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Sample records for close galaxy pairs

  1. PRIMUS: Enhanced Specific Star Formation Rates in Close Galaxy Pairs

    NASA Astrophysics Data System (ADS)

    Wong, Kenneth C.; Blanton, Michael R.; Burles, Scott M.; Coil, Alison L.; Cool, Richard J.; Eisenstein, Daniel J.; Moustakas, John; Zhu, Guangtun; Arnouts, Stéphane

    2011-02-01

    Tidal interactions between galaxies can trigger star formation, which contributes to the global star formation rate (SFR) density of the universe and could be a factor in the transformation of blue, star-forming galaxies to red, quiescent galaxies over cosmic time. We investigate tidally triggered star formation in isolated close galaxy pairs drawn from the Prism Multi-Object Survey (PRIMUS), a low-dispersion prism redshift survey that has measured ~120,000 robust galaxy redshifts over 9.1 deg2 out to z ~ 1. We select a sample of galaxies in isolated galaxy pairs at redshifts 0.25 <= z <= 0.75, with no other objects within a projected separation of 300 h -1 kpc and Δz/(1 + z) = 0.01, and compare them to a control sample of isolated galaxies to test for systematic differences in their rest-frame FUV - r and NUV - r colors as a proxy for relative specific star formation rates (SSFRs). We find that galaxies in rp <= 50 h -1 kpc pairs have bluer dust-corrected UV - r colors on average than the control galaxies by -0.134 ± 0.045 mag in FUV - r and -0.075 ± 0.038 mag in NUV - r, corresponding to an ~15%-20% increase in SSFR. This indicates an enhancement in SSFR due to tidal interactions. We also find that this relative enhancement is greater for a subset of rp <= 30 h -1 kpc pair galaxies, for which the average color offsets are -0.193 ± 0.065 mag in FUV - r and -0.159 ± 0.048 mag in NUV - r, corresponding to an ~25%-30% increase in SSFR. We test for evolution in the enhancement of tidally triggered star formation with redshift across our sample redshift range and find marginal evidence for a decrease in SSFR enhancement from 0.25 <= z <= 0.5 to 0.5 <= z <= 0.75. This indicates that a change in enhanced star formation triggered by tidal interactions in low-density environments is not a contributor to the decline in the global SFR density across this redshift range.

  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. Supernovae in paired galaxies

    NASA Astrophysics Data System (ADS)

    Nazaryan, T. A.; Petrosian, A. R.; Hakobyan, A. A.; Adibekyan, V. Zh.; Kunth, D.; Mamon, G. A.; Turatto, M.; Aramyan, L. S.

    2014-07-01

    We investigate the influence of close neighbor galaxies on the properties of supernovae (SNe) and their host galaxies using 56 SNe located in pairs of galaxies with different levels of star formation (SF) and nuclear activity. The mean distance of type II SNe from nuclei of hosts is greater by about a factor of 2 than that of type Ibc SNe. The distributions and mean distances of SNe are consistent with previous results compiled with the larger sample. For the first time it is shown that SNe Ibc are located in pairs with significantly smaller difference of radial velocities between components than pairs containing SNe Ia and II. We consider this as a result of higher star formation rate (SFR) of these closer systems of galaxies.

  4. WHERE DO WET, DRY, AND MIXED GALAXY MERGERS OCCUR? A STUDY OF THE ENVIRONMENTS OF CLOSE GALAXY PAIRS IN THE DEEP2 GALAXY REDSHIFT SURVEY

    SciTech Connect

    Lin, Lihwai; Cooper, Michael C.; Willmer, Christopher N. A.; Jian, Hung-Yu; Chiueh, Tzihong; Koo, David C.; Guhathakurta, Puragra; Yan, Renbin; Coil, Alison L.; Croton, Darren J.; Gerke, Brian F.; Newman, Jeffrey A.

    2010-08-01

    We study the environments of wet, dry, and mixed galaxy mergers at 0.75 < z < 1.2 using close pairs in the DEEP2 Galaxy Redshift Survey. We find that the typical environment of dry and mixed merger candidates is denser than that of wet mergers, mostly due to the color-density relation. While the galaxy companion rate (N{sub c}) is observed to increase with overdensity, using N-body simulations, we find that the fraction of pairs that will eventually merge decreases with the local density, predominantly because interlopers are more common in dense environments. After taking into account the merger probability of pairs as a function of local density, we find only marginal environment dependence of the galaxy merger rate for wet mergers. On the other hand, the dry and mixed merger rates increase rapidly with local density due to the increased population of red galaxies in dense environments, implying that the dry and mixed mergers are most effective in overdense regions. We also find that the environment distribution of K+A galaxies is similar to that of wet mergers alone and of wet+mixed mergers, suggesting a possible connection between K+A galaxies and wet and/or wet+mixed mergers. Based on our results, we therefore expect that the properties, including structures and masses, of red-sequence galaxies should be different between those in underdense regions and those in overdense regions since the dry mergers are significantly more important in dense environments. We conclude that, as early as z {approx} 1, high-density regions are the preferred environment in which dry mergers occur, and that present-day red-sequence galaxies in overdense environments have, on average, undergone 1.2 {+-} 0.3 dry mergers since this time, accounting for (38 {+-} 10)% of their mass accretion in the last 8 billion years. The main uncertainty in this finding is the conversion from the pair fraction to the galaxy merger rate, which is possibly as large as a factor of 2. Our findings

  5. Cosmic Evolution of Star Formation Enhancement in Close Major-merger Galaxy Pairs Since z = 1

    NASA Astrophysics Data System (ADS)

    Xu, C. K.; Shupe, D. L.; Béthermin, M.; Aussel, H.; Berta, S.; Bock, J.; Bridge, C.; Conley, A.; Cooray, A.; Elbaz, D.; Franceschini, A.; Le Floc'h, E.; Lu, N.; Lutz, D.; Magnelli, B.; Marsden, G.; Oliver, S. J.; Pozzi, F.; Riguccini, L.; Schulz, B.; Scoville, N.; Vaccari, M.; Vieira, J. D.; Wang, L.; Zemcov, M.

    2012-11-01

    The infrared (IR) emission of "M * galaxies" (1010.4 <= M star <= 1011.0 M ⊙) in galaxy pairs, derived using data obtained in Herschel (PEP/HerMES) and Spitzer (S-COSMOS) surveys, is compared to that of single-disk galaxies in well-matched control samples to study the cosmic evolution of the star formation enhancement induced by galaxy-galaxy interaction. Both the mean IR spectral energy distribution and mean IR luminosity of star-forming galaxies (SFGs) in SFG+SFG (S+S) pairs in the redshift bin of 0.6 < z < 1 are consistent with no star formation enhancement. SFGs in S+S pairs in a lower redshift bin of 0.2 < z < 0.6 show marginal evidence for a weak star formation enhancement. Together with the significant and strong sSFR enhancement shown by SFGs in a local sample of S+S pairs (obtained using previously published Spitzer observations), our results reveal a trend for the star formation enhancement in S+S pairs to decrease with increasing redshift. Between z = 0 and z = 1, this decline of interaction-induced star formation enhancement occurs in parallel with the dramatic increase (by a factor of ~10) of the sSFR of single SFGs, both of which can be explained by the higher gas fraction in higher-z disks. SFGs in mixed pairs (S+E pairs) do not show any significant star formation enhancement at any redshift. The difference between SFGs in S+S pairs and in S+E pairs suggests a modulation of the sSFR by the intergalactic medium (IGM) in the dark matter halos hosting these pairs. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

  6. COSMIC EVOLUTION OF STAR FORMATION ENHANCEMENT IN CLOSE MAJOR-MERGER GALAXY PAIRS SINCE z = 1

    SciTech Connect

    Xu, C. K.; Shupe, D. L.; Bock, J.; Bridge, C.; Cooray, A.; Lu, N.; Schulz, B.; Bethermin, M.; Aussel, H.; Elbaz, D.; Le Floc'h, E.; Riguccini, L.; Conley, A.; Franceschini, A.; Marsden, G.; Oliver, S. J.; Pozzi, F.; and others

    2012-11-20

    The infrared (IR) emission of 'M {sub *} galaxies' (10{sup 10.4} {<=} M {sub star} {<=} 10{sup 11.0} M {sub Sun }) in galaxy pairs, derived using data obtained in Herschel (PEP/HerMES) and Spitzer (S-COSMOS) surveys, is compared to that of single-disk galaxies in well-matched control samples to study the cosmic evolution of the star formation enhancement induced by galaxy-galaxy interaction. Both the mean IR spectral energy distribution and mean IR luminosity of star-forming galaxies (SFGs) in SFG+SFG (S+S) pairs in the redshift bin of 0.6 < z < 1 are consistent with no star formation enhancement. SFGs in S+S pairs in a lower redshift bin of 0.2 < z < 0.6 show marginal evidence for a weak star formation enhancement. Together with the significant and strong sSFR enhancement shown by SFGs in a local sample of S+S pairs (obtained using previously published Spitzer observations), our results reveal a trend for the star formation enhancement in S+S pairs to decrease with increasing redshift. Between z = 0 and z = 1, this decline of interaction-induced star formation enhancement occurs in parallel with the dramatic increase (by a factor of {approx}10) of the sSFR of single SFGs, both of which can be explained by the higher gas fraction in higher-z disks. SFGs in mixed pairs (S+E pairs) do not show any significant star formation enhancement at any redshift. The difference between SFGs in S+S pairs and in S+E pairs suggests a modulation of the sSFR by the intergalactic medium (IGM) in the dark matter halos hosting these pairs.

  7. Supernovae in paired host galaxies

    NASA Astrophysics Data System (ADS)

    Nazaryan, T. A.; Petrosian, A. R.; Hakobyan, A. A.; Adibekyan, V. Zh.; Kunth, D.; Mamon, G. A.; Turatto, M.; Aramyan, L. S.

    2014-12-01

    We investigate the influence of close neighbor galaxies on the properties of supernovae (SNe) and their host galaxies using 56 SNe located in pairs of galaxies with different levels of star formation (SF) and nuclear activity. The mean distance of type II SNe from nuclei of hosts is greater by about a factor of 2 than that of type Ibc SNe. For the first time it is shown that SNe Ibc are located in pairs with significantly smaller difference of radial velocities between components than pairs containing SNe Ia and II. We consider this as a result of higher star formation rate (SFR) of these closer systems of galaxies. SN types are not correlated with the luminosity ratio of host and neighbor galaxies in pairs. The orientation of SNe with respect to the preferred direction toward neighbor galaxy is found to be isotropic and independent of kinematical properties of the galaxy pair.

  8. 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.

  9. Isolated galaxies, pairs, and groups of galaxies

    NASA Technical Reports Server (NTRS)

    Kuneva, I.; Kalinkov, M.

    1990-01-01

    The authors searched for isolated galaxies, pairs and groups of galaxies in the CfA survey (Huchra et al. 1983). It was assumed that the distances to galaxies are given by R = V/H sub o, where H sub o = 100 km s(exp -1) Mpc(exp -1) and R greater than 6 Mpc. The searching procedure is close to those, applied to find superclusters of galaxies (Kalinkov and Kuneva 1985, 1986). A sphere with fixed radius r (asterisk) is described around each galaxy. The mean spatial density in the sphere is m. Let G (sup 1) be any galaxy and G (sup 2) be its nearest neighbor at a distance R sub 2. If R sub 2 exceeds the 95 percent quintile in the distribution of the distances of the second neighbors, then G (sup 1) is an isolated galaxy. Let the midpoint of G (sup 1) and G (sup 2) be O sub 2 and r sub 2=R sub 2/2. For the volume V sub 2, defined with the radius r sub 2, the density D sub 2 less than k mu, the galaxy G (sup 2) is a single one and the procedure for searching for pairs and groups, beginning with this object is over and we have to pass to another object. Here the authors present the groups - isolated and nonisolated - with n greater than 3, found in the CfA survey in the Northern galactic hemisphere. The parameters used are k = 10 and r (asterisk) = 5 Mpc. Table 1 contains: (1) the group number, (2) the galaxy, nearest to the multiplet center, (3) multiplicity n, (4) the brightest galaxy if it is not listed in (2); (5) and (6) are R.A. and Dec. (1950), (7) - mean distance D in Mpc. Further there are the mean density rho (8) of the multiplet (galaxies Mpc (exp -3), (9) the density rho (asterisk) for r (asterisk) = 5 Mpc and (10) the density rho sub g for the group with its nearest neighbor. The parenthesized digits for densities in the last three columns are powers of ten.

  10. Dynamical interactions of galaxy pairs

    NASA Technical Reports Server (NTRS)

    Athanassoula, E.

    1990-01-01

    Here the author briefly reviews the dynamics of sinking satellites and the effect of companions on elliptical galaxies. The author then discusses recent work on interacting disk systems, and finally focuses on a favorite interacting pair, NGC 5194/5195.

  11. Morphology transformation in pairs of galaxies - the local sample

    NASA Astrophysics Data System (ADS)

    Junqueira, S.; de Mello, D. F.; Infante, L.

    1998-04-01

    We present photometric analysis of a local sample of 14 isolated pairs of galaxies. The photometric properties analyzed in the local pairs are: colors, morphology, tidal effects and activity. We verify that close pairs have an excess of early-type galaxies and many elliptical galaxies in this pairs are, in fact, lenticular galaxies. Many late-pairs in our sample show strong tidal damage and blue star formation regions. We conclude that pairs of different morphologies may have passed through different evolution processes which violently transformed their morphology. Pairs with at least one early-type component may be descendents of groups of galaxies. However, late-type pairs are probably long-lived showing clearly signs of interaction. Some of them could be seen as an early stage of mergers. These photometric databases will be used for future comparison with more distant pairs in order to study galaxy evolution.

  12. Mass of Galaxies in Pairs

    NASA Astrophysics Data System (ADS)

    Junqueira, S.; Chan, R.

    We have compared the frequency distribution of the dynamical observed quantity log (V r), for a sample of 46 pairs of elliptical galaxies, to the distribution of this quantity obtained from numerical simulations of pairs of galaxies. From such an analysis, where we have considered the structure of the galaxies and its influence in the orbital evolution of the system, we have obtained the characteristic mass and the mass-luminosity ratio for the sample. Our results show that the hypothesis of point-mass in elliptical orbits is, for this sample, an approximation as good as the model that takes into account the structure of the galaxies. The statistical method used here gives an estimate of a more reliable mass, it minimizes the contamination of spurious pairs and it considers adequately the contribution of the physical pairs. We have obtained a characteristic mass to the 46 elliptical pairs of 1.68 × 10^12 +/- 7.01 × 10^11 M_solar with M/L = 17.6 +/- 7.3 (H_0 = 60 km s^-1 Mpc^-1).

  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. FIR statistics of paired galaxies

    NASA Technical Reports Server (NTRS)

    Sulentic, Jack W.

    1990-01-01

    Much progress has been made in understanding the effects of interaction on galaxies (see reviews in this volume by Heckman and Kennicutt). Evidence for enhanced emission from galaxies in pairs first emerged in the radio (Sulentic 1976) and optical (Larson and Tinsley 1978) domains. Results in the far infrared (FIR) lagged behind until the advent of the Infrared Astronomy Satellite (IRAS). The last five years have seen numerous FIR studies of optical and IR selected samples of interacting galaxies (e.g., Cutri and McAlary 1985; Joseph and Wright 1985; Kennicutt et al. 1987; Haynes and Herter 1988). Despite all of this work, there are still contradictory ideas about the level and, even, the reality of an FIR enhancement in interacting galaxies. Much of the confusion originates in differences between the galaxy samples that were studied (i.e., optical morphology and redshift coverage). Here, the authors report on a study of the FIR detection properties for a large sample of interacting galaxies and a matching control sample. They focus on the distance independent detection fraction (DF) statistics of the sample. The results prove useful in interpreting the previously published work. A clarification of the phenomenology provides valuable clues about the physics of the FIR enhancement in galaxies.

  15. Galaxy pairs align with Galactic filaments

    NASA Astrophysics Data System (ADS)

    Tempel, E.; Tamm, A.

    2015-04-01

    Context. Gravitational collapse theory and numerical simulations suggest that the velocity field within large-scale galaxy filaments is dominated by motions along the filaments. Aims: Our aim is to check whether observational data reveal any preferred orientation of galaxy pairs with respect to the underlying filaments as a result of the expectedly anisotropic velocity field. Methods: We use galaxy pairs and galaxy filaments identified from Sloan Digital Sky Survey data. For filament extraction, we use the Bisous model that is based on the marked point process technique. During the filament detection, we use the centre point of each pair instead of the positions of galaxies to avoid a built-in influence of pair orientation on the filament construction. For pairs lying within filaments (3012 cases), we calculate the angle between the line connecting the galaxies of each pair and their host filaments. To avoid redshift-space distortions, the angle is measured in the plane of the sky. Results: The alignment analysis shows that the orientation of galaxy pairs correlates strongly with their host filaments. The alignment signal is stronger for loose pairs, with at least 25% excess of aligned pairs compared to a random distribution. The alignment of galaxy pairs and filaments measured from the observational data is in good agreement with the alignment in the Millennium simulation and thus provides support to the ΛCDM formalism.

  16. Paired galaxies with different activity levels and their supernovae

    NASA Astrophysics Data System (ADS)

    Nazaryan, T. A.; Petrosian, A. R.; Hakobyan, A. A.; Adibekyan, V. Z.; Kunth, D.; Mamon, G. A.; Turatto, M.; Aramyan, L. S.

    2013-10-01

    We investigate the influence of close neighbor galaxies on the properties of supernovae (SNe) and their host galaxies using 56 SNe located in pairs of galaxies with different levels of star formation (SF) and nuclear activity. The statistical study of SN hosts shows that there is no significant difference between morphologies of hosts in our sample and the larger general sample of SN hosts in the Sloan Digital Sky Survey (SDSS) Data Release 8 (DR8). The mean distance of type II SNe from nuclei of hosts is greater by about a factor of 2 than that of type Ibc SNe. The distributions and mean distances of SNe are consistent with previous results compiled with the larger sample. For the first time it is shown that SNe Ibc are located in pairs with significantly smaller difference of radial velocities between components than pairs containing SNe Ia and II. We consider this as a result of higher star formation rate (SFR) of these closer systems of galaxies. SN types are not correlated with the luminosity ratio of host and neighbor galaxies in pairs. The orientation of SNe with respect to the preferred direction toward neighbor galaxy is found to be isotropic and independent of kinematical properties of the galaxy pair.

  17. Probing the tides in interacting galaxy pairs

    NASA Technical Reports Server (NTRS)

    Borne, Kirk D.

    1990-01-01

    Detailed spectroscopic and imaging observations of colliding elliptical galaxies revealed unmistakable diagnostic signatures of the tidal interactions. It is possible to compare both the distorted luminosity distributions and the disturbed internal rotation profiles with numerical simulations in order to model the strength of the tidal gravitational field acting within a given pair of galaxies. Using the best-fit numerical model, one can then measure directly the mass of a specific interacting binary system. This technique applies to individual pairs and therefore complements the classical methods of measuring the masses of galaxy pairs in well-defined statistical samples. The 'personalized' modeling of galaxy pairs also permits the derivation of each binary's orbit, spatial orientation, and interaction timescale. Similarly, one can probe the tides in less-detailed observations of disturbed galaxies in order to estimate some of the physical parameters for larger samples of interacting galaxy pairs. These parameters are useful inputs to the more universal problems of (1) the galaxy merger rate, (2) the strength and duration of the driving forces behind tidally stimulated phenomena (e.g., starbursts and maybe quasi steller objects), and (3) the identification of long-lived signatures of interaction/merger events.

  18. Radio structures in QSO-galaxy pairs

    NASA Technical Reports Server (NTRS)

    Akujor, Chidi E.

    1990-01-01

    It is now generally agreed that if quasars and nearby low redshift galaxies are associated, then there should be luminous connections between them. However, most of the observational evidence being presented is in the optical domain, whereas such evidence should also exist at radio frequencies. The author is, therefore, investigating some quasar-galaxy pairs at radio frequencies to search for luminous connections and other structural peculiarities. Radio maps of some of these sources are presented.

  19. Older Galaxy Pair Has Surprisingly Youthful Glow

    NASA Technical Reports Server (NTRS)

    2007-01-01

    [figure removed for brevity, see original site] Poster Version

    A pair of interacting galaxies might be experiencing the galactic equivalent of a mid-life crisis. For some reason, the pair, called Arp 82, didn't make their stars early on as is typical of most galaxies. Instead, they got a second wind later in life -- about 2 billion years ago -- and started pumping out waves of new stars as if they were young again.

    Arp 82 is an interacting pair of galaxies with a strong bridge and a long tail. NGC 2535 is the big galaxy and NGC 2536 is its smaller companion. The disk of the main galaxy looks like an eye, with a bright 'pupil' in the center and oval-shaped 'eyelids.' Dramatic 'beads on a string' features are visible as chains of evenly spaced star-formation complexes along the eyelids. These are presumably the result of large-scale gaseous shocks from a grazing encounter. The colors of this galaxy indicate that the observed stars are young to intermediate in age, around 2 million to 2 billion years old, much less than the age of the universe (13.7 billion years).

    The puzzle is: why didn't Arp 82 form many stars earlier, like most galaxies of that mass range? Scientifically, it is an oddball and provides a relatively nearby lab for studying the age of intermediate-mass galaxies.

    This picture is a composite captured by Spitzer's infrared array camera with light at wavelength 8 microns shown in red, NASA's Galaxy Evolution Explorer combined 1530 and 2310 Angstroms shown in blue, and the Southeastern Association for Research in Astronomy Observatory light at 6940 Angstroms shown in green.

  20. Stellar kinematics of elliptical galaxies in pairs

    NASA Technical Reports Server (NTRS)

    Madejsky, Rainer; Bender, Ralf

    1990-01-01

    In both galaxy pairs Arp 166 and 3C 278 the authors find radially increasing velocity dispersions indicating a perturbed, non-equilibrium state of the galaxies after the tidal interaction. In all galaxies, the increase is most pronounced in the regions which correspond to the centers of the outer isophotes. The authors suggest a scenario in which the galaxies are strongly decelerated on their orbits during the encounter. The deceleration depends on the radial position in the perturbed galaxy and vanishes in the center of the perturbed galaxy (Spitzer, 1958). In addition, the crossing time of the stars near the center is very short, implying that the tidal perturbations can be averaged over several orbital periods (e.g., Binney and Tremaine, 1987). In consequence, the central parts are not affected by the tidal interaction while the outer parts are strongly decelerated. This leads to a displacement of the central parts of the galaxies with respect to their envelopes in an anti-symmetrical way for the two components of each galaxy pair. The motions of the central parts subsequently are opposed by dynamical friction with the surrounding envelopes. Due to dynamical friction, the density of the stars increases in the wakes of the moving central parts (Mulder, 1983). The overdensity of stars in the wakes of the moving central parts efficiently decelerates the motions of the central parts. The reaction of the stars in the overdensity regions leads to an increase of the velocity dispersion mainly along the orbits of the moving central parts. The presented observations, especially the asymmetrical luminosity profiles and the radially increasing velocity dispersions support consistently the above scenario of tidal interaction between galaxies. Further spectroscopic observations are necessary in order to investigate the degree of anisotropy in the kinematically perturbed regions.

  1. Paired and interacting galaxies: Conference summary

    NASA Technical Reports Server (NTRS)

    Norman, Colin A.

    1990-01-01

    The author gives a summary of the conference proceedings. The conference began with the presentation of the basic data sets on pairs, groups, and interacting galaxies with the latter being further discussed with respect to both global properties and properties of the galactic nuclei. Then followed the theory, modelling and interpretation using analytic techniques, simulations and general modelling for spirals and ellipticals, starbursts and active galactic nuclei. Before the conference the author wrote down the three questions concerning pairs, groups and interacting galaxies that he hoped would be answered at the meeting: (1) How do they form, including the role of initial conditions, the importance of subclustering, the evolution of groups to compact groups, and the fate of compact groups; (2) How do they evolve, including issues such as relevant timescales, the role of halos and the problem of overmerging, the triggering and enhancement of star formation and activity in the galactic nuclei, and the relative importance of dwarf versus giant encounters; and (3) Are they important, including the frequency of pairs and interactions, whether merging and interactions are very important aspects of the life of a normal galaxy at formation, during its evolution, in forming bars, shells, rings, bulges, etc., and in the formation and evolution of active galaxies? Where possible he focuses on these three central issues in the summary.

  2. Galaxy pairs in the Sloan Digital Sky Survey - X. Does gas content alter star formation rate enhancement in galaxy interactions?

    NASA Astrophysics Data System (ADS)

    Scudder, Jillian M.; Ellison, Sara L.; Momjian, Emmanuel; Rosenberg, Jessica L.; Torrey, Paul; Patton, David R.; Fertig, Derek; Mendel, J. Trevor

    2015-06-01

    New spectral line observations, obtained with the Jansky Very Large Array (VLA), of a sample of 34 galaxies in 17 close pairs are presented in this paper. The sample of galaxy pairs is selected to contain galaxies in close, major interactions (i.e. projected separations <30 h_{70}^{-1} kpc, and mass ratios less extreme than 4:1), while still having a sufficiently large angular separation that the VLA can spatially resolve both galaxies in the pair. Of the 34 galaxies, 17 are detected at >3σ. We compare the H I gas fraction of the galaxies with the triggered star formation present in that galaxy. When compared to the star formation rates (SFRs) of non-pair galaxies matched in mass, redshift, and local environment, we find that the star formation enhancement is weakly positively correlated (˜2.5σ) with H I gas fraction. In order to help understand the physical mechanisms driving this weak correlation, we also present results from a small suite of binary galaxy merger simulations with varying gas fractions. The simulated galaxies indicate that larger initial gas fractions are associated with lower levels of interaction-triggered star formation (relative to an identical galaxy in isolation), but also show that high gas fraction galaxies have higher absolute SFRs prior to an interaction. We show that when interaction-driven SFR enhancements are calculated relative to a galaxy with an average gas fraction for its stellar mass, the relationship between SFR and initial gas fraction dominates over the SFR enhancements driven by the interaction. Simulated galaxy interactions that are matched in stellar mass but not in gas fraction, like our VLA sample, yield the same general positive correlation between SFR enhancement and gas fraction that we observe.

  3. 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.

  4. Quantization of redshift differences in isolated galaxy pairs

    SciTech Connect

    Tifft, W.G.; Cocke, W.J.

    1989-01-01

    Improved 21 cm data on isolated galaxy pairs are presented which eliminate questions of inhomogeneity in the data on such pairs and reduce observational error to below 5 km/s. Quantization is sharpened, and the zero peak is shown to be displaced from zero to a location near 24 km/s. An exclusion principle is suggested whereby identical redshifts are forbidden in limited volumes. The radio data and data from Schweizer (1987) are combined with the best optical data on close Karachentsev pairs to provide a cumulative sample of 84 of the best differentials now available. New 21 cm observations are used to test for the presence of small differentials in very wide pairs, and the deficiency near zero is found to continue to very wide spacings. A loss of wide pairs by selection bias cannot produce the observed zero deficiency. A new test using pairs selected from the Fisher-Tully catalog is used to demonstrate quantization properties of third components associated with possible pairs. 27 references.

  5. Pair Cascades in Blazars and Radio Galaxies

    NASA Astrophysics Data System (ADS)

    Roustazadeh Sheikhyousefi, Parisa

    2012-05-01

    Recently some intermediate BL Lac objects (IBL), low frequency peak BL Lac objects (LBL) and flat spectrum radio quasars (FSRQs) were detected as very high energy gamma-ray sources (VHE; E > 100 GeV) by the Major Atmospheric Gamma-ray Imaging Cherenkov Telescope (MAGIC), the High Energy Stereoscopic System (H.E.S.S) and the Very Energetic Radiation Imaging Telescope Array System (VERITAS). These discoveries suggest that VHE gamma-rays may be produced in all types of active galactic nuclei (AGN) and that this is not only a common property of high frequency peaked BL Lac objects (HBL). The detection of the radio galaxies M87, Cen A and NGC 1275 supports this idea. In those AGN, VHE photons may interact with low energy photons from the broadline region (BLR), accretion disk around the black hole or thermal infrared photons form a dust torus by photon-photon pair production if the total center-of-momentum frame energy is above threshold to produce an electron-positron pair. These particles can produce new high energy photons by Compton up-scattering, and again these high energy photons can interact with soft photons to produce a pair of particles. This process will continue, leading to a shower (cascade) of particles and radiation. As the shower develops, it will expand laterally. This may explain the detection of the radio galaxies as VHE gamma-ray sources. The central part of my Ph.D. research work deals with the theoretical simulation of very high energy gamma-ray induced pair cascades in blazars and radio galaxies. Gamma-rays from the core of the AGN interact with low energy photons from the AGN environment and produce pairs of electrons and positrons resulting in Compton supported pair cascades. I developed a Monte Carlo code which treats the processes of gamma-gamma absorption and pair production, gamma-ray and electron/positron propagation, and Compton scattering, tracking particle trajectories in full 3-dimensional geometry. I showed that even for a very weak

  6. Cosmic ray antiprotons in closed galaxy model

    NASA Technical Reports Server (NTRS)

    Protheroe, R.

    1981-01-01

    The flux of secondary antiprotons expected for the leaky-box model was calculated as well as that for the closed galaxy model of Peters and Westergard (1977). The antiproton/proton ratio observed at several GeV is a factor of 4 higher than the prediction for the leaky-box model but is consistent with that predicted for the closed galaxy model. New low energy data is not consistent with either model. The possibility of a primary antiproton component is discussed.

  7. Emission line galaxy pairs up to z=1.5 from the WISP survey

    NASA Astrophysics Data System (ADS)

    Teplitz, Harry I.; Dai, Yu Sophia; Malkan, Matthew Arnold; Scarlata, Claudia; Colbert, James W.; Atek, Hakim; Bagley, Micaela B.; Baronchelli, Ivano; Bedregal, Alejandro; Beck, Melanie; Bunker, Andrew; Dominguez, Alberto; Hathi, Nimish P.; Henry, Alaina L.; Mehta, Vihang; Pahl, Anthony; Rafelski, Marc; Ross, Nathaniel; Rutkowski, Michael J.; Siana, Brian D.; WISPs Team

    2016-01-01

    We present a sample of spectroscopically identified emission line galaxy pairs up to z=1.5 from WISPs (WFC3 Infrared Spectroscopic Parallel survey) using high resolution direct and grism images from HST. We searched ~150 fields with a covered area of ~600 arcmin^2, and a comoving volume of > 400 Gpc^3 at z=1-2, and found ~80 very close physical pairs (projected separation Dp < 50 h^{-1}kpc, relative velocity d_v < 500 kms^{-1}), and ~100 close physical pairs (50 < Dp < 100 h^{-1}kpc, d_v < 1000 kms^{-1}) of emission line galaxies, including two dozen triplets and quadruples. In this poster we present the multi-wavelength data, star formation rate (SFR), mass ratio, and study the merger rate evolution with this special galaxy pair sample.

  8. Mapping IR Enhancements in Closely Interacting Spiral-Spiral Pairs: I. ISO CAM and ISO SWS Observations

    NASA Technical Reports Server (NTRS)

    Xu, C.; Gao, Y.; Mazzarella, J.; Lu, N.; Sulentic, J.; Domingue, D.

    2000-01-01

    Mid-infrared (MIR) imaging and spectroscopic observations are presented for a well defined sample of eight closely interacting (CLO) pairs of spiral galaxies that have overlapping disks and show enhanced far-infrared (FIR) emission.

  9. Paired and Interacting Galaxies: International Astronomical Union Colloquium No. 124

    NASA Technical Reports Server (NTRS)

    Sulentic, Jack W. (Editor); Keel, William C. (Editor); Telesco, C. M. (Editor)

    1990-01-01

    The proceedings of the International Astronomical Union Colloquium No. 124, held at the University of Alabama at Tuscaloosa, on December 4 to 7, are given. The purpose of the conference was to describe the current state of theoretical and observational knowledge of interacting galaxies, with particular emphasis on galaxies in pairs.

  10. STUDYING INTERCLUSTER GALAXY FILAMENTS THROUGH STACKING gmBCG GALAXY CLUSTER PAIRS

    SciTech Connect

    Zhang Yuanyuan; Dietrich, Joerg P.; McKay, Timothy A.; Nguyen, Alex T. Q.; Sheldon, Erin S.

    2013-08-20

    We present a method to study the photometric properties of galaxies in filaments by stacking the galaxy populations between pairs of galaxy clusters. Using Sloan Digital Sky Survey data, this method can detect the intercluster filament galaxy overdensity with a significance of {approx}5{sigma} out to z = 0.40. Using this approach, we study the g - r color and luminosity distribution of filament galaxies as a function of redshift. Consistent with expectation, filament galaxies are bimodal in their color distribution and contain a larger blue galaxy population than clusters. Filament galaxies are also generally fainter than cluster galaxies. More interestingly, the observed filament population seems to show redshift evolution at 0.12 < z < 0.40: the blue galaxy fraction has a trend to increase at higher redshift; such evolution is parallel to the ''Butcher-Oemler effect'' of galaxy clusters. We test the dependence of the observed filament density on the richness of the cluster pair: richer clusters are connected by higher density filaments. We also test the spatial dependence of filament galaxy overdensity: this quantity decreases when moving away from the intercluster axis between a cluster pair. This method provides an economical way to probe the photometric properties of filament galaxies and should prove useful for upcoming projects like the Dark Energy Survey.

  11. The Influence of Companion Morphology on Dust Properties and Star Formation in Galaxy Pairs

    NASA Astrophysics Data System (ADS)

    Domingue, Donovan L.; Cao, Chen; Xu, C. Kevin; Jarrett, Tom; Ronca, Joseph; Hill, Emily

    2016-01-01

    We present an analysis of dust properties of a sample of close major-merger galaxy pairs selected by Ks magnitude and redshift. The pairs represent the two populations of spiral-spiral (S+S) and mixed morphology spiral-elliptical (S+E). The CIGALE (Code Investigating GALaxy Emission) is used to fit dust models to the 2MASS, WISE and Herschel flux measurements and derive the parameters describing the PAH contribution, interstellar radiation field (ISRF) and photo-dissociation regions (PDRs). Model fits verify our previous Spitzer Space Telescope analysis that S+S and S+E pairs do not have the same level of enhancement of star formation and differ in dust composition. The spirals of mixed morphology galaxy pairs do not exhibit the enhancements in interstellar radiation field and therefore dust temperature for spirals in S+S pairs in contrast to what would be expected according to standard models of gas redistribution due to encounter torques. This suggests the importance of the companion environment/morphology in determining the dust properties of a spiral galaxy in a close major-merger pair.

  12. Modeling the initial conditions of interacting galaxy pairs using Identikit

    NASA Astrophysics Data System (ADS)

    Mortazavi, S. Alireza; Lotz, Jennifer M.; Barnes, Joshua E.; Snyder, Gregory F.

    2016-01-01

    We develop and test an automated technique to model the dynamics of interacting galaxy pairs. We use Identikit as a tool for modelling and matching the morphology and kinematics of the interacting pairs of equal-mass galaxies. In order to reduce the effect of subjective human judgement, we automate the selection of phase space regions used to match simulations to data, and we explore how selection of these regions affects the random uncertainties of parameters in the best-fitting model. In this work, we use an independent set of GADGET SPH simulations as input data to determine the systematic bias in the measured encounter parameters based on the known initial conditions of these simulations. We test both cold gas and young stellar components in the GADGET simulations to explore the effect of choosing H I versus H α as the line-of-sight velocity tracer. We find that we can group the results into tests with good, fair, and poor convergence based on the distribution of parameters of models close to the best-fitting model. For tests with good and fair convergence, we rule out large fractions of parameter space and recover merger stage, eccentricity, pericentric distance, viewing angle, and initial disc orientations within 3σ of the correct value. All of tests on prograde-prograde systems have either good or fair convergence. The results of tests on edge-on discs are less biased than face-on tests. Retrograde and polar systems do not converge and may require constraints from regions other than the tidal tails and bridges.

  13. Galaxy pairs in deep HST images: Evidence for evolution in the galaxy merger rate

    NASA Technical Reports Server (NTRS)

    Burkey, Jordan M.; Keel, William C.; Windhorst, Rogier A.; Franklin, Barbara E.

    1994-01-01

    We use four deep serendipitous fields observed with the Hubble Space Telescope (HST) Wide-Field Camera to constrain the rate of galaxy merging between the current epoch and z approximately equals 0.7. Since most mergers occur between members of bound pairs, the merger rate is given to a good approximation by (half) the rate of disappearance of galaxies in pairs. An objective criterion for pair membership shows that 34% +/- 9% of our HST galaxies with I = 18-22 belong to pairs, compared to 7% locally. This means that about 13% of the galaxy population has disappeared due to merging in the cosmic epoch corresponding to this magnitude interval (or 0.1 approximately less than z approximately less than 0.7). Our pair fraction is a lower limit: correction for pair members falling below our detection threshold might raise the fraction to approximately 50%. Since we address only two-galaxy merging, these values do not include physical systems of higher multiplicity. Incorporating I-band field-galaxy redshift distributions, the pair fraction grows with redshift as alpha(1 + z)(exp 3.5 +/- 0.5) and the merger rate as (1 + z)(exp 2.5 +/- 0.5). This may have significant implications for the interpretation of galaxy counts (disappearance of faint blue galaxies), the cosmological evolution of faint radio sources and quasars (which evolve approximately as (1 + z)(exp 3), the similarity in the power law is necessary but not sufficient evidence for a causal relation), statistics of QSO companions, the galaxy content in distant clusters, and the merging history of a 'typical' galaxy.

  14. Evolution of the major merger galaxy pair fraction at z < 1

    SciTech Connect

    Keenan, R. C.; Hsieh, B. C.; Lin, L.; Chou, R. C. Y.; Huang, S.; Lin, J. H.; Chang, K. H.; Foucaud, S.; De Propris, R.

    2014-11-10

    We present a study of the largest available sample of near-infrared selected (i.e., stellar mass selected) dynamically close pairs of galaxies at low redshifts (z < 0.3). We combine this sample with new estimates of the major merger pair fraction for stellar mass selected galaxies at z < 0.8, from the Red Sequence Cluster Survey (RCS1). We construct our low-redshift K-band selected sample using photometry from the UKIRT Infrared Deep Sky Survey and the Two Micron All Sky Survey (2MASS) in the K band (∼2.2 μm). Combined with all available spectroscopy, our K-band selected sample contains ∼250, 000 galaxies and is >90% spectroscopically complete. The depth and large volume of this sample allow us to investigate the low-redshift pair fraction and merger rate of galaxies over a wide range in K-band luminosity. We find the major merger pair fraction to be flat at ∼2% as a function of K-band luminosity for galaxies in the range 10{sup 8}-10{sup 12} L {sub ☉}, in contrast to recent results from studies in the local group that find a substantially higher low-mass pair fraction. This low-redshift major merger pair fraction is ∼40%-50% higher than previous estimates drawn from K-band samples, which were based on 2MASS photometry alone. Combining with the RCS1 sample, we find a much flatter evolution (m = 0.7 ± 0.1) in the relation f {sub pair}∝(1 + z) {sup m} than indicated in many previous studies. These results indicate that a typical L ∼ L* galaxy has undergone ∼0.2-0.8 major mergers since z = 1 (depending on the assumptions of merger timescale and percentage of pairs that actually merge).

  15. Submillimeter Imaging of the Luminous Infrared Galaxy Pair VV114

    NASA Technical Reports Server (NTRS)

    Frayer, D.; Ivison, R. J.; Smail, I.; Yun, M. S.; Armus, L.

    1999-01-01

    We report on 450 and 850 mue observations of the interacting galaxy pair, VV114E+W (IC 1623), taken with the SCUBA camera on the James Clerk Maxwell Telescope, and near-infrared observations taken with UFTI on the UK Infrared Telescope.

  16. 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.

  17. The Arecibo Galaxy Environment Survey: Observations towards the NGC 7817/7798 Galaxy Pair

    NASA Astrophysics Data System (ADS)

    Harrison, Amanda; Robert Minchin

    2016-01-01

    The Arecibo Galaxy Environment Survey (AGES) examines the environment of neutral hydrogen gas in the interstellar medium. AGES uses the 305m Arecibo Radio Telescope and the Arecibo L-Band Feed Array to create a deep field neutral hydrogen survey which we used to detect galaxies in an area five square degrees around the galaxy pair NGC 7817/7798. By finding and investigating hydrogen rich galaxies we hope to gain a better understanding of how the environment affects galaxy evolution. H1 line profiles were made for the detected H1 emission and ten galaxies which had the characteristic double-horned feature were found. NGC 7798 was not detected, but NGC 7817 and the other galaxies were cross-identified in NASA/IPAC Extragalactic Database as well as in Sloan Digital Sky Survey to obtain optical data. Out of the ten, two of the sources were uncatalogued. We analyzed the hydrogen spectra and aperture photometry to learn about the characteristics of these galaxies such as their heliocentric velocity, flux, and mass of the neutral hydrogen. Furthermore, we graphed the Tully-Fisher and the Baryonic Tully-Fisher of the ten sources and found that most followed the relation. One that is the biggest outlier is suspected be a galaxy cluster while other outliers may be caused by ram pressure stripping deforming the galaxy.

  18. The ALHAMBRA survey: accurate merger fractions derived by PDF analysis of photometrically close pairs

    NASA Astrophysics Data System (ADS)

    López-Sanjuan, C.; Cenarro, A. J.; Varela, J.; Viironen, K.; Molino, A.; Benítez, N.; Arnalte-Mur, P.; Ascaso, B.; Díaz-García, L. A.; Fernández-Soto, A.; Jiménez-Teja, Y.; Márquez, I.; Masegosa, J.; Moles, M.; Pović, M.; Aguerri, J. A. L.; Alfaro, E.; Aparicio-Villegas, T.; Broadhurst, T.; Cabrera-Caño, J.; Castander, F. J.; Cepa, J.; Cerviño, M.; Cristóbal-Hornillos, D.; Del Olmo, A.; González Delgado, R. M.; Husillos, C.; Infante, L.; Martínez, V. J.; Perea, J.; Prada, F.; Quintana, J. M.

    2015-04-01

    Aims: Our goal is to develop and test a novel methodology to compute accurate close-pair fractions with photometric redshifts. Methods: We improved the currently used methodologies to estimate the merger fraction fm from photometric redshifts by (i) using the full probability distribution functions (PDFs) of the sources in redshift space; (ii) including the variation in the luminosity of the sources with z in both the sample selection and the luminosity ratio constrain; and (iii) splitting individual PDFs into red and blue spectral templates to reliably work with colour selections. We tested the performance of our new methodology with the PDFs provided by the ALHAMBRA photometric survey. Results: The merger fractions and rates from the ALHAMBRA survey agree excellently well with those from spectroscopic work for both the general population and red and blue galaxies. With the merger rate of bright (MB ≤ -20-1.1z) galaxies evolving as (1 + z)n, the power-law index n is higher for blue galaxies (n = 2.7 ± 0.5) than for red galaxies (n = 1.3 ± 0.4), confirming previous results. Integrating the merger rate over cosmic time, we find that the average number of mergers per galaxy since z = 1 is Nmred = 0.57 ± 0.05 for red galaxies and Nmblue = 0.26 ± 0.02 for blue galaxies. Conclusions: Our new methodology statistically exploits all the available information provided by photometric redshift codes and yields accurate measurements of the merger fraction by close pairs from using photometric redshifts alone. Current and future photometric surveys will benefit from this new methodology. Based on observations collected at the German-Spanish Astronomical Center, Calar Alto, jointly operated by the Max-Planck-Institut für Astronomie (MPIA) at Heidelberg and the Instituto de Astrofísica de Andalucía (CSIC).The catalogues, probabilities, and figures of the ALHAMBRA close pairs detected in Sect. 5.1 are available at http://https://cloud.iaa.csic.es/alhambra/catalogues/ClosePairs

  19. THE INTERACTING GALAXY PAIR KPG 390: H{alpha} KINEMATICS

    SciTech Connect

    Repetto, P.; Rosado, M.; Gabbasov, R.; Fuentes-Carrera, I.

    2010-04-15

    In this work, we present scanning Fabry-Perot (FP) H{alpha} observations of the isolated interacting galaxy pair NGC 5278/79 obtained with the PUMA FP interferometer. We derived velocity fields and rotation curves for both galaxies. For NGC 5278 we also obtained the residual velocity map to investigate the non-circular motions, and estimated its mass by fitting the rotation curve with disk+halo components. We test three different types of halos (pseudo-isothermal, Hernquist, and Navarro-Frenk-White) and obtain satisfactory fits to the rotation curve for all profiles. The amount of dark matter required by the pseudo-isothermal profile is about 10 times smaller than that for the other two halo distributions. Finally, our kinematical results together with the analysis of dust lane distribution and of surface brightness profiles along the minor axis allowed us to determine univocally that both components of the interacting pair are trailing spirals.

  20. The Interacting Galaxy Pair KPG 390: Hα Kinematics

    NASA Astrophysics Data System (ADS)

    Repetto, P.; Rosado, M.; Gabbasov, R.; Fuentes-Carrera, I.

    2010-04-01

    In this work, we present scanning Fabry-Perot (FP) Hα observations of the isolated interacting galaxy pair NGC 5278/79 obtained with the PUMA FP interferometer. We derived velocity fields and rotation curves for both galaxies. For NGC 5278 we also obtained the residual velocity map to investigate the non-circular motions, and estimated its mass by fitting the rotation curve with disk+halo components. We test three different types of halos (pseudo-isothermal, Hernquist, and Navarro-Frenk-White) and obtain satisfactory fits to the rotation curve for all profiles. The amount of dark matter required by the pseudo-isothermal profile is about 10 times smaller than that for the other two halo distributions. Finally, our kinematical results together with the analysis of dust lane distribution and of surface brightness profiles along the minor axis allowed us to determine univocally that both components of the interacting pair are trailing spirals.

  1. Uncovering Binary Supermassive Black Holes in Merging Galaxy Pairs

    NASA Astrophysics Data System (ADS)

    McNulty, Paul; Satyapal, Shobita; Ellison, Sara L.; Secrest, Nathan; Gliozzi, Mario; Rothberg, Barry

    2016-01-01

    It is now well known that virtually all galaxies host a central supermassive black hole (SMBH) and that galaxy interactions are ubiquitous. Theory predicts these interactions would funnel gas toward the central regions of galaxies, potentially triggering gas accretion onto the SMBH, causing them to appear as binary active galactic nuclei (AGN). However, despite decades of searching and strong theoretical reasons that they should exist, observationally confirmed cases of binary AGNs are extremely rare, and most have been discovered serendipitously. Since galaxy mergers are likely to be characterized by dusty environments, it is possible that the optical signatures of a significant number of binary AGNs are obscured. Observations from the Wide-field Infrared Survey Explorer (WISE) may hold the key for increasing the rate of discovery of binary AGN in late-stage mergers. Starting with a sample of ~4,000 galaxy pairs, we searched for mid-IR signatures of binary AGNs. In this poster, we report on the detection frequency of binary AGNs identified through mid-infrared observations and explore its dependence on merger stage.

  2. Stellar dynamics in E+E pairs of galaxies. 2: Simulations and interpretation

    NASA Astrophysics Data System (ADS)

    Combes, F.; Rampazzo, R.; Bonfanti, P. P.; Prugniel, P.; Sulentic, J. W.

    1995-05-01

    We have presented in a companion article a kinematic study of three E+E galaxy pairs, NGC741/742, 1587/1588 (CPG 99) and 2672/2673 (CPG 175). We find some evidence for perturbed velocity dispersion profiles. These perturbation features are now reported for 14 galaxies in the literature. They occur, or require observations for detection, at large radii where the S/N in the data is low. While observations of individual galaxies are sometimes uncertain, the large number of objects where such features are suspected gives confidence that they are real. These perturbations can be attributed to projection effects contamination along the line of sight, or directly to the tidal interaction. We report the results of several self-gravitating simulations of unbound pairs in an effort to better understand these perturbations another generic features of close E+E pairs reported in the literature. The models frequently show off-center envelopes created by the asymmetry of tidal forces during interpenetrating encounters. The envelopes last for a few 108 yrs, which explains the frequency of such features in observed pairs. This phenomenon is stronger in the self-gravitating simulations than in the MTBA runs. U-shaped (and an equal number of inverse U shaped velocity profiles are seen in the simulations, a result of ablation in the outer envelopes. Simulations including inner galaxy rotation also preserve this feature, irrespective of the spin vector direction in each galaxy. U-shape velocity structure is found to be a robust indicator of the ongoing interaction. All simulations show evidence for enhanced velocity dispersion between the galaxies even in the case of simple superposition of two non interacting objects. We therefore conclude that this cannot be considered an unambiguous indicator of the interaction.

  3. Disk Galaxy Warp Formation via Close Encounters

    NASA Astrophysics Data System (ADS)

    Kim, Jeonghwan; Peirani, S.; Kim, S.; Yoon, S.

    2012-01-01

    Warped disks appear to be ubiquitous among spiral galaxies. We present a new scenario for the warp formation, in which galactic fly-by encounters are main drivers of the warp structure. Based on N-body simulation using a publicly available code Gadget2, we investigate morphological and kinematical structures of disk galaxies while the galaxies are undergoing fly-by encounters with adjacent dark matter halos. In this study, we find that warps can be excited by impulsive encounters and sustained for a few billion years. We also find that encounters cause the initially spherical halos to deform into intricate shape halos at the inner regions where warps are generated. Most of the warps from the simulation show inclination angles that are comparable to the observations. The creation of warps, their inclination and their lifetimes are governed primarily by the following three parameters: the impact parameter (the minimum distance between two halos), the mass ratio between two galaxies, and the incoming angle of the intruder. We discuss pros and cons about our alternative scenario in comparison with existing explanations.

  4. Searching for Tidal Features in Galaxy Pair ARP 142

    NASA Astrophysics Data System (ADS)

    Ronca, Joseph; Domingue, Donovan L.

    2016-01-01

    We present the beginning of an ongoing research project to detect tidal features in galaxy pairs with the test case of ARP 142 (NGC 2936 & NGC 2937). Using the 0.6 meter telescope at the Pohl Observatory of Georgia College and State University, a series of sixty, fifteen second luminance exposures, were taken using an SBIG 9XE CCD. In order to reduce the background sky brightness, images were calibrated using standard techniques, as well as using additional flats created from nearby sections of the sky.

  5. A CLOSE-PAIR ANALYSIS OF DAMP MERGERS AT INTERMEDIATE REDSHIFTS

    SciTech Connect

    Chou, Richard C. Y.; Abraham, Roberto G.; Bridge, Carrie R. E-mail: abraham@astro.utoronto.ca

    2012-12-01

    We have studied the kinematics of {approx}2800 candidate close-pair galaxies at 0.1 < z < 1.2 identified from the Canada-France-Hawaii Telescope Legacy Survey fields. Spectra of these systems were obtained using spectrometers on the 6.5 m Magellan and 5 m Hale telescopes. These data allow us to constrain the rate of dry mergers at intermediate redshifts and to test the 'hot halo' model for quenching of star formation. Using virial radii estimated from the correlation between dynamical and stellar masses published by Leauthaud et al., we find that around 1/5 of our candidate pairs are likely to share a common dark matter halo (our metric for close physical association). These pairs are divided into red-red, blue-red, and blue-blue systems using the rest-frame colors classification method introduced in Chou et al.. Galaxies classified as red in our sample have very low star formation rates, but they need not be totally quiescent, and hence we refer to them as 'damp', rather than 'dry', systems. After correcting for known selection effects, the fraction of blue-blue pairs is significantly greater than that of red-red and blue-red pairs. Red-red pairs are almost entirely absent from our sample, suggesting that damp mergers are rare at z {approx} 0.5. Our data support models with a short merging timescale (<0.5 Gyr) in which star formation is enhanced in the early phase of mergers, but quenched in the late phase. Hot halo models may explain this behavior, but only if virial shocks that heat gas are inefficient until major mergers are nearly complete.

  6. Galaxy pairs in the Sloan Digital Sky Survey - XI. A new method for measuring the influence of the closest companion out to wide separations

    NASA Astrophysics Data System (ADS)

    Patton, David R.; Qamar, Farid D.; Ellison, Sara L.; Bluck, Asa F. L.; Simard, Luc; Mendel, J. Trevor; Moreno, Jorge; Torrey, Paul

    2016-09-01

    We describe a statistical approach for measuring the influence that a galaxy's closest companion has on the galaxy's properties out to arbitrarily wide separations. We begin by identifying the closest companion for every galaxy in a large spectroscopic sample of Sloan Digital Sky Survey galaxies. We then characterize the local environment of each galaxy by using the number of galaxies within 2 Mpc and by determining the isolation of the galaxy pair from other neighbouring galaxies. We introduce a sophisticated algorithm for creating a statistical control sample for each galaxy, matching on stellar mass, redshift, local density and isolation. Unlike traditional studies of close galaxy pairs, this approach is effective in a wide range of environments, regardless of how faraway the closest companion is (although a very distant closest companion is unlikely to have a measurable influence on the galaxy in question). We apply this methodology to measurements of galaxy asymmetry, and find that the presence of nearby companions drives a clear enhancement in galaxy asymmetries. The asymmetry excess peaks at the smallest projected separations (<10 kpc), where the mean asymmetry is enhanced by a factor of 2.0 ± 0.2. Enhancements in mean asymmetry decline as pair separation increases, but remain statistically significant (1σ-2σ) out to projected separations of at least 50 kpc.

  7. Underwater acoustic source localization using closely spaced hydrophone pairs

    NASA Astrophysics Data System (ADS)

    Sim, Min Seop; Choi, Bok-Kyoung; Kim, Byoung-Nam; Lee, Kyun Kyung

    2016-07-01

    Underwater sound source position is determined using a line array. However, performance degradation occurs owing to a multipath environment, which generates incoherent signals. In this paper, a hydrophone array is proposed for underwater source position estimation robust to a multipath environment. The array is composed of three pairs of sensors placed on the same line. The source position is estimated by performing generalized cross-correlation (GCC). The proposed system is not affected by a multipath time delay because of the close distance between closely spaced sensors. The validity of the array is confirmed by simulation using acoustic signals synthesized by eigenrays.

  8. Cosmic ray antiprotons in the closed galaxy model

    NASA Technical Reports Server (NTRS)

    Protheroe, R. J.

    1981-01-01

    A calculation is made of the flux of secondary antiprotons expected for the leaky box model and for the closed galaxy model of Peters and Westergaard (1977). The antiproton/proton ratio observed at several GeV is a factor of 4 higher than the prediction for the leaky box model but is consistent with that predicted for the closed galaxy model. It is found that new low-energy data are not consistent with either model. Attention is given to the possibility of a primary antiproton component.

  9. Accumulation of Raman gain between closely spaced pulse pairs.

    PubMed

    Marshall, L R; Piper, J A

    1990-12-01

    The short-pulse conversion efficiency of stimulated Raman scattering in Pb vapor is increased from 15% to 35% by using a novel technique that employs a closely spaced pair of pump pulses. The second pulse scatters off the coherent excitation induced in the medium by the first pulse, with a resultant enhancement in efficiency. To our knowledge these results give the first observation of such long-lived cooperative phenomena in stimulated Raman scattering. We have also observed this phenomenon in H(2) and show that this technique is readily applicable to other Raman-active media. PMID:19771085

  10. Close up view of the pair of Rudder Pedals in ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Close up view of the pair of Rudder Pedals in the Commander's Satiation on the Flight Deck of the Orbiter Discovery. The rudder pedals command orbiter acceleration in yaw by positioning the rudder during atmospheric flight. However, because the flight control software automatically performs turn coordination during banking maneuvers, the rudder pedals are not operationally used during glided flight. It is not until after touchdown that the crew uses them for nose wheel steering during rollout. Depressing the upper portion of the rudder pedals provides braking. Differential braking may also be used for directional control during rollout. This view was take at Johnson Space Center. - Space Transportation System, Orbiter Discovery (OV-103), Lyndon B. Johnson Space Center, 2101 NASA Parkway, Houston, Harris County, TX

  11. Peek-a-boo: Mapping Dust in Galaxies with Spitzer IRAC Imaging of Back-lit Galaxy Pairs

    NASA Astrophysics Data System (ADS)

    Kulkarni, Varsha; Higdon, Sarah; Higdon, James

    2010-06-01

    Interstellar dust affects the chemistry and energy budget of galaxies, and can profoundly affect studies of the distant universe. However, very little is known about the nature of interstellar dust in normal galaxies beyond the Milky Way and the Magellanic Clouds. A direct way to probe dust in galaxies is by using partially overlapping (backlit) pairs of galaxies. While this technique has been applied to a few galaxy pairs, it has been used primarily with optical data in B and I bands (and occasionally K band), which are all subject to substantial amounts of dust extinction. Here we propose to observe 15 backlit pairs/polar ring galaxies in IRAC 3.6 and 4.5 micron bands which are much less affected by dust. Our goals are: (1) to obtain essentially un-extinguished reference images for comparison with the existing optical images and thus to determine dust extinction more accurately across different parts of the foreground galaxies; (2) to determine the opacity of some nearby spiral disks and examine whether dust grain sizes decrease in outer parts of disks; (3) to probe large-scale dust structure in some elliptical galaxies; (4) to examine whether dust exhibits fractal structure; and (5) to map star formation rate across the galaxies using the 3.6/4.5 micron flux ratio. The very local nature of our sample allows a detailed look at dust properties at different positions within the galaxies, and examine what galaxy properties drive the variation in dust properties. Our study will provide new implications for observations of the distant universe that are necessarily affected by the presence of dust in foreground galaxies.

  12. A geometric measure of dark energy with pairs of galaxies.

    PubMed

    Marinoni, Christian; Buzzi, Adeline

    2010-11-25

    Observations indicate that the expansion of the Universe is accelerating, which is attributed to a ‘dark energy’ component that opposes gravity. There is a purely geometric test of the expansion of the Universe (the Alcock–Paczynski test), which would provide an independent way of investigating the abundance (Ω(X)) and equation of state (W(X)) of dark energy. It is based on an analysis of the geometrical distortions expected from comparing the real-space and redshift-space shape of distant cosmic structures, but it has proved difficult to implement. Here we report an analysis of the symmetry properties of distant pairs of galaxies from archival data. This allows us to determine that the Universe is flat. By alternately fixing its spatial geometry at Ω(k)≡0 and the dark energy equation-of-state parameter at W(X)≡-1, and using the results of baryon acoustic oscillations, we can establish at the 68.3% confidence level that and -0.85>W(X)>-1.12 and 0.60<Ω(X)<0.80. PMID:21107424

  13. Binary pairs of supermassive black holes - Formation in merging galaxies

    NASA Astrophysics Data System (ADS)

    Valtaoja, L.; Valtonen, M. J.; Byrd, G. G.

    1989-08-01

    A process in which supermassive binary blackholes are formed in nuclei of supergiant galaxies due to galaxy mergers is examined. There is growing evidence that mergers of galaxies are common and that supermassive black holes in center of galaxies are also common. Consequently, it is expected that binary black holes should arise in connection with galaxy mergers. The merger process in a galaxy modeled after M87 is considered. The capture probability of a companion is derived as a function of its mass. Assuming a correlation between the galaxy mass and the blackholes mass, the expected mass ratio in binary black holes is calculated. The binary black holes formed in this process are long lived, surviving longer than the Hubble time unless they are perturbed by black holes from successive mergers. The properties of these binaries agree with Gaskell's (1988) observational work on quasars and its interpretation in terms of binary black holes.

  14. Isolated Galaxies versus Interacting Pairs with MaNGA

    NASA Astrophysics Data System (ADS)

    Fernández, María; Yuan, Fangting; Shen, Shiyin; Yin, Jun; Chang, Ruixiang; Feng, Shuai

    2015-10-01

    We present preliminary results of the spectral analysis on the radial distributions of the star formation history in both, a galaxy merger and a spiral isolated galaxy observed with MaNGA. We find that the central part of the isolated galaxy is composed by older stellar population ($\\sim$2 Gyr) than in the outskirts ($\\sim$7 Gyr). Also, the time-scale is gradually larger from 1 Gyr in the inner part to 3 Gyr in the outer regions of the galaxy. In the case of the merger, the stellar population in the central region is older than in the tails, presenting a longer time-scale in comparison to central part in the isolated galaxy. Our results are in agreement with a scenario where spiral galaxies are built from inside-out. In the case of the merger, we find evidence that interactions enhance star formation in the central part of the galaxy.

  15. What can the occult do for you? Understanding dust geometry in other galaxies from overlapping galaxy pairs.

    NASA Astrophysics Data System (ADS)

    Holwerda, Benne Willem

    2015-08-01

    Interstellar dust is still the dominant uncertainty in Astronomy, limiting precision in e.g., cosmological distance estimates and models of how light is re-processed within a galaxy. When a foreground galaxy serendipitously overlaps a more distant one, the latter backlights the dusty structures in the nearer foreground galaxy. Such an overlapping or occulting galaxy pair can be used to measure the distribution of dust in the closest galaxy with great accuracy. My STARSMOG program uses HST observation of occulting galaxy pairs to accurately map the distribution of dust in foreground galaxies in fine (<100 pc) detail.The primary motivation is threefold: first, almost half of the light from stars in spiral galaxies is absorbed by the interstellar dust grains and re-emitted at longer wavelengths. To model this accurately, one needs to know the distribution and detailed geometry of dust in galaxies. The travel of light through an inhomogeneous medium is radically different from the smooth one and depends strongly on the medium’s inner structure. Secondly, the model for our Universe today includes dark energy, inferred from the distances to supernova, which themselves may be dimmed by intervening dust. An accurate model for the dust extinction in supernova host galaxies is critical to evolve this technique to the next level of accuracy needed to map dark energy. And finally, the fine-scale maps of dust extinction in occuling galaxies can be used to trace the molecular cloud sizes and the role of turbulence in the ISM of these disks. Furthermore, Integral Field Unit observations of such pairs will map the effective extinction curve in these occulting galaxies, disentangling the role of fine-scale geometry and grain composition on these curves.The overlapping galaxy technique promises to deliver a clear understanding of the dust in galaxies: the dust geometry, a probability function of the amount of dimming as a function of galaxy type, its dependence on wavelength and

  16. MERGING COLD FRONTS IN THE GALAXY PAIR NGC 7619 AND NGC 7626

    SciTech Connect

    Randall, S. W.; Jones, C.; Kraft, R.; Forman, W. R.; O'Sullivan, E.

    2009-05-10

    We present results from Chandra observations of the galaxy pair NGC 7619 and NGC 7626, the two dominant members of the Pegasus group. The X-ray images show a brightness edge associated with each galaxy, which we identify as merger cold fronts. The edges are sharp, and the axes of symmetry of the edges are roughly antiparallel, suggesting that these galaxies are falling toward one another in the plane of the sky. The detection of merger cold fronts in each of the two dominant member galaxies implies a merging subgroup scenario, since the alternative is that the galaxies are falling into a preexisting {approx}1 keV halo without a dominant galaxy of its own, and such objects are not observed. We estimate the three-dimensional velocities from the cold fronts and, using the observed radial velocities of the galaxies, show that the velocity vectors are indeed most likely close to the plane of the sky, with a relative velocity of {approx}1190 km s{sup -1}. The relative velocity is consistent with what is expected from the infall of two roughly equal mass subgroups whose total viral mass equals that of the Pegasus group. We conclude that the Pegasus cluster is most likely currently forming from a major merger of two subgroups, dominated by NGC 7619 and NGC 7626. NGC 7626 contains a strong radio source, consisting of a core with two symmetric jets, and radio lobes. Although we find no associated structure in the X-ray surface brightness map, the temperature map reveals a clump of cool gas just outside the southern lobe, presumably entrained by the lobe, and possibly an extension of cooler gas into the lobe itself. The jet axis is parallel with the projected direction of motion of NGC 7626 (inferred from the symmetry axis of the merger cold front), and the southern leading jet is foreshortened as compared to the northern trailing one, possibly due to the additional ram pressure encountered by the forward jet.

  17. VizieR Online Data Catalog: Isolated galaxies, pairs and triplets (Argudo-Fernandez+, 2015)

    NASA Astrophysics Data System (ADS)

    Argudo-Fernandez, M.; Verley, S.; Bergond, G.; Duarte Puertas, S.; Ramos Carmona, E.; Sabater, J.; Fernandez, Lorenzo M.; Espada, D.; Sulentic, J.; Ruiz, J. E.; Leon, S.

    2015-04-01

    Catalogues of isolated galaxies, isolated pairs, and isolated triplets in the local Universe with positions, redshifts, and degrees of relation with their physical and large-scale environments. (5 data files).

  18. The Isolated Interacting Galaxy Pair NGC 5426/27 (Arp 271)

    NASA Astrophysics Data System (ADS)

    Fuentes-Carrera, I.; Rosado, M.; Amram, P.; Dultzin-Hacyan, D.; Bernal, A.; Salo, H.; Laurikainen, E.; Cruz-González, I.; Le Coarer, E.

    2001-03-01

    The isolated interacting galaxy pair NGC 5426/27 (Arp 271) was observed using the scanning Fabry-Perot interferometer PUMA. The velocity field, various kinematical parameters and rotation curve for each galaxy were derived. We found a small bar-like structure in NGC 5426 and a severely distorted velocity field for NGC 5427. A range of possible masses was computed for each galaxy.

  19. Modeling the Dynamics of Interacting Galaxy Pairs - Testing Identikit Using GADGET SPH Simulations

    NASA Astrophysics Data System (ADS)

    Mortazavi, S. Alireza; Lotz, Jennifer; Barnes, Joshua E.

    2015-01-01

    We develop and test an automated technique to model the dynamics of interacting galaxy pairs. We use Identikit (Barnes & Hibbard 2009; Barnes 2011) as a tool for modeling and matching the morphology and kinematics of the interacting pairs of similar-size galaxies. In order to reduce the effect of subjective human interference, we automate the selection of phase-space regions used to match simulations to data, and we explore how selection of these regions affects the random uncertainties of parameters in the best-fit model. In this work, we used an independent set of GADGET SPH simulations as input data, so we determined the systematic bias in the measured encounter parameters based on the known initial conditions of these simulations. We tested both cold gas and young stellar components in the GADGET simulations to explore the effect of choosing HI vs. Hα as the line of sight velocity tracer. We found that we can group the results into tests with good, fair, and poor convergence based on the distribution of parameters of models close enough to the best-fit model. For tests with good and fair convergence, we ruled out large fractions of parameter space and recovered merger stage, eccentricity, viewing angle, and pericentric distance within 2σ of the correct value. All of tests on gaseous component of prograde systems had either good or fair convergence. Retrograde systems and most of tests on young stars had poor convergence and may require constraints from regions other than the tidal tails. In this work we also present WIYN SparsePak IFU data for a few interacting galaxies, and we show the result of applying our method on this data set.

  20. A dynamical proximity analysis of interacting galaxy pairs

    NASA Technical Reports Server (NTRS)

    Chatterjee, Tapan K.

    1990-01-01

    Using the impulsive approximation to study the velocity changes of stars during disk-sphere collisions and a method due to Bottlinger to study the post collision orbits of stars, the formation of various types of interacting galaxies is studied as a function of the distance of closest approach between the two galaxies.

  1. VLA Reveals a Close Pair of Potential Planetary Systems

    NASA Astrophysics Data System (ADS)

    1998-09-01

    Planets apparently can form in many more binary-star systems than previously thought, according to astronomers who used the National Science Foundation's Very Large Array (VLA) radio telescope to image protoplanetary disks around a close pair of stars. "Most stars in the universe are not alone, like our Sun, but are part of double or triple systems, so this means that the number of potential planets is greater than we realized," said Luis Rodriguez, of the National Autonomous University in Mexico City, who led an international observing team that made the discovery. The astronomers announced their results in the Sept. 24 issue of the scientific journal Nature. The researchers used the VLA to study a stellar nursery - a giant cloud of gas and dust - some 450 light-years distant in the constellation Taurus, where stars the size of the Sun or smaller are being formed. They aimed at one particular object, that, based on previous infrared and radio observations, was believed to be a very young star. The VLA observations showed that the object was not a single young star but a pair of young stars, separated only slightly more than the Sun and Pluto. The VLA images show that each star in the pair is surrounded by an orbiting disk of dust, extending out about as far as the orbit of Saturn. Such dusty disks are believed to be the material from which planets form. Similar disks are seen around single stars, but the newly-discovered disks around the stars in the binary system are about ten times smaller, their size limited by the gravitational effect of the other, nearby star. Their existence indicates, however, that such protoplanetary disks, though truncated in size, still can survive in such a close double-star system. "It was surprising to see these disks in a binary system with the stars so close together," said Rodriguez. "Each of these disks contains enough mass to form a solar system like our own," said David Wilner, of the Harvard-Smithsonian Center for Astrophysics

  2. MAJOR-MERGER GALAXY PAIRS IN THE COSMOS FIELD-MASS-DEPENDENT MERGER RATE EVOLUTION SINCE z = 1

    SciTech Connect

    Xu, C. Kevin; Zhao, Yinghe; Gao, Y.; Scoville, N.; Capak, P.; Drory, N.

    2012-03-10

    We present results of a statistical study of the cosmic evolution of the mass-dependent major-merger rate since z = 1. A stellar mass limited sample of close major-merger pairs (the CPAIR sample) was selected from the archive of the COSMOS survey. Pair fractions at different redshifts derived using the CPAIR sample and a local K-band-selected pair sample show no significant variations with stellar mass. The pair fraction exhibits moderately strong cosmic evolution, with the best-fitting function of f{sub pair} = 10{sup -1.88({+-}0.03)}(1 + z){sup 2.2({+-}0.2)}. The best-fitting function for the merger rate is R{sub mg} (Gyr{sup -1}) = 0.053 Multiplication-Sign (M{sub star}/10{sup 10.7} M{sub Sun} ){sup 0.3}(1 + z){sup 2.2}/(1 + z/8). This rate implies that galaxies of M{sub star} {approx} 10{sup 10}-10{sup 11.5} M{sub Sun} have undergone {approx}0.5-1.5 major mergers since z = 1. Our results show that, for massive galaxies (M{sub star} {>=} 10{sup 10.5} M{sub Sun }) at z {<=} 1, major mergers involving star-forming galaxies (i.e., wet and mixed mergers) can account for the formation of both ellipticals and red quiescent galaxies (RQGs). On the other hand, major mergers cannot be responsible for the formation of most low mass ellipticals and RQGs of M{sub star} {approx}< 10{sup 10.3} M{sub Sun }. Our quantitative estimates indicate that major mergers have significant impact on the stellar mass assembly of the most massive galaxies (M{sub star} {>=} 10{sup 11.3} M{sub Sun }), but for less massive galaxies the stellar mass assembly is dominated by the star formation. Comparison with the mass-dependent (ultra)luminous infrared galaxies ((U)LIRG) rates suggests that the frequency of major-merger events is comparable to or higher than that of (U)LIRGs.

  3. Pairs of galaxies in low density regions of a combined redshift catalog

    NASA Technical Reports Server (NTRS)

    Charlton, Jane C.; Salpeter, Edwin E.

    1990-01-01

    The distributions of projected separations and radial velocity differences of pairs of galaxies in the CfA and Southern Sky Redshift Survey (SSRS) redshift catalogs are examined. The authors focus on pairs that fall in low density environments rather than in clusters or large groups. The projected separation distribution is nearly flat, while uncorrelated galaxies would have given one linearly rising with r sub p. There is no break in this curve even below 50 kpc, the minimum halo size consistent with measured galaxy rotation curves. The significant number of pairs at small separations is inconsistent with the N-body result that galaxies with overlapping halos will rapidly merge, unless there are significant amounts of matter distributed out to a few hundred kpc of the galaxies. This dark matter may either be in distinct halos or more loosely distributed. Large halos would allow pairs at initially large separations to head toward merger, replenishing the distribution at small separations. In the context of this model, the authors estimate that roughly 10 to 25 percent of these low density galaxies are the product of a merger, compared with the elliptical/SO fraction of 18 percent, observed in low density regions of the sample.

  4. THE ARECIBO GALAXY ENVIRONMENT SURVEY. III. OBSERVATIONS TOWARD THE GALAXY PAIR NGC 7332/7339 AND THE ISOLATED GALAXY NGC 1156

    SciTech Connect

    Minchin, R. F.; Momjian, E.; Auld, R.; Davies, J. I.; Smith, M. W. L.; Taylor, R.; Valls-Gabaud, D.; Van Driel, W.; Karachentsev, I. D.; Henning, P. A.; O'Neil, K. L.

    2010-10-15

    Two 5 deg{sup 2} regions around the NGC 7332/9 galaxy pair and the isolated galaxy NGC 1156 have been mapped in the 21 cm line of neutral hydrogen (H I) with the Arecibo L-band Feed Array out to a redshift of {approx}0.065 ({approx}20,000 km s{sup -1}) as part of the Arecibo Galaxy Environment Survey. One of the aims of this survey is to investigate the environment of galaxies by identifying dwarf companions and interaction remnants; both of these areas provide the potential for such discoveries. The neutral hydrogen observations were complemented by optical and radio follow-up observations with a number of telescopes. A total of 87 galaxies were found, of which 39 (45%) were previously cataloged and 15 (17%) have prior redshifts. Two dwarf galaxies have been discovered in the NGC 7332 group and a single dwarf galaxy in the vicinity of NGC 1156. A parallel optical search of the area revealed one further possible dwarf galaxy near NGC 7332.

  5. VLT/VIMOS observations of an occulting galaxy pair: redshifts and effective extinction curve

    NASA Astrophysics Data System (ADS)

    Holwerda, B. W.; Böker, T.; Dalcanton, J. J.; Keel, W. C.; de Jong, R. S.

    2013-07-01

    We present Very Large Telescope/Visible Multiobject Spectrograph Integral Field Unit observations of an occulting galaxy pair previously discovered in Hubble Space Telescope (HST) observations. The foreground galaxy is a low-inclination spiral disc, which causes clear attenuation features seen against the bright bulge and disc of the background galaxy. We find redshifts of z = 0.064 ± 0.003 and 0.065 for the foreground and background galaxy, respectively. This relatively small difference does not rule out gravitational interaction between the two galaxies. Emission line ratios point to a star-forming, not active galactic nuclei dominated foreground galaxy. We fit the Cardelli, Clayton and Mathis extinction law to the spectra of individual fibres to derive slope (RV) and normalization (AV). The normalization agrees with the HST attenuation map and the slope is lower than the Milky Way relation (RV < 3.1), which is likely linked to the spatial sampling of the disc. We speculate that the values of RV point to either coherent interstellar medium structures in the disc larger than usual (˜9 kpc) or higher starting values of RV, indicative of recent processing of the dust. The foreground galaxy is a low stellar mass spiral (M* ˜ 3 × 109 M⊙) with a high dust content (Mdust ˜ 0.5 × 106 M⊙). The dust disc geometry visible in the HST image would explain the observed spectral energy distribution properties of smaller galaxies: a lower mean dust temperature, a high dust-to-stellar mass ratio but relatively little optical attenuation. Ongoing efforts to find occulting pairs with a small foreground galaxy will show how common this geometry is.

  6. Kiloparsec Mass/Light Offsets in the Galaxy Pair-Lyα Emitter Lens System SDSS J1011+0143

    NASA Astrophysics Data System (ADS)

    Shu, Yiping; Bolton, Adam S.; Moustakas, Leonidas A.; Stern, Daniel; Dey, Arjun; Brownstein, Joel R.; Burles, Scott; Spinrad, Hyron

    2016-03-01

    We report the discovery of significant mass/light offsets in the strong gravitational lensing system SDSS J1011+0143. We use the high-resolution Hubble Space Telescope (HST) F555W- and F814W-band imaging and Sloan Digital Sky Survey (SDSS) spectroscopy of this system, which consists of a close galaxy pair with a projected separation of ≈ 4.2 {{kpc}} at zlens ˜ 0.331 lensing an Lyα emitter (LAE) at zsource = 2.701. Comparisons between the mass peaks inferred from lens models and light peaks from HST imaging data reveal significant spatial mass/light offsets as large as 1.72 ± 0.24 ± 0.34 kpc in both filter bands. Such large mass/light offsets, not seen in isolated field lens galaxies and relaxed galaxy groups, may be related to the interactions between the two lens galaxies. The detected mass/light offsets can potentially serve as an important test for the self-interacting dark matter model. However, other mechanisms such as dynamical friction on spatially differently distributed dark matter and stars could produce similar offsets. Detailed hydrodynamical simulations of galaxy-galaxy interactions with self-interacting dark matter could accurately quantify the effects of different mechanisms. The background LAE is found to contain three distinct star-forming knots with characteristic sizes from 116 to 438 pc. It highlights the power of strong gravitational lensing in probing the otherwise too faint and unresolved structures of distance objects below subkiloparsec or even 100 pc scales through its magnification effect. 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 AURA, Inc., under NASA contract NAS 5-26555. These observations are associated with program #10831.

  7. A close-pair binary in a distant triple supermassive black hole system.

    PubMed

    Deane, R P; Paragi, Z; Jarvis, M J; Coriat, M; Bernardi, G; Fender, R P; Frey, S; Heywood, I; Klöckner, H-R; Grainge, K; Rumsey, C

    2014-07-01

    Galaxies are believed to evolve through merging, which should lead to some hosting multiple supermassive black holes. There are four known triple black hole systems, with the closest black hole pair being 2.4 kiloparsecs apart (the third component in this system is at 3 kiloparsecs), which is far from the gravitational sphere of influence (about 100 parsecs for a black hole with mass one billion times that of the Sun). Previous searches for compact black hole systems concluded that they were rare, with the tightest binary system having a separation of 7 parsecs (ref. 10). Here we report observations of a triple black hole system at redshift z = 0.39, with the closest pair separated by about 140 parsecs and significantly more distant from Earth than any other known binary of comparable orbital separation. The effect of the tight pair is to introduce a rotationally symmetric helical modulation on the structure of the large-scale radio jets, which provides a useful way to search for other tight pairs without needing extremely high resolution observations. As we found this tight pair after searching only six galaxies, we conclude that tight pairs are more common than hitherto believed, which is an important observational constraint for low-frequency gravitational wave experiments. PMID:24990745

  8. Caltech Faint Galaxy Redshift Survey. XI. The Merger Rate to Redshift 1 from Kinematic Pairs.

    PubMed

    Carlberg; Cohen; Patton; Blandford; Hogg; Yee; Morris; Lin; Hall; Sawicki; Wirth; Cowie; Hu; Songaila

    2000-03-20

    The rate of mass accumulation due to galaxy merging depends on the mass, density, and velocity distribution of galaxies in the near neighborhood of a host galaxy. The fractional luminosity in kinematic pairs combines all of these effects in a single estimator that is relatively insensitive to population evolution. Here we use a k-corrected and evolution-compensated volume-limited sample having an R-band absolute magnitude of Mk,eRGalaxy Redshift Survey and 3000 from the Canadian Network for Observational Cosmology field galaxy survey to measure the rate and redshift evolution of merging. The combined sample has an approximately constant comoving number and luminosity density from redshift 0.1 to 1.1 (OmegaM=0.2, OmegaLambda=0.8); hence, any merger evolution will be dominated by correlation and velocity evolution, not density evolution. We identify kinematic pairs with projected separations less than either 50 or 100 h-1 kpc and rest-frame velocity differences of less than 1000 km s-1. The fractional luminosity in pairs is modeled as fL&parl0;Deltav,rp,Mk,er&parr0;&parl0;1+z&parr0;mL, where &sqbl0;fL,mL&sqbr0; are &sqbl0;0.14+/-0.07,0+/-1.4&sqbr0; and &sqbl0;0.37+/-0.7,0.1+/-0.5&sqbr0; for rppair density, a merger probability, and a mean in-spiral time. The resulting mass accretion rate per galaxy (M1,M2>/=0.2M*) is 0.02+/-0.01&parl0;1+z&parr0;0.1+/-0.5M* Gyr-1. Present-day high-luminosity galaxies therefore have accreted approximately 0.15M* of their mass over the approximately 7 Gyr to redshift 1. Since merging is likely only weakly dependent on the host mass, the fractional effect, deltaM&solm0;M approximately 0.15M*&solm0;M, is dramatic for lower mass

  9. The isolated interacting galaxy pair NGC 5426/27 (Arp 271)

    NASA Astrophysics Data System (ADS)

    Fuentes-Carrera, I.; Rosado, M.; Amram, P.; Dultzin-Hacyan, D.; Cruz-González, I.; Salo, H.; Laurikainen, E.; Bernal, A.; Ambrocio-Cruz, P.; Le Coarer, E.

    2004-02-01

    We present Hα observations of the isolated interacting galaxy pair NGC 5426/27 using the scanning Fabry-Perot interferometer PUMA. The velocity field, various kinematical parameters and rotation curve for each galaxy were derived. The FWHM map and the residual velocities map were also computed to study the role of non-circular motions of the gas. Most of these motions can be associated with the presence of spiral arms and structure such as central bars. We found a small bar-like structure in NGC 5426, a distorted velocity field for NGC 5427 and a bridge-like feature between both galaxies which seems to be associated with NGC 5426. Using the observed rotation curves, a range of possible masses was computed for each galaxy. These were compared with the orbital mass of the pair derived from the relative motion of the participants. The rotation curve of each galaxy was also used to fit different mass distribution models considering the most common theoretical dark halo models. An analysis of the interaction process is presented and a possible 3D scenario for this encounter is also suggested. Table 1 is only available in electronic form at http://www.edpsciences.org

  10. Radio continuum observations of the quasar-galaxy pair 3C 232-NGC 3067

    NASA Technical Reports Server (NTRS)

    Haxthausen, Eric; Carilli, Chris; Vangorkom, Jacqueline H.

    1990-01-01

    The quasar-galaxy pair 3C 232-NGC 3067 is well known to show absorption by gas associated with the foreground galaxy against the background quasar (see Stocke et al. this volume). Observations by Carilli, van Gorkom, and Stocke (Nature 338, 134, 1989) found that the absorbing gas is located in a long tail of gas which extends from the galaxy toward the quasar and beyond (in projection). Though the HI observations of NGC 3067 indicate that the galaxy has been severely disturbed, there is no obvious candidate in the field which could cause such a disturbance, leading to the conclusion that the system has undergone a recent merger. The radio continuum observations of this system were designed to study the nature of this highly disturbed galaxy. New continuum observations confirm the notion that NGC 3067 is a highly disturbed system, and, in particular, the notion that the western half of the galaxy extends only 1/2 as far in radius as the eastern half. This disturbance must have occurred recently, since the galactic rotation would smooth out the observed asymmetry in about 10(exp 8) years. Researchers are left with the problem that there are no obvious candidates which could have caused such a disturbance.

  11. Formation of ring structures in galactic disks during close passages of galaxies

    NASA Astrophysics Data System (ADS)

    Tutukov, A. V.; Fedorova, A. V.

    2016-01-01

    The formation of ring structures in galactic disks is investigated. It is shown that, in addition to the known mechanism of forming rings in "head-on" collisions between galaxies, ring structures can be formed during close passages of galaxies if the perturbing galaxy moves in a plane close to the equatorial plane of the perturbed disk galaxy, opposite to the direction of rotation of the disk. Numerical simulations of the formation of structures in the disk of a massive galaxy undergoing a passage with another galaxy are considered. The results of these cmputations show the formation of pronounced ring structures in the galactic disk when the initial inclination of the trajectory of the perturbing galaxy to the equatorial plane of the perturbed galaxy is no more than ~25°. However, the probability of close passages of galaxies with these parameters is small, as is the probability of head-on collisions. The characteristic time scale for the existence of pronounced rings is of order the dynamical time scale at the edge of the galaxy, 200-300 million years, close to the corresponding time for head-on collisions. The evolution of the rings has the same character in both cases: they gradually expand and move toward the periphery of the galaxy. The results of these simulations can also be applied to a close passage of one star by another star with a protoplanetary disk. According to the computation results, the characteristic time scale for the existence of pronounced rings in such a protoplanetary disk depends mainly on the size of the disk; this time scale can reach several tens of thousands of years for a disk radius of about 1000 AU. The formation of ring structures in such a disk could influence the formation and evolution of planetesimals, and possibly the character of the formation of planets and the distribution of their orbital semi-major axes.

  12. Probing the magnetic field of the nearby galaxy pair Arp 269

    NASA Astrophysics Data System (ADS)

    Nikiel-Wroczyński, B.; Jamrozy, M.; Soida, M.; Urbanik, M.; Knapik, J.

    2016-06-01

    We present a multiwavelength radio study of the nearby galaxy pair Arp 269 (NGC 4490/85). High sensitivity to extended structures gained by using the merged interferometric and single-dish maps allowed us to reveal a previously undiscovered extension of the radio continuum emission. Its direction is significantly different from that of the neutral gas tail, suggesting that different physical processes might be involved in their creation. The population of radio-emitting electrons is generally young, signifying an ongoing, vigorous star formation - this claim is supported by strong magnetic fields (over 20 μG), similar to the ones found in much larger spiral galaxies. From the study of the spectral energy distribution, we conclude that the electron population in the intergalactic bridge between member galaxies originates from the disc areas, and therefore its age (approximately 3.7-16.9 Myr, depending on the model used) reflects the time-scale of the interaction. We have also discovered an angularly near compact steep source - which is a member of a different galaxy pair - at a redshift of approximately 0.125.

  13. VizieR Online Data Catalog: Spectral galaxy pairs from SDSS DR9 (Yang+, 2014)

    NASA Astrophysics Data System (ADS)

    Yang, H.; Luo, A.; Chen, X.; Zhang, J.; Hou, W.; Cai, J.; Wei, P.; Ren, J.; Liu, X.; Zhao, Y.

    2015-04-01

    Spectral galaxy pairs (hereafter as SGPs) are composite galaxy spectra that contain two independent redshift systems. These spectra are useful for studying the dust properties of the foreground galaxies. In this article, a total of 165 spectra of SGPs are mined from the Sloan Digital Sky Survey (SDSS) Data Release 9 (DR9) using the concept of 'membership degree' from fuzzy set theory, especially defined to be suitable for fuzzy identification of emission lines. The spectra and images of this sample are classified according to their membership degree and image features, respectively. Many of the second redshift systems are too small or too dim to select from SDSS images alone, making the sample a potentially unique source of information on dust effects in low-luminosity or low surface brightness galaxies, which are underrepresented in morphological pair samples. The dust extinction of those objects with high membership degree is also estimated by Balmer decrement. Additionally, analyses for a series of spectroscopic observations of one SGP from 165 systems indicate that a newly star-forming region of our Milky Way might exist. (1 data file).

  14. A CANDIDATE MASSIVE BLACK HOLE IN THE LOW-METALLICITY DWARF GALAXY PAIR MRK 709

    SciTech Connect

    Reines, Amy E.; Condon, James J.; Plotkin, Richard M.; Russell, Thomas D.; Mezcua, Mar; Sivakoff, Gregory R.; Johnson, Kelsey E.

    2014-06-01

    The incidence and properties of present-day dwarf galaxies hosting massive black holes (BHs) can provide important constraints on the origin of high-redshift BH seeds. Here we present high-resolution X-ray and radio observations of the low-metallicity, star-forming, dwarf-galaxy system Mrk 709 with the Chandra X-ray Observatory and the Karl G. Jansky Very Large Array. These data reveal spatially coincident hard X-ray and radio point sources with luminosities suggesting the presence of an accreting massive BH (M {sub BH} ∼ 10{sup 5-7} M {sub ☉}). Based on imaging from the Sloan Digital Sky Survey (SDSS), we find that Mrk 709 consists of a pair of compact dwarf galaxies that appear to be interacting with one another. The position of the candidate massive BH is consistent with the optical center of the southern galaxy (Mrk 709 S), while no evidence for an active BH is seen in the northern galaxy (Mrk 709 N). We derive stellar masses of M {sub *} ∼ 2.5 × 10{sup 9} M {sub ☉} and M {sub *} ∼ 1.1 × 10{sup 9} M {sub ☉} for Mrk 709 S and Mrk 709 N, respectively, and present an analysis of the SDSS spectrum of the BH host Mrk 709 S. At a metallicity of just ∼10% solar, Mrk 709 is among the most metal-poor galaxies with evidence for an active galactic nucleus. Moreover, this discovery adds to the growing body of evidence that massive BHs can form in dwarf galaxies and that deep, high-resolution X-ray and radio observations are ideally suited to reveal accreting massive BHs hidden at optical wavelengths.

  15. Determining the evolutionary history of galaxies by astrocladistics : some results on close galaxies.

    NASA Astrophysics Data System (ADS)

    Fraix-Burnet, D.

    2006-06-01

    Astrocladistics, a methodology borrowed from biology, is an objective way of understanding galaxy diversity through evolutionary relationships. It is based on the evolution of all the available parameters describing galaxies and thus integrates the complexity of these objects. Through the formalization of the concepts around galaxy formation and evolution, and the identification of the processes of diversification (build up, secular evolution, interaction, merging/accretion, sweeping/ejection), galaxy diversity can be expected to organize itself in a hierarchy. About 500 galaxies described by about 40 observables have now been analysed and several robust trees found. For instance, we show that the Dwarf Galaxies of the Local Group all derive from a common ancestral kind of objects. We identify three evolutionary groups, each one having its own characteristics and own evolution. The Virgo galaxies present a relatively regular diversification, with rather few violent events such as major mergers. Diversification in another sample made of gas-poor galaxies in different environments appears to be slightly more complicated with several diverging evolutionary groups. Work on a large sample of galaxies at non-zero redshifts is in progress and is pioneering a brand new approach to exploit data from the big extragalactic surveys.

  16. A sample of galaxy pairs identified from the LAMOST spectral survey and the Sloan Digital Sky Survey

    NASA Astrophysics Data System (ADS)

    Shen, Shi-Yin; Argudo-Fernández, Maria; Chen, Li; Chen, Xiao-Yan; Feng, Shuai; Hou, Jin-Liang; Hou, Yong-Hui; Jiang, Peng; Jing, Yi-Peng; Kong, Xu; Luo, A.-Li; Luo, Zhi-Jian; Shao, Zheng-Yi; Wang, Ting-Gui; Wang, Wen-Ting; Wang, Yue-Fei; Wu, Hong; Wu, Xue-Bing; Yang, Hai-Feng; Yang, Ming; Yuan, Fang-Ting; Yuan, Hai-Long; Zhang, Hao-Tong; Zhang, Jian-Nan; Zhang, Yong

    2016-03-01

    A small fraction (< 10%) of the SDSS main galaxy (MG) sample has not been targeted with spectroscopy due to the effect of fiber collisions. These galaxies have been compiled into the input catalog of the LAMOST ExtraGAlactic Surveys and named the complementary galaxy sample. In this paper, we introduce this project and status of the spectroscopies associated with the complementary galaxies in the first two years of the LAMOST spectral survey (till Sep. of 2014). Moreover, we present a sample of 1102 galaxy pairs identified from the LAMOST complementary galaxies and SDSS MGs, which are defined as two members that have a projected distance smaller than 100 h-170kpc and a recessional velocity difference smaller than 500 km s-1. Compared with galaxy pairs that are only selected from SDSS, the LAMOST-SDSS pairs have the advantages of not being biased toward large separations and therefore act as a useful supplement in statistical studies of galaxy interaction and galaxy merging.

  17. Statistical analysis of close pairs of QSOs. [in support of noncosmological red shift hypothesis

    NASA Technical Reports Server (NTRS)

    Burbidge, E. M.; Burbidge, G. R.; Odell, S. L.

    1974-01-01

    The observation of close pairs of QSOs with very different redshifts has been suggested by some as evidence in support of the noncosmological redshift hypothesis. A method is described for determining the statistical significance of such pairs. As an example, it is shown that the statistical significance of the pair 1548+115a,b is not well defined and ranges from approximately 99% confidence to about 60%. If statistical methods are to be used in such cases, they must not be argued a posteriori.

  18. Using Close White Dwarf + M Dwarf Stellar Pairs to Constrain the Flare Rates in Close Stellar Binaries

    NASA Astrophysics Data System (ADS)

    Morgan, Dylan P.; West, Andrew A.; Becker, Andrew C.

    2016-05-01

    We present a study of the statistical flare rates of M dwarfs (dMs) with close white dwarf (WD) companions (WD+dM; typical separations <1 au). Our previous analysis demonstrated that dMs with close WD companions are more magnetically active than their field counterparts. One likely implication of having a close binary companion is increased stellar rotation through disk-disruption, tidal effects, and/or angular momentum exchange; increased stellar rotation has long been associated with an increase in stellar activity. Previous studies show a strong correlation between dMs that are magnetically active (showing Hα in emission) and the frequency of stellar flare rates. We examine the difference between the flare rates observed in close WD+dM binary systems and field dMs. Our sample consists of a subset of 181 close WD+dM pairs from Morgan et al. observed in the Sloan Digital Sky Survey Stripe 82, where we obtain multi-epoch observations in the Sloan ugriz-bands. We find an increase in the overall flaring fraction in the close WD+dM pairs (0.09 ± 0.03%) compared to the field dMs (0.0108 ± 0.0007%) and a lower flaring fraction for active WD+dMs (0.05 ± 0.03%) compared to active dMs (0.28 ± 0.05%). We discuss how our results constrain both the single and binary dM flare rates. Our results also constrain dM multiplicity, our knowledge of the Galactic transient background, and may be important for the habitability of attending planets around dMs with close companions.

  19. Time-Dependence of VHE Gamma-Ray induced Pair Cascades in Radio Galaxies

    NASA Astrophysics Data System (ADS)

    Roustazadeh, Parisa; Boettcher, Markus; Thrush, Samantha

    2016-04-01

    Recently, several intermediate frequency peaked BL Lac objects (IBL), low frequency peaked BL Lac objects (LBL) and flat spectrum radio quasars (FSRQ) were detected as very high energy ( VHE, E > 100 ˜ GeV) γ-ray sources. These discoveries suggest that γγ absorption and pair cascades might occur in those objects, leading to excess γ-ray emission which may be observable also in off-axis viewing directions (i.e., like in radio galaxies) when deflected by moderately strong magnetic fields. Here, we investigate the time dependence of the Compton γ-ray emission from such VHE γ-ray induced pair cascades. We show that the cascade emission is variable on time scales much shorter than the light-crossing time across the characteristic extent of the external radiation field, depending on the viewing angle and γ-ray energy. Thus, we find that the cascade Compton interpretation for the Fermi γ-ray emission from radio galaxies is still consistent with the day-scale variability detected in the Fermi γ-ray emission of radio galaxies, such as NGC 1275, which we use as a specific example.

  20. 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.

  1. Changing ionization conditions in SDSS galaxies with active galactic nuclei as a function of environment from pairs to clusters

    SciTech Connect

    Khabiboulline, Emil T.; Steinhardt, Charles L.; Silverman, John D.; Ellison, Sara L.; Mendel, J. Trevor; Patton, David R.

    2014-11-01

    We study how active galactic nucleus (AGN) activity changes across environments from galaxy pairs to clusters using 143,843 galaxies with z < 0.2 from the Sloan Digital Sky Survey. Using a refined technique, we apply a continuous measure of AGN activity, characteristic of the ionization state of the narrow-line emitting gas. Changes in key emission-line ratios ([N II] λ6548/Hα, [O III] λ5007/Hβ) between different samples allow us to disentangle different environmental effects while removing contamination. We confirm that galaxy interactions enhance AGN activity. However, conditions in the central regions of clusters are inhospitable for AGN activity even if galaxies are in pairs. These results can be explained through models of gas dynamics in which pair interactions stimulate the transfer of gas to the nucleus and clusters suppress gas availability for accretion onto the central black hole.

  2. Changing Ionization Conditions in SDSS Galaxies with Active Galactic Nuclei as a Function of Environment from Pairs to Clusters

    NASA Astrophysics Data System (ADS)

    Khabiboulline, Emil T.; Steinhardt, Charles L.; Silverman, John D.; Ellison, Sara L.; Mendel, J. Trevor; Patton, David R.

    2014-11-01

    We study how active galactic nucleus (AGN) activity changes across environments from galaxy pairs to clusters using 143,843 galaxies with z < 0.2 from the Sloan Digital Sky Survey. Using a refined technique, we apply a continuous measure of AGN activity, characteristic of the ionization state of the narrow-line emitting gas. Changes in key emission-line ratios ([N II] λ6548/Hα, [O III] λ5007/Hβ) between different samples allow us to disentangle different environmental effects while removing contamination. We confirm that galaxy interactions enhance AGN activity. However, conditions in the central regions of clusters are inhospitable for AGN activity even if galaxies are in pairs. These results can be explained through models of gas dynamics in which pair interactions stimulate the transfer of gas to the nucleus and clusters suppress gas availability for accretion onto the central black hole.

  3. A Z = 5.34 Galaxy Pair in the Hubble Deep Field

    NASA Astrophysics Data System (ADS)

    Spinrad, Hyron; Stern, Daniel; Bunker, Andrew; Dey, Arjun; Lanzetta, Kenneth; Yahil, Amos; Pascarelle, Sebastian; Fernández-Soto, Alberto

    1998-12-01

    We present spectrograms of the faint V-drop (V_606 = 28.1, I_814 = 25.6) galaxy pair HDF 3-951.1 and HDF 3-951.2 obtained at the Keck II Telescope. In a recent study, Fernández-Soto, Lanzetta, & Yahil derive a photometric redshift of z_ph=5.28^+0.34_-0.41 (2 sigma) for these galaxies; our integrated spectrograms show a large and abrupt discontinuity near 7710 +/- 5 Å. This break is almost certainly due to the Lyalpha forest because its amplitude (1-f^short_nu/f^long_nu>0.87, 95% confidence limit) exceeds any discontinuities observed in stellar or galactic rest-frame optical spectra. The resulting absorption break redshift is z = 5.34 +/- 0.01. Optical/near-IR photometry from the HDF yields an exceptionally red (V_606 - I_814) color, consistent with this large break. A more accurate measure of the continuum depression blueward of Lyalpha utilizing the imaging photometry yields D_A = 0.88. The system as a whole is slightly brighter than L^*_1500 relative to the z ~ 3 Lyman break population, and the total star formation rate inferred from the UV continuum is ~22 h^-2_50 M_⊙ yr^-1 (q_0 = 0.5) assuming the absence of dust extinction. The two individual galaxies are quite small (size scales <~1 h^-1_50 kpc). Thus these galaxies superficially resemble the ``building blocks'' of Pascarelle and coworkers; if they comprise a gravitationally bound system, the pair will likely merge in a timescale ~100 Myr.

  4. Radio line and continuum observations of quasar-galaxy pairs and the origin of low reshift quasar absorption line systems

    NASA Technical Reports Server (NTRS)

    Carilli, C. L.; Vangorkom, J. H.; Hauxthausen, E. M.; Stocke, J. T.; Salzer, J.

    1990-01-01

    There are a number of known quasars for which our line of sight to the high redshift quasar passes within a few Holmberg radii of a low redshift galaxy. In a few of these cases, spectra of the quasar reveal absorption by gas associated with the low redshift galaxy. A number of these pairs imply absorption by gas which lies well outside the optical disk of the associated galaxy, leading to models of galaxies with 'halos' or 'disks' of gas extending to large radii. The authors present observations of 4 such pairs. In three of the four cases, they find that the associated galaxy is highly disturbed, typically due to a gravitational interaction with a companion galaxy, while in the fourth case the absorption can be explained by clouds in the optical disk of the associated galaxy. They are led to an alternative hypothesis concerning the origin of the low redshift absorption line systems: the absorption is by gas clouds which have been gravitationally stripped from the associated galaxy. These galaxies are rapidly evolving, and should not be used as examples of absorption by clouds in halos of field spirals. The authors conclude by considering the role extended gas in interacting systems plays in the origin of higher redshift quasar absorption line systems.

  5. Tunneling spectroscopy of close-spaced dangling-bond pairs in Si(001):H

    PubMed Central

    Engelund, Mads; Zuzak, Rafał; Godlewski, Szymon; Kolmer, Marek; Frederiksen, Thomas; García-Lekue, Aran; Sánchez-Portal, Daniel; Szymonski, Marek

    2015-01-01

    We present a combined experimental and theoretical study of the electronic properties of close-spaced dangling-bond (DB) pairs in a hydrogen-passivated Si(001):H p-doped surface. Two types of DB pairs are considered, called “cross” and “line” structures. Our scanning tunneling spectroscopy (STS) data show that, although the spectra taken over different DBs in each pair exhibit a remarkable resemblance, they appear shifted by a constant energy that depends on the DB-pair type. This spontaneous asymmetry persists after repeated STS measurements. By comparison with density functional theory (DFT) calculations, we demonstrate that the magnitude of this shift and the relative position of the STS peaks can be explained by distinct charge states for each DB in the pair. We also explain how the charge state is modified by the presence of the scanning tunneling microscopy (STM) tip and the applied bias. Our results indicate that, using the STM tip, it is possible to control the charge state of individual DBs in complex structures, even if they are in close proximity. This observation might have important consequences for the design of electronic circuits and logic gates based on DBs in passivated silicon surfaces. PMID:26404520

  6. A Comprehensive X-Ray and Multiwavelength Study of the Colliding Galaxy Pair NGC 2207/IC 2163

    NASA Astrophysics Data System (ADS)

    Mineo, S.; Rappaport, S.; Levine, A.; Pooley, D.; Steinhorn, B.; Homan, J.

    2014-12-01

    We present a comprehensive study of the total X-ray emission from the colliding galaxy pair NGC 2207/IC 2163, based on Chandra, Spitzer, and GALEX data. We detect 28 ultraluminous X-ray sources (ULXs), 7 of which were not detected previously because of X-ray variability. Twelve sources show significant long-term variability, with no correlated spectral changes. Seven sources are transient candidates. One ULX coincides with an extremely blue star cluster (B - V = -0.7). We confirm that the global relation between the number and luminosity of ULXs and the integrated star-formation rate (SFR) of the host galaxy also holds on local scales. We investigate the effects of dust extinction and age on the X-ray binary (XRB) population on subgalactic scales. The distributions of N X and L X are peaked at L IR/L NUV ~ 1, which may be associated with an age of ~10 Myr for the underlying stellar population. We find that approximately one-third of the XRBs are located in close proximity to young star complexes. The luminosity function of the XRBs is consistent with that typical for high-mass XRBs and appears unaffected by variability. We disentangle and compare the X-ray diffuse spectrum with that of the bright XRBs. The hot interstellar medium dominates the diffuse X-ray emission at E <~ 1 keV and has a temperature kT=0.28+0.05-0.04 keV and intrinsic 0.5-2 keV luminosity of 7.9× 1040 {erg} {s}-1, a factor of ~2.3 higher than the average thermal luminosity produced per unit SFR in local star-forming galaxies. The total X-ray output of NGC 2207/IC 2163 is 1.5× 1041 {erg} {s}-1, and the corresponding total integrated SFR is 23.7 M ⊙ yr-1.

  7. 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.

  8. Faint Companions in the Close Environment of Starforming Dwarf Galaxies: possible overlooked starburst triggers? (Oral Contribution)

    NASA Astrophysics Data System (ADS)

    Noeske, K. G.; Iglesias-Páramo, J.; Vílchez, J. M.; Papaderos, P.; Fricke, K. J.

    Using the NASA Extragalactic Database, we have searched the close environment of 98 star-forming dwarf galaxies (SFDGs) from field- and low density environments for companion galaxies. Most of the found companions are dwarf galaxies, previously disregarded in environmental studies of SFDGs. Using a subsample at low redshifts, cz < 2000 km/s, i.e. less biased against dwarf companions, we find that 30% of the SFDGs have close companions within a projected linear separation s_p < 100 kpc and a redshift difference of (Delta cz) < 500 km/s. This fraction must be considered a lower limit, given the incompleteness of the available data sets and the non-negligible frequency of HI clouds in the vicinity of SFDGs, so that the majority of SFDGs should not be considered isolated. The redshift differences between companion candidates and sample SFDGs are typically smaller than ~250 km/s and concentrated towards lower values. This is similarly observed for dwarf satellites of spiral galaxies and suggests a physical association between the companion candidates and the sample SFDGs. SFDGs with a close companion do not show significant differences in their H(beta) equivalent widths and B-V colours as compared to isolated ones. However, the available data do not allow to rule out close dwarf companions as an influencing factor for star formation activity.

  9. An interaction scenario of the galaxy pair NGC 3893/96 (KPG 302): A single passage?

    SciTech Connect

    Gabbasov, R. F.; Rosado, M.; Klapp, J.

    2014-05-20

    Using the data obtained previously from Fabry-Perot interferometry, we study the orbital characteristics of the interacting pair of galaxies KPG 302 with the aim to estimate a possible interaction history, the conditions necessary for the spiral arm formation, and initial satellite mass. We found by performing N-body/smoothed particle hydrodynamics simulations of the interaction that a single passage can produce a grand design spiral pattern in less than 1 Gyr. Although we reproduce most of the features with the single passage, the required satellite to host mass ratio should be ∼1:5, which is not confirmed by the dynamical mass estimate made from the measured rotation curve. We conclude that a more realistic interaction scenario would require several passages in order to explain the mass ratio discrepancy.

  10. An efficient positive potential-density pair expansion for modelling galaxies

    NASA Astrophysics Data System (ADS)

    Rojas-Niño, A.; Read, J. I.; Aguilar, L.; Delorme, M.

    2016-07-01

    We present a novel positive potential-density pair expansion for modelling galaxies, based on the Miyamoto-Nagai disc. By using three sets of such discs, each one of them aligned along each symmetry axis, we are able to reconstruct a broad range of potentials that correspond to density profiles from exponential discs to 3D power-law models with varying triaxiality (henceforth simply `twisted' models). We increase the efficiency of our expansion by allowing the scalelength parameter of each disc to be negative. We show that, for suitable priors on the scalelength and scaleheight parameters, these `MNn discs' (Miyamoto-Nagai negative) have just one negative density minimum. This allows us to ensure global positivity by demanding that the total density at the global minimum is positive. We find that at better than 10 per cent accuracy in our density reconstruction, we can represent a radial and vertical exponential disc over 0.1-10 scalelengths/scaleheights with four MNn discs; a Navarro, Frenk and White (NFW) profile over 0.1-10 scalelengths with four MNn discs; and a twisted triaxial NFW profile with three MNn discs per symmetry axis. Our expansion is efficient, fully analytic, and well suited to reproducing the density distribution and gravitational potential of galaxies from discs to ellipsoids.

  11. Submilliarcsecond VLBI Using Compact Close Pairs of Radio Sources: Error Analysis

    NASA Technical Reports Server (NTRS)

    Morabito, D. D.

    1984-01-01

    The potential accuracy attainable for (delta) VLBI positional measurements (submilliarc second level) is reached by simultaneously observing pairs of compact radio sources whose angular separation are smaller than the beamwidth of each antenna. Simultaneous (delta) VLBI (SVLBI) enables significant cancellation of measurement errors. Solar plasma is the dominant fluctuating error source in SVLBI positional measurements since there is enhanced cancellation of the troposphere and ionosphere, and complete cancellation of oscillator instabilities. Of the nonfluctuating error sources, errors due to universal time predominate. By performing SVLBI experiments over several years with many different close pairs of radio sources, limits can be placed on reference frame stability. Intrinsic properties of the sources, such as source structure and proper motion, will limit measurements. The SVLBI differential phase and corruptive noise sources will be discussed here along with estimated results.

  12. Kinematic Modeling of Separation Compression for Paired Approaches to Closely-Spaced Parallel Runways

    NASA Technical Reports Server (NTRS)

    Madden, Michael M.

    2014-01-01

    In a simultaneous paired approach to closely-spaced parallel runways, a pair of aircraft flies in close proximity on parallel approach paths. The longitudinal separation between the aircraft must be maintained within a range that avoids wake encounters and, if one of the aircraft blunders, avoids collision. To increase operational availability, the approach procedure must accommodate a mixture of aircraft sizes and, consequently, approach speeds. In these procedures, the slower aircraft is placed in the lead position. The faster aircraft maintains separation from the slow aircraft in a dependent operation until final approach and flies independently afterward. Due to the higher approach speed of the fast aircraft, longitudinal separation will decrease during final approach. Therefore, the fast aircraft must position itself before the final approach so that it will remain within the safe range of separation as separation decreases. Given the approach geometry and speed schedule for each aircraft, one can use kinematics to estimate the separation loss between a pair of aircraft. A kinematic model can complement fast-time Monte-Carlo simulations of the approach by enabling a tailored reduction in the variation of starting position for the fast aircraft. One could also implement the kinematic model in ground-based or on-board decision support tools to compute the optimal initial separation for a given pair of aircraft. To better match the auto-coupled flight of real aircraft, the paper derives a kinematic model where the speed schedule is flown using equivalent airspeed. The predicted time of flight using the equivalent airspeed kinematic model compares well against a high-fidelity aircraft simulation performing the same approach. This model also demonstrates a modest increase in the predicted loss of separation when contrasted against a kinematic model that assumes the scheduled speed is true airspeed.

  13. The occulting galaxy pair UGC 3995. Dust properties from HST and CALIFA data

    NASA Astrophysics Data System (ADS)

    Holwerda, B. W.; Keel, W. C.

    2013-08-01

    UGC 3995 is an interacting and occulting galaxy pair. UGC 3995B is a foreground face-on spiral and UGC 3995A a bright background spiral with an AGN. We present analysis of the dust in the disc of UGC 3995B based on archival Hubble Space Telescope (HST) WFPC2 and PPAK IFU data from the CALIFA survey's first data release. From the HST F606W image, we construct an extinction map by modeling the isophotes of the background galaxy UGC 3995A and the resulting transmission through UGC 3995B. This extinction map of UGC 3995B shows several distinct spiral extinction features. The radial distribution of AV values declines slowly with peaks corresponding to the spiral structures. The distribution of AV values in the HST extinction map peaks near AV = 0.3-0.4. Beyond this point, the distribution of AV values drops like an exponential: N(AV) = N0 × e(-AV/0.5). The 0.5 value is higher than typical for a spiral galaxy. The outer arms may be tidally distended; the extinction in the corresponding interarm regions is small to an unusually small radius. To analyze the PPAK IFU data, we take the ratio of a fibre spectrum in the overlap region and the corresponding background fiber spectrum to construct an extinction curve. We fit the Cardelli, Clayton and Mathis (CCM) curve to the extinction curve of each fiber element in the overlap region. A map of the extinction constructed from PPEX IFU data-cubes shows the same spiral structure of the HST extinction map but the some differences in the distribution of the normalization of the CCM fits (AV). The inferred extinction slopes (RV) maps do not display any structure and a range of values partly due to the sampling effects of the disc by fibers, sometimes due to bad fits, and possibly partly due to some reprocessing of dust grains in the interacting disc. We compare these findings to our other analysis of an occulting pair with HST and IFU data. In both cases the canonical RV = 3.1 is not recovered even though there is enough signal in

  14. Brain State-Dependent Closed-Loop Modulation of Paired Associative Stimulation Controlled by Sensorimotor Desynchronization

    PubMed Central

    Royter, Vladislav; Gharabaghi, Alireza

    2016-01-01

    Background: Pairing peripheral electrical stimulation (ES) and transcranial magnetic stimulation (TMS) increases corticospinal excitability when applied with a specific temporal pattern. When the two stimulation techniques are applied separately, motor imagery (MI)-related oscillatory modulation amplifies both ES-related cortical effects—sensorimotor event-related desynchronization (ERD), and TMS-induced peripheral responses—motor-evoked potentials (MEP). However, the influence of brain self-regulation on the associative pairing of these stimulation techniques is still unclear. Objective: The aim of this pilot study was to investigate the effects of MI-related ERD during associative ES and TMS on subsequent corticospinal excitability. Method: The paired application of functional electrical stimulation (FES) of the extensor digitorum communis (EDC) muscle and subsequent single-pulse TMS (110% resting motor threshold (RMT)) of the contralateral primary motor cortex (M1) was controlled by beta-band (16–22 Hz) ERD during MI of finger extension and applied within a brain-machine interface environment in six healthy subjects. Neural correlates were probed by acquiring the stimulus-response curve (SRC) of both MEP peak-to-peak amplitude and area under the curve (AUC) before and after the intervention. Result: The application of approximately 150 pairs of associative FES and TMS resulted in a significant increase of MEP amplitudes and AUC, indicating that the induced increase of corticospinal excitability was mediated by the recruitment of additional neuronal pools. MEP increases were brain state-dependent and correlated with beta-band ERD, but not with the background EDC muscle activity; this finding was independent of the FES intensity applied. Conclusion: These results could be relevant for developing closed-loop therapeutic approaches such as the application of brain state-dependent, paired associative stimulation (PAS) in the context of neurorehabilitation. PMID

  15. Pac-Man in Space? ASAS-SN Discovery of A Probable Supernova in Galaxy Pair CGCG 314-006

    NASA Astrophysics Data System (ADS)

    Guo, Zhen; Holoien, T. W.-S.; Dong, Subo; Stanek, K. Z.; Kochanek, C. S.; Brown, J. S.; Godoy-Rivera, D.; Basu, U.; Shappee, B. J.; Prieto, J. L.; Bersier, D.; Chen, Ping; Brimacombe, J.

    2015-12-01

    During the ongoing All Sky Automated Survey for SuperNovae (ASAS-SN or "Assassin"), using data from the quadruple 14-cm "Brutus" telescope in Haleakala, Hawaii, we discovered a new transient source, most likely a supernova, in the middle of the Pac-Man-shaped galaxy pair CGCG 314-006.

  16. 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.

  17. Wake Encounter Analysis for a Closely Spaced Parallel Runway Paired Approach Simulation

    NASA Technical Reports Server (NTRS)

    Mckissick,Burnell T.; Rico-Cusi, Fernando J.; Murdoch, Jennifer; Oseguera-Lohr, Rosa M.; Stough, Harry P, III; O'Connor, Cornelius J.; Syed, Hazari I.

    2009-01-01

    A Monte Carlo simulation of simultaneous approaches performed by two transport category aircraft from the final approach fix to a pair of closely spaced parallel runways was conducted to explore the aft boundary of the safe zone in which separation assurance and wake avoidance are provided. The simulation included variations in runway centerline separation, initial longitudinal spacing of the aircraft, crosswind speed, and aircraft speed during the approach. The data from the simulation showed that the majority of the wake encounters occurred near or over the runway and the aft boundaries of the safe zones were identified for all simulation conditions.

  18. A NEW METHOD TO DIRECTLY MEASURE THE JEANS SCALE OF THE INTERGALACTIC MEDIUM USING CLOSE QUASAR PAIRS

    SciTech Connect

    Rorai, Alberto; Hennawi, Joseph F.; White, Martin

    2013-10-01

    Although the baryons in the intergalactic medium (IGM) trace dark matter fluctuations on megaparsec scales, on smaller scales ∼100 kpc, fluctuations are suppressed because the finite temperature gas is pressure supported against gravity, analogous to the classical Jeans argument. This Jeans filtering scale, which quantifies the small-scale structure of the IGM, has fundamental cosmological implications. First, it provides a thermal record of heat injected by ultraviolet photons during cosmic reionization events, and thus constrains the thermal and reionization history of the universe. Second, the Jeans scale determines the clumpiness of the IGM, a critical ingredient in models of cosmic reionization. Third, it sets the minimum mass scale for gravitational collapse from the IGM, and hence plays a pivotal role in galaxy formation. Unfortunately, it is extremely challenging to measure the Jeans scale via the standard technique of analyzing purely longitudinal Lyα forest spectra, because the thermal Doppler broadening of absorption lines along the line-of-sight, is highly degenerate with Jeans smoothing. In this work, we show that the Jeans filtering scale can be directly measured by characterizing the coherence of correlated Lyα forest absorption in close quasar pairs, with separations small enough ∼100 kpc to resolve it. We present a novel technique for this purpose, based on the probability density function (PDF) of phase angle differences of homologous longitudinal Fourier modes in close quasar pair spectra. A Bayesian formalism is introduced based on the phase angle PDF, and Markov Chain Monte Carlo techniques are used to characterize the precision of a hypothetical Jeans scale measurement, and explore degeneracies with other thermal parameters governing the IGM. A semi-analytical model of the Lyα forest is used to generate a large grid (500) of thermal models from a dark matter only simulation. Our full parameter study indicates that a realistic sample of

  19. VizieR Online Data Catalog: Dynamics in E+E pairs of galaxies (Bonfanti+, 1995)

    NASA Astrophysics Data System (ADS)

    Bonfanti, P.; Rampazzo, R.; Combes, F.; Prugniel, P.; Sulentic, J. W.

    1994-10-01

    NGC 741/742, 1587/1588 (CPG 99) and 2672/2673 (CPG 175). All three pairs show a similar morphological distortion (i.e. the off-centering of inner versus outer isophotes; Davoust & Prugniel 1988) which is ascribed to the ongoing interaction. The data was obtained at the CFHT equipped with the Herzberg Spectrograph at a resolution of 0.88 Apx-1. NGC 741 and 2673 show significant rotation along the apparent minor axis. Both components of CPG 99 rotate very fast (with no evidence for rotation along the minor axis of either component). None of the galaxies show abnormally high central velocity dispersion. We report some of the first clear detections of well defined velocity dispersion curves for interacting pairs. They show a systematic decrease with distance from the center, as expected for normal ellipticals. They do not show obvious heating in the outer parts as was previously reported. NGC 741 and 2672 show, respectively, possible U and inverse U-shaped structure in their velocity profiles. (1 data file).

  20. A COMPREHENSIVE X-RAY AND MULTIWAVELENGTH STUDY OF THE COLLIDING GALAXY PAIR NGC 2207/IC 2163

    SciTech Connect

    Mineo, S.; Rappaport, S.; Levine, A.; Homan, J.; Pooley, D.; Steinhorn, B. E-mail: sar@mit.edu E-mail: jeroen@space.mit.edu E-mail: bsteinho@mit.edu

    2014-12-20

    We present a comprehensive study of the total X-ray emission from the colliding galaxy pair NGC 2207/IC 2163, based on Chandra, Spitzer, and GALEX data. We detect 28 ultraluminous X-ray sources (ULXs), 7 of which were not detected previously because of X-ray variability. Twelve sources show significant long-term variability, with no correlated spectral changes. Seven sources are transient candidates. One ULX coincides with an extremely blue star cluster (B – V = –0.7). We confirm that the global relation between the number and luminosity of ULXs and the integrated star-formation rate (SFR) of the host galaxy also holds on local scales. We investigate the effects of dust extinction and age on the X-ray binary (XRB) population on subgalactic scales. The distributions of N {sub X} and L {sub X} are peaked at L {sub IR}/L {sub NUV} ∼ 1, which may be associated with an age of ∼10 Myr for the underlying stellar population. We find that approximately one-third of the XRBs are located in close proximity to young star complexes. The luminosity function of the XRBs is consistent with that typical for high-mass XRBs and appears unaffected by variability. We disentangle and compare the X-ray diffuse spectrum with that of the bright XRBs. The hot interstellar medium dominates the diffuse X-ray emission at E ≲ 1 keV and has a temperature kT=0.28{sub −0.04}{sup +0.05} keV and intrinsic 0.5-2 keV luminosity of 7.9×10{sup 40} erg s{sup −1}, a factor of ∼2.3 higher than the average thermal luminosity produced per unit SFR in local star-forming galaxies. The total X-ray output of NGC 2207/IC 2163 is 1.5×10{sup 41} erg s{sup −1}, and the corresponding total integrated SFR is 23.7 M {sub ☉} yr{sup –1}.

  1. Role of the Closing Base Pair for d(GCA) Hairpin Stability: Free Energy Analysis and Folding Simulations

    SciTech Connect

    Kannan, Srinivasaraghavan; Zacharias, Martin W.

    2011-06-30

    Hairpin loops belong to the most important structural motifs in folded nucleic acids. The d(GNA) sequence in DNA can form very stable trinucleotide hairpin loops depending, however, strongly on the closing base pair. Replica-exchange molecular dynamics (REMD) were employed to study hairpin folding of two DNA sequences, d(gcGCAgc) and d(cgGCAcg), with the same central loop motif but different closing base pairs starting from singlestranded structures. In both cases, conformations of the most populated conformational cluster at the lowest temperature showed close agreement with available experimental structures. For the loop sequence with the less stable G:C closing base pair, an alternative loop topology accumulated as second most populated conformational state indicating a possible loop structural heterogeneity. Comparative-free energy simulations on induced loop unfolding indicated higher stability of the loop with a C:G closing base pair by 3 kcal mol1 (compared to a G:C closing base pair) in very good agreement with experiment. The comparative energetic analysis of sampled unfolded, intermediate and folded conformational states identified electrostatic and packing interactions as the main contributions to the closing base pair dependence of the d(GCA) loop stability.

  2. Open-Closed Homotopy Algebras and Strong Homotopy Leibniz Pairs Through Koszul Operad Theory

    NASA Astrophysics Data System (ADS)

    Hoefel, Eduardo; Livernet, Muriel

    2012-08-01

    Open-closed homotopy algebras (OCHA) and strong homotopy Leibniz pairs (SHLP) were introduced by Kajiura and Stasheff in 2004. In an appendix to their paper, Markl observed that an SHLP is equivalent to an algebra over the minimal model of a certain operad, without showing that the operad is Koszul. In the present paper, we show that both OCHA and SHLP are algebras over the minimal model of the zeroth homology of two versions of the Swiss-cheese operad and prove that these two operads are Koszul. As an application, we show that the OCHA operad is non-formal as a 2-colored operad but is formal as an algebra in the category of 2-collections.

  3. Rotation of halos in open and closed universes - differentiated merging and natural selection of galaxy types

    SciTech Connect

    Zurek, W.H.; Quinn, P.J.; Salmon, J.K.

    1988-07-01

    Computer simulations are used here to study the properties of galactic halos formed from Gaussian initial density perturbations in both open and closed dark matter universes. It is shown that if galaxies form through gravitational collapse from initial, Gaussian density perturbations, then their luminous parts do not have the original values of either specific angular momentum (ellipticals) or spin parameter lambda (spirals). The rotational properties of a halo depend only weakly on either the halo density or the density of its environment. Variations of the large-scale density of the environment have an expected, dramatic effect on the density of individual halos. Dissipationless merging forces the cores of the merging objects into the core of the merger product. In the process, cores become more bound and lose angular momentum. These findings are extrapolated to propose a model for galaxy formation in which both ellipticals and spirals come into being through mergers. 59 references.

  4. The incidence of nuclear activity in galaxy pairs with different morphologies (E+E), (E+S) and (S+S)

    NASA Astrophysics Data System (ADS)

    Hernández-Ibarra, Francisco J.; Krongold, Yair; Dultzin, Deborah; del Olmo, Ascensión; Perea, Jaime; González, Jesús; Mendoza-Castrejón, Sandro; Bitsakis, Theodoros

    2016-06-01

    We analysed 385 Sloan Digital Sky Survey Data Release 7 (SDSS-DR7) galactic spectra that belong to the catalogue of isolated pairs of galaxies by Karachentsev. The spectra correspond to physical pairs of galaxies defined by a difference in velocity ≤1200 km s-1 and a pair separation ≤100 kpc. We study the incidence of nuclear activity, both star formation and non-thermal - active galactic nuclei (AGNs). After a careful extraction of the nuclear spectra, we use diagnostic diagrams and find that the incidence of AGNs is 48 per cent in emission line paired galaxies and 40 per cent for the total sample (as compared to ˜43 per cent and 41 per cent, respectively, in a sample of isolated galaxies). These results remain after dissecting the effects of morphological type and galactic stellar mass (with only a small, non significant, enhancement of the AGN fraction in galaxy pairs). These results suggest that weak interactions are not necessary and/or sufficient to trigger low-luminosity AGN. Since the fraction of AGN is predominant in early-type spiral galaxies, we conclude that the role of a bulge, and a large gas reservoir are both essential for the triggering of nuclear activity. The most striking result is that Type 1 nuclei are absent from the AGN sample. This result is in conflict with the Unified Model, and suggests that high accretion rates are essential to form the broad line region in active galaxies.

  5. Galaxy And Mass Assembly (GAMA): the life and times of L★ galaxies

    NASA Astrophysics Data System (ADS)

    Robotham, A. S. G.; Liske, J.; Driver, S. P.; Sansom, A. E.; Baldry, I. K.; Bauer, A. E.; Bland-Hawthorn, J.; Brough, S.; Brown, M. J. I.; Colless, M.; Christodoulou, L.; Drinkwater, M. J.; Grootes, M. W.; Hopkins, A. M.; Kelvin, L. S.; Norberg, P.; Loveday, J.; Phillipps, S.; Sharp, R.; Taylor, E. N.; Tuffs, R. J.

    2013-05-01

    In this work, we investigate in detail the effects the local environment (groups and pairs) has on galaxies with stellar mass similar to the Milky Way (L* galaxies). A volume limited sample of 6150 galaxies are visually classified to determine the emission features, morphological type and presence of a disc. This large sample allows for the significant characteristics of galaxies to be isolated (e.g. stellar mass and group halo mass), and their codependencies determined. We observe that galaxy-galaxy interactions play the most important role in shaping the evolution within a group halo; the main role of halo mass is in gathering the galaxies together to encourage such interactions. Dominant pair galaxies find their overall star formation enhanced when the pair's mass ratio is close to 1; otherwise, we observe the same galaxies as we would in an unpaired system. The minor galaxy in a pair is greatly affected by its companion galaxy, and while the star-forming fraction is always suppressed relative to equivalent stellar mass unpaired galaxies, it becomes lower still when the mass ratio of a pair system increases. We find that, in general, the close galaxy-galaxy interaction rate drops as a function of halo mass for a given amount of stellar mass. We find evidence of a local peak of interactions for Milky Way stellar mass galaxies in Milky Way halo mass groups. Low-mass haloes, and in particular Local Group mass haloes, are an important environment for understanding the typical evolutionary path of a unit of stellar mass. We find compelling evidence for galaxy conformity in both groups and pairs, where morphological type conformity is dominant in groups, and emission class conformity is dominant in pairs. This suggests that group scale conformity is the result of many galaxy encounters over an extended period of time, while pair conformity is a fairly instantaneous response to a transitory interaction.

  6. Properties of low-redshift QSO absorption systems - QSO-galaxy pairs

    NASA Technical Reports Server (NTRS)

    Womble, Donna S.

    1993-01-01

    The chance proximity of QSOs and galaxies provides unique opportunities to probe the extent and content of gas in the foreground galaxies through evaluation of the incidence and strength of absorption lines in the spectra of the background QSOs. Recent results on the observed properties of these low-redshift, heavy-element absorption systems are summarized. These results are discussed in the context of the galaxy morphologies and environments and are briefly compared with Galactic absorption and with the inferred properties of higher-redshift QSO absorption systems.

  7. The spiral-compact galaxy pair AM 2208-251: Computer simulations versus observations

    NASA Technical Reports Server (NTRS)

    Klaric, Mario; Byrd, Gene G.

    1990-01-01

    The system AM2208-251 is a roughly edge-on spiral extending east-west with a smaller round compact E system about 60 arcsec east of the spiral nucleus along the major axis of the spiral. Bertola, Huchtmeier, and Zeilinger (1990) have presented optical spectroscopic as well as single dish 21 cm observations of this system. Their spectroscopic data show, via emission lines lambda lambda 3727-29A, a rising rotation curve near the nucleus. These spectroscopic observations may indicate a tidal interaction in the system. In order to learn more about such pairs, the authors simulated the interaction using the computer model developed by Miller (1976 a,b, 1978) and modified by the authors (Byrd 1986, 1987, 1988). To do the simulation they need an idea of the mutual orbits of the two galaxies. Their computer model is a two-dimensional polar N-body program. It consists of a self-gravitating disk of particles, within an inert axially symmetric stabilizing halo potential. The particles are distributed in a 24(radial) by 36(azimuthal) polar grid. Self consistent calculations can be done only within the grid area. The disk is modeled with a finite Mestel disk, where all the particles initially move in circular orbits with constant tangential velocities (Mestel 1963), resulting in a flat rotation curve. The gas particles in the spiral's disk, which make up 30 percent of its mass, collide in the following manner. The number of particles in each bin of the polar grid is counted every time step. If it is greater than a given critical density, all the particles in the bin collide, obtaining in the result the same velocities, equal to the average for the bin. This process produces clumps of gas particles-the star formation sites. The authors suppress the collision in the inner part of the disk (within the circle r = 6) to represent the hole seen in the gas in the nuclear bulge of spirals. They thus avoid spurious effects due to collisions in that region. They also varied the size of

  8. The spiral-compact galaxy pair AM 2208-251: Computer simulations versus observations

    NASA Astrophysics Data System (ADS)

    Klaric, Mario; Byrd, Gene G.

    1990-11-01

    The system AM2208-251 is a roughly edge-on spiral extending east-west with a smaller round compact E system about 60 arcsec east of the spiral nucleus along the major axis of the spiral. Bertola, Huchtmeier, and Zeilinger (1990) have presented optical spectroscopic as well as single dish 21 cm observations of this system. Their spectroscopic data show, via emission lines lambda lambda 3727-29A, a rising rotation curve near the nucleus. These spectroscopic observations may indicate a tidal interaction in the system. In order to learn more about such pairs, the authors simulated the interaction using the computer model developed by Miller (1976 a,b, 1978) and modified by the authors (Byrd 1986, 1987, 1988). To do the simulation they need an idea of the mutual orbits of the two galaxies. Their computer model is a two-dimensional polar N-body program. It consists of a self-gravitating disk of particles, within an inert axially symmetric stabilizing halo potential. The particles are distributed in a 24(radial) by 36(azimuthal) polar grid. Self consistent calculations can be done only within the grid area. The disk is modeled with a finite Mestel disk, where all the particles initially move in circular orbits with constant tangential velocities (Mestel 1963), resulting in a flat rotation curve. The gas particles in the spiral's disk, which make up 30 percent of its mass, collide in the following manner. The number of particles in each bin of the polar grid is counted every time step. If it is greater than a given critical density, all the particles in the bin collide, obtaining in the result the same velocities, equal to the average for the bin. This process produces clumps of gas particles-the star formation sites. The authors suppress the collision in the inner part of the disk (within the circle r = 6) to represent the hole seen in the gas in the nuclear bulge of spirals. They thus avoid spurious effects due to collisions in that region. They also varied the size of

  9. 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.

  10. Phase space matching and finite lifetime effects for top-pair production close to threshold

    SciTech Connect

    Hoang, Andre H.; Reisser, Christoph J.; Ruiz-Femenia, Pedro

    2010-07-01

    The top-pair tt production cross section close to threshold in e{sup +}e{sup -} collisions is strongly affected by the small lifetime of the top quark. Since the cross section is defined through final states containing the top decay products, a consistent definition of the cross section depends on prescriptions of how these final states are accounted for the cross section. Experimentally, these prescriptions are implemented, for example, through cuts on kinematic quantities such as the reconstructed top quark invariant masses. As long as these cuts do not reject final states that can arise from the decay of a top and an antitop quark with a small off-shellness compatible with the nonrelativistic power counting, they can be implemented through imaginary phase space matching conditions in nonrelativistic QCD. The prescription-dependent cross section can then be determined from the optical theorem using the e{sup +}e{sup -} forward scattering amplitude. We compute the phase space matching conditions associated to cuts on the top and antitop invariant masses at next-to-next-to-leading logarithmic order and partially at next-to-next-to-next-to-leading logarithmic order in the nonrelativistic expansion accounting also for higher order QCD effects. Together with finite lifetime and electroweak effects known from previous work, we analyze their numerical impact on the tt cross section. We show that the phase space matching contributions are essential to make reliable nonrelativistic QCD predictions, particularly for energies below the peak region, where the cross section is small. We find that irreducible background contributions associated to final states that do not come from top decays are strongly suppressed and can be neglected for the theoretical predictions.

  11. Formation of Small-Scale Vortex Rings from Vortex Pairs Close to the Ground

    NASA Astrophysics Data System (ADS)

    Asselin, Daniel; Williamson, Charles

    2013-11-01

    In this research, we examine the effect of a solid boundary on the dynamics and instabilities of a pair of counter-rotating vortices. An isolated vortex pair is subject to a short-wave elliptic instability and a long-wave Crow (1970) instability. Near a wall, the boundary layer between the primary vortices and the wall can separate, leading to the generation of secondary vorticity. These secondary vortices can be subject to small-scale instabilities (Harris & Williamson, 2012) as they come under the influence of the primary vortices. In contrast, in the present study we are interested in the long-wave Crow instability interrupted by interaction with a wall. This can cause significant axial flow, resulting in a periodic concentration of fluid containing vorticity at the peaks of each wavy vortex tube and a corresponding evacuation of fluid containing vorticity from the troughs. It appears that this axial flow is driven at least in part by the formation of vortex ring-like structures in the secondary vortex as it is deformed by the primary vortex. Furthermore, additional small scale-vortex rings evolve from the secondary vorticity and from the concentrated vortical regions in the primary vorticity. In both cases, these rings cause vorticity to rebound away from the ground.

  12. 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.

  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. Closed timelike curves produced by pairs of moving cosmic strings - Exact solutions

    NASA Technical Reports Server (NTRS)

    Gott, J. Richard, III

    1991-01-01

    Exact solutions of Einstein's field equations are presented for the general case of two moving straight cosmic strings that do not intersect. The solutions for parallel cosmic strings moving in opposite directions show closed timelike curves (CTCs) that circle the two strings as they pass, allowing observers to visit their own past. Similar results occur for nonparallel strings, and for masses in (2+1)-dimensional spacetime. For finite string loops the possibility that black-hole formation may prevent the formation of CTCs is discussed.

  15. Frequency Shift and Sub-band Effect in Pair-Production Process Under Adiabatic Closing the External Field

    NASA Astrophysics Data System (ADS)

    Song, Xinfang; Wang, Wenyuan; Fu, Libin

    2016-04-01

    Oscillating electric field is chosen to investigate the electron-positron pair production process by using a quantum kinetic theory and the effective mass model [Phys. Rev. Lett. 112, 050402 (2014)]. The particle yield exhibits a characteristic oscillatory structure which is related to the multi-photon thresholds. The true peak positions are typically slightly above the naive threshold estimate, which is defined as frequency shift. During the numerical calculations, we find the frequency shift can be affected by the system parameters under adiabatic closing the external field, it is worthwhile to study in detail. In this paper, we investigate the frequency shift and the sub-band effect in electron-positron pair production with oscillating electric field. First, a quantum kinetic theory and the effective mass are presented to obtain the frequency shift, the results are fitted very well. And we find the frequency shift and the sub-band effect can be influenced by pulse duration, photon number, and strength of the external field. The frequency shift becomes evident as increases of photon number and the external field strength. The sub-band width is relatively lower at longer pulse duration, higher photon number region, and weaker external field. The results shown in the paper are helpful for understanding multi-photon pair production process in the strong field.

  16. Frequency Shift and Sub-band Effect in Pair-Production Process Under Adiabatic Closing the External Field

    NASA Astrophysics Data System (ADS)

    Song, Xinfang; Wang, Wenyuan; Fu, Libin

    2016-09-01

    Oscillating electric field is chosen to investigate the electron-positron pair production process by using a quantum kinetic theory and the effective mass model [Phys. Rev. Lett. 112, 050402 (2014)]. The particle yield exhibits a characteristic oscillatory structure which is related to the multi-photon thresholds. The true peak positions are typically slightly above the naive threshold estimate, which is defined as frequency shift. During the numerical calculations, we find the frequency shift can be affected by the system parameters under adiabatic closing the external field, it is worthwhile to study in detail. In this paper, we investigate the frequency shift and the sub-band effect in electron-positron pair production with oscillating electric field. First, a quantum kinetic theory and the effective mass are presented to obtain the frequency shift, the results are fitted very well. And we find the frequency shift and the sub-band effect can be influenced by pulse duration, photon number, and strength of the external field. The frequency shift becomes evident as increases of photon number and the external field strength. The sub-band width is relatively lower at longer pulse duration, higher photon number region, and weaker external field. The results shown in the paper are helpful for understanding multi-photon pair production process in the strong field.

  17. 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.

  18. A Tale of Two Narrow-line Regions: Ionization, Kinematics, and Spectral Energy Distributions for a Local Pair of Merging Obscured Active Galaxies

    NASA Astrophysics Data System (ADS)

    Hainline, Kevin N.; Hickox, Ryan C.; Chen, Chien-Ting; Carroll, Christopher M.; Jones, Mackenzie L.; Zervos, Alexandros S.; Goulding, Andrew D.

    2016-05-01

    We explore the gas ionization and kinematics, as well as the optical-IR spectral energy distributions for UGC 11185, a nearby pair of merging galaxies hosting obscured active galactic nuclei (AGNs), also known as SDSS J181611.72+423941.6 and J181609.37+423923.0 (J1816NE and J1816SW, z ≈ 0.04). Due to the wide separation between these interacting galaxies (∼23 kpc), observations of these objects provide a rare glimpse of the concurrent growth of supermassive black holes at an early merger stage. We use BPT line diagnostics to show that the full extent of the narrow-line emission in both galaxies is photoionized by an AGN, and confirm the existence of a 10 kpc-scale ionization cone in J1816NE, while in J1816SW the AGN narrow-line region is much more compact (1–2 kpc) and relatively undisturbed. Our observations also reveal the presence of ionized gas that nearly spans the entire distance between the galaxies, which is likely in a merger-induced tidal stream. In addition, we carry out a spectral analysis of the X-ray emission using data from XMM-Newton. These galaxies represent a useful pair to explore how the [O iii] luminosity of an AGN is dependent on the size of the region used to explore the extended emission. Given the growing evidence for AGN “flickering” over short timescales, we speculate that the appearances and impacts of these AGNs may change multiple times over the course of the galaxy merger, which is especially important given that these objects are likely the progenitors of the types of systems commonly classified as “dual AGNs.”

  19. Close, stable homolog juxtaposition during meiosis in budding yeast is dependent on meiotic recombination, occurs independently of synapsis, and is distinct from DSB-independent pairing contacts

    PubMed Central

    Peoples, Tamara L.; Dean, Eric; Gonzalez, Oscar; Lambourne, Lindsey; Burgess, Sean M.

    2002-01-01

    A site-specific recombination system that probes the relative probabilities that pairs of chromosomal loci collide with one another in living cells of budding yeast was used to explore the relative contributions of pairing, recombination, synaptonemal complex formation, and telomere clustering to the close juxtaposition of homologous chromosome pairs during meiosis. The level of Cre-mediated recombination between a pair of loxP sites located at an allelic position on homologous chromosomes was 13-fold greater than that between a pair of loxP sites located at ectopic positions on nonhomologous chromosomes. Mutations affecting meiotic recombination initiation and the processing of DNA double-strand breaks (DSBs) into single-end invasions (SEIs) reduced the levels of allelic Cre-mediated recombination levels by three- to sixfold. The severity of Cre/loxP phenotypes is presented in contrast to relatively weak DSB-independent pairing defects as assayed using fluorescence in situ hybridization for these mutants. Mutations affecting synaptonemal complex (SC) formation or crossover control gave wild-type levels of allelic Cre-mediated recombination. A delay in attaining maximum levels of allelic Cre-mediated recombination was observed for a mutant defective in telomere clustering. None of the mutants affected ectopic levels of recombination. These data suggest that stable, close homolog juxtaposition in yeast is distinct from pre-DSB pairing interactions, requires both DSB and SEI formation, but does not depend on crossovers or SC. PMID:12101126

  20. Stellar dynamics in E+E pairs of galaxies. 1: NGC 741/742, 1587/88 and 2672/73. The data

    NASA Astrophysics Data System (ADS)

    Bonfanti, P.; Rampazzo, R.; Combes, F.; Prugniel, P.; Sulentic, J. W.

    1995-05-01

    We present a kinematic study ofthree E+E galaxy pairs, NGC, 741/642, 1587/1588 (CPG 99) and 2672/2673 (CPG 175) All three pairs show a similar morpological distortion (i.e. the off-centering of inner versus outer isphototes; Davoust & Prungniel 1988) which is ascribed to the ongoing interaction. The data was obtained at the CFHT equipped with the Herzberg Spectrograph at a resolution of 0.88 A px-1 NGC741 and 2673 show significant rotation along the apparent minor axis. Both components of CPG 99 rotate very fast (with no evidence for rotation along the mirror axis of either component). None of the galaxies show abnormally high central velocity dispersion. We report some of the first clear detections of well defined velocity dispersions curves for interacting pairs. They show a systematic decrease with distance from the center, as expected for normal ellipticals. They do not show obvious heating in the outer parts as was previously reported. NGC 741 and 2672 show, respectively, possible U and inverse U-shaped structure in their velocity profiles.

  1. First Connection between Cold Gas in Emission and Absorption: CO Emission from a Galaxy-Quasar Pair

    NASA Astrophysics Data System (ADS)

    Neeleman, Marcel; Prochaska, J. Xavier; Zwaan, Martin A.; Kanekar, Nissim; Christensen, Lise; Dessauges-Zavadsky, Miroslava; Fynbo, Johan P. U.; van Kampen, Eelco; Møller, Palle; Zafar, Tayyaba

    2016-04-01

    We present the first detection of molecular emission from a galaxy selected to be near a projected background quasar using the Atacama Large Millimeter/submillimeter Array (ALMA). The ALMA detection of CO(1-0) emission from the z = 0.101 galaxy toward quasar PKS 0439-433 is coincident with its stellar disk and yields a molecular gas mass of Mmol ≈ 4.2 × 109 M⊙ (for a Galactic CO-to-H2 conversion factor), larger than the upper limit on its atomic gas mass. We resolve the CO velocity field, obtaining a rotational velocity of 134 ± 11 km s-1 and a resultant dynamical mass of ≥4 × 1010 M⊙. Despite its high metallicity and large molecular mass, the z = 0.101 galaxy has a low star formation rate, implying a large gas consumption timescale, larger than that typical of late-type galaxies. Most of the molecular gas is hence likely to be in a diffuse extended phase, rather than in dense molecular clouds. By combining the results of emission and absorption studies, we find that the strongest molecular absorption component toward the quasar cannot arise from the molecular disk, but is likely to arise from diffuse gas in the galaxy’s circumgalactic medium. Our results emphasize the potential of combining molecular and stellar emission line studies with optical absorption line studies to achieve a more complete picture of the gas within and surrounding high-redshift galaxies.

  2. Keck/ESI Long-slit Spectroscopy of SBS 1421+511: A Recoiling Quasar Nucleus in an Active Galaxy Pair?

    NASA Astrophysics Data System (ADS)

    Sun, Luming; Zhou, Hongyan; Hao, Lei; Jiang, Peng; Ge, Jian; Ji, Tuo; Ma, Jingzhe; Zhang, Shaohua; Shu, Xinwen

    2016-02-01

    We present Keck/Echellette Spectrograph and Imager long-slit spectroscopy of SBS 1421+511, a system consisting of a quasar at z = 0.276 and an extended source 3″ north of the quasar. The quasar shows a blue-skewed profile of Balmer broad emission lines, which can be well modeled as emissions from a circular disk with a blueshift velocity of ˜1400 km s-1. The blueshift is better interpreted as resulting from a recoiling active black hole than from a super-massive black hole binary, since the line profile almost kept steady for over one decade in the quasar rest frame. Alternative interpretations are possible as well, such as emissions from a bipolar outflow or a circular disk with spiral emissivity perturbations. The extended source shows Seyfert-like narrow-line ratios and a [O iii] luminosity of \\gt 1.4× {10}8{L}⊙ , with almost the same redshift as the quasar and a projected distance of 12.5 kpc at the redshift. SBS 1421+511 is thus likely to be an interacting galaxy pair with a dual active galactic nucleus. Alternatively, the quasar companion only appears to be active but not necessarily so: the gas before/in/behind the companion galaxy is illuminated by the quasar as an extended emission-line region is detected at a similar distance in the opposite direction southern to the quasar, which may be generated either by tidal interactions between the galaxy pair or large-scale outflows from the quasar.

  3. IRAS 14348-1447, an Ultraluminous Pair of Colliding, Gas-Rich Galaxies: The Birth of a Quasar?

    PubMed

    Sanders, D B; Scoville, N Z; Soifer, B T

    1988-02-01

    Ground-based observations of the object IRAS 14348-1447, which was discovered with the Infrared Astronomical Satellite, show that it is an extremely luminous colliding galaxy system that emits more than 95 percent of its energy at far-infrared wavelengths. IRAS 14348-1447, which is receeding from the sun at 8 percent of the speed of light, has a bolometric luminosity more than 100 times larger than that of our galaxy, and is therefore as luminous as optical quasars. New optical, infrared, and spectroscopic measurements suggest that the dominant luminosity source is a dustenshrouded quasar. The fuel for the intense activity is an enormous supply of molecular gas. Carbon monoxide emission has been detected at a wavelength of 2.6 millimeters by means of a new, more sensitive receiver recently installed on the 12-meter telescope of the National Radio Astronomy Observatory. IRAS 14348-1447 is the most distant and luminous source of carbon monoxide line emission yet detected. The derived mass of interstellar molecular hydrogen is 6 x 10(10) solar masses. This value is approximately 20 times that of the molecular gas content of the Milky Way and is similar to the largest masses of atomic hydrogen found in galaxies. A large mass of molecular gas may be a prerequisite for the formation of quasars during strong galactic collisions. PMID:17759060

  4. A LACK OF SHORT-PERIOD MULTIPLANET SYSTEMS WITH CLOSE-PROXIMITY PAIRS AND THE CURIOUS CASE OF KEPLER-42

    SciTech Connect

    Steffen, Jason H.; Farr, Will M.

    2013-09-01

    Many Kepler multiplanet systems have planet pairs near low-order, mean-motion resonances. In addition, many Kepler multiplanet systems have planets with orbital periods less than a few days. With the exception of Kepler-42, however, there are no examples of systems with both short orbital periods and nearby companion planets while our statistical analysis predicts {approx}17 such pairs. For orbital periods of the inner planet that are less than three days, the minimum period ratio of adjacent planet pairs follows the rough constraint P{identical_to}P{sub 2}/P{sub 1}{approx}>2.3 (P{sub 1}/day){sup -2/3}. This absence is not due to a lack of planets with short orbital periods. We also show a statistically significant excess of small, single-candidate systems with orbital periods below three days over the number of multiple candidate systems with similar periods-perhaps a small-planet counterpart to the hot Jupiters.

  5. IRAS 14348-1447, an ultraluminous pair of colliding, gas-rich galaxies - The birth of a quasar?

    NASA Technical Reports Server (NTRS)

    Sanders, D. B.; Soifer, B. T.; Scoville, N. Z.

    1988-01-01

    Ground-baed observations of the object IRAS 14348-1447, which was discovered with the Infrared Astronomical Satellite, show that it is an extremely luminous colliding galaxy system that emits more than 95 percent of its energy at FIR wavelengths. IRAS 14348-1447, which is receeding from the sun at 8 percent of the speed of light, has a bolometric luminosity more than 100 times larger than that of the Galaxy, and is therefore as luminous as optical quasars. New optical, infrared, and spectroscopic measurements suggest that the dominant luminosity source is a dust-enshrouded quasar. The fuel for the intense activity is an enormous supply of molecular gas. Carbon monoxide emission has been detected at a wavelength of 2.6 millimeters by means of a new, more sensitive receiver recently installed on the 12-meter telescope of the National Radio Astronomy Observatory. IRAS 14348-1447 is the most distant and luminous source of carbon monoxide line emission yet detected.

  6. Paired quasars near NGC 2639 - Evidence for quasars in superclusters

    NASA Technical Reports Server (NTRS)

    Ford, H.; Ciardullo, R.; Harms, R.

    1983-01-01

    Arp (1979, 1980) has found quasars with similar redshifts which appear to be paired across low-redshift galaxies. Arp concludes that the pairings provide evidence for an association between high-redshift quasars and a small, low-redshift galaxy. Oort et al. (1981) suggested an alternative hypothesis to explain the close redshift pairs. They proposed that the two closest pairs are in superclusters at the cosmological distances implied by the quasars' redshifts. The low-redshift quasar pair U7/U10 (0.303/0.305) is close enough to allow detection of any associated clusters of galaxies on deep red photographs. The present investigation had originally the objective to test the supercluster hypothesis by searching for faint clusters which might comprise a supercluster at z approximately 0.3. Unfortunately, the disappearance of the pairs makes it impossible to test the hypothesis in this field. The search for a supercluster at z = 0.30 revealed a faint rich cluster of galaxies near the quasar U10 (z = 0.305). It was found that U10 is not associated with the cluster.

  7. GOODS-Herschel: the impact of galaxy-galaxy interactions on the far-infrared properties of galaxies

    NASA Astrophysics Data System (ADS)

    Hwang, H. S.; Elbaz, D.; Dickinson, M.; Charmandaris, V.; Daddi, E.; Le Borgne, D.; Buat, V.; Magdis, G. E.; Altieri, B.; Aussel, H.; Coia, D.; Dannerbauer, H.; Dasyra, K.; Kartaltepe, J.; Leiton, R.; Magnelli, B.; Popesso, P.; Valtchanov, I.

    2011-11-01

    Aims: We study the impact of galaxy-galaxy interactions on the far-infrared properties of galaxies and its evolution at 0 < z < 1.2. Methods: Using the high-z galaxies in the fields of Great Observatories Origins Deep Survey (GOODS) observed by the Herschel Space Observatory in the framework of the GOODS-Herschel key program and the local IRAS or AKARI-selected galaxies in the field of Sloan Digital Sky Survey Data Release 7, we investigate the dependence of galaxy properties on the morphology of and the distance to the nearest neighbor galaxy. Results: We find that the star-formation rates (SFRs) and the specific SFRs (SSFRs) of galaxies on average depend on the morphology of and the distance to the nearest neighbor galaxy in this redshift range. When a late-type galaxy has a close neighbor galaxy, the SFR and the SSFR increase as it approaches a late-type neighbor, which is supported by Kolmogorov-Smirnov (K-S) and Monte Carlo (MC) tests with a significance level of >99%. However, the SFR and the SSFR decrease or do not change much as the galaxy approaches an early-type neighbor. The bifurcations of SFRs and SSFRs depending on the neighbor's morphology seem to occur at Rn ≈ 0.5rvir,nei (virial radius of the neighbor), which is supported by K-S and MC tests with a significance level of >98%. For all redshift bins, the SSFRs of late-type galaxies interacting with late-type neighbors are increased by factors of about 1.8 ± 0.7 and 4.0 ± 1.2 compared to those of non-interacting galaxies when the pair separation is smaller than 0.5rvir,nei and 0.1rvir,nei, respectively. The dust temperature of both local and high-z late-type galaxies that strongly interact with late-type neighbors (i.e. Rn ≤ 0.1rvir,nei) appears to be higher than that of non-interacting galaxies with a significance level of 96-99%. However, the dust temperature of local late-type galaxies that strongly interact with early-type neighbors seems to be lower than or similar to that of non

  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. The CARMA Paired Antenna Calibration System: Atmospheric Phase Correction for Millimeter Wave Interferometry and Its Application to Mapping the Ultraluminous Galaxy Arp 193

    NASA Astrophysics Data System (ADS)

    Zauderer, B. Ashley; Bolatto, Alberto D.; Vogel, Stuart N.; Carpenter, John M.; Peréz, Laura M.; Lamb, James W.; Woody, David P.; Bock, Douglas C.-J.; Carlstrom, John E.; Culverhouse, Thomas L.; Curley, Roger; Leitch, Erik M.; Plambeck, Richard L.; Pound, Marc W.; Marrone, Daniel P.; Muchovej, Stephen J.; Mundy, Lee G.; Teng, Stacy H.; Teuben, Peter J.; Volgenau, Nikolaus H.; Wright, Melvyn C. H.; Wu, Dalton

    2016-01-01

    Phase fluctuations introduced by the atmosphere are the main limiting factor in attaining diffraction limited performance in extended interferometric arrays at millimeter and submillimeter wavelengths. We report the results of C-PACS, the Combined Array for Research in Millimeter-Wave Astronomy Paired Antenna Calibration System. We present a systematic study of several hundred test observations taken during the 2009–2010 winter observing season where we utilize CARMA's eight 3.5 m antennas to monitor an atmospheric calibrator while simultaneously acquiring science observations with 6.1 and 10.4 m antennas on baselines ranging from a few hundred meters to ∼2 km. We find that C-PACS is systematically successful at improving coherence on long baselines under a variety of atmospheric conditions. We find that the angular separation between the atmospheric calibrator and target source is the most important consideration, with consistently successful phase correction at CARMA requiring a suitable calibrator located ≲6° away from the science target. We show that cloud cover does not affect the success of C-PACS. We demonstrate C-PACS in typical use by applying it to the observations of the nearby very luminous infrared galaxy Arp 193 in 12CO(2-1) at a linear resolution of ≈70 pc (0.″12 × 0.″18), 3 times better than previously published molecular maps of this galaxy. We resolve the molecular disk rotation kinematics and the molecular gas distribution and measure the gas surface densities and masses on 90 pc scales. We find that molecular gas constitutes ∼30% of the dynamical mass in the inner 700 pc of this object with a surface density ∼104 M⊙ pc‑2 we compare these properties to those of the starburst region of NGC 253.

  10. The CARMA Paired Antenna Calibration System: Atmospheric Phase Correction for Millimeter Wave Interferometry and Its Application to Mapping the Ultraluminous Galaxy Arp 193

    NASA Astrophysics Data System (ADS)

    Zauderer, B. Ashley; Bolatto, Alberto D.; Vogel, Stuart N.; Carpenter, John M.; Peréz, Laura M.; Lamb, James W.; Woody, David P.; Bock, Douglas C.-J.; Carlstrom, John E.; Culverhouse, Thomas L.; Curley, Roger; Leitch, Erik M.; Plambeck, Richard L.; Pound, Marc W.; Marrone, Daniel P.; Muchovej, Stephen J.; Mundy, Lee G.; Teng, Stacy H.; Teuben, Peter J.; Volgenau, Nikolaus H.; Wright, Melvyn C. H.; Wu, Dalton

    2016-01-01

    Phase fluctuations introduced by the atmosphere are the main limiting factor in attaining diffraction limited performance in extended interferometric arrays at millimeter and submillimeter wavelengths. We report the results of C-PACS, the Combined Array for Research in Millimeter-Wave Astronomy Paired Antenna Calibration System. We present a systematic study of several hundred test observations taken during the 2009-2010 winter observing season where we utilize CARMA's eight 3.5 m antennas to monitor an atmospheric calibrator while simultaneously acquiring science observations with 6.1 and 10.4 m antennas on baselines ranging from a few hundred meters to ˜2 km. We find that C-PACS is systematically successful at improving coherence on long baselines under a variety of atmospheric conditions. We find that the angular separation between the atmospheric calibrator and target source is the most important consideration, with consistently successful phase correction at CARMA requiring a suitable calibrator located ≲6° away from the science target. We show that cloud cover does not affect the success of C-PACS. We demonstrate C-PACS in typical use by applying it to the observations of the nearby very luminous infrared galaxy Arp 193 in 12CO(2-1) at a linear resolution of ≈70 pc (0.″12 × 0.″18), 3 times better than previously published molecular maps of this galaxy. We resolve the molecular disk rotation kinematics and the molecular gas distribution and measure the gas surface densities and masses on 90 pc scales. We find that molecular gas constitutes ˜30% of the dynamical mass in the inner 700 pc of this object with a surface density ˜104 M⊙ pc-2 we compare these properties to those of the starburst region of NGC 253.

  11. Associations between quasi-stellar objects and galaxies

    NASA Technical Reports Server (NTRS)

    Burbidge, G.; Hewitt, A.; Narlikar, J. V.; Gupta, P. Das

    1990-01-01

    A table is presented here listing all close pairs of QSOs and galaxies that were found in a computer-aided search of catalogs of QSOs and bright galaxies and an extensive search of the literature. There is a large excess of pairs with separations of 2 arcmin lor less, or about 60 kpc, over the numbers expected if the configurations were accidental. The angular separation for 392 pairs adds to the evidence for physical association, and it is shown that selection effects are not important. A general rule is stated that QSOs tend to lie in the vicinity of normal galaxies much more often than is expected by chance whether or not the galaxies and the QSOs have the same redshifts. It is emphasized that this rule cannot be explained in terms of gravitational microlensing, and it is concluded that some part of the redshift of all classes of active nuclei is not associated with the expansion of the universe.

  12. Oxygen isotope exchange kinetics of mineral pairs in closed and open systems: Applications to problems of hydrothermal alteration of igneous rocks and Precambrian iron formations

    USGS Publications Warehouse

    Gregory, R.T.; Criss, R.E.; Taylor, H.P., Jr.

    1989-01-01

    The systematics of stable-isotope exchange between minerals and fluids are examined in the context of modal mineralogical variations and mass-balance considerations, both in closed and in open systems. On mineral-pair ??18O plots, samples from terranes that have exchanged with large amounts of fluid typically map out steep positively-sloped non-equilibrium arrays. Analytical models are derived to explain these effects; these models allow for different exchange rates between the various minerals and the external fluids, as well as different fluid fluxes. The steep arrays are adequately modelled by calculated isochron lines that involve the whole family of possible exchange trajectories. These isochrons have initially-steep near-vertical positive slopes that rotate toward a 45?? equilibrium slope as the exchange process proceeds to completion. The actual data-point array is thus analogous to the hand of an "isotopic clock" that measures the duration of the hydrothermal episode. The dimensionless ratio of the volumetric fluid flux to the kinetic rate parameter ( u k) determines the shape of each individual exchange trajectory. In a fluid-buffered system ( u k ??? 1), the solutions to the equations: (1) are independent of the mole fractions of the solid phases; (2) correspond to Taylor's open-system water/rock equation; and (3) yield straight-line isochrons that have slopes that approach 1 f, where f is the fraction reacted of the more sluggishly exchanging mineral. The isochrons for this simple exchange model are closely congruent with the isochrons calculated for all of the more complex models, thereby simplifying the application of theory to actual hydrothermal systems in nature. In all of the models an order of magnitude of time (in units of kt) separates steep non-equilibrium arrays (e.g., slope ??? 10) from arrays approaching an equilibrium slope of unity on a ??-?? diagram. Because we know the approximate lifetimes of many hydrothermal systems from geologic and

  13. 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.

  14. Probing the large and massive circumgalactic medium of a galaxy at z ∼ 0.2 using a pair of quasars

    SciTech Connect

    Muzahid, Sowgat

    2014-03-20

    We present an analysis of two O VI absorbers at redshift z {sub abs} = 0.227, which were detected in the spectra of two closely spaced QSO sightlines (Q 0107–025A and B) and observed with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope. At the same redshift, the presence of a single bright (∼1.2L {sub *}) galaxy at an impact parameter of ∼200 kpc (proper) from both the sightlines was reported by Crighton et al. Using detailed photoionization models, we show that the high ionization phases of both the O VI absorbers have similar ionization conditions (e.g., log U ∼ –1.1 to –0.9), chemical enrichment (e.g., log Z ∼ –1.4 to –1.0), total hydrogen column density (e.g., log N {sub H}(cm{sup –2}) ∼ 19.6 – 19.7), and line of sight thickness (e.g., l {sub los} ∼ 600-800 kpc). Therefore we speculate that the O VI absorbers are tracing different parts of same large-scale structure, presumably the circumgalactic medium (CGM) of the identified galaxy. Using sizes along and transverse to the line of sight, we estimate the size of the CGM to be R ∼ 330 kpc. The baryonic mass associated with this large CGM as traced by O VI absorption is ∼1.2 × 10{sup 11} M {sub ☉}. A low ionization phase is detected in one of the O VI systems with near-solar metallicity (log Z = 0.20 ± 0.20) and parsec scale size (l {sub los} ∼ 6 pc), possibly tracing the neutral phase of a high-velocity cloud embedded within the CGM.

  15. Galaxy dynamics in clustered environments

    NASA Astrophysics Data System (ADS)

    Pereira, Maria J. R. R.

    Galaxy orientations have been studied statistically for over 70 years now, but it is only recently that alignments have been found on scales larger than those of close interacting pairs. Large scale alignments between galaxies and their surrounding tidal fields are expected to occur during formation, but what happens when these galaxies fall into larger systems? Can their orientations tell us anything about the accretion process itself? In this dissertation I will focus on the radial alignment of satellite galaxies, in which a satellite's long axis points preferentially toward the center of its host. I present observational evidence for this type of galaxy alignment in the SDSS DR3 using a sample of X-ray selected massive clusters. Then, using results from N-body cosmological simulations, I will argue that this effect is the result of a secular tidal interaction between the galaxies and their host potential. The analysis shows that subhalos are effectively torqued by their host throughout their orbits, so that their major axes tend to be aligned with the gradient of the host potential. The significant discrepancy between the magnitude of the effect as seen in these simulations and that detected in observations motivates the work of the next chapter, where I perform numerical experiments on idealized, high resolution N-body models of elliptical galaxies. These experiments show that the more centrally concentrated luminous components of galaxies take longer to react to the external torque, and, in the particular case of mildly eccentric orbits, their orientations can figure rotate in periodic patterns that are not radially aligned on average. The mechanism is more effective on galaxies that have larger triaxialities, but the overall effect of torquing is to make galaxies rounder, since radially misaligned galaxies tend to become more spherical as they are torqued towards equilibrium. In the last chapter, I briefly discuss the impact of these results for galaxy

  16. 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

  17. HIGH-RESOLUTION SIMULATIONS OF THE REIONIZATION OF AN ISOLATED MILKY WAY-M31 GALAXY PAIR

    SciTech Connect

    Ocvirk, P.; Aubert, D.; Chardin, J.; Knebe, A.; Yepes, G.; Libeskind, N.; Gottlöber, S.; Hoffman, Y.

    2013-11-01

    We present the results of a set of numerical simulations aimed at studying reionization at the galactic scale. We use a high-resolution realization of the formation of the Milky Way (MW)-M31 system to simulate the reionization of the Local Group. The reionization calculation was performed with the post-processing radiative transfer code ATON and the underlying cosmological simulation was performed as part of the CLUES project (http://www.clues-project.org). We vary the source models to bracket the range of source properties used in the literature. We investigate the structure and propagation of the galactic ionization fronts by a visual examination of our reionization maps. Within the progenitors, we find that reionization is patchy and proceeds locally inside-out. The process becomes patchier with decreasing source photon output. It is generally dominated by one major H II region and one to four additional isolated smaller bubbles, which eventually overlap. Higher emissivity results in faster and earlier local reionization. In all models, the reionization of the MW and M31 are similar in duration, i.e., between 203 Myr and 22 Myr depending on the source model, placing their z{sub reion} between 8.4 and 13.7. In all models except the most extreme, the MW and M31 progenitors reionize internally, ignoring each other despite being relatively close to each other, even during the epoch of reionization. Only in the case of strong supernova feedback suppressing star formation in halos less massive than 10{sup 9} M{sub ☉}, and using our highest emissivity, do we find that the MW is reionized by M31.

  18. Twins born in different environments? Nuclei of two dSphs: isolated galaxy KKS3 and ESO269-66, a close neighbor of NGC5128

    NASA Astrophysics Data System (ADS)

    Sharina, Margarita; Karachentsev, Igor; Kniazev, Alexei

    2015-08-01

    The close vicinity of giant neighbors determines the environmental mechanisms that have been considered responsible for the evolution of dwarf spheroidal galaxies (dSphs). In the recent years, Karachentsev and collaborators have reported on the discovery of a few truly isolated dSphs in the Local volume. This study focuses on one of these unusual objects, KKs3 (MV=-12.3 mag). It contains a massive globular cluster (GC) (MV=-8.5 mag) near its optical center. We have performed the estimation of its radial velocity using a medium-resolution spectrum obtained with the RSS spectrograph at the Southern African Large Telescope (SALT). The signal-to-noise ratio in the spectrum was sufficient to estimate the age and metallicity for the GC using simple stellar population models, and the methods of full spectrum fitting and Lick index diagnostic diagrams. The results contribute to the knowledge about the origin of massive star clusters and their host dSphs.In the same way we have analyzed another luminous GC (MV=-10) in the center of ESO269-66 (MB=-15.4), a close dSph neighbor of the giant S0 Cen A. The cluster was observed with SALT in the same instrumental configuration. The structure and star formation histories of the two galaxies look rather similar. Both of them have experienced several star-forming events. The most recent ones occurred 1÷2 Gyr ago, and most powerful bursts happened 12÷14 Gyrs ago. Our analysis has shown that both GCs appear to be 1÷2 Gyr younger and 0.2÷0.3 dex more metal-rich than the most ancient metal-poor stars in the host dSphs. We examine signatures of multiple stellar population in the GCs using out data. Since central star-forming bursts were extended in time, the massive clusters might be considered as nuclei of the galaxies.

  19. 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.

  20. The statistical investigation of the First and Second Byurakan survey galaxies and their neighbors

    NASA Astrophysics Data System (ADS)

    Nazaryan, Tigran A.

    2014-05-01

    In the thesis we study close pairs of galaxies with the aim of understanding the influence of gravitational interaction on nuclear activity and star formation of paired galaxies. For this purpose we investigate dependences of integral parameters of galaxies, their star formation and properties of nuclei on kinematic parameters of systems and their large-scale environment. The thesis has an introduction, three main chapters, a summary, lists of abbreviations and references, and three appendices. In the first chapter, the methods of selection of sample of pairs of galaxies and measurements of physical parameters of the First Byurakan Survey (Markarian) galaxies and their neighbors are presented, and the databases in appendices A and B are described, which contain parameters of neighbors of Markarian galaxies measured by us, and the parameters of pairs having Markarian galaxies, based on the Sloan Digital Sky Survey (SDSS) data. The selection effects of sample of pairs are discussed, and the statistical comparison of Markarian galaxies and their neighbors is done. The results of statistical study of star formation and activity of nuclei in pairs having Markarian galaxies are presented, as well as the correlations between properties of galaxies in pairs and the physical mechanisms behind them. In the second chapter, the results of statistical study of the Second Byurakan Survey (SBS) galaxies and their neighbors, and star formation and activity of nuclei in those pairs are presented and discussed. In the third chapter, possibilities of using supernovae as indicators of star formation are discussed, the sample of supernovae in pairs of galaxies is presented, and study of star formation in pairs of interacting galaxies by means of that sample of supernovae is done. Also а conclusion about the nature of progenitors of different types of supernovae is made. The short summary of main results of the study concludes the thesis. The thesis has 158 pages. The main results

  1. 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).

  2. On the dynamical and physical state of the {open_quotes}diffuse ionized medium{close_quotes} in nearby spiral galaxies

    SciTech Connect

    Wang, J.; Heckman, T.M.; Lehnert, M.D.

    1997-12-01

    We report the initial results from a program to study the morphology, physical state, and kinematics of the {open_quotes}diffuse ionized medium{close_quotes} (DIM) in a sample of the nearest and brightest late-type galaxies. For each of five galaxies (NGC 2403, M81, NGC 4395, M51, and M101), we have analyzed deep narrowband H{alpha} images of the entire star-forming disk and long-slit spectra of the inner ({approximately}10kpc) disk with a resolution of 40{endash}75kms{sup {minus}1}. We find that the DIM covers most of the star-forming disk and is morphologically related to the presence of high surface brightness gas (the giant HII regions). The DIM and the giant HII regions differ systematically in their physical and dynamical state. The DIM is characterized by enhanced emission in the low-ionization forbidden lines ([OI], [NII], and [SII]), and even the high-ionization [OIII] {lambda}5007 line is moderately strong in the DIM in at least three cases. This last result contrasts with upper limits on the [OIII] surface brightness in the local DIM of our own Galaxy (the {open_quotes}Reynolds Layer{close_quotes}). We directly verify the inference made by Lehnert and Heckman that the DIM contributes significantly to the spatially integrated (global) emission-line ratios measured in late-type galaxies. We also find that the DIM is more disturbed kinematically than the gas in the giant HII regions. The deconvolved (intrinsic) widths of the H{alpha} and [NII] {lambda}6584 lines range from 30 to 100kms{sup {minus}1} (FWHM) in the DIM compared to 20{endash}50kms{sup {minus}1} in the giant HII regions. The high-ionization gas in the DIM is more kinematically disturbed than the low-ionization gas: the [OIII] {lambda}5007 lines have intrinsic widths of 70{endash}150kms{sup {minus}1}. The differing kinematics implies that the DIM is not a single monolithic phase of the ISM. Instead, it may consist of a {open_quotes}quiescent{close_quotes} DIM with a low ionization state and

  3. COMPARATIVE STUDY OF ASYMMETRY ORIGIN OF GALAXIES IN DIFFERENT ENVIRONMENTS. I. OPTICAL OBSERVATIONS

    SciTech Connect

    Plauchu-Frayn, I.; Coziol, R. E-mail: rcoziol@astro.ugto.m

    2010-06-15

    This paper presents the first of two analyses about the influence of environment on the formation and evolution of galaxies observed in the nearby universe. For our study, we used three different samples representing different density environments: galaxies in Compact Groups (HCGs), Isolated Pairs of Galaxies (KPGs), and Isolated Galaxies (KIGs), which were taken as references. Usingboth characteristic isophotal parameters and evidence of asymmetries in the optical and the near-infrared, we are able to establish differences in the characteristics of galaxies with different morphologies in different environments, allowing us to better understand their different formation histories. In this first paper, we present the isophotal and asymmetry analyses of a sample of 214 galaxies in different environments observed in the optical (V and I images). For each galaxy, we have determined different characteristic isophotal parameters and V - I color profiles, as a function of semi-major axis, and performed a full asymmetry analysis in residual images using the V filter. Evidence of asymmetry in the optical is almost missing in the KIG sample and significantly more common in the KPG than in the HCG samples. Our isophotal analysis suggests that the stellar populations in the HCG galaxies are older and more dynamically relaxed than in the KPG. The HCG galaxies seem to be at a more advanced stage of interaction than the KPGs. One possible explanation is that these structures formed at different epochs: compact groups of galaxies would have formed before close pairs of galaxies, which only began interacting recently. However, similarities in the formation process of galaxies with same morphology suggest CGs and close pairs of galaxies share similar conditions; they are new structures forming relatively late in low-density environments.

  4. DISTANT CLUSTER OF GALAXIES [left

    NASA Technical Reports Server (NTRS)

    2002-01-01

    constellation Serpens. Based on the colors and the statistical distribution of the galaxies in 3C 324's vicinity, astronomers conclude a remote cluster is at the same distance as a radio galaxy. [center right] This pair of elliptical galaxies, seen together with a few fainter companions, is remarkably similar in shape, light distribution, and color to their present day descendants. This Hubble image provides evidence that ellipticals formed remarkably early in the universe. [top right] Some of the objects in this compact tangled group resemble today's spiral galaxies. However, they have irregular shapes and appear disrupted and asymmetric. This might be due to a high frequency of galaxy collisions and close encounters in the early universe. Credit: Mark Dickinson (STScI) and NASA

  5. Induced star formation in interacting galaxies

    NASA Technical Reports Server (NTRS)

    Kennicutt, R. C.; Roettiger, K. A.; Keel, W. C.; Vanderhulst, J. M.; Hummel, E.

    1987-01-01

    Measurements of H alpha emission line fluxes and FIR fluxes in approx. 100 interacting spirals were used to investigate the effects of close tidal interactions on the disk and nuclear star formation rates in galaxies. Two samples of interacting spirals were studied, a complete sample of close pairs, and a set of strongly perturbed systems from the Arp atlas. Both the integrated H alpha luminosities and FIR luminosities are enhanced in the interacting galaxies, indicating that the encounters indeed trigger massive star formation in many cases. The response of individual galaxies is highly variable, however. A majority of the interacting spirals exhibit normal star formation rates, while a small fraction are undergoing bursts with luminosities which are rarely, if ever, observed in noninteracting systems. Virtually all of the latter are in the Arp sample, indicating that the Arp atlas is heavily biased to the most active star forming systems.

  6. The environmental properties of galaxies probed by marked statistics

    NASA Astrophysics Data System (ADS)

    Mateus, A.

    2014-10-01

    Galaxies are generally treated as point particles in clustering analysis. However, these objects have physical and stellar population properties that must be taken into account if one wants to study the environmental effects on galaxy evolution. In this work, we applied a statistical method to investigate the role of environment in driving galaxy properties based on the marked correlation function. This methodology was applied to a galaxy sample drawn from the Sloan Digital Sky Survey Data Release 7, where the clustering of galaxies was weighted by particular galaxy properties, like luminosity and stellar mass, thus more directly quantifying the correlations between these attributes and large-scale environment. We show that marked statistics are powerful to reproduce environmental trends for variables like luminosities and stellar masses, as well as to quantify the relative importance of them with respect to the environment. For low density regions in the local universe, mark correlations relative to the mean are stronger compared to dense regions. This implies that the clustering of stellar mass, for instance, is more sensitive to environments associated to individual halos in close galaxy pairs than to massive halos found in clusters, where the correlations don't show any difference relative to the mean. We conclude that in nearby galaxy clusters, dominated by massive objects, galaxies are equally clustered (marked correlation = average clustering). On the other hand, galaxies in low density regions span a wide range in stellar mass (halo sizes) where the correlations appear more dramatically.

  7. 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.

  8. Spatial distribution of low-surface-brightness galaxies

    NASA Astrophysics Data System (ADS)

    Mo, H. J.; McGaugh, Stacy S.; Bothun, Gregory D.

    1994-03-01

    The spatial distribution of low-surface-brightness (LSB) galaxies is important both as a test of theories of large-scale structure formation and for the physical understanding of the environmental effects that influence the evolution of galaxies. In this paper we calculate, using redshift samples, the cross-correlation functions [ξ_AB_(r)] of LSB galaxies with normal galaxies in complete samples (i.e. CLA and IRAS). This enables us to compare directly the amplitudes and shapes of the correlation functions for LSB galaxies with those for CfA and IRAS galaxies. For pair separations r >~ 2 h^-1^ Mpc, we find ξ_AB_(r) is proportional to r^-γ^ with γ ~ 1.7. This shape of {XI}_AB_ is in agreement with that of the correlation functions for other galaxies. The amplitudes (A ) of ξ_AB_(r) are lower than those of the autocorrelation functions for the CfA and IRAS samples, with A_LSB-CfA_:A_CfA-CfA_~0.4 and A_LSB-IRAS_:A_IRAS-0IRAS_~0.6. These results suggest that LSB galaxies are embedded in the same large-scale structure as other galaxies, but are less strongly clustered. This offers the hope that LSB galaxies may be unbiased tracers of the mass density on large scales. For r <~ 2 h^-1^ Mpc, the cross-correlation functions are significantly lower than that expected from the extrapolation of CAB on larger scales, showing that the formation and survival of LSB galaxies may be inhibited by interaction with neighbouring galaxies. We show that a simple hierarchical model, in which LSB galaxies are formed only in haloes lacking close interactions with other haloes, reproduces both the deficit of pairs at small separations and the low amplitude of the correlation function. This model suggests that LSB galaxies should, on average, be younger than normal galaxies, consistent with direct observations. The model also suggests that a strong luminosity (mass) segregation in galaxy clustering is not a necessary consequence of biased galaxy formation, unless the effect of surface

  9. Evidence for major mergers of galaxies at 2 ≲ z < 4 in the VVDS and VUDS surveys

    NASA Astrophysics Data System (ADS)

    Tasca, L. A. M.; Le Fèvre, O.; López-Sanjuan, C.; Wang, P.-W.; Cassata, P.; Garilli, B.; Ilbert, O.; Le Brun, V.; Lemaux, B. C.; Maccagni, D.; Tresse, L.; Bardelli, S.; Contini, T.; Charlot, S.; Cucciati, O.; Fontana, A.; Giavalisco, M.; Kneib, J.-P.; Salvato, M.; Taniguchi, Y.; Vergani, D.; Zamorani, G.; Zucca, E.

    2014-05-01

    Context. The mass assembly of galaxies can proceed through different physical processes. Here we report on the spectroscopic identification of close physical pairs of galaxies at redshifts 2 ≲ z< 4 and discuss the impact of major mergers in building galaxies at these early cosmological times. Aims: We aim to identify and characterize close physical pairs of galaxies destined to merge and use their properties to infer the contribution of merging processes to the early mass assembly of galaxies. Methods: We searched for galaxy pairs with a transverse separation rp ≤ 25h-1 kpc and a velocity difference Δv ≤ 500 km s-1 using early data from the VIMOS Ultra Deep Survey (VUDS) that comprise a sample of 1111 galaxies with spectroscopic redshifts measurements at redshifts 1.8 ≤ z ≤ 4 in the COSMOS, ECDFS, and VVDS-02h fields, combined with VVDS data. We analysed their spectra and associated visible and near-infrared photometry to assess the main properties of merging galaxies that have an average stellar mass M⋆ = 2.3 × 1010 M⊙ at these redshifts. Results: Using the 12 physical pairs found in our sample we obtain a first robust measurement of the major merger fraction at these redshifts, fMM = 19.4-6+9%. These pairs are expected to merge within 1 Gyr on average each producing a more massive galaxy by the time the cosmic star formation peaks at z ~ 1 - 2. Using the pairs' merging time scales, we derive a merging rate of RMM = 0.17-0.05+0.08 Gyr-1. From the average mass ratio between galaxies in the pairs, the stellar mass of the resulting galaxy after merging will be ~60% higher than the most massive galaxy in the pair before merging. We conclude that major merging of galaxy pairs is on-going at 2 ≲ z< 4 and is significantly contributing to the major mass assembly phase of galaxies at this early epoch. Based on data obtained with the European Southern Observatory Very Large Telescope, Paranal, Chile, under Large Programmes 070.A-9007, 177.A-0837, and 185.A

  10. Merging Galaxies Create a Binary Quasar

    NASA Astrophysics Data System (ADS)

    2010-02-01

    Astronomers have found the first clear evidence of a binary quasar within a pair of actively merging galaxies. Quasars are the extremely bright centers of galaxies surrounding super-massive black holes, and binary quasars are pairs of quasars bound together by gravity. Binary quasars, like other quasars, are thought to be the product of galaxy mergers. Until now, however, binary quasars have not been seen in galaxies that are unambiguously in the act of merging. But images of a new binary quasar from the Carnegie Institution's Magellan telescope in Chile show two distinct galaxies with "tails" produced by tidal forces from their mutual gravitational attraction. "This is really the first case in which you see two separate galaxies, both with quasars, that are clearly interacting," says Carnegie astronomer John Mulchaey who made observations crucial to understanding the galaxy merger. Most, if not all, large galaxies, such as our galaxy the Milky Way, host super-massive black holes at their centers. Because galaxies regularly interact and merge, astronomers have assumed that binary super-massive black holes have been common in the Universe, especially during its early history. Black holes can only be detected as quasars when they are actively accreting matter, a process that releases vast amounts of energy. A leading theory is that galaxy mergers trigger accretion, creating quasars in both galaxies. Because most such mergers would have happened in the distant past, binary quasars and their associated galaxies are very far away and therefore difficult for most telescopes to resolve. The binary quasar, labeled SDSS J1254+0846, was initially detected by the Sloan Digital Sky Survey, a large scale astronomical survey of galaxies and over 120,000 quasars. Further observations by Paul Green of the Harvard-Smithsonian Center for Astrophysics and colleagues* using NASA's Chandra's X-ray Observatory and telescopes at Kitt Peak National Observatory in Arizona and Palomar

  11. ACTIVE GALACTIC NUCLEUS PAIRS FROM THE SLOAN DIGITAL SKY SURVEY. I. THE FREQUENCY ON {approx}5-100 kpc SCALES

    SciTech Connect

    Liu Xin; Shen Yue; Strauss, Michael A.; Hao Lei

    2011-08-20

    Galaxy-galaxy mergers and close interactions have long been regarded as a viable mechanism for channeling gas toward the central supermassive black holes (SMBHs) of galaxies which are triggered as active galactic nuclei (AGNs). AGN pairs, in which the central SMBHs of a galaxy merger are both active, are expected to be common from such events. We conduct a systematic study of 1286 AGN pairs at z-bar {approx}0.1 with line-of-sight velocity offsets {Delta}v < 600 km s{sup -1} and projected separations r{sub p} < 100 h{sup -1}{sub 70} kpc, selected from the Seventh Data Release of the Sloan Digital Sky Survey (SDSS). This AGN pair sample was drawn from 138,070 AGNs optically identified based on diagnostic emission line ratios and/or line widths. The fraction of AGN pairs with 5 h{sup -1}{sub 70} kpc {approx}< r{sub p} < 100 h{sup -1}{sub 70} kpc among all spectroscopically selected AGNs at 0.02 < z < 0.16 is 3.6% after correcting for SDSS spectroscopic incompleteness; {approx}30% of these pairs show morphological tidal features in their SDSS images, and the fraction becomes {approx}> 80% for pairs with the brightest nuclei. Our sample increases the number of known AGN pairs on these scales by more than an order of magnitude. We study their AGN and host-galaxy star formation properties in a companion paper.

  12. Ring Galaxies

    NASA Astrophysics Data System (ADS)

    Dennefeld, M.; Materne, J.

    1980-09-01

    Among the 338 exotic, intriguing and/or fascinating objects contained in Arp's catalogue of peculiar galaxies, two, Arp 146 and 147, are calling special attention as a presumably separate class of objects displaying closed rings with almost empty interior. It is difficult to find out when, historically speaking, attention was called first to this type of object as a peculiar class, but certainly ga1axies with rings were widely found and recognized in the early sixties, ul}der others by Vorontsov-Velyaminov (1960), Sandage (1961) in the Hubble Atlas or de Vaucouleurs (1964) in the first reference catalogue of ga1axies. The most recent estimates by Arp and Madore (1977) from a search on about 200 Schmidt plates covering 7,000 square degrees give 3.6 per cent of ring galaxies among 2,784 peculiar galaxies found. However, despite the mythological perfection associated with a circle, some ordering is necessary before trying to understand the nature of such objects. This is particularly true because a large fraction of those galaxies with rings are probably normal spiral galaxies of type RS or S(r) as defined by de Vaucouleurs, where the spiral arms are simply "closing the circle". A good example of such "ordinary" galaxy is NGC 3081 in the Hubble Atlas .

  13. 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

  14. The role of interactions in triggering bars, spiral arms and AGN in disk galaxies

    NASA Astrophysics Data System (ADS)

    Nair, Preethi; Ellison, Sara L.; Patton, David R.

    2016-01-01

    The role of secular structures like bars, rings and spiral arms in triggering star formation and AGN activity in disk galaxies are not well understood. In addition, the mechanisms which create and destroy these structures are not well characterized. Mergers are considered to be one of the main mechanisms which can trigger bars in massive disk galaxies. Using a sample of ~8000 close pair galaxies at 0.02 < z < 0.06 from the Sloan Digital Sky Survey, I will present results illustrating the role of mergers in triggering bars, rings, spiral arms and AGN as a function of close pair separation and merger ratios as well as their dependence on morphology and other physical properties of the galaxies. Time permitting, I will show how resolved IFU observations from SDSS MaNGA will help to place stronger constraints on the role of these structures in triggering star formation and AGN.

  15. 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

  16. VizieR Online Data Catalog: Heschel obs. of major-merger pairs of z<0.1 galaxies (Cao+, 2016)

    NASA Astrophysics Data System (ADS)

    Cao, C.; Xu, C. K.; Domingue, D.; Buat, V.; Cheng, Y.-W.; Gao, Y.; Huang, J.; Jarrett, T. H.; Lisenfeld, U.; Lu, N.; Mazzarella, J.; Sun, W.-H.; Wu, H.; Yun, M. S.; Ronca, J.; Jacques, A.

    2016-03-01

    Pairs in H-KPAIR were observed successfully using PACS and SPIRE photometers in the three PACS bands (70, 100, 160um) and three SPIRE bands (250, 350, 500um). The observations of 83 pairs were carried out within our own proposal (OT2cxu2). The remaining 5 pairs in H-KPAIR were observed by other OT and KPGT projects, and their Herschel data were taken from the archives. SPIRE images of two pairs (J1101+5720 and J1429+3534) were taken directly from HerMES data release v2. (4 data files).

  17. A pair of O VI and broad Ly α absorbers probing warm gas in a galaxy group environment at z ˜ 0.4

    NASA Astrophysics Data System (ADS)

    Pachat, Sachin; Narayanan, Anand; Muzahid, Sowgat; Khaire, Vikram; Srianand, Raghunathan; Wakker, Bart P.; Savage, Blair D.

    2016-05-01

    We report the detection of two O VI absorbers at z = 0.416 14 and 0.419 50 (|Δv| = 710 km s-1), towards SBS 0957+599. Both absorbers are multiphase systems tracing substantial reservoirs of warm baryons. The low- and intermediate-ionization metals in the z = 0.416 14 absorber are consistent with an origin in photoionized gas. O VI has a velocity structure different from other metal species. Ly α shows the presence of a broad feature. The linewidths for O VI and the broad Ly α suggest T = 7.1 × 105 K. This warm medium is probing a baryonic column, which is an order of magnitude more than the total hydrogen in the cooler photoionized gas. The second absorber is detected only in H I and O VI. Here a temperature of 4.6 × 104 K supports O VI originating in a low-density photoionized gas. A broad component is seen in Ly α, offset from O VI. The temperature in the broad Ly α is T ≲ 2.1 × 105 K. The absorbers reside in a galaxy overdensity region with seven spectroscopically identified galaxies within ˜10 Mpc and Δv ˜ 1000 km s-1 of the z = 0.416 14 absorber, and two galaxies inside a similar separation from the z = 0.419 50 absorber. The distribution of galaxies relative to the absorbers suggests that the line of sight could be intercepting a large-scale filament connecting galaxy groups, or the extended halo of a sub-L* galaxy. Though kinematically proximate, the two absorbers reaffirm the diversity in the physical conditions of low red-shift O VI systems and the galactic environments they inhabit.

  18. Vortex pairs on surfaces

    SciTech Connect

    Koiller, Jair

    2009-05-06

    A pair of infinitesimally close opposite vortices moving on a curved surface moves along a geodesic, according to a conjecture by Kimura. We outline a proof. Numerical simulations are presented for a pair of opposite vortices at a close but nonzero distance on a surface of revolution, the catenoid. We conjecture that the vortex pair system on a triaxial ellipsoid is a KAM perturbation of Jacobi's geodesic problem. We outline some preliminary calculations required for this study. Finding the surfaces for which the vortex pair system is integrable is in order.

  19. Possible Signatures of a Cold-flow Disk from MUSE Using a z ˜ 1 Galaxy-Quasar Pair toward SDSS J1422-0001

    NASA Astrophysics Data System (ADS)

    Bouché, N.; Finley, H.; Schroetter, I.; Murphy, M. T.; Richter, P.; Bacon, R.; Contini, T.; Richard, J.; Wendt, M.; Kamann, S.; Epinat, B.; Cantalupo, S.; Straka, L. A.; Schaye, J.; Martin, C. L.; Péroux, C.; Wisotzki, L.; Soto, K.; Lilly, S.; Carollo, C. M.; Brinchmann, J.; Kollatschny, W.

    2016-04-01

    We use a background quasar to detect the presence of circumgalactic gas around a z=0.91 low-mass star-forming galaxy. Data from the new Multi Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope show that the galaxy has a dust-corrected star formation rate (SFR) of 4.7 ± 2.0 M⊙ yr-1, with no companion down to 0.22 M⊙ yr-1 (5σ) within 240 {h}-1 kpc (“30”). Using a high-resolution spectrum of the background quasar, which is fortuitously aligned with the galaxy major axis (with an azimuth angle α of only 15°), we find, in the gas kinematics traced by low-ionization lines, distinct signatures consistent with those expected for a “cold-flow disk” extending at least 12 kpc (3× {R}1/2). We estimate the mass accretion rate {\\dot{M}}{{in}} to be at least two to three times larger than the SFR, using the geometric constraints from the IFU data and the H i column density of log {N}{{H}{{I}}}/{{cm}}-2 ≃ 20.4 obtained from a Hubble Space Telescope/COS near-UV spectrum. From a detailed analysis of the low-ionization lines (e.g., Zn ii, Cr ii, Ti ii, Mn ii, Si ii), the accreting material appears to be enriched to about 0.4 {Z}⊙ (albeit with large uncertainties: {log} Z/{Z}⊙ =-0.4\\quad +/- \\quad 0.4), which is comparable to the galaxy metallicity (12 + log O/H = 8.7 ± 0.2), implying a large recycling fraction from past outflows. Blueshifted Mg ii and Fe ii absorptions in the galaxy spectrum from the MUSE data reveal the presence of an outflow. The Mg ii and Fe ii absorption line ratios indicate emission infilling due to scattering processes, but the MUSE data do not show any signs of fluorescent Fe ii* emission. Based on observations made at the ESO telescopes under program 080.A-0364 (SINFONI), 079.A-0600 (UVES), and as part of MUSE commissioning (ESO program 060.A-9100). Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities

  20. The Penrose photoproduction scenario for NGC 4151: A black hole gamma-ray emission mechanism for active galactic nuclei and Seyfert galaxies. [Compton scattering and pair production

    NASA Technical Reports Server (NTRS)

    Leiter, D.

    1979-01-01

    A consistent theoretical interpretation is given for the suggestion that a steepening of the spectrum between X-ray and gamma ray energies may be a general, gamma-ray characteristic of Seyfert galaxies, if the diffuse gamma ray spectrum is considered to be a superposition of unresolved contributions, from one or more classes of extragalactic objects. In the case of NGC 4151, the dominant process is shown to be Penrose Compton scattering in the ergosphere of a Kerr black hole, assumed to exist in the Seyfert's active galactic nucleus.

  1. Tidal Dwarf Galaxies In Gas-rich Interacting Galaxy Groups

    NASA Astrophysics Data System (ADS)

    Eigenthaler, Paul

    2014-01-01

    Galaxy-galaxy interactions in gas-rich galaxy groups or pairs can form tidal bridges and tails. These tidal arms can contain kinematically decoupled structures with active star formation in the same mass range as dwarf galaxies, so-called tidal dwarf galaxies (TDGs). They differ from ordinary dwarf galaxies by their lack of dark matter and higher metallicity content. Compact groups of galaxies are an ideal environment to study the origin and evolution of TDGs since the high spatial volume density of member galaxies allows for frequent and efficient interactions between galaxies forming tidal tails. Hunsberger et al. (1996) identified 47 TDG candidates in Hickson compact groups (HCGs) and estimated that more than 50% of all dwarf galaxies in compact groups are former TDGs. Statistical considerations based on observations of interacting galaxies illustrate that a significant fraction of today's dwarf galaxies could have had a tidal origin. In their early evolution, TDGs can easily be distinguished from classical dwarf galaxies as they are still embedded in large tidal structures and show ongoing star formation, identified via strong Hα emission in these aggregates. Simulations of interacting galaxies, and of TDGs in particular, have shown that TDGs can survive their first starburst event and turn into long-lived dwarf sized objects. Preliminary results from deep Hα imaging with the SOAR telescope to detect new TDGs in a sample of 10 Hickson compact groups will be presented.

  2. 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

  3. ACTIVE GALACTIC NUCLEUS PAIRS FROM THE SLOAN DIGITAL SKY SURVEY. II. EVIDENCE FOR TIDALLY ENHANCED STAR FORMATION AND BLACK HOLE ACCRETION

    SciTech Connect

    Liu Xin; Shen Yue; Strauss, Michael A.

    2012-01-20

    Active galactic nuclei (AGNs) are occasionally seen in pairs, suggesting that tidal encounters are responsible for the accretion of material by both central supermassive black holes (BHs). In Paper I of this series, we selected a sample of AGN pairs with projected separations r{sub p} < 100 h{sup -1}{sub 70} kpc and velocity offsets <600 km s{sup -1} from the Seventh Data Release of the Sloan Digital Sky Survey and quantified their frequency. In this paper, we address the BH accretion and recent star formation properties in their host galaxies. AGN pairs experience stronger BH accretion, as measured by their [O III] {lambda}5007 luminosities (corrected for contribution from star formation) and Eddington ratios, than do control samples of single AGNs matched in redshift and host-galaxy stellar mass. Their host galaxies have stronger post-starburst activity and younger mean stellar ages, as indicated by stronger H{delta} absorption and smaller 4000 A break in their spectra. The BH accretion and recent star formation in the host galaxies both increase with decreasing projected separation in AGN pairs, for r{sub p} {approx}< 10-30 h{sup -1}{sub 70} kpc. The intensity of BH accretion, the post-starburst strength, and the mean stellar ages are correlated between the two AGNs in a pair. The luminosities and Eddington ratios of AGN pairs are correlated with recent star formation in their host galaxies, with a scaling relation consistent with that observed in single AGNs. Our results suggest that galaxy tidal interactions enhance both BH accretion and host-galaxy star formation in close AGN pairs, even though the majority of low-redshift AGNs are not coincident with on-going interactions.

  4. How Do Galaxies Grow?

    NASA Astrophysics Data System (ADS)

    2008-08-01

    to the most massive galaxies belonging to clusters. "Most surprising is that in three of the four groups, the brightest galaxy also has a bright companion galaxy. These galaxy pairs are merging systems," says Tran. The brightest galaxy in each group can be ordered in a time sequence that shows how luminous galaxies continue to grow by merging until recently, that is, in the last 5 billion years. It appears that due to the most recent episode of this 'galactic cannibalism', the brightest galaxies became at least 50% more massive. This discovery provides unique and powerful validation of hierarchical formation as manifested in both galaxy and cluster assembly. "The stars in these galaxies are already old and so we must conclude that the recent merging did not produce a new generation of stars," concludes Tran. "Most of the stars in these galaxies were born at least 7 billion years ago." The team is composed of Kim-Vy H. Tran (Institute for Theoretical Physics, University of Zürich, Switzerland), John Moustakas (New York University, USA), Anthony H. Gonzalez and Stefan J. Kautsch (University of Florida, Gainesville, USA), and Lei Bai and Dennis Zaritsky (Steward Observatory, University of Arizona, USA). The results presented here are published in the Astrophysical Journal Letters: "The Late Stellar Assembly Of Massive Cluster Galaxies Via Major Merging", by Tran et al.

  5. Hairpin loops consisting of single adenine residues closed by sheared A.A and G.G pairs formed by the DNA triplets AAA and GAG: solution structure of the d(GTACAAAGTAC) hairpin.

    PubMed

    Chou, S H; Zhu, L; Gao, Z; Cheng, J W; Reid, B R

    1996-12-20

    The DNA undecamers GTACAAAGTAC (AAA 11-mer) and GTACGAGGTAC (GAG 11-mer) have been studied in solution by high-resolution NMR spectroscopy. Both duplexes form stable hairpins containing single deoxyadenosine loops and stems containing five base-pairs that are closed at the loop end by sheared AxA and GxC pairs, respectively. These molecules thus contain new AAA and GAG loop turn motifs. All protons, including the chiral H5'/H5" protons of the loop residues, were assigned using NOESY, DQF-COSY and heteronuclear 1H-31P COSY experiments. The backbone torsion angles were constrained using experimental data from NOE crosspeaks, three-bond 1H-1H coupling constants and four-bond 1H-31P coupling constants and four-bond 1H-31P coupling constants. The AAA and GAG 11-mers form similar structures in solution. The detailed structure of the AAA 11-mer was determined by the combined use of NMR, distance geometry and energy minimization methods. This structure exhibits good stacking of the loop adenosine base on the closing 5Ax7A sheared pair, with the 6A base stacking on the 5A base and the 6A deoxyribose stacking with the 7A base. All sugars in the AAA 11-mer hairpin adopt the typical DNA C2'-endo conformation and a sharp backbone turn occurs between residues 6A and 7A. This loop turn is brought about mainly by a change in the backbone phosphate torsion angles from zeta(g-) alpha(g-) to zeta(g+) alphat(g+) at the turn. The gamma torsion angle of residue 7A in the closing sheared pair also changes from gauche+ to trans. In Pu1NPu2 loop turns of the GCA, AAA and GAG types, the chemical shift of the H4' proton of the loop deoxyribose depends on the nature of Pu2; this reflects the stacking of the loop sugar on the Pu2 base and the different ring current effects of A or G in this position. PMID:9000625

  6. 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)

  7. 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.

  8. Understanding the size growth of massive galaxies through stellar populations

    NASA Astrophysics Data System (ADS)

    Ferreras, I.; Trujillo, I.; Mármol-Queraltó, E.; Pérez-González, P.

    Massive early-type galaxies undergo a significant process of evolution with redshift on the stellar mass vs size plane. Furthermore, this trend does not depend on the age of their stellar populations. Therefore, such an evolution should involve processes that do not include a significant amount of star formation, leaving (mostly) dry mergers as the main growth channel. By studying close pairs involving a massive galaxy, one can quantify the role of mergers on the growth of massive galaxies. A recent study based on the SHARDS dataset reveals that minor mergers cannot be the dominant mechanism to explain the bulk of size growth in these systems. Merging is found to provide a constant fractional growth rate of ~10% per Gyr from redshift z=1, corresponding to an overall stellar mass increase of 2× between z=1 and z=0.

  9. Understanding the size growth of massive galaxies through stellar populations

    NASA Astrophysics Data System (ADS)

    Ferreras, Ignacio

    2015-08-01

    The growth of massive galaxies remains an open problem. The observational evidence seems to converge on a two-stage scenario, where a compact massive core is formed during an early, intense burst, followed by a more extended process of mass and size growth at intermediate redshift (z<2). This talk focuses on the latter, exploring the growth of massive galaxies through a detailed analysis of the stellar populations in close pairs, to study their formation history. Two surveys are explored (SHARDS and GAMA), probing the stellar populations of pre-merging systems out to z~1.3, and down to a mass ratio ~1:100. We will compare the results between medium band spectral fitting (SHARDS) and those from a more targeted analysis of line strengths in the GAMA data. The combination of the two datasets provide a unique insight of the growth channel of massive galaxies via mergers.

  10. Critical Schwinger Pair Production

    NASA Astrophysics Data System (ADS)

    Gies, Holger; Torgrimsson, Greger

    2016-03-01

    We investigate Schwinger pair production in spatially inhomogeneous electric backgrounds. A critical point for the onset of pair production can be approached by fields that marginally provide sufficient electrostatic energy for an off-shell long-range electron-positron fluctuation to become a real pair. Close to this critical point, we observe features of universality which are analogous to continuous phase transitions in critical phenomena with the pair-production rate serving as an order parameter: electric backgrounds can be subdivided into universality classes and the onset of pair production exhibits characteristic scaling laws. An appropriate design of the electric background field can interpolate between power-law scaling, essential Berezinskii-Kosterlitz-Thouless-type scaling, and a power-law scaling with log corrections. The corresponding critical exponents only depend on the large-scale features of the electric background, whereas the microscopic details of the background play the role of irrelevant perturbations not affecting criticality.

  11. Critical Schwinger Pair Production.

    PubMed

    Gies, Holger; Torgrimsson, Greger

    2016-03-01

    We investigate Schwinger pair production in spatially inhomogeneous electric backgrounds. A critical point for the onset of pair production can be approached by fields that marginally provide sufficient electrostatic energy for an off-shell long-range electron-positron fluctuation to become a real pair. Close to this critical point, we observe features of universality which are analogous to continuous phase transitions in critical phenomena with the pair-production rate serving as an order parameter: electric backgrounds can be subdivided into universality classes and the onset of pair production exhibits characteristic scaling laws. An appropriate design of the electric background field can interpolate between power-law scaling, essential Berezinskii-Kosterlitz-Thouless-type scaling, and a power-law scaling with log corrections. The corresponding critical exponents only depend on the large-scale features of the electric background, whereas the microscopic details of the background play the role of irrelevant perturbations not affecting criticality. PMID:26991162

  12. 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.

  13. Binary satellite galaxies

    NASA Astrophysics Data System (ADS)

    Evslin, Jarah

    2014-05-01

    Suggestions have appeared in the literature that the following four pairs of Milky Way and Andromeda satellite galaxies are gravitationally bound: Draco and Ursa Minor, Leo IV and V, Andromeda I and III, and NGC 147 and 185. Assuming that a given pair is gravitationally bound, the Virial theorem provides a crude estimate of its total mass and so its instantaneous tidal radius. In the case of each pair except for Leo IV and Leo V, the estimated tidal radius is inferior to the separation between the two satellites, suggesting that these pairs are not currently gravitationally bound. Their proximities may be explained if each pair condensed from the remnants of a formerly gravitationally bound structure, but such a scenario is in tension with the absence of older pairs with a wider separation.

  14. 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

  15. Colliding Galaxies: Hubble Space Telescope

    NASA Astrophysics Data System (ADS)

    1997-10-01

    NASA's Hubble Space Telescope looks deep within the violent center where the two Antennae Galaxies were merging. The Hubble's high resolution and sensitivity reveals the birth of young star clusters formed in the collision. New Hubble images of young star clusters help investigators put the evolutionary sequence into the right order. The Hubble Space Telescope images are: (1) zoom into the antennae galaxies; (2) galaxy merger evolution sequence; (3) the formation of the antennae pair; and (4) artist's conception of the collision of Milky-Way Galaxy with the Andromeda.

  16. 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.

  17. Pick a Pair. Pancake Pairs

    ERIC Educational Resources Information Center

    Miller, Pat

    2005-01-01

    Cold February weather and pancakes are a traditional pairing. Pancake Day began as a way to eat up the foods that were abstained from in Lent--traditionally meat, fat, eggs and dairy products. The best-known pancake event is The Pancake Day Race in Buckinghamshire, England, which has been run since 1445. This column describes pairs of books that…

  18. The cosmic evolution of halo pairs - I. Global trends

    NASA Astrophysics Data System (ADS)

    Moreno, Jorge

    2012-01-01

    Accumulating evidence suggests that galaxy interactions play an important role in shaping the properties of galaxies. For this reason, cosmological studies focused on the evolution of halo/subhalo pairs are vital. In this paper I describe a large catalogue of halo pairs extracted from the publicly available Millennium Simulation, the largest of its kind to date. (Throughout this work I use the term 'halo' to refer both to individual haloes in the field and to subhaloes embedded in larger structures.) Pairs are selected according to whether or not they come within a given critical (comoving) distance dcrit, without the pre-requisite that they must merge. Moreover, a condition requiring haloes to surpass a critical mass Mcrit during their history is imposed. The primary catalogue, consisting of 502 705 pairs, is selected by setting dcrit= 1 Mpc h-1 and Mcrit= 8.6 × 1010 M⊙ h-1 (equivalent to 100 simulation particles). One of the central goals of this paper is to evaluate the effects of modifying these criteria. For this purpose, additional subcatalogues with more stringent proximity and mass conditions are constructed (i.e. dcrit= 200 kpc h-1 or/and Mcrit= 8.6 × 1011 M⊙ h-1= 1000 simulation particles - see Table 1 for a summary). I use a simple five-stage picture to perform statistical analyses of their separations, redshifts, masses, mass ratios and relevant lifetimes. The fraction of pairs that never merge (because one of the members in the pair is absorbed by a third halo or both members survive until the present time) is accounted for. These results provide a broad picture that captures the essential characteristics behind the evolution of these halo pairs. This is the first of a series of papers aimed to explore the huge wealth of information encoded in this catalogue. Such investigations will play a fundamental role in future cosmological studies of interacting galaxies and binary (and multiple) quasars.1 Halo pair sets shown in the panels of all figures

  19. Hidden Pair of Supermassive Black Holes

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2015-08-01

    Could a pair of supermassive black holes (SMBHs) be lurking at the center of the galaxy Mrk 231? A recent study finds that this may be the case and the unique spectrum of this galaxy could be the key to discovering more hidden binary SMBH systems.Where Are the Binary Supermassive Black Holes?Its believed that most, if not all, galaxies have an SMBH at their centers. As two galaxies merge, the two SMBHs should evolve into a closely-bound binary system before they eventually merge. Given the abundance of galaxy mergers, we would expect to see the kinematic and visual signatures of these binary SMBHs among observed active galactic nuclei yet such evidence for sub-parsec binary SMBH systems remains scarce and ambiguous. This has led researchers to wonder: is there another way that we might detect these elusive systems?A collaboration led by Chang-Shuo Yan (National Astronomical Observatories, Chinese Academy of Sciences) thinks that there is. The group suggests that these systems might have distinct signatures in their optical-to-UV spectra, and they identify a system that might be just such a candidate: Mrk 231.A Binary CandidateProposed model of Mrk 231. Two supermassive black holes, each with their own mini-disk, orbit each other in the center of a circumbinary disk. The secondary black hole has cleared gap in the circumbinary disk as a result of its orbit around the primary black hole. [Yan et al. 2015]Mrk 231 is a galaxy with a disturbed morphology and tidal tails strong clues that it might be in the final stages of a galactic merger. In addition to these signs, Mrk 231 also has an unusual spectrum for a quasar: its continuum emission displays an unexpected drop in the near-UV band.Yan and her collaborators propose that the odd behavior of Mrk 231s spectrum can be explained if the center of the galaxy houses a pair of SMBHs each with its own mini accretion disk surrounded by a circumbinary accretion disk. As the secondary SMBH orbits the primary SMBH (with a

  20. 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.

  1. Star formation rates in isolated galaxies selected from the Two-Micron All-Sky Survey

    NASA Astrophysics Data System (ADS)

    Melnyk, O.; Karachentseva, V.; Karachentsev, I.

    2015-08-01

    We have considered the star formation properties of 1616 isolated galaxies from the 2MASS XSC (Extended Source Catalog) selected sample (2MIG) with the far-ultraviolet GALEX magnitudes. This sample was then compared with corresponding properties of isolated galaxies from the Local Orphan Galaxies (LOG) catalogue and paired galaxies. We found that different selection algorithms define different populations of isolated galaxies. The population of the LOG catalogue, selected from non-clustered galaxies in the Local Supercluster volume, mostly consists of low-mass spiral and late-type galaxies. The specific star formation rate (SSFR) upper limit in isolated and paired galaxies does not exceed the value of ˜dex(-9.4). This is probably common for galaxies of differing activity and environment (at least at z < 0.06). The fractions of quenched galaxies are nearly twice as high in the paired galaxy sample as in the 2MIG isolated galaxy sample. From the behaviour of (S)SFR versus M* relations we deduced that the characteristic value influencing evolutionary processes is the galaxy mass. However, the environmental influence is notable: paired massive galaxies with logM* > 11.5 have higher (S)SFR than isolated galaxies. Our results suggest that the environment helps to trigger the star formation in the highest mass galaxies. We found that the fraction of AGN in the paired sample is only a little higher than in our isolated galaxy sample. We assume that AGN phenomenon is probably defined by secular galaxy evolution.

  2. Hole localization and spin coupling in [pi]-mono- and [pi]-dications of [mu]-oxoporphyrin dimers, relevance to structure of oxidized [open quotes]special pair[close quotes] in photosynthetic reaction centers

    SciTech Connect

    Binstead, R.A.; Hush, N.S. )

    1993-12-16

    The antiferromagnetically coupled cofacial [mu]-oxoiron(III) dimers of octaethylporphyrin (OEP) and [alpha],[beta],[gamma],[Delta]-tetraphenylporphyrin (TPP) can be oxidized in two one-electron steps to yield [pi]-monocations and [pi]-dications. Hitherto unreported absorption bands are observed in the mid-infrared region in the spectra of the monocations. These are identified as intervalence transitions of dynamically trapped holes. The electron-phonon coupling energies (CH[sub 2]Cl[sub 2] solution, 295 K) are 0.31 [+-] 0.04 eV, and the inter-ring, predominantly through-space, electronic coupling constants J are 0.07 and 0.03 eV, respectively. The small values of J are a consequence of the large mean plane separation of the porphyrin rings (4.53 A). Since it is impossible that the electron-phonon coupling energies will vary greatly between cofacial porphyrin dimers, it is suggested that absorption hands around 1 eV in the [pi]-monocations of [open quotes]sandwich[close quotes] compounds such as M[sup III]P[sub 2] or M[sup IV]P[sub 2][sup +], where P is a porphyrin and M are lanthanide, actinide, or transition metals (3-12) observed under similar conditions will have electronic ground states that are delocalized on at least the vibrational time scale, with frequency maxima equal to 2J in the tight-binding approximation. The thermal inter-ring hole-transfer times in the [mu]-oxo dimer monocations are estimated to be approximately 1 ps. The relevance of these results to the problem of the structure of the oxidized [open quotes]special pair[close quotes] in the photosynthetic reaction center is briefly discussed. 52 refs., 4 figs., 5 tabs.

  3. Colliding Galaxies in the Big Data of the Huge Universe (BIDHU) project

    NASA Astrophysics Data System (ADS)

    Rossi, Rocio; Nascimento, Ana Carolina; Barbosa, Walysson; Borges, Airton; Goya, Milton; Puga, Sandra; De Mello, Duilia F.

    2015-01-01

    Colliding galaxies are excellent laboratories to study star formation under extreme environments. Recently, we have started a project aiming at identifying bright colliding galaxies, in pairs and in groups, using the Sloan Digital Sky Survey (SDSS III). Here we present the method we have used to select our sample as part of the project Big Data of the Huge Universe (BIDHU). We started with a small equatorial slice of the SDSS data and adopted a maximum angular separation of 1 arcmin to select a sample of 70 pairs in close contact. The search has now been expanded to the entire Sloan Survey and a machine learning code has been built to identify close pairs out of approximately 45,000 pair-candidates. The BIDHU colliding-galaxy sample will be made available to the community and will have excellent targets for follow up observations with large telescopes. Our major goal is to use ALMA and large ground-based telescopes to understand how stars are formed in tidal interaction.

  4. 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

  5. Probing a Starburst Galaxy's Superwind

    NASA Astrophysics Data System (ADS)

    Stocke, John

    The Cosmic Origins Spectrograph Science Team for IGM studies proposes to observe the bright QSO/starburst galaxy pair, SBS1108+560/M108 for the following purposes: 1. To measure the FUV brightness of the QSO to determine whether an HST/COS observation is viable and to set its exposure times. 2. To determine the locations of the brighter star forming regions in the disk of M108 to compare wth high resolution HI 21cm, H alpha and soft X-ray continuum maps which show supershells, line-emitting loops and extra-planar clumps of hot gas. 3. To use the relative extinctions of near-side and far-side star forming regions to determine the orientation of M108 in space. This determination is required in order to correctly interpret the kinematics of any QSO absorption line system(s) found in our COS spectrum of SBS1108+560. M108 (NGC3556) is a moderate starburst from the IRAS-selected sample of Lehnert & Heckman, moderately inclined on the sky (75 deg.) and very nearby (14 Mpc). The proximity of SBS1108+560 to M108 (25 kpc) and its location quite close to the minor-axis of M108 make this pairing quite unusual (one of only 3 to be observed by COS) and an important opportunity for understanding the nature and dynamics of starburst superwinds. An important question we hope to answer with this set of GALEX and HST data is whether starburst winds from massive spiral galaxies actually escape the gaalxy's gravitational potential and so enrich the IGM with metals."

  6. Winning Pairs.

    ERIC Educational Resources Information Center

    Monsour, Florence

    2000-01-01

    Mentoring programs that pair experienced and first-time teachers are gaining prominence in supporting, developing, and retaining new teachers. The successful Beginning Teacher Assistance program at University of Wisconsin-River Falls was designed to give new K-12 teachers the opportunity for yearlong, structured support from mentor teachers. (MLH)

  7. The ultraviolet attenuation law in backlit spiral galaxies

    SciTech Connect

    Keel, William C.; Manning, Anna M.; Holwerda, Benne W.; Lintott, Chris J.; Schawinski, Kevin E-mail: ammanning@bama.ua.edu E-mail: Twitter@BenneHolwerda E-mail: Twitter@chrislintott E-mail: Twitter@kevinschawinski

    2014-02-01

    The effective extinction law (attenuation behavior) in galaxies in the emitted ultraviolet (UV) regime is well known only for actively star-forming objects and combines effects of the grain properties, fine structure in the dust distribution, and relative distributions of stars and dust. We use Galaxy Evolution Explorer, XMM Optical Monitor, and Hubble Space Telescope (HST) data to explore the UV attenuation in the outer parts of spiral disks which are backlit by other UV-bright galaxies, starting with the candidate list of pairs provided by Galaxy Zoo participants. New optical images help to constrain the geometry and structure of the target galaxies. Our analysis incorporates galaxy symmetry, using non-overlapping regions of each galaxy to derive error estimates on the attenuation measurements. The entire sample has an attenuation law across the optical and UV that is close to the Calzetti et al. form; the UV slope for the overall sample is substantially shallower than found by Wild et al., which is a reasonable match to the more distant galaxies in our sample but not to the weighted combination including NGC 2207. The nearby, bright spiral NGC 2207 alone gives an accuracy almost equal to the rest of our sample, and its outer arms have a very low level of foreground starlight. Thus, this widespread, fairly 'gray' law can be produced from the distribution of dust alone, without a necessary contribution from differential escape of stars from dense clouds. Our results indicate that the extrapolation needed to compare attenuation between backlit galaxies at moderate redshifts from HST data, and local systems from Sloan Digital Sky Survey and similar data, is mild enough to allow the use of galaxy overlaps to trace the cosmic history of dust in galaxies. For NGC 2207, HST data in the near-UV F336W band show that the covering factor of clouds with small optical attenuation becomes a dominant factor farther into the UV, which opens the possibility that widespread

  8. 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.

  9. Protected Flux Pairing Qubit

    NASA Astrophysics Data System (ADS)

    Bell, Matthew; Zhang, Wenyuan; Ioffe, Lev; Gershenson, Michael

    2014-03-01

    We have studied the coherent flux tunneling in a qubit containing two submicron Josephson junctions shunted by a superinductor (a dissipationless inductor with an impedance much greater than the resistance quantum). The two low energy quantum states of this device, close=">" open="|"> 0 and close=">" open="|"> 1, are represented by even and odd number of fluxes in the loop, respectively. This device is dual to the charge pairing Josephson rhombi qubit. The spectrum of the device, studied by microwave spectroscopy, reflects the interference between coherent quantum phase slips in the two junctions (the Aharonov-Casher effect). The time domain measurements demonstrate the suppression of the qubit's energy relaxation in the protected regime, which illustrates the potential of this flux pairing device as a protected quantum circuit. Templeton Foundation, NSF, and ARO.

  10. A BRIGHT RING OF STAR BIRTH AROUND A GALAXY'S CORE

    NASA Technical Reports Server (NTRS)

    2002-01-01

    n image from NASA's Hubble Space Telescope reveals clusters of infant stars that formed in a ring around the core of the barred-spiral galaxy NGC 4314. This stellar nursery, whose inhabitants were created within the past 5 million years, is the only place in the entire galaxy where new stars are being born. The Hubble image is being presented today (June 11) at the American Astronomical Society meeting in San Diego, Calif. This close-up view by Hubble also shows other interesting details in the galaxy's core: dust lanes, a smaller bar of stars, dust and gas embedded in the stellar ring, and an extra pair of spiral arms packed with young stars. These details make the center resemble a miniature version of a spiral galaxy. While it is not unusual to have dust lanes and rings of gas in the centers of galaxies, it is uncommon to have spiral arms full of young stars in the cores. NGC 4314 is one of the nearest (only 40 million light-years away in the constellation Coma Berenices) examples of a galaxy with a ring of infant stars close to the core. This stellar ring - whose radius is 1,000 light-years - is a great laboratory to study star formation in galaxies. The left-hand image, taken in February 1996 by the 30-inch telescope Prime Focus Camera at the McDonald Observatory in Texas, shows the entire galaxy, including the bar of stars bisecting the core and the outer spiral arms, which begin near the ends of this bar. The box around the galaxy's core pinpoints the focus of the Hubble image. The right-hand image shows Hubble's close-up view of the galaxy's core, taken in December 1995 by the Wide Field and Planetary Camera 2. The bluish-purple clumps that form the ring are the clusters of infant stars. Two dark, wispy lanes of dust and a pair of blue spiral arms are just outside the star-forming ring. The lanes of dust are being shepherded into the ring by the longer, primary stellar bar seen in the ground-based (left-hand) image. The gas is trapped inside the ring

  11. Galaxy collisions - A preliminary study

    NASA Technical Reports Server (NTRS)

    Miller, R. H.; Smith, B. F.

    1980-01-01

    Collisions of spherical galaxies were studied in a series of numerical experiments to see what happens when galaxies collide. Each experiment starts with two model galaxies, each consisting of 50,000 stars, moving toward each other along a specified orbit. The series of experiments provides a systematic sampling of the parameter space spanned by the initial orbital energy and the initial angular momentum. Deeply penetrating collisions are emphasized. The collisions reported here scale to relative velocities as great as 500 km/s, well into the range for collisions within clusters of galaxies. It is found that: (1) the galaxies contract momentarily to about half their original sizes shortly after close passage; and (2) the initial galaxies blend into a single dynamical system while they are near each other.

  12. DYNAMICS OF LYMAN BREAK GALAXIES AND THEIR HOST HALOS

    SciTech Connect

    Lowenthal, James D.; Koo, David C.; Van Kampen, Eelco E-mail: koo@ucolick.or E-mail: evkampen@eso.or

    2009-09-20

    We present deep two-dimensional spectra of 22 candidate and confirmed Lyman break galaxies (LBGs) at redshifts 2 < z < 4 in the Hubble Deep Field (HDF) obtained at the Keck II telescope. The targets were preferentially selected with spatial extent and/or multiple knot morphologies, and we used slitmasks and individual slits tilted to optimize measurement of any spatially resolved kinematics. Our sample is more than 1 mag fainter and is at higher redshift than the kinematic LBG targets previously studied by others. The median target magnitude was I {sub 814} = 25.3, and total exposure times ranged from 10 to 50 ks. We measure redshifts, some new, ranging from z = 0.2072 to z = 4.056, including two interlopers at z < 1, and resulting in a sample of 14 LBGs with a median redshift z = 2.424. The morphologies and kinematics of the close pairs and multiple knot sources in our sample are generally inconsistent with galaxy formation scenarios postulating that LBGs occur only at the bottom of the potential wells of massive host halos; rather, they support 'collisional starburst' models with significant major merger rates and a broad halo occupation distribution. For 13 LBGs with possible kinematic signatures, we estimate a simple dynamical mass, subject to numerous caveats and uncertainties, of the galaxies and/or their host dark matter halos. Dynamical mass estimates of individual galaxies range from 4 x 10{sup 9} h {sup -1} M{sub sun} to 1.1 x 10{sup 11} h {sup -1} M{sub sun} and mass estimates of halos, based on close LBG pairs, range from <10{sup 10} h {sup -1} to {approx}10{sup 14} h {sup -1} M{sub sun} with a median value 1 x 10{sup 13} M{sub sun}. Comparison with a recent numerical galaxy formation model implies that indeed the pairwise velocities might not reflect true dynamical masses. We compare our dynamical mass estimates directly to stellar masses estimated for the same galaxies from SEDs, and find no evidence for a strong correlation. The diversity of

  13. Star Formation and Dense Gas in Galaxy Mergers from the VIXENS Survey

    NASA Astrophysics Data System (ADS)

    Heiderman, Amanda L.; VIXENS Team

    2016-01-01

    We present our λ= 3 mm IRAM and NRO single dish line survey for a sample of 15 interacting galaxies in the VIRUS-P Investigation of the eXtreme ENvironments of Starbursts (VIXENS) survey. Our sample of merging galaxies range from early to late interaction stages (close pairs to merger remnants, respectively). A variety of molecular lines are detected including dense gas tracers HCN, HCO+, HNC, CS, CN (and others) as well as 12CO and 13CO. We compare the dense gas fractions with 12CO and 13CO as well as star formation efficiencies defined by infrared-to-dense gas tracer luminosity ratio and discuss trends with interaction stage. We also investigate relations between star formation and dense gas content in our merger sample and compare them to non-interacting star forming galaxies and Galactic star forming regions in the Milky Way.

  14. A COMPARISON OF THE CLUSTERING PROPERTIES BETWEEN GALAXIES AND GROUPS OF GALAXIES

    SciTech Connect

    Deng Xinfa

    2013-03-01

    In this study, I apply cluster analysis and perform comparative studies of clustering properties between galaxies and groups of galaxies. It is found that the number of objects N{sub max} of the richest system and the maximal length D{sub max} of the largest system for groups in all samples are apparently larger than ones for galaxies, and that galaxies preferentially form isolated, paired, and small systems, while groups preferentially form grouped and clustered systems. These results show that groups are more strongly clustered than galaxies, which is consistent with statistical results of the correlation function.

  15. 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

  16. 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

  17. Controversies in kidney paired donation.

    PubMed

    Gentry, Sommer E; Montgomery, Robert A; Segev, Dorry L

    2012-07-01

    Kidney paired donation represented 10% of living kidney donation in the United States in 2011. National registries around the world and several separate registries in the United States arrange paired donations, although with significant variations in their practices. Concerns about ethical considerations, clinical advisability, and the quantitative effectiveness of these approaches in paired donation result in these variations. For instance, although donor travel can be burdensome and might discourage paired donation, it was nearly universal until convincing analysis showed that living donor kidneys can sustain many hours of cold ischemia time without adverse consequences. Opinions also differ about whether the last donor in a chain of paired donation transplants initiated by a nondirected donor should donate immediately to someone on the deceased donor wait-list (a domino or closed chain) or should be asked to wait some length of time and donate to start another sequence of paired donations later (an open chain); some argue that asking the donor to donate later may be coercive, and others focus on balancing the probability that the waiting donor withdraws versus the number of additional transplants if the chain can be continued. Other controversies in paired donation include simultaneous versus nonsimultaneous donor operations, whether to enroll compatible pairs, and interactions with desensitization protocols. Efforts to expand public awareness of and participation in paired donation are needed to generate more transplant opportunities. PMID:22732046

  18. Property (RD) for Hecke Pairs

    NASA Astrophysics Data System (ADS)

    Shirbisheh, Vahid

    2012-06-01

    As the first step towards developing noncommutative geometry over Hecke C ∗-algebras, we study property (RD) (Rapid Decay) for Hecke pairs. When the subgroup H in a Hecke pair ( G, H) is finite, we show that the Hecke pair ( G, H) has (RD) if and only if G has (RD). This provides us with a family of examples of Hecke pairs with property (RD). We also adapt Paul Jolissant's works in Jolissaint (J K-Theory 2:723-735, 1989; Trans Amer Math Soc 317(1):167-196, 1990) to the setting of Hecke C ∗-algebras and show that when a Hecke pair ( G, H) has property (RD), the algebra of rapidly decreasing functions on the set of double cosets is closed under holomorphic functional calculus of the associated (reduced) Hecke C ∗-algebra. Hence they have the same K 0-groups.

  19. The orbital evolution of binary galaxies

    NASA Astrophysics Data System (ADS)

    Chan, R.; Junqueira, S.

    2001-02-01

    We present the results of self-consistent numerical simulations performed to study the orbital circularization of binary galaxies. We have generalized a previous model (Junqueira & de Freitas Pacheco 1994) and confirmed partially their results. The orbital evolution of pairs of galaxies is faster when we consider interacting pairs with contacting ``live'' galaxy halos but the circularization time remains larger than the Hubble time. Besides, the time behavior of the orbits has changed in comparison with previous work because of tidal forces and dynamical friction acting on the halos.

  20. Statistics of associations among IR galaxies

    NASA Technical Reports Server (NTRS)

    Gallimore, Jack F.; Keel, William C.

    1990-01-01

    In the course of expanding the search of Kleinmann et. al. (1988) for distant, infrared-luminous objects, the authors noticed (as is often remarked) that a large number of infrared-selected galaxies have close neighbors or show merger characteristics (e.g., tidal tails, distorted disks). Because the sample size is large (567 infrared galaxies and 2182 field galaxies), this sample is ideal for statistically examining the importance of interactions among infrared galaxies. In particular, the authors compare the nearest-neighbor distribution and the two-point correlation function of their sample with that of a control sample of field galaxies.

  1. Galaxy masses

    NASA Astrophysics Data System (ADS)

    Courteau, Stéphane; Cappellari, Michele; de Jong, Roelof S.; Dutton, Aaron A.; Emsellem, Eric; Hoekstra, Henk; Koopmans, L. V. E.; Mamon, Gary A.; Maraston, Claudia; Treu, Tommaso; Widrow, Lawrence M.

    2014-01-01

    Galaxy masses play a fundamental role in our understanding of structure formation models. This review addresses the variety and reliability of mass estimators that pertain to stars, gas, and dark matter. The different sections on masses from stellar populations, dynamical masses of gas-rich and gas-poor galaxies, with some attention paid to our Milky Way, and masses from weak and strong lensing methods all provide review material on galaxy masses in a self-consistent manner.

  2. The dwarf galaxy UGC 5272 and its small companion galaxy

    NASA Technical Reports Server (NTRS)

    Hopp, U.; Schulte-Ladbeck, R. E.

    1991-01-01

    The present study of optical images and spectroscopy of the dwarf irregular galaxy UGC 5272 notes the presence, at 3.6 kpc, of a small neighboring galaxy which is also of irregular type and has a Holmberg diameter of 0.6 kpc. Attention is given to the possibility that the two galaxies, which are resolved into single stars, may form a physical pair. It is suggested that the blue-to-red supergiant ratio of UGC 5272 is high due to its low metallicity. While its extremely blue colors are suggestive of a recent starburst, the structural parameters of the galaxy are surprisingly normal. The gas contribution to total mass is high.

  3. Andromeda Galaxy

    NASA Technical Reports Server (NTRS)

    2003-01-01

    [figure removed for brevity, see original site]

    This image is a Galaxy Evolution Explorer observation of the large galaxy in Andromeda, Messier 31. The Andromeda galaxy is the most massive in the local group of galaxies that includes our Milky Way. Andromeda is the nearest large galaxy to our own. The image is a mosaic of 10 separate Galaxy Evolution Explorer images taken in September, 2003. The color image (with near ultraviolet shown by red and far ultraviolet shown by blue) shows blue regions of young, hot, high mass stars tracing out the spiral arms where star formation is occurring, and the central orange-white 'bulge' of old, cooler stars formed long ago. The star forming arms of Messier 31 are unusual in being quite circular rather than the usual spiral shape. Several companion galaxies can also be seen. These include Messier 32, a dwarf elliptical galaxy directly below the central bulge and just outside the spiral arms, and Messier 110 (M110), which is above and to the right of the center. M110 has an unusual far ultraviolet bright core in an otherwise 'red,' old star halo. Many other regions of star formation can be seen far outside the main body of the galaxy.

  4. Starburst galaxies

    NASA Technical Reports Server (NTRS)

    Weedman, Daniel W.

    1987-01-01

    The infrared properties of star-forming galaxies, primarily as determined by the Infrared Astronomy Satellite (IRAS), are compared to X-ray, optical, and radio properties. Luminosity functions are reviewed and combined with those derived from optically discovered samples using 487 Markarian galaxies with redshifts and published IRAS 60 micron fluxes, and 1074 such galaxies in the Center for Astrophysics redshift survey. It is found that the majority of infrared galaxies which could be detected are low luminosity sources already known from the optical samples, but non-infrared surveys have found only a very small fraction of the highest luminosity sources. Distributions of infrared to optical fluxes and available spectra indicate that the majority of IRAS-selected galaxies are starburst galaxies. Having a census of starburst galaxies and associated dust allow severl important global calculations. The source counts are predicted as a function of flux limits for both infrared and radio fluxes. These galaxies are found to be important radio sources at faint flux limits. Taking the integrated flux to z = 3 indicates that such galaxies are a significant component of the diffuse X-ray background, and could be the the dominant component depending on the nature of the X-ray spectra and source evolution.

  5. 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).

  6. OT2_cxu_2: Local Benchmarks for Cosmic Evolution of Major-Merger Pairs -- A Herschel Study of SFR, Dust and Gas Content

    NASA Astrophysics Data System (ADS)

    Xu, C. K.

    2011-09-01

    We propose to map a complete sample of 88 local star-forming major-merger pairs (median redshift 0.04), using PACS and SPIRE photometers in 6 bands at 70, 100, 160, 250, 350 and 500 micron. The goal is to set the local benchmarks for the cosmic evolution of the SFR-to-gas relation (the Kennicutt-Schmidt law) for major-merger pairs, complementing a study on the K-S law for high-z mergers in the COSMOS field using the PEP and HerMES data. The K-S law for major mergers may be significantly different from that for normal galaxies. The SPIRE imaging at 250, 350, and 500 micron, together with PACS maps at shorter wavelengths, will probe the gas mass estimated from the dust mass. Dust is arguably the best proxy for total gas in galaxies spanning a wide redshift range, given the fact that it is still impossible to observe the HI gas in high redshift galaxies through the 21cm line emission. The PACS imaging at 70, 100, and 160 micron will map the star formation in these systems, with good angular resolutions (6 -- 12 arcsec) and at the wavelengths near the peak of the infrared dust emission. The local sample closely matches the high-z COSMOS pairs sample (278 pairs) in the pair selection criteria, both being stellar mass selected and including only spiral-spiral (S+S) and spiral-elliptical (S+E) major-merger pairs. This will facilitate studies on stellar mass dependence of the K-S law for major mergers with different redshifts. The large sample size enables good statistics even after separating the sample into subsamples of S+S pairs and of S+E pairs, and into several mass bins.

  7. A Multiwavelength Investigation of non-U/LIRG Galaxy Interactions: An Unexplored Frontier

    NASA Astrophysics Data System (ADS)

    Satyapal, Shobita

    Based on the current cold dark matter paradigm, it is now well-established that galaxy interactions are ubiquitous and that they play a pivotal role in the formation and evolution of galaxies. These interactions are likely responsible for a number of important phenomena such as the triggering of starbursts, the growth of massive black holes, and the formation of spheroids. Although significant progress has been made in the observational investigation of galaxy interactions, past studies have focused primarily on the most luminous galaxies and hence those with the most active star formation, or, have been limited to observations in the UV or optical, where the emission from the youngest stars or from a recently ignited AGN, is likely to be obscured. As a result, existing studies generally capture a very specific interaction stage, which may miss the onset of star formation or accretion activity in the galaxy centers. To address this serious deficiency, we propose a comprehensive multiwavelength spectroscopic study of a sample of non-U/LIRG interacting galaxies for which archival Spitzer high-resolution spectroscopic observations are available. Our sample includes both mergers with clear morphological signatures of interactions, as well as physically associated pairs with no evidence of tidal distortion or structural peculiarity. In this proposed study, we will analyze the archival Spitzer IRS high resolution spectra and GALEX images for this sample. We will: 1) search for buried AGNs, including binary AGNs, and determine their effects on the surrounding ISM, 2) constrain the nuclear star formation properties, 3) explore the morphology of the extended star formation, and 4) characterize the state of the ISM. The proposed galaxy sample was strategically chosen to target a previously unexplored population of interacting galaxies, which will complement more extensively studied samples of isolated normal galaxies and more infrared luminous galaxies. Together with these

  8. Effect of Halo Mass on HI Gas Content of Galaxies in Groups and Clusters

    NASA Astrophysics Data System (ADS)

    Yoon, Ilsang; Rosenberg, J. L.

    2014-01-01

    We combine the Sloan Digital Sky Survey (SDSS) and the Arecibo Legacy Fast ALFA (ALFALFA) Survey to study the distribution of cold atomic gas fraction of galaxies that reside in groups and clusters in local Universe. A careful cross-matching between galaxies in SDSS, ALFALFA, and SDSS halo group catalog produces a sample of galaxies with decent statistics in the stellar mass range 108.4 M⊙ ≦ M* ≦ 1010.6 M⊙ and the halo mass range 1012.5 h-1 M⊙ ≦ Mh ≦ 1015.0 h-1 M⊙ for a range of projected distance from the group center 0.04 ≦ r/rvir ≦ 2.0. In order to limit our study to group and cluster interaction processes (not tidal stripping in pairs), we remove close pairs that may be undergoing tidal interactions from the sample. We construct a comparison sample from the isolated field galaxies and investigate the radial distribution of the gas-to-stellar mass ratio for galaxies in groups and clusters relative to the comparison samples with similar stellar mass and redshift. We find that the gas-to-stellar mass ratio decreases toward the centers of groups with halo mass greater than ≈ 1013.8 h-1 M⊙ but find no such trend for galaxies in small halo mass groups. This halo mass dependent effect suggests that there is a threshold for efficient gas stripping due to interaction between galaxies and intracluster medium (ICM). This trend together with the HI line profile properties of our sample galaxies in groups and clusters is consistent with the ram pressure stripping. In particular, the observed relationship between stripping and halo mass is predicted by the classical Gunn-Gott ram pressure stripping criterion modified by scaling relations for galaxies and dark matter halo, which indicates that there is a threshold halo mass for efficient ram pressure stripping for given galaxy stellar mass and ICM temperature. This study was funded by NSF grant AST-000167932.

  9. Velocity correlations of galaxy clusters

    NASA Technical Reports Server (NTRS)

    Cen, Renyue; Bahcall, Neta A.; Gramann, Mirt

    1994-01-01

    We determine the velocity correlation function, pairwise peculiar velocity difference, and rms pairwise peculiar velocity dispersion of rich clusters of galaxies, as a function of pair separation, for three cosmological models: Omega = 1 and Omega = 0.3 cold dark matter (CDM), and Omega = 0.3 primeval baryonic isocurvature (PBI) models (all flat and Cosmic Background Explorer (COBE)-normalized). We find that close cluster pairs, with separation r is less than or equal to 10/h Mpc, exhibit strong attractive peculiar velocities in all models; the cluster pairwise velocities depend sensitively on the model. The mean pairwise attractive velocity of clusters on 5/h Mpc scale ranges from approximately 1700 km/s for Omega = 1 CDM to approximately 1000 km/s for PBI to approximately 700 km/s for Omega = 0.3 CDM. The small-scale pairwise velocities depend also on cluster mass: richer, more massive clusters exhibit stronger attractive velocities than less massive clusters. On large scales, from approximately 20 to 200/h Mpc, the cluster peculiar velocities are increasingly dominated by bulk and random motions; they are independent of cluster mass. The cluster velocity correlation function is negative on small scales for Omega = 1 and Omega = 0.3 CDM, indicating strong pairwise motion relative to bulk motion on small scales; PBI exhibits relatively larger bulk motions. The cluster velocity correlation function is positive on very large scales, from r approximately 10/h Mpc to r approximately 200/h Mpc, for all models. These positive correlations, which decrease monotonically with scale, indicate significant bulk motions of clusters up to approximately 200/h Mpc. The strong dependence of the cluster velocity functions on models, especially at small separations, makes them useful tools in constraining cosmological models when compared with observations.

  10. Galaxy Zoo: Mergers - Dynamical models of interacting galaxies

    NASA Astrophysics Data System (ADS)

    Holincheck, Anthony J.; Wallin, John F.; Borne, Kirk; Fortson, Lucy; Lintott, Chris; Smith, Arfon M.; Bamford, Steven; Keel, William C.; Parrish, Michael

    2016-06-01

    The dynamical history of most merging galaxies is not well understood. Correlations between galaxy interaction and star formation have been found in previous studies, but require the context of the physical history of merging systems for full insight into the processes that lead to enhanced star formation. We present the results of simulations that reconstruct the orbit trajectories and disturbed morphologies of pairs of interacting galaxies. With the use of a restricted three-body simulation code and the help of citizen scientists, we sample 105 points in parameter space for each system. We demonstrate a successful recreation of the morphologies of 62 pairs of interacting galaxies through the review of more than 3 million simulations. We examine the level of convergence and uniqueness of the dynamical properties of each system. These simulations represent the largest collection of models of interacting galaxies to date, providing a valuable resource for the investigation of mergers. This paper presents the simulation parameters generated by the project. They are now publicly available in electronic format at http://data.galaxyzoo.org/mergers.html. Though our best-fitting model parameters are not an exact match to previously published models, our method for determining uncertainty measurements will aid future comparisons between models. The dynamical clocks from our models agree with previous results of the time since the onset of star formation from starburst models in interacting systems and suggest that tidally induced star formation is triggered very soon after closest approach.

  11. 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

  12. Anisotropic magnification distortion of the 3D galaxy correlation. II. Fourier and redshift space

    SciTech Connect

    Hui Lam; Gaztanaga, Enrique; LoVerde, Marilena

    2008-03-15

    In paper I of this series we discuss how magnification bias distorts the 3D correlation function by enhancing the observed correlation in the line-of-sight (LOS) orientation, especially on large scales. This lensing anisotropy is distinctive, making it possible to separately measure the galaxy-galaxy, galaxy-magnification and magnification-magnification correlations. Here we extend the discussion to the power spectrum and also to redshift space. In real space, pairs oriented close to the LOS direction are not protected against nonlinearity even if the pair separation is large; this is because nonlinear fluctuations can enter through gravitational lensing at a small transverse separation (or i.e. impact parameter). The situation in Fourier space is different: by focusing on a small wave number k, as is usually done, linearity is guaranteed because both the LOS and transverse wave numbers must be small. This is why magnification distortion of the galaxy correlation appears less severe in Fourier space. Nonetheless, the effect is non-negligible, especially for the transverse Fourier modes, and should be taken into account in interpreting precision measurements of the galaxy power spectrum, for instance those that focus on the baryon oscillations. The lensing induced anisotropy of the power spectrum has a shape that is distinct from the more well-known redshift space anisotropies due to peculiar motions and the Alcock-Paczynski effect. The lensing anisotropy is highly localized in Fourier space while redshift space distortions are more spread out. This means that one could separate the magnification bias component in real observations, implying that potentially it is possible to perform a gravitational lensing measurement without measuring galaxy shapes.

  13. 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

  14. A Microlensing Measurement of Dark Matter Fractions in Three Lensing Galaxies

    NASA Astrophysics Data System (ADS)

    Bate, N. F.; Floyd, D. J. E.; Webster, R. L.; Wyithe, J. S. B.

    2011-04-01

    Direct measurements of dark matter distributions in galaxies are currently only possible through the use of gravitational lensing observations. Combinations of lens modeling and stellar velocity dispersion measurements provide the best constraints on dark matter distributions in individual galaxies, however they can be quite complex. In this paper, we use observations and simulations of gravitational microlensing to measure the smooth (dark) matter mass fraction at the position of lensed images in three lens galaxies: MG 0414+0534, SDSS J0924+0219, and Q2237+0305. The first two systems consist of early-type lens galaxies, and both display a flux ratio anomaly in their close image pair. Anomalies such as these suggest that a high smooth matter percentage is likely, and indeed we prefer ~50% smooth matter in MG 0414+0534 and ~80% in SDSS J0924+0219 at the projected locations of the lensed images. Q2237+0305 differs somewhat in that its lensed images lie in the central kiloparsec of the barred spiral lens galaxy, where we expect stars to dominate the mass distribution. In this system, we find a smooth matter percentage that is consistent with zero. This paper uses data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

  15. A MICROLENSING MEASUREMENT OF DARK MATTER FRACTIONS IN THREE LENSING GALAXIES

    SciTech Connect

    Bate, N. F.; Webster, R. L.; Wyithe, J. S. B.; Floyd, D. J. E.

    2011-04-10

    Direct measurements of dark matter distributions in galaxies are currently only possible through the use of gravitational lensing observations. Combinations of lens modeling and stellar velocity dispersion measurements provide the best constraints on dark matter distributions in individual galaxies, however they can be quite complex. In this paper, we use observations and simulations of gravitational microlensing to measure the smooth (dark) matter mass fraction at the position of lensed images in three lens galaxies: MG 0414+0534, SDSS J0924+0219, and Q2237+0305. The first two systems consist of early-type lens galaxies, and both display a flux ratio anomaly in their close image pair. Anomalies such as these suggest that a high smooth matter percentage is likely, and indeed we prefer {approx}50% smooth matter in MG 0414+0534 and {approx}80% in SDSS J0924+0219 at the projected locations of the lensed images. Q2237+0305 differs somewhat in that its lensed images lie in the central kiloparsec of the barred spiral lens galaxy, where we expect stars to dominate the mass distribution. In this system, we find a smooth matter percentage that is consistent with zero.

  16. 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.

  17. 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.

  18. The Assembly of Galaxy Clusters

    SciTech Connect

    Berrier, Joel C.; Stewart, Kyle R.; Bullock, James S.; Purcell, Chris W.; Barton, Elizabeth J.; Wechsler, Risa H.

    2008-05-16

    We study the formation of fifty-three galaxy cluster-size dark matter halos (M = 10{sup 14.0-14.76} M{sub {circle_dot}}) formed within a pair of cosmological {Lambda}CDM N-body simulations, and track the accretion histories of cluster subhalos with masses large enough to host {approx} 0.1L{sub *} galaxies. By associating subhalos with cluster galaxies, we find the majority of galaxies in clusters experience no 'pre-processing' in the group environment prior to their accretion into the cluster. On average, {approx} 70% of cluster galaxies fall into the cluster potential directly from the field, with no luminous companions in their host halos at the time of accretion; and less than {approx} 12% are accreted as members of groups with five or more galaxies. Moreover, we find that cluster galaxies are significantly less likely to have experienced a merger in the recent past ({approx}< 6 Gyr) than a field halo of the same mass. These results suggest that local, cluster processes like ram-pressure stripping, galaxy harassment, or strangulation play the dominant role in explaining the difference between cluster and field populations at a fixed stellar mass; and that pre-evolution or past merging in the group environment is of secondary importance for setting cluster galaxy properties for most clusters. The accretion times for z = 0 cluster members are quite extended, with {approx} 20% incorporated into the cluster halo more than 7 Gyr ago and {approx} 20% within the last 2 Gyr. By comparing the observed morphological fractions in cluster and field populations, we estimate an approximate time-scale for late-type to early-type transformation within the cluster environment to be {approx} 6 Gyr.

  19. DECISION TREE CLASSIFIERS FOR STAR/GALAXY SEPARATION

    SciTech Connect

    Vasconcellos, E. C.; Ruiz, R. S. R.; De Carvalho, R. R.; Capelato, H. V.; Gal, R. R.; LaBarbera, F. L.; Frago Campos Velho, H.; Trevisan, M.

    2011-06-15

    We study the star/galaxy classification efficiency of 13 different decision tree algorithms applied to photometric objects in the Sloan Digital Sky Survey Data Release Seven (SDSS-DR7). Each algorithm is defined by a set of parameters which, when varied, produce different final classification trees. We extensively explore the parameter space of each algorithm, using the set of 884,126 SDSS objects with spectroscopic data as the training set. The efficiency of star-galaxy separation is measured using the completeness function. We find that the Functional Tree algorithm (FT) yields the best results as measured by the mean completeness in two magnitude intervals: 14 {<=} r {<=} 21 (85.2%) and r {>=} 19 (82.1%). We compare the performance of the tree generated with the optimal FT configuration to the classifications provided by the SDSS parametric classifier, 2DPHOT, and Ball et al. We find that our FT classifier is comparable to or better in completeness over the full magnitude range 15 {<=} r {<=} 21, with much lower contamination than all but the Ball et al. classifier. At the faintest magnitudes (r > 19), our classifier is the only one that maintains high completeness (>80%) while simultaneously achieving low contamination ({approx}2.5%). We also examine the SDSS parametric classifier (psfMag - modelMag) to see if the dividing line between stars and galaxies can be adjusted to improve the classifier. We find that currently stars in close pairs are often misclassified as galaxies, and suggest a new cut to improve the classifier. Finally, we apply our FT classifier to separate stars from galaxies in the full set of 69,545,326 SDSS photometric objects in the magnitude range 14 {<=} r {<=} 21.

  20. 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

  1. 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

  2. Exploring Evolution Through the Effects of Galaxy-Galaxy and Group Interactions on Gas Content

    NASA Astrophysics Data System (ADS)

    Fertig, Derek; Rosenberg, J. L.; Patton, D. R.; Ellison, S. L.

    2014-01-01

    Galaxy-galaxy interactions are a driving force in galaxy evolution, producing changes in color, morphology, metallicity and enhancing star formation. Many factors contributing to these changes have been well studied such as environment and orientation of the interaction, however studies of the gas content have been limited. To address the question of how interactions affect the gas content of galaxy pairs, we present results from two studies taking different approaches to the question. We present results from a combined optical and HI 21 cm study of 102 galaxy pairs with projected separations up to 120 kpc and velocity differences less than 500 km/s. These pairs were selected from the SDSS spectroscopic survey and were also observed by the ALFALFA HI 21 cm survey. We use these data to study how interactions effect the SFE and HI gas content of these systems. From the second study we present initial results from VLA D-array observations of a galaxy group in which interactions appear to be removing much of the cold gas from the galaxies creating a large reservoir in the inter-group medium. We investigate how this removal of gas and subsequent reservoir impact the evolution of the galaxies within the group, particularly two systems which are transitioning through the green valley. This work has been supported by NSF grant AST-000167932 and a George Mason University Presidential Fellowship.

  3. 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.

  4. Slowly fading super-luminous supernovae that are not pair-instability explosions.

    PubMed

    Nicholl, M; Smartt, S J; Jerkstrand, A; Inserra, C; McCrum, M; Kotak, R; Fraser, M; Wright, D; Chen, T-W; Smith, K; Young, D R; Sim, S A; Valenti, S; Howell, D A; Bresolin, F; Kudritzki, R P; Tonry, J L; Huber, M E; Rest, A; Pastorello, A; Tomasella, L; Cappellaro, E; Benetti, S; Mattila, S; Kankare, E; Kangas, T; Leloudas, G; Sollerman, J; Taddia, F; Berger, E; Chornock, R; Narayan, G; Stubbs, C W; Foley, R J; Lunnan, R; Soderberg, A; Sanders, N; Milisavljevic, D; Margutti, R; Kirshner, R P; Elias-Rosa, N; Morales-Garoffolo, A; Taubenberger, S; Botticella, M T; Gezari, S; Urata, Y; Rodney, S; Riess, A G; Scolnic, D; Wood-Vasey, W M; Burgett, W S; Chambers, K; Flewelling, H A; Magnier, E A; Kaiser, N; Metcalfe, N; Morgan, J; Price, P A; Sweeney, W; Waters, C

    2013-10-17

    Super-luminous supernovae that radiate more than 10(44) ergs per second at their peak luminosity have recently been discovered in faint galaxies at redshifts of 0.1-4. Some evolve slowly, resembling models of 'pair-instability' supernovae. Such models involve stars with original masses 140-260 times that of the Sun that now have carbon-oxygen cores of 65-130 solar masses. In these stars, the photons that prevent gravitational collapse are converted to electron-positron pairs, causing rapid contraction and thermonuclear explosions. Many solar masses of (56)Ni are synthesized; this isotope decays to (56)Fe via (56)Co, powering bright light curves. Such massive progenitors are expected to have formed from metal-poor gas in the early Universe. Recently, supernova 2007bi in a galaxy at redshift 0.127 (about 12 billion years after the Big Bang) with a metallicity one-third that of the Sun was observed to look like a fading pair-instability supernova. Here we report observations of two slow-to-fade super-luminous supernovae that show relatively fast rise times and blue colours, which are incompatible with pair-instability models. Their late-time light-curve and spectral similarities to supernova 2007bi call the nature of that event into question. Our early spectra closely resemble typical fast-declining super-luminous supernovae, which are not powered by radioactivity. Modelling our observations with 10-16 solar masses of magnetar-energized ejecta demonstrates the possibility of a common explosion mechanism. The lack of unambiguous nearby pair-instability events suggests that their local rate of occurrence is less than 6 × 10(-6) times that of the core-collapse rate. PMID:24132291

  5. Slowly fading super-luminous supernovae that are not pair-instability explosions

    NASA Astrophysics Data System (ADS)

    Nicholl, M.; Smartt, S. J.; Jerkstrand, A.; Inserra, C.; McCrum, M.; Kotak, R.; Fraser, M.; Wright, D.; Chen, T.-W.; Smith, K.; Young, D. R.; Sim, S. A.; Valenti, S.; Howell, D. A.; Bresolin, F.; Kudritzki, R. P.; Tonry, J. L.; Huber, M. E.; Rest, A.; Pastorello, A.; Tomasella, L.; Cappellaro, E.; Benetti, S.; Mattila, S.; Kankare, E.; Kangas, T.; Leloudas, G.; Sollerman, J.; Taddia, F.; Berger, E.; Chornock, R.; Narayan, G.; Stubbs, C. W.; Foley, R. J.; Lunnan, R.; Soderberg, A.; Sanders, N.; Milisavljevic, D.; Margutti, R.; Kirshner, R. P.; Elias-Rosa, N.; Morales-Garoffolo, A.; Taubenberger, S.; Botticella, M. T.; Gezari, S.; Urata, Y.; Rodney, S.; Riess, A. G.; Scolnic, D.; Wood-Vasey, W. M.; Burgett, W. S.; Chambers, K.; Flewelling, H. A.; Magnier, E. A.; Kaiser, N.; Metcalfe, N.; Morgan, J.; Price, P. A.; Sweeney, W.; Waters, C.

    2013-10-01

    Super-luminous supernovae that radiate more than 1044 ergs per second at their peak luminosity have recently been discovered in faint galaxies at redshifts of 0.1-4. Some evolve slowly, resembling models of `pair-instability' supernovae. Such models involve stars with original masses 140-260 times that of the Sun that now have carbon-oxygen cores of 65-130 solar masses. In these stars, the photons that prevent gravitational collapse are converted to electron-positron pairs, causing rapid contraction and thermonuclear explosions. Many solar masses of 56Ni are synthesized; this isotope decays to 56Fe via 56Co, powering bright light curves. Such massive progenitors are expected to have formed from metal-poor gas in the early Universe. Recently, supernova 2007bi in a galaxy at redshift 0.127 (about 12 billion years after the Big Bang) with a metallicity one-third that of the Sun was observed to look like a fading pair-instability supernova. Here we report observations of two slow-to-fade super-luminous supernovae that show relatively fast rise times and blue colours, which are incompatible with pair-instability models. Their late-time light-curve and spectral similarities to supernova 2007bi call the nature of that event into question. Our early spectra closely resemble typical fast-declining super-luminous supernovae, which are not powered by radioactivity. Modelling our observations with 10-16 solar masses of magnetar-energized ejecta demonstrates the possibility of a common explosion mechanism. The lack of unambiguous nearby pair-instability events suggests that their local rate of occurrence is less than 6 × 10-6 times that of the core-collapse rate.

  6. Satellites as probes of the masses of spiral galaxies.

    PubMed

    Erickson, L K; Gottesman, S T; Hunter, J H

    1998-12-30

    We present atomic hydrogen (HI) observations and analyses of the kinematics of satellite-primary galaxy pairs. Two estimates for the masses of the primaries are available, one from their rotation curves and one from the orbital properties of the satellites. Defining chi as the ratio of these two mass estimates, it is a measure of the presence, or absence, of a significant halo. The chi distribution is presented and the selection effects are discussed. We show that our data, compared with the more numerous pairs identified by Zaritsky et al., have similar distributions for projected separations of less than 200 kpc, even though the selection criteria employed were quite different. Observational biases have a negligible effect; the biased and unbiased distributions are essentially identical. N-body calculations were executed to simulate the dynamical behavior of relatively low mass satellites orbiting primary disk galaxies with and without extended halos. In addition, we made a partially analytical analysis of the behavior of orbits in a logarithmic potential. We find that a "generic" model, characterized by a single disk-halo combination, cannot reproduce the observed P(chi) distribution. However, a simple two-component population of galaxies, composed of not more than 60% with halos and 40% without halos, is successful, if galaxies have dimensions of order 200 kpc. If galaxies are considerably larger with sizes extending to 400 kpc or more, no generic model can describe the full range of the observed P(chi), particularly if the distribution for r(p) < 200 kpc is compared with that for r(p) > 200 kpc. Regardless of the mix of orbital eccentricities, neither pure halo, nor canonical models (disk and halo masses are comparable within the disk radius) will work. A multicomponent approximation can be constructed; the canonical model must be mixed with a small fraction of systems essentially devoid of a massive dark halo. Only by including these complexities can the full

  7. 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.

  8. 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.

  9. Andromeda Galaxy

    NASA Astrophysics Data System (ADS)

    Walterbos, R.; Murdin, P.

    2000-11-01

    The Andromeda galaxy is the closest SPIRAL GALAXY to the MILKY WAY, just visible to the naked eye on a dark night as a faint smudge of light in the constellation Andromeda. The earliest records of the Andromeda nebula, as it is still often referred to, date back to AD 964, to the `Book of the Fixed Stars' published by the Persian astronomer AL-SÛFI. The first European to officially note the Andro...

  10. 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

  11. Environment of Seyfert 2 galaxies: the group of galaxies around NGC5252.

    NASA Astrophysics Data System (ADS)

    Freudling, W.; Prieto, M. Almudena

    1996-02-01

    The relatively large neutral hydrogen contents and enhanced density of companion galaxies around Seyfert 2 galaxies suggests that tidal interaction could play a major role in the evolution of Seyfert 2 galaxies. Recent observations of the distribution of neutral hydrogen in the active S0 galaxy NGC5252 have shown a disturbed morphology which suggests that the HI in this galaxy could have been acquired through interaction with neighboring galaxies (Prieto & Freudling 1993 and 1995). We have searched for other HI rich galaxies within a radius of 25 arcmin and a redshift range of +/-600km/s around the center location and redshift of NGC5252. A total of five galaxies were found, four of them are cataloged galaxies with no previous redshifts available. These five galaxies were mapped with the VLA in order to search for signs of recent tidal interactions. The maps and derived HI parameters are presented and compared to the one of NGC5252, the sixth member of the group. Two of the galaxies (UGC 8635) are an interacting pair. No signs of other recent interactions were found. Using the Arecibo telescope, we also searched for intergalactic neutral hydrogen between the group members as another potential source of gas for NGC5252. Upper limits on intergroup gas are given for three positions. The lack of evidence for interaction among the galaxies could be interpreted in two different ways. Either interaction occurred in the distant past and triggered activity in this galaxy over a long period of time. Alternatively, factors other than the gas supply might be responsible for the observation that Seyfert 2 galaxies tend to be surrounded by a region of enhanced galaxy density.

  12. Active galaxies and the diffuse gamma-ray background

    NASA Technical Reports Server (NTRS)

    Kazanas, D.; Protheroe, R. J.

    1983-01-01

    Active galaxies are shown to account for the observed gamma ray background radiation if a steepening of the spectra above about 100 keV is present. An analytical model is discussed in which protons undergo Fermi acceleration at a shock in a spherical accretion flow onto a massive black hole. Relativistic protons with power law spectra, nuclear interactions producing gamma rays from neutal pion decay and electrons from pion-mu meson-electron decay, with a power law spectrum above several hundred MeV, synchrotron and inverse Compton losses steepening the electron spectrum, a photon spectrum close to the pion gamma spectrum and a high-energy gamma ray spectrum steepened by photon-photon pair production interactions with X rays are covered in the model. Comparisons are made with HEAO 2 data on active galaxies, which have estimated luminosities and radii consistent with the compactness necessary for producing the steepening predicted by the model. The active galaxies spectra would be described by a spherical accretion-shock model.

  13. The Zurich Environmental Study (ZENS) of Galaxies in Groups along the Cosmic Web. V. Properties and Frequency of Merging Satellites and Centrals in Different Environments

    NASA Astrophysics Data System (ADS)

    Pipino, A.; Cibinel, A.; Tacchella, S.; Carollo, C. M.; Lilly, S. J.; Miniati, F.; Silverman, J. D.; van Gorkom, J. H.; Finoguenov, A.

    2014-12-01

    We use the Zurich Environmental Study database to investigate the environmental dependence of the merger fraction Γ and merging galaxy properties in a sample of ~1300 group galaxies with M > 109.2 M ⊙ and 0.05 < z < 0.0585. In all galaxy mass bins investigated in our study, we find that Γ decreases by a factor of ~2-3 in groups with halo masses M HALO > 1013.5 M ⊙ relative to less massive systems, indicating a suppression of merger activity in large potential wells. In the fiducial case of relaxed groups only, we measure a variation of ΔΓ/Δlog (M HALO) ~ -0.07 dex-1, which is almost independent of galaxy mass and merger stage. At galaxy masses >1010.2 M ⊙, most mergers are dry accretions of quenched satellites onto quenched centrals, leading to a strong increase of Γ with decreasing group-centric distance at these mass scales. Both satellite and central galaxies in these high-mass mergers do not differ in color and structural properties from a control sample of nonmerging galaxies of equal mass and rank. At galaxy masses of <1010.2 M ⊙ where we mostly probe satellite-satellite pairs and mergers between star-forming systems close pairs (projected distance <10-20 kpc) show instead ~2 × enhanced (specific) star formation rates and ~1.5 × larger sizes than similar mass, nonmerging satellites. The increase in both size and star formation rate leads to similar surface star formation densities in the merging and control-sample satellite populations. Based on observations collected at the European Southern Observatory, La Silla Chile. Program ID 177.A-0680.

  14. THE ZURICH ENVIRONMENTAL STUDY (ZENS) OF GALAXIES IN GROUPS ALONG THE COSMIC WEB. V. PROPERTIES AND FREQUENCY OF MERGING SATELLITES AND CENTRALS IN DIFFERENT ENVIRONMENTS

    SciTech Connect

    Pipino, A.; Cibinel, A.; Tacchella, S.; Carollo, C. M.; Lilly, S. J.; Miniati, F.; Silverman, J. D.; Van Gorkom, J. H.; Finoguenov, A.

    2014-12-20

    We use the Zurich Environmental Study database to investigate the environmental dependence of the merger fraction Γ and merging galaxy properties in a sample of ∼1300 group galaxies with M > 10{sup 9.2} M {sub ☉} and 0.05 < z < 0.0585. In all galaxy mass bins investigated in our study, we find that Γ decreases by a factor of ∼2-3 in groups with halo masses M {sub HALO} > 10{sup 13.5} M {sub ☉} relative to less massive systems, indicating a suppression of merger activity in large potential wells. In the fiducial case of relaxed groups only, we measure a variation of ΔΓ/Δlog (M {sub HALO}) ∼ –0.07 dex{sup –1}, which is almost independent of galaxy mass and merger stage. At galaxy masses >10{sup 10.2} M {sub ☉}, most mergers are dry accretions of quenched satellites onto quenched centrals, leading to a strong increase of Γ with decreasing group-centric distance at these mass scales. Both satellite and central galaxies in these high-mass mergers do not differ in color and structural properties from a control sample of nonmerging galaxies of equal mass and rank. At galaxy masses of <10{sup 10.2} M {sub ☉} where we mostly probe satellite-satellite pairs and mergers between star-forming systems close pairs (projected distance <10-20 kpc) show instead ∼2 × enhanced (specific) star formation rates and ∼1.5 × larger sizes than similar mass, nonmerging satellites. The increase in both size and star formation rate leads to similar surface star formation densities in the merging and control-sample satellite populations.

  15. Fire within the Antennae Galaxies

    NASA Technical Reports Server (NTRS)

    2004-01-01

    This false-color image composite from NASA's Spitzer Space Telescope reveals hidden populations of newborn stars at the heart of the colliding 'Antennae' galaxies. These two galaxies, known individually as NGC 4038 and 4039, are located around 68 million light-years away and have been merging together for about the last 800 million years. The latest Spitzer observations provide a snapshot of the tremendous burst of star formation triggered in the process of this collision, particularly at the site where the two galaxies overlap.

    The image is a composite of infrared data from Spitzer and visible-light data from Kitt Peak National Observatory, Tucson, Ariz. Visible light from stars in the galaxies (blue and green) is shown together with infrared light from warm dust clouds heated by newborn stars (red).

    The two nuclei, or centers, of the merging galaxies show up as yellow-white areas, one above the other. The brightest clouds of forming stars lie in the overlap region between and left of the nuclei.

    Throughout the sky, astronomers have identified many of these so-called 'interacting' galaxies, whose spiral discs have been stretched and distorted by their mutual gravity as they pass close to one another. The distances involved are so large that the interactions evolve on timescales comparable to geologic changes on Earth. Observations of such galaxies, combined with computer models of these collisions, show that the galaxies often become forever bound to one another, eventually merging into a single, spheroidal-shaped galaxy.

    Wavelengths of 0.44 microns are represented in blue, .70 microns in green and 8.0 microns in red. This image was taken on Dec. 24, 2003.

  16. Towards a complete history of galaxy assembly: Major merger fractions at 2 ≤ z ≤ 6 in the CANDELS fields

    NASA Astrophysics Data System (ADS)

    Duncan, Kenneth James; Conselice, Chris; Mundy, Carl Joseph; CANDELS Collaboration

    2015-08-01

    In recent years, remarkable progress has been made in studying the growth of the first galaxies through studies of the luminosity functions, star-formation rates and stellar masses. However, there are still very few observational constraints on the merger rates of galaxies during this formative period. Such measurements are vital in understanding the importance of mergers in the early lives of today’s most massive galaxies and what role they played (if any) in the creation of the first quiescent galaxies already seen at z ˜ 4. We present new results on the major merger rates (mass ratios from 1:1 to 1:4) of galaxies at 2 ≤ z ≤ 6 in the CANDELS HST survey. By using PDF analysis of photometric close pairs we are able to compute accurate merger fractions for both mass and number density selected samples over the first few billion years of galaxy formation. We present the evolution of the merger fraction as well as the estimated merger rates, exploring their evolution with respect to semi-analytic models and hydrodynamical simulations. In conjunction with similar analysis being applied to wide-area surveys at z ≤ 3 (Mundy et al. in prep), this work represents the first consistent study of major mergers over the bulk of cosmic history. In addition to the evolution of the merger rate itself, we explore the effect of mergers on star-formation rates at high redshift through comparison of the properties of galaxies in merging systems to similar galaxies in isolated environments.

  17. 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

  18. 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.

  19. 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.

  20. 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.

  1. Galaxy formation

    SciTech Connect

    Silk, J.

    1984-11-01

    Implications of the isotropy of the cosmic microwave background on large and small angular scales for galaxy formation are reviewed. In primeval adiabatic fluctuations, a universe dominated by cold, weakly interacting nonbaryonic matter, e.g., the massive photino is postulated. A possible signature of photino annihilation in our galactic halo involves production of cosmic ray antiprotons. If the density is near its closure value, it is necessary to invoke a biasing mechanism for suppressing galaxy formation throughout most of the universe in order to reconcile the dark matter density with the lower astronomical determinations of the mean cosmological density. A mechanism utilizing the onset of primordial massive star formation to strip gaseous protogalaxies is described. Only the densest, early collapsing systems form luminous galaxies. (ESA)

  2. Photometric study of the peculiar galaxy NGC 2685

    SciTech Connect

    Gagen-Torn, V.A.; Popov, I.I.; Iakovleva, V.A.

    1984-04-01

    The results are given of detailed UBV photometry of the peculiar galaxy NGC 2685 based on 10 negatives obtained with the 2.6-m telescope of the Biurakan Observatory. Consideration of all the available observational data (photometric, spectroscopic, and polarization) suggests that NGC 2685 is a pair of colliding galaxies. 18 references.

  3. First Results from the ISO-IRAS Faint Galaxy Survey

    NASA Technical Reports Server (NTRS)

    Wolstencroft, R. D.; Wehrle, A. E.; Levine, D. A.

    1997-01-01

    We present the first result from the ISO-IRAS Faint Galaxy Survey (IIFGS), a program designed to obtain ISO observations of the most distant and luminous galaxies in the IRAS Faint Source Survey by filling short gaps in the ISO observing schedule with pairs of 12um ISOCAM AND 90um ISOPHOT observation.

  4. Late-stage galaxy mergers in cosmos to z ∼ 1

    SciTech Connect

    Lackner, C. N.; Silverman, J. D.; Salvato, M.; Kampczyk, P.; Kartaltepe, J. S.; Sanders, D.; Lee, N.; Capak, P.; Scoville, N.; Civano, F.; Halliday, C.; Ilbert, O.; Le Fèvre, O.; Jahnke, K.; Koekemoer, A. M.; Liu, C. T.; Sheth, K.

    2014-12-01

    The role of major mergers in galaxy and black hole formation is not well-constrained. To help address this, we develop an automated method to identify late-stage galaxy mergers before coalescence of the galactic cores. The resulting sample of mergers is distinct from those obtained using pair-finding and morphological indicators. Our method relies on median-filtering of high-resolution images to distinguish two concentrated galaxy nuclei at small separations. This method does not rely on low surface brightness features to identify mergers, and is therefore reliable to high redshift. Using mock images, we derive statistical contamination and incompleteness corrections for the fraction of late-stage mergers. The mock images show that our method returns an uncontaminated (<10%) sample of mergers with projected separations between 2.2 and 8 kpc out to z∼1. We apply our new method to a magnitude-limited (m{sub FW} {sub 814}<23) sample of 44,164 galaxies from the COSMOS HST/ACS catalog. Using a mass-complete sample with logM{sub ∗}/M{sub ⊙}>10.6 and 0.25galaxies shows that the merger rate for star-forming galaxies increases strongly with redshift, (1+z){sup 4.5±1.3}, while the merger rate for quiescent galaxies is consistent with no evolution, (1+z){sup 1.1±1.2}. The merger rate also becomes steeper with decreasing stellar mass. Limiting our sample to galaxies with spectroscopic redshifts from zCOSMOS, we find that the star formation rates and X-ray selected active galactic nucleus (AGN) activity in likely late-stage mergers are higher by factors of ∼2 relative to those of a control sample. Combining our sample with more

  5. A first site of galaxy cluster formation: complete spectroscopy of a protocluster at z = 6.01

    SciTech Connect

    Toshikawa, Jun; Kashikawa, Nobunari; Ishikawa, Shogo; Onoue, Masafusa; Overzier, Roderik; Shibuya, Takatoshi; Ota, Kazuaki; Shimasaku, Kazuhiro; Tanaka, Masayuki; Hayashi, Masao; Niino, Yuu

    2014-09-01

    We performed a systematic spectroscopic observation of a protocluster at z = 6.01 in the Subaru Deep Field. We took spectroscopy for all 53 i' dropout galaxies down to z' = 27.09 mag in/around the protocluster region. From these observations, we confirmed that 28 galaxies are at z ∼ 6, 10 of which are clustered in a narrow redshift range of Δz < 0.06. To trace the evolution of this primordial structure, we applied the same i' dropout selection and the same overdensity measurements used in the observations to a semi-analytic model built upon the Millennium Simulation. We obtain a relation between the significance of overdensities observed at z ∼ 6 and the predicted dark matter halo mass at z = 0. This protocluster with 6σ overdensity is expected to grow into a galaxy cluster with a mass of ∼5 × 10{sup 14} M {sub ☉} at z = 0. Ten galaxies within 10 comoving Mpc of the overdense region can, with more than an 80% probability, merge into a single dark matter halo by z = 0. No significant differences appeared in UV and Lyα luminosities between the protocluster and field galaxies, suggesting that this protocluster is still in the early phase of cluster formation before the onset of any obvious environmental effects. However, further observations are required to study other properties, such as stellar mass, dust, and age. We do find that galaxies tend to be in close pairs in this protocluster. These pair-like subgroups will coalesce into a single halo and grow into a more massive structure. We may witness an onset of cluster formation at z ∼ 6 toward a cluster as seen in local universe.

  6. 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.

  7. 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.

  8. 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

  9. 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

  10. Evidence for Evolution in the Galaxy Merger Rate

    NASA Astrophysics Data System (ADS)

    Franklin, Barbara E.; Windhorst, Rogier A.; Burkey, Jordan M.; Keel, William C.

    1993-12-01

    We use a set of four deep Cycle 1+2 fields with the HST Wide-Field Camera to constrain the rate of galaxy merging between the current epoch and approximately z=0.7. These fields were selected around weak radio sources not in rich or poor clusters so as to not bias these studies. Since most mergers occur between members of bound pairs, the merger rate is given by (half) the rate of disappearance of galaxy pairs. Using an objective criterion for pair membership, we find that more than 34% of galaxies in the magnitude range I=18-22 mag belong to pairs, while careful study of nearby comparison samples shows that only 7% of local galaxies belong to pairs. Hence, about 13% of the galaxy population has disappeared to merging in the cosmic epoch corresponding to this magnitude interval (or 0.1<= z<=0.7). This pair fraction is a lower limit, since correction for pairs in which one member falls below our detection threshold would raise the fraction of pair members with I=18---22 mag to about 50%. (we do not include physical system of higher multiplicity in these values). Hence, the number of galaxy pairs has dropped significantly between z ~ 0.7 and the current epoch. When using the best available I-band field galaxy redshift distributions, the HST pair-fraction grows with redshift as ~ (1+z)(3.0-3.5) , quite consistent with the expected evolution in the merger-rate from the decrease in comoving volume (~ (1+z)(3) ). This result has very significant implications for the interpretation of the ground-based galaxy counts (it explains the disappearance of faint blue galaxies), the cosmological evolution of faint radio sources and quasars (explains why these should indeed evolve as ~ (1+z)(3) ), the statistics of QSO companions, the galaxy content in distant clusters, and the merging history of a ``typical" galaxy. This work was supported by STScI grants GO-2405.*-87A and GO-3545.*-91A (to WCK and RAW) and in part through EPSCoR grant EHR-9108761 (to WCK).

  11. 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.

  12. 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

  13. Constraints on the merging channel of massive galaxies since z ˜ 1

    NASA Astrophysics Data System (ADS)

    Ferreras, I.; Trujillo, I.; Mármol-Queraltó, E.; Pérez-González, P. G.; Cava, A.; Barro, G.; Cenarro, J.; Hernán-Caballero, A.; Cardiel, N.; Rodríguez-Zaurín, J.; Cebrián, M.

    2014-10-01

    We probe the merging channel of massive galaxies over the z = 0.3-1.3 redshift window by studying close pairs in a sample of 238 galaxies with stellar mass ≳1011 M⊙, from the SHARDS (Survey for High-z Absorption Red and Dead Sources) survey. SHARDS provides medium-band photometry equivalent to low-resolution optical spectra (R ˜ 50), allowing us to obtain extremely accurate photometric redshifts (median |Δz|/(1 + z) ˜ 0.55 per cent) and to improve the constraints on the age distribution of the stellar populations. Our data set is volume limited, probing merger progenitors with mass ratios 1:100 (μ ≡ Msat/Mcen = 0.01) out to z = 1.3. A strong correlation is found between the age difference of host and companion galaxy and stellar mass ratio, from negligible age differences in major mergers to age differences ˜4 Gyr for 1:100 minor mergers. However, this correlation is simply a reflection of the mass-age trend in the general population. The dominant contributor to the growth of massive galaxies corresponds to mass ratios μ ≳ 0.3, followed by a decrease in the fractional mass growth rate linearly proportional to log μ, at least down to μ ˜ 0.01, suggesting a decreasing role of mergers involving low-mass companions, especially if dynamical friction time-scales are taken into account. A simple model results in an upper limit for the average mass growth rate of massive galaxies of (ΔM/M)/Δt ˜ 0.08 ± 0.02 Gyr-1, over the z ≲ 1 range, with an ˜70 per cent fractional contribution from (major) mergers with μ ≳ 0.3. The majority of the stellar mass contributed by mergers does not introduce significantly younger populations, in agreement with the small radial age gradients observed in present-day early-type galaxies.

  14. Sombrero Galaxy (M104) in Infrared Light

    NASA Technical Reports Server (NTRS)

    2003-01-01

    The razor sharp eye of the Hubble Space Telescope (HST) easily resolves the Sombrero galaxy, Messier 104 (M104). 50,000 light-years across, the galaxy is located 28 million light-years from Earth at the southern edge of the rich Virgo cluster of galaxies. Equivalent to 800 billion suns, Sombrero is one of the most massive objects in that group. The hallmark of Sombrero is a brilliant white, bulbous core encircled by the thick dust lanes comprising the spiral structure of the galaxy. As seen from Earth, the galaxy is tilted nearly edge-on. We view it from just six degrees north of its equatorial plane. This rich system of globular clusters is estimated to be nearly 2,000 in number which is 10 times as many as in our Milky Way galaxy. Similar to the clusters in the Milky Way, the ages range from 10-13 billion years old. Embedded in the bright core of M104 is a smaller disk, which is tilted relative to the large disk. The HST paired with the Spitzer infrared telescope, offers this striking composite capturing the magnificence of the Sombrero galaxy. In the Hubble view, the galaxy resembles a broad-rimmed Mexican hat, whereas in the Spitzer striking infrared view, the galaxy looks more like a bulls eye. The full view provided by Spitzer shows the disk is warped, which is often the result of a gravitational encounter with another galaxy, and clumpy areas spotted in the far edges of the ring indicate young star forming regions. Spitzer detected infrared emission not only from the ring, but from the center of the galaxy as well, where there is a huge black hole believed to be a billion times more massive than our Sun. The Marshall Space Flight Center (MSFC) had responsibility for design, development, and construction of the HST.

  15. 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.

  16. A statistical study of merging galaxies: Theory and observations

    NASA Technical Reports Server (NTRS)

    Chatterjee, Tapan K.

    1990-01-01

    A study of the expected frequency of merging galaxies is conducted, using the impulsive approximation. Results indicate that if we consider mergers involving galaxy pairs without halos in a single crossing time or orbital period, the expected frequency of mergers is two orders of magnitude below the observed value for the present epoch. If we consider mergers involving several orbital periods or crossing times, the expected frequency goes up by an order of magnitude. Preliminary calculation indicate that if we consider galaxy mergers between pairs with massive halos, the merger is very much hastened.

  17. 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

  18. Submillimeter Galaxies

    NASA Astrophysics Data System (ADS)

    Blain, A. W.

    2009-12-01

    The Universe was a more exciting place at moderate to high redshifts z˜3, after reionization took place, but before the present day galaxy properties were firmly established. From a wide variety of directions, we are gaining insight into the Universe at these epochs. Less gas was sequestered into stars and had been ejected into the interstellar medium as weakly emitting, slowly cooling debris, because a significant amount of star formation and supermassive blackhole growth in active galactic nuclei (AGNs) was still to occur. Furthermore, the processes that shape today’s galaxies were at work, and can be seen in real time with the appropriate tools. The most active regions of galaxies at these redshifts are deeply obscured at ultraviolet and optical wavelengths by an opaque interstellar medium (ISM) that absorbs most of their radiation, and then re-emits at far-infrared (IR) wavelengths. This emission provides us with a very powerful probe of the regions within galaxies where the most intense activity takes place; both their total energy output, and from spectroscopy, about the physics and chemistry of the atomic and molecular gas that fuels, hides and surrounds these regions. This information is unique, but not complete: radio, mid- and near-IR, optical and X-ray observations each provide unique complementary views. Nevertheless, probing the obscured Universe, with the Atacama Large (Sub-)Millimeter Array (ALMA), James Webb Space Telescope (JWST), Herschel Space Observatory, Wide Field Infrared Survey Explorer (WISE), and missions and telescopes that are not yet in construction, like an actively cooled sub-10-m class IR space telescope and a 25-m class ground-based submillimeter/THz telescope (CCAT) will provide a more complete picture of in which neighborhoods, by what means and how quickly the most vigorous bursts of activity take place.

  19. From Enigma to Tool: Gamma-Ray Burst Reveals Secrets of Host Galaxy

    NASA Astrophysics Data System (ADS)

    2001-05-01

    , astronomers debated whether the explosions were close, in our own Milky Way Galaxy, or far, in distant galaxies. In addition, a plethora of theories attempted to explain the bursts, but a lack of observational data prevented scientists from choosing among the theories. Optical and radio telescopes first spotted the "afterglows" from gamma- ray bursts in 1997. It was quickly determined that the explosions are occurring in very distant galaxies. Subsequent observations, most astronomers believe, have narrowed the theories down to two: either the explosions are the result of pairs of old, superdense neutron stars colliding with each other or are the death throes of young, very massive stars. "This burst in 1998 came from a region near the center of its host galaxy, where star birth is occuring at a rapid rate. This supports the theory that gamma-ray bursts come from the death explosions of very young, massive stars," said Kulkarni. The burst, known as GRB 980703, was detected by a satellite on July 3, 1998, and the VLA first observed it a day later. The astronomers continued to observe the object with the VLA at intervals over the next 1,000 days. This is the longest period over which a gamma-ray-burst afterglow ever has been observed; the previous record-holder was a burst in 1997 that was followed with the VLA for a period of 445 days. "The afterglow of the burst kept getting fainter with time, but we then noticed that the intensity of radio emission was leveling off. We realized that the burst afterglow was still fading, but what was remaining steady was radio emission from the galaxy itself," Berger said. This allowed the scientists to study the characteristics of the galaxy, and of the region within the galaxy where the burst occurred. They concluded that the gamma-ray burst occurred near the center of the galaxy in a region where the galaxy is experiencing its maximum amount of star formation. "If, as we believe, gamma-ray bursts come from the super-explosions of massive

  20. 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.

  1. THE PROPERTIES OF TYPE Ia SUPERNOVA HOST GALAXIES FROM THE SLOAN DIGITAL SKY SURVEY

    SciTech Connect

    Han, Du-Hwan; Park, Myeong-Gu; Park, Changbom; Choi, Yun-Young E-mail: mgp@knu.ac.k E-mail: yychoi@khu.ac.k

    2010-11-20

    We investigate the properties and environments of Type Ia Supernova (SN Ia) host galaxies in the Stripe 82 of the Sloan Digital Sky Survey-II Supernova Survey centered on the celestial equator. Host galaxies are defined as the galaxy nearest to the supernova (SN) in terms of angular distance whose velocity difference from the SN is less than 1000 km s{sup -1}. Eighty seven SN Ia host galaxies are selected from the SDSS Main galaxy sample with the apparent r-band magnitude m{sub r} < 17.77, and compared with the SDSS Main galaxies. The SN Ia rates for early- and late-type galaxies are 0.81 {+-} 0.19 SN (100 yr){sup -1} and 0.99 {+-} 0.21 SN (100 yr){sup -1}, respectively. We find that the host galaxies have a color distribution consistent with that of the Main galaxies, regardless of their morphology. However, host galaxies are on average brighter than the Main galaxies by {approx}0.3 mag over the range of -18.3>M{sub r} > - 21.3. But the brighter ends of their luminosity distributions are similar. The distribution of the distance to the nearest neighbor galaxy shows that SNe Ia are more likely to occur in isolated galaxies without close neighbors. We also find that the SN Ia host galaxies are preferentially located in a region close to massive galaxy clusters compared to the Main galaxies.

  2. A Compact Group of Galaxies at z = 2.48 Hosting an AGN-driven Outflow

    NASA Astrophysics Data System (ADS)

    Shih, Hsin-Yi; Stockton, Alan

    2015-12-01

    We present observations of a remarkable compact group of galaxies at z = 2.48. Four galaxies, all within 40 kpc of each other, surround a powerful high-redshift radio source. This group comprises two compact red passive galaxies and a pair of merging galaxies. One of the red galaxies, with an apparent stellar mass of 3.6 × 1011M⊙ and an effective radius of 470 pc, is one of the most extreme examples of a massive quiescent compact galaxy found so far. One of the pair of merging galaxies hosts the active galactic nucleus (AGN) producing the large powerful radio structure. The merger is massive and enriched, consistent with the mass-metallicity relation expected at this redshift. Close to the merging nuclei, the emission lines exhibit broad and asymmetric profiles that suggest outflows powered either by a very young expanding radio jet or by AGN radiation. At ≳50 kpc from the system, we found a fainter extended-emission region that may be a part of a radio-jet-driven outflow. Some of the data presented herein were obtained 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 Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The work is also based, in part, on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan, and on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciência, Tecnologia e Inovação (Brazil), and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina).

  3. Pair Production of Black Holes on Cosmic Strings

    NASA Astrophysics Data System (ADS)

    Hawking, S. W.; Ross, Simon F.

    1995-11-01

    We discuss the pair creation of black holes by the breaking of a cosmic string. We obtain an instanton describing this process from the C metric, and calculate its probability. This is very low for the strings that have been suggested for galaxy formation.

  4. 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

  5. Pairing forces in nuclei

    SciTech Connect

    Chasman, R.R.

    1996-12-31

    In this contribution, the author mentions some features of pairing forces that are unique to nuclei and cover some areas of major interest in nuclear structure research, that involve pairing. At the level of most nuclear structure studies, nuclei are treated as consisting of two kinds of fermions (protons and neutrons) in a valence space with rather few levels. These features give rise to unique aspects of pairing forces in nuclei: (1) n-p pairing in T = 0 as well as the usual T = 1 pairing that is characteristic of like fermions; (2) a need to correct pairing calculations for the (1/N) effects that can typically be neglected in superconducting solids. An issue of current concern is the nature of the pairing interaction: several recent studies suggest a need for a density dependent form of the pairing interaction. There is a good deal of feedback between the questions of accurate calculations of pairing interactions and the form and magnitude of the pairing interaction. Finally, the authors discuss some many-body wave functions that are a generalization of the BCS wave function form, and apply them to a calculation of energy level spacings in superdeformed rotational bands.

  6. The role of interactions in galaxy evolution: A new perspective from the CALIFA and MaNGA Integral Field Spectroscopic surveys.

    NASA Astrophysics Data System (ADS)

    Barrera-Ballesteros, J. K.; Sanchez, S. F.; Califa Collaboration

    2016-06-01

    Interactions and mergers have been playing a paramount role to understand how galaxies evolve. In recent years integral field spectroscopic (IFS) observations have become routinely allowing researchers to conduct large IFS surveys. In this context, these surveys are providing a new observational scenario to probe the properties of galaxies at different stages of the interaction —from close pairs to post-merger galaxies. Even more, these surveys also include homogeneous observations of non-interacting galaxies which in turns allows to distinguish the processes induce by secular evolution from those driven by interactions. In this talk, We review the studies of interacting studies from the CALIFA survey. They consider from the thorough analysis of a single interactive systems (e.g., the Mice, Wild et al. 2014) to the the statistical study of physical properties of a large sample of interacting/merging galaxies such as their internal structure via their stellar and gas line-of-sight kinematic maps (Barrera-Ballesteros et al. 2015a) or the spatial distribution of the star-forming gas in these galaxies (Barrera-Ballesteros et al. 2015b). Then we present some of the on-going studies within the MaNGA survey. Due to its statistical power (sample size ~10000 objects), this survey will allow us to probe the properties of galaxies in a wide range of the interaction-parameter space. This in turn provides a unique view on the key parameters that affect the internal structure and properties of galaxies during the interaction and subsequent merger.

  7. Galaxy interactions and strength of nuclear activity

    NASA Technical Reports Server (NTRS)

    Simkin, S. M.

    1990-01-01

    Analysis of data in the literature for differential velocities and projected separations of nearby Seyfert galaxies with possible companions shows a clear difference in projected separations between type 1's and type 2's. This kinematic difference between the two activity classes reinforces other independent evidence that their different nuclear characteristics are related to a non-nuclear physical distinction between the two classes. The differential velocities and projected separations of the galaxy pairs in this sample yield mean galaxy masses, sizes, and mass to light ratios which are consistent with those found by the statistical methods of Karachentsev. Although the galaxy sample discussed here is too small and too poorly defined to provide robust support for these conclusions, the results strongly suggest that nuclear activity in Seyfert galaxies is associated with gravitational perturbations from companion galaxies, and that there are physical distinctions between the host companions of Seyfert 1 and Seyfert 2 nuclei which may depend both on the environment and the structure of the host galaxy itself.

  8. Multi-messenger Efforts in the Search for Supermassive Black Hole Pairs

    NASA Astrophysics Data System (ADS)

    Spolaor, Sarah; LAZIO, J.; Pulsar Timing Array, Parkes

    2013-01-01

    A number of electromagnetic phenomena have been suggested to imply the presence of a supermassive black hole (SMBH) binary in the emission's host galaxy. No systems have been conclusively demonstrated to be a close binary (i.e. orbital periods <100 years, orbital separations < 30pc), despite that a positive identification would contribute to knowledge of the expected gravitational waveform from these objects and their role in cosmic evolution. We consider several cases where radio imaging on pc to kpc scales can clarify purported signatures of SMBH pairs or binaries. In some cases, pulsar timing's limits on gravitational waves from these systems can provide a powerful means to constrain, support, or disprove a binary SMBH hypothesis, and/or provide constraints on the origin of larger-scale jet behaviours in AGN. Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.

  9. 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.

  10. Dynamical analysis of the cluster pair: A3407 + A3408

    NASA Astrophysics Data System (ADS)

    Nascimento, R. S.; Ribeiro, A. L. B.; Trevisan, M.; Carrasco, E. R.; Plana, H.; Dupke, R.

    2016-08-01

    We carried out a dynamical study of the galaxy cluster pair A3407 \\& A3408 based on a spectroscopic survey obtained with the 4 meter Blanco telescope at the CTIO, plus 6dF data, and ROSAT All-Sky-Survey. The sample consists of 122 member galaxies brighter than $m_R=20$. Our main goal is to probe the galaxy dynamics in this field and verify if the sample constitutes a single galaxy system or corresponds to an ongoing merging process. Statistical tests were applied to clusters members showing that both the composite system A3407 + A3408 as well as each individual cluster have Gaussian velocity distribution. A velocity gradient of $\\sim 847\\pm 114$ $\\rm km\\;s^{-1}$ was identified around the principal axis of the projected distribution of galaxies, indicating that the global field may be rotating. Applying the KMM algorithm to the distribution of galaxies we found that the solution with two clusters is better than the single unit solution at the 99\\% c.l. This is consistent with the X-ray distribution around this field, which shows no common X-ray halo involving A3407 and A3408. We also estimated virial masses and applied a two-body model to probe the dynamics of the pair. The more likely scenario is that in which the pair is gravitationally bound and probably experiences a collapse phase, with the cluster cores crossing in less than $\\sim$1 $h^{-1}$ Gyr, a pre-merger scenario. The complex X-ray morphology, the gas temperature, and some signs of galaxy evolution in A3408 suggests a post-merger scenario, with cores having crossed each other $\\sim 1.65 h^{-1}$Gyr ago, as an alternative solution.

  11. Dynamical analysis of the cluster pair: A3407 + A3408

    NASA Astrophysics Data System (ADS)

    Nascimento, R. S.; Ribeiro, A. L. B.; Trevisan, M.; Carrasco, E. R.; Plana, H.; Dupke, R.

    2016-08-01

    We carried out a dynamical study of the galaxy cluster pair A3407 and A3408 based on a spectroscopic survey obtained with the 4 metre Blanco telescope at the Cerro Tololo Interamerican Observatory, plus 6dF data, and ROSAT All-Sky Survey. The sample consists of 122 member galaxies brighter than mR = 20. Our main goal is to probe the galaxy dynamics in this field and verify if the sample constitutes a single galaxy system or corresponds to an ongoing merging process. Statistical tests were applied to clusters members showing that both the composite system A3407 + A3408 as well as each individual cluster have Gaussian velocity distribution. A velocity gradient of ˜847 ± 114 km s- 1 was identified around the principal axis of the projected distribution of galaxies, indicating that the global field may be rotating. Applying the KMM algorithm to the distribution of galaxies, we found that the solution with two clusters is better than the single unit solution at the 99 per cent cl. This is consistent with the X-ray distribution around this field, which shows no common X-ray halo involving A3407 and A3408. We also estimated virial masses and applied a two-body model to probe the dynamics of the pair. The more likely scenario is that in which the pair is gravitationally bound and probably experiences a collapse phase, with the cluster cores crossing in less than ˜1 h-1 Gyr, a pre-merger scenario. The complex X-ray morphology, the gas temperature, and some signs of galaxy evolution in A3408 suggest a post-merger scenario, with cores having crossed each other ˜1.65 h-1 Gyr ago, as an alternative solution.

  12. Matched-pair classification

    SciTech Connect

    Theiler, James P

    2009-01-01

    Following an analogous distinction in statistical hypothesis testing, we investigate variants of machine learning where the training set comes in matched pairs. We demonstrate that even conventional classifiers can exhibit improved performance when the input data has a matched-pair structure. Online algorithms, in particular, converge quicker when the data is presented in pairs. In some scenarios (such as the weak signal detection problem), matched pairs can be generated from independent samples, with the effect not only doubling the nominal size of the training set, but of providing the structure that leads to better learning. A family of 'dipole' algorithms is introduced that explicitly takes advantage of matched-pair structure in the input data and leads to further performance gains. Finally, we illustrate the application of matched-pair learning to chemical plume detection in hyperspectral imagery.

  13. 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.

  14. Enhancement of galaxy images for improved classification

    NASA Astrophysics Data System (ADS)

    Jenkinson, John; Grigoryan, Artyom M.; Agaian, Sos S.

    2015-03-01

    In this paper, the classification accuracy of galaxy images is demonstrated to be improved by enhancing the galaxy images. Galaxy images often contain faint regions that are of similar intensity to stars and the image background, resulting in data loss during background subtraction and galaxy segmentation. Enhancement darkens these faint regions, enabling them to be distinguished from other objects in the image and the image background, relative to their original intensities. The heap transform is employed for the purpose of enhancement. Segmentation then produces a galaxy image which closely resembles the structure of the original galaxy image, and one that is suitable for further processing and classification. 6 Morphological feature descriptors are applied to the segmented images after a preprocessing stage and used to extract the galaxy image structure for use in training the classifier. The support vector machine learning algorithm performs training and validation of the original and enhanced data, and a comparison between the classification accuracy of each data set is included. Principal component analysis is used to compress the data sets for the purpose of classification visualization and a comparison between the reduced and original feature spaces. Future directions for this research include galaxy image enhancement by various methods, and classification performed with the use of a sparse dictionary. Both future directions are introduced.

  15. 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

  16. Hubble and Keck team up to find farthest known galaxy in the Universe

    NASA Astrophysics Data System (ADS)

    2004-02-01

    Galaxy cluster Abell 2218 hi-res Size hi-res: 5212 Kb Credits: European Space Agency, NASA, J.-P. Kneib (Observatoire Midi-Pyrénées) and R. Ellis (Caltech) Close-up of the large galaxy cluster Abell 2218 This close-up of the large galaxy cluster Abell 2218 shows how this cluster acts as one of nature’s most powerful ‘gravitational telescopes’ and amplifies and stretches all galaxies lying behind the cluster core (seen as red, orange and blue arcs). Such natural gravitational ‘telescopes’ allow astronomers to see extremely distant and faint objects that could otherwise not be seen. A new galaxy (split into two ‘images’ marked with an ellipse and a circle) was detected in this image taken with the Advanced Camera for Surveys on board the NASA/ESA Hubble Space Telescope. The extremely faint galaxy is so far away that its visible light has been stretched into infrared wavelengths, making the observations particularly difficult. The galaxy may have set a new record in being the most distant known galaxy in the Universe. Located an estimated 13 billion light-years away (z~7), the object is being viewed at a time only 750 million years after the big bang, when the Universe was barely 5 percent of its current age. In the image the distant galaxy appears as multiple ‘images’, an arc (left) and a dot (right), as its light is forced along different paths through the cluster’s complex clumps of mass (the yellow galaxies) where the magnification is quite large. The colour of the different lensed galaxies in the image is a function of their distances and galaxy types. The orange arc is for instance an elliptical galaxy at moderate redshift (z=0.7) and the blue arcs are star forming galaxies at intermediate redshift (z between 1 and 2.5). An image of Abell 2218 hi-res Size hi-res: 29 563 Kb Credits: European Space Agency, NASA, J.-P. Kneib (Observatoire Midi-Pyrénées) and R. Ellis (Caltech) A ground-based wide-angle image of Abell 2218 This wide

  17. 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.

  18. Galaxy Groups

    NASA Astrophysics Data System (ADS)

    Tully, R. Brent

    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}12}{{M}⊙ } 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}matter}˜ 0.15 in a flat topology, with a 68% probability of being less than 0.44.

  19. Deep MUSE observations in the HDFS. Morpho-kinematics of distant star-forming galaxies down to 108M⊙

    NASA Astrophysics Data System (ADS)

    Contini, T.; Epinat, B.; Bouché, N.; Brinchmann, J.; Boogaard, L. A.; Ventou, E.; Bacon, R.; Richard, J.; Weilbacher, P. M.; Wisotzki, L.; Krajnović, D.; Vielfaure, J.-B.; Emsellem, E.; Finley, H.; Inami, H.; Schaye, J.; Swinbank, M.; Guérou, A.; Martinsson, T.; Michel-Dansac, L.; Schroetter, I.; Shirazi, M.; Soucail, G.

    2016-06-01

    Aims: Whereas the evolution of gas kinematics of massive galaxies is now relatively well established up to redshift z ~ 3, little is known about the kinematics of lower mass (M⋆≤ 1010M⊙) galaxies. We use MUSE, a powerful wide-field, optical integral-field spectrograph (IFS) recently mounted on the VLT, to characterize this galaxy population at intermediate redshift. Methods: We made use of the deepest MUSE observations performed so far on the Hubble Deep Field South (HDFS). This data cube, resulting from 27 h of integration time, covers a one arcmin2 field of view at an unprecedented depth (with a 1σ emission-line surface brightness limit of 1 × 10-19 erg s-1 cm-2 arcsec-2) and a final spatial resolution of ≈0.7''. We identified a sample of 28 resolved emission-line galaxies, extending over an area that is at least twice the seeing disk, spread over a redshift interval of 0.2 galaxies are at z ~ 0.3 - 0.7, which is a redshift range poorly studied so far with IFS kinematics. We used the public HST images and multiband photometry over the HDFS to constrain the stellar mass and star formation rate (SFR) of the galaxies and to perform a morphological analysis using Galfit, providing estimates of the disk inclination, disk scale length, and position angle of the major axis. We derived the resolved ionized gas properties of these galaxies from the MUSE data and model the disk (both in 2D and in 3D with GalPaK3D) to retrieve their intrinsic gas kinematics, including the maximum rotation velocity and velocity dispersion. Results: We build a sample of resolved emission-line galaxies of much lower stellar mass and SFR (by ~1 - 2 orders of magnitude) than previous IFS surveys. The gas kinematics of most of the spatially resolved MUSE-HDFS galaxies is consistent with disk-like rotation, but about 20% have velocity dispersions that are larger than the rotation velocities and 30% are part of a close pair and/or show clear signs of recent

  20. Pairing, pseudogap and Fermi arcs in cuprates

    SciTech Connect

    Kaminski, Adam; Kondo, Takeshi; Takeuchi, Tsunehiro; Gu, Genda

    2014-04-29

    We use Angle Resolved Photoemission Spectroscopy (ARPES) to study the relationship between the pseudogap, pairing and Fermi arcs in cuprates. High quality data measured over a wide range of dopings reveals a consistent picture of Fermiology and pairing in these materials. The pseudogap is due to an ordered state that competes with superconductivity rather than preformed pairs. Pairing does occur below Tpair ~ 150K and significantly above Tc, but well below T* and the doping dependence of this temperature scale is distinct from that of the pseudogap. The d-wave gap is present below Tpair, and its interplay with strong scattering creates “artificial” Fermi arcs for Tc ≤ T ≤ Tpair. However, above Tpair, the pseudogap exists only at the antipodal region. This leads to presence of real, gapless Fermi arcs close to the node. The length of these arcs remains constant up to T*, where the full Fermi surface is recovered. As a result, we demonstrate that these findings resolve a number of seemingly contradictory scenarios.

  1. Cooper Pairs in Insulators?!

    ScienceCinema

    James Valles

    2010-01-08

    Nearly 50 years elapsed between the discovery of superconductivity and the emergence of the microscopic theory describing this zero resistance state. The explanation required a novel phase of matter in which conduction electrons joined in weakly bound pairs and condensed with other pairs into a single quantum state. Surprisingly, this Cooper pair formation has also been invoked to account for recently uncovered high-resistance or insulating phases of matter. To address this possibility, we have used nanotechnology to create an insulating system that we can probe directly for Cooper pairs. I will present the evidence that Cooper pairs exist and dominate the electrical transport in these insulators and I will discuss how these findings provide new insight into superconductor to insulator quantum phase transitions. 

  2. Pair contact process with diffusion of pairs

    NASA Astrophysics Data System (ADS)

    Santos, F. L.; Dickman, Ronald; Fulco, U. L.

    2011-03-01

    The pair contact process (PCP) is a nonequilibrium stochastic model which, like the basic contact process (CP), exhibits a phase transition to an absorbing state. The two models belong to the directed percolation (DP) universality class, despite the fact that the PCP possesses infinitely many absorbing configurations whereas the CP has but one. The critical behavior of the PCP with hopping by particles (PCPD) is as yet unclear. Here we study a version of the PCP in which nearest-neighbor particle pairs can hop but individual particles cannot. Using quasistationary simulations for three values of the diffusion probability (D = 0.1, 0.5 and 0.9), we find convincing evidence of DP-like critical behavior.

  3. Host Galaxies of X-Shaped Radio Sources

    SciTech Connect

    Springmann, Alessondra; /Wellesley Coll. /SLAC

    2006-09-27

    The majority of radiation from galaxies containing active galactic nuclei (AGNs) is emitted not by the stars composing the galaxy, but from an active source at the galactic center, most likely a supermassive black hole. Of particular interest are radio galaxies, the active galaxies emitting much of their radiation at radio wavelengths. Within each radio galaxy, an AGN powers a pair of collimated jets of relativistic particles, forming a pair of giant lobes at the end of the jets and thus giving a characteristic double-lobed appearance. A particular class of radio galaxies have an ''X''-shaped morphology: in these, two pairs of lobes appear to originate from the galactic center, producing a distinctive X-shape. Two main mechanisms have been proposed to explain the X-shape morphology: one being through the merger of a binary supermassive black hole system and the second being that the radio jets are expanding into an asymmetric medium. By analyzing radio host galaxy shapes, we probe the distribution of the stellar mass to compare the differing model expectations regarding the distribution of the surrounding gas and stellar material about the AGN.

  4. The Spectral Energy Distributions of Interacting Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Liss, Sandra; Johnson, Kelsey E.; Stierwalt, Sabrina; Kallivayalil, Nitya; Besla, Gurtina; Patton, David R.; Privon, George C.

    2016-01-01

    We present spectral energy distributions (SEDs) for the TiNy Titans survey, the first systematic study of interactions between dwarf galaxies. Galaxy interactions are known to be of fundamental importance to the evolution of massive galaxies -- they have been observed to impact morphology, star formation rates, and ISM composition. Such interactions also occur frequently between low mass dwarf galaxies, but this process is poorly understood and largely overlooked in comparison. Although the majority of mergers at all redshifts are expected to take place between low mass galaxies, until now there have not been comparable systematic studies of dwarf galaxy interactions, leaving open the question of whether interactions between low mass galaxies can strongly affect their own evolution. The TiNy Titans survey, a complete sample of isolated dwarf galaxy pairs selected from the Sloan Digital Sky Survey (SDSS), is specifically designed to address this gap in our understanding of galaxy evolution. The SEDs presented here, generated from archival WISE, SDSS, and GALEX photometric data, allow us to characterize the typical interacting dwarf galaxy, as well as quantify the deviations from this average distribution. We also present trends in the SEDs as a function of projected radial separation, a proxy for interaction stage.

  5. 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

  6. HOST GALAXIES OF X-SHAPED RADIO SOURCES

    SciTech Connect

    Springmann, A.; Cheung, C.

    2007-01-01

    Most radiation from galaxies containing active galactic nuclei (AGNs) is emitted not by the stars composing the galaxy, but from an active source at the galactic center, most likely a supermassive black hole. Of particular interest are radio galaxies, active galaxies that emit much of their radiation at radio wavelengths. Within each radio galaxy, an AGN powers a pair of collimated jets of relativistic particles, forming a pair of giant lobes at the end of the jets and thus giving a characteristic double-lobed appearance. A particular class of radio galaxies has an “X”-or winged-shaped morphology: in these, two pairs of lobes appear to originate from the galactic center, producing a distinctive X-shape. Two main mechanisms have been proposed to explain the X-shape morphology: one being a realignment of the black hole within the AGN and the second positing that the radio jets are expanding into an asymmetric medium, causing backflow and producing secondary wings. By analyzing radio host galaxy shapes, the distribution of the stellar mass is compared to the differing model expectations regarding the distribution of the surrounding gas and stellar material about the AGN. Results show elliptical host galaxies with an orthogonal offset between the semi-major axis of the host galaxy and the secondary radio wings, which lends support to the hydrodynamical model. However, results also show circular host galaxies with radio wings, making the realignment scenario a more likely model to describe the formation of these X-shaped radio sources.

  7. LESS THAN 10 PERCENT OF STAR FORMATION IN z approx 0.6 MASSIVE GALAXIES IS TRIGGERED BY MAJOR INTERACTIONS

    SciTech Connect

    Robaina, Aday R.; Bell, Eric F.; Skelton, Rosalind E.; Rix, Hans-Walter; Gallazzi, Anna; Jahnke, Knud; McIntosh, Daniel H.; Somerville, Rachel S.; Zheng Xianzhong; Bacon, David; Balogh, Michael; Barazza, Fabio D.; Barden, Marco; Van Kampen, Eelco; Caldwell, John A. R.; Gray, Meghan E.; Haeussler, Boris; Heymans, Catherine; Jogee, Shardha

    2009-10-10

    Both observations and simulations show that major tidal interactions or mergers between gas-rich galaxies can lead to intense bursts of star formation. Yet, the average enhancement in star formation rate (SFR) in major mergers and the contribution of such events to the cosmic SFR are not well estimated. Here we use photometric redshifts, stellar masses, and UV SFRs from COMBO-17, 24 mum SFRs from Spitzer, and morphologies from two deep Hubble Space Telescope (HST) cosmological survey fields (ECDFS/GEMS and A901/STAGES) to study the enhancement in SFR as a function of projected galaxy separation. We apply two-point projected correlation function techniques, which we augment with morphologically selected very close pairs (separation <2'') and merger remnants from the HST imaging. Our analysis confirms that the most intensely star-forming systems are indeed interacting or merging. Yet, for massive (M{sub *} >= 10{sup 10} M{sub sun}) star-forming galaxies at 0.4 < z < 0.8, we find that the SFRs of galaxies undergoing a major interaction (mass ratios <=1:4 and separations <=40 kpc) are only 1.80 +- 0.30 times higher than the SFRs of non-interacting galaxies when averaged over all interactions and all stages of the interaction, in good agreement with other observational works. Our results also agree with hydrodynamical simulations of galaxy interactions, which produce some mergers with large bursts of star formation on approx100 Myr timescales, but only a modest SFR enhancement when averaged over the entire merger timescale. We demonstrate that these results imply that only approx<10% of star formation at 0.4 <= z <= 0.8 is triggered directly by major mergers and interactions; these events are not important factors in the build-up of stellar mass since z = 1.

  8. Tracking star formation in dwarf cluster galaxies

    NASA Astrophysics Data System (ADS)

    Rude, Cody Millard

    The evolution of galaxies in dense environments can be affected by close encounters with neighboring galaxies and interactions with the intracluster medium (ICM). Dwarf galaxies may be especially susceptible to these effects due to their low mass. The goal of my dissertation research is to look for signs of star formation in cluster dwarf galaxies by measuring and comparing the r- and u-band luminosity functions of 15 low redshift Abell galaxy clusters using archival data from the Canada-France-Hawaii Telescope (CFHT). Luminosity functions, dwarf-to-giant ratios, and blue fractions are measured in four cluster-centric annuli from stacked cluster data. To account for differences in cluster optical richness, each cluster is scaled according to r200, where r200 is the radius of a sphere, centered on the cluster, whose average density is 200 times the critical density of the universe. The outer region of the cluster sample shows an increase in the faint-end slope of the u-band luminosity function relative to the r-band, indicating star formation in dwarf galaxies. The blue fraction for dwarf galaxies steadily rises with increasing cluster-centric radii. The change in the blue fraction of giant galaxies also increases, but at a lower rate. Additionally, the inner regions of clusters ranging from 0.185 < z < 0.7 from the "Cluster Lensing and Supernova survey with Hubble (CLASH)" are used to generate blue- and red-band luminosity functions, dwarf-to-giant ratios, and blue fractions. Comparisons of the inner region of the CLASH and CFHT clusters show an increase in the blue fraction of dwarf galaxies with redshift that is not present in giant galaxies.

  9. Tidal Disruption Events Prefer Unusual Host Galaxies

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

    Tidal Disruption Events (TDEs) are transient events observed when a star passes close enough to a supermassive black hole to be tidally destroyed. Many TDE candidates have been discovered in host galaxies whose spectra have weak or no line emission yet strong Balmer line absorption, indicating a period of intense star formation that has recently ended. As such, TDE host galaxies fall into the rare class of quiescent Balmer-strong galaxies. Here, we quantify the fraction of galaxies in the Sloan Digital Sky Survey (SDSS) with spectral properties like those of TDE hosts, determining the extent to which TDEs are over-represented in such galaxies. Galaxies whose spectra have Balmer absorption {{H}}{δ }{{A}} - σ(H{δ }{{A}}) > 4 Å (where σ(H{δ }{{A}}) is the error in the Lick {{H}}{δ }{{A}} index) and Hα emission equivalent width (EW) < 3 Å have had a strong starburst in the last ˜Gyr. They represent 0.2% of the local galaxy population, yet host 3 of 8 (37.5%) optical/UV-selected TDE candidates. A broader cut, {{H}}{δ }{{A}}\\quad \\gt 1.31 Å and Hα EW < 3 Å, nets only 2.3% of SDSS galaxies, but 6 of 8 (75%) optical/UV TDE hosts. Thus, quiescent Balmer-strong galaxies are over-represented among the TDE hosts by a factor of 33-190. The high-energy-selected TDE Swift J1644 also lies in a galaxy with strong Balmer lines and weak Hα emission, implying a \\gt 80× enhancement in such hosts and providing an observational link between the γ/X-ray-bright and optical/UV-bright TDE classes.

  10. Host Galaxies of X-Shaped Extragalactic Radio Sources

    NASA Astrophysics Data System (ADS)

    Springmann, Alessondra; Cheung, C. C.

    2007-05-01

    The majority of radiation from galaxies containing active galactic nuclei (AGNs) is emitted not by the stars composing the galaxy, but from an active source at the galactic center, most likely a supermassive black hole. Of particular interest are radio galaxies, the active galaxies emitting much of their radiation at radio wavelengths. Classical double-lobed radio galaxies are characterized by a single pair of "active" radio lobes. A small subset show an additional pair of lower surface brightness 'wings' of emission, thus forming an overall winged or X-shaped appearance. Two competing mechanisms have been proposed to explain the "winged" morphology. One model posits that these are the remnants left over from a relatively recent merger of a binary supermassive black hole system. Others have argued that they result naturally from strong backflow in a radio jet cocoon expanding into an asymmetric medium. We used available Sloan Digital Sky Survey r-band images of 11 X-shaped sources to measure the host galaxy ellipticities. By analyzing the host galaxy shapes, we trace the surrounding gas distribution. The radio morphologies are compared to the host galaxy parameters to analogize between differing model expectations. This work was funded by the Department of Energy's Student Undergraduate Laboratory Internship Program and the Stanford Linear Accelerator Center.

  11. Electron pairing without superconductivity.

    PubMed

    Cheng, Guanglei; Tomczyk, Michelle; Lu, Shicheng; Veazey, Joshua P; Huang, Mengchen; Irvin, Patrick; Ryu, Sangwoo; Lee, Hyungwoo; Eom, Chang-Beom; Hellberg, C Stephen; Levy, Jeremy

    2015-05-14

    Strontium titanate (SrTiO3) is the first and best known superconducting semiconductor. It exhibits an extremely low carrier density threshold for superconductivity, and possesses a phase diagram similar to that of high-temperature superconductors--two factors that suggest an unconventional pairing mechanism. Despite sustained interest for 50 years, direct experimental insight into the nature of electron pairing in SrTiO3 has remained elusive. Here we perform transport experiments with nanowire-based single-electron transistors at the interface between SrTiO3 and a thin layer of lanthanum aluminate, LaAlO3. Electrostatic gating reveals a series of two-electron conductance resonances-paired electron states--that bifurcate above a critical pairing field Bp of about 1-4 tesla, an order of magnitude larger than the superconducting critical magnetic field. For magnetic fields below Bp, these resonances are insensitive to the applied magnetic field; for fields in excess of Bp, the resonances exhibit a linear Zeeman-like energy splitting. Electron pairing is stable at temperatures as high as 900 millikelvin, well above the superconducting transition temperature (about 300 millikelvin). These experiments demonstrate the existence of a robust electronic phase in which electrons pair without forming a superconducting state. Key experimental signatures are captured by a model involving an attractive Hubbard interaction that describes real-space electron pairing as a precursor to superconductivity. PMID:25971511

  12. Electron pairing without superconductivity

    NASA Astrophysics Data System (ADS)

    Cheng, Guanglei; Tomczyk, Michelle; Lu, Shicheng; Veazey, Joshua P.; Huang, Mengchen; Irvin, Patrick; Ryu, Sangwoo; Lee, Hyungwoo; Eom, Chang-Beom; Hellberg, C. Stephen; Levy, Jeremy

    2015-05-01

    Strontium titanate (SrTiO3) is the first and best known superconducting semiconductor. It exhibits an extremely low carrier density threshold for superconductivity, and possesses a phase diagram similar to that of high-temperature superconductors--two factors that suggest an unconventional pairing mechanism. Despite sustained interest for 50 years, direct experimental insight into the nature of electron pairing in SrTiO3 has remained elusive. Here we perform transport experiments with nanowire-based single-electron transistors at the interface between SrTiO3 and a thin layer of lanthanum aluminate, LaAlO3. Electrostatic gating reveals a series of two-electron conductance resonances--paired electron states--that bifurcate above a critical pairing field Bp of about 1-4 tesla, an order of magnitude larger than the superconducting critical magnetic field. For magnetic fields below Bp, these resonances are insensitive to the applied magnetic field; for fields in excess of Bp, the resonances exhibit a linear Zeeman-like energy splitting. Electron pairing is stable at temperatures as high as 900 millikelvin, well above the superconducting transition temperature (about 300 millikelvin). These experiments demonstrate the existence of a robust electronic phase in which electrons pair without forming a superconducting state. Key experimental signatures are captured by a model involving an attractive Hubbard interaction that describes real-space electron pairing as a precursor to superconductivity.

  13. Electron pairing without superconductivity

    NASA Astrophysics Data System (ADS)

    Levy, Jeremy

    Strontium titanate (SrTiO3) is the first and best known superconducting semiconductor. It exhibits an extremely low carrier density threshold for superconductivity, and possesses a phase diagram similar to that of high-temperature superconductors--two factors that suggest an unconventional pairing mechanism. Despite sustained interest for 50 years, direct experimental insight into the nature of electron pairing in SrTiO3 has remained elusive. Here we perform transport experiments with nanowire-based single-electron transistors at the interface between SrTiO3 and a thin layer of lanthanum aluminate, LaAlO3. Electrostatic gating reveals a series of two-electron conductance resonances--paired electron states--that bifurcate above a critical pairing field Bp of about 1-4 tesla, an order of magnitude larger than the superconducting critical magnetic field. For magnetic fields below Bp, these resonances are insensitive to the applied magnetic field; for fields in excess of Bp, the resonances exhibit a linear Zeeman-like energy splitting. Electron pairing is stable at temperatures as high as 900 millikelvin, well above the superconducting transition temperature (about 300 millikelvin). These experiments demonstrate the existence of a robust electronic phase in which electrons pair without forming a superconducting state. Key experimental signatures are captured by a model involving an attractive Hubbard interaction that describes real-space electron pairing as a precursor to superconductivity. Support from AFOSR, ONR, ARO, NSF, DOE and NSSEFF is gratefully acknowledged.

  14. Communication: Improved pair approximations in local coupled-cluster methods

    SciTech Connect

    Schwilk, Max; Werner, Hans-Joachim; Usvyat, Denis

    2015-03-28

    In local coupled cluster treatments the electron pairs can be classified according to the magnitude of their energy contributions or distances into strong, close, weak, and distant pairs. Different approximations are introduced for the latter three classes. In this communication, an improved simplified treatment of close and weak pairs is proposed, which is based on long-range cancellations of individually slowly decaying contributions in the amplitude equations. Benchmark calculations for correlation, reaction, and activation energies demonstrate that these approximations work extremely well, while pair approximations based on local second-order Møller-Plesset theory can lead to errors that are 1-2 orders of magnitude larger.

  15. COMPARATIVE STUDY OF ASYMMETRY ORIGIN OF GALAXIES IN DIFFERENT ENVIRONMENTS. II. NEAR-INFRARED OBSERVATIONS

    SciTech Connect

    Plauchu-Frayn, I.; Coziol, R. E-mail: rcoziol@astro.ugto.m

    2010-08-15

    In this second paper of two analyses, we present near-infrared (NIR) morphological and asymmetry studies performed in a sample of 92 galaxies found in different density environments: galaxies in compact groups (CGs; HCGs in the Hickson Catalog of Compact Groups of Galaxies), isolated pairs of galaxies (KPGs in Karachentsev's list of isolated pairs of galaxies), and isolated galaxies (KIGs in Karachentseva's Catalog of Isolated Galaxies). Both studies have proved useful for identifying the effect of interactions on galaxies. In the NIR, the properties of the galaxies in HCGs, KPGs, and KIGs are more similar than they are in the optical. This is because the NIR band traces the older stellar populations, which formed earlier and are more relaxed than the younger populations. However, we found asymmetries related to interactions in both KPG and HCG samples. In HCGs, the fraction of asymmetric galaxies is even higher than what we found in the optical. In the KPGs the interactions look like very recent events, while in the HCGs galaxies are more morphologically evolved and show properties suggesting they suffered more frequent interactions. The key difference seems to be the absence of star formation in the HCGs; while interactions produce intense star formation in the KPGs, we do not see this effect in the HCGs. This is consistent with the dry merger hypothesis; the interaction between galaxies in CGs is happening without the presence of gas. If the gas was spent in stellar formation (to build the bulge of the numerous early-type galaxies), then the HCGs possibly started interacting sometime before the KPGs. On the other hand, the dry interaction condition in CGs suggests that the galaxies are on merging orbits, and consequently such system cannot be that much older either. Cosmologically speaking, the difference in formation time between pairs of galaxies and CGs may be relatively small. The two phenomena are typical of the formation of structures in low

  16. Encounters of spherical galaxies. I - Galaxy models with one stellar population. II - Galaxy models with two stellar populations

    NASA Technical Reports Server (NTRS)

    Biermann, P.; Silk, J.

    1976-01-01

    Close encounters between two spherical galaxies of equal size and consisting of only one stellar population are calculated using models of elliptical galaxies constructed according to King's (1966) method. The mass loss and the change in internal energy are computed under the assumption that the stars do not change their velocity or density distributions during the encounters. The results for a specific case are compared with the calculations of Gallagher and Ostriker (1972), who employed the observed brightness distribution and the derived density distribution of the E1 galaxy NGC 3379. For models with one stellar population, the results suggest that the radius of a galactic halo would have to be at least 200 kpc for appreciable mass loss to occur over the history of a galaxy in a rich cluster. The calculations are then extended to include a halo population characterized by a high central velocity dispersion. In this case, it is found that the halo population of sufficiently large galaxies can be dispersed without appreciably affecting the main population. It is suggested that the missing mass of many clusters of galaxies may be located in an intergalactic sea of faint stars making up an envelope for the centrally located gE galaxies.

  17. Two-photon production of ω pairs

    NASA Astrophysics Data System (ADS)

    Albrecht, H.; Hamacher, T.; Hofmann, R. P.; Kirchhoff, T.; Mankel, R.; Nau, A.; Nowak, S.; Reßing, D.; Schröder, H.; Schulz, H. D.; Walter, M.; Wurth, R.; Hast, C.; Kapitza, H.; Kolanoski, H.; Kosche, A.; Lange, A.; Lindner, A.; Schieber, M.; Siegmund, T.; Spaan, B.; Thurn, H.; Töpfer, D.; Wegener, D.; Eckstein, P.; Frankl, C.; Graf, J.; Schmidtler, M.; Schramm, M.; Schubert, K. R.; Schwierz, R.; Waldi, R.; Reim, K.; Wegener, H.; Eckmann, R.; Kuipers, H.; Mai, O.; Mundt, R.; Oest, T.; Reiner, R.; Schmidt-Parzefall, W.; Stiewe, J.; Werner, S.; Ehret, K.; Hofmann, W.; Hüpper, A.; Knöpfle, K. T.; Spengler, J.; Krieger, P.; Macfarlane, D. B.; Prentice, J. D.; Saull, P. R. B.; Tzamariudaki, K.; van de Water, R. G.; Yoon, T.-S.; Schneider, M.; Weseler, S.; Kernel, G.; Križan, P.; Križnič, E.; Podobnik, T.; Živko, T.; Balagura, V.; Barsuk, S.; Belyaev, I.; Chistov, R.; Danilov, M.; Eiges, V.; Gershtein, L.; Gershtein, Yu.; Golutvin, A.; Igonkina, O.; Korolko, I.; Kostina, G.; Litvintsev, D.; Pakhlov, P.; Semenov, S.; Snizhko, A.; Tichomirov, I.; Zaitsev, Yu.; Argus Collaboration

    1996-02-01

    A maximum likelihood analysis of ARGUS data on two-photon production of π+π+π0π0π-π- is presented. A small fraction of events is due to the production of omega pairs. The γγ → ωω cross section has its maximum value close to threshold.

  18. Measuring the Red Sequence Slope in a Distant Galaxy Cluster

    NASA Astrophysics Data System (ADS)

    Schultz, Erin; Rudnick, G.

    2013-01-01

    Our project goal is to constrain the possible stellar mass dependence of galaxy ages for red sequence galaxies. We use the Y, J, and K-band data collected from the Very Large Telescope in Chile of the z = 1.62 galaxy cluster XMM-LSS J02182-051020. This spectroscopically confirmed galaxy cluster is one of the only known massive clusters at an epoch close to the time when stars stopped forming within red sequence galaxies. For red sequence galaxies, which have little recent star formation and little dust, the color is an indicator of the luminosity weighted age of the stars. This is in turn correlated to the last epoch of significant star formation. At the same time, the mass of such a galaxy is correlated to its magnitude. The more stars a galaxy contains, the more massive and brighter the galaxy. The slope of the red sequence in color-magnitude space, therefore, gives an indication of the dependence of galaxy age on stellar mass. We use the age-sensitive Y-J color and measure a slope of zero for the red sequence in Y-J vs. J. We interpret this to mean that the age does not depend strongly on the mass of the galaxy. We will present the limits on the slope of the color-magnitude relation and will discuss what limits this corresponds to on the age dependence with mass.

  19. Constraining the Luminous Red Galaxy Halo Occupation Distribution Using Counts-In-Cylinders

    NASA Astrophysics Data System (ADS)

    Reid, Beth A.; Spergel, David N.

    2009-06-01

    The low number density of the Sloan Digital Sky Survey (SDSS) luminous red galaxies (LRGs) suggests that LRGs occupying the same dark matter halo can be separated from pairs occupying distinct dark matter halos with high fidelity. We present a new technique, Counts-in-Cylinders (CiC), to constrain the parameters of the satellite contribution to the LRG halo occupation distribution once the parameters of the central galaxy contribution have been fixed. For a fiber-collision-corrected SDSS spectroscopic LRG subsample at 0.16 < z < 0.36, we find that the CiC multiplicity function is fitted by a halo model where the average number of satellites in a halo of mass M is = ((M - M cut)/M 1)α with M cut = 5.0+1.5 -1.3(+2.9 -2.6) × 1013 M sun, M 1 = 4.95+0.37 -0.26(+0.79 -0.53) × 1014 M sun, and α = 1.035+0.10 -0.17(+0.24 -0.31) at the 68% and 95% confidence levels using a WMAP3 cosmology and z = 0.2 halo catalog. Our method tightly constrains the fraction of LRGs that are satellite galaxies, 6.36+0.38 -0.39%, and the combination M cut/1014 M sun + α = 1.53+0.08 -0.09 at the 95% confidence level, though these constraints may be relaxed when cosmological parameters and the central galaxy parameters are allowed to vary simultaneously. We also find that mocks based on a halo catalog produced by a spherical overdensity finder reproduce both the measured CiC multiplicity function and the projected correlation function, while mocks based on a Friends-of-Friends halo catalog has a deficit of close pairs at ~1 h -1 Mpc separations. Because the CiC method relies on higher order statistics of close pairs, it is robust to the choice of halo finder, and yields mock catalogs reproducing Finger-of-God (FOG) features in the observations probed by the CiC group multiplicity function. In a companion paper, we will apply this technique to optimize FOG compression to eliminate the one-halo contribution to the LRG power spectrum.

  20. MASSIVE BLACK HOLE PAIRS IN CLUMPY, SELF-GRAVITATING CIRCUMNUCLEAR DISKS: STOCHASTIC ORBITAL DECAY

    SciTech Connect

    Fiacconi, Davide; Mayer, Lucio; Roškar, Rok; Colpi, Monica

    2013-11-01

    We study the dynamics of massive black hole pairs in clumpy gaseous circumnuclear disks. We track the orbital decay of the light, secondary black hole M {sub .2} orbiting around the more massive primary at the center of the disk, using N-body/smoothed particle hydrodynamic simulations. We find that the gravitational interaction of M {sub .2} with massive clumps M {sub cl} erratically perturbs the otherwise smooth orbital decay. In close encounters with massive clumps, gravitational slingshots can kick the secondary black hole out of the disk plane. The black hole moving on an inclined orbit then experiences the weaker dynamical friction of the stellar background, resulting in a longer orbital decay timescale. Interactions between clumps can also favor orbital decay when the black hole is captured by a massive clump that is segregating toward the center of the disk. The stochastic behavior of the black hole orbit emerges mainly when the ratio M {sub .2}/M {sub cl} falls below unity, with decay timescales ranging from ∼1 to ∼50 Myr. This suggests that describing the cold clumpy phase of the interstellar medium in self-consistent simulations of galaxy mergers, albeit so far neglected, is important to predict the black hole dynamics in galaxy merger remnants.

  1. Paired Straight Hearth Furnace

    SciTech Connect

    2009-04-01

    This factsheet describes a research project whose goals are to design, develop, and evaluate the scalability and commercial feasibility of the PSH Paired Straight Hearth Furnace alternative ironmaking process.

  2. 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

  3. 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)

  4. NMR analysis of base-pair opening kinetics in DNA

    PubMed Central

    Szulik, Marta W.; Voehler, Markus; Stone, Michael P.

    2014-01-01

    Base pairing in nucleic acids plays a crucial role in their structure and function. Differences in the base pair opening and closing kinetics of individual double stranded DNA sequences or between chemically modified base pairs provide insight into the recognition of these base pairs by DNA processing enzymes. This unit describes how to quantify the kinetics for localized base pairs by observing changes in the imino proton signals by nuclear magnetic resonance spectroscopy. The determination of all relevant parameters using state of the art techniques and NMR instrumentation, including cryoprobes, is discussed. PMID:25501592

  5. 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

  6. Cooper Pair Insulators

    NASA Astrophysics Data System (ADS)

    Valles, James

    One of the recent advances in the field of the Superconductor to Insulator Transition (SIT) has been the discovery and characterization of the Cooper Pair Insulator phase. This bosonic insulator, which consists of localized Cooper pairs, exhibits activated transport and a giant magneto-resistance peak. These features differ markedly from the weakly localized transport that emerges as pairs break at a ``fermionic'' SIT. I will describe how our experiments on films nano-patterned with a nearly triangular array of holes have enabled us to 1) distinguish bosonic insulators from fermionic insulators, 2) show that Cooper pairs, rather than quasi-particles dominate the transport in the Cooper Pair insulator phase, 3) demonstrate that very weak, sub nano-meter thickness inhomogeneities control whether a bosonic or fermionic insulator forms at an SIT and 4) reveal that Cooper pairs disintegrate rather than becoming more tightly bound deep in the localized phase. We have also developed a method, using a magnetic field, to tune flux disorder reversibly in these films. I will present our latest results on the influence of magnetic flux disorder and random gauge fields on phenomena near bosonic SITs. This work was performed in collaboration with M. D. Stewart, Jr., Hung Q. Nguyen, Shawna M. Hollen, Jimmy Joy, Xue Zhang, Gustavo Fernandez, Jeffrey Shainline and Jimmy Xu. It was supported by NSF Grants DMR 1307290 and DMR-0907357.

  7. 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.

  8. SHINING LIGHT ON MERGING GALAXIES. I. THE ONGOING MERGER OF A QUASAR WITH A 'GREEN VALLEY' GALAXY

    SciTech Connect

    Da Silva, Robert L.; Xavier Prochaska, J.; Rosario, David; Tripp, Todd M.

    2011-07-01

    Serendipitous observations of a pair z = 0.37 interacting galaxies (one hosting a quasar) show a massive gaseous bridge of material connecting the two objects. This bridge is photoionized by the quasar (QSO), revealing gas along the entire projected 38 h{sup -1}{sub 70} kpc sightline connecting the two galaxies. The emission lines that result give an unprecedented opportunity to study the merger process at this redshift. We determine the kinematics, ionization parameter (log U {approx} -2.5 {+-} 0.03), column density (N{sub H,perpendicular} {approx} 10{sup 21} cm{sup -2}), metallicity ([M/H] {approx} - 0.20 {+-} 0.15), and mass ({approx}10{sup 8} M{sub sun}) of the gaseous bridge. We simultaneously constrain properties of the QSO host (M{sub DM} > 8.8 x 10{sup 11} M{sub sun}) and its companion galaxy (M{sub DM} > 2.1 x 10{sup 11} M{sub sun}; M{sub *} {approx} 2 x 10{sup 10} M{sub sun}; stellar burst age = 300-800 Myr; SFR {approx}6 M{sub sun} yr{sup -1}; and metallicity 12 + log (O/H) = 8.64 {+-} 0.2). The general properties of this system match the standard paradigm of a galaxy-galaxy merger caught between first and second passages while one of the galaxies hosts an active quasar. The companion galaxy lies in the so-called green valley, with a stellar population consistent with a recent starburst triggered during the first passage of the merger and has no discernible active galactic nucleus activity. In addition to providing case studies of quasars associated with galaxy mergers, quasar/galaxy pairs with QSO-photoionized tidal bridges such as this one offer unique insights into the galaxy properties while also distinguishing an important and inadequately understood phase of galaxy evolution.

  9. Close encounters between two nanoshells.

    PubMed

    Lassiter, J Britt; Aizpurua, Javier; Hernandez, Luis I; Brandl, Daniel W; Romero, Isabel; Lal, Surbhi; Hafner, Jason H; Nordlander, Peter; Halas, Naomi J

    2008-04-01

    Plasmonic nanoparticle pairs known as "dimers" embody a simple system for generating intense nanoscale fields for surface enhanced spectroscopies and for developing an understanding of coupled plasmons. Individual nanoshell dimers in directly adjacent pairs and touching geometries show dramatically different plasmonic properties. At close distances, hybridized plasmon modes appear whose energies depend extremely sensitively on the presence of a small number of molecules in the interparticle junction. When touching, a new plasmon mode arising from charge transfer oscillations emerges. The extreme modification of the overall optical response due to minute changes in very reduced volumes opens up new approaches for ultrasensitive molecular sensing and spectroscopy. PMID:18345644

  10. 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.

  11. The Gaseous Extent of Galaxies and the Origin of Lyα Absorption Systems. III. Hubble Space Telescope Imaging of Lyα-absorbing Galaxies at z < 1

    NASA Astrophysics Data System (ADS)

    Chen, Hsiao-Wen; Lanzetta, Kenneth M.; Webb, John K.; Barcons, Xavier

    1998-05-01

    We present initial results of a program to obtain and analyze Hubble Space Telescope (HST) Wide Field Planetary Camera 2 images of galaxies identified in an imaging and spectroscopic survey of faint galaxies in fields of HST spectroscopic target QSOs. We measure properties of 87 galaxies, of which 33 are associated with corresponding Lyα absorption systems and 24 do not produce corresponding Lyα absorption lines to within sensitive upper limits. Considering only galaxy and absorber pairs that are likely to be physically associated and excluding galaxy and absorber pairs within 3000 km s-1 of the background QSOs leaves 26 galaxy and absorber pairs and seven galaxies that do not produce corresponding Lyα absorption lines to within sensitive upper limits. Redshifts of the galaxy and absorber pairs range from 0.0750 to 0.8912 with a median of 0.3718, and impact parameter separations of the galaxy and absorber pairs range from 12.4 to 157.4 h-1 kpc with a median of 62.4 h-1 kpc. The primary result of the analysis is that the amount of gas encountered along the line of sight depends on the galaxy impact parameter and B-band luminosity but does not depend strongly on the galaxy average surface brightness, disk-to-bulge ratio, or redshift. This result confirms and improves upon the anticorrelation between Lyα absorption equivalent width and galaxy impact parameter found previously by Lanzetta et al. in 1995. Spherical halos cannot be distinguished from flattened disks on the basis of the current observations, and there is no evidence that galaxy interactions play an important role in distributing tenuous gas around galaxies in most cases. Galaxies might account for all Lyα absorption systems with W > 0.3 Å, but this depends on the unknown luminosity function and gaseous cross sections of low-luminosity galaxies as well as on the uncertainties of the observed number density of Lyα absorption systems. Based on observations with the NASA/ESA Hubble Space Telescope

  12. Two Galaxy Clusters: A3565 and A3560

    NASA Astrophysics Data System (ADS)

    Willmer, C. N. A.; Maia, M. A. G.; Mendes, S. O.; Alonso, M. V.; Rios, L. A.; Chaves, O. L.; de Mello, D. F.

    1999-09-01

    We report 102 new redshifts and magnitudes for a sample of galaxies to R_F~15.5 mag in a 2.17dx2.17d region centered on the galaxy IC 4296, the most luminous member of the A3565 Cluster. Up to the limiting magnitude, we find 29 cluster members and measure a velocity dispersion of sigma=228 km s^-1. The estimated total mass for this system is ~3.0x10^13 h^-1 M_solar [where h=H_0/(100 km s^-1 Mpc^-1)], and its dynamical properties are quite typical of poor clusters presenting X-ray emission. We also find that galaxies with absorption lines are more concentrated toward the center of the cluster, while systems with emission lines are mainly located in the outer parts. The small velocity dispersion of the cluster, coupled with the known presence of an interacting pair of galaxies, and the large extent of the brightest cluster galaxy, could indicate that galaxy formation through mergers may still be underway in this system. The surveyed region also contains galaxies belonging to the Shapley concentration cluster A3560. Within 30' of the cluster center, we detect 32 galaxies, for which we measure a velocity dispersion of 588 km s^-1 and a mass of ~2x10^14 h^-1 M_solar. However, because our sample is restricted to galaxies brighter than M^*, these values should be considered only as rough estimates.

  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. Electron Pairing Without Superconductivity

    NASA Astrophysics Data System (ADS)

    Levy, Jeremy; Cheng, G.; Tomczyk, M.; Lu, S.; Veazey, J. P.; Huang, M.; Irvin, P.; Ryu, S.; Lee, H.; Eom, C.-B.; Hellberg, C. S.

    2015-03-01

    Strontium titanate (SrTiO3) exhibits an extremely low carrier density threshold for superconductivity, and possesses a phase diagram similar to high-temperature superconductors--two factors that suggest an unconventional pairing mechanism. We describe transport experiments with nanowire-based quantum dots localized at the interface between SrTiO3 and LaAlO3. Electrostatic gating of the quantum dot reveals a series of two-electron conductance resonances--paired electron states--that bifurcate above a critical magnetic field Bp 1-4 Tesla, an order of magnitude larger than the superconducting critical magnetic field. For B Bp, the resonances exhibit a linear Zeeman-like energy splitting. Electron pairing is stable at temperatures as high as T = 900 mK, far above the superconducting transition temperature (Tc 300 mK). These experiments demonstrate the existence of a robust electronic phase in which electrons pair without forming a superconducting state. Key experimental signatures are captured by an attractive-U Hubbard model that describes real-space electron pairing as a precursor to superconductivity. This work was supported by ARO MURI W911NF-08-1-0317 (J.L.), AFOSR MURI FA9550-10-1-0524 (C.-B.E., J.L.) and FA9550-12-1-0342 (C.-B.E.), and grants from the National Science Foundation DMR-1104191 (J.L.), DMR.

  15. Extended LY alpha -absorbing Halos around Nearby Galaxies

    NASA Astrophysics Data System (ADS)

    Bowen, David V.; Blades, J. Chris; Pettini, Max

    1996-06-01

    In order to establish the Lyα absorption cross section of present-day galaxies, we have identified 38 galaxies with z = 0-0.08 that lie within 40-500 h^-1^ kpc of the line of sight to a QSO observed with the Faint Object Spectrograph aboard the Hubble Space Telescope (HST). Including three galaxies in the field of 3C 273 investigated by previous authors, we find that nine of 41 galaxies have associated Lyα absorption. If the identified Lyα absorption systems are genuinely associated with the galaxies, then the covering factor of gas around galaxies remains roughly constant at ~40% between 100 and 300 h^-1^ kpc. Beyond 300 h^-1^ kpc, the incidence of absorption drops sharply. We conclude that (1) nearby galaxies do not possess Lyα-absorbing halos beyond 300 h^-1^ kpc in radius and (2) the covering factor of present-day galaxies between 50 and 300 h^-1^ kpc is 44% at an equivalent width limit of W >= 0.3 A. For the nine galaxies with associated Lyα absorption lines, differences in the galaxies systemic velocities and the velocity of the absorption line, {DELTA}v, range over +/- 300 km s^-1^, consistent with the distribution found at redshifts > 0.1 by Lanzetta et al. and Le Brun, Bergeron, & Boisse. Values of {DELTA}v spanning several hundred km s^-1^ are probably real for some of the QSO-galaxy pairs, however, and do not simply arise from errors in measuring cz_gal_ or cz_abs_. This suggests that the absorbing clouds are kinematically tied to the galaxy disks and that the distribution of {DELTA}v may arise because of the effects of galaxy inclination. We find no evidence for a correlation between Lyα equivalent width and galaxy line-of-sight separation, which weakens the argument that the identified galaxies are directly associated with the Lyα lines. Also, we find that absorption does not arise only from bright galaxies, since there are several examples in which low-luminosity galaxies apparently cause absorption. Yet we show that the absorbing halos around

  16. Probing the extent and content of low ionization gas in galaxies: QSO absorption and HI emission

    NASA Technical Reports Server (NTRS)

    Womble, Donna S.

    1993-01-01

    The small projected separations of some QSO's and low-redshift galaxies provide unique opportunities to study the extent and content of gas in galaxies through observation of absorption in the QSO spectra. Observations of these systems provide valuable information on the connection between the absorbing gas and the galaxy, as well as detailed information on the morphology and environment of the galaxy itself. While there is direct evidence that galaxies can produce the intervening-type QSO absorption lines, over the past decade, the study of such 'QSO-galaxy pairs' (at low redshift) has been considered unsuccessful because new detections of absorption were seldom made. A fundamental problem concerning the relation between these low-redshift systems and those seen at moderate to high redshift remains unresolved. Direct and indirect measures of galaxy absorption cross sections at moderate to high redshifts (z is approximately greater than 20.5) are much larger than the optical and HI sizes of local galaxies. However, direct comparison of the low and moderate to high redshift systems is difficult since different ions are observed in different redshift regimes. Observations are presented for a new sample of QSO-galaxy pairs. Nine new QSO's which shine through nearby galaxies (on the sky-plane) were observed to search for CaII absorption in the QSO spectra at the foreground galaxy redshifts.

  17. The centre of the Galaxy

    NASA Technical Reports Server (NTRS)

    Townes, C. H.; Lacy, J. H.; Geballe, T. R.; Hollenbach, D. J.

    1983-01-01

    X-ray, gamma-ray and IR observations of the Galaxy's nucleus show that it contains the densest concentration of stars in the Galaxy, as well as a quantity of ionized gas and warm dust, which is clumped into a small number of rapidly expanding individual clouds whose velocities approach + or - 300 km/sec. The detection of electron-positron anihilation radiation, and a peculiar radio point source very close to the galactic center, add to the belief that the nucleus may contain some unusual object, such as a black hole, which is responsible for the cloud velocities and dust-heating radiation observed. Attention is given to IR intensity contours of the region, as well as a review of the observational evidence for the presence of a black hole. It is noted that a massive black hole fails to account for the unusual ionizing radiation field detected.

  18. 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.

  19. Applications of balanced pairs

    NASA Astrophysics Data System (ADS)

    Li, HuanHuan; Wang, JunFu; Huang, ZhaoYong

    2016-05-01

    Let $(\\mathscr{X}$, $\\mathscr{Y})$ be a balanced pair in an abelian category. We first introduce the notion of cotorsion pairs relative to $(\\mathscr{X}$, $\\mathscr{Y})$, and then give some equivalent characterizations when a relative cotorsion pair is hereditary or perfect. We prove that if the $\\mathscr{X}$-resolution dimension of $\\mathscr{Y}$ (resp. $\\mathscr{Y}$-coresolution dimension of $\\mathscr{X}$) is finite, then the bounded homotopy category of $\\mathscr{Y}$ (resp. $\\mathscr{X}$) is contained in that of $\\mathscr{X}$ (resp. $\\mathscr{Y}$). As a consequence, we get that the right $\\mathscr{X}$-singularity category coincides with the left $\\mathscr{Y}$-singularity category if the $\\mathscr{X}$-resolution dimension of $\\mathscr{Y}$ and the $\\mathscr{Y}$-coresolution dimension of $\\mathscr{X}$ are finite.

  20. 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

  1. CORRELATIONS AMONG GALAXY PROPERTIES FROM THE SLOAN DIGITAL SKY SURVEY

    SciTech Connect

    Li Zhongmu; Mao Caiyan

    2013-07-01

    Galaxies are complex systems with many properties. Correlations among galaxy properties can supply important clues for studying the formation and evolution of galaxies. Using principal component analysis and least-squares fitting, this paper investigates the correlations among galactic parameters involving more properties (color, morphology, stellar population, and absolute magnitude) than previous studies. We use a volume-limited sample (whole sample) of 75,423 galaxies that was selected from the Sloan Digital Sky Survey Data Release 2 and divided into two subsamples (blue and red samples) using a critical color of (g - r) = 0.70 mag. In addition to recovering some previous results, we also obtain some new results. First, all separators for dividing galaxies into two groups can be related via good parameter-first principal component (PC1) correlations. A critical PC1 that indicates whether or not stellar age (or the evolution of a stellar population over time) is important can be used to separate galaxies. This suggests that a statistical parameter, PC1, is helpful in understanding the physical separators of galaxies. In addition, stellar age is shown to be unimportant for red galaxies, while both stellar age and mass are dominating parameters of blue galaxies. This suggests that the various numbers of dominating parameters of galaxies may result from the use of different samples. Finally, some parameters are shown to be correlated, and quantitative fits for a few correlations are obtained, e.g., log(t) = 8.57 + 1.65 (g - r) for the age (log t) and color (g - r) of blue galaxies and log (M{sub *}) = 4.31 - 0.30 M{sub r} for the stellar mass (log M{sub *}) and absolute magnitude (M{sub r}) of red galaxies. The median relationships between various parameter pairs are also presented for comparison.

  2. Galactic Bridges in Pairs

    NASA Astrophysics Data System (ADS)

    Thierjung, Brianna; Jorge Moreno, Paul Torrey, Phil Hopkins

    2016-01-01

    We employ a suite of 75 simulations of galaxies in idealized major mergers to investigate the bridges formed by interactions. These simulations are based on the Feedback in Realistic Environments (FIRE) model (Hopkins et al. 2011). Moreover, unlike past work, we have both the resolution and diversity in merging orbits to make statistically meaningful predictions. We find that very dense, star forming bridges can be characterized as strong bridges. In particular, prograde mergers with high eccentricities and high impact parameters produce the most mass of stars in the bridge.

  3. 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.

  4. Multi-pair states in electron-positron pair creation

    NASA Astrophysics Data System (ADS)

    Wöllert, Anton; Bauke, Heiko; Keitel, Christoph H.

    2016-09-01

    Ultra strong electromagnetic fields can lead to spontaneous creation of single or multiple electron-positron pairs. A quantum field theoretical treatment of the pair creation process combined with numerical methods provides a description of the fermionic quantum field state, from which all observables of the multiple electron-positron pairs can be inferred. This allows to study the complex multi-particle dynamics of electron-positron pair creation in-depth, including multi-pair statistics as well as momentum distributions and spin. To illustrate the potential benefit of this approach, it is applied to the intermediate regime of pair creation between nonperturbative Schwinger pair creation and perturbative multiphoton pair creation where the creation of multi-pair states becomes nonnegligible but cascades do not yet set in. Furthermore, it is demonstrated how spin and helicity of the created electrons and positrons are affected by the polarization of the counterpropagating laser fields, which induce the creation of electron-positron pairs.

  5. Modeling abundances in star forming galaxies

    NASA Astrophysics Data System (ADS)

    Kobayashi, Chiaki

    2015-08-01

    Heavy elements are produced from various types of supernovae (and AGB stars). I first show that elemental abundances of extremely metal-poor stars are consistent not with pair-instability supernovae but with faint supernovae. Then I introduce subclasses of Type Ia supernovae such as SN 2002cx-like objects and sub-Chandrasekhar mass explosions. These "minor" supernovae are important in the early Universe or metal-poor systems such as dwarf spheroidal galaxies. With "major" chemical enrichment sources, I show cosmic chemical enrichment in our cosmological, hydrodynamical simulations. The feedback from active galactic nuclei (AGN) is also included with a new model for the formation of black holes motivated by the first star formation. AGN-driven outflows transport metals into the circumgalactic medium and the intergalactic medium. Nonetheless, the metallicity changes of galaxies are negligible, and the mass-metallicity relations, which are mainly generated by supernova feedback at the first star burst, are preserved. Within galaxies, metallicity radial gradients are produced, which can be affected by AGN feedback but are more sensitive to the merging histories. We find a weak correlation between the gradients and galaxy mass, which is consistent with available observations. These simulations also provide predictions of supernova/hypernova/GRB rates and the properties of their host galaxies.

  6. HUBBLE REVEALS STELLAR FIREWORKS ACCOMPANYING GALAXY COLLISION

    NASA Technical Reports Server (NTRS)

    2002-01-01

    This Hubble Space Telescope image provides a detailed look at a brilliant 'fireworks show' at the center of a collision between two galaxies. Hubble has uncovered over 1,000 bright, young star clusters bursting to life as a result of the head-on wreck. [Left] A ground-based telescopic view of the Antennae galaxies (known formally as NGC 4038/4039) - so named because a pair of long tails of luminous matter, formed by the gravitational tidal forces of their encounter, resembles an insect's antennae. The galaxies are located 63 million light-years away in the southern constellation Corvus. [Right] The respective cores of the twin galaxies are the orange blobs, left and right of image center, crisscrossed by filaments of dark dust. A wide band of chaotic dust, called the overlap region, stretches between the cores of the two galaxies. The sweeping spiral- like patterns, traced by bright blue star clusters, shows the result of a firestorm of star birth activity which was triggered by the collision. This natural-color image is a composite of four separately filtered images taken with the Wide Field Planetary Camera 2 (WFPC2), on January 20, 1996. Resolution is 15 light-years per pixel (picture element). Credit: Brad Whitmore (STScI), and NASA

  7. 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.

  8. 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.

  9. REVISITING THE FIRST GALAXIES: THE EFFECTS OF POPULATION III STARS ON THEIR HOST GALAXIES

    SciTech Connect

    Muratov, Alexander L.; Gnedin, Oleg Y.; Zemp, Marcel; Gnedin, Nickolay Y.

    2013-08-01

    We revisit the formation and evolution of the first galaxies using new hydrodynamic cosmological simulations with the adaptive refinement tree code. Our simulations feature a recently developed model for H{sub 2} formation and dissociation, and a star formation recipe that is based on molecular rather than atomic gas. Here, we develop and implement a recipe for the formation of metal-free Population III (Pop III) stars in galaxy-scale simulations that resolve primordial clouds with sufficiently high density. We base our recipe on the results of prior zoom-in simulations that resolved the protostellar collapse in pre-galactic objects. We find the epoch during which Pop III stars dominated the energy and metal budget of the first galaxies to be short-lived. Galaxies that host Pop III stars do not retain dynamical signatures of their thermal and radiative feedback for more than 10{sup 8} years after the lives of the stars end in pair-instability supernovae, even when we consider the maximum reasonable efficiency of the feedback. Though metals ejected by the supernovae can travel well beyond the virial radius of the host galaxy, they typically begin to fall back quickly, and do not enrich a large fraction of the intergalactic medium. Galaxies with a total mass in excess of 3 Multiplication-Sign 10{sup 6} M{sub Sun} re-accrete most of their baryons and transition to metal-enriched Pop II star formation.

  10. Comparing the clustering of galaxies and galaxy group by using the SDSS DR7

    NASA Astrophysics Data System (ADS)

    Wang, Yiran; Brunner, R. J.

    2014-01-01

    By using the angular two-point correlation function, we measure the clustering strength of a clean sample of galaxies (explored in Wang, Brunner, & Dolence 2013) for the Sloan Digital Sky Survey Data Release Seven. By using these same data, we first find isolated pairs, triplets, quads, and larger groups of galaxies, and subsequently measure the clustering of these subsamples. We find the clustering strength increases with groups size, which supports the halo model of galaxy clustering and demonstrates the efficacy of our isolated group catalog for general studies such as the galaxy merger rate. Finally, we explore the effects of galaxy spectral type and photometric redshift on the clustering behavior of these galaxy group samples. References: Blake, C., Collister, A., Lahav, O. 2008, MNRAS, 385, 1257 Hickson, P. 1982, ApJ, 255, 382 Ross, A. J., Brunner, R. J. 2009, MNRAS, 399, 878 Wang Y., Brunner R. J., Dolence J. C. 2013, MNRAS, 432, 1961 Zehavi, I., et al. 2004, ApJ, 608, 16

  11. HUBBLE AND KECK DISCOVER GALAXY BUILDING BLOCK

    NASA Technical Reports Server (NTRS)

    2002-01-01

    This NASA Hubble Space Telescope image shows a very small, faint galaxy 'building block' newly discovered by a unique collaboration between ground- and space-based telescopes. Hubble and the 10-meter Keck Telescopes in Hawaii joined forces, using a galaxy cluster which acts as gravitational lens to detect what scientists believe is one of the smallest very distant objects ever found. The galaxy cluster Abell 2218 was used by a team of European and American astronomers led by Richard Ellis (Caltech) in their systematic search for intrinsically faint distant star-forming systems. Without help from Abell 2218's exceptional magnifying power to make objects appear about 30 times brighter, the galaxy building block would have been undetectable. In the image to the right, the object is seen distorted into two nearly identical, very red 'images' by the gravitational lens. The image pair represents the magnified result of a single background object gravitationally lensed by Abell 2218 and viewed at a distance of 13.4 billion light-years. The intriguing object contains only one million stars, far fewer than a mature galaxy, and scientists believe it is very young. Such young star-forming systems of low mass at early cosmic times are likely to be the objects from which present-day galaxies have formed. In the image to the left, the full overview of the galaxy cluster Abell 2218 is seen. This image was taken by Hubble in 1999 at the completion of Hubble Servicing Mission 3A. Credit: NASA, ESA, Richard Ellis (Caltech) and Jean-Paul Kneib (Observatoire Midi-Pyrenees, France) Acknowledgment: NASA, A. Fruchter and the ERO Team (STScI and ST-ECF)

  12. Demographic mechanisms of inbreeding adjustment through extra-pair reproduction

    PubMed Central

    Reid, Jane M; Duthie, A Bradley; Wolak, Matthew E; Arcese, Peter; van de Pol, Martijn

    2015-01-01

    One hypothesis explaining extra-pair reproduction is that socially monogamous females mate with extra-pair males to adjust the coefficient of inbreeding (f) of extra-pair offspring (EPO) relative to that of within-pair offspring (WPO) they would produce with their socially paired male. Such adjustment of offspring f requires non-random extra-pair reproduction with respect to relatedness, which is in turn often assumed to require some mechanism of explicit pre-copulatory or post-copulatory kin discrimination. We propose three demographic processes that could potentially cause mean f to differ between individual females’ EPO and WPO given random extra-pair reproduction with available males without necessarily requiring explicit kin discrimination. Specifically, such a difference could arise if social pairings formed non-randomly with respect to relatedness or persisted non-randomly with respect to relatedness, or if the distribution of relatedness between females and their sets of potential mates changed during the period through which social pairings persisted. We used comprehensive pedigree and pairing data from free-living song sparrows (Melospiza melodia) to quantify these three processes and hence investigate how individual females could adjust mean offspring f through instantaneously random extra-pair reproduction. Female song sparrows tended to form social pairings with unrelated or distantly related males slightly less frequently than expected given random pairing within the defined set of available males. Furthermore, social pairings between more closely related mates tended to be more likely to persist across years than social pairings between less closely related mates. However, these effects were small and the mean relatedness between females and their sets of potential extra-pair males did not change substantially across the years through which social pairings persisted. Our framework and analyses illustrate how demographic and social structuring

  13. Computers vs. Humans in Galaxy Classification

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-04-01

    In this age of large astronomical surveys, one major scientific bottleneck is the analysis of enormous data sets. Traditionally, this task requires human input but could computers eventually take over? A pair of scientists explore this question by testing whether computers can classify galaxies as well as humans.Examples of disagreement: galaxies that Galaxy-Zoo humans classified as spirals with 95% agreement, but the computer algorithm classified as ellipticals with 70% certainty. Most are cases where the computer got it wrong but not all of them. [Adapted from Kuminski et al. 2016]Limits of Citizen ScienceGalaxy Zoo is an internet-based citizen science project that uses non-astronomer volunteers to classify galaxy images. This is an innovative way to provide more manpower, but its still only practical for limited catalog sizes. How do we handle the data from upcoming surveys like the Large Synoptic Survey Telescope (LSST), which will produce billions of galaxy images when it comes online?In a recent study by Evan Kuminski and Lior Shamir, two computer scientists at Lawrence Technological University in Michigan, a machine learning algorithm known as Wndchrm was used to classify a dataset of Sloan Digital Sky Survey (SDSS) galaxies into ellipticals and spirals. The authors goal is to determine whether their algorithm can classify galaxies as accurately as the human volunteers for Galaxy Zoo.Automatic ClassificationAfter training their classifier on a small set of spiral and elliptical galaxies, Kuminski and Shamir set it loose on a catalog of ~3 million SDSS galaxies. The classifier first computes a set of 2,885 numerical descriptors (like textures, edges, and shapes) for each galaxy image, and then uses these descriptors to categorize the galaxy as spiral or elliptical.Rate of agreement of the computer classification with human classification (for the Galaxy Zoo superclean subset) for different ranges of computed classification certainties. For certainties above

  14. GAMA: Stellar Mass Assembly in Galaxy Bulges and Disks

    NASA Astrophysics Data System (ADS)

    Moffett, Amanda J.; Driver, Simon P.; Lange, Rebecca; Robotham, Aaron; Kelvin, Lee; GAMA Team

    2016-01-01

    The Galaxy And Mass Assembly (GAMA) survey has to date obtained spectra, redshifts, and 21-band multi-facility photometry for over 200,000 galaxies in five survey regions that total nearly 300 square degrees on sky. We consider here a low-redshift (z<0.06), volume-limited subsample of ~8,000 GAMA galaxies that have been morphologically classified by the survey team. In order to quantify the separate bulge and disk properties of these galaxies, we apply a large-scale automated procedure for fitting images with 2D, multi-component structure models, including evaluation of fit convergence using a grid of input parameter values for each galaxy. From this analysis, we calculate the total bulge and disk contributions to the local galaxy stellar mass budget and derive mass-size relations for both pure spheroid/disk systems and the separate bulge/disk components of multi-component galaxies. We further examine the fraction of total stellar mass assembled in spheroid and disk structures as a function of galaxy environment, where environment is quantified on multiple scales from membership in large-scale filaments to groups/clusters and down to local pairings. We then discuss the effect of environmental conditions on the mechanisms of stellar mass assembly, including the implied balance between merger accumulation and in situ mass growth in different environment regimes.

  15. USING COLORS TO IMPROVE PHOTOMETRIC METALLICITY ESTIMATES FOR GALAXIES

    SciTech Connect

    Sanders, N. E.; Soderberg, A. M.; Levesque, E. M.

    2013-10-01

    There is a well known correlation between the mass and metallicity of star-forming galaxies. Because mass is correlated with luminosity, this relation is often exploited, when spectroscopy is not available, to estimate galaxy metallicities based on single band photometry. However, we show that galaxy color is typically more effective than luminosity as a predictor of metallicity. This is a consequence of the correlation between color and the galaxy mass-to-light ratio and the recently discovered correlation between star formation rate (SFR) and residuals from the mass-metallicity relation. Using Sloan Digital Sky Survey spectroscopy of ∼180, 000 nearby galaxies, we derive 'LZC relations', empirical relations between metallicity (in seven common strong line diagnostics), luminosity, and color (in 10 filter pairs and four methods of photometry). We show that these relations allow photometric metallicity estimates, based on luminosity and a single optical color, that are ∼50% more precise than those made based on luminosity alone; galaxy metallicity can be estimated to within ∼0.05-0.1 dex of the spectroscopically derived value depending on the diagnostic used. Including color information in photometric metallicity estimates also reduces systematic biases for populations skewed toward high or low SFR environments, as we illustrate using the host galaxy of the supernova SN 2010ay. This new tool will lend more statistical power to studies of galaxy populations, such as supernova and gamma-ray burst host environments, in ongoing and future wide-field imaging surveys.

  16. Revisiting The First Galaxies: The Epoch of Population III Stars

    NASA Astrophysics Data System (ADS)

    Muratov, Alexander; Gnedin, O. Y.; Gnedin, N. Y.; Zemp, M. K.

    2013-01-01

    We study the formation of the first galaxies using new hydrodynamic cosmological simulations with the ART code. Our simulations feature a recently developed model for dust-based formation of molecular gas. Here, we develop and implement a new recipe for the formation of metal-free Pop III stars. We reach a spatial resolution of 2 pc at z=10 and resolve star-forming galaxies with the masses above 10^6 solar masses. We find the epoch during which Pop III stars dominate the energy and metal budget of the universe to be short-lived. While these stars seed their host galaxies with metals, they cannot drive significant outflows to enrich the IGM in our simulations. Feedback from pair instability supernovae causes Pop III star formation to self-terminate within their host galaxies, but is not strong enough to suppress star formation in external galaxies. Within any individual galaxy, Pop II stars overtake Pop III stars within ~50-150 Myr. A threshold of M = 3 * 10^6 solar masses separates galaxies that lose a significant fraction of their baryons due to Pop III feedback from those that do not. Understanding the nature of the transition between Pop III and Pop II star formation is of key importance for studying the dawn of galaxy formation.

  17. 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.

  18. Stellar kinematics and structural properties of virgo cluster dwarf early-type galaxies from the SMAKCED project. I. Kinematically decoupled cores and implications for infallen groups in clusters

    SciTech Connect

    Toloba, E.; Guhathakurta, P.; Boissier, S.; Boselli, A.; Den Brok, M.; Falcón-Barroso, J.; Ryś, A.; Janz, J.; Lisker, T.; Laurikainen, E.; Salo, H.; Paudel, S.

    2014-03-10

    We present evidence for kinematically decoupled cores (KDCs) in two dwarf early-type (dE) galaxies in the Virgo cluster, VCC 1183 and VCC 1453, studied as part of the SMAKCED stellar absorption-line spectroscopy and imaging survey. These KDCs have radii of 1.''8 (0.14 kpc) and 4.''2 (0.33 kpc), respectively. Each of these KDCs is distinct from the main body of its host galaxy in two ways: (1) inverted sense of rotation and (2) younger (and possibly more metal-rich) stellar population. The observed stellar population differences are probably associated with the KDC, although we cannot rule out the possibility of intrinsic radial gradients in the host galaxy. We describe a statistical analysis method to detect, quantify the significance of, and characterize KDCs in long-slit rotation curve data. We apply this method to the two dE galaxies presented in this paper and to five other dEs for which KDCs have been reported in the literature. Among these seven dEs, there are four significant KDC detections, two marginal KDC detections, and one dE with an unusual central kinematic anomaly that may be an asymmetric KDC. The frequency of occurrence of KDCs and their properties provide important constraints on the formation history of their host galaxies. We discuss different formation scenarios for these KDCs in cluster environments and find that dwarf-dwarf wet mergers or gas accretion can explain the properties of these KDCs. Both of these mechanisms require that the progenitor had a close companion with a low relative velocity. This suggests that KDCs were formed in galaxy pairs residing in a poor group environment or in isolation whose subsequent infall into the cluster quenched star formation.

  19. Stellar Kinematics and Structural Properties of Virgo Cluster Dwarf Early-type Galaxies from the SMAKCED Project. I. Kinematically Decoupled Cores and Implications for Infallen Groups in Clusters

    NASA Astrophysics Data System (ADS)

    Toloba, E.; Guhathakurta, P.; van de Ven, G.; Boissier, S.; Boselli, A.; den Brok, M.; Falcón-Barroso, J.; Hensler, G.; Janz, J.; Laurikainen, E.; Lisker, T.; Paudel, S.; Peletier, R. F.; Ryś, A.; Salo, H.

    2014-03-01

    We present evidence for kinematically decoupled cores (KDCs) in two dwarf early-type (dE) galaxies in the Virgo cluster, VCC 1183 and VCC 1453, studied as part of the SMAKCED stellar absorption-line spectroscopy and imaging survey. These KDCs have radii of 1.''8 (0.14 kpc) and 4.''2 (0.33 kpc), respectively. Each of these KDCs is distinct from the main body of its host galaxy in two ways: (1) inverted sense of rotation and (2) younger (and possibly more metal-rich) stellar population. The observed stellar population differences are probably associated with the KDC, although we cannot rule out the possibility of intrinsic radial gradients in the host galaxy. We describe a statistical analysis method to detect, quantify the significance of, and characterize KDCs in long-slit rotation curve data. We apply this method to the two dE galaxies presented in this paper and to five other dEs for which KDCs have been reported in the literature. Among these seven dEs, there are four significant KDC detections, two marginal KDC detections, and one dE with an unusual central kinematic anomaly that may be an asymmetric KDC. The frequency of occurrence of KDCs and their properties provide important constraints on the formation history of their host galaxies. We discuss different formation scenarios for these KDCs in cluster environments and find that dwarf-dwarf wet mergers or gas accretion can explain the properties of these KDCs. Both of these mechanisms require that the progenitor had a close companion with a low relative velocity. This suggests that KDCs were formed in galaxy pairs residing in a poor group environment or in isolation whose subsequent infall into the cluster quenched star formation.

  20. Disk Galaxy Stellar Velocity Ellipsoids

    NASA Astrophysics Data System (ADS)

    Westfall, Kyle B.; Bershady, M. A.; Verheijen, M. A. W.; Andersen, D. R.; Swaters, R. A.

    2007-12-01

    We have measured the disk stellar velocity ellipsoids in a subset of spiral galaxies observed for the Disk-Mass Survey, which provide information on disk stability and secular heating mechanisms. Our methodology invokes our 2D ionized gas and stellar kinematics and a suite of dynamical assumptions based on the Jeans' equations. When combined with orthogonal axes from our 2D data, either the epicycle approximation (EA) or asymmetric drift (AD) equation may close the necessary equation set, individually. We have isolated large observational and inherent systematic effects via EA-only, AD-only, and EA+AD ellipsoid decomposition methodologies. In an attempt to minimize these effects and generate robust ellipsoid measurements we explore constraints provided by higher order expansions of the Jeans' equations and direct orbital integrations. We compare our best ellipsoid axial ratio estimates to similar measurements made by, e.g., van der Kruit & de Grijs (1999, A&A, 352, 129) and Shapiro et al. (2003, AJ, 126, 2707). Finally, we discuss possibilities for the measurement of vertical velocity dispersions in low-surface-brightness galaxies by applying the characterization of the stellar velocity ellipsoid in late-type galaxies. This work is supported by the National Science Foundation (AST-0607516).

  1. The polar-ring galaxies NGC 2685 and NGC 3808B (VV 300)

    NASA Technical Reports Server (NTRS)

    Reshetnikov, V. P.; Yakovleva, V. A.

    1990-01-01

    Polar-ring galaxies (PRG) are among the most interesting examples of interaction between galaxies. A PRG is a galaxy with an elongated main body surrounded by a ring (or a disk) of stars, gas, and dust rotating in a near-polar plane (Schweizer, Whitmore, and Rubin, 1983). Accretion of matter by a massive lenticular galaxy from either intergalactic medium or a companion galaxy is usually considered as an explanation of the observed structure of PRG. In the latter case there are two possibilities: capture and merging of a neighbor galaxy, and accretion of mass from a companion galaxy during a close encounter. Two PRG formation scenarios just mentioned are illustrated here by the results of our observations of the peculiar galaxies NGC 2685 and NGC 3808B.

  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. Suites of Dwarfs around nearby Giant Galaxies

    NASA Astrophysics Data System (ADS)

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

    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 Θ1, 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 Θ1. All suite members with positive Θ1 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 -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 MB = -18m. 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 Local Group, do not quite seem to be a typical

  4. Multi-color imaging of selected southern interacting galaxies

    NASA Technical Reports Server (NTRS)

    Smith, Eric P.; Hintzen, Paul

    1990-01-01

    The authors present preliminary results from a study of selected Arp-Madore Southern Hemisphere peculiar galaxies. Broadband charge coupled device (CCD) images (BVRI) of a subset of these galaxies allow us to study each galaxy's optical morphology, color, and (in a crude manner) degree of nuclear activity, and to compare them with similar data we possess on other active galaxies. Many of these galaxies have optical morphologies closely resembling those of powerful radio galaxies (Smith and Heckman 1989), yet their radio emission is unremarkable. Accurate positions for subsequent spectroscopic studies have been determined along with broad band photometry and morphology studies. Detailed observations of these comparatively bright, low-redshift, well-resolved interacting systems should aid our understanding of the role interactions play in triggering galaxy activity. This work is the initial effort in a long term project to study the role played by the dynamics of the interaction in the production and manifestations of activity in galaxies, and the frequency of galaxy mergers.

  5. 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.

  6. The galaxy-dark matter halo connection: which galaxy properties are correlated with the host halo mass?

    NASA Astrophysics Data System (ADS)

    Contreras, S.; Baugh, C. M.; Norberg, P.; Padilla, N.

    2015-09-01

    We demonstrate how the properties of a galaxy depend on the mass of its host dark matter subhalo, using two independent models of galaxy formation. For the cases of stellar mass and black hole mass, the median property value displays a monotonic dependence on subhalo mass. The slope of the relation changes for subhalo masses for which heating by active galactic nuclei becomes important. The median property values are predicted to be remarkably similar for central and satellite galaxies. The two models predict considerable scatter around the median property value, though the size of the scatter is model dependent. There is only modest evolution with redshift in the median galaxy property at a fixed subhalo mass. Properties such as cold gas mass and star formation rate, however, are predicted to have a complex dependence on subhalo mass. In these cases, subhalo mass is not a good indicator of the value of the galaxy property. We illustrate how the predictions in the galaxy property-subhalo mass plane differ from the assumptions made in some empirical models of galaxy clustering by reconstructing the model output using a basic subhalo abundance matching scheme. In its simplest form, abundance matching generally does not reproduce the clustering predicted by the models, typically resulting in an overprediction of the clustering signal. Using the predictions of the galaxy formation model for the correlations between pairs of galaxy properties, the basic abundance matching scheme can be extended to reproduce the model predictions more faithfully for a wider range of galaxy properties. Our results have implications for the analysis of galaxy clustering, particularly for low abundance samples.

  7. 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

  8. 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

  9. Decision trees and decision committee applied to star/galaxy separation problem

    NASA Astrophysics Data System (ADS)

    Vasconcellos, Eduardo Charles

    Vasconcellos et al [1] study the efficiency of 13 diferente decision tree algorithms applied to photometric data in the Sloan Digital Sky Digital Survey Data Release Seven (SDSS-DR7) to perform star/galaxy separation. Each algorithm is defined by a set fo parameters which, when varied, produce diferente final classifications trees. In that work we extensively explore the parameter space of each algorithm, using the set of 884,126 SDSS objects with spectroscopic data as the training set. We find that Functional Tree algorithm (FT) yields the best results by the mean completeness function (galaxy true positive rate) in two magnitude intervals:14<=r<=21 (85.2%) and r>=19 (82.1%). We compare FT classification to the SDSS parametric, 2DPHOT and Ball et al (2006) classifications. At the faintest magnitudes (r > 19), our classifier is the only one that maintains high completeness (>80%) while simultaneously achieving low contamination ( 2.5%). We also examine the SDSS parametric classifier (psfMag - modelMag) to see if the dividing line between stars and galaxies can be adjusted to improve the classifier. We find that currently stars in close pairs are often misclassified as galaxies, and suggest a new cut to improve the classifier. Finally, we apply our FT classifier to separate stars from galaxies in the full set of 69,545,326 SDSS photometric objects in the magnitude range 14 <= r <= 21. We now study the performance of a decision committee composed by FT classifiers. We will train six FT classifiers with random selected objects from the same 884,126 SDSS-DR7 objects with spectroscopic data that we use before. Both, the decision commitee and our previous single FT classifier will be applied to the new ojects from SDSS data releses eight, nine and ten. Finally we will compare peformances of both methods in this new data set. [1] Vasconcellos, E. C.; de Carvalho, R. R.; Gal, R. R.; LaBarbera, F. L.; Capelato, H. V.; Fraga Campos Velho, H.; Trevisan, M.; Ruiz, R. S. R

  10. 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

  11. A CA(+) pair adjacent to a sheared GA or AA pair stabilizes size-symmetric RNA internal loops.

    PubMed

    Chen, Gang; Kennedy, Scott D; Turner, Douglas H

    2009-06-23

    RNA internal loops are often important sites for folding and function. Residues in internal loops can have pKa values shifted close to neutral pH because of the local structural environment. A series of RNA internal loops were studied at different pH by UV absorbance versus temperature melting experiments and imino proton nuclear magnetic resonance (NMR). A stabilizing CA pair forms at pH 7 in the CG/AA and CA/AA nearest neighbors when the CA pair is the first noncanonical pair (loop-terminal pair) in 3 x 3 nucleotide and larger size-symmetric internal loops. These CG/AA and CA/AA nearest neighbors, with CA adjacent to a closing Watson-Crick pair, are further stabilized when the pH is lowered from 7 to 5.5. The results are consistent with a significantly larger fraction (from approximately 20% at pH 7 to approximately 90% at pH 5.5) of adenines being protonated at the N1 position to form stabilizing wobble CA+ pairs adjacent to a sheared GA or AA pair. The noncanonical pair adjacent to the GA pair in CG/AA can either stabilize or destabilize the loop, consistent with the sequence-dependent thermodynamics of GA pairs. No significant pH-dependent stabilization is found for most of the other nearest neighbor combinations involving CA pairs (e.g., CA/AG and AG/CA), which is consistent with the formation of various nonwobble pairs observed in different local sequence contexts in crystal and NMR structures. A revised free-energy model, including stabilization by wobble CA+ pairs, is derived for predicting stabilities of medium-size RNA internal loops. PMID:19485416

  12. 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.

  13. 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.

  14. Infrared Polarimetry of Galaxies

    NASA Astrophysics Data System (ADS)

    Jones, T. J.

    2005-12-01

    Imaging polarimetry at near infrared wavelengths can probe the magnetic field geometry in external galaxies in regions of high extinction inaccessible to optical techniques. Polarization of starlight from deep into dustlanes, blowouts, and dust enshrouded nuclei can be measured. A total of twelve galaxies showing only interstellar polarization have been observed to date. Normal galaxies such as NGC 4565 show a magnetic field geometry lying in the plane of the disk and a polarization strength very similar to what is observed in the Milky Way. Ultraluminous galaxies and galaxies with starburst nuclei show a polar magnetic field geometry in the nucleus, causing a crossed polaroid effect and reduced polarization. Interestingly, galaxies with active disks, but otherwise normal, such as NGC 891 show the effects of blowouts in the polarization maps.

  15. 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.

  16. E+A and companion galaxies - I. A catalogue and statistics

    NASA Astrophysics Data System (ADS)

    Yamauchi, Chisato; Yagi, Masafumi; Goto, Tomotsugu

    2008-10-01

    Based on our intensive spectroscopic campaign with the GoldCam spectrograph on the Kitt Peak National Observatory (KPNO) 2.1-m telescope, we have constructed the first catalogue of E+A galaxies with spectroscopic companion galaxies, and investigated a probability that an E+A galaxy has close companion galaxies. We selected 660 E+A galaxies with 4.0 Å < Hδ EW at a redshift of <0.167 from the Data Release 5 of the Sloan Digital Sky Survey (SDSS). We selected their companion candidates from the SDSS imaging data, and classified them into true companions, fore/background galaxies and companion candidates using the SDSS and our KPNO spectra. We observed 26 companion candidates of E+A galaxies at the KPNO to measure their redshifts. Their spectra showed that 17 targets are true companion galaxies. The number of spectroscopically confirmed E+A's companions is now 34. This becomes the first catalogue of E+A galaxies with spectroscopic companion systems. We found that E+A galaxies have 54 per cent larger probability of having companion galaxies (7.88 per cent) as compared to the comparison sample of normal galaxies (5.12 per cent). A statistical test shows that the probabilities are different with 99.7 per cent significance. Our results based on spectroscopy tighten the connection between the dynamical merger/interaction and the origin of E+A galaxies.

  17. Close Encounters of the Stellar Kind

    NASA Astrophysics Data System (ADS)

    2003-07-01

    exchange partners in intricate dances. The data suggest that X-ray binary systems are formed in dense clusters known as globular clusters about once a day somewhere in the universe. Observations by NASA's Uhuru X-ray satellite in the 1970's showed that globular clusters seemed to contain a disproportionately large number of X-ray binary sources compared to the Galaxy as a whole. Normally only one in a billion stars is a member of an X-ray binary system containing a neutron star, whereas in globular clusters, the fraction is more like one in a million. The present research confirms earlier suggestions that the chance of forming an X-ray binary system is dramatically increased by the congestion in a globular cluster. Under these conditions two processes, known as three-star exchange collisions, and tidal captures, can lead to a thousandfold increase in the number of X-ray sources in globular clusters. 47 Tucanae 47 Tucanae In an exchange collision, a lone neutron star encounters a pair of ordinary stars. The intense gravity of the neutron star can induce the most massive ordinary star to "change partners," and pair up with the neutron star while ejecting the lighter star. A neutron star could also make a grazing collision with a single normal star, and the intense gravity of the neutron star could distort the gravity of the normal star in the process. The energy lost in the distortion, could prevent the normal star from escaping from the neutron star, leading to what is called tidal capture. "In addition to solving a long-standing mystery, Chandra data offer an opportunity for a deeper understanding of globular cluster evolution," said Heinke. "For example, the energy released in the formation of close binary systems could keep the central parts of the cluster from collapsing to form a massive black hole." NASA's Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for the Office of Space Science, NASA Headquarters, Washington. Northrop Grumman of

  18. Existence of best proximity pairs and equilibrium pairs

    NASA Astrophysics Data System (ADS)

    Kim, Won Kyu; Lee, Kyoung Hee

    2006-04-01

    In this paper, using the fixed point theorem for Kakutani factorizable multifunctions, we shall prove new existence theorems of best proximity pairs and equilibrium pairs for free abstract economies, which include the previous fixed point theorems and equilibrium existence theorems.

  19. 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.

  20. 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).

  1. A homogeneous sample of binary galaxies: Basic observational properties

    NASA Technical Reports Server (NTRS)

    Karachentsev, I. D.

    1990-01-01

    A survey of optical characteristics for 585 binary systems, satisfying a condition of apparent isolation on the sky, is presented. Influences of various selection effects distorting the average parameters of the sample are noted. The pair components display mutual similarity over all the global properties: luminosity, diameter, morphological type, mass-to-luminosity ratio, angular momentum etc., which is not due only to selection effects. The observed correlations must be caused by common origin of pair members. Some features (nuclear activity, color index) could acquire similarity during synchronous evolution of double galaxies. Despite the observed isolation, the sample of double systems is seriously contaminated by accidental pairs, and also by members of groups and clusters. After removing false pairs estimates of orbital mass-to-luminosity ratio range from 0 to 30 f(solar), with the mean value (7.8 plus or minus 0.7) f(solar). Binary galaxies possess nearly circular orbits with a typical eccentrity e = 0.25, probably resulting from evolutionary selection driven by component mergers under dynamical friction. The double-galaxy population with space abundance 0.12 plus or minus 0.02 and characteristic merger timescale 0.2 H(exp -1) may significantly influence the rate of dynamical evolution of galaxies.

  2. HUBBLE PEEKS INTO A STELLAR NURSERY IN A NEARBY GALAXY

    NASA Technical Reports Server (NTRS)

    2002-01-01

    HUBBLE PEEKS INTO A STELLAR NURSERY IN A NEARBY GALAXY NASA's Hubble Space Telescope has peered deep into a neighboring galaxy to reveal details of the formation of new stars. Hubble's target was a newborn star cluster within the Small Magellanic Cloud, a small galaxy that is a satellite of our own Milky Way. The new images show young, brilliant stars cradled within a nebula, or glowing cloud of gas, cataloged as N 81. These massive, recently formed stars inside N 81 are losing material at a high rate, sending out strong stellar winds and shock waves and hollowing out a cocoon within the surrounding nebula. The two most luminous stars, seen in the Hubble image as a very close pair near the center of N 81, emit copious ultraviolet radiation, causing the nebula to glow through fluorescence. Outside the hot, glowing gas is cooler material consisting of hydrogen molecules and dust. Normally this material is invisible, but some of it can be seen in silhouette against the nebular background, as long dust lanes and a small, dark, elliptical-shaped knot. It is believed that the young stars have formed from this cold matter through gravitational contraction. Few features can be seen in N 81 from ground-based telescopes, earning it the informal nick-name 'The Blob.' Astronomers were not sure if just one or a few hot stars were embedded in the cloud, or if it was a stellar nursery containing a large number of less massive stars. Hubble's high-resolution imaging shows the latter to be the case, revealing that numerous young, white-hot stars---easily visible in the color picture---are contained within N 81. This crucial information bears strongly on theories of star formation, and N 81 offers a singular opportunity for a close-up look at the turbulent conditions accompanying the birth of massive stars. The brightest stars in the cluster have a luminosity equal to 300,000 stars like our own Sun. Astronomers are especially keen to study star formation in the Small Magellanic

  3. Galaxy bias and primordial non-Gaussianity

    NASA Astrophysics Data System (ADS)

    Assassi, Valentin; Baumann, Daniel; Schmidt, Fabian

    2015-12-01

    We present a systematic study of galaxy biasing in the presence of primordial non-Gaussianity. For a large class of non-Gaussian initial conditions, we define a general bias expansion and prove that it is closed under renormalization, thereby showing that the basis of operators in the expansion is complete. We then study the effects of primordial non-Gaussianity on the statistics of galaxies. We show that the equivalence principle enforces a relation between the scale-dependent bias in the galaxy power spectrum and that in the dipolar part of the bispectrum. This provides a powerful consistency check to confirm the primordial origin of any observed scale-dependent bias. Finally, we also discuss the imprints of anisotropic non-Gaussianity as motivated by recent studies of higher-spin fields during inflation.

  4. 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.

  5. 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 ...

  6. Photometry of compact galaxies.

    NASA Technical Reports Server (NTRS)

    Shen, B. S. P.; Usher, P. D.; Barrett, J. W.

    1972-01-01

    Photometric histories of the N galaxies 3C 390.3 and PKS 0521-36. Four other compact galaxies, Markarian 9, I Zw 92, 2 Zw 136, and III Zw 77 showed no evidence of variability. The photometric histories were obtained from an exhaustive study of those plates of the Harvard collection taken with large aperture cameras. The images of all galaxies reported were indistinguishable from stars due to the camera f-ratios and low surface brightness of the outlying nebulosities of the galaxies. Standard techniques for the study of variable stars are therefore applicable.

  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. Ripples in disk galaxies

    SciTech Connect

    Schweizer, F.; Seitzer, P.

    1988-05-01

    Evidence is presented that ripples occur not only in ellipticals but also in disk galaxies of Hubble types S0, S0/Sa, and Sa, and probably even in the Sbc galaxy NGC 3310. It is argued that the ripples cannot usually have resulted from transient spiral waves or other forced vibrations in existing disks, but instead consist of extraneous sheetlike 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. The implications of ripples in early-type disk galaxies are addressed. 40 references.

  9. Starbursts in colliding galaxies.

    NASA Astrophysics Data System (ADS)

    Mirabel, I. F.; Duc, P. A.

    Global starbursts are a consequence of rapid changes in the dynamics of the interstellar gas. The most violent starbursts take place in the nuclear regions of galaxies, when galaxy-galaxy encounters cause a sudden reduction of angular momentum, with the subsequent infall to the central regions of a large fraction of the overall interstellar gas. Although starbursts are also observed in the central regions of isolated barred spiral galaxies, most of the starbursts with bolometric luminosities above 1012Lsun occur in mergers. Super-starbursts in galactic nuclei seem to require high infall rates of interstellar gas that can only be produced during mergers. The authors discuss the phenomenon of extranuclear starbursts in relation to the formation of dwarf galaxies during galaxy-galaxy collisions. As a consequence of tidal interactions a fraction of the less gravitationally bound atomic hydrogen that populates the outskirts of disk galaxies may escape into the intergalactic medium. It is found that the ejected gas may assemble again and collapse, leading to the formation of intergalactic starbursts, namely, tidal dwarf galaxies.

  10. From tidal dwarf galaxies to satellite galaxies

    NASA Astrophysics Data System (ADS)

    Bournaud, F.; Duc, P.-A.

    2006-09-01

    The current popular cosmological models have granted the population of dwarf satellite galaxies a key role: their number, location, and masses constrain both the distribution of dark matter and the physical evolution of their hosts. In the past years, there has been increasing observational evidence that objects with masses of dwarf galaxies can form in the tidal tails of colliding galaxies, as well as speculations that they could become satellite-like galaxies orbiting around their progenitors and thus be cosmologically important. Yet, whether the so-called "Tidal Dwarf Galaxy" (TDG) candidates are really long-lived objects and not transient features only present in young interacting systems is still largely an open question to which numerical simulations may give precise answers. We present here a set of 96 N-body simulations of colliding galaxies with various mass ratios and encounter geometries, including gas dynamics and star formation. We study the formation and long-term evolution of their TDG candidates. Among the 593 substructures initially identified in tidal tails, about 75% fall back onto their progenitor or are disrupted in a few 108 years. The remaining 25% become long-lived bound objects that typically survive more than 2 Gyr with masses above 108 M⊙. These long-lived, satellite-like objects, are found to form in massive gaseous accumulations originally located in the outermost regions of the tidal tails. Studying the statistical properties of the simulated TDGs, we infer several basic properties that dwarf galaxies should meet to have a possible tidal origin and apply these criteria to the Local Group dwarfs. We further found that the presence of TDGs would foster the anisotropy observed in the distribution of classical satellite galaxies around their host. Identifying the conditions fulfilled by interacting systems that were able to form long-lived tidal dwarfs - a spiral merging with a galaxy between 1/4 and 8 times its mass, on a prograde orbit

  11. 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.

  12. Galaxy redshift surveys with sparse sampling

    SciTech Connect

    Chiang, Chi-Ting; Wullstein, Philipp; Komatsu, Eiichiro; Jee, Inh; Jeong, Donghui; Blanc, Guillermo A.; Ciardullo, Robin; Gronwall, Caryl; Hagen, Alex; Schneider, Donald P.; Drory, Niv; Fabricius, Maximilian; Landriau, Martin; Finkelstein, Steven; Jogee, Shardha; Cooper, Erin Mentuch; Tuttle, Sarah; Gebhardt, Karl; Hill, Gary J.

    2013-12-01

    Survey observations of the three-dimensional locations of galaxies are a powerful approach to measure the distribution of matter in the universe, which can be used to learn about the nature of dark energy, physics of inflation, neutrino masses, etc. A competitive survey, however, requires a large volume (e.g., V{sub survey} ∼ 10Gpc{sup 3}) to be covered, and thus tends to be expensive. A ''sparse sampling'' method offers a more affordable solution to this problem: within a survey footprint covering a given survey volume, V{sub survey}, we observe only a fraction of the volume. The distribution of observed regions should be chosen such that their separation is smaller than the length scale corresponding to the wavenumber of interest. Then one can recover the power spectrum of galaxies with precision expected for a survey covering a volume of V{sub survey} (rather than the volume of the sum of observed regions) with the number density of galaxies given by the total number of observed galaxies divided by V{sub survey} (rather than the number density of galaxies within an observed region). We find that regularly-spaced sampling yields an unbiased power spectrum with no window function effect, and deviations from regularly-spaced sampling, which are unavoidable in realistic surveys, introduce calculable window function effects and increase the uncertainties of the recovered power spectrum. On the other hand, we show that the two-point correlation function (pair counting) is not affected by sparse sampling. While we discuss the sparse sampling method within the context of the forthcoming Hobby-Eberly Telescope Dark Energy Experiment, the method is general and can be applied to other galaxy surveys.

  13. 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.

  14. 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

  15. Large-Scale Structures around Quasar Pairs at z ˜ 1

    NASA Astrophysics Data System (ADS)

    Sodré, L., Jr.; Boris, N. V.; Lima Neto, G. B.; Cypriano, E. S.; Santos, W. A.; Mendes de Oliveira, C.; West, M.

    2009-05-01

    We have used Gemini telescopes to study the photometric properties of four fields around the high-redshift quasar pairs QP1310+0007, QP1355-0032, QP0110-0219, and QP0114-3140z ˜ 1 with the aim of identifying large-scale structures -galaxy clusters or groups- around them. Our analysis reveals that QP0110-0219very strong and QP1310+0007 - QP1355-0032some evidence for the presence of rich galaxy clusters in direct vicinity of the pairs. On the other hand, QP0114-3140be an isolated pair in a poor environment. This work suggest that z ˜ 1 quasar pairs are excellent tracers of high density environments.

  16. 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

  17. 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.

  18. How do galaxies get their gas?

    NASA Astrophysics Data System (ADS)

    Kereš, Dušan; Katz, Neal; Weinberg, David H.; Davé, Romeel

    2005-10-01

    conflicts with the colours of ellipticals and the cut-off of the galaxy luminosity function. The transition at Mhalo~ 1011.4Msolar between cold-mode domination and hot-mode domination is similar to that found by Birnboim & Dekel using one-dimensional simulations and analytic arguments. The corresponding baryonic mass is tantalizingly close to the scale at which Kauffmann et al. find a marked shift in galaxy properties, and we speculate on possible connections between these theoretical and observational transitions.

  19. Growth of galaxies in SPH simulations

    NASA Astrophysics Data System (ADS)

    Keres, Dusan

    resolving conflicts with the colors of ellipticals and the cutoff of the galaxy luminosity function. The transition at M halo ~ 10 11.4 [Special characters omitted.] between cold and hot mode domination is similar to that found by Birnboim & Dekel (2003) using 1-d simulations and analytic arguments. The corresponding baryonic mass is tantalizingly close to the scale at which Kauffmann et al. (2003a) find a marked shift in galaxy properties, and we speculate on possible connections between these theoretical and observational transitions. (Abstract shortened by UMI.)

  20. A Bayesian Method For Finding Galaxies That Cause Quasar Absorption Lines

    NASA Astrophysics Data System (ADS)

    Shoemaker, Emileigh Suzanne; Laubner, David Andrew; Scott, Jennifer E.

    2016-01-01

    We present a study of candidate absorber-galaxy pairs for 39 low redshift quasar sightlines (0.06 < z < 0.85) using a statistical approach to match absorbers with galaxies near the quasar lines of sight. Of the 75 quasars observed with HST/Cosmic Origins Spectrograph (COS) and archived on the Mikulski Archive for Space Telescopes (MAST), 39 overlap with the footprint of the Sloan Digital Sky Survey (SDSS). We downloaded the COS linelists for these quasar spectra from MAST and queried the SDSS DR12 database for photometric data on all galaxies within 1 Mpc of each of these quasar lines of sight. We calculated photometric redshifts for all the SDSS galaxies using the Bayesian Photometric Redshift code. We used all these absorber and galaxy data as input into an absorber-galaxy matching code which also employs a Bayesian scheme, along with known statistics of the intergalactic medium and circumgalactic media of galaxies, for finding the most probable galaxy match for each absorber. We compare our candidate absorber-galaxy matches to existing studies in the literature and explore trends in the absorber and galaxy properties among the matched and non-matched populations. This method of matching absorbers and galaxies can be used to find targets for follow up spectroscopic studies.

  1. Pair-instability supernovae in the local universe

    SciTech Connect

    Whalen, Daniel J.; Smidt, Joseph; Heger, Alexander; Hirschi, Raphael; Yusof, Norhasliza; Even, Wesley; Fryer, Chris L.; Stiavelli, Massimo; Chen, Ke-Jung; Joggerst, Candace C.

    2014-12-10

    The discovery of 150-300 M {sub ☉} stars in the Local Group and pair-instability supernova candidates at low redshifts has excited interest in this exotic explosion mechanism. Realistic light curves for pair-instability supernovae at near-solar metallicities are key to identifying and properly interpreting these events as more are found. We have modeled pair-instability supernovae of 150-500 M {sub ☉} Z ∼ 0.1-0.4 Z {sub ☉} stars. These stars lose up to 80% of their mass to strong line-driven winds and explode as bare He cores. We find that their light curves and spectra are quite different from those of Population III pair-instability explosions, which therefore cannot be used as templates for low-redshift events. Although non-zero metallicity pair-instability supernovae are generally dimmer than their Population III counterparts, in some cases they will be bright enough to be detected at the earliest epochs at which they can occur, the formation of the first galaxies at z ∼ 10-15. Others can masquerade as dim, short duration supernovae that are only visible in the local universe and that under the right conditions could be hidden in a wide variety of supernova classes. We also report for the first time that some pair-instability explosions can create black holes with masses of ∼100 M {sub ☉}.

  2. Ultraluminous infrared galaxies in the AKARI all-sky survey

    SciTech Connect

    Kilerci Eser, E.; Goto, T.; Doi, Y. E-mail: doi@ea.c.u-tokyo.ac.jp

    2014-12-10

    We present a new catalog of 118 ultraluminous infrared galaxies (ULIRGs) and one hyperluminous infrared galaxy (HLIRG) by cross-matching the AKARI all-sky survey with the Sloan Digital Sky Survey Data Release 10 (SDSS DR10) and the final data release of the Two-Degree Field Galaxy Redshift Survey. Forty of the ULIRGs and one HLIRG are new identifications. We find that ULIRGs are interacting pair galaxies or ongoing or postmergers. This is consistent with the widely accepted view: ULIRGs are major mergers of disk galaxies. We confirm the previously known positive trend between the active galactic nucleus fraction and infrared luminosity. We show that ULIRGs have a large offset from the main sequence up to z ∼ 1; their offset from the z ∼ 2 'main sequence' is relatively smaller. We find a result consistent with the previous studies showing that, compared to local star-forming SDSS galaxies of similar mass, local ULIRGs have lower oxygen abundances. We demonstrate for the first time that ULIRGs follow the fundamental metallicity relation (FMR). The scatter of ULIRGs around the FMR (0.09 dex-0.5 dex) is comparable to the scatter of z ∼ 2-3 galaxies. We provide the largest local (0.050

  3. Binary stars and the UVX in early-type galaxies

    NASA Astrophysics Data System (ADS)

    Hernández-Pérez, Fabiola; Bruzual, Gustavo

    2014-11-01

    We use the Hernández-Pérez and Bruzual (HB13) stellar population synthesis models to study the role of interacting binary pairs as progenitors of extreme horizontal branch (EHB) stars. We assemble a sample of 3417 early-type galaxies observed both in the optical (SDSS-DR8) and the UV (GALEX-GR6). The galaxies in our sample can be classified according to their position in the colour-colour diagram as UV-weak or red-sequence galaxies (˜48 per cent), UV-strong or UVX galaxies (˜9 per cent), and recent star-forming galaxies (˜43 per cent). Analysing this sample using the HB13 models for various choices of basic model parameters, we conclude that (a) the UVr colours of UV-weak and UV-strong galaxies are reproduced by the models as long as the fraction of binary stars is at least 15 per cent. (b) Higher metallicity models (Z = 0.02 and 0.03) reproduce the colours of UV-weak and UV-strong galaxies better than lower Z models. The Z = 0.03 model is slightly bluer than the Z = 0.02 model in the UV-strong region, indicating a weak relationship between UVX and Z. (c) The strength of UVX increases with age in the model population. This is at variance with the results of other models that include binary stars as progenitors of EHB stars.

  4. Chandra Sees Wealth Of Black Holes In Star-Forming Galaxies

    NASA Astrophysics Data System (ADS)

    2001-06-01

    NASA's Chandra X-ray Observatory has found new populations of suspected mid-mass black holes in several starburst galaxies, where stars form and explode at an unusually high rate. Although a few of these objects had been found previously, this is the first time they have been detected in such large numbers and could help explain their relationship to star formation and the production of even more massive black holes. At the 198th meeting of the American Astronomical Society in Pasadena, California, three independent teams of scientists reported finding dozens of X-ray sources in galaxies aglow with star formation. These X-ray objects appear point-like and are ten to a thousand times more luminous in X-rays than similar sources found in our Milky Way and the M81 galaxy. "Chandra gives us the ability to study the populations of individual bright X-ray sources in nearby galaxies in extraordinary detail," said Andreas Zezas, lead author from the Harvard-Smithsonian Center for Astrophysics team that observed The Antennae, a pair of colliding galaxies, and M82, a well-known starburst galaxy. "This allows us to build on earlier detections of these objects and better understand their relationship to starburst galaxies." Antennae-True Color Image True Color Image of Antennae Credit: NASA/SAO/G.Fabbiano et al. Press Image and Caption Kimberly Weaver, of NASA's Goddard Space Flight Center in Greenbelt, MD, lead scientist of the team that studied the starburst galaxy NGC 253, discussed the importance of the unusual concentration of these very luminous X-ray sources near the center of that galaxy. Four sources, which are tens to thousands of times more massive than the Sun, are located within 3,000 light years of the galaxy core. "This may imply that these black holes are gravitating toward the center of the galaxy where they could coalesce to form a single supermassive black hole," Weaver suggested. "It could be that this starburst galaxy is transforming itself into a quasar

  5. 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.

  6. 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.

  7. New data on the peculiar galaxy MRK 273

    NASA Technical Reports Server (NTRS)

    Asatrian, A. S.; Petrosian, A. R.; Boerngen, F.

    1990-01-01

    Colorimetric and spectral investigations of Markarian 273 and its three neighbors were performed on the basis of direct ultraviolet blue visual (UBV) and spectral observations with the 2-m Tautenburg telescope and the 6-m telescope of the Special Astrophysical Observatory of the USSR Academy of Sciences. The results obtained suggest that this galaxy is a close system of two objects with active nuclei. The observed straight tail with a thermal emission character is probably the result of the interaction of these galaxies.

  8. 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.

  9. Students' Perceptions of Dynamics Concept Pairs and Correlation with Their Problem-Solving Performance

    ERIC Educational Resources Information Center

    Fang, Ning

    2012-01-01

    A concept pair is a pair of concepts that are fundamentally different but closely related. To develop a solid conceptual understanding in dynamics (a foundational engineering science course) and physics, students must understand the fundamental difference and relationship between two concepts that are included in each concept pair. However, all…

  10. Two Galaxies for a Unique Event

    NASA Astrophysics Data System (ADS)

    2009-04-01

    To celebrate the 100 Hours of Astronomy, ESO is sharing two stunning images of unusual galaxies, both belonging to the Sculptor group of galaxies. The images, obtained at two of ESO's observatories at La Silla and Paranal in Chile, illustrate the beauty of astronomy. ESO PR Photo 14a/09 Irregular Galaxy NGC 55 ESO PR Photo 14b/09 Spiral Galaxy NGC 7793 As part of the International Year of Astronomy 2009 Cornerstone project, 100 Hours of Astronomy, the ambitious "Around the World in 80 Telescopes" event is a unique live webcast over 24 hours, following night and day around the globe to some of the most advanced observatories on and off the planet. To provide a long-lasting memory of this amazing world tour, observatories worldwide are revealing wonderful, and previously unseen, astronomical images. For its part, ESO is releasing outstanding pictures of two galaxies, observed with telescopes at the La Silla and Paranal observatories. The first of these depicts the irregular galaxy NGC 55, a member of the prominent Sculptor group of galaxies in the southern constellation of Sculptor. The galaxy is about 70 000 light-years across, that is, a little bit smaller than our own Milky Way. NGC 55 actually resembles more our galactic neighbour, the Large Magellanic Cloud (LMC), although the LMC is seen face-on, whilst NGC 55 is edge-on. By studying about 20 planetary nebulae in this image, a team of astronomers found that NGC 55 is located about 7.5 million light-years away. They also found that the galaxy might be forming a bound pair with the gorgeous spiral galaxy NGC 300 . Planetary nebulae are the final blooming of Sun-like stars before their retirement as white dwarfs. This striking image of NGC 55, obtained with the Wide Field Imager on the 2.2-metre MPG/ESO telescope at La Silla, is dusted with a flurry of reddish nebulae, created by young, hot massive stars. Some of the more extended ones are not unlike those seen in the LMC, such as the Tarantula Nebula. The quality

  11. 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.

  12. 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.

  13. 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.

  14. Multiprocessor switch with selective pairing

    SciTech Connect

    Gara, Alan; Gschwind, Michael K; Salapura, Valentina

    2014-03-11

    System, method and computer program product for a multiprocessing system to offer selective pairing of processor cores for increased processing reliability. A selective pairing facility is provided that selectively connects, i.e., pairs, multiple microprocessor or processor cores to provide one highly reliable thread (or thread group). Each paired microprocessor or processor cores that provide one highly reliable thread for high-reliability connect with a system components such as a memory "nest" (or memory hierarchy), an optional system controller, and optional interrupt controller, optional I/O or peripheral devices, etc. The memory nest is attached to a selective pairing facility via a switch or a bus

  15. 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

  16. 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.)

  17. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    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.

  19. 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.

  20. 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.

  1. Multiple origins of asteroid pairs

    NASA Astrophysics Data System (ADS)

    Jacobson, Seth A.

    2016-01-01

    Rotationally fissioned asteroids produce unbound asteroid pairs that have very similar heliocentric orbits. Backward integration of their current heliocentric orbits provides an age of closest proximity that can be used to date the rotational fission event. Most asteroid pairs follow a predicted theoretical relationship between the primary spin period and the mass ratio of the two pair members that is a direct consequence of the YORP-induced rotational fission hypothesis. If the progenitor asteroid has strength, asteroid pairs may have higher mass ratios or faster rotating primaries. However, the process of secondary fission leaves the originally predicted trend unaltered. We also describe the characteristics of pair members produced by four alternative routes from a rotational fission event to an asteroid pair. Unlike direct formation from the event itself, the age of closest proximity of these pairs cannot generally be used to date the rotational fission event since considerable time may have passed.

  2. Insights on galaxy formation

    NASA Astrophysics Data System (ADS)

    Bullock, James Steven

    1999-12-01

    Recent advances in theoretical modeling coupled with a wealth of new observational data, provide a unique opportunity for gaining insight into process of galaxy formation. I present results which test and develop current theories. The analysis utilizes state of the art theoretical modeling and makes predictions aimed at comparisons with some of the latest and upcoming observational data sets. In part I, I discuss an analysis of the structure and properties of dark matter halos (believed to govern the dynamical evolution of galaxies). The results make use of very high-resolution N-body simulations, and are derived from a new hierarchical halo finder, designed especially for these projects and to complement advancements in simulation technology. I present information on the dark matter halo substructure, density profiles, angular momentum structure, and collision rates. In part II, I discuss some aspects of galaxy formation theory in light of new observational data. The discussion includes an investigation of the nature of high-redshift galaxies, the local velocity function of galaxies, and the use of gamma ray telescopes to probe the extra-galactic background light-the latter analysis is done in the context of semi-analytic modeling of galaxy formation. The most important conclusions of this thesis are as follows. (1)Dark matter halos at high redshift are much less concentrated than previously believed. implying that quiescently star-forming galaxies at high redshift are larger and dimmer than expected. (2)The observed bright. abundant. and highly clustered high- redshift (Lyman-break) galaxies are likely starbursts driven by collisions between relatively small galaxies at z ~ 3. And (3)there is a real possibility of using the growing advances in γ-ray astronomy to probe many poorly constrained processes of galaxy formation, including the stellar initial mass function and the star formation history of the universe.

  3. 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

  4. Pairing, pseudogap and Fermi arcs in cuprates

    DOE PAGESBeta

    Kaminski, Adam; Kondo, Takeshi; Takeuchi, Tsunehiro; Gu, Genda

    2014-04-29

    We use Angle Resolved Photoemission Spectroscopy (ARPES) to study the relationship between the pseudogap, pairing and Fermi arcs in cuprates. High quality data measured over a wide range of dopings reveals a consistent picture of Fermiology and pairing in these materials. The pseudogap is due to an ordered state that competes with superconductivity rather than preformed pairs. Pairing does occur below Tpair ~ 150K and significantly above Tc, but well below T* and the doping dependence of this temperature scale is distinct from that of the pseudogap. The d-wave gap is present below Tpair, and its interplay with strong scatteringmore » creates “artificial” Fermi arcs for Tc ≤ T ≤ Tpair. However, above Tpair, the pseudogap exists only at the antipodal region. This leads to presence of real, gapless Fermi arcs close to the node. The length of these arcs remains constant up to T*, where the full Fermi surface is recovered. As a result, we demonstrate that these findings resolve a number of seemingly contradictory scenarios.« less

  5. Spatial clustering in the ESO-Sculptor survey: two-point correlation functions by galaxy type at redshifts 0.1-0.5

    NASA Astrophysics Data System (ADS)

    de Lapparent, V.; Slezak, E.

    2007-09-01

    Context: Galaxy clustering shows segregation effects with galaxy type, color and luminosity, which bring clues on the relationship with the underlying density field. Aims: We explore these effects among the populations of giant and dwarf galaxies detected in the ESO-Sculptor survey. Methods: We calculate the spatial two-point auto and cross-correlation functions for the 765 galaxies with R_c≤ 21.5 and 0.1 ≤ z ≤ 0.51 and for subsets by spectral type and luminosity. Results: At separation of 0.3 h-1 Mpc, pairs of early-type galaxies dominate the clustering over all the other types of pairs. At intermediate scales, 0.3-5 h-1 Mpc, mixed pairs of dwarf and giant galaxies contribute equally as pairs of giant galaxies, whereas the latter dominate at ≃10 h-1 Mpc. Moreover, the correlation functions per galaxy type display the expected transition between the 1-halo and 2-halo regimes in the scenario of hierarchical merging of dark matter halos. The 1-halo component of the early-type galaxies largely outdoes that for the late spiral galaxies, and that for the dwarf galaxies is intermediate between both. In contrast, the 2-halo component of the early-type galaxies and late spiral galaxies are comparable, whereas that for the dwarf galaxies is consistent with null clustering. Conclusions: We link the clustering segregation of the early-type and late spiral galaxies to their spatial distribution within the underlying dark matter halos. The early-type galaxies are preferentially located near the centers of the most massive halos, whereas late spiral galaxies tend to occupy their outskirts or the centers of less massive halos. This appears to be independent of luminosity for the early-type galaxies, whereas faint late spiral galaxies might reside in less dense regions than their bright analogs. The present analysis also unveils unprecedented results on the contribution from dwarf galaxies: at the scale at which they significantly cluster inside the halos (≤0.3 h-1 Mpc

  6. Interstellar MG II Absorption Lines from Low-Redshift Galaxies

    NASA Astrophysics Data System (ADS)

    Bowen, David V.; Blades, J. Chris; Pettini, Max

    1995-08-01

    We have used the GHRS aboard HST to search for interstellar Mg II 2796, 2803 absorption from the disks and halos of 17 low-redshift galaxies, using as probes QSOs and extragalactic supernovae whose sight lines pass close to, or through, intervening galaxies. The galaxies studied are of diverse morphological type, reside in different environments, and lie at separations of p' ≃ 2-113 h-1 kpc from a QSO line of sight. Ten of 11 galaxies at separations 31-113 h-1 kpc show no absorption to equivalent width limits of W(λ2796) <40-90 mÅ, which corresponds to N(Mg II) ≃1-4 × 1012 cm-2. Six galaxies lie at p' ≤ 9 kpc, and of these, four (NGC 4319, the LMC, M81, and the Milky Way) show absorption. Two early-type galaxies (NGC 1380 and Leo I) show no absorption at p' < 9 kpc: these nondetections are surprising because the separations are small and point to the possibility that the existence of extended absorbing halos may be a function of galaxy type. All of the galaxies which produce absorption are plausibly members of interacting systems. For absorbing galaxies probed below 9 kpc, the sight line passes within the optical radius of the galaxy, where the interstellar medium (ISM) is expected to have a high covering factor, and we do not attribute the absorption to the interactions. However, we do find that the environment of the absorbing galaxies affects the characteristics of the absorption detected the strength of lines, the complexity of line components, the ionization state of the gas and we warn of the dangers inherent in constructing models of generic halos based on statistical properties of QSO absorption-line surveys. Our data suggest that the covering factor of Mg II absorption is high for galaxies within ≍10 kpc, but very small beyond ≍30 h-1 kpc, a result consistent with the size found of Mg II halos deduced for galaxies at redshifts z > 0.2. The low-redshift galaxies observed in this study which show Mg II absorption are probably drawn from the same

  7. 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

  8. 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.

  9. 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.

  10. 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.

  11. Are spiral galaxies heavy smokers

    SciTech Connect

    Davies, J.; Disney, M.; Phillipps, S )

    1990-07-01

    The dustiness of spiral galaxies is discussed. Starburst galaxies and the shortage of truly bright spiral galaxies is cited as evidence that spiral galaxies are far dustier than has been thought. The possibility is considered that the dust may be hiding missing mass.

  12. New water and remote galaxies complete ISO's observations

    NASA Astrophysics Data System (ADS)

    300 young stars have been identified to date, many of which were previously not recognized," Nordh and Olofsson say. "Most of the latter objects have luminosities 10-100 times lower than revealed by earlier observations. Our preliminary analysis indicates that at least ten per cent of the embedded young stars will become small brown dwarfs, or ownerless super-planets, less than one-tenth of the mass of the Sun." Colliding galaxies Some galaxies are unusually bright in the infrared because of cosmic traffic accidents that bring them into collision with other galaxies. The result is a frenzy of star formation called a starburst. The explosion of short-lived stars then creates a pall of warm dust which ISO observes in the infrared. The relative intensities of different wavelengths enable astronomers to distinguish starburst events from other sources of strong infrared rays, such as the environment of a black hole in the nucleus of a galaxy. Collisions and starbursts play an important part in the evolution of galaxies. A famous pair of colliding galaxies called the Antennae was one of the first objects to be examined by ISO. Continuing study of the Antennae over the past two years has revealed a clear picture of a starburst occurring exactly where the dense disks of the galaxies intersect. The nuclei of the two galaxies are plainly distinguished too. Centaurus A is a galaxy that first attracted the attention of astronomers by its strong of radio emissions. In its visible appearance, a large, round (elliptical) galaxy has a dark band across its face. This too turns out to be the result of a galactic collision. The dark band is a flat, disk-shaped galaxy seen almost edge-on. Centaurus A is the nearest case of a phenomenon seen elsewhere by ISO, in which a flat galaxy has merged with an elliptical galaxy while preserving its flat configuration. ISOCAM gives an image of Centaurus A in which the disk galaxy is the more conspicuous object. The orientation of the disk becomes

  13. 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

  14. Stereo Pair, Honolulu, Oahu

    NASA Technical Reports Server (NTRS)

    2000-01-01

    Honolulu, on the island of Oahu, is a large and growing urban area. This stereoscopic image pair, combining a Landsat image with topography measured by the Shuttle Radar Topography Mission (SRTM), shows how topography controls the urban pattern. This color image can be viewed in 3-D by viewing the left image with the right eye and the right image with the left eye (cross-eyed viewing), or by downloading and printing the image pair, and viewing them with a stereoscope.

    Features of interest in this scene include Diamond Head (an extinct volcano near the bottom of the image), Waikiki Beach (just above Diamond Head), the Punchbowl National Cemetary (another extinct volcano, near the image center), downtown Honolulu and Honolulu harbor (image left-center), and offshore reef patterns. The slopes of the Koolau mountain range are seen in the right half of the image. Clouds commonly hang above ridges and peaks of the Hawaiian Islands, but in this synthesized stereo rendition appear draped directly on the mountains. The clouds are actually about 1000 meters (3300 feet) above sea level.

    This stereoscopic image pair was generated using topographic data from the Shuttle Radar Topography Mission, combined with a Landsat 7 Thematic Mapper image collected at the same time as the SRTM flight. The topography data were used to create two differing perspectives, one for each eye. When stereoscopically merged, the result is a vertically exaggerated view of the Earth's surface in its full three dimensions. The United States Geological Survey's Earth Resources Observations Systems (EROS) Data Center, Sioux Falls, South Dakota, provided the Landsat data.

    The Shuttle Radar Topography Mission (SRTM), launched on February 11, 2000, used the same radar instrument that comprised the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) that flew twice on the Space Shuttle Endeavour in 1994. The mission was designed to collect three-dimensional measurements of the

  15. Heterospecific pairing and hybridization between Nasutitermes corniger and N. ephratae

    NASA Astrophysics Data System (ADS)

    Hartke, Tamara R.; Rosengaus, Rebeca B.

    2011-09-01

    The sympatric neotropical termites Nasutitermes corniger and Nasutitermes ephratae are clearly distinguishable based on morphology, nest architecture, defensive secretion composition, and molecular markers. However, given the extensive ecological, geographical, and behavioral overlap of these closely related species, the potential for interbreeding may exist. To explore this possibility, heterospecific pairs were formed experimentally to examine courtship and colony-establishment behaviors, and reproductive potential. Courtship and nest construction behavior occurred in heterospecific pairs in a similar manner to that of conspecific pairs. Survival of pairs depended upon the species of the female partner. N. ephratae females paired with N. corniger males produced as many offspring as conspecific pairs. N. corniger females mated to N. ephratae males, however, produced significantly fewer offspring at 60 days post-establishment than the reciprocal cross or conspecific N. ephratae or N. corniger pairs. This was also the only pairing in which any aggression was observed. Heterospecific pairs and groups formed in mate choice mesocosms, suggesting that species recognition between these two termites is not an important aspect of mate choice. Overall, species mismatch tolerance and hybrid offspring viability are high. The present data, together with previous evidence from defensive secretions and isozyme analysis, suggest that hybridization may periodically occur in nature, and that reproductive barriers between these two species may be incomplete. Hybridization could provide a rare but important source of genetic diversity and may ensure mating opportunities for the more abundant sex of alates in each species.

  16. 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

  17. Stereo Pair, Pasadena, California

    NASA Technical Reports Server (NTRS)

    2000-01-01

    This stereoscopic image pair is a perspective view that shows the western part of the city of Pasadena, California, looking north toward the San Gabriel Mountains. Portions of the cities of Altadena and La Canada Flintridge are also shown. The cluster of large buildings left of center, at the base of the mountains, is the Jet Propulsion Laboratory. This image shows the power of combining data from different sources to create planning tools to study problems that affect large urban areas. In addition to the well-known earthquake hazards, Southern California is affected by a natural cycle of fire and mudflows. Data shown in this image can be used to predict both how wildfires spread over the terrain and how mudflows are channeled down the canyons.

    The image was created from three datasets: the Shuttle Radar Topography Mission (SRTM) supplied the elevation, U. S. Geological Survey digital aerial photography provided the image detail, and the Landsat Thematic Mapper provided the color. The United States Geological Survey's Earth Resources Observations Systems (EROS) Data Center, Sioux Falls, South Dakota, provided the Landsat data and the aerial photography. The image can be viewed in 3-D by viewing the left image with the right eye and the right image with the left eye (cross-eyed viewing), or by downloading and printing the image pair, and viewing them with a stereoscope.

    The Shuttle Radar Topography Mission (SRTM), launched on February 11, 2000, used the same radar instrument that comprised the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) that flew twice on the Space Shuttle Endeavour in 1994. The mission was designed to collect three-dimensional measurements of the Earth's surface. To collect the 3-D data, engineers added a 60-meter-long (200-foot) mast, an additional C-band imaging antenna and improved tracking and navigation devices. The mission is a cooperative project between the National Aeronautics and Space Administration

  18. PROBING THE INTERSTELLAR MEDIUM OF z {approx} 1 ULTRALUMINOUS INFRARED GALAXIES THROUGH INTERFEROMETRIC OBSERVATIONS OF CO AND SPITZER MID-INFRARED SPECTROSCOPY

    SciTech Connect

    Pope, Alexandra; Kirkpatrick, Allison; Wagg, Jeff; Frayer, David; Armus, Lee; Chary, Ranga-Ram; Desai, Vandana; Daddi, Emanuele; Elbaz, David; Gabor, Jared

    2013-08-01

    We explore the relationship between gas, dust, and star formation in a sample of 12 ultraluminous infrared galaxies (ULIRGs) at high-redshift compared to a similar sample of local galaxies. We present new CO observations and/or Spitzer mid-IR spectroscopy for six 70 {mu}m selected galaxies at z {approx} 1 in order to quantify the properties of the molecular gas reservoir, the contribution of an active galactic nucleus (AGN) to the mid-IR luminosity, and the star formation efficiency (SFE = L{sub IR}/L{sup '}{sub CO}). The mid-IR spectra show strong polycyclic aromatic hydrocarbon (PAH) emission, and our spectral decomposition suggests that the AGN makes a minimal contribution (<25%) to the mid-IR luminosity. The 70 {mu}m selected ULIRGs, which we find to be spectroscopic close pairs, are observed to have high SFE, similar to local ULIRGs and high-redshift submillimeter galaxies, consistent with enhanced IR luminosity due to an ongoing major merger. Combined with existing observations of local and high-redshift ULIRGs, we further compare the PAH, IR, and CO luminosities. We show that the ratio L{sub PAH,6.2}/L{sub IR} decreases with increasing IR luminosity for both local and high-redshift galaxies, but the trend for high-redshift galaxies is shifted to higher IR luminosities; the average L{sub PAH,6.2}/L{sub IR} ratio at a given L{sub IR} is {approx}3 times higher at high-redshift. When we normalize by the molecular gas, we find this trend to be uniform for galaxies at all redshifts and that the molecular gas is correlated with the PAH dust emission. The similar trends seen in the [C II] to molecular gas ratios in other studies suggests that PAH emission, like [C II], continues to be a good tracer of photodissociation regions even at high-redshift. Together the CO, PAH, and far-IR fine structure lines should be useful for constraining the interstellar medium conditions in high-redshift galaxies.

  19. Young Galaxy's Magnetism Surprises Astronomers

    NASA Astrophysics Data System (ADS)

    2008-10-01

    Astronomers have made the first direct measurement of the magnetic field in a young, distant galaxy, and the result is a big surprise. Looking at a faraway protogalaxy seen as it was 6.5 billion years ago, the scientists measured a magnetic field at least 10 times stronger than that of our own Milky Way. They had expected just the opposite. The GBT Robert C. Byrd Green Bank Telescope CREDIT: NRAO/AUI/NSF The scientists made the discovery using the National Science Foundation's ultra-sensitive Robert C. Byrd Green Bank Telescope (GBT) in West Virginia. "This new measurement indicates that magnetic fields may play a more important role in the formation and evolution of galaxies than we have realized," said Arthur Wolfe, of the University of California-San Diego (UCSD). At its great distance, the protogalaxy is seen as it was when the Universe was about half its current age. According to the leading theory, cosmic magnetic fields are generated by the dynamos of rotating galaxies -- a process that would produce stronger fields with the passage of time. In this scenario, the magnetic fields should be weaker in the earlier Universe, not stronger. The new, direct magnetic-field measurement comes on the heels of a July report by Swiss and American astronomers who made indirect measurements that also implied strong magnetic fields in the early Universe. "Our results present a challenge to the dynamo model, but they do not rule it out," Wolfe said. There are other possible explanations for the strong magnetic field seen in the one protogalaxy Wolfe's team studied. "We may be seeing the field close to the central region of a massive galaxy, and we know such fields are stronger toward the centers of nearby galaxies. Also, the field we see may have been amplified by a shock wave caused by the collision of two galaxies," he said. The protogalaxy studied with the GBT, called DLA-3C286, consists of gas with little or no star formation occurring in it. The astronomers suspect that

  20. The Gaseous Extent of Galaxies and the Origin of Lyα Absorption Systems. V. Optical and Near-Infrared Photometry of Lyα-absorbing Galaxies at z<1

    NASA Astrophysics Data System (ADS)

    Chen, Hsiao-Wen; Lanzetta, Kenneth M.; Webb, John K.; Barcons, Xavier

    2001-10-01

    We present results of a program to obtain and analyze HST WFPC2 images and ground-based images of galaxies identified in an imaging and spectroscopic survey of faint galaxies in fields of HST spectroscopic target QSOs. Considering a sample of physically correlated galaxy and absorber pairs with galaxy-absorber cross-correlation amplitude ξga(v,ρ)>1 and with galaxy impact parameter ρ<200 h-1 kpc, we confirm and improve the results presented by Lanzetta et al. and Chen et al. that (1) extended gaseous envelopes are a common and generic feature of galaxies of a wide range of luminosity and morphological type, (2) the extent of tenuous gas [N(H I)>~1014 cm-2] around galaxies scales with galaxy B-band luminosity as r~L0.39+/-0.09B, and (3) galaxy interactions do not play an important role in distributing tenuous gas around galaxies in most cases. We further demonstrate that (4) the gaseous extent of galaxies scales with galaxy K-band luminosity as r~L0.28+/-0.08K, and (5) tenuous gas around typical L* galaxies is likely to be distributed in spherical halos of radius ~180 h-1 kpc of covering factor of nearly unity. The sample consists of 34 galaxy and absorber pairs and 13 galaxies that do not produce Lyα absorption lines to within sensitive upper limits. Redshifts of the galaxy and absorber pairs range from z=0.0752 to 0.8920 with a median of z=0.3567; impact parameter separations of the galaxy and absorber pairs range from ρ=12.4 to 175.2 h-1 kpc with a median of ρ=62.2 h-1 kpc. Of the galaxies, 15 (32%) are of B-band luminosity LB<0.25 LB* and six (13%) are of low surface brightness. The galaxy sample is therefore representative of the galaxy population over a large fraction of the Hubble time. Because galaxies of all morphological types possess extended gaseous halos and because the extent of tenuous gas around galaxies scales with galaxy K-band luminosity, we argue that galaxy mass-rather than recent star formation activity-is likely to be the dominant factor

  1. 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

  2. Rebuilding Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    2005-01-01

    Major Observing Programme Leads to New Theory of Galaxy Formation Summary Most present-day large galaxies are spirals, presenting a disc surrounding a central bulge. Famous examples are our own Milky Way or the Andromeda Galaxy. When and how did these spiral galaxies form? Why do a great majority of them present a massive central bulge? An international team of astronomers [1] presents new convincing answers to these fundamental questions. For this, they rely on an extensive dataset of observations of galaxies taken with several space- and ground-based telescopes. In particular, they used over a two-year period, several instruments on ESO's Very Large Telescope. Among others, their observations reveal that roughly half of the present-day stars were formed in the period between 8,000 million and 4,000 million years ago, mostly in episodic burst of intense star formation occurring in Luminous Infrared Galaxies. From this and other evidence, the astronomers devised an innovative scenario, dubbed the "spiral rebuilding". They claim that most present-day spiral galaxies are the results of one or several merger events. If confirmed, this new scenario could revolutionise the way astronomers think galaxies formed. PR Photo 02a/05: Luminosity - Oxygen Abundance Relation for Galaxies (VLT) PR Photo 02b/05: The Spiral Rebuilding Scenario A fleet of instruments How and when did galaxies form? How and when did stars form in these island universes? These questions are still posing a considerable challenge to present-day astronomers. Front-line observational results obtained with a fleet of ground- and space-based telescopes by an international team of astronomers [1] provide new insights into these fundamental issues. For this, they embarked on an ambitious long-term study at various wavelengths of 195 galaxies with a redshift [2] greater than 0.4, i.e. located more than 4000 million light-years away. These galaxies were studied using ESO's Very Large Telescope, as well as the

  3. Evidence for Tidal Interactions and Mergers as the Origin of Galaxy Morphology Evolution in Compact Groups

    NASA Astrophysics Data System (ADS)

    Coziol, R.; Plauchu-Frayn, I.

    2007-06-01

    We present the results of a morphological study based on NIR images of 25 galaxies, with different levels of nuclear activity (star formation or AGN), in eight compact groups (CGs) of galaxies. We independently perform two different analyses: a study of the deviations of the isophotal levels from pure ellipses and a study of morphological asymmetries. The results yielded by the two analyses are highly consistent. For the first time, it is possible to show that deviations from pure ellipses are produced by inhomogeneous stellar mass distributions related to galaxy interactions and mergers. We find evidence of mass asymmetries in 74% of the galaxies in our sample. In 59% of these cases, the asymmetries come in pairs and are consistent with tidal effects produced by the proximity of companion galaxies. The symmetric galaxies are generally small in size or mass and inactive, and have an early-type morphology. They may have already lost their gas and least-attached envelope of stars to their more massive companions. In 20% of the galaxies we find evidence for cannibalism: a big galaxy swallowing a smaller companion. In 36% of the early-type galaxies the color gradient is positive (blue nucleus) or flat. Summing up these results, as much as 52% of the galaxies in our sample could show evidence of an ongoing or past merger. Our observations also suggest that galaxies in CGs merge more frequently under ``dry'' conditions (that is, once they have lost most of their gas). The high frequency of interacting and merging galaxies observed in our study is consistent with the bias of our sample toward CGs of type B, which represent the most active phase in the evolution of the groups. In these groups we also find a strong correlation between asymmetries and nuclear activity in early-type galaxies. This correlation allows us to identify tidal interactions and mergers as the cause of galaxy morphology transformation in CGs.

  4. Featured Image: Spitzer Galaxies

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2015-11-01

    These three galaxies (click for a full view!) were imaged as a part of the Spitzer Survey of Stellar Structure in Galaxies (S4G), a recent survey of 2352 nearby galaxies with deep imaging at 3.6 and 4.5 m. The bottom panels show false-color near-UV and far-UV images previously obtained with GALEX. The top panels show the new images obtained with Spitzer as part of S4G. The three galaxies shown here represent three types of galaxies that have a high concentration of mass in their centers, yet still have a high specific star-formation rate (the star formation rate per unit stellar mass):Barred galaxies with a prominent ring around their nucleus, like NGC 7552Interacting systems, like NGC 2782Galaxies with compact bulges and smooth extended disks, like NGC 3642To learn why this is the case, and to see more results from S4G, see the original paper below.CitationJuan Carlos Muoz-Mateos et al 2015 ApJS 219 3. doi:10.1088/0067-0049/219/1/3

  5. Very wide binary stars as the primary source of stellar collisions in the galaxy

    SciTech Connect

    Kaib, Nathan A.; Raymond, Sean N.

    2014-02-20

    We present numerical simulations modeling the orbital evolution of very wide binaries, pairs of stars separated by over ∼10{sup 3} AU. Due to perturbations from other passing stars and the Milky Way's tide, the orbits of very wide binary stars occasionally become extremely eccentric, which forces close encounters between the companion stars. We show that this process causes a stellar collision between very wide binary companion stars once every 1000-7500 yr on average in the Milky Way. One of the main uncertainties in this collision rate is the amount of energy dissipated by dynamic tides during close (but not collisional) periastron passages. This dissipation presents a dynamical barrier to stellar collisions and can instead transform very wide binaries into close or contact binaries. However, for any plausible tidal dissipation model, very wide binary stars are an unrealized, and potentially the dominant, source of stellar collisions in our Galaxy. Such collisions should occur throughout the thin disk of the Milky Way. Stellar collisions within very wide binaries should yield a small population of single, Li-depleted, rapidly rotating massive stars.

  6. A Slow Merger History of Field Galaxies since z ~ 1

    NASA Astrophysics Data System (ADS)

    Bundy, Kevin; Fukugita, Masataka; Ellis, Richard S.; Kodama, Tadayuki; Conselice, Christopher J.

    2004-02-01

    Using deep infrared observations conducted with the CISCO imager on the Subaru Telescope, we investigate the field-corrected pair fraction and the implied merger rate of galaxies in redshift survey fields with Hubble Space Telescope (HST) imaging. In the redshift interval, 0.5pairs increases only modestly with redshift to 7%+/-6% at z~1. This is nearly a factor of 3 less than the fraction, 22%+/-8%, determined using the same technique on HST optical images and as measured in a previous similar study. Tests support the hypothesis that optical pair fractions at z~1 are inflated by bright star-forming regions that are unlikely to be representative of the underlying mass distribution. By determining stellar masses for the companions, we estimate the mass accretion rate associated with merging galaxies. At z~1, we estimate this to be 2×109+/-0.2 Msolar galaxy-1 Gyr-1. Although uncertainties remain, our results suggest that the growth of galaxies via the accretion of preexisting fragments remains as significant a phenomenon in the redshift range studied as that estimated from ongoing star formation in independent surveys. Based on data acquired at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

  7. Frustrated Lewis Pairs.

    PubMed

    Stephan, Douglas W

    2015-08-19

    The articulation of the notion of "frustrated Lewis pairs" (FLPs), which emerged from the discovery that H2 can be reversibly activated by combinations of sterically encumbered Lewis acids and bases, has prompted a great deal of recent activity. Perhaps the most remarkable consequence has been the development of FLP catalysts for the hydrogenation of a range of organic substrates. In the past 9 years, the substrate scope has evolved from bulky polar species to include a wide range of unsaturated organic molecules. In addition, effective stereoselective metal-free hydrogenation catalysts have begun to emerge. The mechanism of this activation of H2 has been explored, and the nature and range of Lewis acid/base combinations capable of effecting such activation have also expanded to include a variety of non-metal species. The reactivity of FLPs with a variety of other small molecules, including olefins, alkynes, and a range of element oxides, has also been developed. Although much of this latter chemistry has uncovered unique stoichiometric transformations, metal-free catalytic hydroamination, CO2 reduction chemistry, and applications in polymerization have also been achieved. The concept is also beginning to find applications in bioinorganic and materials chemistry as well as heterogeneous catalysis. This Perspective highlights many of these developments and discusses the relationship between FLPs and established chemistry. Some of the directions and developments that are likely to emerge from FLP chemistry in the future are also presented. PMID:26214241

  8. Pygmy stars: first pair.

    PubMed

    Zwicky, F

    1966-07-01

    The binary LP 101-15/16 having the proper motion of 1.62 seconds of arc per year has been studied with the prime-focus spectrograph of the 200-inch (508 cm) telescope. Indications are that LP 101-15/16 is the first pair of pygmy stars ever discovered. One of its components, LP 101-16, is probably a blue pygmy star which is at least four magnitudes fainter than the ordinary white dwarfs. Also, two of the Balmer lines in absorption appear to be displaced toward the red by amounts which indicate the existence of an Einstein gravitational red shift corresponding to about 1000 km sec-1. On the other hand LP 101-15 is red and shows an entirely new type of spectrum, which suggests that it may be a first representative of a type of red pygmy star which is 2.5 magnitudes fainter than the M-type dwarf stars of the main sequence. PMID:17730606

  9. Supernova 2007bi as a pair-instability explosion.

    PubMed

    Gal-Yam, A; Mazzali, P; Ofek, E O; Nugent, P E; Kulkarni, S R; Kasliwal, M M; Quimby, R M; Filippenko, A V; Cenko, S B; Chornock, R; Waldman, R; Kasen, D; Sullivan, M; Beshore, E C; Drake, A J; Thomas, R C; Bloom, J S; Poznanski, D; Miller, A A; Foley, R J; Silverman, J M; Arcavi, I; Ellis, R S; Deng, J

    2009-12-01

    Stars with initial masses such that 10M[symbol: see text] or= 140M[symbol: see text] (if such exist) develop oxygen cores with masses, M(core), that exceed 50M[symbol: see text], where high temperatures are reached at relatively low densities. Conversion of energetic, pressure-supporting photons into electron-positron pairs occurs before oxygen ignition and leads to a violent contraction which triggers a nuclear explosion that unbinds the star in a pair-instability supernova. Transitional objects with 100M[symbol: see text] < M(initial) < 140M[symbol: see text] may end up as iron-core-collapse supernovae following violent mass ejections, perhaps as a result of brief episodes of pair instability, and may already have been identified. Here we report observations of supernova SN 2007bi, a luminous, slowly evolving object located within a dwarf galaxy. We estimate the exploding core mass to be M(core) approximately 100M[symbol: see text], in which case theory unambiguously predicts a pair-instability supernova. We show that >3M[symbol: see text] of radioactive (56)Ni was synthesized during the explosion and that our observations are well fitted by models of pair-instability supernovae. This indicates that nearby dwarf galaxies probably host extremely massive stars, above the apparent Galactic stellar mass limit, which perhaps result from processes similar to those that created the first stars in the Universe. PMID:19956255

  10. Cluster galaxies die hard

    NASA Astrophysics Data System (ADS)

    Weinmann, Simone M.; Kauffmann, Guinevere; von der Linden, Anja; De Lucia, Gabriella

    2010-08-01

    We investigate how the specific star formation rates of galaxies of different masses depend on cluster-centric radius and on the central/satellite dichotomy in both field and cluster environments. Recent data from a variety of sources, including the cluster catalogue of von der Linden et al., are compared to the semi-analytic models of De Lucia & Blaizot. We find that these models predict too many passive satellite galaxies in clusters, too few passive central galaxies with low stellar masses and too many passive central galaxies with high masses. We then outline a series of modifications to the model necessary to solve these problems: (a) instead of instantaneous stripping of the external gas reservoir after a galaxy becomes a satellite, the gas supply is assumed to decrease at the same rate that the surrounding halo loses mass due to tidal stripping and (b) the active galactic nuclei (AGN) feedback efficiency is lowered to bring the fraction of massive passive centrals in better agreement with the data. We also allow for radio mode AGN feedback in satellite galaxies. (c) We assume that satellite galaxies residing in host haloes with masses below 1012h-1Msolar do not undergo any stripping. We highlight the fact that in low-mass galaxies, the external reservoir is composed primarily of gas that has been expelled from the galactic disc by supernovae-driven winds. This gas must remain available as a future reservoir for star formation, even in satellite galaxies. Finally, we present a simple recipe for the stripping of gas and dark matter in satellites that can be used in models where subhalo evolution is not followed in detail.

  11. Excitation Conditions in the Multi-component Submillimeter Galaxy SMM J00266+1708

    NASA Astrophysics Data System (ADS)

    Sharon, Chelsea E.; Baker, Andrew J.; Harris, Andrew I.; Tacconi, Linda J.; Lutz, Dieter; Longmore, Steven N.

    2015-01-01

    We present multiline CO observations of the complex submillimeter galaxy SMM J00266+1708. Using the Zpectrometer on the Green Bank Telescope, we provide the first precise spectroscopic measurement of its redshift (z = 2.742). Based on followup CO(1-0), CO(3-2), and CO(5-4) mapping, SMM J00266+1708 appears to have two distinct components separated by ~500 km s-1 that are nearly coincident along our line of sight. The two components show hints of different kinematics, with the blueshifted component dispersion-dominated and the redshifted component showing a clear velocity gradient. CO line ratios differ slightly between the two components, indicating that the physical conditions in their molecular gas may not be alike. We tentatively infer that SMM J00266+1708 is an ongoing merger with a mass ratio of (7.8 ± 4.0)/sin 2(i), with its overall size and surface brightness closely resembling that of other merging systems. We perform large velocity gradient modeling of the CO emission from both components and find that each component's properties are consistent with a single phase of molecular gas (i.e., a single temperatures and density); additional multi-phase modeling of the redshifted component, although motivated by a CO(1-0) size larger than the CO(3-2) size, is inconclusive. SMM J00266+1708 provides evidence of early stage mergers within the submillimeter galaxy population. Continuum observations of J00266 at the ~1'' resolution of our observations could not have distinguished between the two components due to their separation (0.''73 ± 0.''06), illustrating that the additional velocity information provided by spectral line studies is important for addressing the prevalence of unresolved galaxy pairs in low-resolution submillimeter surveys. Based on observations carried out with the IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).

  12. Corrugated velocity pattern in spiral galaxies: NGC 278, NGC 1058, NGC 2500 and UGC 3574

    NASA Astrophysics Data System (ADS)

    Sánchez Gil, M. C.; Alfaro, E. J.; Pérez, E.

    2011-11-01

    We report the detection in Hα emission of a radial corrugation pattern in the vertical velocity field of a sample of nearby face-on, spiral galaxies. We obtain long-slit spectra with the double arm ISIS spectrograph, attached to the 4.2 m William Herschel Telescope. The existence of corrugations has been already reported, e.g. Alfaro et al. (2001), Matthews & Uson (2008). Corrugations are closely link, as cause/effect, to the large scale star formation processes: density waves, tidal interactions, galactic bores, collisions of high velocity clouds with disk, etc. Which mechanism is the origin of disk corrugations is still an open problem. In this work not only the existence of radial and azimuthal corrugations are clearly observed, we report a first systematic study on the velocity corrugations in a sample of nearly face-on spiral galaxies. NGC 278 and NGC 1058 show a similar behavior to NGC 5427 (Alfaro et al. 2001), with a clear displacement between the velocities and emission line peaks. Where the approaching velocity peaks occur in the convex border of the arms, and the receding maxima are located behind the Hα emission maxima, in the concave side. This kinematical behavior is similar to the one expected in a galactic bore generated by the interaction of a spiral density wave with a thick gaseous disk. NGC 2500 and UGC 3574 do not show so clear this last relation between the velocity and emission line peaks, a possible cause should a fainter and discontinuous Hα emission. Oddly, these two pairs of galaxies also differ between them in their ionization mechanism features obtained from diagnostic diagrams.

  13. EXCITATION CONDITIONS IN THE MULTI-COMPONENT SUBMILLIMETER GALAXY SMM J00266+1708

    SciTech Connect

    Sharon, Chelsea E.; Baker, Andrew J.; Harris, Andrew I.; Tacconi, Linda J.; Lutz, Dieter; Longmore, Steven N.

    2015-01-10

    We present multiline CO observations of the complex submillimeter galaxy SMM J00266+1708. Using the Zpectrometer on the Green Bank Telescope, we provide the first precise spectroscopic measurement of its redshift (z = 2.742). Based on followup CO(1-0), CO(3-2), and CO(5-4) mapping, SMM J00266+1708 appears to have two distinct components separated by ∼500 km s{sup –1} that are nearly coincident along our line of sight. The two components show hints of different kinematics, with the blueshifted component dispersion-dominated and the redshifted component showing a clear velocity gradient. CO line ratios differ slightly between the two components, indicating that the physical conditions in their molecular gas may not be alike. We tentatively infer that SMM J00266+1708 is an ongoing merger with a mass ratio of (7.8 ± 4.0)/sin {sup 2}(i), with its overall size and surface brightness closely resembling that of other merging systems. We perform large velocity gradient modeling of the CO emission from both components and find that each component's properties are consistent with a single phase of molecular gas (i.e., a single temperatures and density); additional multi-phase modeling of the redshifted component, although motivated by a CO(1-0) size larger than the CO(3-2) size, is inconclusive. SMM J00266+1708 provides evidence of early stage mergers within the submillimeter galaxy population. Continuum observations of J00266 at the ∼1'' resolution of our observations could not have distinguished between the two components due to their separation (0.''73 ± 0.''06), illustrating that the additional velocity information provided by spectral line studies is important for addressing the prevalence of unresolved galaxy pairs in low-resolution submillimeter surveys.

  14. Ultra-flat galaxies selected from RFGC catalog. II. Orbital estimates of halo masses

    NASA Astrophysics Data System (ADS)

    Karachentsev, I. D.; Karachentseva, V. E.; Kudrya, Yu. N.

    2016-04-01

    We used the Revised Flat Galaxy Catalog (RFGC) to select 817 ultra-flat (UF) edge-on disk galaxies with blue and red apparent axial ratios of ( a/ b)B > 10.0 and ( a/ b)R > 8.5. The sample covering the whole sky, except the Milky Way zone, contains 490 UF galaxies with measured radial velocities. Our inspection of the neighboring galaxies around them revealed only 30 companions with radial velocity difference of | ΔV |< 500 kms-1 inside the projected separation of R p < 250 kpc. Wherein, the wider area around the UF galaxy within R p < 750 kpc contains no other neighbors brighter than the UF galaxy itself in the same velocity span. The resulting sample galaxies mostly belong to the morphological types Sc, Scd, Sd. They have a moderate rotation velocity curve amplitude of about 120 km s-1 and a moderate K-band luminosity of about 1010 L ⊙. The median difference of radial velocities of their companions is 87 km s-1, yielding the median orbital mass estimate of about 5 × 1011 M ⊙. Excluding six probable non-isolated pairs, we obtained a typical halo-mass-to-stellar-mass of UF galaxies of about 30, what is almost the same one as in the principal spiral galaxies, like M31 and M81 in the nearest groups. We also note that ultra-flat galaxies look two times less "dusty" than other spirals of the same luminosity.

  15. Accurate and efficient halo-based galaxy clustering modelling with simulations

    NASA Astrophysics Data System (ADS)

    Zheng, Zheng; Guo, Hong

    2016-06-01

    Small- and intermediate-scale galaxy clustering can be used to establish the galaxy-halo connection to study galaxy formation and evolution and to tighten constraints on cosmological parameters. With the increasing precision of galaxy clustering measurements from ongoing and forthcoming large galaxy surveys, accurate models are required to interpret the data and extract relevant information. We introduce a method based on high-resolution N-body simulations to accurately and efficiently model the galaxy two-point correlation functions (2PCFs) in projected and redshift spaces. The basic idea is to tabulate all information of haloes in the simulations necessary for computing the galaxy 2PCFs within the framework of halo occupation distribution or conditional luminosity function. It is equivalent to populating galaxies to dark matter haloes and using the mock 2PCF measurements as the model predictions. Besides the accurate 2PCF calculations, the method is also fast and therefore enables an efficient exploration of the parameter space. As an example of the method, we decompose the redshift-space galaxy 2PCF into different components based on the type of galaxy pairs and show the redshift-space distortion effect in each component. The generalizations and limitations of the method are discussed.

  16. 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

  17. 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. PMID:21737732

  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. 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.

  20. Lone pairs: an electrostatic viewpoint.

    PubMed

    Kumar, Anmol; Gadre, Shridhar R; Mohan, Neetha; Suresh, Cherumuttathu H

    2014-01-16

    A clear-cut definition of lone pairs has been offered in terms of characteristics of minima in molecular electrostatic potential (MESP). The largest eigenvalue and corresponding eigenvector of the Hessian at the minima are shown to distinguish lone pair regions from the other types of electron localization (such as π bonds). A comparative study of lone pairs as depicted by various other scalar fields such as the Laplacian of electron density and electron localization function is made. Further, an attempt has been made to generalize the definition of lone pairs to the case of cations. PMID:24372481

  1. Methods for Identifying Pair Halos

    NASA Astrophysics Data System (ADS)

    Wells, Brendan; Caputo, Regina; Atwood, William; Ritz, Steven M.

    2016-01-01

    The flux of very high energy gamma rays from active galactic nuclei (AGN) is attenuated via interactions with extragalactic background photons and is converted into e+e- pairs. With non-zero intergalactic magnetic fields, the electrons and positrons will deflect as they propagate and simultaneously lose energy by upscattering cosmic microwave background photons. "Pair halos," the visible consequences of these electromagnetic cascades, are faint and difficult to observe against their AGN counterparts. We investigate three methods for indirectly identifying pair halos, using a two-component approach to model the AGN core/halo image. We estimate each method's sensitivity by utilizing a new, detailed Monte Carlo pair-halo simulation.

  2. 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

  3. 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.

  4. Optical imaging for the Spitzer Survey of Stellar Structure in Galaxies. Data release and notes on interacting galaxies

    NASA Astrophysics Data System (ADS)

    Knapen, Johan H.; Erroz-Ferrer, Santiago; Roa, Javier; Bakos, Judit; Cisternas, Mauricio; Leaman, Ryan; Szymanek, Nik

    2014-09-01

    Context. The Spitzer Survey for Stellar Structure in Galaxies (S4G) and its more recently approved extension will lead to a set of 3.6 and 4.5 μm images for 2829 galaxies, which can be used to study many different aspects of the structure and evolution of local galaxies. Aims: We have collected and re-reduced optical images of 1768 of the survey galaxies, aiming to make these available to the community as ready-to-use FITS files to be used in conjunction with the mid-IR images. Our sky-subtraction and mosaicking procedures were optimised for imaging large galaxies. We also produce false-colour images of some of these galaxies to be used for illustrative and public outreach purposes. Methods: We collected and re-processed images in five bands from the Sloan Digital Sky Survey for 1657 galaxies, which are publicly released with the publication of this paper. We observed, in only the g-band, an additional 111 S4G galaxies in the northern hemisphere with the 2.5 m Liverpool Telescope, so that optical imaging is released for 1768 galaxies, or for 62% of the S4G sample. We visually checked all images. We noted interactions and close companions in our optical data set and in the S4G sample, confirming them by determining the galaxies' radial velocities and magnitudes in the NASA-IPAC Extragalactic Database. Results: We find that 17% of the S4G galaxies (21% of those brighter than 13.5 mag) have a close companion (within a radius of five times the diameter of the sample galaxy, a recession velocity within ± 200 km s-1 and not more than 3 mag fainter) and that around 5% of the bright part of the S4G sample show significant morphological evidence of an ongoing interaction. This confirms and further supports previous estimates of these fractions. Conclusions: The over 8000 science images described in this paper, the re-processed Sloan Digital Sky Survey ones, the new Liverpool Telescope images, the set of 29 false-colour pictures, and the catalogue of companion and

  5. Galaxy Star Formation as a function of Environment

    NASA Astrophysics Data System (ADS)

    Castander, F. J.; Balogh, M. L.; Bernardi, M.; Bower, R. G.; Connolly, A. J.; Gilbank, D. G.; Gómez, P. L.; Goto, T.; Hopkins, A. M.; Miller, C. J.; Nichol, R. C.; Schneider, D. P.; Seth, R.; Zabludoff, A. I.

    We study the galaxy star formation rate (SFR) as a function of environment using the SDSS EDR data. We find that the SFR is depressed in dense environments (clusters and groups) compared to the field. We find that the suppression of the SFR starts to be noticeable at around 4 virial radii. We find no evidence for SF triggering as galaxies fall into the clusters. We also present a project to study these effects in cluster pairs systems where the effects of filaments and large scale structure may be noticeable.

  6. Lung pair phantom

    DOEpatents

    Olsen, P.C.; Gordon, N.R.; Simmons, K.L.

    1993-11-30

    The present invention is a material and method of making the material that exhibits improved radiation attenuation simulation of real lungs, i.e., an ``authentic lung tissue`` or ALT phantom. Specifically, the ALT phantom is a two-part polyurethane medium density foam mixed with calcium carbonate, potassium carbonate if needed for K-40 background, lanthanum nitrate, acetone, and a nitrate or chloride form of a radionuclide. This formulation is found to closely match chemical composition and linear attenuation of real lungs. The ALT phantom material is made according to established procedures but without adding foaming agents or preparing thixotropic concentrate and with a modification for ensuring uniformity of density of the ALT phantom that is necessary for accurate simulation. The modification is that the polyurethane chemicals are mixed at a low temperature prior to pouring the polyurethane mixture into the mold.

  7. Lung pair phantom

    DOEpatents

    Olsen, Peter C.; Gordon, N. Ross; Simmons, Kevin L.

    1993-01-01

    The present invention is a material and method of making the material that exhibits improved radiation attenuation simulation of real lungs, i.e., an "authentic lung tissue" or ALT phantom. Specifically, the ALT phantom is a two-part polyurethane medium density foam mixed with calcium carbonate, potassium carbonate if needed for K-40 background, lanthanum nitrate, acetone, and a nitrate or chloride form of a radionuclide. This formulation is found to closely match chemical composition and linear attenuation of real lungs. The ALT phantom material is made according to established procedures but without adding foaming agents or preparing thixotropic concentrate and with a modification for ensuring uniformity of density of the ALT phantom that is necessary for accurate simulation. The modification is that the polyurethane chemicals are mixed at a low temperature prior to pouring the polyurethane mixture into the mold.

  8. CO-ORBITING PLANES OF SUB-HALOS ARE SIMILARLY UNLIKELY AROUND PAIRED AND ISOLATED HOSTS

    SciTech Connect

    Pawlowski, Marcel S.; McGaugh, Stacy S.

    2014-07-01

    Sub-halos in dark-matter-based cosmological simulations tend to be distributed approximately isotropically around their host. The existence of highly flattened, co-orbiting planes of satellite galaxies has therefore been identified as a possible problem for these cosmological models, but so far studies have not considered the hosts' environments. That satellite planes are now known around both major galaxies in the Local Group raises the question whether they are more likely to be found around paired hosts. In a first attempt to investigate this possibility, we focus on the flattening and orbital coherence of the 11 brightest satellite galaxies of the vast polar structure (VPOS) around the Milky Way (MW). We search for VPOS analogs in the ''Exploring the Local Volume in Simulations'' suite of cosmological simulations, which consist of 24 paired and 24 isolated host halos. We do not find significant differences between the properties of sub-halo distributions around paired and isolated hosts. The observed flattening and the observed orbital alignment are each reproduced by only 0.2%-2% of paired and isolated systems incorporating the obscuration of satellites by randomly oriented galactic disks. Only 1 of all 4800 analyzed realizations (0.02%) reproduces both parameters simultaneously, but the average orbital pole of this sub-halo system does not align as well with the normal to the plane fit as observed. That the MW is part of a galaxy pair thus does not help to explain the existence of the VPOS if the satellite galaxies are identified with sub-halos found in dissipationless simulations.

  9. Pairs of promoter pairs in a web of transcription.

    PubMed

    Kaplan, Craig D

    2016-08-30

    A new analysis has characterized a fundamental building block of complex transcribed loci. Constellations of core promoters can generally be reduced to pairs of divergent transcription units, where the distance between the pairs of transcription units correlates with constraints on genomic context, which in turn contribute to transcript fate. PMID:27573684

  10. Shocks and Cavities from Multiple Outbursts in the Galaxy Group NGC 5813: A Window to Active Galactic Nucleus Feedback

    NASA Astrophysics Data System (ADS)

    Randall, S. W.; Forman, W. R.; Giacintucci, S.; Nulsen, P. E. J.; Sun, M.; Jones, C.; Churazov, E.; David, L. P.; Kraft, R.; Donahue, M.; Blanton, E. L.; Simionescu, A.; Werner, N.

    2011-01-01

    We present results from new Chandra, GMRT, and SOAR observations of NGC 5813, the dominant central galaxy in a nearby galaxy group. The system shows three pairs of collinear cavities at 1 kpc, 8 kpc, and 20 kpc from the central source, from three distinct outbursts of the central active galactic nucleus (AGN), which occurred 3 × 106, 2 × 107, and 9 × 107 yr ago. The Hα and X-ray observations reveal filaments of cool gas that has been uplifted by the X-ray cavities. The inner two cavity pairs are filled with radio-emitting plasma, and each pair is associated with an elliptical surface brightness edge, which we unambiguously identify as shocks (with measured temperature jumps) with Mach numbers of M ≈ 1.7 and M ≈ 1.5 for the inner and outer shocks, respectively. Such clear signatures from three distinct AGN outbursts in an otherwise dynamically relaxed system provide a unique opportunity to study AGN feedback and outburst history. The mean power of the two most recent outbursts differs by a factor of six, from (1.5-10)×1042 erg s-1, indicating that the mean jet power changes significantly over long (~107 yr) timescales. The total energy output of the most recent outburst is also more than an order of magnitude less than the total energy of the previous outburst (1.5 × 1056 erg versus 4 × 1057 erg), which may be a result of the lower mean power, or may indicate that the most recent outburst is ongoing. The outburst interval implied by both the shock and cavity ages (~107 yr) indicates that, in this system, shock heating alone is sufficient to balance radiative cooling close to the central AGN, which is the relevant region for regulating feedback between the intracluster medium and the central supermassive black hole.

  11. A Portrait of One Hundred Thousand and One Galaxies

    NASA Astrophysics Data System (ADS)

    2002-08-01

    NGC 300 and the surrounding sky field, obtained in 1999 and 2000 with the Wide-Field Imager (WFI) on the MPG/ESO 2.2-m telescope at the La Silla Observatory. See the text for details about the many different uses of this photo. Smaller areas in this large field are shown in Photos 18b-h/02 , cf. below. The High-Res version of this image has been compressed by a factor 4 (2 x 2 pixel rebinning) to reduce it to a reasonably transportable size. Technical information about this and the other photos is available at the end of this communication. Located some 7 million light-years away, the spiral galaxy NGC 300 [1] is a beautiful representative of its class, a Milky-Way-like member of the prominent Sculptor group of galaxies in the southern constellation of that name. NGC 300 is a big object in the sky - being so close, it extends over an angle of almost 25 arcmin, only slightly less than the size of the full moon. It is also relative bright, even a small pair of binoculars will unveil this magnificent spiral galaxy as a hazy glowing patch on a dark sky background. The comparatively small distance of NGC 300 and its face-on orientation provide astronomers with a wonderful opportunity to study in great detail its structure as well as its various stellar populations and interstellar medium. It was exactly for this purpose that some images of NGC 300 were obtained with the Wide-Field Imager (WFI) on the MPG/ESO 2.2-m telescope at the La Silla Observatory. This advanced 67-million pixel digital camera has already produced many impressive pictures, some of which are displayed in the WFI Photo Gallery [2]. With its large field of view, 34 x 34 arcmin 2 , the WFI is optimally suited to show the full extent of the spiral galaxy NGC 300 and its immediate surroundings in the sky, cf. PR Photo 18a/02 . NGC 300 and "Virtual Astronomy" In addition to being a beautiful sight in its own right, the present WFI-image of NGC 300 is also a most instructive showcase of how astronomers with

  12. 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.

  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. Erratum: A Comparison of Radio Axis with Host Galaxy Plane Axis in Seyfert Galaxies

    NASA Astrophysics Data System (ADS)

    Schmitt, Henrique R.; Kinney, Anne L.; Storchi-Bergmann, Thaisa; Antonucci, Robert

    1997-08-01

    In the paper ``A Comparison of Radio Axis with Host Galaxy Plane Axis in Seyfert Galaxies'' by Henrique R. Schmitt, Anne L. Kinney, Thaisa Storchi-Bergmann, & Robert Antonucci (ApJ, 477, 623 [1997]), there are errors in Table 1 and Figure 6, and there is a reference to a previous work that should be stated. With respect to the latter, the authors compare the position angle of small-scale radio structures in Seyfert galaxies with the position angle of their host galaxy major axis. In their analysis they find a zone of avoidance, where the small-scale radio axis avoids close alignment with the host galaxy minor axis. The authors wish to note that J. S. Ulvestad and A. S. Wilson (ApJ, 285, 439 [1984]) already observed a paucity of radio structures aligned with the host galaxy minor axis in Seyfert 2 galaxies, although on a smaller sample. Ulvestad & Wilson was referenced in their paper as Ulvestad & Wilson (1984b). In Table 1 there were errors in the references listed in the note to the table. A new version of Table 1 with correct references is given here, and the following reference entries should be added to the reference list of the original paper: Mulchaey, J. S., Wilson, A. S., & Tsvetanov, Z. I. 1996, ApJS, 102, 309; Oke, J. B., & Lauer, T. R. 1979, ApJ, 230, 360; Simkin, S. M. 1975, ApJ, 200, 567. Figure 6a was printed twice, once correctly and once incorrectly in place of Figure 6c. The correct version of Figure 6c appears below.

  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. PMID:11452300

  17. J1216+0709: A Radio Galaxy with Three Episodes of AGN Jet Activity

    NASA Astrophysics Data System (ADS)

    Singh, Veeresh; Ishwara-Chandra, C. H.; Kharb, Preeti; Srivastava, Shweta; Janardhan, P.

    2016-08-01

    We report the discovery of a “triple-double radio galaxy,” J1216+0709, detected in deep low-frequency Giant Metrewave Radio Telescope (GMRT) observations. J1216+0709 is only the third radio galaxy, after B0925+420 and Speca, with three pairs of lobes resulting from three different episodes of active galactic nucleus (AGN) jet activity. The 610 MHz GMRT image clearly displays an inner pair of lobes, a nearly coaxial middle pair of lobes, and a pair of outer lobes that is bent with respect to the axis of the inner pair of lobes. The total end-to-end projected sizes of the inner, middle, and outer lobes are 40″ (∼95 kpc), 1.‧65 (∼235 kpc), and 5.‧7 (∼814 kpc), respectively. Unlike the outer pair of lobes, both the inner and middle pairs of lobes exhibit asymmetries in arm lengths and flux densities, but in the opposite sense, i.e., the eastern sides are farther and also brighter than the western sides, thus, suggesting the possibility of the jet being intrinsically asymmetric rather than due to a relativistic beaming effect. The host galaxy is a bright elliptical (m r ∼ 16.56) with M SMBH ∼ 3.9 × 109 M ⊙ and a star formation rate of ∼{4.66}-1.61{{+4.65}} M ⊙ yr‑1. The host galaxy resides in a small group of three galaxies (m r ≤ 17.77) and is possibly going through an interaction with faint dwarf galaxies in the neighborhood, which may have triggered the recent episodes of AGN activity.

  18. J1216+0709: A Radio Galaxy with Three Episodes of AGN Jet Activity

    NASA Astrophysics Data System (ADS)

    Singh, Veeresh; Ishwara-Chandra, C. H.; Kharb, Preeti; Srivastava, Shweta; Janardhan, P.

    2016-08-01

    We report the discovery of a “triple-double radio galaxy,” J1216+0709, detected in deep low-frequency Giant Metrewave Radio Telescope (GMRT) observations. J1216+0709 is only the third radio galaxy, after B0925+420 and Speca, with three pairs of lobes resulting from three different episodes of active galactic nucleus (AGN) jet activity. The 610 MHz GMRT image clearly displays an inner pair of lobes, a nearly coaxial middle pair of lobes, and a pair of outer lobes that is bent with respect to the axis of the inner pair of lobes. The total end-to-end projected sizes of the inner, middle, and outer lobes are 40″ (˜95 kpc), 1.‧65 (˜235 kpc), and 5.‧7 (˜814 kpc), respectively. Unlike the outer pair of lobes, both the inner and middle pairs of lobes exhibit asymmetries in arm lengths and flux densities, but in the opposite sense, i.e., the eastern sides are farther and also brighter than the western sides, thus, suggesting the possibility of the jet being intrinsically asymmetric rather than due to a relativistic beaming effect. The host galaxy is a bright elliptical (m r ˜ 16.56) with M SMBH ˜ 3.9 × 109 M ⊙ and a star formation rate of ˜{4.66}-1.61{{+4.65}} M ⊙ yr‑1. The host galaxy resides in a small group of three galaxies (m r ≤ 17.77) and is possibly going through an interaction with faint dwarf galaxies in the neighborhood, which may have triggered the recent episodes of AGN activity.

  19. 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.

  20. 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.