive stars are born in these powerful engines, at rates up to a thousand times higher than in our own Milky Way Galaxy. In the majority of starbursts the upsurge in star's births is triggered when two galaxies merge, or come too close to each other. The mutual attraction between the galaxies causes immense turmoil in the gas and dust, causing the sudden 'burst' in star formation. ESO PR Photo 43b/06 ESO PR Photo 43b/06 Larger View of NGC 1313

  20. Did galaxies reionize the universe?

    NASA Astrophysics Data System (ADS)

    Schenker, Matthew A.

    The epoch of reionization remains one of the last uncharted eras of cosmic history, yet this time is of crucial importance, encompassing the formation of both the first galaxies and the first metals in the universe. In this thesis, I present four related projects that both characterize the abundance and properties of these first galaxies and uses follow-up observations of these galaxies to achieve one of the first observations of the neutral fraction of the intergalactic medium during the heart of the reionization era. First, we present the results of a spectroscopic survey using the Keck telescopes targeting 6.3 < z < 8.8 star-forming galaxies. We secured observations of 19 candidates, initially selected by applying the Lyman break technique to infrared imaging data from the Wide Field Camera 3 (WFC3) onboard the Hubble Space Telescope (HST). This survey builds upon earlier work from Stark et al. (2010, 2011), which showed that star-forming galaxies at 3 < z < 6, when the universe was highly ionized, displayed a significant increase in strong Lyman alpha emission with redshift. Our work uses the LRIS and NIRSPEC instruments to search for Lyman alpha emission in candidates at a greater redshift in the observed near-infrared, in order to discern if this evolution continues, or is quenched by an increase in the neutral fraction of the intergalactic medium. Second, we characterize the abundance of star-forming galaxies at z > 6.5 again using WFC3 onboard the HST. This project conducted a detailed search for candidates both in the Hubble Ultra Deep Field as well as a number of additional wider Hubble Space Telescope surveys to construct luminosity functions at both z ~ 7 and 8, reaching 0.65 and 0.25 mag fainter than any previous surveys, respectively. We show that an extension of the luminosity function down to MUV = -13.0, coupled with a low level of star-formation out to higher redshift, can fit all available constraints on the ionization history of the universe

  1. An enhanced merger fraction within the galaxy population of the SSA22 protocluster at z = 3.1

    NASA Astrophysics Data System (ADS)

    Hine, N. K.; Geach, J. E.; Alexander, D. M.; Lehmer, B. D.; Chapman, S. C.; Matsuda, Y.

    2016-01-01

    The overdense environments of protoclusters of galaxies in the early Universe (z > 2) are expected to accelerate the evolution of galaxies, with an increased rate of stellar mass assembly and black hole accretion compared to co-eval galaxies in the average density `field'. These galaxies are destined to form the passive population of massive galaxies that dominate the cores of rich clusters today. While signatures of the accelerated growth of galaxies in the SSA22 protocluster (z = 3.1) have been observed, the mechanism driving this remains unclear. Here we show an enhanced rate of galaxy-galaxy mergers could be responsible. We morphologically classify Lyman-break Galaxies (LBGs) in the SSA22 protocluster and compare these to those of galaxies in the field at z = 3.1 as either active mergers or non-merging using Hubble Space Telescope ACS/F814W imaging, probing the rest-frame ultraviolet stellar light. We measure a merger fraction of 48 ± 10 per cent for LBGs in the protocluster compared to 30 ± 6 per cent in the field. Although the excess is marginal, an enhanced rate of mergers in SSA22 hints that galaxy-galaxy mergers are one of the key channels driving accelerated star formation and AGN growth in protocluster environments.

  2. Dark energy in systems of galaxies

    NASA Astrophysics Data System (ADS)

    Chernin, A. D.

    2013-11-01

    The precise observational data of the Hubble Space Telescope have been used to study nearby galaxy systems. The main result is the detection of dark energy in groups, clusters, and flows of galaxies on a spatial scale of about 1-10 Mpc. The local density of dark energy in these systems, which is determined by various methods, is close to the global value or even coincides with it. A theoretical model of the nearby Universe has been constructed, which describes the Local Group of galaxies with the flow of dwarf galaxies receding from this system. The key physical parameter of the group-flow system is zero gravity radius, which is the distance at which the gravity of dark matter is compensated by dark-energy antigravity. The model predicts the existence of local regions of space where Einstein antigravity is stronger than Newton gravity. Six such regions have been revealed in the data of the Hubble space telescope. The nearest of these regions is at a distance of 1-3 Mpc from the center of the Milky Way. Antigravity in this region is several times stronger than gravity. Quasiregular flows of receding galaxies, which are accelerated by the dark-energy antigravity, exist in these regions. The model of the nearby Universe at the scale of groups of galaxies (˜1 Mpc) can be extended to the scale of clusters (˜10 Mpc). The systems of galaxies with accelerated receding flows constitute a new and probably widespread class of metagalactic populations. Strong dynamic effects of local dark energy constitute the main characteristic feature of these systems.

  3. Dynamics & Morphology of Coma Cluster Galaxies

    NASA Astrophysics Data System (ADS)

    Beijersbergen, M.; van der Hulst, J. M.

    The principal aim of this project is to explore the link between the cluster and its environment, and to study the effects that changes in environment have on the properties of galaxies. Coma, the richest of the nearby clusters, appears to be a close equivalent to clusters at higher redshift. The most remarkable similarity is the presence of blue disk galaxies and galaxies with E+A type spectra, making Coma the perfect link between nearby and distant clusters. Despite numerous observations, many aspects of both the dynamics of the Coma cluster and of its galaxy populations remain unexplained. One of the most notable pieces of information that is as yet unavailable, is a proper, unbiased HI survey of the entire Coma area. The few pointed observations that have been done show a variety in HI properties: stripped disks, blue disk galaxies with quite a range in HI content and galaxies with low surface brightness companions. We have used the Westerbork Synthesis Radio Telescope (WSRT) to perform a blind survey of galaxies in Coma in the redshifted HI line. We have covered an area of 4.6 square degrees with 17 MHz bandwidth in 432 hours of total integration time. This allows us to study the HI properties as function of environment and assess the importance of merging and stripping. The HI observations will be used in combination with optical data from the wide field camera on the Isaac Newton Telescope (INT) to address a large number of interesting problems. Our data sets are unrivalled by what is available for any other cluster and will greatly enhance the ability to study the structure and dynamics of Coma. Here, I will discuss the data and the status of this ongoing project.

  4. Backwards Spiral Galaxy

    NASA Technical Reports Server (NTRS)

    1999-01-01

    Astronomers using NASA's Hubble Space Telescope have found a spiral galaxy that may rotate in the opposite direction from what was expected.

    A picture of the oddball galaxy is available at http://heritage.stsci.edu or http://oposite.stsci.edu/pubinfo/pr/2002/03 or http://www.jpl.nasa.gov/images/wfpc . It was taken in May 2001 by Hubble's Wide Field and Planetary Camera 2, designed and built by NASA's Jet Propulsion Laboratory, Pasadena, Calif.

    The picture showed which side of galaxy NGC 4622 is closer to Earth; that information helped astronomers determine that the galaxy may be spinning clockwise. The image shows NGC 4622 and its outer pair of winding arms full of new stars, shown in blue.

    Astronomers are puzzled by the clockwise rotation because of the direction the outer spiral arms are pointing. Most spiral galaxies have arms of gas and stars that trail behind as they turn. But this galaxy has two 'leading' outer arms that point toward the direction of the galaxy's clockwise rotation. NGC 4622 also has a 'trailing' inner arm that is wrapped around the galaxy in the opposite direction. Based on galaxy simulations, a team of astronomers had expected that the galaxy was turning counterclockwise.

    NGC 4622 is a rare example of a spiral galaxy with arms pointing in opposite directions. Astronomers suspect this oddity was caused by the interaction of NGC 4622 with another galaxy. Its two outer arms are lopsided, meaning that something disturbed it. The new Hubble image suggests that NGC 4622 consumed a smaller companion galaxy.

    Galaxies, which consist of stars, gas, and dust, rotate very slowly. Our Sun, one of many stars in our Milky Way galaxy, completes a circuit around the Milky Way every 250 million years. NGC 4622 lies 111 million light-years away in the direction of the constellation Centaurus.

    The science team, consisting of Drs. Ron Buta and Gene Byrd from the University of Alabama, Tuscaloosa, and Tarsh Freeman of Bevill State

  5. Hubble's deepest view ever of the Universe unveils earliest galaxies

    NASA Astrophysics Data System (ADS)

    2004-03-01

    Hubble sees galaxies galore hi-res Size hi-res: 446 kb Credits: NASA, ESA, and S. Beckwith (STScI) and the HUDF Team Hubble sees galaxies galore Galaxies, galaxies everywhere - as far as the NASA/ESA Hubble Space Telescope can see. This view of nearly 10,000 galaxies is the deepest visible-light image of the cosmos. Called the Hubble Ultra Deep Field, this galaxy-studded view represents a ‘deep’ core sample of the universe, cutting across billions of light-years. Hubble reveals galactic drama hi-res Size hi-res: 879 kb Credits: NASA, ESA, and S. Beckwith (STScI) and the HUDF Team Hubble reveals galactic drama A galactic brawl. A close encounter with a spiral galaxy. Blue wisps of galaxies. These close-up snapshots of galaxies in the Hubble Ultra Deep Field reveal the drama of galactic life. Here three galaxies just below centre are enmeshed in battle, their shapes distorted by the brutal encounter. Hubble reveals galactic drama hi-res Size hi-res: 886 kb Credits: NASA, ESA, and S. Beckwith (STScI) and the HUDF Team Hubble reveals galactic drama A galactic brawl. A close encounter with a spiral galaxy. Blue wisps of galaxies. These close-up snapshots of galaxies in the Hubble Ultra Deep Field reveal the drama of galactic life. Here three galaxies just below centre are enmeshed in battle, their shapes distorted by the brutal encounter. Hubble reveals galactic drama hi-res Size hi-res: 892 kb Credits: NASA, ESA, and S. Beckwith (STScI) and the HUDF Team Hubble reveals galactic drama A galactic brawl. A close encounter with a spiral galaxy. Blue wisps of galaxies. These close-up snapshots of galaxies in the Hubble Ultra Deep Field reveal the drama of galactic life. The galaxies in this panel were plucked from a harvest of nearly 10,000 galaxies in the Ultra Deep Field, the deepest visible-light image of the cosmos. This historic new view is actually made up by two separate images taken by Hubble's Advanced Camera for Surveys (ACS) and the Near Infrared Camera and

  6. Dark Matter Equilibria in Galaxies and Galaxy Systems

    NASA Astrophysics Data System (ADS)

    Lapi, A.; Cavaliere, A.

    2009-02-01

    In the dark matter (DM) halos embedding galaxies and galaxy systems the "entropy" K ≡ σ2/ρ2/3 (a quantity that combines the radial velocity dispersion σ with the density ρ) is found from intensive N-body simulations to follow a power-law run K vprop r α throughout the halos' bulk, with α around 1.25. Taking up from phenomenology just that α≈ const. applies, we cut through the rich analytic contents of the Jeans equation describing the self-gravitating equilibria of the DM; we specifically focus on computing and discussing a set of novel physical solutions that we name α-profiles, marked by the entropy slope α itself, and by the maximal gravitational pull κcrit(α) required for a viable equilibrium to hold. We then use an advanced semianalytic description for the cosmological buildup of halos to constrain the values of α to within the narrow range 1.25-1.29 from galaxies to galaxy systems; these correspond to halos' current masses in the range 1011-1015 M sun. Our range of α applies since the transition time that—both in our semianalytic description and in state-of-the-art numerical simulations—separates two development stages: an early violent collapse that comprises a few major mergers and enforces dynamical mixing, followed by smoother mass addition through slow accretion. In our range of α we provide a close fit for the relation κcrit(α), and discuss a related physical interpretation in terms of incomplete randomization of the infall kinetic energy through dynamical mixing. We also give an accurate analytic representation of the α-profiles with parameters derived from the Jeans equation; this provides straightforward precision fits to recent detailed data from gravitational lensing in and around massive galaxy clusters, and thus replaces the empirical Navarro-Frenk-White formula relieving the related problems of high concentration and old age. We finally stress how our findings and predictions as to α and κcrit contribute to

  7. Small Break Air Ingress Experiment

    SciTech Connect

    Chang Oh; Eung Soo Kim

    2011-09-01

    The small break air-ingress experiment, described in this report, is designed to investigate air-ingress phenomena postulated to occur in pipes in a very high temperature gas-cooled reactor (VHTRs). During this experiment, air-ingress rates were measured for various flow and break conditions through small holes drilled into a pipe of the experimental apparatus. The holes were drilled at right angles to the pipe wall such that a direction vector drawn from the pipe centerline to the center of each hole was at right angles with respect to the pipe centerline. Thus the orientation of each hole was obtained by measuring the included angle between the direction vector of each hole with respect to a reference line anchored on the pipe centerline and pointing in the direction of the gravitational force. Using this reference system, the influence of several important parameters on the air ingress flow rate were measured including break orientation, break size, and flow velocity . The approach used to study the influence of these parameters on air ingress is based on measuring the changes in oxygen concentrations at various locations in the helium flow circulation system as a function of time using oxygen sensors (or detectors) to estimate the air-ingress rates through the holes. The test-section is constructed of a stainless steel pipe which had small holes drilled at the desired locations.

  8. Baryon and chiral symmetry breaking

    SciTech Connect

    Gorsky, A.; Krikun, A.

    2014-07-23

    We briefly review the generalized Skyrmion model for the baryon recently suggested by us. It takes into account the tower of vector and axial mesons as well as the chiral symmetry breaking. The generalized Skyrmion model provides the qualitative explanation of the Ioffe’s formula for the baryon mass.

  9. Strong coupling electroweak symmetry breaking

    SciTech Connect

    Barklow, T.L.; Burdman, G.; Chivukula, R.S.

    1997-04-01

    The authors review models of electroweak symmetry breaking due to new strong interactions at the TeV energy scale and discuss the prospects for their experimental tests. They emphasize the direct observation of the new interactions through high-energy scattering of vector bosons. They also discuss indirect probes of the new interactions and exotic particles predicted by specific theoretical models.

  10. Breaking Through the Literacy Ceiling.

    ERIC Educational Resources Information Center

    Jordan, Marean; Schoenbach, Ruth

    2003-01-01

    Describes collaborative efforts by the Strategic Literacy Initiative at WestEd and secondary teachers and administrators in California to develop and implement an interactive approach to reading improvement called Reading Apprenticeship in an effort to help adolescent readers break through the "literacy ceiling" in all their subject area courses.…

  11. How do accretion discs break?

    NASA Astrophysics Data System (ADS)

    Dogan, Suzan

    2016-07-01

    Accretion discs are common in binary systems, and they are often found to be misaligned with respect to the binary orbit. The gravitational torque from a companion induces nodal precession in misaligned disc orbits. In this study, we first calculate whether this precession is strong enough to overcome the internal disc torques communicating angular momentum. We compare the disc precession torque with the disc viscous torque to determine whether the disc should warp or break. For typical parameters precession wins: the disc breaks into distinct planes that precess effectively independently. To check our analytical findings, we perform 3D hydrodynamical numerical simulations using the PHANTOM smoothed particle hydrodynamics code, and confirm that disc breaking is widespread and enhances accretion on to the central object. For some inclinations, the disc goes through strong Kozai cycles. Disc breaking promotes markedly enhanced and variable accretion and potentially produces high-energy particles or radiation through shocks. This would have significant implications for all binary systems: e.g. accretion outbursts in X-ray binaries and fuelling supermassive black hole (SMBH) binaries. The behaviour we have discussed in this work is relevant to a variety of astrophysical systems, for example X-ray binaries, where the disc plane may be tilted by radiation warping, SMBH binaries, where accretion of misaligned gas can create effectively random inclinations and protostellar binaries, where a disc may be misaligned by a variety of effects such as binary capture/exchange, accretion after binary formation.

  12. Sweating the small stuff: simulating dwarf galaxies, ultra-faint dwarf galaxies, and their own tiny satellites

    NASA Astrophysics Data System (ADS)

    Wheeler, Coral; Oñorbe, Jose; Bullock, James S.; Boylan-Kolchin, Michael; Elbert, Oliver D.; Garrison-Kimmel, Shea; Hopkins, Philip F.; Kereš, Dušan

    2015-10-01

    We present Feedback in Realistic Environment (FIRE)/GIZMO hydrodynamic zoom-in simulations of isolated dark matter haloes, two each at the mass of classical dwarf galaxies (Mvir ≃ 1010 M⊙) and ultra-faint galaxies (Mvir ≃ 109 M⊙), and with two feedback implementations. The resulting central galaxies lie on an extrapolated abundance matching relation from M⋆ ≃ 106 to 104 M⊙ without a break. Every host is filled with subhaloes, many of which form stars. Each of our dwarfs with M⋆ ≃ 106 M⊙ has 1-2 well-resolved satellites with M⋆ = 3-200 × 103 M⊙. Even our isolated ultra-faint galaxies have star-forming subhaloes. If this is representative, dwarf galaxies throughout the Universe should commonly host tiny satellite galaxies of their own. We combine our results with the Exploring the Local Volume in Simulations (ELVIS) simulations to show that targeting ˜ 50 kpc regions around nearby isolated dwarfs could increase the chances of discovering ultra-faint galaxies by ˜35 per cent compared to random pointings, and specifically identify the region around the Phoenix dwarf galaxy as a good potential target. The well-resolved ultra-faint galaxies in our simulations (M⋆ ≃ 3-30 × 103 M⊙) form within Mpeak ≃ 0.5-3 × 109 M⊙ haloes. Each has a uniformly ancient stellar population ( > 10 Gyr) owing to reionization-related quenching. More massive systems, in contrast, all have late-time star formation. Our results suggest that Mhalo ≃ 5 × 109 M⊙ is a probable dividing line between haloes hosting reionization `fossils' and those hosting dwarfs that can continue to form stars in isolation after reionization.

  13. Enhanced X-ray emission from Lyman break analogues and a possible LX-SFR-metallicity plane

    NASA Astrophysics Data System (ADS)

    Brorby, M.; Kaaret, P.; Prestwich, A.; Mirabel, I. F.

    2016-04-01

    The source of energetic photons that heated and reionized the early Universe remains uncertain. Early galaxies had low metallicity and recent population synthesis calculations suggest that the number and luminosity of high-mass X-ray binaries are enhanced in star-forming galaxies with low metallicity, offering a potentially important and previously overlooked source of heating and reionization. Lyman break analogue (LBA) galaxies are local galaxies that strongly resemble the high-redshift, star-forming Lyman break galaxies and have been suggested as local analogues to these metal-deficient galaxies found in the early Universe. We studied a sample of 10 LBAs in order to measure the relation between star formation rate and X-ray luminosity. We found that for LBAs with metallicities in the range 12 + log10(O/H) = 8.15-8.80, the LX -SFR relation was log _{10} (L_X/SFR {[erg s^{-1} M_{⊙}^{-1} yr]}) = 39.85(± 0.10) in the 0.5-8 keV band with a dispersion of σ = 0.25 dex. This is an enhancement of nearly a factor of 2 in the L0.5-8 keV-SFR relation relative to results for nearby, near-solar metallicity galaxies. The enhancement is significant at the 98.2 per cent level (2.4σ). Our enhanced LX/SFR relation is consistent with the metallicity-dependent predicted value from population synthesis models. We discuss the possibility of an LX-SFR-metallicity plane for star-forming galaxies. These results are important to our understanding of reionization and the formation of early galaxies.

  14. Bars Triggered By Galaxy Flybys

    NASA Astrophysics Data System (ADS)

    Holley-Bockelmann, Kelly; Lang, Meagan; Sinha, Manodeep

    2015-05-01

    Galaxy mergers drive galaxy evolution and are a key mechanism by which galaxies grow and transform. Unlike galaxy mergers where two galaxies combine into one remnant, galaxy flybys occur when two independent galaxy halos interpenetrate but detach at a later time; these one-time events are surprisingly common and can even out-number galaxy mergers at low redshift for massive halos. Although these interactions are transient and occur far outside the galaxy disk, flybys can still drive a rapid and large pertubations within both the intruder and victim halos. We explored how flyby encounters can transform each galaxy using a suite of N-body simulations. We present results from three co-planar flybys between disk galaxies, demonstrating that flybys can both trigger strong bar formation and can spin-up dark matter halos.

  15. THE IMPACT OF BARS ON DISK BREAKS AS PROBED BY S{sup 4}G IMAGING

    SciTech Connect

    Munoz-Mateos, Juan Carlos; Sheth, Kartik; Kim, Taehyun; Meidt, Sharon; Athanassoula, E.; Bosma, Albert; Comeron, Sebastien; Laine, Jarkko; Laurikainen, Eija; Elmegreen, Bruce G.; Erroz-Ferrer, Santiago; Knapen, Johan H.; Gadotti, Dimitri A.; Hinz, Joannah L.; Ho, Luis C.; Madore, Barry F.; Holwerda, Benne; Jarrett, Thomas H.; and others

    2013-07-01

    We have analyzed the radial distribution of old stars in a sample of 218 nearby face-on disks, using deep 3.6 {mu}m images from the Spitzer Survey of Stellar Structure in Galaxies. In particular, we have studied the structural properties of those disks with a broken or down-bending profile. We find that, on average, disks with a genuine single-exponential profile have a scale length and a central surface brightness which are intermediate to those of the inner and outer components of a down-bending disk with the same total stellar mass. In the particular case of barred galaxies, the ratio between the break and the bar radii (R{sub br}/R{sub bar}) depends strongly on the total stellar mass of the galaxy. For galaxies more massive than 10{sup 10} M{sub Sun }, the distribution is bimodal, peaking at R{sub br}/R{sub bar} {approx} 2 and {approx}3.5. The first peak, which is the most populated one, is linked to the outer Lindblad resonance of the bar, whereas the second one is consistent with a dynamical coupling between the bar and the spiral pattern. For galaxies below 10{sup 10} M{sub Sun }, breaks are found up to {approx}10 R{sub bar}, but we show that they could still be caused by resonances given the rising nature of rotation curves in these low-mass disks. While not ruling out star formation thresholds, our results imply that radial stellar migration induced by non-axisymmetric features can be responsible not only for those breaks at {approx}2 R{sub bar}, but also for many of those found at larger radii.

  16. Evolution of galaxy habitability

    NASA Astrophysics Data System (ADS)

    Gobat, R.; Hong, S. E.

    2016-08-01

    We combine a semi-analytic model of galaxy evolution with constraints on circumstellar habitable zones and the distribution of terrestrial planets in order to probe the suitability of galaxies of different mass and type to host habitable planets, and how it evolves with time. We find that the fraction of stars with terrestrial planets in their habitable zone (known as habitability) depends only weakly on galaxy mass, with a maximum around 4 × 1010M⊙. We estimate that 0.7% of all stars in Milky Way-type galaxies to host a terrestrial planet within their habitable zone, consistent with the value derived from Kepler observations. On the other hand, the habitability of passive galaxies is slightly but systematically higher, unless we assume an unrealistically high sensitivity of planets to supernovae. We find that the overall habitability of galaxies has not changed significantly in the last ~8 Gyr, with most of the habitable planets in local disk galaxies having formed ~1.5 Gyr before our own solar system. Finally, we expect that ~1.4 ×109 planets similar to present-day Earth have existed so far in our galaxy.

  17. Superluminous Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Ogle, Patrick M.; Lanz, Lauranne; Nader, Cyril; Helou, George

    2016-02-01

    We report the discovery of spiral galaxies that are as optically luminous as elliptical brightest cluster galaxies, with r-band monochromatic luminosity Lr = 8-14L* (4.3-7.5 × 1044 erg s-1). These super spiral galaxies are also giant and massive, with diameter D = 57-134 kpc and stellar mass Mstars = 0.3-3.4 × 1011M⊙. We find 53 super spirals out of a complete sample of 1616 SDSS galaxies with redshift z < 0.3 and Lr > 8L*. The closest example is found at z = 0.089. We use existing photometry to estimate their stellar masses and star formation rates (SFRs). The SDSS and Wide-field Infrared Survey Explorer colors are consistent with normal star-forming spirals on the blue sequence. However, the extreme masses and rapid SFRs of 5-65 M⊙ yr-1 place super spirals in a sparsely populated region of parameter space, above the star-forming main sequence of disk galaxies. Super spirals occupy a diverse range of environments, from isolation to cluster centers. We find four super spiral galaxy systems that are late-stage major mergers—a possible clue to their formation. We suggest that super spirals are a remnant population of unquenched, massive disk galaxies. They may eventually become massive lenticular galaxies after they are cut off from their gas supply and their disks fade.

  18. UPDATED NEARBY GALAXY CATALOG

    SciTech Connect

    Karachentsev, Igor D.; Makarov, Dmitry I.; Kaisina, Elena I.

    2013-04-15

    We present an all-sky catalog of 869 nearby galaxies having individual distance estimates within 11 Mpc or corrected radial velocities V{sub LG} < 600 km s{sup -1}. The catalog is a renewed and expanded version of the Catalog of Neighboring Galaxies by Karachentsev et al. It collects data on the following galaxy observables: angular diameters, apparent magnitudes in far-UV, B, and K{sub s} bands, H{alpha} and H I fluxes, morphological types, H I-line widths, radial velocities, and distance estimates. In this Local Volume (LV) sample, 108 dwarf galaxies still remain without measured radial velocities. The catalog yields also calculated global galaxy parameters: linear Holmberg diameter, absolute B magnitude, surface brightness, H I mass, stellar mass estimated via K-band luminosity, H I rotational velocity corrected for galaxy inclination, indicative mass within the Holmberg radius, and three kinds of ''tidal index,'' which quantify the local density environment. The catalog is supplemented with data based on the local galaxies, which presents their optical and available H{alpha} images, as well as other services. We briefly discuss the Hubble flow within the LV and different scaling relations that characterize galaxy structure and global star formation in them. We also trace the behavior of the mean stellar mass density, H I-mass density, and star formation rate density within the volume considered.

  19. Hubble's galaxy nomenclature

    NASA Astrophysics Data System (ADS)

    Baldry, Ivan K.

    2008-10-01

    It is widely written and believed that Edwin Hubble introduced the terms ``early'' and ``late types'' to suggest an evolutionary sequence for galaxies. This is incorrect. Hubble took these terms from spectral classification of stars to signify a sequence related to complexity of appearance, albeit based on images, not spectra. The temporal connotations had been abandoned before his 1926 paper on classification of galaxies.

  20. Brightest Cluster Galaxy Identification

    NASA Astrophysics Data System (ADS)

    Leisman, Luke; Haarsma, D. B.; Sebald, D. A.; ACCEPT Team

    2011-01-01

    Brightest cluster galaxies (BCGs) play an important role in several fields of astronomical research. The literature includes many different methods and criteria for identifying the BCG in the cluster, such as choosing the brightest galaxy, the galaxy nearest the X-ray peak, or the galaxy with the most extended profile. Here we examine a sample of 75 clusters from the Archive of Chandra Cluster Entropy Profile Tables (ACCEPT) and the Sloan Digital Sky Survey (SDSS), measuring masked magnitudes and profiles for BCG candidates in each cluster. We first identified galaxies by hand; in 15% of clusters at least one team member selected a different galaxy than the others.We also applied 6 other identification methods to the ACCEPT sample; in 30% of clusters at least one of these methods selected a different galaxy than the other methods. We then developed an algorithm that weighs brightness, profile, and proximity to the X-ray peak and centroid. This algorithm incorporates the advantages of by-hand identification (weighing multiple properties) and automated selection (repeatable and consistent). The BCG population chosen by the algorithm is more uniform in its properties than populations selected by other methods, particularly in the relation between absolute magnitude (a proxy for galaxy mass) and average gas temperature (a proxy for cluster mass). This work supported by a Barry M. Goldwater Scholarship and a Sid Jansma Summer Research Fellowship.

  1. GALAXY EVOLUTION IN OVERDENSE ENVIRONMENTS AT HIGH REDSHIFT: PASSIVE EARLY-TYPE GALAXIES IN A CLUSTER AT z {approx} 2

    SciTech Connect

    Strazzullo, V.; Gobat, R.; Daddi, E.; Onodera, M.; Carollo, M.; Dickinson, M.; Renzini, A.; Arimoto, N.; Cimatti, A.; Finoguenov, A.; Chary, R.-R.

    2013-08-01

    We present a study of galaxy populations in the central region of the IRAC-selected, X-ray-detected galaxy cluster Cl J1449+0856 at z = 2. Based on a sample of spectroscopic and photometric cluster members, we investigate stellar populations and the morphological structure of cluster galaxies over an area of {approx}0.7 Mpc{sup 2} around the cluster core. The cluster stands out as a clear overdensity both in redshift space and in the spatial distribution of galaxies close to the center of the extended X-ray emission. The cluster core region (r < 200 kpc) shows a clearly enhanced passive fraction with respect to field levels. However, together with a population of massive, passive galaxies mostly with early-type morphologies, the cluster core also hosts massive, actively star-forming, often highly dust reddened sources. Close to the cluster center, a multi-component system of passive and star-forming galaxies could represent the future brightest cluster galaxy still forming. We observe a clear correlation between passive stellar populations and an early-type morphology, in agreement with field studies at similar redshift. Passive early-type galaxies in this cluster are typically a factor of 2-3 smaller than similarly massive early types at z {approx} 0. On the other hand, these same objects are on average larger by a factor of {approx}2 than field early-types at similar redshift, lending support to recent claims of an accelerated structural evolution in high-redshift dense environments. These results point toward the early formation of a population of massive galaxies, already evolved both in their structure and stellar populations, coexisting with still actively forming massive galaxies in the central regions of young clusters 10 billion years ago.

  2. GALAXIES: SNAPSHOTS IN TIME

    NASA Technical Reports Server (NTRS)

    2002-01-01

    This sequence of NASA Hubble Space Telescope (HST) images of remote galaxies offers tantalizing initial clues to the evolution of galaxies in the universe. [far left column] These are traditional spiral and elliptical-shaped galaxies that make up the two basic classes of island star cities that inhabit the universe we see in our current epoch (14 billion years after the birth of the universe in the Big Bang). Elliptical galaxies contain older stars, while spirals have vigorous ongoing star formation in their dusty, pancake-shaped disks. Our Milky Way galaxy is a typical spiral, or disk-shaped galaxy, on the periphery of the great Virgo cluster. Both galaxies in this column are a few tens of millions of light-years away, and therefore represent our current stage of the universe s evolution. [center left column] These galaxies existed in a rich cluster when the universe was approximately two-thirds its present age. Elliptical galaxies (top) appear fully evolved because they resemble today's descendants. By contrast, some spirals have a frothier appearance, with loosely shaped arms of young star formation. The spiral population appears more disrupted due to a variety of possible dynamical effects that result from dwelling in a dense cluster. [center right column] Distinctive spiral structure appears more vague and disrupted in galaxies that existed when the universe was nearly one-third its present age. These objects do not have the symmetry of current day spirals and contain irregular lumps of starburst activity. However, even this far back toward the beginning of time, the elliptical galaxy (top) is still clearly recognizable. However, the distinction between ellipticals and spirals grows less certain with increasing distance. [far right column] These extremely remote, primeval objects existed with the universe was nearly one-tenth its current age. The distinction between spiral and elliptical galaxies may well disappear at this early epoch. However, the object in

  3. Probing AGN Unification with galaxy neighbours: pitfalls and prospects

    NASA Astrophysics Data System (ADS)

    Villarroel, B.

    2015-09-01

    Statistical tests of AGN unification harbour many caveats. One way of constraining the validity of the AGN unification is through studies of close neighbours to Type-1 and Type-2 AGN. Examining thousands of AGN- galaxy pairs from the Sloan Digital Sky Survey Data Release 7 and the Galaxy Zoo project, we found that Type-2 AGN appear to reside in more star-forming environments than Type-1 AGN.

  4. Nucleosynthesis in the Magellanic Clouds and the Galaxy.

    NASA Technical Reports Server (NTRS)

    Burbidge, G.

    1971-01-01

    Available evidence on the chemical composition of the Magellanic Clouds (when compared to the Galaxy) is not sufficient for a detailed theory of the chemical evolution of the Clouds to be developed at present. However, this evidence is thus far compatible with the view that much of the material of the Clouds went through a considerable amount of nucleosynthesis early in its history. The Clouds could once have been part of the Galaxy, or they could have formed as satellites when the protogalaxy condensed. The general problem of the chemical evolution is tied closely to the problem of galaxy formation which remains unsolved.

  5. MULTIPLE GALAXY COLLISIONS

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Here is a sampling of 15 ultraluminous infrared galaxies viewed by NASA's Hubble Space Telescope. Hubble's sharp vision reveals more complexity within these galaxies, which astronomers are interpreting as evidence of a multiple-galaxy pileup. These images, taken by the Wide Field and Planetary Camera 2, are part of a three-year study of 123 galaxies within 3 billion light-years of Earth. The study was conducted in 1996, 1997, and 1999. False colors were assigned to these photos to enhance fine details within these coalescing galaxies. Credits: NASA, Kirk Borne (Raytheon and NASA Goddard Space Flight Center, Greenbelt, Md.), Luis Colina (Instituto de Fisica de Cantabria, Spain), and Howard Bushouse and Ray Lucas (Space Telescope Science Institute, Baltimore, Md.)

  6. Colliding and merging galaxies.

    PubMed

    Schweizer, F

    1986-01-17

    Aided by advances in computer technology and observations from space, astronomers have begun to unravel the mysteries of galaxy formation and evolution. Galaxies evolve by interacting with their environment and especially with each other. During brief but often fierce galactic encounters, gravitational forces generate strong tides that survive as telltale signatures for billions of years. Because these so-called collisions dissipate orbital energy, galaxies on bound orbits may eventually merge. Collisions and mergers are responsible for a great variety of phenomena, including the triggering of widespread star formation in galaxies and the fueling of nuclear activity in quasars. Evidence is accumulating that not all galaxies formed shortly after the Big Bang. A sizable fraction of them may have formed later, and many are still experiencing significant dynamical evolution. PMID:17769643

  7. Galaxy Messier 83

    NASA Technical Reports Server (NTRS)

    2003-01-01

    This image of the spiral galaxy Messier 83 was taken by NASA's Galaxy Evolution Explorer on June 7, 2003. Located 15 million light years from Earth and known as the Southern Pinwheel Galaxy, Messier 83 displays significant amounts of ultraviolet emissions far from the optically bright portion of the galaxy. It is also known to have an extended hydrogen disc that appears to radiate a faint ultraviolet emission. The red stars in the foreground of the image are Milky Way stars.

    The Galaxy Evolution Explorer mission is led by the California Institute of Technology, which is also responsible for the science operations and data analysis. NASA's Jet Propulsion Laboratory, Pasadena, Calif., a division of Caltech, manages the mission and built the science instrument. The mission was developed under NASA's Explorers Program, managed by the Goddard Space Flight Center, Greenbelt, Md. The mission's international partners include South Korea and France.

  8. The galaxy ancestor problem

    NASA Astrophysics Data System (ADS)

    Disney, M. J.; Lang, R. H.

    2012-11-01

    The Hubble Space Telescope (HST) findsgalaxies whose Tolman dimming exceeds 10 mag. Could evolution alone explain these as our ancestor galaxies or could they be representatives of quite a different dynasty whose descendants are no longer prominent today? We explore the latter hypothesis and argue that surface brightness selection effects naturally bring into focus quite different dynasties from different redshifts. Thus, the HST z = 7 galaxies could be examples of galaxies whose descendants are both too small and too choked with dust to be recognizable in our neighbourhood easily today. Conversely, the ancestors of the Milky Way and its obvious neighbours would have completely sunk below the sky at z > 1.2, unless they were more luminous in the past, although their diffused light could account for the missing re-ionization flux. This Succeeding Prominent Dynasties Hypothesis (SPDH) fits the existing observations both naturally and well even without evolution, including the bizarre distributions of galaxy surface brightness found in deep fields, the angular size ˜(1 + z)-1 law, 'downsizing' which turns out to be an 'illusion' in the sense that it does not imply evolution, 'infant mortality', that is, the discrepancy between stars born and stars seen, the existence of 'red nuggets', and finally the recently discovered and unexpected excess of quasar absorption line damped Lyα systems at high redshift. If galaxies were not significantly brighter in the past and the SPDH were true, then a large proportion of galaxies could remain sunk from sight, possibly at all redshifts, and these sunken galaxies could supply the missing re-ionization flux. We show that fishing these sunken galaxies out of the sky by their optical emissions alone is practically impossible, even when they are nearby. More ingenious methods are needed to detect them. It follows that disentangling galaxy evolution through studying ever higher redshift galaxies may be a forlorn hope because one could

  9. The influence of halo evolution on galaxy structure

    NASA Astrophysics Data System (ADS)

    White, Simon

    2015-03-01

    If Einstein-Newton gravity holds on galactic and larger scales, then current observations demonstrate that the stars and interstellar gas of a typical bright galaxy account for only a few percent of its total nonlinear mass. Dark matter makes up the rest and cannot be faint stars or any other baryonic form because it was already present and decoupled from the radiation plasma at z = 1000, long before any nonlinear object formed. The weak gravito-sonic waves so precisely measured by CMB observations are detected again at z = 4 as order unity fluctuations in intergalactic matter. These subsequently collapse to form today's galaxy/halo systems, whose mean mass profiles can be accurately determined through gravitational lensing. High-resolution simulations link the observed dark matter structures seen at all these epochs, demonstrating that they are consistent and providing detailed predictions for all aspects of halo structure and growth. Requiring consistency with the abundance and clustering of real galaxies strongly constrains the galaxy-halo relation, both today and at high redshift. This results in detailed predictions for galaxy assembly histories and for the gravitational arena in which galaxies live. Dark halos are not expected to be passive or symmetric but to have a rich and continually evolving structure which will drive evolution in the central galaxy over its full life, exciting warps, spiral patterns and tidal arms, thickening disks, producing rings, bars and bulges. Their growth is closely related to the provision of new gas for galaxy building.

  10. Record-Breaking in Geophysics

    NASA Astrophysics Data System (ADS)

    Newman, W. I.; Turcotte, D. L.; Nicewicz, M. A.

    2008-12-01

    The probabilistic theory of record-breaking was developed by Tata (1969), Nezvorov (1986) and others to describe the frequency of occurrence of record-breaking events in random trials. These results have been applied by Redner and Peterson (2006) in exploring the possible role of global warming on the statistics of record-breaking temperatures and by Newman and Turcotte (2008) to the rate of occurrence of record- breaking earthquakes. In addition, van Aalsburg et al. (2008) have derived the expected values of record- breaking earthquake magnitudes globally and compared this with cataloged observations. We review some of the underlying theory relevant to the distribution of events in time which we then extend to the spatial distribution of record-breaking events. In particular, we derive the distribution function associated with an otherwise random background of events and the emergence of spatial clustering in such situations. Moreover, we employ large-scale Monte-Carlo simulations to extend our analytic results to 2 and 3 dimensions. These results yield some remarkable scaling features including hierarchical behavior, resulting in power-law and fractal features, in situations where one would not intuitively expect to observe such pattern. Furthermore, they provide a "null-hypothesis" that can be used in testing the distribution and spatial scaling of real seismic events such as those studied by Davidsen and Paczuski (2005) and Davidsen, Grassberger, and Paczuski (2006, 2088). Tata, M.N., Z. Wahrscheinlichkeitstheorie verw. Geb. 12, 9- 20 (1969). Nezvorov, V.B., Theory, Prob. Appl., 32(2), 201-228, translated from Russian (2006). Redner, S. and Peterson, M.V., Phys. Rev. E 74, 061114 )2006). Newman, W.I. and Turcotte, D.L., 2008 Association of Pacific Rim Universities Symposium "Multi-Hazards around the Pacific Rim," University of California, Davis, August 21-22, 2008. Van Aalsburg, J., Newman, W.I., Turcotte, D.L., and Rundle, J.B., Fall AGU Meeting (this session

  11. ON THE SHAPES AND STRUCTURES OF HIGH-REDSHIFT COMPACT GALAXIES

    SciTech Connect

    Chevance, Melanie; Damjanov, Ivana; Abraham, Roberto G.; Weijmans, Anne-Marie; Simard, Luc; Van den Bergh, Sidney; Caris, Evelyn; Glazebrook, Karl

    2012-08-01

    Recent deep Hubble Space Telescope WFC3 imaging suggests that a majority of compact quiescent massive galaxies at z {approx} 2 may contain disks. To investigate this claim, we have compared the ellipticity distribution of 31 carefully selected high-redshift massive quiescent compact galaxies to a set of mass-selected ellipticity and Sersic index distributions obtained from two-dimensional structural fits to {approx}40, 000 nearby galaxies from the Sloan Digital Sky Survey. A Kolmogorov-Smirnov test shows that the distribution of ellipticities for the high-redshift galaxies is consistent with the ellipticity distribution of a similarly chosen sample of massive early-type galaxies. However, the distribution of Sersic indices for the high-redshift sample is inconsistent with that of local early-type galaxies, and instead resembles that of local disk-dominated populations. The mismatch between the properties of high-redshift compact galaxies and those of both local early-type and disk-dominated systems leads us to conclude that the basic structures of high-redshift compact galaxies probably do not closely resemble those of any single local galaxy population. Any galaxy population analog to the high-redshift compact galaxies that exists at the current epoch is either a mix of different types of galaxies, or possibly a unique class of objects on their own.

  12. Closed and Not Closed: Mitigating a Mystery on Chandra's Door

    NASA Technical Reports Server (NTRS)

    Odom, Brian

    2015-01-01

    The Chandra X-ray Observatory is part of NASA's fleet of "Great Observatories" along with the Hubble Space Telescope, the Spitzer Space Telescope, and the now deorbited Compton Gamma Ray Observatory. The observatory was designed to detect x-ray emissions from some of the hottest regions of the galaxy including exploded stars, clusters of galaxies, and matter around black holes. One of the observatory's key scientific instruments is the Advanced CCD Imaging Spectrometer (ACIS), which is one of four primary and two focal plane instruments. Due to the sensitivity of the charged coupled devices (CCD's), an aperture door was designed and built by Lockheed-Martin that protected the instrument during testing and the time leading up to launch. The design called for a system of wax actuators (manufactured by STARSYS Corp) to be used as components in a rotary actuator that would open and close the door during ground testing and on-orbit operations. Another feature of the design was an internal shear disc located in each actuator to prevent excessive internal pressure and to shield other components from damage.

  13. A Curious Pair of Galaxies

    NASA Astrophysics Data System (ADS)

    2009-03-01

    The ESO Very Large Telescope has taken the best image ever of a strange and chaotic duo of interwoven galaxies. The images also contain some surprises -- interlopers both far and near. ESO PR Photo 11a/09 A Curious Pair of Galaxies ESO PR Video 11a/09 Arp 261 zoom in ESO PR Video 11b/09 Pan over Arp 261 Sometimes objects in the sky that appear strange, or different from normal, have a story to tell and prove scientifically very rewarding. This was the idea behind Halton Arp's catalogue of Peculiar Galaxies that appeared in the 1960s. One of the oddballs listed there is Arp 261, which has now been imaged in more detail than ever before using the FORS2 instrument on ESO's Very Large Telescope. The image proves to contain several surprises. Arp 261 lies about 70 million light-years distant in the constellation of Libra, the Scales. Its chaotic and very unusual structure is created by the interaction of two galaxies that are engaged in a slow motion, but highly disruptive close encounter. Although individual stars are very unlikely to collide in such an event, the huge clouds of gas and dust certainly do crash into each other at high speed, leading to the formation of bright new clusters of very hot stars that are clearly seen in the picture. The paths of the existing stars in the galaxies are also dramatically disrupted, creating the faint swirls extending to the upper left and lower right of the image. Both interacting galaxies were probably dwarfs not unlike the Magellanic Clouds orbiting our own galaxy. The images used to create this picture were not actually taken to study the interacting galaxies at all, but to investigate the properties of the inconspicuous object just to the right of the brightest part of Arp 261 and close to the centre of the image. This is an unusual exploding star, called SN 1995N, that is thought to be the result of the final collapse of a massive star at the end of its life, a so-called core collapse supernova. SN 1995N is unusual because

  14. A Cluster and a Sea of Galaxies

    NASA Astrophysics Data System (ADS)

    2010-05-01

    A new wide-field image released today by ESO displays many thousands of distant galaxies, and more particularly a large group belonging to the massive galaxy cluster known as Abell 315. As crowded as it may appear, this assembly of galaxies is only the proverbial "tip of the iceberg", as Abell 315 - like most galaxy clusters - is dominated by dark matter. The huge mass of this cluster deflects light from background galaxies, distorting their observed shapes slightly. When looking at the sky with the unaided eye, we mostly only see stars within our Milky Way galaxy and some of its closest neighbours. More distant galaxies are just too faint to be perceived by the human eye, but if we could see them, they would literally cover the sky. This new image released by ESO is both a wide-field and long-exposure one, and reveals thousands of galaxies crowding an area on the sky roughly as large as the full Moon. These galaxies span a vast range of distances from us. Some are relatively close, as it is possible to distinguish their spiral arms or elliptical halos, especially in the upper part of the image. The more distant appear just like the faintest of blobs - their light has travelled through the Universe for eight billion years or more before reaching Earth. Beginning in the centre of the image and extending below and to the left, a concentration of about a hundred yellowish galaxies identifies a massive galaxy cluster, designated with the number 315 in the catalogue compiled by the American astronomer George Abell in 1958 [1]. The cluster is located between the faint, red and blue galaxies and the Earth, about two billion light-years away from us. It lies in the constellation of Cetus (the Whale). Galaxy clusters are some of the largest structures in the Universe held together by gravity. But there is more in these structures than the many galaxies we can see. Galaxies in these giants contribute to only ten percent of the mass, with hot gas in between galaxies

  15. Magnetic Fields in Galaxies

    NASA Astrophysics Data System (ADS)

    Beck, Rainer

    The origin and evolution of cosmic magnetic fields, their strength and structure in intergalactic space, their first occurrence in young galaxies, and their dynamical importance for galaxy evolution remain widely unknown. Radio synchrotron emission, its polarization and its Faraday rotation are powerful tools to study the strength and structure of magnetic fields in galaxies. Unpolarized radio synchrotron emission traces isotropic turbulent fields which are strongest in spiral arms and bars (20-30 μG) and in central starburst regions (50-100 μG). Such fields are dynamically important; they can affect gas flows and drive gas inflows in central regions. Polarized radio emission traces ordered fields which can be regular or anisotropic turbulent, generated from isotropic turbulent fields by compression or shear. The strongest ordered fields of 10-15 μG strength are generally found in interarm regions and follow the orientation of adjacent gas spiral arms. In galaxies with strong density waves, ordered (anisotropic turbulent) fields are also observed at the inner edges of the spiral arms. Ordered fields with spiral patterns exist in grand-design, barred and flocculent galaxies, and in central regions of starburst galaxies. Ordered fields in interacting galaxies have asymmetric distributions and are an excellent tracer of past interactions between galaxies or with the intergalactic medium. Irregular galaxies host isotropic turbulent fields often of similar strength as in spiral galaxies, but only weak ordered fields. Faraday rotation measures (RM) of the diffuse polarized radio emission from the disks of several galaxies reveal large-scale spiral patterns that can be described by the superposition of azimuthal modes; these are signatures of regular fields generated by a mean-field α -Ω dynamo. So far no indications were found in external galaxies of large-scale field reversals, like the one in the Milky Way. Ordered magnetic fields are also observed in radio halos

  16. Early-type galaxies have been the predominant morphological class for massive galaxies since only z ˜ 1

    NASA Astrophysics Data System (ADS)

    Buitrago, Fernando; Trujillo, Ignacio; Conselice, Christopher J.; Häußler, Boris

    2013-01-01

    Present-day massive galaxies are composed mostly of early-type objects. It is unknown whether this was also the case at higher redshifts. In a hierarchical assembling scenario the morphological content of the massive population is expected to change with time from disc-like objects in the early Universe to spheroid-like galaxies at present. In this paper we have probed this theoretical expectation by compiling a large sample of massive (Mstellar ≥ 1011 h- 270 M⊙) galaxies in the redshift interval 0 < z < 3. Our sample of 1082 objects comprises 207 local galaxies selected from Sloan Digital Sky Survey plus 875 objects observed with the Hubble Space Telescope belonging to the Palomar Observatory Wide-field InfraRed/DEEP2 and GOODS NICMOS Survey surveys. 639 of our objects have spectroscopic redshifts. Our morphological classification is performed as close as possible to the optical rest frame according to the photometric bands available in our observations both quantitatively (using the Sérsic index as a morphological proxy) and qualitatively (by visual inspection). Using both techniques we find an enormous change on the dominant morphological class with cosmic time. The fraction of early-type galaxies among the massive galaxy population has changed from ˜20-30 per cent at z ˜ 3 to ˜70 per cent at z = 0. Early-type galaxies have been the predominant morphological class for massive galaxies since only z ˜ 1.

  17. Temporomandibular Joint, Closed

    MedlinePlus

    ... Oral Health > The Temporomandibular Joint, Closed The Temporomandibular Joint, Closed Main Content Title: The Temporomandibular Joint, Closed Description: The temporomandibular joint connects the lower ...

  18. Logistic Stick-Breaking Process

    PubMed Central

    Ren, Lu; Du, Lan; Carin, Lawrence; Dunson, David B.

    2013-01-01

    A logistic stick-breaking process (LSBP) is proposed for non-parametric clustering of general spatially- or temporally-dependent data, imposing the belief that proximate data are more likely to be clustered together. The sticks in the LSBP are realized via multiple logistic regression functions, with shrinkage priors employed to favor contiguous and spatially localized segments. The LSBP is also extended for the simultaneous processing of multiple data sets, yielding a hierarchical logistic stick-breaking process (H-LSBP). The model parameters (atoms) within the H-LSBP are shared across the multiple learning tasks. Efficient variational Bayesian inference is derived, and comparisons are made to related techniques in the literature. Experimental analysis is performed for audio waveforms and images, and it is demonstrated that for segmentation applications the LSBP yields generally homogeneous segments with sharp boundaries. PMID:25258593

  19. 'Dynamical Supersymmetry Breaking, with Flavor'

    SciTech Connect

    Craig, Nathaniel; Essig, Rouven; Franco, Sebastian; Kachru, Shamit; Torroba, Gonzalo; /Stanford U., Phys. Dept. /SLAC /Santa Barbara, KITP /UC, Santa Barbara

    2010-08-26

    We explore calculable models with low-energy supersymmetry where the flavor hierarchy is generated by quark and lepton compositeness, and where the composites emerge from the same sector that dynamically breaks supersymmetry. The observed pattern of Standard Model fermion masses and mixings is obtained by identifying the various generations with composites of different dimension in the ultraviolet. These 'single-sector' supersymmetry breaking models give rise to various spectra of soft masses which are, in many cases, quite distinct from what is commonly found in models of gauge or gravity mediation. In typical models which satisfy all flavor-changing neutral current constraints, both the first and second generation sparticles have masses of order 20 TeV, while the stop mass is a few TeV. In other cases, all sparticles obtain masses of order a few TeV predominantly from gauge mediation, even though the first two generations are composite.

  20. Gas Kinematics In and Around Edge-on Galaxies from MaNGA Observations

    NASA Astrophysics Data System (ADS)

    Bizyaev, D.

    2016-06-01

    Mapping Nearby Galaxies at APO (MaNGA) is a massive Integral Field Unit survey of a large number of relatively nearby galaxies that started in 2014 as a part of SDSS-IV at the Apache Point Observatory. After the first year of observations MaNGA has obtained IFU spectra of about a thousand of objects, with several dozens of edge-on galaxies among them. The two-dimensional spectra help us constrain parameters of galactic components with superior rotation curves. There is a significant fraction of galaxies in which the extra-planar gas emission is confidently detected. The extra-planar gas velocity fields in several galaxies show signs of lagging rotation with respect to the gas motion close to the galactic plane. We show progress of MaNGA survey in observations of edge-on galaxies and discuss their impact on our understanding of gas kinematics in and around spiral galaxies after finishing the survey.

  1. Measurable Relationship between Bright Galaxies and Their Faint Companions in WHL J085910.0+294957, a Galaxy Cluster at z = 0.30: Vestiges of Infallen Groups?

    NASA Astrophysics Data System (ADS)

    Lee, Joon Hyeop; Lee, Hye-Ran; Kim, Minjin; Seon, Kwang-Il; Kim, Sang Chul; Yang, Soung-Chul; Ree, Chang Hee; Lee, Jong Chul; Jeong, Hyunjin; Ko, Jongwan; Choi, Changsu

    2014-08-01

    The properties of satellite galaxies are closely related to their host galaxies in galaxy groups. In cluster environments, on the other hand, the interaction between close neighbors is known to be limited. Our goal is to examine the relationships between host and satellite galaxies in the harsh environment of a galaxy cluster. To achieve this goal, we study a galaxy cluster WHL J085910.0+294957 at z = 0.30 using deep images obtained with CQUEAN CCD camera mounted on the 2.1 m Otto Struve Telescope. After member selection based on the scaling relations of photometric and structural parameters, we investigate the relationship between bright (Mi <= -18) galaxies and their faint (-18 < Mi <= -15) companions. The weighted mean color of faint companion galaxies shows no significant dependence (<1σ to bootstrap uncertainties) on cluster-centric distance and local luminosity density as well as the luminosity and concentration of an adjacent bright galaxy. However, the weighted mean color shows marginal dependence (~2.2σ) on the color of an adjacent bright galaxy when the sample is limited to bright galaxies with at least two faint companions. By using a permutation test, we confirm that the correlation in color between bright galaxies and their faint companions in this cluster is statistically significant with a confidence level of 98.7%. The statistical significance increases if we additionally remove non-members using the Sloan Digital Sky Survey photometric redshift information (~2.6σ and 99.3%). Our results suggest three possible scenarios: (1) vestiges of infallen groups, (2) dwarf capturing, and (3) tidal tearing of bright galaxies.

  2. Measurable relationship between bright galaxies and their faint companions in WHL J085910.0+294957, a galaxy cluster at z = 0.30: vestiges of infallen groups?

    SciTech Connect

    Lee, Joon Hyeop; Lee, Hye-Ran; Kim, Minjin; Seon, Kwang-Il; Kim, Sang Chul; Yang, Soung-Chul; Ree, Chang Hee; Lee, Jong Chul; Jeong, Hyunjin; Ko, Jongwan; Choi, Changsu

    2014-08-20

    The properties of satellite galaxies are closely related to their host galaxies in galaxy groups. In cluster environments, on the other hand, the interaction between close neighbors is known to be limited. Our goal is to examine the relationships between host and satellite galaxies in the harsh environment of a galaxy cluster. To achieve this goal, we study a galaxy cluster WHL J085910.0+294957 at z = 0.30 using deep images obtained with CQUEAN CCD camera mounted on the 2.1 m Otto Struve Telescope. After member selection based on the scaling relations of photometric and structural parameters, we investigate the relationship between bright (M{sub i} ≤ –18) galaxies and their faint (–18 < M{sub i} ≤ –15) companions. The weighted mean color of faint companion galaxies shows no significant dependence (<1σ to bootstrap uncertainties) on cluster-centric distance and local luminosity density as well as the luminosity and concentration of an adjacent bright galaxy. However, the weighted mean color shows marginal dependence (∼2.2σ) on the color of an adjacent bright galaxy when the sample is limited to bright galaxies with at least two faint companions. By using a permutation test, we confirm that the correlation in color between bright galaxies and their faint companions in this cluster is statistically significant with a confidence level of 98.7%. The statistical significance increases if we additionally remove non-members using the Sloan Digital Sky Survey photometric redshift information (∼2.6σ and 99.3%). Our results suggest three possible scenarios: (1) vestiges of infallen groups, (2) dwarf capturing, and (3) tidal tearing of bright galaxies.

  3. Polarisation properties of Milky-Way-like galaxies

    NASA Astrophysics Data System (ADS)

    Sun, X. H.; Reich, W.

    2012-07-01

    Aims: We study the polarisation properties, magnetic field strength, and synchrotron emission scale-height of Milky-Way-like galaxies in comparison with other spiral galaxies. Methods: We used our 3D-emission model of the Milky Way Galaxy for viewing the Milky Way from outside at various inclinations in the way that spiral galaxies are observed. We analysed these Milky Way maps with techniques used to obtain the strength of magnetic fields, rotation measures (RMs), and scale-heights of synchrotron emission from observations of resolved galaxies and compared the results with the Milky Way model parameter. We also simulated a large sample of unresolved Milky-Way-like galaxies to study their statistical polarisation properties. Results: When seen edge-on, the synchrotron emission from the Milky Way has an exponential scale-height of about 0.74 kpc, which is much lower than the values obtained from previous models. We find that current analysis methods overestimate the scale-height of synchrotron emission of galaxies by about 10% at an inclination of 80° and about 40% at an inclination of 70° because of contamination from the disk. The observed RMs for face-on galaxies derived from high-frequency polarisation measurements approximate to the Faraday depths (FDs) when scaled by a factor of two. For edge-on galaxies, the observed RMs are indicative of the orientation of the large-scale magnetic field, but are not closely related with the FDs. Assuming energy equipartition between the magnetic field and particles for the Milky Way results in an average magnetic-field strength that is about twice as high as the intrinsic value for a K factor of 100. The number distribution of the integrated polarisation percentages of a large sample of unresolved Milky-Way-like galaxies peaks at about 4.2% at 4.8 GHz and at about 0.8% at 1.4 GHz. Integrated polarisation angles rotated by 90° align very well with the position angles of the major axes, implying that unresolved galaxies do

  4. Chaotic inflation and supersymmetry breaking

    SciTech Connect

    Kallosh, Renata; Linde, Andrei; Rube, Tomas; Olive, Keith A.

    2011-10-15

    We investigate the recently proposed class of chaotic inflation models in supergravity with an arbitrary inflaton potential V({phi}). These models are extended to include matter fields in the visible sector and we employ a mechanism of supersymmetry breaking based on a particular phenomenological version of the KKLT mechanism (the KL model). We describe specific features of reheating in this class of models and show how one can solve the cosmological moduli and gravitino problems in this context.

  5. Magnetic field evolution in interacting galaxies

    NASA Astrophysics Data System (ADS)

    Drzazga, R. T.; Chyży, K. T.; Jurusik, W.; Wiórkiewicz, K.

    2011-09-01

    Aims: Violent gravitational interactions can change the morphologies of galaxies and, by means of merging, transform them into elliptical galaxies. We aim to investigate how they affect the evolution of galactic magnetic fields. Methods: We selected 16 systems of interacting galaxies with available VLA archive radio data at 4.86 and 1.4 GHz and compared their radio emission and estimated magnetic field strengths with their star-forming activity, far-infrared emission, and the stage of tidal interaction. Results: The estimated mean of total magnetic field strength for our sample of interacting galaxies is 14 ± 5 μG, which is larger than for the non-interacting objects. The field regularity (of 0.27 ± 0.09) is lower than in typical spirals and indicates enhanced production of random magnetic fields in the interacting objects. We find a general evolution of magnetic fields: for weak interactions the strength of magnetic field is almost constant (10-15 μG) as interaction advances, then it increases up to 2× , peaks at the nuclear coalescence (25 μG), and decreases again, down to 5-6 μG, for the post-merger remnants. The main production of magnetic fields in colliding galaxies thus terminates somewhere close to the nuclear coalescence, after which magnetic field diffuses. The magnetic field strength for whole galaxies is weakly affected by the star formation rate (SFR), while the dependence is higher for galactic centres. We show that the morphological distortions visible in the radio total and polarized emission do not depend statistically on the global or local SFRs, while they do increase (especially in the polarization) with the advance of interaction. The constructed radio-far-infrared relations for interacting and non-interacting galaxies display a similar balance between the generation of cosmic rays, magnetic fields, and the production of the thermal energy and dust radiation. Conclusions: The regular magnetic fields are much more sensitive to

  6. The Aromatic Features in Very Faint Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Wu, Ronin; Hogg, David W.; Moustakas, John

    2011-04-01

    We present optical and mid-infrared photometry of a statistically complete sample of 29 dwarf galaxies (Mr > - 15 mag) selected from the Sloan Digital Sky Survey (SDSS) spectroscopic sample and observed in the mid-infrared with Spitzer IRAC. This sample contains nearby (redshift lsim0.005) galaxies 3 mag fainter than previously studied samples. We compare our sample with other star-forming galaxies that have been observed with both IRAC and SDSS. We examine the relationship of the infrared color, [3.6]-[7.8], sensitive to polycyclic aromatic hydrocarbon (PAH) abundance and also hot dust and stellar continuum, with star formation rates (SFRs), oxygen abundances, and radiation hardness, all estimated by optical emission lines. Consistent with studies of more luminous dwarfs, we find that these dwarf galaxies show much redder [3.6]-[7.8] color than luminous galaxies with similar specific SFRs. Unlike luminous galaxies, we find that these dwarf galaxies show no significant dependence at all of the [3.6]-[7.8] color on SFR, oxygen abundance, or radiation hardness, despite the fact that the sample spans a significant range in all of these quantities. When the dwarfs in our sample are compared with more luminous dwarfs, we find that the [3.6]-[7.8] color, potentially tracing the PAH emission, depends on oxygen abundance and radiation hardness. However, these two parameters are correlated with one another as well; we break this degeneracy by looking at the PAH-oxygen abundance relation at a fixed radiation hardness and the PAH-hardness relation at a fixed oxygen abundance. This test shows that the [3.6]-[7.8] color in dwarf galaxies appears to depend more directly on oxygen abundance based on the data currently available.

  7. Galaxy 'Hunting' Made Easy

    NASA Astrophysics Data System (ADS)

    2007-09-01

    Galaxies found under the Glare of Cosmic Flashlights Astronomers using ESO's Very Large Telescope have discovered in a single pass about a dozen otherwise invisible galaxies halfway across the Universe. The discovery, based on a technique that exploits a first-class instrument, represents a major breakthrough in the field of galaxy 'hunting'. ESO PR Photo 40a/07 ESO PR Photo 40a/07 Newly Found Galaxies (SINFONI/VLT) The team of astronomers led by Nicolas Bouché have used quasars to find these galaxies. Quasars are very distant objects of extreme brilliance, which are used as cosmic beacons that reveal galaxies lying between the quasar and us. The galaxy's presence is revealed by a 'dip' in the spectrum of the quasar - caused by the absorption of light at a specific wavelength. The team used huge catalogues of quasars, the so-called SDSS and 2QZ catalogues, to select quasars with dips. The next step was then to observe the patches of the sky around these quasars in search for the foreground galaxies from the time the Universe was about 6 billion years old, almost half of its current age. "The difficulty in actually spotting and seeing these galaxies stems from the fact that the glare of the quasar is too strong compared to the dim light of the galaxy," says Bouché. This is where observations taken with SINFONI on ESO's VLT made the difference. SINFONI is an infrared 'integral field spectrometer' that simultaneously delivers very sharp images and highly resolved colour information (spectra) of an object on the sky. ESO PR Photo 32e/07 ESO PR Photo 40b/07 Chasing 'Hidden' Galaxies (Artist's Impression) With this special technique, which untangles the light of the galaxy from the quasar light, the team detected 14 galaxies out of the 20 pre-selected quasar patches of sky, a hefty 70% success rate. "This high detection rate alone is a very exciting result," says Bouché. "But, these are not just ordinary galaxies: they are most notable ones, actively forming a lot of

  8. HETDEX: Nearby Galaxies

    NASA Astrophysics Data System (ADS)

    Drory, Niv; Gebhardt, K.; Jogee, S.; Fabricius, M.; Greene, J.; HETDEX Collaboration

    2012-01-01

    The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) is a blind spectroscopic survey using the VIRUS instrument. VIRUS consists of 75 IFUs distributed across the 22-arcmin field of the upgraded 9.2-m HET. Each 50x50 arcsec IFU is made up of 448 1.5-arcsec fibers, and feeds a pair of spectrographs with a fixed bandpass of 350-550 nm and resolving power R 700. The IFUs have a fill-factor of 1/3 which will be filled-in by dithering. We cover 1/4.5 of our 300-square-degree main survey area with fibers. We reach m_AB 22.6 (21.5,20.7) at S/N 3 (5,10) per resolution element. With these limits, g 17 spiral galaxies will have S/N>3 per resolution element per fiber in the continuum to 2 effective radii, and emission line spectra to at least their optical radius. HETDEX will spatially resolve 4000 local galaxies to that limit without any pre-selection; an additional 9000 local galaxies will have spatially resolved spectroscopy beyond that limit. At g 19 we still obtain integrated galaxy spectra at S/N 10 per resolution element in the continuum. These spatially resolved absorption and emission spectra provide information on star formation, the state of the IGM, and stellar populations, as well as rotation curves for an unbiased galaxy sample unprecedented in size. Since a wealth of information about a galaxy's formation history is encoded in gradients across the galaxy, moving from single-fiber (SDSS-like) spectra to large samples of spatially resolved galaxy spectroscopy opens a new parameter space for future studies of galaxy formation.

  9. SDSS IV MaNGA: Gradients in Recent Star Formation Histories as Diagnostics for Galaxy Growth and Death

    NASA Astrophysics Data System (ADS)

    Li, Cheng; MaNGA Team

    2016-01-01

    The spatially resolved spectroscopy from MaNGA allows the radial gradients of recent star formation histories (SFH), as indicated by the 4000Å break (D4000) and the equivalent width of both Hδ absorption line and Hα emission line, to be obtained with high accuracy for a large sample of galaxies in the nearby universe. Analyses of both a dozen galaxies observed by the MaNGA prototype run (P-MaNGA) and ~700 galaxies in the current MaNGA sample have shown that the SFH gradients are useful for understanding disk growth and star formation cessation in local galaxies. We find the SFH gradient of a galaxy to strongly depend on the evolution stage of its central region. Centrally star-forming galaxies generally show very weak or no radial variations. In contrast, centrally quiescent galaxies present significant radial gradients in the sense that Dn(4000) decreases, while both EW(HδA) and EW(Hα) increase from the galactic center outward. This effect is seen mainly for high-mass galaxies with stellar mass above a few ×1010 M⊙, and depends weakly on galaxy morphology type. These results are consistent with a picture in which the cessation of star formation propagates from the center of a galaxy outward as it moves to the red sequence. In this talk I will present these analyses and discuss their implications on galaxy evolution.

  10. The abundance and colours of galaxies in high-redshift clusters in the cold dark matter cosmology

    NASA Astrophysics Data System (ADS)

    Merson, Alexander I.; Baugh, Carlton M.; Gonzalez-Perez, Violeta; Abdalla, Filipe B.; Lagos, Claudia del P.; Mei, Simona

    2016-02-01

    High-redshift galaxy clusters allow us to examine galaxy formation in extreme environments. Here we compile data for 15 z > 1 galaxy clusters to test the predictions from a state-of-the-art semi-analytical model of galaxy formation. The model gives a good match to the slope and zero-point of the cluster red sequence. The model is able to match the cluster galaxy luminosity function at faint and bright magnitudes, but underestimates the number of galaxies around the break in the cluster luminosity function. We find that simply assuming a weaker dust attenuation improves the model predictions for the cluster galaxy luminosity function, but worsens the predictions for the red sequence at bright magnitudes. Examination of the properties of the bright cluster galaxies suggests that the default dust attenuation is large due to these galaxies having large reservoirs of cold gas as well as small radii. We find that matching the luminosity function and colours of high-redshift cluster galaxies, whilst remaining consistent with local observations, poses a challenge for galaxy formation models.

  11. Lyman alpha emitting galaxies at high redshift: Direct detection of young galaxies in a young universe

    NASA Astrophysics Data System (ADS)

    Dawson, Steven Arthur

    /DEIMOS follow-up observations to candidates selected in the Large Area Lyman Alpha (LALA) survey. We conclude that if there is evolution in the Lya luminosity function over these epochs, its significance is below the statistical uncertainty of these data. This result supports the conclusion from several smaller samples of high-redshift Lya---emitters that the intergalactic medium remains largely reionized from the local universe out to z [approximate] 6.5. However, it is somewhat at odds with the pronounced drop in the cosmic star formation rate density recently measured between z ~ 3 and z ~ 6 in Lyman-break galaxies, and therefore potentially sheds light on the relationship between the two populations. (Abstract shortened by UMI.)

  12. Morphologies of ~190,000 Galaxies at z = 0-10 Revealed with HST Legacy Data. II. Evolution of Clumpy Galaxies

    NASA Astrophysics Data System (ADS)

    Shibuya, Takatoshi; Ouchi, Masami; Kubo, Mariko; Harikane, Yuichi

    2016-04-01

    We investigate the evolution of clumpy galaxies with Hubble Space Telescope (HST) samples of ˜17,000 photo-z and Lyman break galaxies at z ≃ 0-8. We detect clumpy galaxies with off-center clumps in a self-consistent algorithm that is well tested with previous study results, and we measure the number fraction of clumpy galaxies at the rest-frame UV, {f}{{clumpy}}{{UV}}. We identify an evolutionary trend of {f}{{clumpy}}{{UV}} over z ≃ 0-8 for the first time: {f}{{clumpy}}{{UV}} increases from z ≃ 8 to z ≃ 1-3 and subsequently decreases from z ≃ 1 to z ≃ 0, which follows the trend of the Madau-Lilly plot. A low average Sérsic index of n ≃ 1 is found in the underlining components of our clumpy galaxies at z ≃ 0-2, indicating that typical clumpy galaxies have disk-like surface brightness profiles. Our {f}{{clumpy}}{{UV}} values correlate with physical quantities related to star formation activities for star-forming galaxies at z ≃ 0-7. We find that clump colors tend to be red at a small galactocentric distance for massive galaxies with {log}{M}*/{M}⊙ ≳ 11. All of these results are consistent with the picture that a majority of clumps form in the violent disk instability and migrate into the galactic centers.

  13. Massive Elliptical Galaxies at High Redshift: NICMOS Imaging of z~1 Radio Galaxies

    NASA Astrophysics Data System (ADS)

    Zirm, Andrew W.; Dickinson, Mark; Dey, Arjun

    2003-03-01

    We present deep, ~1.6 μm, continuum images of 11 high-redshift (0.811galaxies observed with NICMOS on board the Hubble Space Telescope. Our NICMOS images probe the rest-frame optical light where stars are expected to dominate the galaxy luminosity. The rest-frame ultraviolet light of eight of these galaxies demonstrates the well-known ``alignment effect,'' with extended and often complex morphologies elongated along an axis close to that of the Fanaroff-Riley type II (FRII) radio source. As has been previously noted from ground-based near-infrared imaging, most of the radio galaxies have rounder, more symmetric morphologies at rest-frame optical wavelengths. Here we show the most direct evidence that in most cases the stellar hosts are normal elliptical galaxies with r1/4-law light profiles. For a few galaxies, very faint traces (less than 4% of the total H-band light) of the UV-bright aligned component are also visible in the infrared images. We derive both the effective radius and surface brightness for nine of 11 sample galaxies by fitting one- and two-dimensional surface-brightness models to them. We compare the high-redshift radio galaxies to lower redshift counterparts. We find that their sizes are similar to those of local FRII radio source hosts and are in general larger than other local galaxies. The derived host galaxy luminosities are very high and lie at the bright end of luminosity functions constructed at similar redshifts. This indicates that the high-redshift radio galaxies are likely rare, massive sources. The galaxies in our sample are also brighter than the rest-frame size-surface-brightness locus defined by the low-redshift sources. Passive evolution roughly aligns the z~1 galaxies with the low-redshift samples with a slope equal to 4.7. This value is intermediate between the canonical Kormendy relation (~3.5) and a constant luminosity line (=5). The optical host is sometimes centered on a local minimum in the rest-frame UV

  14. Sustaining Star Formation Rates in Spiral Galaxies Supernova-driven Turbulent Accretion Disk Models Applied to THINGS Galaxies

    NASA Astrophysics Data System (ADS)

    Vollmer, Bernd; Leroy, Adam K.

    2011-01-01

    Gas disks of spiral galaxies can be described as clumpy accretion disks without a coupling of viscosity to the actual thermal state of the gas. The model description of a turbulent disk consisting of emerging and spreading clumps contains free parameters, which can be constrained by observations of molecular gas, atomic gas, and the star formation rate for individual galaxies. Radial profiles of 18 nearby spiral galaxies from THINGS, HERACLES, SINGS, and GALEX data are used to compare the observed star formation efficiency, molecular fraction, and velocity dispersion to the model. The observed radially decreasing velocity dispersion can be reproduced by the model. In the framework of this model, the decrease in the inner disk is due to the stellar mass distribution which dominates the gravitational potential. Introducing a radial break in the star formation efficiency into the model improves the fits significantly. This change in the star formation regime is realized by replacing the free-fall time in the prescription of the star formation rate with the molecule formation timescale. Depending on the star formation prescription, the break radius is located near the transition region between the molecular-gas-dominated and atomic-gas-dominated parts of the galactic disk or closer to the optical radius. It is found that only less massive galaxies (log M(M ⊙) <~ 10) can balance gas loss via star formation by radial gas accretion within the disk. These galaxies can thus access their gas reservoirs with large angular momentum. On the other hand, the star formation of massive galaxies is determined by the external gas mass accretion rate from a putative spherical halo of ionized gas or from satellite accretion. In the absence of this external accretion, star formation slowly exhausts the gas within the optical disk within the star formation timescale.

  15. Searching for cosmological signatures of the Einstein equivalence principle breaking

    NASA Astrophysics Data System (ADS)

    Holanda, R. F. L.; Barros, K. N. N. O.

    2016-07-01

    Modifications of gravity generated by a multiplicative coupling of a scalar field to the electromagnetic Lagrangian lead to a breaking of the Einstein equivalence principle (EEPB), as well as to variations of fundamental constants. In these theoretical frameworks, deviations of standard values of the fine structure constant, Δ α /α =ϕ , and of the cosmic distance duality relation, DL(1 +z )-2/DA=η =1 , where DL and DA are the luminosity and angular diameter distances, respectively, are unequivocally linked. In this paper, we search for cosmological signatures of the EEPB by using angular diameter distance from galaxy clusters, obtained via their Sunyaev-Zel'dovich effect (SZE) and x-ray observations, and distance modulus of type Ia supernovae (SNe Ia). The crucial point here is that we take into account the dependence of the SZE/x-ray technique with ϕ and η . Our new results show no indication of the EEPB.

  16. THE ACS NEARBY GALAXY SURVEY TREASURY

    SciTech Connect

    Dalcanton, Julianne J.; Williams, Benjamin F.; Rosema, Keith; Gogarten, Stephanie M.; Christensen, Charlotte; Gilbert, Karoline; Hodge, Paul; Seth, Anil C.; Dolphin, Andrew; Holtzman, Jon; Skillman, Evan D.; Weisz, Daniel; Cole, Andrew; Girardi, Leo; Karachentsev, Igor D.; Olsen, Knut; Freeman, Ken; Gallart, Carme; De Jong, Roelof S. E-mail: ben@astro.washington.edu E-mail: stephanie@astro.washington.edu E-mail: fabio@astro.washington.edu E-mail: aseth@cfa.harvard.edu

    2009-07-15

    The ACS Nearby Galaxy Survey Treasury (ANGST) is a systematic survey to establish a legacy of uniform multi-color photometry of resolved stars for a volume-limited sample of nearby galaxies (D < 4 Mpc). The survey volume encompasses 69 galaxies in diverse environments, including close pairs, small and large groups, filaments, and truly isolated regions. The galaxies include a nearly complete range of morphological types spanning a factor of {approx}10{sup 4} in luminosity and star formation rate. The survey data consist of images taken with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST), supplemented with archival data and new Wide Field Planetary Camera 2 (WFPC2) imaging taken after the failure of ACS. Survey images include wide field tilings covering the full radial extent of each galaxy, and single deep pointings in uncrowded regions of the most massive galaxies in the volume. The new wide field imaging in ANGST reaches median 50% completenesses of m {sub F475W} = 28.0 mag, m {sub F606W} = 27.3 mag, and m {sub F814W} = 27.3 mag, several magnitudes below the tip of the red giant branch (TRGB). The deep fields reach magnitudes sufficient to fully resolve the structure in the red clump. The resulting photometric catalogs are publicly accessible and contain over 34 million photometric measurements of >14 million stars. In this paper we present the details of the sample selection, imaging, data reduction, and the resulting photometric catalogs, along with an analysis of the photometric uncertainties (systematic and random), for both ACS and WFPC2 imaging. We also present uniformly derived relative distances measured from the apparent magnitude of the TRGB.

  17. Dynamics of Nuclear Regions of Galaxies

    NASA Technical Reports Server (NTRS)

    Miller, Richard H.

    1996-01-01

    Current research carried out with the help of the ASEE-NASA Summer Faculty Program, at NASA-Ames, is concentrated on the dynamics of nuclear regions of galaxies. From a dynamical point of view a galaxy is a collection of around 10(sup 11) stars like our Sun, each of which moves in the summed gravitational field of all the remaining stars. Thus galaxy dynamics becomes a self-consistent n-body problem with forces given by Newtonian gravitation. Strong nonlinearity in the gravitational force and the inherent nonlinearity of self-consistent problems both argue for a numerical approach. The technique of numerical experiments consis of constructing an environment in the computer that is as close as possible to the physical conditions in a real galaxy and then carrying out experiments much like laboratory experiments in physics or engineering, in this environment. Computationally, an experiment is an initial value problem, and a good deal of thought and effort goes into the design of the starting conditions that serve as initial values. Experiments are run at Ames because all the 'equipment' is in place-the programs, the necessary computational power, and good facilities for post-run analysis. Our goal for this research program is to study the nuclear regions in detail and this means replacing most of the galaxy by a suitable boundary condition to allow the full capability of numerical experiments to be brought to bear on a small region perhaps 1/1000 of the linear dimensions of an entire galaxy. This is an extremely delicate numerical problem, one in which some small feature overlook, can easily lead to a collapse or blow-up of the entire system. All particles attract each other in gravitational problems, and the 1/r(sup 2) force is: (1) nonlinear; (2) strong at short range; (3) long-range, and (4) unscreened at any distance.

  18. Investigating galaxy-filament alignments in hydrodynamic simulations using density ridges

    NASA Astrophysics Data System (ADS)

    Chen, Yen-Chi; Ho, Shirley; Tenneti, Ananth; Mandelbaum, Rachel; Croft, Rupert; DiMatteo, Tiziana; Freeman, Peter E.; Genovese, Christopher R.; Wasserman, Larry

    2015-12-01

    In this paper, we study the filamentary structures and the galaxy alignment along filaments at redshift z = 0.06 in the MassiveBlack-II simulation, a state-of-the-art, high-resolution hydrodynamical cosmological simulation which includes stellar and AGN feedback in a volume of (100 Mpc h-1)3. The filaments are constructed using the subspace constrained mean shift (SCMS; Ozertem & Erdogmus; Chen et al.). First, we show that reconstructed filaments using galaxies and reconstructed filaments using dark matter particles are similar to each other; over 50 per cent of the points on the galaxy filaments have a corresponding point on the dark matter filaments within distance 0.13 Mpc h-1 (and vice versa) and this distance is even smaller at high-density regions. Second, we observe the alignment of the major principal axis of a galaxy with respect to the orientation of its nearest filament and detect a 2.5 Mpc h-1 critical radius for filament's influence on the alignment when the subhalo mass of this galaxy is between 109 M⊙ h-1 and 1012 M⊙ h-1. Moreover, we find the alignment signal to increase significantly with the subhalo mass. Third, when a galaxy is close to filaments (less than 0.25 Mpc h-1), the galaxy alignment towards the nearest galaxy group is positively correlated with the galaxy subhalo mass. Finally, we find that galaxies close to filaments or groups tend to be rounder than those away from filaments or groups.

  19. Spiral Galaxies Stripped Bare

    NASA Astrophysics Data System (ADS)

    2010-10-01

    Six spectacular spiral galaxies are seen in a clear new light in images from ESO's Very Large Telescope (VLT) at the Paranal Observatory in Chile. The pictures were taken in infrared light, using the impressive power of the HAWK-I camera, and will help astronomers understand how the remarkable spiral patterns in galaxies form and evolve. HAWK-I [1] is one of the newest and most powerful cameras on ESO's Very Large Telescope (VLT). It is sensitive to infrared light, which means that much of the obscuring dust in the galaxies' spiral arms becomes transparent to its detectors. Compared to the earlier, and still much-used, VLT infrared camera ISAAC, HAWK-I has sixteen times as many pixels to cover a much larger area of sky in one shot and, by using newer technology than ISAAC, it has a greater sensitivity to faint infrared radiation [2]. Because HAWK-I can study galaxies stripped bare of the confusing effects of dust and glowing gas it is ideal for studying the vast numbers of stars that make up spiral arms. The six galaxies are part of a study of spiral structure led by Preben Grosbøl at ESO. These data were acquired to help understand the complex and subtle ways in which the stars in these systems form into such perfect spiral patterns. The first image shows NGC 5247, a spiral galaxy dominated by two huge arms, located 60-70 million light-years away. The galaxy lies face-on towards Earth, thus providing an excellent view of its pinwheel structure. It lies in the zodiacal constellation of Virgo (the Maiden). The galaxy in the second image is Messier 100, also known as NGC 4321, which was discovered in the 18th century. It is a fine example of a "grand design" spiral galaxy - a class of galaxies with very prominent and well-defined spiral arms. About 55 million light-years from Earth, Messier 100 is part of the Virgo Cluster of galaxies and lies in the constellation of Coma Berenices (Berenice's Hair, named after the ancient Egyptian queen Berenice II). The third

  20. Topics in Galaxy Evolution: Early Star Formation and Quenching

    NASA Astrophysics Data System (ADS)

    Goncalves, Thiago Signorini

    In this thesis, we present three projects designed to shed light on yet unanswered questions on galaxy formation and evolution. The first two concern a sample of UV-bright starburst galaxies in the local universe (z ˜0.2). These objects are remarkably similar to star-forming galaxies that were abundant at high redshifts (2 < z < 3)---the Lyman break galaxies---and can help explain the very distinctive properties observed at such epochs. Thus, these galaxies are denominated Lyman break analogs, or LBAs. First, we describe a survey of kinematics of the nebular gas in such objects, and how that can help explain the formation process, including gas assembly, in these starbursts. We show strong evidence that the gas kinematics resemble those observed at high redshifts. However, by artificially manipulating our observations to mimic our objects at greater distances, we show how low resolution and signal-to-noise ratios can lead to erroneous conclusions, in particular when attempting to diagnose mergers as the origin of the starburst. Then, we present results from a pilot survey to study the cold, molecular gas reservoir in such objects. Again, we show that the observed properties are analogous to those observed at high redshift, in particular with respect to baryonic gas fractions in the galaxy, higher than normally found in low-extinction objects in the local universe. Furthermore, we show how gas surface density and star-formation surface density follow the same relation as local galaxies, albeit at much higher values. Finally, we discuss an observational project designed to measure the mass flux density from the blue sequence to the red sequence across the so-called green valley. We obtain the deepest spectra ever observed of green valley galaxies at intermediate redshifts (z˜0.8) in order to measure spectral features from which we can measure the star formation histories of individual galaxies. We measure a mass flux ratio that is higher than observed in the local

  1. LOW-REDSHIFT Lyalpha SELECTED GALAXIES FROM GALEX SPECTROSCOPY: A COMPARISON WITH BOTH UV-CONTINUUM SELECTED GALAXIES AND HIGH-REDSHIFT Lyalpha EMITTERS

    SciTech Connect

    Cowie, Lennox L.; Barger, Amy J.; Hu, Esther M. E-mail: barger@astro.wisc.ed

    2010-03-10

    We construct a sample of low-redshift Lyalpha emission-line selected sources from Galaxy Evolution Explorer (GALEX) grism spectroscopy of nine deep fields to study the role of Lyalpha emission in galaxy populations with cosmic time. Our final sample consists of 119 (141) sources selected in the redshift interval z = 0.195-0.44 (z = 0.65-1.25) from the FUV (NUV) channel. We classify the Lyalpha sources as active galactic nuclei (AGNs) if high-ionization emission lines are present in their UV spectra and as possible star-forming galaxies otherwise. We classify additional sources as AGNs using line widths for our Lyalpha emitter (LAE) analysis. These classifications are broadly supported by comparisons with X-ray and optical spectroscopic observations, though the optical spectroscopy identifies a small number of additional AGNs. Defining the GALEX LAE sample in the same way as high-redshift LAE samples, we show that LAEs constitute only about 5% of NUV-continuum selected galaxies at z {approx} 0.3. We also show that they are less common at z {approx} 0.3 than they are at z {approx} 3. We find that the z {approx} 0.3 optically confirmed Lyalpha galaxies lie below the metallicity-luminosity relation of the z {approx} 0.3 NUV-continuum selected galaxies but have similar Halpha velocity widths at similar luminosities, suggesting that they also lie below the metallicity-mass relation of the NUV-continuum selected galaxies. We show that, on average, the Lyalpha galaxies have bluer colors, lower extinctions as measured from the Balmer line ratios, and more compact morphologies than the NUV-continuum selected galaxies. Finally, we confirm that the z {approx} 2 Lyman break galaxies have relatively low metallicities for their luminosities, and we find that they lie in the same metallicity range as the z {approx} 0.3 Lyalpha galaxies.

  2. Chandra Observations of Starburst Galaxies

    NASA Technical Reports Server (NTRS)

    Prestwich, Andrea; Lavoie, Anthony R. (Technical Monitor)

    2000-01-01

    We present early X-ray results from Chandra for two starburst galaxies, M82 and NGC3256, obtained using AXAF CCD Imaging Spectrometer (ACIS-I) and the HRC. For M82 the arcsecond spatial resolution enables us to separate the point source component from the extended emission for the first time. Astrometry reveals that most of the X-ray sources are not coincident with the family of compact radio sources believed to be Super Nova Remnants (SNRs). In addition, based on three epoch Chandra observations, several of the X-ray sources are clearly variable indicating that they are binaries. When we deconvolve the extended and point source components detected in the hard X-ray band, we find that 50 percent arises from the extended component. This fact, together with its morphology, constrains the various models proposed to explain the hard X-ray emission. For NGC3256 we resolve two closely separated nuclei. These new data support a pure starburst origin for the total X-ray emission rather than a composite AGN/starburst, thereby making NGC3256 one of the most X-ray luminous starburst galaxies known.

  3. The First Galaxies

    NASA Astrophysics Data System (ADS)

    Bromm, Volker

    2009-03-01

    An important open frontier in astrophysics is to understand how the first sources of light, the first stars and galaxies, ended the cosmic dark ages at redshifts z ≃ 15 - 20. Their formation signaled the transition from the simple initial state of the universe to one of ever increasing complexity. We here review recent progress in understanding the assembly process of the first galaxies with numerical simulations, starting with cosmological initial conditions and modelling the detailed physics of star formation. The key drivers in building up the primordial galaxies are the feedback effects from the first stars, due to their input of radiation and of heavy chemical elements in the wake of supernova explosions. In addition, the conditions inside the first galaxies are governed by the gravitationally-driven turbulence generated during the virialization of the dark matter host halo. Our theoretical predictions will be tested with upcoming near-infrared observatories, such as the James Webb Space Telecope, in the decade ahead.

  4. Galaxy Messier 51

    NASA Technical Reports Server (NTRS)

    2003-01-01

    NASA's Galaxy Evolution Explorer took this image of the spiral galaxy Messier 51 on June 19 and 20, 2003. Messier 51 is located 27 million light-years from Earth. Due to a lack of star formation, the companion galaxy in the top of the picture is barely visible as a near ultraviolet object.

    The Galaxy Evolution Explorer mission is led by the California Institute of Technology, which is also responsible for the science operations and data analysis. NASA's Jet Propulsion Laboratory, Pasadena, Calif., a division of Caltech, manages the mission and built the science instrument. The mission was developed under NASA's Explorers Program, managed by the Goddard Space Flight Center, Greenbelt, Md. The mission's international partners include South Korea and France.

  5. Galaxy NGC5398

    NASA Technical Reports Server (NTRS)

    2003-01-01

    This is an ultraviolet color image of the galaxy NGC5398 taken by NASA's Galaxy Evolution Explorer on June 7, 2003. NGC5398 is a barred spiral galaxy located 60 million light-years from Earth. The star formation is concentrated in the two bright regions of the image.

    The Galaxy Evolution Explorer mission is led by the California Institute of Technology, which is also responsible for the science operations and data analysis. NASA's Jet Propulsion Laboratory, Pasadena, Calif., a division of Caltech, manages the mission and built the science instrument. The mission was developed under NASA's Explorers Program, managed by the Goddard Space Flight Center, Greenbelt, Md. The mission's international partners include South Korea and France.

  6. Galaxy M101

    NASA Technical Reports Server (NTRS)

    2003-01-01

    This three-color image of galaxy M101 was taken by NASA's Galaxy Evolution Explorer on June 20, 2003. The far ultraviolet emissions are shown in blue, the near ultraviolet emissions are green, and the red emissions, which were taken from NASA's Digital Sky Survey, represent visible light. This image combines short, medium, and long 'exposure' pictures to best display the evolution of star formation in a spiral galaxy.

    The Galaxy Evolution Explorer mission is led by the California Institute of Technology, which is also responsible for the science operations and data analysis. NASA's Jet Propulsion Laboratory, Pasadena, Calif., a division of Caltech, manages the mission and built the science instrument. The mission was developed under NASA's Explorers Program, managed by the Goddard Space Flight Center, Greenbelt, Md. The mission's international partners include South Korea and France.

  7. Ripples in disk galaxies

    NASA Astrophysics Data System (ADS)

    Schweizer, Francois; Seitzer, Patrick

    1988-05-01

    The authors present evidence that ripples ("shells") occur not only in ellipticals, as hitherto believed, but also in disk galaxies of Hubble types S0, S0/Sa, and Sa, and probably even in the Sbc galaxy NGC 3310. This evidence includes the discovery of ripples in the northern disk galaxies NGC 3032, 3619, 4382, 5548 (a Seyfert), and 5739, and in the "diskless S0" NGC 7600. It is argued that these ripples cannot usually have resulted form transient spiral waves or other forced vibrations in the existing disks, but instead consist of extraneous sheet-like matter. The frequent presence of major disk-shaped companions suggests that ripple material may be acquired not only through wholesale mergers, but also through mass transfer from neighbor galaxies.

  8. PEARS Emission Line Galaxies

    NASA Technical Reports Server (NTRS)

    Pirzkal, Nor; Rothberg, Barry; Ly, Chun; Rhoads, James E.; Malhotra, Sangeeta; Grogin, Norman A.; Dahlen, Tomas; Meurer, Gerhardt R.; Walsh, Jeremy; Hathi, Nimish P.; Cohen, Seth; Belini, Andrea; Holwerda, Benne W.; Straughn, Amber; Mechtley, Matthew

    2012-01-01

    We present a full analysis of the Probing Evolution And Reionization Spectroscopically (PEARS) slitless grism spectroscopic data obtained vl'ith the Advanced Camera for Surveys on HST. PEARS covers fields within both the Great Observatories Origins Deep Survey (GOODS) North and South fields, making it ideal as a random surveY of galaxies, as well as the availability of a wide variety of ancillary observations to support the spectroscopic results. Using the PEARS data we are able to identify star forming galaxies within the redshift volume 0 < z < 1.5. Star forming regions in the PEARS survey are pinpointed independently of the host galaxy. This method allOW8 us to detect the presence of multiple emission line regions (ELRs) within a single galaxy. 1162 [OII], [OIII] and/or H-alpha emission lines have been identified in the PEARS sample of approx 906 galaxies down to a limiting flux of approx 10 - 18 erg/s/sq cm . The ELRs have also been compared to the properties of the host galaxy, including morphology, luminosity, and mass. From this analysis we find three key results: 1) The computed line luminosities show evidence of a flattening in the luminosity function with increasing redshift; 2) The star forming systems show evidence of disturbed morphologies, with star formation occurring predominantly within one effective (half-light) radius. However, the morphologies show no correlation with host stellar mass; and 3) The number density of star forming galaxies with M(*) >= 10(exp 9) Solar M decreases by an order of magnitude at z<=0.5 relative to the number at 0.5 < z < 0.9 in support of the argument for galaxy downsizing.

  9. Abundance of field galaxies

    NASA Astrophysics Data System (ADS)

    Klypin, Anatoly; Karachentsev, Igor; Makarov, Dmitry; Nasonova, Olga

    2015-12-01

    We present new measurements of the abundance of galaxies with a given circular velocity in the Local Volume: a region centred on the Milky Way Galaxy and extending to distance ˜10 Mpc. The sample of ˜750 mostly dwarf galaxies provides a unique opportunity to study the abundance and properties of galaxies down to absolute magnitudes MB ≈ -10 and virial masses M_vir= 109{ M_{⊙}}. We find that the standard Λ cold dark matter (ΛCDM) model gives remarkably accurate estimates for the velocity function of galaxies with circular velocities V ≳ 70 kms-1 and corresponding virial masses M_vir≳ 5× 10^{10}{ M_{⊙}}, but it badly fails by overpredicting ˜5 times the abundance of large dwarfs with velocities V = 30-40 kms-1. The warm dark matter (WDM) models cannot explain the data either, regardless of mass of WDM particle. Just as in previous observational studies, we find a shallow asymptotic slope dN/dlog V ∝ Vα, α ≈ -1 of the velocity function, which is inconsistent with the standard ΛCDM model that predicts the slope α = -3. Though reminiscent to the known overabundance of satellite problem, the overabundance of field galaxies is a much more difficult problem. For the standard ΛCDM model to survive, in the 10 Mpc radius of the Milky Way there should be 1000 not yet detected galaxies with virial mass M_vir≈ 10^{10}{ M_{⊙}}, extremely low surface brightness and no detectable H I gas. So far none of this type of galaxies have been discovered.

  10. Chandra Galaxy Atlas

    NASA Astrophysics Data System (ADS)

    Kim, Dong-Woo; Anderson, Craig; Burke, Doug; Fabbiano, Giuseppina; Fruscione, Antonella; Lauer, Jennifer L.; McCollough, Michael L.; Morgan, Doug; Mossman, Amy; O'Sullivan, Ewan; Paggi, Alessandro; Trinchieri, Ginevra

    2016-01-01

    We present the new results from the Chandra Galaxy Atlas prpject. We have systematically analyzed the archival Chandra data of 50 early type galaxies to study their hot ISM. Taking full advantage of the Chandra capabilities, we produced spatially resolved data products with additional spectral information. We will make these products publicly available and use them for our focused science goals, e.g., gas morphology, scaling relation, X-ray based mass profile, circum-nuclear gas.

  11. Galaxy Formation and Evolution

    NASA Astrophysics Data System (ADS)

    Nagamine, Kentaro; Reddy, Naveen; Daddi, Emanuele; Sargent, Mark T.

    2016-07-01

    In this chapter, we discuss the current status of observational and computational studies on galaxy formation and evolution. In particular, a joint analysis of star-formation rates (SFRs), stellar masses, and metallicities of galaxies throughout cosmic time can shed light on the processes by which galaxies build up their stellar mass and enrich the environment with heavy elements. Comparison of such observations and the results of numerical simulations can give us insights on the physical importance of various feedback effects by supernovae and active galactic nuclei. In Sect. 1, we first discuss the primary methods used to deduce the SFRs, stellar masses, and (primarily) gas-phase metallicities in high-redshift galaxies. Then, we show how these quantities are related to each other and evolve with time. In Sect. 2, we further examine the distribution of SFRs in galaxies following the `Main Sequence' paradigm. We show how the so-called `starbursts' display higher specific SFRs and SF efficiencies by an order of magnitude. We use this to devise a simple description of the evolution of the star-forming galaxy population since z ˜3 that can successfully reproduce some of the observed statistics in the infrared (IR) wavelength. We also discuss the properties of molecular gas. In Sect. 3, we highlight some of the recent studies of high-redshift galaxy formation using cosmological hydrodynamic simulations. We discuss the physical properties of simulated galaxies such as luminosity function and escape fraction of ionizing photons, which are important statistics for reionization of the Universe. In particular the escape fraction of ionizing photons has large uncertainties, and studying gamma-ray bursts (which is the main topic of this conference) can also set observational constraints on this uncertain physical parameter as well as cosmic star formation rate density.

  12. Life in the Galaxy?

    NASA Astrophysics Data System (ADS)

    Shostak, G. S.

    The arguments for and against the SETI (Search for Extra Terrestrial Intelligence) program are discussed. Based on apparently reasonable assumptions regarding the number of civilizations likely to exist in the Galaxy, it seems that ten million years would be sufficient time for an ambitious group of aliens to colonize the Galaxy; since no concrete evidence of aliens has turned up, the assumptions have to be reconsidered. The views of Sagan, Hart, Drake and a number of other researchers are noted.

  13. The environment of barred galaxies in the low-redshift universe

    SciTech Connect

    Lin, Ye; Sodi, Bernardo Cervantes; Li, Cheng; Wang, Lixin; Wang, Enci E-mail: leech@shao.ac.cn

    2014-12-01

    We present a study of the environment of barred galaxies using a volume-limited sample of over 30,000 galaxies drawn from the Sloan Digital Sky Survey. We use four different statistics to quantify the environment: the projected two-point cross-correlation function, the background-subtracted number count of neighbor galaxies, the overdensity of the local environment, and the membership of our galaxies to galaxy groups to segregate central and satellite systems. For barred galaxies as a whole, we find a very weak difference in all the quantities compared to unbarred galaxies of the control sample. When we split our sample into early- and late-type galaxies, we see a weak but significant trend for early-type galaxies with a bar to be more strongly clustered on scales from a few 100 kpc to 1 Mpc when compared to unbarred early-type galaxies. This indicates that the presence of a bar in early-type galaxies depends on the location within their host dark matter halos. This is confirmed by the group catalog in the sense that for early-types, the fraction of central galaxies is smaller if they have a bar. For late-type galaxies, we find fewer neighbors within ∼50 kpc around the barred galaxies when compared to unbarred galaxies from the control sample, suggesting that tidal forces from close companions suppress the formation/growth of bars. Finally, we find no obvious correlation between overdensity and the bars in our sample, showing that galactic bars are not obviously linked to the large-scale structure of the universe.

  14. GALAXIES IN X-RAY GROUPS. III. SATELLITE COLOR AND MORPHOLOGY TRANSFORMATIONS

    SciTech Connect

    George, Matthew R.; Ma, Chung-Pei; Bundy, Kevin; Leauthaud, Alexie; Vulcani, Benedetta; Tinker, Jeremy; Wechsler, Risa H.; Finoguenov, Alexis

    2013-06-20

    While the star formation rates and morphologies of galaxies have long been known to correlate with their local environment, the process by which these correlations are generated is not well understood. Galaxy groups are thought to play an important role in shaping the physical properties of galaxies before entering massive clusters at low redshift, and transformations of satellite galaxies likely dominate the buildup of local environmental correlations. To illuminate the physical processes that shape galaxy evolution in dense environments, we study a sample of 116 X-ray selected galaxy groups at z = 0.2-1 with halo masses of 10{sup 13}-10{sup 14} M{sub Sun} and centroids determined with weak lensing. We analyze morphologies based on Hubble Space Telescope imaging and colors determined from 31 photometric bands for a stellar mass-limited population of 923 satellite galaxies and a comparison sample of 16,644 field galaxies. Controlling for variations in stellar mass across environments, we find significant trends in the colors and morphologies of satellite galaxies with group-centric distance and across cosmic time. Specifically at low stellar mass (log (M{sub *}/M{sub Sun }) = 9.8-10.3), the fraction of disk-dominated star-forming galaxies declines from >50% among field galaxies to <20% among satellites near the centers of groups. This decline is accompanied by a rise in quenched galaxies with intermediate bulge+disk morphologies, and only a weak increase in red bulge-dominated systems. These results show that both color and morphology are influenced by a galaxy's location within a group halo. We suggest that strangulation and disk fading alone are insufficient to explain the observed morphological dependence on environment, and that galaxy mergers or close tidal encounters must play a role in building up the population of quenched galaxies with bulges seen in dense environments at low redshift.

  15. Strongly Time-Variable Ultra-Violet Metal Line Emission from the Circum-Galactic Medium of High-Redshift Galaxies

    NASA Astrophysics Data System (ADS)

    Sravan, Niharika; Faucher-Giguère, Claude-André; van de Voort, Freeke; Kereš, Dušan; Muratov, Alexander L.; Hopkins, Philip F.; Feldmann, Robert; Quataert, Eliot; Murray, Norman

    2016-08-01

    We use cosmological simulations from the Feedback In Realistic Environments (FIRE) project, which implement a comprehensive set of stellar feedback processes, to study ultra-violet (UV) metal line emission from the circum-galactic medium of high-redshift (z = 2 - 4) galaxies. Our simulations cover the halo mass range Mh ˜ 2 × 1011 - 8.5 × 1012 M⊙ at z = 2, representative of Lyman break galaxies. Of the transitions we analyze, the low-ionization C III (977 Å) and Si III (1207 Å) emission lines are the most luminous, with C IV (1548 Å) and Si IV (1394 Å) also showing interesting spatially-extended structures. The more massive halos are on average more UV-luminous. The UV metal line emission from galactic halos in our simulations arises primarily from collisionally ionized gas and is strongly time variable, with peak-to-trough variations of up to ˜2 dex. The peaks of UV metal line luminosity correspond closely to massive and energetic mass outflow events, which follow bursts of star formation and inject sufficient energy into galactic halos to power the metal line emission. The strong time variability implies that even some relatively low-mass halos may be detectable. Conversely, flux-limited samples will be biased toward halos whose central galaxy has recently experienced a strong burst of star formation. Spatially-extended UV metal line emission around high-redshift galaxies should be detectable by current and upcoming integral field spectrographs such as the Multi Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope and Keck Cosmic Web Imager (KCWI).

  16. A giant stream of metal-rich stars in the halo of the galaxy M31.

    PubMed

    Ibata, R; Irwin, M; Lewis, G; Ferguson, A M; Tanvir, N

    2001-07-01

    Recent observations have revealed streams of gas and stars in the halo of the Milky Way that are the debris from interactions between our Galaxy and some of its dwarf companion galaxies; the Sagittarius dwarf galaxy and the Magellanic clouds. Analysis of the material has shown that much of the halo is made up of cannibalized satellite galaxies, and that dark matter is distributed nearly spherically in the Milky Way. It remains unclear, however, whether cannibalized substructures are as common in the haloes of galaxies as predicted by galaxy-formation theory. Here we report the discovery of a giant stream of metal-rich stars within the halo of the nearest large galaxy, M31 (the Andromeda galaxy). The source of this stream could be the dwarf galaxies M32 and NGC205, which are close companions of M31 and which may have lost a substantial number of stars owing to tidal interactions. The results demonstrate that the epoch of galaxy building still continues, albeit at a modest rate, and that tidal streams may be a generic feature of galaxy haloes.

  17. Morphological evolution of galaxies

    NASA Astrophysics Data System (ADS)

    Gardner, Jonathan P.; Heap, Sara R.; Malumuth, Eliot M.; Hill, Robert S.; Smith, Eric P.

    1997-05-01

    Recent studies of the Hubble Deep Field (Abraham et al. 1996) [1] and Medium Deep Survey (Driver, Windhorst & Griffiths 1995) [6] find that the frequency of irregular/peculiar/merger systems rises with increasing redshift. However, this finding must be carefully interpreted in light of UV images of low-redshift galaxies obtained by the Ultraviolet Imaging Telescope (Stecher et al. 1992) [9]. These UV images imply that K-correction effects may be at least partially responsible for the apparent increase in Irr galaxies with redshift. To assess the degree to which there is an overabundance of Irregular galaxies (relative to the present epoch), we must understand the degree to which the K-correction biases morphological studies. We demonstrate the importance of the morphological K-correction to the classification schemes used in the HDF. We find that high-redshift spiral galaxies are misclassified as Irr galaxies, while Elliptical/S0 galaxies, should not be affected substantially. We have been granted 40 orbits in Cycle 7 with STIS to place these conclusions on a statistical basis.

  18. Surface tension effects in wave breaking

    NASA Astrophysics Data System (ADS)

    Deike, Luc; Melville, W. K.; Popinet, Stephane

    2014-11-01

    We present a numerical study of wave breaking by solving the full Navier-Stokes equations for two-phase air-water flows using the solver Gerris. We describe a parametric study of the influence of capillary effects on wave breaking using two-dimensional simulations. The onset of wave breaking as a function of the Bond number, Bo, and the initial wave steepness S is determined and a phase diagram in terms of (S,Bo) is presented that distinguishes between non-breaking gravity waves, parasitic capillaries on a gravity wave, spilling breakers and plunging breakers. The wave energy dissipation is computed for each wave regime and is found to be in good agreement with experimental results for breaking waves. Moreover, the enhanced dissipation just by parasitic capillaries is comparable to the dissipation due to breaking. Extending the simulations to three dimensions permits studies of the generation and statistics of bubbles and spray during breaking.

  19. Symmetry breaking in neural nets.

    PubMed

    Pessa, E

    1988-01-01

    In this paper two well-known homogeneous models of neural nets undergoing symmetry-breaking transitions are studied in order to see if, after the transition, there is the appearance of Goldstone modes. These have been found only in an approximate way; there are indications, however, that they can play a prominent role when the tissue is subjected to external inputs, constraining it to be slaved to the characteristics of those. This circumstance should be essential in explaining how a structured net can store complex inputs and give subsequently ordered outputs.

  20. Leaders break ground for INFINITY

    NASA Technical Reports Server (NTRS)

    2008-01-01

    Community leaders from Mississippi and Louisiana break ground for the new INFINITY at NASA Stennis Space Center facility during a Nov. 20 ceremony. Groundbreaking participants included (l to r): Gottfried Construction representative John Smith, Mississippi Highway Commissioner Wayne Brown, INFINITY board member and Apollo 13 astronaut Fred Haise, Stennis Director Gene Goldman, Studio South representative David Hardy, Leo Seal Jr. family representative Virginia Wagner, Hancock Bank President George Schloegel, Mississippi Rep. J.P. Compretta, Mississippi Band of Choctaw Indians representative Charlie Benn and Louisiana Sen. A.G. Crowe.

  1. Give Young Scientists a Break

    SciTech Connect

    Wiley, H. S.

    2009-11-01

    There has been much concern about the impact of tight funding on the careers of young scientists. When only a small percentage of grants are approved, even the smallest problem or error with an application can push it out of the funding range. Unfortunately, the relative lack of grant writing skills by new investigators often has this effect. To avoid a situation where only experienced investigators with polished writing skills are funded, the National Institutes of Health has instituted a more generous ranking scale for new investigators. Not surprisingly, some senior investigators have protested, calling it reverse discrimination. I say that their anger is misplaced. New investigators do deserve a break.

  2. History of electroweak symmetry breaking

    NASA Astrophysics Data System (ADS)

    Kibble, T. W. B.

    2015-07-01

    In this talk, I recall the history of the development of the unified electroweak theory, incorporating the symmetry-breaking Higgs mechanism, as I saw it from my standpoint as a member of Abdus Salam's group at Imperial College. I start by describing the state of physics in the years after the Second World War, explain how the goal of a unified gauge theory of weak and electromagnetic interactions emerged, the obstacles encountered, in particular the Goldstone theorem, and how they were overcome, followed by a brief account of more recent history, culminating in the historic discovery of the Higgs boson in 2012.

  3. Unparticles and electroweak symmetry breaking

    SciTech Connect

    Lee, Jong-Phil

    2008-11-23

    We investigate a scalar potential inspired by the unparticle sector for the electroweak symmetry breaking. The scalar potential contains the interaction between the standard model fields and unparticle sector. It is described by the non-integral power of fields that originates from the nontrivial scaling dimension of the unparticle operator. It is found that the electroweak symmetry is broken at tree level when the interaction is turned on. The scale invariance of unparticle sector is also broken simultaneously, resulting in a physical Higgs and a new lighter scalar particle.

  4. Directional excitation without breaking reciprocity

    NASA Astrophysics Data System (ADS)

    Ramezani, Hamidreza; Dubois, Marc; Wang, Yuan; Shen, Y. Ron; Zhang, Xiang

    2016-09-01

    We propose a mechanism for directional excitation without breaking reciprocity. This is achieved by embedding an impedance matched parity-time symmetric potential in a three-port system. The amplitude distribution within the gain and loss regions is strongly influenced by the direction of the incoming field. Consequently, the excitation of the third port is contingent on the direction of incidence while transmission in the main channel is immune. Our design improves the four-port directional coupler scheme, as there is no need to implement an anechoic termination to one of the ports.

  5. Inflationary implications of supersymmetry breaking

    SciTech Connect

    Borghese, Andrea; Roest, Diederik; Zavala, Ivonne

    2013-07-23

    We discuss a general bound on the possibility to realise inflation in any minimal supergravity with F-terms. The derivation crucially depends on the sGoldstini, the scalar field directions that are singled out by spontaneous supersymmetry breaking. The resulting bound involves both slow-roll parameters and the geometry of the Kähler manifold of the chiral scalars. We analyse the inflationary implications of this bound, and in particular discuss to what extent the requirements of single field and slow-roll can both be met in F-term inflation.

  6. Galaxy Evolution Explorer Spies Band of Stars

    NASA Technical Reports Server (NTRS)

    2007-01-01

    The Galaxy Evolution Explorer's ultraviolet eyes have captured a globular star cluster, called NGC 362, in our own Milky Way galaxy. In this new image, the cluster appears next to stars from a more distant neighboring galaxy, known as the Small Magellanic Cloud.

    Globular clusters are densely packed bunches of old stars scattered in galaxies throughout the universe. NGC 362, located 30,000 light-years away, can be spotted as the dense collection of mostly yellow-tinted stars surrounding a large white-yellow spot toward the top-right of this image. The white spot is actually the core of the cluster, which is made up of stars so closely packed together that the Galaxy Evolution Explorer cannot see them individually.

    The light blue dots surrounding the cluster core are called extreme horizontal branch stars. These stars used to be very similar to our sun and are nearing the end of their lives. They are very hot, with temperatures reaching up to about four times that of the surface of our sun (25,000 Kelvin or 45,500 degrees Fahrenheit).

    A star like our sun spends most of its life fusing hydrogen atoms in its core into helium. When the star runs out of hydrogen in its core, its outer envelope will expand. The star then becomes a red giant, which burns hydrogen in a shell surrounding its inner core. Throughout its life as a red giant, the star loses a lot of mass, then begins to burn helium at its core. Some stars will have lost so much mass at the end of this process, up to 85 percent of their envelopes, that most of the envelope is gone. What is left is a very hot ultraviolet-bright core, or extreme horizontal branch star.

    Blue dots scattered throughout the image are hot, young stars in the Small Magellanic Cloud, a satellite galaxy of the Milky Way located approximately 200,000 light-years away. The stars in this galaxy are much brighter intrinsically than extreme horizontal branch stars, but they appear just as bright because they are farther

  7. Transformations of galaxies - III. Encounter dynamics and tidal response as functions of galaxy structure

    NASA Astrophysics Data System (ADS)

    Barnes, Joshua E.

    2016-01-01

    Tidal interactions between disc galaxies depend on galaxy structure, but the details of this relationship are incompletely understood. I have constructed a three-parameter grid of bulge/disc/halo models broadly consistent with Λ cold dark matter, and simulated an extensive series of encounters using these models. Halo mass and extent strongly influence the dynamics of orbit evolution. In close encounters, the transfer of angular momentum mediated by the dynamical response of massive, extended haloes can reverse the direction of orbital motion of the central galaxies after their first passage. Tidal response is strongly correlated with the ratio ve/vc of escape to circular velocity within the participating discs. Moreover, the same ratio also correlates with the rate at which tidal tails are reaccreted by their galaxies of origin; consequently, merger remnants with `twin tails', such as NGC 7252, may prove hard to reproduce unless (ve/vc)2 ≲ 5.5. The tidal morphology of an interacting system can provide useful constraints on progenitor structure. In particular, encounters in which halo dynamics reverses orbital motion exhibit a distinctive morphology which may be recognized observationally. Detailed models attempting to reproduce observations of interacting galaxies should explore the likely range of progenitor structures along with other encounter parameters.

  8. How does a thermal binary crystal break under shear?

    PubMed

    Horn, Tobias; Löwen, Hartmut

    2014-12-14

    When exposed to strong shearing, the particles in a crystal will rearrange and ultimately, the crystal will break by forming large nonaffine defects. Even for the initial stage of this process, only little effort has been devoted to the understanding of the breaking process on the scale of the individual particle size for thermalized mixed crystals. Here, we explore the shear-induced breaking for an equimolar two-dimensional binary model crystal with a high interaction asymmetry between the two different species such that the initial crystal has an intersecting square sublattice of the two constituents. Using Brownian dynamics computer simulations, we show that the combination of shear and thermal fluctuations leads to a characteristic hierarchical breaking scenario where initially, the more strongly coupled particles are thermally distorted, paving the way for the weakly coupled particles to escape from their cage. This in turn leads to mobile defects which may finally merge, proliferating a cascade of defects, which triggers the final breakage of the crystal. This scenario is in marked contrast to the breakage of one-component crystals close to melting. Moreover, we explore the orientational dependence of the initial shear direction relative to the crystal orientation and compare this to the usual melting scenario without shear. Our results are verifiable in real-space experiments of superparamagnetic colloidal mixtures at a pending air-water interface in an external magnetic field where the shear can be induced by an external laser field.

  9. Breaking time reversal in a simple smooth chaotic system

    NASA Astrophysics Data System (ADS)

    Tomsovic, Steven; Ullmo, Denis; Nagano, Tatsuro

    2003-06-01

    Within random matrix theory, the statistics of the eigensolutions depend fundamentally on the presence (or absence) of time reversal symmetry. Accepting the Bohigas-Giannoni-Schmit conjecture, this statement extends to quantum systems with chaotic classical analogs. For practical reasons, much of the supporting numerical studies of symmetry breaking have been done with billiards or maps, and little with simple, smooth systems. There are two main difficulties in attempting to break time reversal invariance in a continuous time system with a smooth potential. The first is avoiding false time reversal breaking. The second is locating a parameter regime in which the symmetry breaking is strong enough to transform the fluctuation properties fully to the broken symmetry case, and yet remain weak enough so as not to regularize the dynamics sufficiently that the system is no longer chaotic. We give an example of a system of two coupled quartic oscillators whose energy level statistics closely match with those of the Gaussian unitary ensemble, and which possesses only a minor proportion of regular motion in its phase space.

  10. Prevalence of galaxy-galaxy interactions in AGN hosts

    NASA Astrophysics Data System (ADS)

    Lim, Jeremy; Kuo, Cheng-Yu; Tang, Ya-Wen; Greene, Jenny; Ho, Paul T. P.

    2004-11-01

    Studies in optical starlight have failed to reach a consensus on the importance of either galaxy interactions, bars, or nuclear spirals in triggering luminous active galactic nuclei (AGNs). Here, we present the first systematic imaging study of Seyfert (disk) galaxies in the 21-cm line of neutral atomic hydrogen (HI) gas. HI is the most sensitive and enduring tracer of galaxy interactions, and can reveal tidal features not otherwise visible in optical starlight. Our sample comprises all twenty-eight galaxies in the Véron-Cetty & Véron (1998) catalog with nuclear magnitudes -19 ≥ MB > -23 (including Seyfert, LINER, and HII galaxies) at 0.015 ≤ z ≤ 0.017 in the northern hemisphere, and a matched control sample of twenty-seven inactive galaxies at z≈0.008. We have detected nearly all the galaxies observed, and find a much higher incidence of tidal interactions -- usually not seen in optical starlight -- among the Seyfert galaxies by comparison with the matched control sample. Those Seyferts with uncertain or no clear tidal features show disturbed HI morphologies and/or kinematics, as well as HI companion galaxies, more frequently than the control sample. Our study suggests that the undisturbed optical appearence of active galaxies may be deceptive, and imply that galaxy-galaxy interactions trigger a significant fraction luminous AGNs at low redshifts. The majority of the Seyfert galaxies in our sample appear to be at a relatively early stage of an encounter rather than late in a merger.

  11. Galaxy Zoo User Behaviors 1: User classification trends

    NASA Astrophysics Data System (ADS)

    Pritchett, Brian; Gay, P. L.; CS390/490 Class, SIUE; Galaxy Zoo Team

    2010-01-01

    In this poster we examine patterns of classification behavior among Galaxy Zoo users. The Galaxy Zoo project (Lintott 2008) asks users to look at images of galaxies from the Sloan Digital Sky Survey and to classify them based on their appearance. The success of this project, measured through 14 scientific journal articles, comes in large part from the dedicated contributions from over 230,000 registered users. These users have each contributed anywhere from a small handful of galaxy classifications to a few tens-of-thousands of classifications. While user behaviors vary greatly, we find that there are certain patterns of behavior that predict which individuals will make significant numbers of classifications over the course of their involvement in the project. Specifically, we study how the number of classifications a person makes shortly after they register for the site can predict future classification behavior. We also look for patterns in what events trigger users registering for the site and returning to site. Where possible, we break patterns of behavior down by gender, and study differences between populations who join at pivotal moments (site launch, major announcement, etc), join as the result of one-on-one contact with a member of the Galaxy Zoo collaboration, and the remaining population. The research was funded by NASA ROSES NNX09AD34G.

  12. Ultraluminous Infrared Mergers: Elliptical Galaxies in Formation?

    NASA Astrophysics Data System (ADS)

    Genzel, R.; Tacconi, L. J.; Rigopoulou, D.; Lutz, D.; Tecza, M.

    2001-12-01

    We report high-quality near-IR spectroscopy of 12 ultraluminous infrared galaxy mergers (ULIRGs). Our new VLT and Keck data provide ~0.5" resolution, stellar and gas kinematics of these galaxies, most of which are compact systems in the last merger stages. We confirm that ULIRG mergers are ``ellipticals in formation.'' Random motions dominate their stellar dynamics, but significant rotation is common. Gasdynamics and stellar dynamics are decoupled in most systems. ULIRGs fall on or near the fundamental plane of hot stellar systems, and especially on its less evolution-sensitive, reff-σ projection. The ULIRG velocity dispersion distribution, their location in the fundamental plane, and their distribution of vrotsini/σ closely resemble those of intermediate-mass (~L*), elliptical galaxies with moderate rotation. As a group ULIRGs do not resemble giant ellipticals with large cores and little rotation. Our results are in good agreement with other recent studies indicating that disky ellipticals with compact cores or cusps can form through dissipative mergers of gas-rich disk galaxies while giant ellipticals with large cores have a different formation history. Based on observations at the European Southern Observatory, Chile (ESO 65.N-0266, 65.N-0289), and on observations at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, The University of California, and the National Aeronautics and Space Administration. The Keck Observatory was made possible by the general financial support by the W. M. Keck Foundation.

  13. The Clustering of Massive Galaxies at z ~ 1

    NASA Astrophysics Data System (ADS)

    Overzier, R. A.; Röttgering, H. J. A.; Wilman, R. J.; Rengelink, R. B.

    2003-05-01

    We use the angular two-point correlation function to estimate the spatial correlation length of radio sources taken from the large-area 1.4 GHz NVSS radio survey. At the median survey redshift of z ~ 1, r0 is found to be increasing with flux density. This is consistent with a scenario in which powerful (i.e. FRII) radio galaxies probe significantly more massive spatial structures than less powerful radio galaxies. The large spatial correlation length that we derive for FRIIs is remarkably close to that of extremely red objects (EROs). This implies that powerful radio galaxies and EROs trace equally massive structures at z ~ 1. Moreover, because powerful radio galaxies and EROs are both associated with luminous early-type galaxies we propose that they could be the same objects seen at different evolutionary stages. The correlation length of massive, luminous galaxies at z ~ 1 is comparable to that of bright ellipticals locally, suggesting that r0 (comoving) of these massive galaxies has changed little from z ~ 1 to z ~ 0. This is in excellent agreement with current ΛCDM hierarchical model predictions.

  14. The Environment of Bright Submillimeter Galaxies at z 2

    NASA Astrophysics Data System (ADS)

    Aravena, Manuel

    2010-01-01

    Submillimeter galaxies are luminous and massive systems undergoing vigorous star formation activity. Their large masses, number density and clustering properties indicate that they are related to the formation of structures at high redshift, and possibly they may the precursors of luminous local ellipticals. In this talk, I will present a study of the environment of the SMGs detected with MAMBO in the COSMOS field and with LABOCA in the ECDF-S. Using density maps of low- and high-redshift BzK galaxies we investigate whether some of the brightest SMGs are located in galaxy overdensities. A few SMGs in these surveys appear to be linked to significant overdensities of star-forming galaxies at z>1. Such overdensities are compact in size, similar to what is found in QSO fields at similar redshifts. We use accurate optical/IR photometric redshifts to give an estimate of the actual redshift of these associations. Using the angular cross-correlation function between SMGs and BzK galaxies at high-redshift we find that there is a close relationship between both populations in scales 10". Such compact groups could trigger the extreme star-forming activity seen in some SMGs and they represent good targets for studies of star and structure formation in normal star-forming to vigorous starburst galaxies in the crucial epoch of galaxy assembly.

  15. The ergodicity bias in the observed galaxy distribution

    SciTech Connect

    Pan, Jun; Zhang, Pengjie E-mail: pjzhang@shao.ac.cn

    2010-08-01

    The spatial distribution of galaxies we observed is subject to the given condition that we, human beings are sitting right in a galaxy — the Milky Way. Thus the ergodicity assumption is questionable in interpretation of the observed galaxy distribution. The resultant difference between observed statistics (volume average) and the true cosmic value (ensemble average) is termed as the ergodicity bias. We perform explicit numerical investigation of the effect for a set of galaxy survey depths and near-end distance cuts. It is found that the ergodicity bias in observed two- and three-point correlation functions in most cases is insignificant for modern analysis of samples from galaxy surveys and thus close a loophole in precision cosmology. However, it may become non-negligible in certain circumstances, such as those applications involving three-point correlation function at large scales of local galaxy samples. Thus one is reminded to take extra care in galaxy sample construction and interpretation of the statistics of the sample, especially when the characteristic redshift is low.

  16. THE ESCAPE FRACTION OF IONIZING RADIATION FROM GALAXIES

    SciTech Connect

    Benson, Andrew; Venkatesan, Aparna; Shull, J. Michael E-mail: avenkatesan@usfca.edu

    2013-06-10

    The escape of ionizing radiation from galaxies plays a critical role in the evolution of gas in galaxies, and the heating and ionization history of the intergalactic medium. We present semi-analytic calculations of the escape fraction of ionizing radiation for both hydrogen and helium from galaxies ranging from primordial systems to disk-type galaxies that are not heavily dust-obscured. We consider variations in the galaxy density profile, source type, location, and spectrum, and gas overdensity/distribution factors. For sufficiently hard first-light sources, the helium ionization fronts closely track or advance beyond that of hydrogen. Key new results in this work include calculations of the escape fractions for He I and He II ionizing radiation, and the impact of partial ionization from X-rays from early active galactic nuclei or stellar clusters on the escape fractions from galaxy halos. When factoring in frequency-dependent effects, we find that X-rays play an important role in boosting the escape fractions for both hydrogen and helium, but especially for He II. We briefly discuss the implications of these results for recent observations of the He II reionization epoch at low redshifts, as well as the UV data and emission-line signatures from early galaxies anticipated from future satellite missions.

  17. Simulated galaxy interactions as probes of merger spectral energy distributions

    SciTech Connect

    Lanz, Lauranne; Zezas, Andreas; Smith, Howard A.; Ashby, Matthew L. N.; Fazio, Giovanni G.; Hernquist, Lars; Hayward, Christopher C.; Brassington, Nicola

    2014-04-10

    We present the first systematic comparison of ultraviolet-millimeter spectral energy distributions (SEDs) of observed and simulated interacting galaxies. Our sample is drawn from the Spitzer Interacting Galaxy Survey and probes a range of galaxy interaction parameters. We use 31 galaxies in 14 systems which have been observed with Herschel, Spitzer, GALEX, and 2MASS. We create a suite of GADGET-3 hydrodynamic simulations of isolated and interacting galaxies with stellar masses comparable to those in our sample of interacting galaxies. Photometry for the simulated systems is then calculated with the SUNRISE radiative transfer code for comparison with the observed systems. For most of the observed systems, one or more of the simulated SEDs match reasonably well. The best matches recover the infrared luminosity and the star formation rate of the observed systems, and the more massive systems preferentially match SEDs from simulations of more massive galaxies. The most morphologically distorted systems in our sample are best matched to the simulated SEDs that are close to coalescence, while less evolved systems match well with the SEDs over a wide range of interaction stages, suggesting that an SED alone is insufficient for identifying the interaction stage except during the most active phases in strongly interacting systems. This result is supported by our finding that the SEDs calculated for simulated systems vary little over the interaction sequence.

  18. GETTING TO THE HEART OF A GALAXY

    NASA Technical Reports Server (NTRS)

    2002-01-01

    This collage of images in visible and infrared light reveals how the barred spiral galaxy NGC 1365 is feeding material into its central region, igniting massive star birth and probably causing its bulge of stars to grow. The material also is fueling a black hole in the galaxy's core. A galaxy's bulge is a central, football-shaped structure composed of stars, gas, and dust. The black-and-white image in the center, taken by a ground-based telescope, displays the entire galaxy. But the telescope's resolution is not powerful enough to reveal the flurry of activity in the galaxy's hub. The blue box in the galaxy's central region outlines the area observed by the NASA Hubble Space Telescope's visible-light camera, the Wide Field and Planetary Camera 2 (WFPC2). The red box pinpoints a narrower view taken by the Hubble telescope's infrared camera, the Near Infrared Camera and Multi-Object Spectrometer (NICMOS). A barred spiral is characterized by a lane of stars, gas, and dust slashing across a galaxy's central region. It has a small bulge that is dominated by a disk of material. The spiral arms begin at both ends of the bar. The bar is funneling material into the hub, which triggers star formation and feeds the bulge. The visible-light picture at upper left is a close-up view of the galaxy's hub. The bright yellow orb is the nucleus. The dark material surrounding the orb is gas and dust that is being funneled into the central region by the bar. The blue regions pinpoint young star clusters. In the infrared image at lower right, the Hubble telescope penetrates the dust seen in the WFPC2 picture to reveal more clusters of young stars. The bright blue dots represent young star clusters; the brightest of the red dots are young star clusters enshrouded in dust and visible only in the infrared image. The fainter red dots are older star clusters. The WFPC2 image is a composite of three filters: near-ultraviolet (3327 Angstroms), visible (5552 Angstroms), and near-infrared (8269

  19. H1 in RSA galaxies

    NASA Technical Reports Server (NTRS)

    Richter, OTTO-G.

    1993-01-01

    The original Revised Shapley-Ames (RSA) galaxy sample of almost 1300 galaxies has been augmented with further bright galaxies from the RSA appendix as well as newer galaxy catalogs. A complete and homogeneous, strictly magnitude-limited all-sky sample of 2345 galaxies brighter than 13.4 in apparent blue magnitude was formed. New 21 cm H1 line observations for more than 600 RSA galaxies have been combined with all previously available H1 data from the literature. This new extentise data act allows detailed tests of widely accepted 'standard' reduction and analysis techniques.

  20. An Elegant Galaxy in an Unusual Light

    NASA Astrophysics Data System (ADS)

    2010-09-01

    A new image taken with the powerful HAWK-I camera on ESO's Very Large Telescope at Paranal Observatory in Chile shows the beautiful barred spiral galaxy NGC 1365 in infrared light. NGC 1365 is a member of the Fornax cluster of galaxies, and lies about 60 million light-years from Earth. NGC 1365 is one of the best known and most studied barred spiral galaxies and is sometimes nicknamed the Great Barred Spiral Galaxy because of its strikingly perfect form, with the straight bar and two very prominent outer spiral arms. Closer to the centre there is also a second spiral structure and the whole galaxy is laced with delicate dust lanes. This galaxy is an excellent laboratory for astronomers to study how spiral galaxies form and evolve. The new infrared images from HAWK-I are less affected by the dust that obscures parts of the galaxy than images in visible light (potw1037a) and they reveal very clearly the glow from vast numbers of stars in both the bar and the spiral arms. These data were acquired to help astronomers understand the complex flow of material within the galaxy and how it affects the reservoirs of gas from which new stars can form. The huge bar disturbs the shape of the gravitational field of the galaxy and this leads to regions where gas is compressed and star formation is triggered. Many huge young star clusters trace out the main spiral arms and each contains hundreds or thousands of bright young stars that are less than ten million years old. The galaxy is too remote for single stars to be seen in this image and most of the tiny clumps visible in the picture are really star clusters. Over the whole galaxy, stars are forming at a rate of about three times the mass of our Sun per year. While the bar of the galaxy consists mainly of older stars long past their prime, many new stars are born in stellar nurseries of gas and dust in the inner spiral close to the nucleus. The bar also funnels gas and dust gravitationally into the very centre of the galaxy

  1. How often precipitation records break?

    NASA Astrophysics Data System (ADS)

    Papalexiou, Simon Michael; Oikonomou, Maria; Floutsakou, Athina; Bessas, Nikolaos; Mamassis, Nikos

    2016-04-01

    How often precipitation records break? Are there any factors that determine the average time needed for the next maximum to occur? In order to investigate these simple questions we use several hundreds of daily precipitation records (more than 100 years long each) and we study the time intervals between each successive maximum precipitation value. We investigate if the record breaking time interval is related (a) to the autocorrelation structure, (b) to probability dry, and (c) to the tail of the marginal distribution. For the last, we first, evaluate which type of tail is better fitted by choosing among three general types of tails corresponding to the distributions Pareto, Lognormal and Weibull; and second, we assess the heaviness of the tail based on the estimated shape parameter. The performance of each tail is evaluated in terms of return period values, i.e., we compare the empirical return periods of precipitation values above a threshold with the predicted ones by each of the three types of fitted tails.

  2. Giant Radio Jet Coming From Wrong Kind of Galaxy

    NASA Astrophysics Data System (ADS)

    2003-01-01

    black holes at their cores. The discovery that the jet was coming from a spiral galaxy dubbed 0313-192 required using a combination of radio, optical and infrared observations to examine the galaxy and its surroundings. The story began more than 20 years ago, when Owen began a survey of 500 galaxy clusters using the National Science Foundation's then-new VLA to make radio images of the clusters. In the 1990s, Ledlow joined the project, making optical-telescope images of the same clusters as part of his research for a Ph.D dissertation at the University of New Mexico. An optical image from Kitt Peak National Observatory gave a hint that this galaxy, clearly seen with a jet in the VLA images, might be a spiral. Nearly a billion light-years from Earth, 0313-192 proved an elusive target, however. Subsequent observations with the VLA and the 3.5-meter telescope at Apache Point Observatory supported the idea that the galaxy might be a spiral but still were inconclusive. In the Spring of 2002, astronauts installed the Advanced Camera for Surveys on the Hubble Space Telescope. This new facility produced a richly-detailed image of 0313-192, showing that it is a dust-rich spiral seen almost exactly edge-on. "The finely-detailed Hubble image resolved any doubt and proved that this galaxy is a spiral," Ledlow said. Infrared images with the Gemini-South telescope complemented the Hubble images and further confirmed the galaxy's spiral nature. Now, the astronomers seek to understand why this one spiral galaxy, unlike all others seen so far, is producing the bright jets seen with the VLA and other radio telescopes. Several factors may have combined, the researchers feel. "This galaxy's disk is twisted, and that may indicate that it has been disturbed by a close passage of another galaxy or may have swallowed up a companion dwarf galaxy," Keel said. He added, "This galaxy shows signs of having a very massive black hole at its core, and the jets are taking the shortest path out of the

  3. Kinematics and stellar population of the lenticular galaxy NGC 4124

    NASA Astrophysics Data System (ADS)

    Zasov, A. V.; Sil'chenko, O. K.; Katkov, I. Yu.; Dodonov, S. N.

    2013-01-01

    Results of spectroscopic and photometric studies for the locally isolated lenticular galaxy NGC 4124 are presented. A model of the mass distribution consistent with photometric data has been constructed on the basis of a kinematic analysis. In this model, the halo mass within the optical radius is almost half the diskmass. The disk is shown to be in a dynamical state close to amarginally stable one. This rules out dynamical disk heating for the galaxy through a strong external action or a merger with a massive system. However, the presence of a gaseous disk inclined to the main plane of the galaxy in the central kiloparsec region suggests probable cannibalization of a small satellite that also produced a late starburst in the central region. This is confirmed by the younger mean age (˜2 Gyr) of the stellar population in the galaxy's central region than the disk age (5-7 Gyr).

  4. Exploring the Overabundance of ULXs in Metal- and Dust-poor Local Lyman Break Analogs

    NASA Astrophysics Data System (ADS)

    Basu-Zych, Antara R.; Lehmer, Bret; Fragos, Tassos; Hornschemeier, Ann; Yukita, Mihoko; Zezas, Andreas; Ptak, Andy

    2016-02-01

    We have studied high-mass X-ray binary (HMXB) populations within two low-metallicity, starburst galaxies, Haro 11 and VV 114. These galaxies serve as analogs to high-redshift (z\\gt 2) Lyman break galaxies and, within the larger sample of Lyman break analogs (LBAs), they are sufficiently nearby (<87 Mpc) to be spatially resolved by Chandra. Previous studies of the X-ray emission in LBAs have found that the 2-10 keV luminosity per star formation rate (SFR) in these galaxies is elevated, potentially because of their low metallicities (12+{log}[{{O}}/{{H}}]=8.3{--}8.4). Theoretically, the progenitors of XRBs forming in lower metallicity environments lose less mass from stellar winds over their lifetimes, producing more massive compact objects (i.e., neutron stars and black holes), and thus resulting in more numerous and luminous HMXBs per SFR. In this paper, we have performed an in-depth study of the only two LBAs that have spatially resolved 2-10 keV emission with Chandra to present the bright end of the X-ray luminosity distribution of HMXBs ({L}{{X}} ≳ 1039 erg s-1 ultraluminous X-ray sources, ULXs) in these low-metallicity galaxies, based on eight detected ULXs. Compared with the star-forming galaxy X-ray luminosity function (XLF) presented by Mineo et al., Haro 11 and VV 114 host ≈ 4 times more {L}{{X}} \\gt {10}40 erg s-1 sources than expected given their SFRs. We simulate the effects of source blending from crowded lower-luminosity HMXBs using the star-forming galaxy XLF and then vary the XLF normalizations and bright-end slopes until we reproduce the observed point source luminosity distributions. We find that these LBAs have a shallower bright-end slope ({γ }2=1.90) than the standard XLF ({γ }2=2.73). If we conservatively assume that the brightest X-ray source from each galaxy is powered by an accreting supermassive black hole rather than an HMXB and eliminate these sources from consideration, the luminosity distribution becomes poorly constrained but

  5. Chandra ACIS Survey of X-Ray Point Sources in Nearby Galaxies. II. X-Ray Luminosity Functions and Ultraluminous X-Ray Sources

    NASA Astrophysics Data System (ADS)

    Wang, Song; Qiu, Yanli; Liu, Jifeng; Bregman, Joel N.

    2016-09-01

    Based on the recently completed Chandra/ACIS survey of X-ray point sources in nearby galaxies, we study the X-ray luminosity functions (XLFs) for X-ray point sources in different types of galaxies and the statistical properties of ultraluminous X-ray sources (ULXs). Uniform procedures are developed to compute the detection threshold, to estimate the foreground/background contamination, and to calculate the XLFs for individual galaxies and groups of galaxies, resulting in an XLF library of 343 galaxies of different types. With the large number of surveyed galaxies, we have studied the XLFs and ULX properties across different host galaxy types, and confirm with good statistics that the XLF slope flattens from lenticular (α ˜ 1.50 ± 0.07) to elliptical (˜1.21 ± 0.02), to spirals (˜0.80 ± 0.02), to peculiars (˜0.55 ± 0.30), and to irregulars (˜0.26 ± 0.10). The XLF break dividing the neutron star and black hole binaries is also confirmed, albeit at quite different break luminosities for different types of galaxies. A radial dependency is found for ellipticals, with a flatter XLF slope for sources located between D 25 and 2D 25, suggesting the XLF slopes in the outer region of early-type galaxies are dominated by low-mass X-ray binaries in globular clusters. This study shows that the ULX rate in early-type galaxies is 0.24 ± 0.05 ULXs per surveyed galaxy, on a 5σ confidence level. The XLF for ULXs in late-type galaxies extends smoothly until it drops abruptly around 4 × 1040 erg s-1, and this break may suggest a mild boundary between the stellar black hole population possibly including 30 M ⊙ black holes with super-Eddington radiation and intermediate mass black holes.

  6. Discriminating topology in galaxy distributions using network analysis

    NASA Astrophysics Data System (ADS)

    Hong, Sungryong; Coutinho, Bruno C.; Dey, Arjun; Barabási, Albert-L.; Vogelsberger, Mark; Hernquist, Lars; Gebhardt, Karl

    2016-07-01

    The large-scale distribution of galaxies is generally analysed using the two-point correlation function. However, this statistic does not capture the topology of the distribution, and it is necessary to resort to higher order correlations to break degeneracies. We demonstrate that an alternate approach using network analysis can discriminate between topologically different distributions that have similar two-point correlations. We investigate two galaxy point distributions, one produced by a cosmological simulation and the other by a Lévy walk. For the cosmological simulation, we adopt the redshift z = 0.58 slice from Illustris and select galaxies with stellar masses greater than 108 M⊙. The two-point correlation function of these simulated galaxies follows a single power law, ξ(r) ˜ r-1.5. Then, we generate Lévy walks matching the correlation function and abundance with the simulated galaxies. We find that, while the two simulated galaxy point distributions have the same abundance and two-point correlation function, their spatial distributions are very different; most prominently, filamentary structures, absent in Lévy fractals. To quantify these missing topologies, we adopt network analysis tools and measure diameter, giant component, and transitivity from networks built by a conventional friends-of-friends recipe with various linking lengths. Unlike the abundance and two-point correlation function, these network quantities reveal a clear separation between the two simulated distributions; therefore, the galaxy distribution simulated by Illustris is not a Lévy fractal quantitatively. We find that the described network quantities offer an efficient tool for discriminating topologies and for comparing observed and theoretical distributions.

  7. The Luminosity Dependence of the Galaxy Merger Rate

    NASA Astrophysics Data System (ADS)

    Patton, D. R.; Atfield, J. E.

    2008-09-01

    We measure the number of companions per galaxy (Nc) as a function of r-band absolute magnitude for both the Sloan Digital Sky Survey and the Croton and coworkers semianalytic catalog applied to the Millennium Run simulation. For close pairs with projected separations of 5-20 h-1 kpc, velocity differences less than 500 km s-1, and luminosity ratios between 1:2 and 2:1, we find good agreement between the observations and simulations, with Nc consistently close to 0.02 over the range -22 < Mr < - 18. For larger pair separations, Nc(Mr) instead becomes increasingly steep toward the faint end, implying that luminosity-dependent clustering plays an important role on small scales. Using the simulations to assess and correct for projection effects, we infer that the real-space Nc(Mr) for close pairs peaks at about M* and declines by at least a factor of 2 as Mr becomes fainter. Conversely, by measuring the number density of close companions, we estimate that at least 90% of all major mergers occur between galaxies which are fainter than L*. Finally, measurements of the luminosity density of close companions indicate that L* galaxies likely dominate in terms of the overall importance of major mergers in the evolution of galaxy populations at low redshift.

  8. MEASUREMENT OF THE HALO BIAS FROM STACKED SHEAR PROFILES OF GALAXY CLUSTERS

    SciTech Connect

    Covone, Giovanni; Sereno, Mauro

    2014-04-01

    We present observational evidence of the two-halo term in the stacked shear profile of a sample of ∼1200 optically selected galaxy clusters based on imaging data and the public shear catalog from the CFHTLenS. We find that the halo bias, a measure of the correlated distribution of matter around galaxy clusters, has amplitude and correlation with galaxy cluster mass in very good agreement with the predictions based on the LCDM standard cosmological model. The mass-concentration relation is flat but higher than theoretical predictions. We also confirm the close scaling relation between the optical richness of galaxy clusters and their mass.

  9. Turbulent mixing of chemical elements in galaxies

    NASA Astrophysics Data System (ADS)

    Pan, Liubin

    Chemical elements synthesized in stars are released into the interstellar medium (ISM) from discrete and localized events such as supernova (SN) explosions and stellar winds. The efficiency of transport and mixing of the new nucleosynthesis products in the ISM determines the degree of chemical inhomogeneity in the galaxy, which is observable in objects of the same age, such as coeval stars and the ISM today. It also has implications for the transition from metal-poor to normal star formation in high-redshift galaxies. We develop a physical mixing model for chemical homogenization in the turbulent ISM of galaxies using modern theories and methods for passive scalar turbulence. A turbulent velocity field stretches, compresses and folds tracers into structures of smaller and smaller scales that can be homogenized faster by microscopic diffusivity, the only physical process that truly mixes. From a model that incorporates this physical process, an evolution equation for the probability distribution of the tracer concentration is derived. Including the processes of new metal release, infall of low metallicity gas and incorporation of metals into new stars in the equation, we establish a new approach to investigate chemical inhomogeneity in galaxies: a kinetic equation for the metallicity probability distribution function, containing all the 1-point statistical information of the metallicity fluctuations. Motivated by a recent interpretation of ultraviolet properties of high-redshift Lyman Break Galaxies, we apply this approach to study mixing of primordial gas in these galaxies and find that primordial gas can survive for ~ 100 Myr in the presence of continuous metal sources and turbulent mixing if the unlikely efficient mixing in SN shells is excluded. Recent observations show that the Galaxy has been extremely homogeneous during most of its history. In an attempt to understand the homogeneity using our approach, we find that standard chemical evolution models without

  10. The effect of surface brightness dimming in the selection of high-z galaxies

    SciTech Connect

    Calvi, V.; Stiavelli, M.; Bradley, L.; Pizzella, A.; Kim, S.

    2014-12-01

    Cosmological surface brightness (SB) dimming of the form (1 + z){sup –4} affects all sources. The strong dependence of SB dimming on redshift z suggests the presence of a selection bias when searching for high-z galaxies, i.e., we tend to detect only those galaxies with a high SB. However, unresolved knots of emission are not affected by SB dimming, thus providing a way to test the clumpiness of high-z galaxies. Our strategy relies on the comparison of the total flux detected for the same source in surveys characterized by different depth. For all galaxies, deeper images permit the better investigation of low-SB features. Cosmological SB dimming makes these low-SB features hard to detect when going to higher and higher redshifts. We used the GOODS and HUDF Hubble Space Telescope legacy data sets to study the effect of SB dimming on low-SB features of high-z galaxies and compare it to the prediction for smooth sources. We selected a sample of Lyman-break galaxies at z ∼ 4 (i.e., B {sub 435}-band dropouts) detected in all of the data sets and found no significant trend when comparing the total magnitudes measured from images with different depth. Through Monte Carlo simulations we derived the expected trend for galaxies with different SB profiles. The comparison to the data hints at a compact distribution for most of the rest-frame ultraviolet light emitted from high-z galaxies.

  11. Symmetry breaking on density in escaping ants: experiment and alarm pheromone model.

    PubMed

    Li, Geng; Huan, Di; Roehner, Bertrand; Xu, Yijuan; Zeng, Ling; Di, Zengru; Han, Zhangang

    2014-01-01

    The symmetry breaking observed in nature is fascinating. This symmetry breaking is observed in both human crowds and ant colonies. In such cases, when escaping from a closed space with two symmetrically located exits, one exit is used more often than the other. Group size and density have been reported as having no significant impact on symmetry breaking, and the alignment rule has been used to model symmetry breaking. Density usually plays important roles in collective behavior. However, density is not well-studied in symmetry breaking, which forms the major basis of this paper. The experiment described in this paper on an ant colony displays an increase then decrease of symmetry breaking versus ant density. This result suggests that a Vicsek-like model with an alignment rule may not be the correct model for escaping ants. Based on biological facts that ants use pheromones to communicate, rather than seeing how other individuals move, we propose a simple yet effective alarm pheromone model. The model results agree well with the experimental outcomes. As a measure, this paper redefines symmetry breaking as the collective asymmetry by deducing the random fluctuations. This research indicates that ants deposit and respond to the alarm pheromone, and the accumulation of this biased information sharing leads to symmetry breaking, which suggests true fundamental rules of collective escape behavior in ants.

  12. Symmetry breaking on density in escaping ants: experiment and alarm pheromone model.

    PubMed

    Li, Geng; Huan, Di; Roehner, Bertrand; Xu, Yijuan; Zeng, Ling; Di, Zengru; Han, Zhangang

    2014-01-01

    The symmetry breaking observed in nature is fascinating. This symmetry breaking is observed in both human crowds and ant colonies. In such cases, when escaping from a closed space with two symmetrically located exits, one exit is used more often than the other. Group size and density have been reported as having no significant impact on symmetry breaking, and the alignment rule has been used to model symmetry breaking. Density usually plays important roles in collective behavior. However, density is not well-studied in symmetry breaking, which forms the major basis of this paper. The experiment described in this paper on an ant colony displays an increase then decrease of symmetry breaking versus ant density. This result suggests that a Vicsek-like model with an alignment rule may not be the correct model for escaping ants. Based on biological facts that ants use pheromones to communicate, rather than seeing how other individuals move, we propose a simple yet effective alarm pheromone model. The model results agree well with the experimental outcomes. As a measure, this paper redefines symmetry breaking as the collective asymmetry by deducing the random fluctuations. This research indicates that ants deposit and respond to the alarm pheromone, and the accumulation of this biased information sharing leads to symmetry breaking, which suggests true fundamental rules of collective escape behavior in ants. PMID:25551611

  13. New observations of z ∼ 7 galaxies: evidence for a patchy reionization

    SciTech Connect

    Pentericci, L.; Fontana, A.; Castellano, M.; Grazian, A.; Galametz, A.; Giallongo, E.; Paris, D.; Santini, P.; Vanzella, E.; Treu, T.; Mesinger, A.; Dijkstra, M.; Bradač, M.; Conselice, C.; Cristiani, S.; Dunlop, J.; McLure, R.; Giavalisco, M.; Koekemoer, A.; Maiolino, R.

    2014-10-01

    We present new results from our search for z ∼ 7 galaxies from deep spectroscopic observations of candidate z dropouts in the CANDELS fields. Despite the extremely low flux limits achieved by our sensitive observations, only two galaxies have robust redshift identifications, one from its Lyα emission line at z = 6.65, the other from its Lyman break, i.e., the continuum discontinuity at the Lyα wavelength consistent with a redshift of 6.42 but with no emission line. In addition, for 23 galaxies we present deep limits in the Lyα equivalent width derived from the nondetections in ultradeep observations. Using this new data as well as previous samples, we assemble a total of 68 candidate z ∼ 7 galaxies with deep spectroscopic observations, of which 12 have a line detection. With this much enlarged sample we can place solid constraints on the declining fraction of Lyα emission in z ∼ 7 Lyman-break galaxies compared to z ∼ 6, both for bright and faint galaxies. Applying a simple analytical model, we show that the present data favor a patchy reionization process rather than a smooth one.

  14. Evolution of galaxy structure using visual morphologies in CANDELS and Hydro-ART simulations

    NASA Astrophysics Data System (ADS)

    Mozena, Mark W.

    2013-08-01

    present in the simulations with our observations, we are able to probe the model's ability to create realistic galaxy populations. The first chapter of this thesis focuses on visually classifying and studying galaxy populations at z~2 and how they change with redshift for a given mass. The second chapter focuses on applying our techniques to Hydro-ART simulations at z~2 and comparing these mock 'observed' simulations with our real WFC3 HST observations. Both of these chapters closely resemble manuscripts in the process of being submitted for independent publication.

  15. A study of the x ray environment of radio galaxies

    NASA Technical Reports Server (NTRS)

    Rhee, George F.; Burns, Jack O.; Owen, Frazer

    1993-01-01

    We are currently working on a program to use extensive x-ray and radio databases to investigate the relationship between extended radio emission and environment in clusters of galaxies. The radio galaxy morphology is determined using VLA imaging and the x-ray properties are determined from Einstein IPC images. This study is motivated by the hypothesis that the key to understanding radio galaxies lies in the local environment. To test this hypothesis we have studied the detailed relationship between galaxy radio emission and the x-ray morphology of their parent clusters. In this pilot study we have used 35 radio sources found in 27 clusters. We have determined the position angle of the x-ray and radio emission, and x-ray and radio luminosities. The x-ray position was taken to be the position of peak flux of the subclump containing the radio galaxy. The radio position was taken to be the position of the galaxy. We do not find a correlation between the x-ray and radio source position angle. This remains true when the sample is divided into subsamples according to radio morphology (wide angle tail, twin jet, narrow angle tail galaxies). We find a weak correlation between the radio source luminosity and the x-ray luminosity. We have computed the distance from the radio galaxy position to the center of the x-ray clump. We find a mean distance from the x-ray clump center of 0.16 Mpc for the radio galaxies in this sample. The mean distance to the nearest clump of x-ray emission is typically half the distance to the optical cluster center. We thus find strong evidence that radio galaxies are located very close to clumps of x-ray emission. These subclumps are not always affiliated with the central cluster x-ray emission. This supports our hypothesis that x-ray emission may provide a key to understanding radio galaxy morphology. We find evidence that radio galaxies occur in clusters that contain prominent substructures. Radio galaxies may thus provide an added diagnostic of

  16. AGN host galaxy mass function in COSMOS. Is AGN feedback responsible for the mass-quenching of galaxies?

    NASA Astrophysics Data System (ADS)

    Bongiorno, A.; Schulze, A.; Merloni, A.; Zamorani, G.; Ilbert, O.; La Franca, F.; Peng, Y.; Piconcelli, E.; Mainieri, V.; Silverman, J. D.; Brusa, M.; Fiore, F.; Salvato, M.; Scoville, N.

    2016-04-01

    We investigate the role of supermassive black holes in the global context of galaxy evolution by measuring the host galaxy stellar mass function (HGMF) and the specific accretion rate, that is, λSAR, the distribution function (SARDF), up to z ~ 2.5 with ~1000 X-ray selected AGN from XMM-COSMOS. Using a maximum likelihood approach, we jointly fit the stellar mass function and specific accretion rate distribution function, with the X-ray luminosity function as an additional constraint. Our best-fit model characterizes the SARDF as a double power-law with mass-dependent but redshift-independent break, whose low λSAR slope flattens with increasing redshift while the normalization increases. This implies that for a given stellar mass, higher λSAR objects have a peak in their space density at earlier epoch than the lower λSAR objects, following and mimicking the well-known AGN cosmic downsizing as observed in the AGN luminosity function. The mass function of active galaxies is described by a Schechter function with an almost constant M∗⋆ and a low-mass slope α that flattens with redshift. Compared to the stellar mass function, we find that the HGMF has a similar shape and that up to log (M⋆/M⊙) ~ 11.5, the ratio of AGN host galaxies to star-forming galaxies is basically constant (~10%). Finally, the comparison of the AGN HGMF for different luminosity and specific accretion rate subclasses with a previously published phenomenological model prediction for the "transient" population, which are galaxies in the process of being mass-quenched, reveals that low-luminosity AGN do not appear to be able to contribute significantly to the quenching and that at least at high masses, that is, M⋆ > 1010.7 M⊙, feedback from luminous AGN (log Lbol ≳ 46 [erg/s]) may be responsible for the quenching of star formation in the host galaxy.

  17. Galaxy populations in the Antlia cluster - II. Compact elliptical galaxy candidates

    NASA Astrophysics Data System (ADS)

    Smith Castelli, Analía V.; Faifer, Favio R.; Richtler, Tom; Bassino, Lilia P.

    2008-12-01

    Continuing our study of galaxy populations in the Antlia cluster, we present a photometric analysis of four galaxies classified as compact elliptical (cE) galaxies in the 1990 Antlia Group catalogue of Ferguson and Sandage. Until now, there have been only six known members of this rare type of galaxy. Using data from various photometric systems (Washington C, Kron-Cousins R, Bessel V and I, Hubble Space Telesecope F814W and F435W), we measured the brightness and colour profiles, as well as the structural parameters. By comparing these with those of other galaxies in the Antlia cluster, as well as with confirmed cE galaxies from the literature, we found that two of the cE candidates, although spectroscopically confirmed Antlia members, are not cE galaxies. However, one of these objects presents strong ellipticity and position angle variations that resemble those already reported for M32, leading us to speculate about this type of object being a progenitor of a cE galaxy. The other two cE candidates, for which radial velocities are not available, match some features typical of cE galaxies, such as being close in projection to a larger galaxy, displaying flat colour profiles, and having a high degree of compactness. Only one of the remaining cE candidates shows a high central surface brightness, two components in its brightness profile and distinct changes in ellipticity and position angle where the outer component begins to dominate. It seems to follow the same trend as other confirmed cE galaxies in a luminosity versus mean effective surface brightness diagram. Moreover, it shows a distorted inner structure with similar characteristics to those found by simulations of interacting galaxies. Also, an extremely faint structure, which seems to link this object with one of the Antlia dominant galaxies, has been detected in images from the Cerro Tololo Inter-American Observatory MOSAIC, the Very Large Telescope FORS1 and the Hubble Space Telescope Advanced Camera for

  18. Seeing Baby Dwarf Galaxies

    NASA Technical Reports Server (NTRS)

    2009-01-01

    [figure removed for brevity, see original site] [figure removed for brevity, see original site] [figure removed for brevity, see original site] Visible/DSS Click on image for larger version Ultraviolet/GALEX Click on image for larger version Poster Version Click on image for larger version

    The unique ultraviolet vision of NASA's Galaxy Evolution Explorer reveals, for the first time, dwarf galaxies forming out of nothing more than pristine gas likely leftover from the early universe. Dwarf galaxies are relatively small collections of stars that often orbit around larger galaxies like our Milky Way.

    The forming dwarf galaxies shine in the far ultraviolet spectrum, rendered as blue in the call-out on the right hand side of this image. Near ultraviolet light, also obtained by the Galaxy Evolution Explorer, is displayed in green, and visible light from the blue part of the spectrum here is represented by red. The clumps (in circles) are distinctively blue, indicating they are primarily detected in far ultraviolet light.

    The faint blue overlay traces the outline of the Leo Ring, a huge cloud of hydrogen and helium that orbits around two massive galaxies in the constellation Leo (left panel). The cloud is thought likely to be a primordial object, an ancient remnant of material that has remained relatively unchanged since the very earliest days of the universe. Identified about 25 years ago by radio waves, the ring cannot be seen in visible light.

    Only a portion of the Leo Ring has been imaged in the ultraviolet, but this section contains the telltale ultraviolet signature of recent massive star formation within this ring of pristine gas. Astronomers have previously only seen dwarf galaxies form out of gas that has already been cycled through a galaxy and enriched with metals elements heavier than helium produced as stars evolve.

    The visible data come from the Digitized Sky Survey of the Space Telescope Science Institute in Baltimore, Md. The

  19. Galaxies et trous noirs supermassifs

    NASA Astrophysics Data System (ADS)

    Collin-Zahn, Suzy

    2016-08-01

    A few percents of galaxies are classified as « active ». An active galaxy is a galaxy whose nucleus emits more energy than the whole galaxy in the form of electromagnetic radiation, relativistic particles, or mechanical energy. It is activated by a supermassive black hole fueled by matter falling on it, whose characteristics (Eddington luminosity, spin) are recalled. The class includes quasars and Seyfert galaxies. All massive "non active" galaxies contain a supermassive black hole, but there is not enough matter in its environment so as the nucleus becomes luminous. Different items are considered in the paper : how supermassive black holes are fueled, the accretion disc, the jets and the winds, the unified model of active galaxies, how are determined the masses of supermassive black holes, and what is the relation between the evolution of galaxies and supermassive black holes.

  20. Exploring the overabundance of ultraluminous X-ray sources in metal- and dust-poor local Lyman break analogs

    NASA Astrophysics Data System (ADS)

    Basu-Zych, Antara; Lehmer, Bret; Fragos, Tassos; Hornschemeier, Ann E.; Zezas, Andreas; Yukita, Mihoko; Ptak, Andrew

    2016-01-01

    We have studied high mass X-ray binary (HMXB) populations within two low-metallicity, starburst galaxies, Haro 11 and VV 114. These galaxies serve as analogs to high-redshift (z > 2) Lyman break galaxies, and within the larger sample of Lyman break analogs (LBAs) are sufficiently nearby (< 87 Mpc) to be spatially-resolved by Chandra. Previous studies of the X-ray emission in LBAs have found that the 2-10 keV luminosity per star formation rate (SFR) in these galaxies is elevated, potentially because of their low metallicities (12+log[O/H]=8.3-8.4). Theoretically, the progenitors of XRBs forming in lower metallicity environments lose less mass from stellar winds over their lifetimes, producing more massive compact objects (i.e., neutron stars and black holes), and thus resulting in more numerous and luminous HMXBs per SFR. In this talk, I present our in-depth study of the only two LBAs that have spatially-resolved 2-10 keV emission with Chandra to present the bright end of the X-ray luminosity distribution of HMXBs (LX>1039 erg s-1 ultraluminous X-ray sources, ULXs) in these low-metallicity galaxies, based on 8 detected ULXs. Comparing with the star-forming galaxy X-ray luminosity function (XLF), Haro 11 and VV 114 host ~4 times more LX>1040 erg s-1 sources than expected given their SFRs. We simulate the effects of source blending from crowded lower luminosity HMXBs using the star-forming galaxy XLF and then vary the XLF normalizations and bright-end slopes until we reproduce the observed point source luminosity distributions. Based on this analysis, we find that these LBAs have a shallower bright end slope than the standard XLF.

  1. Galaxy Centaurus A

    NASA Technical Reports Server (NTRS)

    2003-01-01

    This image of the active galaxy Centaurus A was taken by NASA's Galaxy Evolution Explorer on June 7, 2003. The galaxy is located 30 million light-years from Earth and is seen edge on, with a prominent dust lane across the major axis. In this image the near ultraviolet emission is represented as green, and the far ultraviolet emission as blue. The galaxy exhibits jets of high energy particles, which were traced by the X-ray emission and measured by NASA's Chandra X-ray Observatory. These X-ray emissions are seen as red in the image. Several regions of ultraviolet emission can be seen where the jets of high energy particles intersect with hydrogen clouds in the upper left corner of the image. The emission shown may be the result of recent star formation triggered by the compression of gas by the jet.

    The Galaxy Evolution Explorer mission is led by the California Institute of Technology, which is also responsible for the science operations and data analysis. NASA's Jet Propulsion Laboratory, Pasadena, Calif., a division of Caltech, manages the mission and built the science instrument. The mission was developed under NASA's Explorers Program, managed by the Goddard Space Flight Center, Greenbelt, Md. The mission's international partners include South Korea and France.

  2. Tidal alignment of galaxies

    NASA Astrophysics Data System (ADS)

    Blazek, Jonathan; Vlah, Zvonimir; Seljak, Uroš

    2015-08-01

    We develop an analytic model for galaxy intrinsic alignments (IA) based on the theory of tidal alignment. We calculate all relevant nonlinear corrections at one-loop order, including effects from nonlinear density evolution, galaxy biasing, and source density weighting. Contributions from density weighting are found to be particularly important and lead to bias dependence of the IA amplitude, even on large scales. This effect may be responsible for much of the luminosity dependence in IA observations. The increase in IA amplitude for more highly biased galaxies reflects their locations in regions with large tidal fields. We also consider the impact of smoothing the tidal field on halo scales. We compare the performance of this consistent nonlinear model in describing the observed alignment of luminous red galaxies with the linear model as well as the frequently used "nonlinear alignment model," finding a significant improvement on small and intermediate scales. We also show that the cross-correlation between density and IA (the "GI" term) can be effectively separated into source alignment and source clustering, and we accurately model the observed alignment down to the one-halo regime using the tidal field from the fully nonlinear halo-matter cross correlation. Inside the one-halo regime, the average alignment of galaxies with density tracers no longer follows the tidal alignment prediction, likely reflecting nonlinear processes that must be considered when modeling IA on these scales. Finally, we discuss tidal alignment in the context of cosmic shear measurements.

  3. THE MERGER-DRIVEN EVOLUTION OF MASSIVE GALAXIES

    SciTech Connect

    Robaina, Aday R.; Van der Wel, Arjen; Skelton, Rosalind E.; Meisenheimer, Klaus; Bell, Eric F.; Somerville, Rachel S.; McIntosh, Daniel H.; Wolf, Christian

    2010-08-10

    We explore the rate and impact of galaxy mergers on the massive galaxy population using the amplitude of the two-point correlation function on small scales for M {sub *} > 5 x 10{sup 10} M {sub sun} galaxies from the COSMOS and COMBO-17 surveys. Using a pair fraction derived from the Sloan Digital Sky Survey as a low-redshift benchmark, the large survey area at intermediate redshifts allows us to determine the evolution of the close-pair fraction with unprecedented accuracy for a mass-selected sample: we find that the fraction of galaxies more massive than 5 x 10{sup 10} M {sub sun} in pairs separated by less than 30 kpc in three-dimensional space evolves as F(z) = (0.0130 {+-} 0.0019) x (1 + z){sup 1.21{+-}0.25} between z = 0 and z = 1.2. Assuming a merger timescale of 0.5 Gyr, the inferred merger rate is such that galaxies with mass in excess of 10{sup 11} M {sub sun} have undergone, on average, 0.5 (0.7) mergers involving progenitor galaxies both more massive than 5 x 10{sup 10} M {sub sun} since z = 0.6 (1.2). We also study the number density evolution of massive red sequence galaxies using published luminosity functions and constraints on the M/L {sub B} evolution from the fundamental plane. Moreover, we demonstrate that the measured merger rate of massive galaxies is sufficient to explain this observed number density evolution in massive red sequence galaxies since z = 1.

  4. Recent Galaxy Mergers and Residual Star Formation of Red Sequence Galaxies in Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Sheen, Yun-Kyeong; Yi, Sukyoung K.; Ree, Chang H.; Jaffé, Yara; Demarco, Ricardo; Treister, Ezequiel

    2016-08-01

    This study explored the Galaxy Evolution Explorer ultraviolet (UV) properties of optical red sequence galaxies in four rich Abell clusters at z≤slant 0.1. In particular, we tried to find a hint of merger-induced recent star formation (RSF) in red sequence galaxies. Using the NUV - r\\prime colors of the galaxies, RSF fractions were derived based on various criteria for post-merger galaxies and normal galaxies. Following k-correction, about 36% of the post-merger galaxies were classified as RSF galaxies with a conservative criterion (NUV - r\\prime ≤slant 5), and that number was doubled (˜72%) when using a generous criterion (NUV - r\\prime ≤slant 5.4). The trend was the same when we restricted the sample to galaxies within 0.5 × R 200. Post-merger galaxies with strong UV emission showed more violent, asymmetric features in the deep optical images. The RSF fractions did not show any trend along the clustocentric distance within R 200. We performed a Dressler–Shectman test to check whether the RSF galaxies had any correlation with the substructures in the galaxy clusters. Within R 200 of each cluster, the RSF galaxies did not appear to be preferentially related to the clusters’ substructures. Our results suggested that only 30% of RSF red sequence galaxies show morphological hints of recent galaxy mergers. This implies that internal processes (e.g., stellar mass loss or hot gas cooling) for the supply of cold gas to early-type galaxies may play a significant role in the residual star formation of early-type galaxies at a recent epoch.

  5. Recent Galaxy Mergers and Residual Star Formation of Red Sequence Galaxies in Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Sheen, Yun-Kyeong; Yi, Sukyoung K.; Ree, Chang H.; Jaffé, Yara; Demarco, Ricardo; Treister, Ezequiel

    2016-08-01

    This study explored the Galaxy Evolution Explorer ultraviolet (UV) properties of optical red sequence galaxies in four rich Abell clusters at z≤slant 0.1. In particular, we tried to find a hint of merger-induced recent star formation (RSF) in red sequence galaxies. Using the NUV - r\\prime colors of the galaxies, RSF fractions were derived based on various criteria for post-merger galaxies and normal galaxies. Following k-correction, about 36% of the post-merger galaxies were classified as RSF galaxies with a conservative criterion (NUV - r\\prime ≤slant 5), and that number was doubled (˜72%) when using a generous criterion (NUV - r\\prime ≤slant 5.4). The trend was the same when we restricted the sample to galaxies within 0.5 × R 200. Post-merger galaxies with strong UV emission showed more violent, asymmetric features in the deep optical images. The RSF fractions did not show any trend along the clustocentric distance within R 200. We performed a Dressler-Shectman test to check whether the RSF galaxies had any correlation with the substructures in the galaxy clusters. Within R 200 of each cluster, the RSF galaxies did not appear to be preferentially related to the clusters’ substructures. Our results suggested that only 30% of RSF red sequence galaxies show morphological hints of recent galaxy mergers. This implies that internal processes (e.g., stellar mass loss or hot gas cooling) for the supply of cold gas to early-type galaxies may play a significant role in the residual star formation of early-type galaxies at a recent epoch.

  6. Exploring the optical and infrared evolution of galaxies

    NASA Astrophysics Data System (ADS)

    Melbourne, Jason

    We track the evolution of galaxy optical and mid-infrared luminosity and color, morphology, and half-light radius, observables that are tied to their star formation history. In agreement with previous studies, we find that the B-band optical and total infrared luminosities of blue galaxies have declined since z = 1. We also find that the infrared luminosity of spiral galaxies has declined more rapidly than for peculiar/merger types. In addition, we find that the optical evolution can be explained by a radius dependent luminosity evolution. Assuming a linear shift in MB with z, we use a maximum likelihood method to quantify the evolution. Under these assumptions, large (R1/2 > 5 kpc), and intermediate sized (3 < R1/2 < 5 kpc) galaxies, have experienced 1.55(+0.10, -0.15) and 1.70(+0.13, -0.10) magnitudes of dimming since z = 1. This luminosity evolution can be explained by a simple exponential decline in star formation with an e-folding tune of ˜ 3 Gyr. Meanwhile, small galaxies, or some subset thereof, have experienced more evolution, 2.40(+/-0.23) magnitudes. This factor of ten decline in luminosity is too large to be explained by simple exponential models, but can be explained by starbursting dwarf systems that fade rapidly, coupled with a decline in burst strength or frequency. This thesis also prepares us for a detailed study of the sites and triggers of star formation in these galaxies. The Center for Adaptive Optics Treasury Survey has been observing the deep HST galaxies fields with high resolution near-infrared imaging with Keck adaptive optics (AO). In this thesis, we demonstrate that the combination of HST optical and near-IR from Keck AO allows us to measure the stellar population of galaxy substructures and to break the dust-age degeneracy. We also demonstrate that 10% photometry on faint extra-galactic systems is possible with Keck AO despite a point-spread-function that is varying both temporally and spatially. With the AO tools developed in this

  7. Z'-mediated supersymmetry breaking.

    PubMed

    Langacker, Paul; Paz, Gil; Wang, Lian-Tao; Yavin, Itay

    2008-02-01

    We consider a class of models in which supersymmetry breaking is communicated dominantly via a U1' gauge interaction, which also helps solve the mu problem. Such models can emerge naturally in top-down constructions and are a version of split supersymmetry. The spectrum contains heavy sfermions, Higgsinos, exotics, and Z' approximately 10-100 TeV, light gauginos approximately 100-1000 GeV, a light Higgs boson approximately 140 GeV, and a light singlino. A specific set of U1' charges and exotics is analyzed, and we present five benchmark models. The implications for the gluino lifetime, cold dark matter, and the gravitino and neutrino masses are discussed. PMID:18352261

  8. Longitudinal vortices beneath breaking waves

    NASA Astrophysics Data System (ADS)

    Nepf, H. M.; Cowen, E. A.; Kimmel, S. J.; Monismith, S. G.

    1995-08-01

    The formation of longitudinal vortices has been observed in a wavy channel flow and appears to be linked to spilling breaking and/or to vertical vorticity generated by a wave instability at the wave maker. Both conditions were present when the wave slope, ak exceeded 0.25. The wave instability produced velocity jets beneath and just downstream of the plunger that could provide the initial perturbation for the CL2 instability mechanism (Faller and Caponi, 1978). The breaker activity could also contribute to the CL2 production mechanism by eliminating the negative, stabilizing shear observed within the wave maker wake and by providing seed perturbations to the vorticity field. As the cells evolved downstream, they were maintained through interaction with the bottom boundary layer. When the vortices were present, both vertical mixing and turbulent kinetic energy were enhanced. Despite some differences in scale these results suggest that Langmuir circulation may produce similar changes in the mixed layer.

  9. Modeling the distribution of Mg II absorbers around galaxies using background galaxies and quasars

    SciTech Connect

    Bordoloi, R.; Lilly, S. J.; Kacprzak, G. G.; Churchill, C. W.

    2014-04-01

    We present joint constraints on the distribution of Mg II absorption around high redshift galaxies obtained by combining two orthogonal probes, the integrated Mg II absorption seen in stacked background galaxy spectra and the distribution of parent galaxies of individual strong Mg II systems as seen in the spectra of background quasars. We present a suite of models that can be used to predict, for different two- and three-dimensional distributions, how the projected Mg II absorption will depend on a galaxy's apparent inclination, the impact parameter b and the azimuthal angle between the projected vector to the line of sight and the projected minor axis. In general, we find that variations in the absorption strength with azimuthal angles provide much stronger constraints on the intrinsic geometry of the Mg II absorption than the dependence on the inclination of the galaxies. In addition to the clear azimuthal dependence in the integrated Mg II absorption that we reported earlier in Bordoloi et al., we show that strong equivalent width Mg II absorbers (W{sub r} (2796) ≥ 0.3 Å) are also asymmetrically distributed in azimuth around their host galaxies: 72% of the absorbers in Kacprzak et al., and 100% of the close-in absorbers within 35 kpc of the center of their host galaxies, are located within 50° of the host galaxy's projected semi minor axis. It is shown that either composite models consisting of a simple bipolar component plus a spherical or disk component, or a single highly softened bipolar distribution, can well represent the azimuthal dependencies observed in both the stacked spectrum and quasar absorption-line data sets within 40 kpc. Simultaneously fitting both data sets, we find that in the composite model the bipolar cone has an opening angle of ∼100° (i.e., confined to within 50° of the disk axis) and contains about two-thirds of the total Mg II absorption in the system. The single softened cone model has an exponential fall off with azimuthal

  10. THE DEEP2 GALAXY REDSHIFT SURVEY: THE VORONOI-DELAUNAY METHOD CATALOG OF GALAXY GROUPS

    SciTech Connect

    Gerke, Brian F.; Newman, Jeffrey A.; Davis, Marc; Coil, Alison L.; Cooper, Michael C.; Dutton, Aaron A.; Faber, S. M.; Guhathakurta, Puragra; Koo, David C.; Phillips, Andrew C.; Noeske, Kai; Rosario, David J.; Weiner, Benjamin J.; Willmer, Christopher N. A.; Yan, Renbin

    2012-05-20

    We present a public catalog of galaxy groups constructed from the spectroscopic sample of galaxies in the fourth data release from the Deep Extragalactic Evolutionary Probe 2 (DEEP2) Galaxy Redshift Survey, including the Extended Groth Strip (EGS). The catalog contains 1165 groups with two or more members in the EGS over the redshift range 0 < z < 1.5 and 1295 groups at z > 0.6 in the rest of DEEP2. Twenty-five percent of EGS galaxies and fourteen percent of high-z DEEP2 galaxies are assigned to galaxy groups. The groups were detected using the Voronoi-Delaunay method (VDM) after it has been optimized on mock DEEP2 catalogs following similar methods to those employed in Gerke et al. In the optimization effort, we have taken particular care to ensure that the mock catalogs resemble the data as closely as possible, and we have fine-tuned our methods separately on mocks constructed for the EGS and the rest of DEEP2. We have also probed the effect of the assumed cosmology on our inferred group-finding efficiency by performing our optimization on three different mock catalogs with different background cosmologies, finding large differences in the group-finding success we can achieve for these different mocks. Using the mock catalog whose background cosmology is most consistent with current data, we estimate that the DEEP2 group catalog is 72% complete and 61% pure (74% and 67% for the EGS) and that the group finder correctly classifies 70% of galaxies that truly belong to groups, with an additional 46% of interloper galaxies contaminating the catalog (66% and 43% for the EGS). We also confirm that the VDM catalog reconstructs the abundance of galaxy groups with velocity dispersions above {approx}300 km s{sup -1} to an accuracy better than the sample variance, and this successful reconstruction is not strongly dependent on cosmology. This makes the DEEP2 group catalog a promising probe of the growth of cosmic structure that can potentially be used for cosmological tests.

  11. CONNECTIONS BETWEEN GALAXY MERGERS AND STARBURST: EVIDENCE FROM THE LOCAL UNIVERSE

    SciTech Connect

    Luo, Wentao; Yang, Xiaohu; Zhang, Youcai E-mail: xyang@sjtu.edu.cn

    2014-07-01

    Major mergers and interactions between gas-rich galaxies with comparable masses are thought to be the main triggers of starburst. In this work, we study, for a large stellar mass range, the interaction rate of the starburst galaxies in the local universe. We focus independently on central and satellite star forming galaxies extracted from the Sloan Digital Sky Survey. Here the starburst galaxies are selected in the star formation rate (SFR) stellar mass plane with SFRs five times larger than the median value found for ''star forming'' galaxies of the same stellar mass. Through visual inspection of their images together with close companions determined using spectroscopic redshifts, we find that ∼50% of the ''starburst'' populations show evident merger features, i.e., tidal tails, bridges between galaxies, double cores, and close companions. In contrast, in the control sample we selected from the normal star forming galaxies, only ∼19% of galaxies are associated with evident mergers. The interaction rates may increase by ∼5% for the starburst sample and 2% for the control sample if close companions determined using photometric redshifts are considered. The contrast of the merger rate between the two samples strengthens the hypothesis that mergers and interactions are indeed the main causes of starburst.

  12. Active galactic nuclei and galaxy interactions

    NASA Astrophysics Data System (ADS)

    Alonso, M. Sol; Lambas, Diego G.; Tissera, Patricia; Coldwell, Georgina

    2007-03-01

    We perform a statistical analysis of active galactic nucleus (AGN) host characteristics and nuclear activity for AGNs in pairs and without companions. Our study concerns a sample of AGNs derived from the Sloan Digital Sky Survey Data Release 4 data by Kauffmann et al. and pair galaxies obtained from the same data set by Alonso et al. An eye-ball classification of images of 1607 close pairs (rp < 25 kpc h-1,ΔV < 350 km s-1) according to the evidence of interaction through distorted morphologies and tidal features provides us with a more confident assessment of galaxy interactions from this sample. We notice that, at a given luminosity or stellar mass content, the fraction of AGNs is larger for pair galaxies exhibiting evidence for strong interaction and tidal features which also show signs of strong star formation activity. Nevertheless, this process accounts only for a ~10per cent increase of the fraction of AGNs. As in previous works, we find AGN hosts to be redder and with a larger concentration morphological index than non-AGN galaxies. This effect does not depend on whether AGN hosts are in pairs or in isolation. The OIII luminosity of AGNs with strong interaction features is found to be significantly larger than that of other AGNs, either in pairs or in isolation. Estimations of the accretion rate, L[OIII]/MBH, show that AGNs in merging pairs are actively feeding their black holes, regardless of their stellar masses. We also find that the luminosity of the companion galaxy seems to be a key parameter in the determination of the black hole activity. At a given host luminosity, both the OIII luminosity and the L[ OIII]/MBH are significantly larger in AGNs with a bright companion (Mr < -20) than otherwise.

  13. Galaxy Evolution Insights from Spectral Modeling of Large Data Sets from the Sloan Digital Sky Survey

    SciTech Connect

    Hoversten, Erik A.

    2007-10-01

    This thesis centers on the use of spectral modeling techniques on data from the Sloan Digital Sky Survey (SDSS) to gain new insights into current questions in galaxy evolution. The SDSS provides a large, uniform, high quality data set which can be exploited in a number of ways. One avenue pursued here is to use the large sample size to measure precisely the mean properties of galaxies of increasingly narrow parameter ranges. The other route taken is to look for rare objects which open up for exploration new areas in galaxy parameter space. The crux of this thesis is revisiting the classical Kennicutt method for inferring the stellar initial mass function (IMF) from the integrated light properties of galaxies. A large data set (~ 105 galaxies) from the SDSS DR4 is combined with more in-depth modeling and quantitative statistical analysis to search for systematic IMF variations as a function of galaxy luminosity. Galaxy Hα equivalent widths are compared to a broadband color index to constrain the IMF. It is found that for the sample as a whole the best fitting IMF power law slope above 0.5 M is Γ = 1.5 ± 0.1 with the error dominated by systematics. Galaxies brighter than around Mr,0.1 = -20 (including galaxies like the Milky Way which has Mr,0.1 ~ -21) are well fit by a universal Γ ~ 1.4 IMF, similar to the classical Salpeter slope, and smooth, exponential star formation histories (SFH). Fainter galaxies prefer steeper IMFs and the quality of the fits reveal that for these galaxies a universal IMF with smooth SFHs is actually a poor assumption. Related projects are also pursued. A targeted photometric search is conducted for strongly lensed Lyman break galaxies (LBG) similar to MS1512-cB58. The evolution of the photometric selection technique is described as are the results of spectroscopic follow-up of the best targets. The serendipitous discovery of two interesting blue compact dwarf galaxies is reported. These

  14. Fragmentation in the First Galaxies

    NASA Astrophysics Data System (ADS)

    Safranek-Shrader, Chalence; Bromm, Volker; Milosavljević, Miloš

    2010-11-01

    Motivated by recent simulations of galaxy formation in which protogalaxies acquire their baryonic content through cold accretion, we study the gravitational fragmentation of cold streams flowing into a typical first galaxy. We use a one-zone hydrodynamical model to examine the thermal evolution of the gas flowing into a 108 M sun dark matter halo at redshift z = 10. The goal is to gain an understanding of the expected fragmentation mass scale and thus the characteristic mass of the first population of stars to form by shock fragmentation. Our model accurately describes the chemical and thermal evolution of the gas as we are specifically concerned with how the chemical abundances and initial conditions of the low-density, metal-enriched, cold accretion streams that pass an accretion shock alter the cooling properties and tendency to fragment in the post-shock gas. Cold accretion flows are not shock heated at the virial radius but instead flow along high-baryonic-density filaments of the cosmic web and penetrate deep into the host halo of the protogalaxy. In this physical regime, if molecular cooling is absent because of a strong Lyman-Werner background, we find there to be a sharp drop in the fragmentation mass at a metallicity of Z ~ 10-4 Z sun. If, however, H2 and HD molecules are present, they dominate the cooling at T < 104 K, and metallicity then has no effect on the fragmentation properties of the cold stream. For a solar abundance pattern of metallicity, O is the most effective metal coolant throughout the evolution, while for a pair instability supernova (PISN) metallicity yield, Si+ is the most effective coolant. PISN abundance patterns also exhibit a slightly smaller critical metallicity. Dust grains are not included in our chemical model, but we argue that their inclusion would not significantly alter the results. We also find that this physical scenario allows for the formation of stellar clusters and large, 104 M sun bound fragments, possibly the

  15. FRAGMENTATION IN THE FIRST GALAXIES

    SciTech Connect

    Safranek-Shrader, Chalence; Bromm, Volker; Milosavljevic, Milos

    2010-11-10

    Motivated by recent simulations of galaxy formation in which protogalaxies acquire their baryonic content through cold accretion, we study the gravitational fragmentation of cold streams flowing into a typical first galaxy. We use a one-zone hydrodynamical model to examine the thermal evolution of the gas flowing into a 10{sup 8} M{sub sun} dark matter halo at redshift z = 10. The goal is to gain an understanding of the expected fragmentation mass scale and thus the characteristic mass of the first population of stars to form by shock fragmentation. Our model accurately describes the chemical and thermal evolution of the gas as we are specifically concerned with how the chemical abundances and initial conditions of the low-density, metal-enriched, cold accretion streams that pass an accretion shock alter the cooling properties and tendency to fragment in the post-shock gas. Cold accretion flows are not shock heated at the virial radius but instead flow along high-baryonic-density filaments of the cosmic web and penetrate deep into the host halo of the protogalaxy. In this physical regime, if molecular cooling is absent because of a strong Lyman-Werner background, we find there to be a sharp drop in the fragmentation mass at a metallicity of Z {approx} 10{sup -4} Z{sub sun}. If, however, H{sub 2} and HD molecules are present, they dominate the cooling at T < 10{sup 4} K, and metallicity then has no effect on the fragmentation properties of the cold stream. For a solar abundance pattern of metallicity, O is the most effective metal coolant throughout the evolution, while for a pair instability supernova (PISN) metallicity yield, Si{sup +} is the most effective coolant. PISN abundance patterns also exhibit a slightly smaller critical metallicity. Dust grains are not included in our chemical model, but we argue that their inclusion would not significantly alter the results. We also find that this physical scenario allows for the formation of stellar clusters and large

  16. Peculiar galaxies and radio sources.

    PubMed

    Arp, H

    1966-03-11

    Pairs of radio sources which are separated by from 2 degrees to 6 degrees on the sky have been investigated. In a number of cases peculiar galaxies have been found approximately midway along a line joining the two radio sources. The central peculiar galaxies belong mainly to a certain class in the recently compiled Atlas of Peculiar Galaxies. Among the radio sources so far associated with the peculiar galaxies are at least five known quasars. These quasars are indicated to be not at cosmological distances (that is, red shifts not caused by expansion of the universe) because the central peculiar galaxies are only at distances of 10 to 100 megaparsecs. The absolute magnitudes of these quasars are indicated to be in the range of brightness of normal galaxies and downward. Some of the radio sources which have been found to be associated with peculiar galaxies are galaxies themselves. It is therefore implied that ejection of material took place within or near the parent peculiar galaxies with speeds between 10(2) and 10(4) kilometers per second. After traveling for times of the order of 10(7) to 10(9) years, the luminous matter (galaxies) and radio sources (plasma) have reached their observed separations from the central peculiar galaxy. The large red shifts measured for the quasars would seem to be either (i) gravitational, (ii) collapse velocities of clouds of material falling toward the center of these compact galaxies, or (iii) some as yet unknown cause.

  17. Kepler View of the Galaxy

    NASA Video Gallery

    Our Sun is just one out of over 200 billion stars in our galaxy, the Milky Way. The Sun is located in the Orion arm of our galaxy about 75,000 light years from the center of the Galaxy. Kepler will...

  18. Constraints on galaxy formation theories

    NASA Technical Reports Server (NTRS)

    Szalay, A. S.

    1986-01-01

    The present theories of galaxy formation are reviewed. The relation between peculiar velocities, temperature fluctuations of the microwave background and the correlation function of galaxies point to the possibility that galaxies do not form uniformly everywhere. The velocity data provide strong constraints on the theories even in the case when light does not follow mass of the universe.

  19. Dark-ages reionization and galaxy formation simulation - IV. UV luminosity functions of high-redshift galaxies

    NASA Astrophysics Data System (ADS)

    Liu, Chuanwu; Mutch, Simon J.; Angel, P. W.; Duffy, Alan R.; Geil, Paul M.; Poole, Gregory B.; Mesinger, Andrei; Wyithe, J. Stuart B.

    2016-10-01

    In this paper, we present calculations of the UV luminosity function (LF) from the Dark-ages Reionization And Galaxy-formation Observables from Numerical Simulations project, which combines N-body, semi-analytic and seminumerical modelling designed to study galaxy formation during the Epoch of Reionization. Using galaxy formation physics including supernova feedback, the model naturally reproduces the UV LFs for high-redshift star-forming galaxies from z ˜ 5 through to z ˜ 10. We investigate the luminosity-star formation rate (SFR) relation, finding that variable SFR histories of galaxies result in a scatter around the median relation of 0.1-0.3 dex depending on UV luminosity. We find close agreement between the model and observationally derived SFR functions. We use our calculated luminosities to investigate the LF below current detection limits, and the ionizing photon budget for reionization. We predict that the slope of the UV LF remains steep below current detection limits and becomes flat at MUV ≳ -14. We find that 48 (17) per cent of the total UV flux at z ˜ 6 (10) has been detected above an observational limit of MUV ˜ -17, and that galaxies fainter than MUV ˜ -17 are the main source of ionizing photons for reionization. We investigate the luminosity-stellar mass relation, and find a correlation for galaxies with MUV < -14 that has the form M_{ast } ∝ 10^{-0.47M_UV}, in good agreement with observations, but which flattens for fainter galaxies. We determine the luminosity-halo mass relation to be M_vir ∝ 10^{-0.35M_UV}, finding that galaxies with MUV = -20 reside in host dark matter haloes of 1011.0±0.1 M⊙ at z ˜ 6, and that this mass decreases towards high redshift.

  20. Microvariability in Seyfert galaxies

    USGS Publications Warehouse

    Carini, M.T.; Noble, J.C.; Miller, H.R.

    2003-01-01

    We present the results of a search for microvariability in a sample of eight Seyfert galaxies. Microvariability (i.e., variations occurring on timescales of tens of minutes to hours) has been conclusively demonstrated to exist in the class of active galactic nuclei (AGNs) known as blazars. Its existence in other classes of AGNs is far less certain. We present the results of a study of eight Seyfert 1 galaxies, which were intensively monitored in order to determine whether such variations exist in these objects. Only one object, Ark 120, displayed any evidence of microvariations. The implications of these results with respect to current models of the mechanisms responsible for the observed emission in Seyfert galaxies are discussed. We compare our results with those obtained from other studies of microvariability in different classes of AGNs.

  1. Local normal galaxies

    NASA Technical Reports Server (NTRS)

    Fichtel, Carl E.

    1990-01-01

    In the near future, high energy (E greater than 20 MeV) gamma ray astronomy offers the promise of a new means of examining the closest galaxies. Two and possibly three local galaxies, the Small and Large Magellanic Clouds and M31, should be visible to the high energy gamma ray telescope on the Gamma Ray Observatory, and the first should be seen by GAMMA-1. With the assumptions of adequate cosmic ray production and reasonable magnetic field strengths, both of which should likely be satisfied, specific predictions of the gamma ray emission can be made separating the concepts of the galactic and universal nature of cosmic rays. A study of the synchrotron radiation from the Large Magellanic Cloud (LMC) suggests that the cosmic ray density is similar to that in the local region of our galaxy, but not uniform. It is hoped the measurements will be able to verify this independent of assumptions about the magnetic fields in the LMC.

  2. High redshift radio galaxies

    NASA Technical Reports Server (NTRS)

    Mccarthy, Patrick J.

    1993-01-01

    High redshift galaxies that host powerful radio sources are examined. An overview is presented of the content of radio surveys: 3CR and 3CRR, 4C and 4C/USS, B2/1 Jy, MG, MRC/1Jy, Parkes/PSR, B3, and ESO Key-Project. Narrow-line radio galaxies in the visible and UV, the source of ionization and excitation of the emission lines, emission-line luminosities, morphology of the line-emitting gas, physical properties and energetics, kinematics of the line-emitting gas, and implications from the emission lines are discussed. The morphologies and environments of the host galaxies, the alignment effect, and spectral energy distributions and ages are also examined.

  3. Edge-on Galaxy

    NASA Technical Reports Server (NTRS)

    1999-01-01

    NASA's Hubble Space Telescope has imaged an unusual edge-on galaxy, revealing remarkable details of its warped dusty disc and showing how colliding galaxies trigger the birth of new stars.

    The image, taken by Hubble's Wide Field and Planetary Camera 2 (WFPC2), is online at http://heritage.stsci.edu and http://www.jpl.nasa.gov/images/wfpc. The camera was designed and built by NASA's Jet Propulsion Laboratory, Pasadena, Calif. During observations of the galaxy, the camera passed a milestone, taking its 100,000th image since shuttle astronauts installed it in Hubble in 1993.

    The dust and spiral arms of normal spiral galaxies, like our Milky Way, look flat when seen edge- on. The new image of the galaxy ESO 510-G13 shows an unusual twisted disc structure, first seen in ground-based photographs taken at the European Southern Observatory in Chile. ESO 510-G13 lies in the southern constellation Hydra, some 150 million light-years from Earth. Details of the galaxy's structure are visible because interstellar dust clouds that trace its disc are silhouetted from behind by light from the galaxy's bright, smooth central bulge.

    The strong warping of the disc indicates that ESO 510-G13 has recently collided with a nearby galaxy and is in the process of swallowing it. Gravitational forces distort galaxies as their stars, gas, and dust merge over millions of years. When the disturbances die out, ESO 510-G13 will be a single galaxy.

    The galaxy's outer regions, especially on the right side of the image, show dark dust and bright clouds of blue stars. This indicates that hot, young stars are forming in the twisted disc. Astronomers believe star formation may be triggered when galaxies collide and their interstellar clouds are compressed.

    The Hubble Heritage Team used WFPC2 to observe ESO 510-G13 in April 2001. Pictures obtained through blue, green, and red filters were combined to make this color-composite image, which emphasizes the contrast between the dusty

  4. Issues in standard model symmetry breaking

    SciTech Connect

    Golden, M.

    1988-04-01

    This work discusses the symmetry breaking sector of the SU(2) x U(1) electroweak model. The first two chapters discuss Higgs masses in two simple Higgs models. The author proves low-enery theorems for the symmetry breaking sector: The threshold behavior of gauge-boson scattering is completely determined, whenever the symmetry breaking sector meets certain simple conditions. The author uses these theorems to derive event rates for the superconducting super collider (SSC). The author shows that the SSC may be able to determine whether the interactions of the symmetry breaking sector are strong or weak. 54 refs.

  5. OPTOPUS spectroscopy of galaxies

    NASA Astrophysics Data System (ADS)

    Schnur, G. F. O.

    The spectra of selected H II regions in the center of the starburst galaxy NGC 1808 and of many faint galaxies surrounding the NGC 1808 were obtained simultaneously, using the Optopus fiber-optics spectrograph facility (described by Lund, 1986) at the ESO 3.6-m telescope. The preparation of Optopus plates (each of which employed more than 40 fibers), observations, and the procedures of data processing and Optopus calibration are described together with the problems caused by cosmic ray events. Preliminary results are included.

  6. Galaxy Alignments: An Overview

    NASA Astrophysics Data System (ADS)

    Joachimi, Benjamin; Cacciato, Marcello; Kitching, Thomas D.; Leonard, Adrienne; Mandelbaum, Rachel; Schäfer, Björn Malte; Sifón, Cristóbal; Hoekstra, Henk; Kiessling, Alina; Kirk, Donnacha; Rassat, Anais

    2015-11-01

    The alignments between galaxies, their underlying matter structures, and the cosmic web constitute vital ingredients for a comprehensive understanding of gravity, the nature of matter, and structure formation in the Universe. We provide an overview on the state of the art in the study of these alignment processes and their observational signatures, aimed at a non-specialist audience. The development of the field over the past one hundred years is briefly reviewed. We also discuss the impact of galaxy alignments on measurements of weak gravitational lensing, and discuss avenues for making theoretical and observational progress over the coming decade.

  7. Dwarf galaxy evolution within the environments of massive galaxies

    NASA Astrophysics Data System (ADS)

    Arraki, Kenza S.; Klypin, Anatoly A.; Ceverino, Daniel; Trujillo-Gomez, Sebastian; Primack, Joel R.

    2016-01-01

    Understanding galaxy evolution depends on connecting large-scale structure determined by the ΛCDM model with, at minimum, the small-scale physics of gas, star formation, and stellar feedback. Formation of galaxies within dark matter halos is sensitive to the physical phenomena occurring within and around the halo. This is especially true for dwarf galaxies, which have the smallest potential wells and are more susceptible to the effects of gas ionization and removal than larger galaxies. At dwarf galaxies scales comparisons of dark matter-only simulations with observations has unveiled various differences including the core-cusp, the missing satellites, and the too-big-to-fail problems. We have run a new suite of hydrodynamical simulations using the ART code to examine the evolution of dwarf galaxies in massive host environments. These are cosmological zoom-in simulations including deterministic star formation and stellar feedback in the form of supernovae feedback, stellar winds, radiation pressure, and photoionization pressure. We simulates galaxies with final halo masses on the order of 1012 M⊙ with high resolution, allowing us to examine the satellite dwarf galaxies and local isolated dwarf galaxies around each primary galaxy. We analyzed the abundance and structure of these dwarfs specifically the velocity function, their star formation rates, core creation and the circumgalactic medium. By reproducing observations of dwarf galaxies in simulations we show how including baryons in simulations relieves tensions seen in comparing dark matter only simulations with observations.

  8. On the Origin of the Mass-Metallicity Relation for GRB Host Galaxies

    SciTech Connect

    Kocevski, Daniel; West, Andrew A.; /Boston U., Dept. Astron.

    2011-06-02

    We investigate the nature of the mass-metallicity (M-Z) relation for long gamma-ray burst (LGRB) host galaxies. Recent studies suggest that the M-Z relation for local LGRB host galaxies may be systematically offset towards lower metallicities relative to the M-Z relation defined by the general star forming galaxy (SDSS) population. The nature of this offset is consistent with suggestions that low metallicity environments may be required to produce high mass progenitors, although the detection of several GRBs in high-mass, high-metallicity galaxies challenges the notion of a strict metallicity cut-off for host galaxies that are capable of producing GRBs. We show that the nature of this reported offset may be explained by a recently proposed anti-correlation between the star formation rate (SFR) and the metallicity of star forming galaxies. If low metallicity galaxies produce more stars than their equally massive, high-metallicity counterparts, then transient events that closely trace the SFR in a galaxy would be more likely to be found in these low metallicity, low mass galaxies. Therefore, the offset between the GRB and SDSS defined M-Z relations may be the result of the different methods used to select their respective galaxy populations, with GRBs being biased towards low metallicity, high SFR, galaxies. We predict that such an offset should not be expected of transient events that do not closely follow the star formation history of their host galaxies, such as short duration GRBs and SN Ia, but should be evident in core collapse SNe found through upcoming untargeted surveys.

  9. Galaxy And Mass Assembly (GAMA) blended spectra catalogue: strong galaxy-galaxy lens and occulting galaxy pair candidates

    NASA Astrophysics Data System (ADS)

    Holwerda, B. W.; Baldry, I. K.; Alpaslan, M.; Bauer, A.; Bland-Hawthorn, J.; Brough, S.; Brown, M. J. I.; Cluver, M. E.; Conselice, C.; Driver, S. P.; Hopkins, A. M.; Jones, D. H.; López-Sánchez, Á. R.; Loveday, J.; Meyer, M. J.; Moffett, A.

    2015-06-01

    We present the catalogue of blended galaxy spectra from the Galaxy And Mass Assembly (GAMA) survey. These are cases where light from two galaxies are significantly detected in a single GAMA fibre. Galaxy pairs identified from their blended spectrum fall into two principal classes: they are either strong lenses, a passive galaxy lensing an emission-line galaxy; or occulting galaxies, serendipitous overlaps of two galaxies, of any type. Blended spectra can thus be used to reliably identify strong lenses for follow-up observations (high-resolution imaging) and occulting pairs, especially those that are a late-type partly obscuring an early-type galaxy which are of interest for the study of dust content of spiral and irregular galaxies. The GAMA survey setup and its AUTOZ automated redshift determination were used to identify candidate blended galaxy spectra from the cross-correlation peaks. We identify 280 blended spectra with a minimum velocity separation of 600 km s-1, of which 104 are lens pair candidates, 71 emission-line-passive pairs, 78 are pairs of emission-line galaxies and 27 are pairs of galaxies with passive spectra. We have visually inspected the candidates in the Sloan Digital Sky Survey (SDSS) and Kilo Degree Survey (KiDS) images. Many blended objects are ellipticals with blue fuzz (Ef in our classification). These latter `Ef' classifications are candidates for possible strong lenses, massive ellipticals with an emission-line galaxy in one or more lensed images. The GAMA lens and occulting galaxy candidate samples are similar in size to those identified in the entire SDSS. This blended spectrum sample stands as a testament of the power of this highly complete, second-largest spectroscopic survey in existence and offers the possibility to expand e.g. strong gravitational lens surveys.

  10. Cosmological Constraints from Galaxy Clusters and Clustering in the Sloan Digital Sky Survey

    NASA Astrophysics Data System (ADS)

    Tinker, Jeremy

    2009-01-01

    I will present constraints on cosmological parameters from a combination of cluster mass to galaxy number ratios combined with halo occupation analysis of the galaxy autocorrelation function. In two-point clustering, cosmology an bias are degenerate; good fits to the correlation function can be obtained for a wide variety of comologies. However, in order to match the observed level of clustering, each cosmology predicts a different number of galaxies per unit mass at the cluster mass scale. A combination of DR7 galaxy clustering results and M/N data from the weak lensing analysis of the maxBCG catalog break the degeneracy between cosmology and bias, leading to constraints on \\Omega_m and \\sigma_8 that are competitive with current CMB results.

  11. Exploring The Gas Cycle In High-redshift Galaxies: A Joint Effort Of Theory And Observations

    NASA Astrophysics Data System (ADS)

    Fumagalli, Michele

    2012-01-01

    The evolution of high-redshift galaxies is regulated by the balance between the inflow of fresh fuel for star formation and the outflow of metal-polluted material from star forming regions. Hydrodynamic cosmological simulations indicate that galaxies at high redshifts are fed by extended streams of cold gas in a smooth component and in merging satellites, but direct evidence of this mode of accretion is lacking. To investigate the signatures of these "cold streams" in observations, we have studied the Lyman-α emission and hydrogen absorption properties in galaxies simulated at high-resolution, using state-of-the-art radiative transfer codes. I will present these model predictions and I will compare and contrast results of simulations with observations of high-redshift Lyman break galaxies. I will also discuss the prospects of mapping the circumgalactic medium with absorption line systems and present preliminary results from ongoing observations.

  12. Unveiling the Secret of a Virgo Dwarf Galaxy

    NASA Astrophysics Data System (ADS)

    2000-05-01

    case of the seemingly inconspicuous dwarf galaxy IC 3382 , the astronomers made an amazing discovery. When the best fitting model was removed from the observed image, a neat and regular spiral structure appeared in the residual image, cf. PR Photo 11/00 ! Nothing like this has ever been seen before in a dwarf elliptical galaxy. The light associated with the spiral constitutes a 3% modulation of the surface brightness. To see this effect at all, requires the excellent image quality of FORS1 and ANTU. The origin of the spiral structure What is the cause for this faintest and smallest spiral ever discovered in a galaxy? Two possible explanations have been proposed by the astronomers. It has been known for several decades that the spiral patterns seen in disk galaxies, like for instance in the Milky Way galaxy, are "density waves". The patterns are due to collective oscillations in the gravitational field that moves the stars and gas back and forth. The presence of a spiral pattern in IC3328 implies that it harbours a thin disk. The available data do not allow to distinguish between a pure disk galaxy, or a disk embedded in a spheroidal mass distribution. Both configurations are known to exist. Transient spiral patterns, as that seen in the well-known, nearby galaxy Messier 51, can be generated by tidal interactions . In the present case, there are two close and faint dwarf galaxies which may have disturbed IC3328 in the past and thereby produced the spiral pattern we now see. If what we see is a pure disk galaxy, the exceptionally small amplitude of the spiral pattern suggests another possibility: it could be swing-amplified noise . A modest amount of cold lumpy gas in the disk may have provided some initial "graininess" which was then gradually amplified by a shearing effect of the stellar orbits in the disk to produce the striking spiral pattern we now see. More information about this project A research article about this discovery is being published in the European

  13. Orbital dynamics in galaxy mergers

    NASA Astrophysics Data System (ADS)

    Hoffman, Loren

    In the favored vacuum energy + cold dark matter (ACDM) cosmology, galaxies form through a hierarchical merging process. Mergers between comparable-mass sys tems are qualitatively different from the ongoing accretion of small objects by much larger ones, in that they can radically transform the nature of the merging objects, e.g. through violent relaxation of the stars and dark matter, triggered starbursts, and quasar activity. This thesis covers two phenomena unique to major galaxy mergers: the formation of supermassive black hole (SMBH) binary and triple systems, and the transformation of the stellar orbit structure through violent relaxation, triggered gas inflow, and star formation. In a major merger, the SMBHs can spiral in and form a bound binary in less than a Hubble time. If the binary lifetime exceeds the typical time between mergers, then triple black hole (BH) systems may form. We study the statistics of close triple-SMBH encounters in galactic nuclei by computing a series of three-body orbits with physically-motivated initial conditions appropriate for giant elliptical galaxies. Our simulations include a smooth background potential consisting of a stellar bulge plus a dark matter halo, drag forces due to gravitational radiation and dynamical friction on the stars and dark matter, and a simple model of the time evolution of the inner density profile under heating and mass ejection by the SMBHs. We find that the binary pair coalesces as a result of repeated close encounters in ~85% of our runs. In about 40% of the runs the lightest BH is left wandering through the galactic halo or escapes the galaxy altogether. The triple systems typically scour out cores with mass deficits ~1-2 times their total mass. The high coalescence rate and prevalence of very high-eccentricity orbits could provide interesting signals for the future Laser Interferometer Space Antenna (LISA). Our study of remnant orbit structure involved 42 disk-disk mergers at various gas fractions

  14. Quantitative constraints on starburst cycles in galaxies with stellar masses in the range 108-1010 M⊙

    NASA Astrophysics Data System (ADS)

    Kauffmann, Guinevere

    2014-07-01

    We have used 4000 Å break and HδA indices in combination with SFR/M* derived from emission line flux measurements to constrain the recent star formation histories of galaxies with stellar masses in the range 108-1010 M⊙. The fraction of the total SFR density in galaxies with ongoing bursts is a strong function of stellar mass, declining from 0.85 at a stellar mass of 108 M⊙ to 0.25 for galaxies with M* ˜ 1010 M⊙. Low-mass galaxies are not all young. The distribution of half-mass formation times for galaxies with stellar masses less than 109 M⊙ is broad, spanning the range 1-10 Gyr. The peak-to-trough variation in star formation rate among the bursting population ranges lies in the range 10-25. In low-mass galaxies, the average duration of the bursts is comparable to the dynamical time of the galaxy. Galaxy structure is correlated with estimated burst mass fraction, but in different ways in low- and high-mass galaxies. High-mass galaxies with large burst mass fractions are more centrally concentrated, indicating that bulge formation is at work. In low-mass galaxies, stellar surface densities μ* decrease as a function of Fburst. These results are in good agreement with the observational predictions of Teyssier et al. and lend further credence to the idea that the cuspy halo problem can be solved by energy input from multiple starbursts over the lifetime of the galaxy. We note that there is no compelling evidence for initial mass function variations in the population of star-forming galaxies in the local Universe.

  15. A Comparison of the Galaxy Populations in the Coma and Distant Clusters: The Evolution of k+a Galaxies and the Role of the Intracluster Medium

    NASA Astrophysics Data System (ADS)

    Poggianti, Bianca M.; Bridges, Terry J.; Komiyama, Y.; Yagi, M.; Carter, Dave; Mobasher, Bahram; Okamura, S.; Kashikawa, N.

    2004-01-01

    The spectroscopic properties of galaxies in the Coma Cluster are compared with those of galaxies in rich clusters at z~0.5, to investigate the evolution of the star formation history in clusters. Luminous galaxies with MV<=-20 and poststarburst/post-star-forming (k+a) spectra that constitute a significant fraction of galaxies in distant cluster samples are absent in Coma, where spectacular cases of k+a spectra are found instead at MV>-18.5 and represent a significant proportion of the cluster dwarf galaxy population. A simple inspection of their positions on the sky indicates that this type of galaxy does not show a preferential location within the cluster, but the bluest and strongest lined group of k+a galaxies lie in projection toward the central 1.4 Mpc of Coma and have radial velocities significantly higher than the cluster mean. We find a striking correlation between the positions of these young and strong poststarburst galaxies and substructure in the hot intracluster medium (ICM) identified from XMM-Newton data, with these galaxies lying close to the edges of two infalling substructures. This result strongly suggests that the interaction with the dense ICM could be responsible for the quenching of the star formation (thus creating the k+a spectrum) and, possibly, for any previous starburst. The evolution with redshift of the luminosity distribution of k+a galaxies can be explained by a ``downsizing effect,'' with the maximum luminosity/mass of actively star-forming galaxies infalling onto clusters decreasing at lower redshift. We discuss the possible physical origin of this downsizing effect and the implications of our results for current scenarios of environmental effects on the star formation in galaxies. Based on observations made with the William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias.

  16. HUBBLE REVEALS 'BACKWARDS' SPIRAL GALAXY

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Astronomers have found a spiral galaxy that may be spinning to the beat of a different cosmic drummer. To the surprise of astronomers, the galaxy, called NGC 4622, appears to be rotating in the opposite direction to what they expected. Pictures by NASA's Hubble Space Telescope helped astronomers determine that the galaxy may be spinning clockwise by showing which side of the galaxy is closer to Earth. A Hubble telescope photo of the oddball galaxy is this month's Hubble Heritage offering. The image shows NGC 4622 and its outer pair of winding arms full of new stars [shown in blue]. Astronomers are puzzled by the clockwise rotation because of the direction the outer spiral arms are pointing. Most spiral galaxies have arms of gas and stars that trail behind as they turn. But this galaxy has two 'leading' outer arms that point toward the direction of the galaxy's clockwise rotation. To add to the conundrum, NGC 4622 also has a 'trailing' inner arm that is wrapped around the galaxy in the opposite direction it is rotating. Based on galaxy simulations, a team of astronomers had expected that the galaxy was turning counterclockwise. NGC 4622 is a rare example of a spiral galaxy with arms pointing in opposite directions. What caused this galaxy to behave differently from most galaxies? Astronomers suspect that NGC 4622 interacted with another galaxy. Its two outer arms are lopsided, meaning that something disturbed it. The new Hubble image suggests that NGC 4622 consumed a small companion galaxy. The galaxy's core provides new evidence for a merger between NGC 4622 and a smaller galaxy. This information could be the key to understanding the unusual leading arms. Galaxies, which consist of stars, gas, and dust, rotate very slowly. Our Sun, one of many stars in our Milky Way Galaxy, completes a circuit around the Milky Way every 250 million years. NGC 4622 resides 111 million light-years away in the constellation Centaurus. The pictures were taken in May 2001 with Hubble

  17. Coevolution (Or Not) of Supermassive Black Holes and Host Galaxies

    NASA Astrophysics Data System (ADS)

    Kormendy, John; Ho, Luis C.

    2013-08-01

    Supermassive black holes (BHs) have been found in 85 galaxies by dynamical modeling of spatially resolved kinematics. The Hubble Space Telescope revolutionized BH research by advancing the subject from its proof-of-concept phase into quantitative studies of BH demographics. Most influential was the discovery of a tight correlation between BH mass [Formula: see text] and the velocity dispersion σ of the bulge component of the host galaxy. Together with similar correlations with bulge luminosity and mass, this led to the widespread belief that BHs and bulges coevolve by regulating each other's growth. Conclusions based on one set of correlations from [Formula: see text] in brightest cluster ellipticals to [Formula: see text] in the smallest galaxies dominated BH work for more than a decade. New results are now replacing this simple story with a richer and more plausible picture in which BHs correlate differently with different galaxy components. A reasonable aim is to use this progress to refine our understanding of BH-galaxy coevolution. BHs with masses of 105-106M⊙ are found in many bulgeless galaxies. Therefore, classical (elliptical-galaxy-like) bulges are not necessary for BH formation. On the other hand, although they live in galaxy disks, BHs do not correlate with galaxy disks. Also, any [Formula: see text] correlations with the properties of disk-grown pseudobulges and dark matter halos are weak enough to imply no close coevolution. The above and other correlations of host-galaxy parameters with each other and with [Formula: see text] suggest that there are four regimes of BH feedback. (1) Local, secular, episodic, and stochastic feeding of small BHs in largely bulgeless galaxies involves too little energy to result in coevolution. (2) Global feeding in major, wet galaxy mergers rapidly grows giant BHs in short-duration, quasar-like events whose energy feedback does affect galaxy evolution. The resulting hosts are classical bulges and coreless

  18. Chiral asymmetry in spiral galaxies?

    PubMed

    Kondepudi, D K; Durand, D J

    2001-07-01

    Spiral galaxies are chiral entities when coupled with the direction of their recession velocity. As viewed from the Earth, the S-shaped and Z-shaped spiral galaxies are two chiral forms. What is the nature of chiral symmetry in spiral galaxies? In the Carnegie Atlas of Galaxies that lists photographs of a total of 1,168 galaxies, we found 540 galaxies, classified as normal or barred spirals, that are clearly identifiable as S- or Z- type. The recession velocities for 538 of these galaxies could be obtained from this atlas and other sources. A statistical analysis of this sample reveals no overall asymmetry but there is a significant asymmetry in certain subclasses: dominance of S-type galaxies in the Sb class of normal spiral galaxies and a dominance of Z-type in the SBb class of barred spiral galaxies. Both S- and Z-type galaxies seem to have similar velocity distribution, indicating no spatial segregation of the two chiral forms.

  19. Break Dancing and Breaking Out; Anglos, Utes, and Navajos in a Border Reservation High School.

    ERIC Educational Resources Information Center

    Deyhle, Donna

    1986-01-01

    Analyzes the importance of break dancing to a subgroup of Ute and Navajo students at a southwestern high school. Describes the break dancers' interactions with other students, their communities, and their school. Break dancing facilitates intragroup communication, creates a unique group identity, and allows the students a kind of success in…

  20. The Quest for the Largest Depleted Galaxy Core: Supermassive Black Hole Binaries and Stalled Infalling Satellites

    NASA Astrophysics Data System (ADS)

    Bonfini, Paolo; Graham, Alister W.

    2016-10-01

    Partially depleted cores are practically ubiquitous in luminous early-type galaxies (M B ≲ -20.5 mag) and are typically smaller than 1 kpc. In one popular scenario, supermassive black hole (SMBH) binaries—established during dry (i.e., gas-poor) galaxy mergers—kick out the stars from a galaxy’s central region via three-body interactions. Here, this “binary black hole scouring scenario” is probed at its extremes by investigating the two galaxies reported to have the largest partially depleted cores found to date: 2MASX J09194427+5622012 and 2MASX J17222717+3207571 (the brightest galaxy in Abell 2261). We have fit these galaxy’s two-dimensional light distribution using the core-Sérsic model and found that the former galaxy has a core-Sérsic break radius {R}b,{cS}=0.55 {{kpc}}, which is three times smaller than the published value. We use this galaxy to caution that other reportedly large break radii may too have been overestimated if they were derived using the “sharp-transition” (inner core)-to-(outer Sérsic) model. In the case of 2MASX J17222717+3207571, we obtain R b,cS = 3.6 kpc. While we confirm that this is the biggest known partially depleted core of any galaxy, we stress that it is larger than expected from the evolution of SMBH binaries—unless one invokes substantial gravitational-wave-induced (black hole-)recoil events. Given the presence of multiple nuclei located (in projection) within the core radius of this galaxy, we explored and found support for the alternative “stalled infalling perturber” core-formation scenario, in which this galaxy’s core could have been excavated by the action of an infalling massive perturber.

  1. AN EXPONENTIAL DECLINE AT THE BRIGHT END OF THE z = 6 GALAXY LUMINOSITY FUNCTION

    SciTech Connect

    Willott, Chris J.; McLure, Ross J.; Bruce, Victoria A.; Hibon, Pascale; McCracken, Henry J.; Kneib, Jean-Paul; Ilbert, Olivier; Bonfield, David G.; Jarvis, Matt J.

    2013-01-01

    We present the results of a search for the most luminous star-forming galaxies at redshifts z Almost-Equal-To 6 based on Canada-France-Hawaii Telescope Legacy Survey data. We identify a sample of 40 Lyman break galaxies (LBGs) brighter than magnitude z' = 25.3 across an area of almost 4 deg{sup 2}. Sensitive spectroscopic observations of seven galaxies provide redshifts for four, of which only two have moderate to strong Ly{alpha} emission lines. All four have clear continuum breaks in their spectra. Approximately half of the LBGs are spatially resolved in 0.7 arcsec seeing images, indicating larger sizes than lower luminosity galaxies discovered with the Hubble Space Telescope, possibly due to ongoing mergers. The stacked optical and infrared photometry is consistent with a galaxy model with stellar mass {approx}10{sup 10} M{sub Sun }. There is strong evidence for substantial dust reddening with a best-fit A{sub V} = 0.75 and A{sub V} > 0.48 at 2{sigma} confidence, in contrast to the typical dust-free galaxies of lower luminosity at this epoch. The spatial extent and spectral energy distribution suggest that the most luminous z Almost-Equal-To 6 galaxies are undergoing merger-induced starbursts. The luminosity function of z = 5.9 star-forming galaxies is derived. This agrees well with previous work and shows strong evidence for an exponential decline at the bright end, indicating that the feedback processes that govern the shape of the bright end are occurring effectively at this epoch.

  2. Stellar Populations of Shell Galaxies

    NASA Astrophysics Data System (ADS)

    Carlsten, Scott; Zenteno, Alfredo

    2016-01-01

    We present a study of the inner (out to ˜1 effective radius) stellar populations in a sample of 9 shell galaxies. We derive stellar population parameters from long slit spectra by both analyzing the Lick indices of the galaxies and by fitting high resolution SSP model spectra to the full galaxy spectra. The results from the two methods agree reasonably well. We find the presence of young stellar populations in several of the galaxies, implying recent star formation and allowing us to speculate on the age of the shells. Analyzing the metallicity gradients in our sample, we find an average metallicity gradient of -0.16±0.10 dex/decade in radius. Finally, we compare this with galaxy evolution models to try to constrain the merging history of shell galaxies. We argue that our galaxies likely have undergone major mergers in their past but it is unclear whether the shells formed from these events or from separate minor mergers.

  3. The Faint-End of the Galaxy Luminosity Function in the Hydra I Cluster

    NASA Astrophysics Data System (ADS)

    Yamanoi, H.; Tanaka, M.

    2007-05-01

    INTRODUCTION: Dwarf galaxies account for a large share of cluster galaxies and their properties should be closely related to the formation and evolution of clusters. Despite the obvious importance, however, the number of very faint (down to M ˜ -10) cluster samples available to date is limited and properties of such faint galaxies remain unclear. In this study, we aim to reveal very faint-end slopes of galaxy luminosity functions (LFs) in the Hydra I cluster (Abell 1060) at z = 0.0126, in which such very faint galaxies have not been probed yet. OBSERVATIONS: We base our analyses on the data taken with the Suprime-Cam on the Subaru telescope at Mauna Kea. A deep photometric survey was carried out in the B- and Rc-bands. We observed the central region as well as a peripheral region of Hydra I. This is because we aim to investigate the environmental dependence of properties of very faint galaxies. We subtract fore-/background galaxy contamination in the cluster fields and obtain intrinsic LFs of the cluster galaxies. RESULTS AND DISCUSSION: We find that the LFs at the fainter magnitudes have a slightly steeper slope than that reported on the same cluster previously. The slope is flatter at faint magnitudes (M > -14) than that at the brighter magnitudes. This tendency is consistent with a composite LF constructed from several nearby clusters by previous work. Although the LFs in the Hydra central region are similar to those in the peripheral region at M < -14, the LF slope in the peripheral region is slightly flatter than that in the central region in the fainter magnitude range. This means that a larger number of dwarf galaxies reside in denser environments. This tend is seen only in the red galaxy LFs when we separate the Hydra member galaxies into red and blue galaxies. The Hydra I cluster is dominated by red galaxies down to M ˜ -10.

  4. The Connection between Galaxies