The Economic Demography of Mass Poverty.

ERIC Educational Resources Information Center

Abegaz, Berhanu, Ed.

1986-01-01

The four papers in this volume discuss various facets of the poverty-demography interaction: the rationale for the desired family size of the poor, the problems of attaining such size, the effect of family size/structure on household economy, and the future well-being of the children of the poor. "Mass Poverty, Demography, and Development…

Lensing is low: cosmology, galaxy formation or new physics?

NASA Astrophysics Data System (ADS)

Leauthaud, Alexie; Saito, Shun; Hilbert, Stefan; Barreira, Alexandre; More, Surhud; White, Martin; Alam, Shadab; Behroozi, Peter; Bundy, Kevin; Coupon, Jean; Erben, Thomas; Heymans, Catherine; Hildebrandt, Hendrik; Mandelbaum, Rachel; Miller, Lance; Moraes, Bruno; Pereira, Maria E. S.; Rodríguez-Torres, Sergio A.; Schmidt, Fabian; Shan, Huan-Yuan; Viel, Matteo; Villaescusa-Navarro, Francisco

2017-05-01

We present high signal-to-noise galaxy-galaxy lensing measurements of the Baryon Oscillation Spectroscopic Survey constant mass (CMASS) sample using 250 deg2 of weak-lensing data from Canada-France-Hawaii Telescope Lensing Survey and Canada-France-Hawaii Telescope Stripe 82 Survey. We compare this signal with predictions from mock catalogues trained to match observables including the stellar mass function and the projected and two-dimensional clustering of CMASS. We show that the clustering of CMASS, together with standard models of the galaxy-halo connection, robustly predicts a lensing signal that is 20-40 per cent larger than observed. Detailed tests show that our results are robust to a variety of systematic effects. Lowering the value of S_8=σ _8 \\sqrt{Ω _m/0.3} compared to Planck Collaboration XIII reconciles the lensing with clustering. However, given the scale of our measurement (r < 10 h-1 Mpc), other effects may also be at play and need to be taken into consideration. We explore the impact of baryon physics, assembly bias, massive neutrinos and modifications to general relativity on ΔΣ and show that several of these effects may be non-negligible given the precision of our measurement. Disentangling cosmological effects from the details of the galaxy-halo connection, the effect of baryons, and massive neutrinos, is the next challenge facing joint lensing and clustering analyses. This is especially true in the context of large galaxy samples from Baryon Acoustic Oscillation surveys with precise measurements but complex selection functions.

Galaxy And Mass Assembly (GAMA): the signatures of galaxy interactions as viewed from small scale galaxy clustering

NASA Astrophysics Data System (ADS)

Gunawardhana, M. L. P.; Norberg, P.; Zehavi, I.; Farrow, D. J.; Loveday, J.; Hopkins, A. M.; Davies, L. J. M.; Wang, L.; Alpaslan, M.; Bland-Hawthorn, J.; Brough, S.; Holwerda, B. W.; Owers, M. S.; Wright, A. H.

2018-06-01

Statistical studies of galaxy-galaxy interactions often utilise net change in physical properties of progenitors as a function of the separation between their nuclei to trace both the strength and the observable timescale of their interaction. In this study, we use two-point auto, cross and mark correlation functions to investigate the extent to which small-scale clustering properties of star forming galaxies can be used to gain physical insight into galaxy-galaxy interactions between galaxies of similar optical brightness and stellar mass. The Hα star formers, drawn from the highly spatially complete Galaxy And Mass Assembly (GAMA) survey, show an increase in clustering on small separations. Moreover, the clustering strength shows a strong dependence on optical brightness and stellar mass, where (1) the clustering amplitude of optically brighter galaxies at a given separation is larger than that of optically fainter systems, (2) the small scale clustering properties (e.g. the strength, the scale at which the signal relative to the fiducial power law plateaus) of star forming galaxies appear to differ as a function of increasing optical brightness of galaxies. According to cross and mark correlation analyses, the former result is largely driven by the increased dust content in optically bright star forming galaxies. The latter could be interpreted as evidence of a correlation between interaction-scale and optical brightness of galaxies, where physical evidence of interactions between optically bright star formers, likely hosted within relatively massive halos, persist over larger separations than those between optically faint star formers.

Dissecting the IRX-β dust attenuation relation: exploring the physical origin of observed variations in galaxies

NASA Astrophysics Data System (ADS)

Popping, Gergö; Puglisi, Annagrazia; Norman, Colin A.

2017-12-01

The use of ultraviolet (UV) emission as a tracer of galaxy star formation rate (SFR) is hampered by dust obscuration. The empirical relationship between UV-slope, β, and the ratio between far-infrared and UV luminosity, IRX, is commonly employed to account for obscured UV emission. We present a simple model that explores the physical origin of variations in the IRX-β dust attenuation relation. A relative increase in FUV compared to NUV attenuation and an increasing stellar population age cause variations towards red UV-slopes for a fixed IRX. Dust geometry effects (turbulence, dust screen with holes, mixing of stars within the dust screen, two-component dust model) cause variations towards blue UV-slopes. Poor photometric sampling of the UV spectrum causes additional observational variations. We provide an analytic approximation for the IRX-β relation invoking a subset of the explored physical processes (dust type, stellar population age, turbulence). We discuss observed variations in the IRX-β relation for local (sub-galactic scales) and high-redshift (normal and dusty star-forming galaxies, galaxies during the epoch of reionization) galaxies in the context of the physical processes explored in our model. High spatial resolution imaging of the UV and sub-mm emission of galaxies can constrain the IRX-β dust attenuation relation for different galaxy types at different epochs, where different processes causing variations may dominate. These constraints will allow the use of the IRX-β relation to estimate intrinsic SFRs of galaxies, despite the lack of a universal relation.

A physical process of the radial acceleration of disc galaxies

NASA Astrophysics Data System (ADS)

Wilhelm, Klaus; Dwivedi, Bhola N.

2018-03-01

An impact model of gravity designed to emulate Newton's law of gravitation is applied to the radial acceleration of disc galaxies. Based on this model (Wilhelm et al. 2013), the rotation velocity curves can be understood without the need to postulate any dark matter contribution. The increased acceleration in the plane of the disc is a consequence of multiple interactions of gravitons (called `quadrupoles' in the original paper) and the subsequent propagation in this plane and not in three-dimensional space. The concept provides a physical process that relates the fit parameter of the acceleration scale defined by McGaugh et al. (2016) to the mean free path length of gravitons in the discs of galaxies. It may also explain the gravitational interaction at low acceleration levels in MOdification of the Newtonian Dynamics (MOND, Milgrom 1983, 1994, 2015, 2016). Three examples are discussed in some detail: the spiral galaxies NGC 7814, NGC 6503 and M 33.

Multi-Wavelength Analysis of Active Galactic Nuclei and Host Galaxies Physical Properties

NASA Astrophysics Data System (ADS)

Azadi, Mojegan

In this dissertation we study the properties of active galactic nuclei (AGN), which are powered by the accretion activity of supermassive black holes residing at the centers of galaxies. While observations propose that growth of AGN and galaxies are globally tied, we investigate whether this connection exists in individual galaxies. We also investigate various AGN selection techniques and star formation rate (SFR) estimates using multi-wavelength data from Chandra, Spitzer and rest-frame optical spectra from the Keck telescope. We find that combining multi-wavelength identification techniques provides a more complete AGN sample, as each selection method suffers from selection biases. In particular, all selection techniques are biased against identifying AGN in lower mass galaxies. Once stellar mass selection biases are taken into account, we find that AGN reside in galaxies with similar physical properties (i.e., SFR) as inactive galaxies. We find that while AGN are prevalent in both star-forming and quiescent galaxies, AGN of a given accretion rate are more likely to reside in star-forming galaxies. The probability of fueling an AGN does not strongly depend on SFR for a star-forming galaxy, though it decreases when star formation is shut down in quiescent galaxies. We also find no evidence for a strong correlation between SFR or stellar mass of the host galaxy and AGN luminosity. These results indicate that while both AGN and galaxy growth are reliant on the same fuel, enhanced star formation activity does not necessarily go hand-in-hand with increased AGN activity. While the star formation activity of galaxies can be traced with various indicators, our investigations indicate that extrapolations from mid-infrared data using calibrations based on local galaxies overestimates SFRs at higher redshift. We show that a combina- tion of mid-infrared and far-infrared data provide a more reliable SFR estimation than the mid-infrared data alone. We also find that the

Internal kinematic and physical properties in a BCD galaxy: Haro 15 in detail

NASA Astrophysics Data System (ADS)

Firpo, V.; Bosch, G.; Hägele, G. F.; Díaz, A. I.; Morrell, N.

2011-11-01

We present a detailed study of the kinematic and physical properties of the ionized gas in multiple knots of the blue compact dwarf galaxy Haro 15. Using echelle and long slit spectroscopy data, obtained with different instruments at Las Campanas Observatory, we study the internal kinematic and physical conditions (electron density and temperature), ionic and total chemical abundances of several atoms, reddening and ionization structure. Applying direct and empirical methods for abundance determination, we perform a comparative analysis between these regions and in their different components. On the other hand, our echelle spectra show complex kinematics in several conspicuous knots within the galaxy. To perform an in-depth 2D spectroscopic study we complete this work with high spatial and spectral resolution spectroscopy using the Integral Field Unit mode on the Gemini Multi-Object Spectrograph instrument at the Gemini South telescope. With these data we are able to resolve the complex kinematical structure within star forming knots in Haro 15 galaxy.

The /a/m ratio of the baryonic matter and the black holes demography in galaxies

NASA Astrophysics Data System (ADS)

Curir, Anna; Mazzei, Paola

2001-06-01

The last years have seen a big progress in establishing the existence of supermassive black holes in the centers of galaxies. There are numerous very good cases [MNRAS 291 (1997) 219] where observations require a deep potential well. These observations raise the problem of when and how they formed and eventually when they gain most of their mass. The formation of a stationary black-hole is constrained by the conditions M>3 M ⊙ and cJ/ GM2≡ a/ m<1, J and M being the angular momentum and the total mass of the configuration which has collapsed to the hole. In this paper we analyze the behaviour of the a/ m ratio of the baryonic content in a protogalaxy, "primordial" scenario, and in a hot galaxy, "evolved" scenario, endowed with a suitable angular momentum distribution. In both the cases the baryonic matter is embedded in the gravitational potential generated by a cosmological Dark Matter (DM) halo. We deduce that the "primordial" scenario is less favourable to the black hole formation than the "evolved" one. Moreover, in the "evolved" scenario we find a twofold behaviour of the a/ m parameter which reflects the observed bimodal distribution of the central brightness in early-type galaxies and agrees with their corresponding degree of nuclear activity. As suggested by results of our SPH simulations of barred galaxies, the treatment of the dissipative processes and the inclusion of the star formation further improve the previous framework showing that barred galaxies provide very good environment for black hole formation.

A classification of the galaxy groups

NASA Technical Reports Server (NTRS)

Anosova, Joanna P.

1990-01-01

A statistical criterion has been proposed to reveal the random and physical clusterings among stars, galaxies and other objects. This criterion has been applied to the galaxy triples of the list by Karachentseva, Karaschentsev and Scherbanovsky, and the double galaxies of the list by Dahari where the primary components are the Seyfert galaxies. The confident physical, probable physical, probable optical and confident optical groups have been identified. The limit difference of radial velocities of components for the confident physical multiple galaxies has also been estimated.

Physical and morphological properties of z ~ 3 Lyman break galaxies: dependence on Lyα line emission

NASA Astrophysics Data System (ADS)

Pentericci, L.; Grazian, A.; Scarlata, C.; Fontana, A.; Castellano, M.; Giallongo, E.; Vanzella, E.

2010-05-01

Aims: We investigate the physical and morphological properties of Lyman break galaxies (LBGs) at redshift ~2.5 to ~3.5, to determine if and how they depend on the nature and strength of the Lyα emission. Methods: We selected U-dropout galaxies from the z-detected GOODS-MUSIC catalog by adapting the classical Lyman break criteria on the GOODS filter set. We kept only those galaxies with spectroscopic confirmation, mainly from VIMOS and FORS public observations. Using the full multi-wavelength 14-bands information (U to IRAC), we determined the physical properties of the galaxies through a standard spectral energy distribution fitting procedure with the updated Charlot & Bruzual (2009) templates. We also added other relevant observations of the GOODS field, i.e. the 24 μm observations from Spitzer/MIPS and the 2 MSec Chandra X-ray observations. Finally, using non parametric diagnostics (Gini, Concentration, Asymmetry, M20 and ellipticity), we characterized the rest-frame UV morphologies of the galaxies. We then analyzed how these physical and morphological properties correlate with the presence of the Lyα emission line in the optical spectra. Results: We find that unlike at higher redshift, the dependence of physical properties on the Lyα line is milder: galaxies without Lyα in emission tend to be more massive and dustier than the rest of the sample, but all other parameters, ages, star formation rates (SFR), X-ray emission and UV morphology do not depend strongly on the presence of the Lyα emission. A simple scenario where all LBGs have intrinsically high Lyα emission, but where the dust and neutral hydrogen content (which shapes the final appearance of the Lyα) depend on the mass of the galaxies, is able to reproduce the majority of the observed properties at z˜3. Some modification might be needed to account for the observed evolution of these properties with cosmic epoch, which is also discussed.

Physical conditions of the molecular gas in metal-poor galaxies

NASA Astrophysics Data System (ADS)

Hunt, L. K.; Weiß, A.; Henkel, C.; Combes, F.; García-Burillo, S.; Casasola, V.; Caselli, P.; Lundgren, A.; Maiolino, R.; Menten, K. M.; Testi, L.

2017-10-01

Studying the molecular component of the interstellar medium (ISM) in metal-poor galaxies has been challenging because of the faintness of carbon monoxide emission, the most common proxy of H2. Here we present new detections of molecular gas at low metallicities, and assess the physical conditions in the gas through various CO transitions for 8 galaxies. For one, NGC 1140 (Z/Z⊙ 0.3), two detections of 13CO isotopologues and atomic carbon, [Ci](1-0) and an upper limit for HCN(1-0) are also reported. After correcting to a common beam size, we compared 12CO(2-1)/12CO(1-0) (R21) and 12CO(3-2)/12CO(1-0) (R31) line ratios of our sample with galaxies from the literature and find that only NGC 1140 shows extreme values (R21 R31 2). Fitting physical models to the 12CO and 13CO emission in NGC 1140 suggests that the molecular gas is cool (kinetic temperature Tkin ≲ 20 K), dense (H2 volume density nH2 ≳ 106 cm-3), with moderate CO column density (NCO 1016 cm-2) and low filling factor. Surprisingly, the [12CO]/[13CO] abundance ratio in NGC 1140 is very low ( 8-20), lower even than the value of 24 found in the Galactic Center. The young age of the starburst in NGC 1140 precludes 13CO enrichment from evolved intermediate-mass stars; instead we attribute the low ratio to charge-exchange reactions and fractionation, because of the enhanced efficiency of these processes in cool gas at moderate column densities. Fitting physical models to 12CO and [Ci](1-0) emission in NGC 1140 gives an unusually low [12CO]/[12C] abundance ratio, suggesting that in this galaxy atomic carbon is at least 10 times more abundant than 12CO. Based on observations carried out with the IRAM 30 m and the Atacama Pathfinder Experiment (APEX). IRAM is supported by the INSU/CNRS (France), MPG (Germany), and IGN (Spain), and APEX is a collaboration between the Max-Planck-Institut fur Radioastronomie, the European Southern Observatory, and the Onsala Space Observatory.

Dark energy and key physical parameters of clusters of galaxies

NASA Astrophysics Data System (ADS)

Bisnovatyi-Kogan, G. S.; Chernin, A. D.

2012-04-01

We study physics of clusters of galaxies embedded in the cosmic dark energy background. Under the assumption that dark energy is described by the cosmological constant, we show that the dynamical effects of dark energy are strong in clusters like the Virgo cluster. Specifically, the key physical parameters of the dark mater halos in clusters are determined by dark energy: (1) the halo cut-off radius is practically, if not exactly, equal to the zero-gravity radius at which the dark matter gravity is balanced by the dark energy antigravity; (2) the halo averaged density is equal to two densities of dark energy; (3) the halo edge (cut-off) density is the dark energy density with a numerical factor of the unity order slightly depending on the halo profile. The cluster gravitational potential well in which the particles of the dark halo (as well as galaxies and intracluster plasma) move is strongly affected by dark energy: the maximum of the potential is located at the zero-gravity radius of the cluster.

Recovering the Physical Properties of Molecular Gas in Galaxies from CO SLED Modeling

NASA Astrophysics Data System (ADS)

Kamenetzky, J.; Privon, G. C.; Narayanan, D.

2018-05-01

Modeling of the spectral line energy distribution (SLED) of the CO molecule can reveal the physical conditions (temperature and density) of molecular gas in Galactic clouds and other galaxies. Recently, the Herschel Space Observatory and ALMA have offered, for the first time, a comprehensive view of the rotational J = 4‑3 through J = 13‑12 lines, which arise from a complex, diverse range of physical conditions that must be simplified to one, two, or three components when modeled. Here we investigate the recoverability of physical conditions from SLEDs produced by galaxy evolution simulations containing a large dynamical range in physical properties. These simulated SLEDs were generally fit well by one component of gas whose properties largely resemble or slightly underestimate the luminosity-weighted properties of the simulations when clumping due to nonthermal velocity dispersion is taken into account. If only modeling the first three rotational lines, the median values of the marginalized parameter distributions better represent the luminosity-weighted properties of the simulations, but the uncertainties in the fitted parameters are nearly an order of magnitude, compared to approximately 0.2 dex in the “best-case” scenario of a fully sampled SLED through J = 10‑9. This study demonstrates that while common CO SLED modeling techniques cannot reveal the underlying complexities of the molecular gas, they can distinguish bulk luminosity-weighted properties that vary with star formation surface densities and galaxy evolution, if a sufficient number of lines are detected and modeled.

Physical Conditions of the Interstellar Medium in Star-forming Galaxies at z1.5

NASA Technical Reports Server (NTRS)

Hayashi, Masao; Ly, Chun; Shimasaku, Kazuhiro; Motohara, Kentaro; Malkan, Matthew A.; Nagao, Tohru; Kashikawa, Nobunari; Goto, Ryosuke; Naito, Yoshiaki

2015-01-01

We present results from Subaru/FMOS near-infrared (NIR) spectroscopy of 118 star-forming galaxies at z approximately equal to 1.5 in the Subaru Deep Field. These galaxies are selected as [O II] lambda 3727 emitters at z approximately equal to 1.47 and 1.62 from narrow-band imaging. We detect H alpha emission line in 115 galaxies, [O III] lambda 5007 emission line in 45 galaxies, and H Beta, [N II] lambda 6584, and [S II]lambda lambda 6716, 6731 in 13, 16, and 6 galaxies, respectively. Including the [O II] emission line, we use the six strong nebular emission lines in the individual and composite rest-frame optical spectra to investigate physical conditions of the interstellar medium in star-forming galaxies at z approximately equal to 1.5. We find a tight correlation between H alpha and [O II], which suggests that [O II] can be a good star formation rate (SFR) indicator for galaxies at z approximately equal to 1.5. The line ratios of H alpha / [O II] are consistent with those of local galaxies. We also find that [O II] emitters have strong [O III] emission lines. The [O III]/[O II] ratios are larger than normal star-forming galaxies in the local Universe, suggesting a higher ionization parameter. Less massive galaxies have larger [O III]/[O II] ratios. With evidence that the electron density is consistent with local galaxies, the high ionization of galaxies at high redshifts may be attributed to a harder radiation field by a young stellar population and/or an increase in the number of ionizing photons from each massive star.

Physical properties of distant red galaxies in the COSMOS/UltraVISTA field

NASA Astrophysics Data System (ADS)

Ma, Zhongyang; Fang, Guanwen; Kong, Xu; Fan, Lulu

2015-10-01

We present a study on physical properties for a large distant red galaxy (DRG) sample, using the K-selected multi-band photometry catalog of the COSMOS/UltraVISTA field and the CANDELS near-infrared data. Our sample includes 4485 DRGs with (J - K)AB > 1.16 and KAB < 23.4 mag, and 132 DRGs have HST/WFC3 morphological measurements. The results of nonparametric measurements of DRG morphology are consistent with our rest-frame UVJ color classification; quiescent DRGs are generally compact while star-forming DRGs tend to have extended structures. We find the star formation rate (SFR) and the stellar mass of star-forming DRGs present tight "main sequence" relations in all redshift bins. Moreover, the specific SFR (sSFR) of DRGs increases with redshift in all stellar mass bins and DRGs with higher stellar masses generally have lower sSFRs, which indicates that galaxies were much more active on average in the past, and star formation contributes more to the mass growth of low-mass galaxies than to high-mass galaxies. The infrared-derived SFR dominates the total SFR of DRGs which occupy the high-mass range, implying that the J - K color criterion effectively selects massive and dusty galaxies. DRGs with higher M* generally have redder (U - V)rest colors, and the (U - V)rest colors of DRGs become bluer at higher redshifts, suggesting high-mass galaxies have higher internal dust extinctions or older stellar ages and they evolve with time. Finally, we find that DRGs have different overlap among extremely red objects, BzK galaxies, IRAC-selected extremely red objects, and high-z ultraluminous infrared galaxies, indicating that DRGs are not a special population and they can also be selected by other color criteria.

Physical Conditions of a Lensed Star-Forming Galaxy at Z=1.7

NASA Technical Reports Server (NTRS)

Rigby, Jane; Wuyts, E.; Gladders, M.; Sharon, K.; Becker, G. D.

2010-01-01

We report rest-frame optical Keck/NIRSPEC spectroscopy of the brightest lensed galaxy yet discovered, RCSGA 032727-132609 at z=1.7037. From precise measurements of the nebular lines, we infer a number of physical properties: redshift, extinction, star formation rate, ionization parameter, electron density, electron temperature, oxygen abundance, and N/O, Ne/O, and Ar/O abundance ratios. The limit on [O III] 4363 A tightly constrains the oxygen abundance via the "direct" or Tc method, for the first time in all metallicity galaxy at z approx.2. We compare this result to several standard "bright-line" O abundance diagnostics, thereby testing these empirically calibrated diagnostics in situ. Finally, we explore the positions of lensed and unlensed galaxies in standard diagnostic diagrams, and explore the diversity of ionization conditions and mass-metallicity ratios at z=2.

Selection and Physical Properties of High-redshift Galaxies

NASA Astrophysics Data System (ADS)

Fang, G. W.

2014-09-01

Extremely Red Objects (EROs) and BzKs continue to attract considerable interest. It has been suggested that they may be the direct progenitors of present-day massive E/S0 galaxies, and can provide crucial constraints on the current galaxy formation and evolution models. Therefore, the key question is to measure the relative fraction of OGs (old galaxies) and DGs (young, and dusty starburst galaxies) in the sample of EROs. Many groups have been currently investigating the fractions of these two ERO populations using a variety of observational approaches, but the fraction of OGs and DGs from different surveys is different. In the meantime, a number of observations suggest that the epoch of z˜2 also plays an important role in galaxy formation and evolution for various reasons: the cosmic star formation rate density (SFRD) begins to drop at z˜2 from a flat plateau at higher redshifts; the morphological type mix of field galaxies changes remarkably at z˜2; the number density of QSOs has a peak at z˜2; and about 50% to 70% of the stellar mass assembly of galaxies took place in the redshift range 1physical properties of passive and star-forming galaxies at z˜2 in the AEGIS field, and (3) the mid-infrared spectroscopy and multi-wavelength study of ultraluminous infrared galaxies (ULIRGs) at z˜2 in the AEGIS field. Chapter 1 gives a brief review on the research progresses of EROs at z˜1, BzKs at z˜2, and ULIRGs at z˜2, respectively. In Chapter 2 we present a quantitative study of the classification of EROs in the UDF and COSMOS field. Our sample includes 5264 (COSMOS, K_{Vega} ≤19.2) and 24 EROs (UDF, K_{Vega}≤22.0) with (i-K)_{AB}≥2.45. Using the fitting method of spectral energy distribution (SED), [3.6]-[8.0] color, and the nonparametric measures of galaxy morphology, we classify EROs into two classes: DGs and OGs. We find

Physical properties of z ~ 4 LBGs: differences between galaxies with and without Lyα emission

NASA Astrophysics Data System (ADS)

Pentericci, L.; Grazian, A.; Fontana, A.; Salimbeni, S.; Santini, P.; de Santis, C.; Gallozzi, S.; Giallongo, E.

2007-08-01

Aims:We analysed the physical properties of z ˜4 Lyman Break Galaxies observed in the GOODS-S survey, in order to investigate possible differences between galaxies where the Lyα is present in emission, and those where the line is absent or in absorption. Methods: The objects were selected from their optical color and then spectroscopically confirmed by Vanzella et al. (2005). From the public spectra we assessed the nature of the Lyα emission and divided the sample into galaxies with Lyα in emission and objects without a Lyα line (i.e. either absent or in absorption). We then used complete photometry, from U band to mid-infrared from the GOODS-MUSIC database, to study the observational properties of the galaxies, such as UV spectral slopes and optical to mid-infrared colors, and the possible differences between the two samples. Lastly, we used standard spectral fitting techniques to determine the physical properties of the galaxies, such as total stellar mass, stellar ages and so on, and again we looked at the possible differences between the two samples. Results: Our results indicate that LBG with Lyα in emission are on average a much younger and less massive population than the LBGs without Lyα emission. Both populations are forming stars very actively and are relatively dust free, although those with line emission seem to be even less dusty on average. We briefly discuss these results in the context of recent models for the evolution of Lyman break galaxies and Lyα emitters.

The Planar Satellite Distributions around Andromeda, the Milky Way and Other Galaxies, and Their Implications for Fundamental Physics

NASA Astrophysics Data System (ADS)

Kroupa, P.

2014-05-01

The existence of dark matter particles is a key hypothesis in present-day cosmology and galactic dynamics. The validity of this hypothesis is challenged significantly by two independent arguments. 1) The dual dwarf galaxy theorem must be true in any realistic cosmological model. But it is found to be falsified when the dark-matter-based model is applied to the observational data. A consistency check of this conclusion comes from the observed significantly disk-like distributions of satellite populations which orbit in the same direction around their hosting galaxy and which cannot be derived from dark-matter models. 2) The action of dynamical friction due to expansive and massive dark matter halos must be evident in the galaxy population. The evidence however for dynamical friction is void or meagre at best. The M81 group fo galaxies already appears to rule out the existence of dynamical friction through dark matter halos, and the Milky Way satellite galaxies have been shown to challenge dark-matter-induced dynamical friction. The implication of this deduction for fundamental physics would be that exotic dark matter particles do not exist and that consequently gravitational physics on the scales of galaxies and beyond ought to be non-Newtonian/Einsteinian. An analysis of the kinematical data in galaxies shows them to be described excellently by scale-invariant dynamics, as discovered by Milgrom. This leads to a natural emergence of laws that galaxies are observed to obey. Such success has not been forthcoming in the dark-matter-based models. A consequence of this novel understanding of galactic astrophysics is that most dwarf satellite galaxies are formed as tidal dwarf galaxies in galaxy-galaxy encounters and that galactic mergers are rare.

Dynamics of Galaxies

NASA Astrophysics Data System (ADS)

Bertin, Giuseppe

2000-08-01

Part I. Basic Phenomenology: 1. Scales; 2. Observational windows; 3. Classifications; 4. Photometry, kinematics, dark matter; 5. Basic questions, semi-empirical approach, dynamical window; Part II. Physical Models: 6. Self-gravity and relation with plasma physics; 7. Relaxation times, absence of thermodynamical equilibrium; 8. Models; 9. Equilibrium and stability: symmetry and symmetry breaking; 10. Classical ellipsoids; 11. Introduction to dispersive waves; 12. Jeans instability; Part III. Spiral Galaxies: 13. Orbits; 14. The basic state: vertical and horizontal equilibrium in the disk; 15. Density waves; 16. Role of gas; 17. Global spiral modes; 18. Spiral structure in galaxies; 19. Bending waves; 20. Dark matter in spiral galaxies; Part IV. Elliptical Galaxies: 21. Orbits; 22. Stellar dynamical approach; 23. Stability; 24. Dark matter in elliptical galaxies; Part V. In Perspective: 25. Selected aspects of formation and evolution; Notes; Index.

Physical conditions of the interstellar medium in star-forming galaxies at z ˜ 1.5

NASA Astrophysics Data System (ADS)

Hayashi, Masao; Ly, Chun; Shimasaku, Kazuhiro; Motohara, Kentaro; Malkan, Matthew A.; Nagao, Tohru; Kashikawa, Nobunari; Goto, Ryosuke; Naito, Yoshiaki

2015-10-01

We present results from Subaru Fiber Multi Object Spectrograph near-infrared spectroscopy of 118 star-forming galaxies at z ˜ 1.5 in the Subaru Deep Field. These galaxies are selected as [O II]λ3727 emitters at z ≈ 1.47 and 1.62 from narrow-band imaging. We detect the Hα emission line in 115 galaxies, the [O III]λ5007 emission line in 45 galaxies, and Hβ, [N II]λ6584, and [S II]λλ6716, 6731 in 13, 16, and 6 galaxies, respectively. Including the [O II] emission line, we use the six strong nebular emission lines in the individual and composite rest-frame optical spectra to investigate the physical conditions of the interstellar medium in star-forming galaxies at z ˜ 1.5. We find a tight correlation between Hα and [O II], which suggests that [O II] can be a good star formation rate indicator for galaxies at z ˜ 1.5. The line ratios of Hα/[O II] are consistent with those of local galaxies. We also find that [O II] emitters have strong [O III] emission lines. The [O III]/[O II] ratios are larger than normal star-forming galaxies in the local universe, suggesting a higher ionization parameter. Less massive galaxies have larger [O III]/[O II] ratios. With evidence that the electron density is consistent with local galaxies, the high ionization of galaxies at high redshifts may be attributed to a harder radiation field by a young stellar population and/or an increase in the number of ionizing photons from each massive star.

nIFTY galaxy cluster simulations - III. The similarity and diversity of galaxies and subhaloes

NASA Astrophysics Data System (ADS)

Elahi, Pascal J.; Knebe, Alexander; Pearce, Frazer R.; Power, Chris; Yepes, Gustavo; Cui, Weiguang; Cunnama, Daniel; Kay, Scott T.; Sembolini, Federico; Beck, Alexander M.; Davé, Romeel; February, Sean; Huang, Shuiyao; Katz, Neal; McCarthy, Ian G.; Murante, Giuseppe; Perret, Valentin; Puchwein, Ewald; Saro, Alexandro; Teyssier, Romain

2016-05-01

We examine subhaloes and galaxies residing in a simulated Λ cold dark matter galaxy cluster (M^crit_{200}=1.1× 10^{15} h^{-1} M_{⊙}) produced by hydrodynamical codes ranging from classic smooth particle hydrodynamics (SPH), newer SPH codes, adaptive and moving mesh codes. These codes use subgrid models to capture galaxy formation physics. We compare how well these codes reproduce the same subhaloes/galaxies in gravity-only, non-radiative hydrodynamics and full feedback physics runs by looking at the overall subhalo/galaxy distribution and on an individual object basis. We find that the subhalo population is reproduced to within ≲10 per cent for both dark matter only and non-radiative runs, with individual objects showing code-to-code scatter of ≲0.1 dex, although the gas in non-radiative simulations shows significant scatter. Including feedback physics significantly increases the diversity. Subhalo mass and Vmax distributions vary by ≈20 per cent. The galaxy populations also show striking code-to-code variations. Although the Tully-Fisher relation is similar in almost all codes, the number of galaxies with 109 h- 1 M⊙ ≲ M* ≲ 1012 h- 1 M⊙ can differ by a factor of 4. Individual galaxies show code-to-code scatter of ˜0.5 dex in stellar mass. Moreover, systematic differences exist, with some codes producing galaxies 70 per cent smaller than others. The diversity partially arises from the inclusion/absence of active galactic nucleus feedback. Our results combined with our companion papers demonstrate that subgrid physics is not just subject to fine-tuning, but the complexity of building galaxies in all environments remains a challenge. We argue that even basic galaxy properties, such as stellar mass to halo mass, should be treated with errors bars of ˜0.2-0.4 dex.

Cluster Physics with Merging Galaxy Clusters

NASA Astrophysics Data System (ADS)

Molnar, Sandor

Collisions between galaxy clusters provide a unique opportunity to study matter in a parameter space which cannot be explored in our laboratories on Earth. In the standard ΛCDM model, where the total density is dominated by the cosmological constant (Λ) and the matter density by cold dark matter (CDM), structure formation is hierarchical, and clusters grow mostly by merging. Mergers of two massive clusters are the most energetic events in the universe after the Big Bang, hence they provide a unique laboratory to study cluster physics. The two main mass components in clusters behave differently during collisions: the dark matter is nearly collisionless, responding only to gravity, while the gas is subject to pressure forces and dissipation, and shocks and turbulence are developed during collisions. In the present contribution we review the different methods used to derive the physical properties of merging clusters. Different physical processes leave their signatures on different wavelengths, thus our review is based on a multifrequency analysis. In principle, the best way to analyze multifrequency observations of merging clusters is to model them using N-body/HYDRO numerical simulations. We discuss the results of such detailed analyses. New high spatial and spectral resolution ground and space based telescopes will come online in the near future. Motivated by these new opportunities, we briefly discuss methods which will be feasible in the near future in studying merging clusters.

The formation of galaxies

NASA Technical Reports Server (NTRS)

Efstathiou, G.; Silk, J.

1983-01-01

Current models of galaxy formation are examined in a review of recent observational and theoretical studies. Observational data on elliptical galaxies, disk galaxies, luminosity functions, clustering, and angular fluctuations in the cosmic microwave background are summarized. Theoretical aspects discussed include the origin and early evolution of small fluctuations, matter and radiation fluctuations, the formation of large-scale structure, dissipationless galaxy formation, galaxy mergers, dissipational galaxy formation, and the implications of particle physics (GUTs, massive neutrinos, and gravitinos) for cosmology.

The Physical Conditions of a Lensed Star-Forming Galaxy at Z=1.7

NASA Technical Reports Server (NTRS)

Rigby, Jane; Wuyts, E.; Gladders, M.; Sharon, K.; Becker, G.

2011-01-01

We report rest-frame optical Keck/NIRSPEC spectroscopy of the brightest lensed galaxy yet discovered, RCSGA 032727-132609 at z=1.7037. From precise measurements of the nebular lines, we infer a number of physical properties: redshift ' extinction, star formation rate ' ionization parameter, electron density, electron temperature, oxygen abundance, and N/O, Ne/O, and Ar/O abundance ratios, The limit on [O III] 4363 A tightly constrains the oxygen abundance via the "direct" or Te method, for the first time in an average-metallicity galaxy at z approx.2. We compare this result to several standard "bright-line" O abundance diagnostics, thereby testing these empirically-calibrated diagnostics in situ. Finally, we explore the positions of lensed and unlensed galaxies in standard diagnostic diagrams, to explore the diversity of ionization conditions and mass-metallicity ratios at z=2.

Modeling the influence of leaf demography on remotely sensed data using DART and PROSPECT-D

NASA Astrophysics Data System (ADS)

Feret, J. B.; Grau, E.; Barbier, N.; Berveiller, D.; Chave, J.; Durrieu, S.; Gastellu-Etchegorry, J. P.; Hmimina, G.; Lefèvre-Fonollosa, M. J.; Proisy, C.; Soudani, K.; Vincent, G.

2016-12-01

The seasonality of Amazon forest productivity and photosynthetic activity has recently been investigated under a new perspective by a series of publications. The debate about possible factors explaining this seasonality is vivid, and the possibility of several hypotheses has been tested, including canopy phenology and leaf demography, and changes in illumination geometry combined with the complex 3D structure of the canopy. A manifold of measurements and techniques have been used to test these hypotheses, including field observations of leaf demography from ground measured litterfall and phenocam, airborne and satellite remote sensing and 3 dimensional radiative transfer modeling. Our study explores the relative influence of leaf demography and illumination geometry on remotely sensed data. To achieve this, we take advantage of the latest advances in the domain of physical modeling at both leaf and canopy scale. The leaf optical properties model PROSPECT-D was used to model leaf optical properties at various growth stages based on field observations and theoretical leaf biochemical composition during its development and senescence. The 3-dimensional radiative transfer model DART was used to simulate various levels of complexity of canopy covers, from a turbid layer to complex canopy derived from airborne LiDAR acquisitions. Data for leaf demography and ontogeny taken from recent publications was used and integrated into canopy simulations corresponding to year-long observations. Data acquisitions were performed in the frame of the HyperTropik project, funded by CNES, Our results focus on analyzing the influence of separated and combined factors such as illumination geometry, leaf biochemistry and leaf demography on various spectral attributes, including Enhanced vegetation index and hyperspectral metrics.

Large-scale galaxy bias

NASA Astrophysics Data System (ADS)

Desjacques, Vincent; Jeong, Donghui; Schmidt, Fabian

2018-02-01

This review presents a comprehensive overview of galaxy bias, that is, the statistical relation between the distribution of galaxies and matter. We focus on large scales where cosmic density fields are quasi-linear. On these scales, the clustering of galaxies can be described by a perturbative bias expansion, and the complicated physics of galaxy formation is absorbed by a finite set of coefficients of the expansion, called bias parameters. The review begins with a detailed derivation of this very important result, which forms the basis of the rigorous perturbative description of galaxy clustering, under the assumptions of General Relativity and Gaussian, adiabatic initial conditions. Key components of the bias expansion are all leading local gravitational observables, which include the matter density but also tidal fields and their time derivatives. We hence expand the definition of local bias to encompass all these contributions. This derivation is followed by a presentation of the peak-background split in its general form, which elucidates the physical meaning of the bias parameters, and a detailed description of the connection between bias parameters and galaxy statistics. We then review the excursion-set formalism and peak theory which provide predictions for the values of the bias parameters. In the remainder of the review, we consider the generalizations of galaxy bias required in the presence of various types of cosmological physics that go beyond pressureless matter with adiabatic, Gaussian initial conditions: primordial non-Gaussianity, massive neutrinos, baryon-CDM isocurvature perturbations, dark energy, and modified gravity. Finally, we discuss how the description of galaxy bias in the galaxies' rest frame is related to clustering statistics measured from the observed angular positions and redshifts in actual galaxy catalogs.

Physical Properties of UV-bright Clumps in Star-forming Galaxies at 0.5 ≤ z < 3

NASA Astrophysics Data System (ADS)

Guo, Yicheng; Rafelski, Marc; Bell, Eric F.; Dekel, Avishai; Mandelker, Nir; Primack, Joel R.; CANDELS

2018-06-01

Studying giant star-forming clumps in distant galaxies is important to understand galaxy formation and evolution. At present, however, observers and theorists have not reached a consensus on whether the observed “clumps” in distant galaxies are the same phenomenon that is seen in simulations. As a step to establish a benchmark of direct comparisons between observations and theories, we publish a sample of clumps constructed to represent the commonly observed “clumps” in the literature. This sample contains 3193 clumps detected from the rest-frame images of 1270 galaxies at 0.5≤z<3.0. The physical properties of clumps (e.g., rest-frame color, stellar mass, star formation rate, age, and dust extinction) are measured by fitting the spectral energy distribution (SED) to synthetic stellar population models. We carefully test the procedures of measuring clump properties, especially the method of subtracting background fluxes from the diffuse component of galaxies. With our fiducial background subtraction, we find a radial clump U-V color variation, where clumps close to galactic centers are redder than those in outskirts. The slope of the color gradient (clump color as a function of their galactocentric distance scaled by the semimajor axis of galaxies) changes with redshift and stellar mass of the host galaxies: at a fixed stellar mass, the slope becomes steeper toward low redshift, and at a fixed redshift, it becomes slightly steeper with stellar mass. Based on our SED fitting, this observed color gradient can be explained by a combination of a negative age gradient, a negative E(B-V) gradient, and a positive specific star formation rate gradient of the clumps. We also find that the color gradients of clumps are steeper than those of intra-clump regions. Correspondingly, the radial gradients of the derived physical properties of clumps are different from those of the diffuse component or intra-clump regions.

Submillimeter evidence for the coeval growth of massive black holes and galaxy bulges.

PubMed

Page, M J; Stevens, J A; Mittaz, J P; Carrera, F J

2001-12-21

The correlation, found in nearby galaxies, between black hole mass and stellar bulge mass implies that the formation of these two components must be related. Here we report submillimeter photometry of eight x-ray-absorbed active galactic nuclei that have luminosities and redshifts characteristic of the sources that produce the bulk of the accretion luminosity in the universe. The four sources with the highest redshifts are detected at 850 micrometers, with flux densities between 5.9 and 10.1 millijanskies, and hence are ultraluminous infrared galaxies. If the emission is from dust heated by starbursts, then the majority of stars in spheroids were formed at the same time as their central black holes built up most of their mass by accretion. This would account for the observed demography of massive black holes in the local universe. The skewed rate of submillimeter detection with redshift is consistent with a high redshift epoch of star formation in radio-quiet active galactic nuclei, similar to that seen in radio galaxies.

Implications of Galaxy Buildup for Putative IMF Variations in Massive Galaxies

NASA Astrophysics Data System (ADS)

Blancato, Kirsten; Genel, Shy; Bryan, Greg

2017-08-01

Recent observational evidence for initial mass function (IMF) variations in massive quiescent galaxies at z = 0 challenges the long-established paradigm of a universal IMF. While a few theoretical models relate the IMF to birth cloud conditions, the physical driver underlying these putative IMF variations is still largely unclear. Here we use post-processing analysis of the Illustris cosmological hydrodynamical simulation to investigate possible physical origins of IMF variability with galactic properties. We do so by tagging stellar particles in the simulation (each representing a stellar population of ≈ {10}6 {M}⊙ ) with individual IMFs that depend on various physical conditions, such as velocity dispersion, metallicity, or star formation rate, at the time and place in which the stars are formed. We then follow the assembly of these populations throughout cosmic time and reconstruct the overall IMF of each z = 0 galaxy from the many distinct IMFs it is composed of. Our main result is that applying the observed relations between IMF and galactic properties to the conditions at the star formation sites does not result in strong enough IMF variations between z = 0 galaxies. Steeper physical IMF relations are required for reproducing the observed IMF trends, and some stellar populations must form with more extreme IMFs than those observed. The origin of this result is the hierarchical nature of massive galaxy assembly, and it has implications for the reliability of the strong observed trends, for the ability of cosmological simulations to capture certain physical conditions in galaxies, and for theories of star formation aiming to explain the physical origin of a variable IMF.

A physical model of the infrared-to-radio correlation in galaxies

NASA Technical Reports Server (NTRS)

Helou, G.; Bicay, M. D.

1993-01-01

We explore the implications of the IR-radio correlation in star-forming galaxies, using a simple physical model constrained by the constant global ratio q of IR to radio emission and by the radial falloff of this ratio in disks of galaxies. The modeling takes into account the diffusion, radiative decay, and escape of cosmic-ray electrons responsible for the synchrotron emission, and the full range of optical depths to dust-heating photons. We introduce two assumptions: that dust-heating photons and radio-emitting cosmic-ray electrons are created in constant proportion to each other as part of the star formation activity, and that gas and magnetic field are well coupled locally, expressed as B proportional to n exp beta, with beta between 1/3 and 2/3. We conclude that disk galaxies would maintain the observed constant ratio q under these assumptions if the disk scale height h(0) and the escape scale length l(esc) for cosmic-ray electrons followed a relation of the form l(esc) proportional to h(0) exp 1/2; the IR-to-radio ratio will then depend very weakly on interstellar density, and, therefore, on magnetic field strength or mean optical depth.

Large-scale galaxy bias

NASA Astrophysics Data System (ADS)

Jeong, Donghui; Desjacques, Vincent; Schmidt, Fabian

2018-01-01

Here, we briefly introduce the key results of the recent review (arXiv:1611.09787), whose abstract is as following. This review presents a comprehensive overview of galaxy bias, that is, the statistical relation between the distribution of galaxies and matter. We focus on large scales where cosmic density fields are quasi-linear. On these scales, the clustering of galaxies can be described by a perturbative bias expansion, and the complicated physics of galaxy formation is absorbed by a finite set of coefficients of the expansion, called bias parameters. The review begins with a detailed derivation of this very important result, which forms the basis of the rigorous perturbative description of galaxy clustering, under the assumptions of General Relativity and Gaussian, adiabatic initial conditions. Key components of the bias expansion are all leading local gravitational observables, which include the matter density but also tidal fields and their time derivatives. We hence expand the definition of local bias to encompass all these contributions. This derivation is followed by a presentation of the peak-background split in its general form, which elucidates the physical meaning of the bias parameters, and a detailed description of the connection between bias parameters and galaxy (or halo) statistics. We then review the excursion set formalism and peak theory which provide predictions for the values of the bias parameters. In the remainder of the review, we consider the generalizations of galaxy bias required in the presence of various types of cosmological physics that go beyond pressureless matter with adiabatic, Gaussian initial conditions: primordial non-Gaussianity, massive neutrinos, baryon-CDM isocurvature perturbations, dark energy, and modified gravity. Finally, we discuss how the description of galaxy bias in the galaxies' rest frame is related to clustering statistics measured from the observed angular positions and redshifts in actual galaxy catalogs.

Stellar Populations and Physical Conditions at 100 pc Resolution in a Lensed Galaxy at z 4

NASA Astrophysics Data System (ADS)

Berg, Danielle

2015-10-01

Large surveys of star-forming galaxies at high redshift (z > 1.5) have provided us with a broad understanding of how galaxies assemble and evolve, but the spatial and spectral limitations inherent in observing faint, distant objects mean that many of the physical processes regulating this dynamic evolution are poorly constrained. Much of our most detailed knowledge of the physical conditions in distant galaxies comes from careful studies of gravitationally lensed sources, few of which are at z>3.5. FOR J0332-3557 is a gravitationally lensed galaxy at z 4 for which we and other groups have obtained a total of 37.3 hours of VLT spectroscopy. The rest-frame UV spectrum is notable for its unusual combination of both strong emission lines in the rest-frame UV and strong Lya and interstellar absorption, and for the unusual spatial variation seen in the nebular emission lines, which are less extended than the underlying stellar continuum. We propose high spatial resolution imaging of FOR J0332-3557 with four broadband filters on WFC3, taking advantage of both the HST resolution and the lensing magnification to study star formation and extinction on 100 pc scales. Because the interpretation of our unusual rest-frame UV and optical spectra requires an accurate reddening estimate, combining these observations with ground-based spectroscopy will give the most complete picture to date of chemical evolution in a distant galaxy.

The SAMI Galaxy Survey: Data Release One with emission-line physics value-added products

NASA Astrophysics Data System (ADS)

Green, Andrew W.; Croom, Scott M.; Scott, Nicholas; Cortese, Luca; Medling, Anne M.; D'Eugenio, Francesco; Bryant, Julia J.; Bland-Hawthorn, Joss; Allen, J. T.; Sharp, Rob; Ho, I.-Ting; Groves, Brent; Drinkwater, Michael J.; Mannering, Elizabeth; Harischandra, Lloyd; van de Sande, Jesse; Thomas, Adam D.; O'Toole, Simon; McDermid, Richard M.; Vuong, Minh; Sealey, Katrina; Bauer, Amanda E.; Brough, S.; Catinella, Barbara; Cecil, Gerald; Colless, Matthew; Couch, Warrick J.; Driver, Simon P.; Federrath, Christoph; Foster, Caroline; Goodwin, Michael; Hampton, Elise J.; Hopkins, A. M.; Jones, D. Heath; Konstantopoulos, Iraklis S.; Lawrence, J. S.; Leon-Saval, Sergio G.; Liske, Jochen; López-Sánchez, Ángel R.; Lorente, Nuria P. F.; Mould, Jeremy; Obreschkow, Danail; Owers, Matt S.; Richards, Samuel N.; Robotham, Aaron S. G.; Schaefer, Adam L.; Sweet, Sarah M.; Taranu, Dan S.; Tescari, Edoardo; Tonini, Chiara; Zafar, T.

2018-03-01

We present the first major release of data from the SAMI Galaxy Survey. This data release focuses on the emission-line physics of galaxies. Data Release One includes data for 772 galaxies, about 20 per cent of the full survey. Galaxies included have the redshift range 0.004 < z < 0.092, a large mass range (7.6 < log M*/ M⊙ < 11.6), and star formation rates of ˜10-4 to ˜101M⊙ yr-1. For each galaxy, we include two spectral cubes and a set of spatially resolved 2D maps: single- and multi-component emission-line fits (with dust-extinction corrections for strong lines), local dust extinction, and star formation rate. Calibration of the fibre throughputs, fluxes, and differential atmospheric refraction has been improved over the Early Data Release. The data have average spatial resolution of 2.16 arcsec (full width at half-maximum) over the 15 arcsec diameter field of view and spectral (kinematic) resolution of R = 4263 (σ = 30 km s-1) around H α. The relative flux calibration is better than 5 per cent, and absolute flux calibration has an rms of 10 per cent. The data are presented online through the Australian Astronomical Observatory's Data Central.

Galaxy And Mass Assembly (GAMA): The M-Z relation for galaxy groups

NASA Astrophysics Data System (ADS)

Lara-López, M. A.; Hopkins, A. M.; Robotham, A.; Owers, M. S.; Colless, M.; Brough, S.; Norberg, P.; Steele, O.; Taylor, E. N.; Thomas, D.

2013-04-01

The stellar mass and metallicity are among the fundamental parameters of galaxies. An understanding of the interplay between those properties as well as their environmental dependence will give us a general picture of the physics and feedback processes ongoing in groups of galaxies. We study the relationships and environmental dependencies between the stellar mass, and gas metallicity for more than 1900 galaxies in groups up to redshift 0.35 using the Galaxy And Mass Assembly (GAMA) survey. Using a control sample of more than 28 000 star-forming field galaxies, we find evidence for a decrement of the gas metallicity for galaxies in groups.

Combining physical galaxy models with radio observations to constrain the SFRs of high-z dusty star-forming galaxies

NASA Astrophysics Data System (ADS)

Lo Faro, B.; Silva, L.; Franceschini, A.; Miller, N.; Efstathiou, A.

2015-03-01

We complement our previous analysis of a sample of z ˜ 1-2 luminous and ultraluminous infrared galaxies [(U)LIRGs], by adding deep Very Large Array radio observations at 1.4 GHz to a large data set from the far-UV to the submillimetre, including Spitzer and Herschel data. Given the relatively small number of (U)LIRGs in our sample with high signal-to-noise (S/N) radio data, and to extend our study to a different family of galaxies, we also include six well-sampled near-infrared (near-IR)-selected BzK galaxies at z ˜ 1.5. From our analysis based on the radtran spectral synthesis code GRASIL, we find that, while the IR luminosity may be a biased tracer of the star formation rate (SFR) depending on the age of stars dominating the dust heating, the inclusion of the radio flux offers significantly tighter constraints on SFR. Our predicted SFRs are in good agreement with the estimates based on rest-frame radio luminosity and the Bell calibration. The extensive spectrophotometric coverage of our sample allows us to set important constraints on the star formation (SF) history of individual objects. For essentially all galaxies, we find evidence for a rather continuous SFR and a peak epoch of SF preceding that of the observation by a few Gyr. This seems to correspond to a formation redshift of z ˜ 5-6. We finally show that our physical analysis may affect the interpretation of the SFR-M⋆ diagram, by possibly shifting, with respect to previous works, the position of the most dust obscured objects to higher M⋆ and lower SFRs.

The physical properties of galaxies with unusually red mid-infrared colours

NASA Astrophysics Data System (ADS)

Kauffmann, Guinevere

2018-02-01

The goal of this paper is to investigate the physical nature of galaxies in the redshift range 0.02 < z < 0.15 that have strong excess emission at mid-infrared wavelengths and to determine whether they host a population of accreting black holes that cannot be identified using optical emission lines. We show that at fixed stellar mass M* and Dn(4000), the distribution of [3.4]-[4.6] μm (Wide-field Infrared Survey Explorer, W1 - W2 band) colours is sharply peaked, with a long tail to much redder W1 - W2 colours. We introduce a procedure to pull out the red outlier population based on a combination of three stellar population diagnostics. When compared with optically selected active galactic nucleus (AGN), red outliers are more likely to be found in massive galaxies, and they tend to have lower stellar mass densities, younger stellar ages and higher dust content than optically selected AGN hosts. They are twice as likely to be detected at radio wavelengths. We examine W1 - W2 colour profiles for a subset of the nearest, reddest outliers and find that most are not centrally peaked, indicating that the hot dust emission is spread throughout the galaxy. We find that radio luminosity is the quantity that is most predictive of a redder central W1 - W2 colour. Radio-loud galaxies with centrally concentrated hot dust emission are almost always morphologically disturbed, with compact, unresolved emission at 1.4 GHz. The 80 per cent of such systems are identifiable as AGN using optical emission line diagnostics.

Galaxy Distribution in Clusters of Galaxies

NASA Astrophysics Data System (ADS)

Okamoto, T.; Yachi, S.; Habe, A.

beta-discrepancy have been pointed out from comparison of optical and X-ray observations of clusters of galaxies. To examine physical reason of beta-discrepancy, we use N-body simulation which contains two components, dark particles and galaxies which are identified by using adaptive-linking friend of friend technique at a certain red-shift. The gas component is not included here, since the gas distribution follows the dark matter distribution in dark halos (Jubio F. Navarro, Carlos S. Frenk and Simon D. M. White 1995). We find that the galaxy distribution follows the dark matter distribution, therefore beta-discrepancy does not exist, and this result is consistent with the interpretation of the beta-discrepancy by Bahcall and Lubin (1994), which was based on recent observation.

Cosmic shear as a probe of galaxy formation physics

DOE PAGES

Foreman, Simon; Becker, Matthew R.; Wechsler, Risa H.

2016-09-01

Here, we evaluate the potential for current and future cosmic shear measurements from large galaxy surveys to constrain the impact of baryonic physics on the matter power spectrum. We do so using a model-independent parametrization that describes deviations of the matter power spectrum from the dark-matter-only case as a set of principal components that are localized in wavenumber and redshift. We perform forecasts for a variety of current and future data sets, and find that at least ~90 per cent of the constraining power of these data sets is contained in no more than nine principal components. The constraining powermore » of different surveys can be quantified using a figure of merit defined relative to currently available surveys. With this metric, we find that the final Dark Energy Survey data set (DES Y5) and the Hyper Suprime-Cam Survey will be roughly an order of magnitude more powerful than existing data in constraining baryonic effects. Upcoming Stage IV surveys (Large Synoptic Survey Telescope, Euclid, and Wide Field Infrared Survey Telescope) will improve upon this by a further factor of a few. We show that this conclusion is robust to marginalization over several key systematics. The ultimate power of cosmic shear to constrain galaxy formation is dependent on understanding systematics in the shear measurements at small (sub-arcminute) scales. Lastly, if these systematics can be sufficiently controlled, cosmic shear measurements from DES Y5 and other future surveys have the potential to provide a very clean probe of galaxy formation and to strongly constrain a wide range of predictions from modern hydrodynamical simulations.« less

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.

Physical properties and evolution of GMCs in the Galaxy and the Magellanic Clouds

NASA Astrophysics Data System (ADS)

Onishi, Toshikazu

2015-08-01

Most stars are born as clusters in Giant Molecular Clouds (hereafter GMCs), and therefore the understanding of the evolution of GMCs in a galaxy is one of the key issues to investigate the evolution of the galaxy. The recent state-of-the-art radio telescopes have been enabling us to reveal the distribution of GMCs extensively in the Galaxy as well as in the nearby galaxies, and the physical properties and the evolution of the GMCs leading to cluster formations are actively being investigated. Here we present a review of studies of spatially resolved GMCs in the Galaxy and in the Large Magellanic Cloud (LMC), aiming at providing a template of GMC properties. For the Galactic GMCs, we will focus on the recent extensive survey of GMCs along the Galactic plane; the recent studies suggest cloud-cloud collision as mechanism of massive star formation. For the extra galactic GMCs, we will present recent high-resolution observations of GMCs in the LMC.The LMC is among the nearest star-forming galaxy (distance ~ 50kpc) and is almost face-on. From these aspects, it is becoming the most popular region for studying interstellar medium over an entire galaxy. For molecular gas, the NANTEN covered the entire LMC with a spatial resolution of 40 pc, revealing 272 molecular clouds whose mass ranges from ~104 to ~107 M⊙, which is the first uniform sample of GMCs in a single galaxy. Our Spitzer SAGE and Herschel HERITAGE surveys show that the interstellar medium has much smaller scale structures; full of filamentary and shell-like structures. In order to resolve the filamentary distributions and pre-stellar cores we definitely need to resolve clouds at sub-pc resolutions with ALMA and to cover regions of active cluster formation which are to be selected based on the Spitzer and Hershel data. Our ALMA targets in Cycle 1 and Cycle 2 include N159, which is the most intense and concentrated molecular cloud as shown by the brightest CO J=3-2 source in the LMC, and GMCs with different

[Romanian demography (1975-1989)].

PubMed

Trebici, V

1990-01-01

The author describes developments in the study of demography in Romania over the period 1975-1989. The books and articles mentioned are classified by subject. The author notes that although few full-length monographs were published during the Ceausescu years, a steady stream of demographic articles appeared, most of which were published in the journal Viitorul Social, now retitled Sociologie Romaneasca.

Multiple Core Galaxies: Implications for M31

NASA Technical Reports Server (NTRS)

Smith, B. F.; Miller, R. H.; Cuzzi, Jeffrey N. (Technical Monitor)

1994-01-01

It is generally perceived that two cores cannot survive very long within the nuclear regions of a galaxy. The recent HST discovery of a double nucleus in M31 brings this question into prominence. Physical conditions in the nuclear regions of a typical galaxy help a second core survive so it can orbit for a long time, possibly for thousands of orbits. Given the nearly uniform mass density in a core, tidal forces within a core radius are compressive in all directions and help the core survive the buffeting it takes as it orbits near the center of the galaxy. We use numerical experiments to illustrate these physical principles. Modifications to the experimental method allow the full power of the experiments to be concentrated on the nuclear regions. Spatial resolution of about 0.2 parsec comfortably resolves detail within the 1.4 parsec core radius of the second, but brighter, core (P1) in M31. The same physical principles apply in other astronomical situations, such as dumbbell galaxies, galaxies orbiting near the center of a galaxy cluster, and subclustering in galaxy clusters. The experiments also illustrate that galaxy encounters and merging are quite sensitive to external tidal forces, such as those produced by the gravitational potential in a group or cluster of galaxies.

Dark Energy and Key Physical Parameters of Clusters of Galaxies

NASA Astrophysics Data System (ADS)

Chernin, A. D.; Bisnovatyi-Kogan, G. S.

We discuss the physics of clusters of galaxies embedded in the cosmic dark energy background and show that 1) the halo cut-off radius of a cluster like the Virgo cluster is practically, if not exactly, equal to the zero-gravity radius at which the dark matter gravity is balanced by the dark energy antigravity; 2) the halo averaged density is equal to two densities of dark energy; 3) the halo edge (cut-off) density is the dark energy density with a numerical factor of the unity order slightly depending on the halo profile.

Demography and Public Health Emergency Preparedness: Making the Connection

PubMed Central

Katz, Rebecca

2009-01-01

The tools and techniques of population sciences are extremely relevant to the discipline of public health emergency preparedness: protecting and securing the population’s health requires information about that population. While related fields such as security studies have successfully integrated demographic tools into their research and literature, the theoretical and practical connection between the methods of demography and the practice of public health emergency preparedness is weak. This article suggests the need to further the interdisciplinary use of demography by examining the need for a systematic use of population science techniques in public health emergency preparedness. Ultimately, we demonstrate how public health emergency preparedness can incorporate demography to develop more effective preparedness plans. Important policy implications emerge: demographers and preparedness experts need to collaborate more formally in order to facilitate community resilience and mitigate the consequences of public health emergencies. PMID:20694030

Detailed Quantitative Classifications of Galaxy Morphology

NASA Astrophysics Data System (ADS)

Nair, Preethi

2018-01-01

Understanding the physical processes responsible for the growth of galaxies is one of the key challenges in extragalactic astronomy. The assembly history of a galaxy is imprinted in a galaxy’s detailed morphology. The bulge-to-total ratio of galaxies, the presence or absence of bars, rings, spiral arms, tidal tails etc, all have implications for the past merger, star formation, and feedback history of a galaxy. However, current quantitative galaxy classification schemes are only useful for broad binning. They cannot classify or exploit the wide variety of galaxy structures seen in nature. Therefore, comparisons of observations with theoretical predictions of secular structure formation have only been conducted on small samples of visually classified galaxies. However large samples are needed to disentangle the complex physical processes of galaxy formation. With the advent of large surveys, like the Sloan Digital Sky Survey (SDSS) and the upcoming Large Synoptic Survey Telescope (LSST) and WFIRST, the problem of statistics will be resolved. However, the need for a robust quantitative classification scheme will still remain. Here I will present early results on promising machine learning algorithms that are providing detailed classifications, identifying bars, rings, multi-armed spiral galaxies, and Hubble type.

Higher Education and Adult Demography.

ERIC Educational Resources Information Center

Brazziel, William F.

This paper examines the changing demographics of American society and the impact of these changes on higher education. Discussions include a historical background of early American demography, the building and expansion of the population base, and census changes through various generations of the baby boom years and beyond. Next, the report…

Demography of Disadvantage in Tennessee.

ERIC Educational Resources Information Center

Jones, Lewis W., Comp.; And Others

In this report, demography conceptualizes significant characteristics to serve as a basis for more intensive study, planning, and procedures focusing on the target group. A compilation of the latest reports available and primarily tabular in form, identifies and locates Tennessee's disadvantaged people, ranking the 95 counties on each of 8…

Statistical study of some Lee galaxy groups

NASA Astrophysics Data System (ADS)

Mohamed, Sabry A.; Fouad, Ahmed M.

2017-12-01

Compact groups of galaxies are systems of small number of galaxies close to each other. They are a good laboratory to study galaxy properties, such as structure, morphology and evolution which are affected by the environment and galaxy interactions. We applied the tree clustering technique (the Euclidean separation distance coefficients) to test the physical reality of groups and used certain criteria (Sabry et al., 2009) depending on the physical attributes of the galaxies. The sample of the data is the quintets groups of Lee compact groups of galaxies (Lee et al., 2004). It is based on a modified version of Hickson's criteria (Hickson, 1982). The results reveal the membership of each galaxy and how it is related to its group. The tables of groups and their members are included. Our results indicates that 12 Groups are real groups with real members while 18 Groups have one galaxy that has attribute discordant and should be discarded from its group.

Scale dependence of galaxy biasing investigated by weak gravitational lensing: An assessment using semi-analytic galaxies and simulated lensing data

NASA Astrophysics Data System (ADS)

Simon, Patrick; Hilbert, Stefan

2018-05-01

Galaxies are biased tracers of the matter density on cosmological scales. For future tests of galaxy models, we refine and assess a method to measure galaxy biasing as a function of physical scale k with weak gravitational lensing. This method enables us to reconstruct the galaxy bias factor b(k) as well as the galaxy-matter correlation r(k) on spatial scales between 0.01 h Mpc-1 ≲ k ≲ 10 h Mpc-1 for redshift-binned lens galaxies below redshift z ≲ 0.6. In the refinement, we account for an intrinsic alignment of source ellipticities, and we correct for the magnification bias of the lens galaxies, relevant for the galaxy-galaxy lensing signal, to improve the accuracy of the reconstructed r(k). For simulated data, the reconstructions achieve an accuracy of 3-7% (68% confidence level) over the above k-range for a survey area and a typical depth of contemporary ground-based surveys. Realistically the accuracy is, however, probably reduced to about 10-15%, mainly by systematic uncertainties in the assumed intrinsic source alignment, the fiducial cosmology, and the redshift distributions of lens and source galaxies (in that order). Furthermore, our reconstruction technique employs physical templates for b(k) and r(k) that elucidate the impact of central galaxies and the halo-occupation statistics of satellite galaxies on the scale-dependence of galaxy bias, which we discuss in the paper. In a first demonstration, we apply this method to previous measurements in the Garching-Bonn Deep Survey and give a physical interpretation of the lens population.

The effects of baryon physics, black holes and active galactic nucleus feedback on the mass distribution in clusters of galaxies

NASA Astrophysics Data System (ADS)

Martizzi, Davide; Teyssier, Romain; Moore, Ben; Wentz, Tina

2012-06-01

The spatial distribution of matter in clusters of galaxies is mainly determined by the dominant dark matter component; however, physical processes involving baryonic matter are able to modify it significantly. We analyse a set of 500 pc resolution cosmological simulations of a cluster of galaxies with mass comparable to Virgo, performed with the AMR code RAMSES. We compare the mass density profiles of the dark, stellar and gaseous matter components of the cluster that result from different assumptions for the subgrid baryonic physics and galaxy formation processes. First, the prediction of a gravity-only N-body simulation is compared to that of a hydrodynamical simulation with standard galaxy formation recipes, and then all results are compared to a hydrodynamical simulation which includes thermal active galactic nucleus (AGN) feedback from supermassive black holes (SMBHs). We find the usual effects of overcooling and adiabatic contraction in the run with standard galaxy formation physics, but very different results are found when implementing SMBHs and AGN feedback. Star formation is strongly quenched, producing lower stellar densities throughout the cluster, and much less cold gas is available for star formation at low redshifts. At redshift z= 0 we find a flat density core of radius 10 kpc in both the dark and stellar matter density profiles. We speculate on the possible formation mechanisms able to produce such cores and we conclude that they can be produced through the coupling of different processes: (I) dynamical friction from the decay of black hole orbits during galaxy mergers; (II) AGN-driven gas outflows producing fluctuations of the gravitational potential causing the removal of collisionless matter from the central region of the cluster; (III) adiabatic expansion in response to the slow expulsion of gas from the central region of the cluster during the quiescent mode of AGN activity.

The Physics of AGN Feedback During Galaxy Formation

NASA Astrophysics Data System (ADS)

Quataert, Eliot

A key lesson in our modern understanding of how galaxies form is that the release of energy by newly formed stars and accreting black holes -- in the form of both radiation and powerful outflows -- has a dramatic effect on the process of star formation and black hole growth itself. As a result, developing more realistic treatments of these stellar and black hole feedback processes is one of the primary challenges facing predictive models of galaxy formation. This proposal centers on understanding the dynamics of gas in galactic nuclei, with an emphasis on how black holes at the centers of galaxies grow and the resulting effects of black hole feedback on the scale of individual galaxies. Some of the calculations we propose will also have direct application to feedback by star formation. Our proposed work consists of two interrelated sets of projects. In the first, we will study in detail the mechanisms by which radiation and outflows from an accreting black hole interact with surrounding gas: this is the key science question at the heart of understanding black hole feedback. It is also important, however, to place this understanding of the key feedback processes in the broader context of gas dynamics in galaxies. With this in mind, we will carry out numerical simulations of gas in galactic nuclei and study, for the first time, the competition between gas inflow, star formation, and stellar and black hole feedback at the radii that the accretion rate onto a central black hole is determined and that galaxy-scale outflows of gas are likely initiated. Our work bears directly on, and will be applied to, observations by current NASA missions such as HST, Chandra, GALEX, Xmm-Newton, Herschel, and NuSTAR, and future missions such as JWST.

SPHEREx: Probing the Physics of Inflation with an All-Sky Spectroscopic Galaxy Survey

NASA Astrophysics Data System (ADS)

Dore, Olivier; SPHEREx Science Team

2018-01-01

SPHEREx, a mission in NASA's Medium Explorer (MIDEX) program that was selected for Phase A in August 2017, is an all-sky survey satellite designed to address all three science goals in NASA’s astrophysics division: probe the origin and destiny of our Universe; explore whether planets around other stars could harbor life; and explore the origin and evolution of galaxies. These themes are addressed by a single survey, with a single instrument.In this poster, we describe how SPHEREx can probe the physics of inflationary non-Gaussianity by measuring large-scale structure with galaxy redshifts over a large cosmological volume at low redshifts, complementing high-redshift surveys optimized to constrain dark energy.SPHEREx will be the first all-sky near-infrared spectral survey, creating a legacy archive of spectra. In particular, it will measure the redshifts of over 500 million galaxies of all types, an unprecedented dataset. Using this catalog, SPHEREx will reduce the uncertainty in fNL -- a parameter describing the inflationary initial conditions -- by a factor of more than 10 compared with CMB measurements. At the same time, this catalog will enable strong scientific synergies with Euclid, WFIRST and LSST

Political demography: Powerful trends under-attended by demographic science.

PubMed

Teitelbaum, Michael S

2015-01-01

The interconnections between politics and the dramatic demographic changes under way around the world have been neglected by the two research disciplines that could contribute most to their understanding: demography and political science. Instead, this area of 'political demography' has largely been ceded to political activists, pundits, and journalists, leading often to exaggerated or garbled interpretation. The terrain includes some of the most politically sensitive and contested issues: alleged demographically determined shifts in the international balance of power; low fertility, population decline, and demographic ageing; international migration; change in national identity; and compositional shifts in politically sensitive social categories and human rights. Meanwhile many governments and non-governmental actors have actively pursued varieties of 'strategic demography', deploying fertility, mortality, or migration as instruments of domestic or international policy. Political scientists and demographers could and should use their knowledge and analytic techniques to improve understanding and to moderate excessive claims and fears on these topics.

OSO-8 X-ray spectra of clusters of galaxies. 1. Observations of twenty clusters: Physical correlations

NASA Technical Reports Server (NTRS)

Mushotzky, R. F.; Serlemitsos, P. J.; Smith, B. W.; Boldt, E. A.; Holt, S. S.

1978-01-01

OSO-8 X-ray spectra from 2 to 20 keV were analyzed for 26 clusters of galaxies. Temperature, emission integrals, iron abundances, and low energy absorption measurements are given. Eight clusters have positive iron emission line detections at the 90% confidence level, and all twenty cluster spectra are consistent with Fe/H=0.000014 by number with the possible exception of Virgo. Physical correlations between X-ray spectral parameters and other cluster properties are examined. It is found that: (1) the X-ray temperature is approximately proportional to the square of the velocity dispersion of the galaxies; (2) the emission integral and therefore the bolometric X-ray luminosity is a strong function of the X-ray temperature; (3) the X-ray temperature and emission integral are better correlated with cluster central galaxy density than with richness; (4) temperature and emission integral are separately correlated with Rood-Sastry type; and (5) the fraction of galaxies which are spirals is correlated with the observed ram pressure in the cluster core.

CLASH: Extending galaxy strong lensing to small physical scales with distant sources highly magnified by galaxy cluster members

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grillo, C.; Christensen, L.; Gobat, R.

2014-05-01

We present a complex strong lensing system in which a double source is imaged five times by two early-type galaxies. We take advantage in this target of the extraordinary multi-band photometric data set obtained as part of the Cluster Lensing And Supernova survey with Hubble (CLASH) program, complemented by the spectroscopic measurements of the VLT/VIMOS and FORS2 follow-up campaign. We use a photometric redshift value of 3.7 for the source and confirm spectroscopically the membership of the two lenses to the galaxy cluster MACS J1206.2–0847 at redshift 0.44. We exploit the excellent angular resolution of the HST/ACS images to modelmore » the two lenses in terms of singular isothermal sphere profiles and derive robust effective velocity dispersion values of 97 ± 3 and 240 ± 6 km s{sup –1}. Interestingly, the total mass distribution of the cluster is also well characterized by using only the local information contained in this lensing system, which is located at a projected distance of more than 300 kpc from the cluster luminosity center. According to our best-fitting lensing and composite stellar population models, the source is magnified by a total factor of 50 and has a luminous mass of approximately (1.0 ± 0.5) × 10{sup 9} M {sub ☉} (assuming a Salpeter stellar initial mass function). By combining the total and luminous mass estimates of the two lenses, we measure luminous over total mass fractions projected within the effective radii of 0.51 ± 0.21 and 0.80 ± 0.32. Remarkably, with these lenses we can extend the analysis of the mass properties of lens early-type galaxies by factors that are approximately two and three times smaller than previously done with regard to, respectively, velocity dispersion and luminous mass. The comparison of the total and luminous quantities of our lenses with those of astrophysical objects with different physical scales, like massive early-type galaxies and dwarf spheroidals, reveals the potential of studies of this

Dark Influences at the Threshold of Galaxy Formation

NASA Astrophysics Data System (ADS)

Boylan-Kolchin, Michael

As the faintest, lowest-luminosity, and most dark-matter-dominated extremes of the galaxy population, dwarf galaxies present unique opportunities for studying galaxy formation and the properties of dark matter. Accordingly, they have been observed in detail from the ground and (by NASA missions) from space with the hopes of unraveling how dwarf galaxies form, the effects of reionization on galaxy formation, and whether signatures of the particle nature of dark matter (DM) interactions can be observed. Such work has gained in importance as efforts to directly detect DM have so far yielded only upper limits to the interaction between DM and normal matter, leaving astrophysical tests as the primary means of investigating the nature of DM. We propose to undertake an extensive yet focused program of cosmological hydrodynamic simulations aimed at understanding the formation of dwarf galaxies. We will focus on the interplay between galaxy formation and dark matter in these galaxies, pointing toward specific observables to disentangle the effects of galaxy formation physics from the effects of DM physics. Our simulation suite will explore collisionless Cold Dark Matter (CDM) and broad classes of alternatives, where DM has a nonnegligible free-streaming length and / or self-scattering cross section. The novel aspects of the proposed work will include: (1) a modern treatment of baryonic physics using GIZMO, a new code that uses accurate meshless methods for hydrodynamics; (2) Feedback In Realistic Environments (FIRE), a suite of galaxy formation parametrizations with well-tested, explicit implementations of stellar feedback; (3) an exploration of realistic models of DM beyond CDM based on an effective theory of structure formation, with full baryonic physics; and (4) detailed mock observations of the simulations in order to identify specific, distinguishing tests for CDM and its alternatives. Our research will provide a framework within which astrophysical inferences about

Anisotropic Galaxy-Galaxy Lensing in the Illustris-1 Simulation

NASA Astrophysics Data System (ADS)

Brainerd, Tereasa G.

2017-06-01

dark matter. The suppression of the anisotropy when using the major axis of the light to define the geometry is indicative of a significant misalignment of mass and light in the Illustris-1 galaxies at large physical radii.

Dwarf elliptical galaxies

NASA Technical Reports Server (NTRS)

Ferguson, Henry C.; Binggeli, Bruno

1994-01-01

Dwarf elliptical (dE) galaxies, with blue absolute magnitudes typically fainter than M(sub B) = -16, are the most numerous type of galaxy in the nearby universe. Tremendous advances have been made over the past several years in delineating the properties of both Local Group satellite dE's and the large dE populations of nearby clusters. We review some of these advances, with particular attention to how well currently availiable data can constrain (a) models for the formation of dE's, (b) the physical and evolutionary connections between different types of galaxies that overlap in the same portion of the mass-spectrum of galaxies, (c) the contribution of dE's to the galaxy luminosity functions in clusters and the field, (d) the star-forming histories of dE's and their possible contribution to faint galaxy counts, and (e) the clustering properties of dE's. In addressing these issues, we highlight the extent to which selection effects temper these constraints, and outline areas where new data would be particularly valuable.

Demography of Honors: The Census of U.S. Honors Programs and Colleges

ERIC Educational Resources Information Center

Scott, Richard I.; Smith, Patricia J.; Cognard-Black, Andrew J.

2017-01-01

Beginning in 2013 and spanning four research articles, we have implemented an empirical analysis protocol for honors education that is rooted in demography (Scott; Scott and Smith; Smith and Scott "Growth"; Smith and Scott, "Demography"). The goal of this protocol is to describe the structure and distribution of the honors…

OSO 8 X-ray spectra of clusters of galaxies. I - Observations of twenty clusters: Physical correlations

NASA Technical Reports Server (NTRS)

Mushotzky, R. F.; Serlemitsos, P. J.; Boldt, E. A.; Holt, S. S.; Smith, B. W.

1978-01-01

OSO 8 X-ray spectra from 2 to 20 keV have been analyzed for 26 clusters of galaxies. For 20 clusters temperatures, emission integrals, iron abundances, and low-energy absorption measurements are presented. The data give, in general, better fits to thermal bremsstrahlung than to power-law models. Eight clusters have positive iron emission-line detections at the 90% confidence level, and all 20 cluster spectra are consistent with Fe/H = 0.000014 by number with the possible exception of Virgo. Thus it is confirmed that X-ray emission in this energy band is predominantly thermal radiation from hot intracluster gas rather than inverse Compton radiation. Physical correlations between X-ray spectral parameters and other cluster properties are examined. It is found that (1) the X-ray temperature is approximately proportional to the square of the velocity dispersion of the galaxies; (2) the emission integral is a strong function of the X-ray temperature; (3) the X-ray temperature and emission integral are better correlated with cluster central-galaxy density than with richness; and (4) the fraction of galaxies which are spirals is correlated with the observed ram pressure in the cluster core.

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.

Cosmic Collisions: Galaxy Mergers and Evolution

NASA Astrophysics Data System (ADS)

Trouille, Laura; Willett, Kyle; Masters, Karen; Lintott, Christopher; Whyte, Laura; Lynn, Stuart; Tremonti, Christina A.

2014-08-01

Over the years evidence has mounted for a significant mode of galaxy evolution via mergers. This process links gas-rich, spiral galaxies; starbursting galaxies; active galactic nuclei (AGN); post-starburst galaxies; and gas-poor, elliptical galaxies, as objects representing different phases of major galaxy mergers. The post-starburst phase is particularly interesting because nearly every galaxy that evolves from star-forming to quiescent must pass through it. In essence, this phase is a sort of galaxy evolution “bottleneck” that indicates that a galaxy is actively evolving through important physical transitions. In this talk I will present the results from the ‘Galaxy Zoo Quench’ project - using post-starburst galaxies to place observational constraints on the role of mergers and AGN activity in quenching star formation. `Quench’ is the first fully collaborative research project with Zooniverse citizen scientists online; engaging the public in all phases of research, from classification to data analysis and discussion to writing the article and submission to a refereed journal.

Evolution of Galaxies

DTIC Science & Technology

1967-01-01

particularly good case was afforded by NGC 4438 in the Virgo Cluster , a photograph of which was published there. Another interesting case is shown in...variety of forms of galaxy in some clusters (for example, the Virgo cluster ) indicates that the initial conditions for the condensation of a galaxy...National Institutes of Health Air Force Office of Scientific Research Army Research Office Office of Naval Research VOLUME III PHYSICAL SCIENCES

Gendered Authorship and Demographic Research: An Analysis of 50 Years of Demography.

PubMed

Krapf, Sandra; Kreyenfeld, Michaela; Wolf, Katharina

2016-08-01

Demography, the official journal of the Population Association of America, has been given the highest rating among demographic journals by the Social Sciences Citation Index (SSCI). Our aim here is to investigate the development of research subfields and female authorship in Demography over the last 50 years. We find that female authorship in Demography has risen considerably since the 1980s and that currently a woman is about as likely as a man to be the sole or the first author of a paper published in the journal. However, we find some differences by subfield. Women seem to be overrepresented in the "family and household" research subfield but underrepresented in the "mortality and health" and "data and methods" categories.

Galaxy Selection and the Surface Brightness Distribution

NASA Astrophysics Data System (ADS)

McGaugh, Stacy S.; Bothun, Gregory D.; Schombert, James M.

1995-08-01

Optical surveys for galaxies are biased against the inclusion of low surface brightness (LSB) galaxies. Disney [Nature, 263,573(1976)] suggested that the constancy of disk central surface brightness noticed by Freeman [ApJ, 160,811(1970)] was not a physical result, but instead was an artifact of sample selection. Since LSB galaxies do exist, the pertinent and still controversial issue is if these newly discovered galaxies constitute a significant percentage of the general galaxy population. In this paper, we address this issue by determining the space density of galaxies as a function of disk central surface brightness. Using the physically reasonable assumption (which is motivated by the data) that central surface brightness is independent of disk scale length, we arrive at a distribution which is roughly flat (i.e., approximately equal numbers of galaxies at each surface brightness) faintwards of the Freeman (1970) value. Brightwards of this, we find a sharp decline in the distribution which is analogous to the turn down in the luminosity function at L^*^. An intrinsically sharply peaked "Freeman law" distribution can be completely ruled out, and no Gaussian distribution can fit the data. Low surface brightness galaxies (those with central surface brightness fainter than 22 B mag arcsec^-2^) comprise >~ 1/2 the general galaxy population, so a representative sample of galaxies at z = 0 does not really exist at present since past surveys have been insensitive to this component of the general galaxy population.

Star-Formation Histories of MUSCEL Galaxies

NASA Astrophysics Data System (ADS)

Young, Jason; Kuzio de Naray, Rachel; Xuesong Wang, Sharon

2018-01-01

The MUSCEL program (MUltiwavelength observations of the Structure, Chemistry and Evolution of LSB galaxies) uses combined ground-based/space-based data to determine the spatially resolved star-formation histories of low surface brightness (LSB) galaxies. LSB galaxies are paradoxical in that they are gas rich but have low star-formation rates. Here we present our observations and fitting technique, and the derived histories for select MUSCEL galaxies. It is our aim to use these histories in tandem with velocity fields and metallicity profiles to determine the physical mechanism(s) that give these faint galaxies low star-formation rates despite ample gas supplies.

The early phase of the SMBH-galaxy coevolution in low-z "young" galaxies

NASA Astrophysics Data System (ADS)

Nagao, Tohru

2014-01-01

It is now widely recognized that most galaxies have a supermassive black hole (SMBH) in their nucleus, and the evolution of SMBHs is closely related with that of their host galaxies (the SMBH-galaxy coevolution). This is suggested by the correlation in the mass of SMBHs and their host galaxies, that has been observed in low redshifts. However, the physics of the coevolution is totally unclear, that prevents us from complete understandings of the galaxy evolution. One possible strategy to tackle this issue is measuring the mass ratio between SMBHs and their host galaxies (M_BH/M_host) at high redshifs, since different scenarios predict different evolution of the ratio ofMBH/Mhost. However it is extremely challenging to measure the mass of the host of high-z quasars, given the faint surface brightness of the host at close to the glaring quasar nucleus. Here we propose a brand-new approach to assess the early phase of the SMBH-galaxy coevolution, by focusing on low-z AGN-hosting "young" galaxies. Specifically, we focus on some very metal-poor galaxies with broadline Balmer lines at z ~ 0.1 - 0.3. By examining the SMBH scaling relations in some low-z metal-poor AGNs through high-resolution IRCS imaging observations, we will discriminate various scenarios for the SMBH-galaxy coevolution.

Teaching Demography to Undergraduates: A Pedagogical Dilemma.

ERIC Educational Resources Information Center

Abowitz, Deborah A.

1990-01-01

Describes a course based on the interdisciplinary approach to demography linked to environmental issues. Analytic and interpretive skills are an integral element in the study of population-related problems. Points out that the interdisciplinary approach maintains demographic literacy while analyzing population problems. (SLM)

Teaching Business Demography Using Case Studies.

PubMed

Swanson, David A; Morrison, Peter A

2010-02-01

Many faculty members consider using case studies but not all end up using them. We provide a brief review of what cases are intended to do and identify three ways in which they can be used. We then use an example to illustrate how we have used the case study method in teaching business demography. Among other benefits, we note that the case studies method not only encourages the acquisition of skills by students, but can be used to promote "deep structure learning," an approach naturally accommodates other features associated with the case studies method-the development of critical thinking skills, the use of real world problems, the emphasis of concepts over mechanics, writing and presentation skills, active cooperative learning and the "worthwhileness" of a course. As noted by others, we understand the limitations of the case study method. However, given its strengths, we believe it has a place in the instructional toolbox for courses in business demography. The fact that courses we teach is a testament to our perceived efficacy of this tool.

Demise of faint satellites around isolated early-type galaxies

NASA Astrophysics Data System (ADS)

Park, Changbom; Hwang, Ho Seong; Park, Hyunbae; Lee, Jong Chul

2018-02-01

The hierarchical galaxy formation scenario in the Cold Dark Matter cosmology with a non-vanishing cosmological constant Λ and geometrically flat space (ΛCDM) has been very successful in explaining the large-scale distribution of galaxies. However, there have been claims that ΛCDM over-predicts the number of satellite galaxies associated with massive galaxies compared with observations—the missing satellite galaxy problem1-3. Isolated groups of galaxies hosted by passively evolving massive early-type galaxies are ideal laboratories for identifying the missing physics in the current theory4-11. Here, we report—based on a deep spectroscopic survey—that isolated massive and passive early-type galaxies without any signs of recent wet mergers or accretion episodes have almost no satellite galaxies fainter than the r-band absolute magnitude of about Mr = -14. If only early-type satellites are used, the cutoff is at the somewhat brighter magnitude of about Mr = -15. Such a cutoff has not been found in other nearby satellite galaxy systems hosted by late-type galaxies or those with merger features. Various physical properties of satellites depend strongly on the host-centric distance. Our observations indicate that the satellite galaxy luminosity function is largely determined by the interaction of satellites with the environment provided by their host.

Observational properties of compact groups of galaxies

NASA Technical Reports Server (NTRS)

Hickson, Paul

1990-01-01

Compact groups are small, relatively isolated, systems of galaxies with projected separations comparable to the diameters of the galaxies themselves. Two well-known examples are Stephan's Quintet (Stephan, 1877) and Seyfert's Sextet (Seyfert 1948a,b). In groups such as these, the apparent space density of galaxies approaches 10(exp 6) Mpc(sub -3), denser even than the cores of rich clusters. The apparent unlikeliness of the chance occurrence of such tight groupings lead Ambartsumyan (1958, 1975) to conclude that compact groups must be physically dense systems. This view is supported by clear signs of galaxy interactions that are seen in many groups. Spectroscopic observations reveal that typical relative velocities of galaxies in the groups are comparable to their internal stellar velocities. This should be conducive to strong gravitational interactions - more so than in rich clusters, where galaxy velocities are typically much higher. This suggests that compact groups could be excellent laboratories in which to study galaxy interactions and their effects. Compact groups often contain one or more galaxies whose redshift differs greatly from those of the other group members. If these galaxies are at the same distance as the other members, either entire galaxies are being ejected at high velocities from these groups, or some new physical phenomena must be occurring. If their redshifts are cosmological, we must explain why so many discordant galaxies are found in compact groups. In recent years much progress has been made in addressing these questions. Here, the author discusses the current observational data on compact groups and their implications.

Energy, entropy and mass scaling relations for elliptical galaxies. Towards a physical understanding of their photometric properties

NASA Astrophysics Data System (ADS)

Márquez, I.; Lima Neto, G. B.; Capelato, H.; Durret, F.; Lanzoni, B.; Gerbal, D.

2001-12-01

In the present paper, we show that elliptical galaxies (Es) obey a scaling relation between potential energy and mass. Since they are relaxed systems in a post violent-relaxation stage, they are quasi-equilibrium gravitational systems and therefore they also have a quasi-constant specific entropy. Assuming that light traces mass, these two laws imply that in the space defined by the three Sérsic law parameters (intensity Sigma0 , scale a and shape nu ), elliptical galaxies are distributed on two intersecting 2-manifolds: the Entropic Surface and the Energy-Mass Surface. Using a sample of 132 galaxies belonging to three nearby clusters, we have verified that ellipticals indeed follow these laws. This also implies that they are distributed along the intersection line (the Energy-Entropy line), thus they constitute a one-parameter family. These two physical laws (separately or combined), allow to find the theoretical origin of several observed photometrical relations, such as the correlation between absolute magnitude and effective surface brightness, and the fact that ellipticals are located on a surface in the [log Reff, -2.5 log Sigma0, log nu ] space. The fact that elliptical galaxies are a one-parameter family has important implications for cosmology and galaxy formation and evolution models. Moreover, the Energy-Entropy line could be used as a distance indicator.

Owned dog ecology and demography in Villa de Tezontepec, Hidalgo, Mexico.

PubMed

Kisiel, Luz Maria; Jones-Bitton, Andria; Sargeant, Jan M; Coe, Jason B; Flockhart, D T Tyler; Reynoso Palomar, Alejandro; Canales Vargas, Erick J; Greer, Amy L

2016-12-01

Dog overpopulation in developing countries has negative implications for the health and safety of people, including the transmission of zoonotic diseases, physical attacks and intimidation to humans and animals, as well as impacts on canine welfare. Understanding the ecology and demographic characteristics of a dog population can help in the planning and monitoring of canine population control programs. Little data exist regarding demography and dynamics of domestic dog populations in semi-urban areas in Mexico. A cross-sectional study was carried out between October 21 and November 7, 2015, to characterize the dog ecology and demography in Villa de Tezontepec, Hidalgo, Mexico. A face-to-face survey was used to collect data from randomly selected households in four contiguous communities using stratified two-stage cluster sampling. Within each household, adults answered questions related to their dogs and their experiences with dog bites and aggression. A total of 328 households were interviewed, representing a participation rate of 90.9% (328/361) and 1,450 people. Approximately 65.2% of the households owned one or more dogs, with a mean of 1.3 (SD=1.5) and 2.0 (SD=1.5) owned dogs in all participant households and dog-owning households, respectively. The human: owned dog ratio for all participant households was 3.4:1 (1450/428), and for the dog-owning households was 2.3:1 (984/428). The owned dog male: female ratio was 1.4:1 (249/179). Approximately 74.4% (95.0% CI=69.8% - 78.7%) of the owned dogs were older than one year (mean age: 2.9 years; SD=2.5). The mean age of owned female dogs at first litter was 1.9 years (SD=1.2) and the mean litter size was 4.2 puppies (SD=2.1). Approximately 36.9% (95.0% CI=31.8% - 46.4%) of the females were spayed, and 14.1% (95.0% CI=10.7% - 19.7%) of the males were neutered. Only 44.9% (95.0% CI=40.1% - 49.7%) were always confined when unsupervised. Approximately 84.4% (95.0% CI=80.6% - 87.7%) were reported to have been vaccinated

Supernova feedback in numerical simulations of galaxy formation: separating physics from numerics

NASA Astrophysics Data System (ADS)

Smith, Matthew C.; Sijacki, Debora; Shen, Sijing

2018-07-01

While feedback from massive stars exploding as supernovae (SNe) is thought to be one of the key ingredients regulating galaxy formation, theoretically it is still unclear how the available energy couples to the interstellar medium and how galactic scale outflows are launched. We present a novel implementation of six sub-grid SN feedback schemes in the moving-mesh code AREPO, including injections of thermal and/or kinetic energy, two parametrizations of delayed cooling feedback and a `mechanical' feedback scheme that injects the correct amount of momentum depending on the relevant scale of the SN remnant resolved. All schemes make use of individually time-resolved SN events. Adopting isolated disc galaxy set-ups at different resolutions, with the highest resolution runs reasonably resolving the Sedov-Taylor phase of the SN, we aim to find a physically motivated scheme with as few tunable parameters as possible. As expected, simple injections of energy overcool at all but the highest resolution. Our delayed cooling schemes result in overstrong feedback, destroying the disc. The mechanical feedback scheme is efficient at suppressing star formation, agrees well with the Kennicutt-Schmidt relation, and leads to converged star formation rates and galaxy morphologies with increasing resolution without fine-tuning any parameters. However, we find it difficult to produce outflows with high enough mass loading factors at all but the highest resolution, indicating either that we have oversimplified the evolution of unresolved SN remnants, require other stellar feedback processes to be included, and require a better star formation prescription or most likely some combination of these issues.

Supernova feedback in numerical simulations of galaxy formation: separating physics from numerics

NASA Astrophysics Data System (ADS)

Smith, Matthew C.; Sijacki, Debora; Shen, Sijing

2018-04-01

While feedback from massive stars exploding as supernovae (SNe) is thought to be one of the key ingredients regulating galaxy formation, theoretically it is still unclear how the available energy couples to the interstellar medium and how galactic scale outflows are launched. We present a novel implementation of six sub-grid SN feedback schemes in the moving-mesh code AREPO, including injections of thermal and/or kinetic energy, two parametrizations of delayed cooling feedback and a `mechanical' feedback scheme that injects the correct amount of momentum depending on the relevant scale of the SN remnant resolved. All schemes make use of individually time-resolved SN events. Adopting isolated disk galaxy setups at different resolutions, with the highest resolution runs reasonably resolving the Sedov-Taylor phase of the SN, we aim to find a physically motivated scheme with as few tunable parameters as possible. As expected, simple injections of energy overcool at all but the highest resolution. Our delayed cooling schemes result in overstrong feedback, destroying the disk. The mechanical feedback scheme is efficient at suppressing star formation, agrees well with the Kennicutt-Schmidt relation and leads to converged star formation rates and galaxy morphologies with increasing resolution without fine tuning any parameters. However, we find it difficult to produce outflows with high enough mass loading factors at all but the highest resolution, indicating either that we have oversimplified the evolution of unresolved SN remnants, require other stellar feedback processes to be included, require a better star formation prescription or most likely some combination of these issues.

Bayesian demography 250 years after Bayes

PubMed Central

Bijak, Jakub; Bryant, John

2016-01-01

Bayesian statistics offers an alternative to classical (frequentist) statistics. It is distinguished by its use of probability distributions to describe uncertain quantities, which leads to elegant solutions to many difficult statistical problems. Although Bayesian demography, like Bayesian statistics more generally, is around 250 years old, only recently has it begun to flourish. The aim of this paper is to review the achievements of Bayesian demography, address some misconceptions, and make the case for wider use of Bayesian methods in population studies. We focus on three applications: demographic forecasts, limited data, and highly structured or complex models. The key advantages of Bayesian methods are the ability to integrate information from multiple sources and to describe uncertainty coherently. Bayesian methods also allow for including additional (prior) information next to the data sample. As such, Bayesian approaches are complementary to many traditional methods, which can be productively re-expressed in Bayesian terms. PMID:26902889

Dark Matter Equilibria in Galaxies and Galaxy Systems

NASA Astrophysics Data System (ADS)

Lapi, A.; Cavaliere, A.

2009-02-01

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

Infrared-Bright Interacting Galaxies

NASA Astrophysics Data System (ADS)

Rojas Ruiz, Sofia; Murphy, Eric Joseph; Armus, Lee; Smith, John-David; Bradford, Charles Matt; Stierwalt, Sabrina

2018-01-01

We present the mid-infrared spectral mapping of eight LIRG-class interacting galaxies: NGC 6670, NGC 7592, IIZw 96, IIIZw 35, Arp 302, Arp 236, Arp 238, Arp 299. The properties of galaxy mergers, which are bright and can be studied at high resolutions at low-z, provide local analogs for sources that may be important contributors to the Far Infrared Background (FIRB.) In order to study star formation and the physical conditions in the gas and dust in our sample galaxies, we used the Spitzer InfraRed Spectrograph (IRS) to map the galaxies over the 5-35 μm window to trace the PAH, molecular hydrogen, and atomic fine structure line emission on scales of 1.4 – 5.3 kpc. Here we present the reduction for low and high-resolution data, and preliminary results in the analysis of fine structure line ratios and dust features in the two nuclei and interacting regions from one of our sample galaxies, NGC 6670.

Dark-ages reionization and galaxy formation simulation - IX. Economics of reionizing galaxies

NASA Astrophysics Data System (ADS)

Duffy, Alan R.; Mutch, Simon J.; Poole, Gregory B.; Geil, Paul M.; Kim, Han-Seek; Mesinger, Andrei; Wyithe, J. Stuart B.

2017-09-01

Using a series of high-resolution hydrodynamical simulations we show that during the rapid growth of high-redshift (z > 5) galaxies, reserves of molecular gas are consumed over a time-scale of 300 Myr, almost independent of feedback scheme. We find that there exists no such simple relation for the total gas fractions of these galaxies, with little correlation between gas fractions and specific star formation rates. The bottleneck or limiting factor in the growth of early galaxies is in converting infalling gas to cold star-forming gas. Thus, we find that the majority of high-redshift dwarf galaxies are effectively in recession, with demand (of star formation) never rising to meet supply (of gas), irrespective of the baryonic feedback physics modelled. We conclude that the basic assumption of self-regulation in galaxies - that they can adjust total gas consumption within a Hubble time - does not apply for the dwarf galaxies thought to be responsible for providing most UV photons to reionize the high-redshift Universe. We demonstrate how this rapid molecular time-scale improves agreement between semi-analytic model predictions of the early Universe and observed stellar mass functions.

Hydride Molecules towards Nearby Galaxies

NASA Astrophysics Data System (ADS)

Monje, Raquel R.; La, Ngoc; Goldsmith, Paul

2018-06-01

Observations carried out by the Herschel Space Observatory revealed strong spectroscopic signatures from light hydride molecules within the Milky Way and nearby active galaxies. To better understand the chemical and physical conditions of the interstellar medium, we conducted the first comprehensive survey of hydrogen fluoride (HF) and water molecular lines observed through the SPIRE Fourier Transform Spectrometer. By collecting and analyzing the sub-millimeter spectra of over two hundred sources, we found that the HF J = 1 - 0 rotational transition which occurs at approximately 1232 GHz was detected in a total of 39 nearby galaxies both in absorption and emission. The analysis will determine the main excitation mechanism of HF in nearby galaxies and provide steady templates of the chemistry and physical conditions of the ISM to be used in the early universe, where observations of hydrides are more scarce.

Brighter galaxy bias: underestimating the velocity dispersions of galaxy clusters

NASA Astrophysics Data System (ADS)

Old, L.; Gray, M. E.; Pearce, F. R.

2013-09-01

We study the systematic bias introduced when selecting the spectroscopic redshifts of brighter cluster galaxies to estimate the velocity dispersion of galaxy clusters from both simulated and observational galaxy catalogues. We select clusters with Ngal ≥ 50 at five low-redshift snapshots from the publicly available De Lucia & Blaziot semi-analytic model galaxy catalogue. Clusters are also selected from the Tempel Sloan Digital Sky Survey Data Release 8 groups and clusters catalogue across the redshift range 0.021 ≤ z ≤ 0.098. We employ various selection techniques to explore whether the velocity dispersion bias is simply due to a lack of dynamical information or is the result of an underlying physical process occurring in the cluster, for example, dynamical friction experienced by the brighter cluster members. The velocity dispersions of the parent dark matter (DM) haloes are compared to the galaxy cluster dispersions and the stacked distribution of DM particle velocities is examined alongside the corresponding galaxy velocity distribution. We find a clear bias between the halo and the semi-analytic galaxy cluster velocity dispersion on the order of σgal/σDM ˜ 0.87-0.95 and a distinct difference in the stacked galaxy and DM particle velocities distribution. We identify a systematic underestimation of the velocity dispersions when imposing increasing absolute I-band magnitude limits. This underestimation is enhanced when using only the brighter cluster members for dynamical analysis on the order of 5-35 per cent, indicating that dynamical friction is a serious source of bias when using galaxy velocities as tracers of the underlying gravitational potential. In contrast to the literature we find that the resulting bias is not only halo mass dependent but also that the nature of the dependence changes according to the galaxy selection strategy. We make a recommendation that, in the realistic case of limited availability of spectral observations, a strictly

NGC 3934: a shell galaxy in a compact galaxy environment

NASA Astrophysics Data System (ADS)

Bettoni, D.; Galletta, G.; Rampazzo, R.; Marino, A.; Mazzei, P.; Buson, L. M.

2011-10-01

Context. Mergers/accretions are considered the main drivers of the evolution of galaxies in groups. We investigate the NGC 3933 poor galaxy association that contains NGC 3934, which is classified as a polar-ring galaxy. Aims: The multi-band photometric analysis of NGC 3934 allows us to investigate the nature of this galaxy and to re-define the NGC 3933 group members with the aim to characterize the group's dynamical properties and its evolutionary phase. Methods: We imaged the group in the far (FUV, λeff = 1539 Å) and near (NUV, λeff = 2316 Å) ultraviolet (UV) bands of the Galaxy Evolution Explorer (GALEX). From the deep optical imaging we determined the fine structure of NGC 3934. We measured the recession velocity of PGC 213894 which shows that it belongs to the NGC 3933 group. We derived the spectral energy distribution (SED) from FUV to far-IR emission of the two brightest members of the group. We compared a grid of smooth particle hydrodynamical (SPH) chemo-photometric simulations with the SED and the integrated properties of NGC 3934 and NGC 3933 to devise their possible formation/evolutionary scenarios. Results: The NGC 3933 group has six bright members: a core composed of five galaxies, which have Hickson's compact group characteristics, and a more distant member, PGC 37112. The group velocity dispersion is relatively low (157 ± 44 km s-1). The projected mass, from the NUV photometry, is ~7 × 1012 M⊙ with a crossing time of 0.04 Hubble times, suggesting that at least in the center the group is virialized. We do not find evidence that NGC 3934 is a polar-ring galaxy, as suggested by the literature, but find that it is a disk galaxy with a prominent dust-lane structure and a wide type-II shell structure. Conclusions: NGC 3934 is a quite rare example of a shell galaxy in a likely dense galaxy region. The comparison between physically motivated SPH simulations with multi-band integrated photometry suggests that NGC 3934 is the product of a major merger.

Constraining Feedback in Galaxy Formation: Using Galaxy and AGN Surveys to Shed Light on ``Gastrophysics"

NASA Astrophysics Data System (ADS)

Monaco, P.

2007-12-01

We present some results of the new MORGANA model for the rise of galaxies and active nuclei, and show that the improved physical motivation of the description of star formation and feedback allows to get hints on the physical processes at play. We propose that the high level of turbulence in star-forming bulges is at the base of the observed downsizing of AGNs. In this framework it is also possible to reproduce the recently obtained evidence that most low-redshift accretion is powered by relatively massive, slowly accreting black holes. Besides, we notice that many galaxy formation models (including MORGANA) fail to reproduce a basic observable, namely the number density of 10^{11} M_⊙ galaxies at z˜1, as traced by the GOODS-MUSIC sample. This points to a possibly missing ingredient in the modeling of stellar feedback.

A Modern Picture of Barred Galaxy Dynamics

NASA Astrophysics Data System (ADS)

Petersen, Michael; Weinberg, Martin; Katz, Neal

2018-01-01

Observations of disk galaxies suggest that bars are responsible for altering global galaxy parameters (e.g. structures, gas fraction, star formation rate). The canonical understanding of the mechanisms underpinning bar-driven secular dynamics in disk galaxies has been largely built upon the analysis of linear theory, despite galactic bars being clearly demonstrated to be nonlinear phenomena in n-body simulations. We present simulations of barred Milky Way-like galaxy models designed to elucidate nonlinear barred galaxy dynamics. We have developed two new methodologies for analyzing n-body simulations that give the best of both powerful analytic linear theory and brute force simulation analysis: orbit family identification and multicomponent torque analysis. The software will be offered publicly to the community for their own simulation analysis.The orbit classifier reveals that the details of kinematic components in galactic disks (e.g. the bar, bulge, thin disk, and thick disk components) are powerful discriminators of evolutionary paradigms (i.e. violent instabilities and secular evolution) as well as the basic parameters of the dark matter halo (mass distribution, angular momentum distribution). Multicomponent torque analysis provides a thorough accounting of the transfer of angular momentum between orbits, global patterns, and distinct components in order to better explain the underlying physics which govern the secular evolution of barred disk galaxies.Using these methodologies, we are able to identify the successes and failures of linear theory and traditional n-body simulations en route to a detailed understanding of the control bars exhibit over secular evolution in galaxies. We present explanations for observed physical and velocity structures in observations of barred galaxies alongside predictions for how structures will vary with dynamical properties from galaxy to galaxy as well as over the lifetime of a galaxy, finding that the transfer of angular

Clumpy Galaxies in CANDELS. II. Physical Properties of UV-bright Clumps at 0.5 ≤ z < 3

NASA Astrophysics Data System (ADS)

Guo, Yicheng; Rafelski, Marc; Bell, Eric F.; Conselice, Christopher J.; Dekel, Avishai; Faber, S. M.; Giavalisco, Mauro; Koekemoer, Anton M.; Koo, David C.; Lu, Yu; Mandelker, Nir; Primack, Joel R.; Ceverino, Daniel; de Mello, Duilia F.; Ferguson, Henry C.; Hathi, Nimish; Kocevski, Dale; Lucas, Ray A.; Pérez-González, Pablo G.; Ravindranath, Swara; Soto, Emmaris; Straughn, Amber; Wang, Weichen

2018-02-01

Studying giant star-forming clumps in distant galaxies is important to understand galaxy formation and evolution. At present, however, observers and theorists have not reached a consensus on whether the observed “clumps” in distant galaxies are the same phenomenon that is seen in simulations. In this paper, as a step to establish a benchmark of direct comparisons between observations and theories, we publish a sample of clumps constructed to represent the commonly observed “clumps” in the literature. This sample contains 3193 clumps detected from 1270 galaxies at 0.5≤slant z< 3.0. The clumps are detected from rest-frame UV images, as described in our previous paper. Their physical properties (e.g., rest-frame color, stellar mass ({M}* ), star formation rate (SFR), age, and dust extinction) are measured by fitting the spectral energy distribution (SED) to synthetic stellar population models. We carefully test the procedures of measuring clump properties, especially the method of subtracting background fluxes from the diffuse component of galaxies. With our fiducial background subtraction, we find a radial clump U ‑ V color variation, where clumps close to galactic centers are redder than those in outskirts. The slope of the color gradient (clump color as a function of their galactocentric distance scaled by the semimajor axis of galaxies) changes with redshift and {M}* of the host galaxies: at a fixed {M}* , the slope becomes steeper toward low redshift, and at a fixed redshift, it becomes slightly steeper with {M}* . Based on our SED fitting, this observed color gradient can be explained by a combination of a negative age gradient, a negative E(B ‑ V) gradient, and a positive specific SFR gradient of the clumps. We also find that the color gradients of clumps are steeper than those of intra-clump regions. Correspondingly, the radial gradients of the derived physical properties of clumps are different from those of the diffuse component or intra

Automatic Approach to Morphological Classification of Galaxies With Analysis of Galaxy Populations in Clusters

NASA Astrophysics Data System (ADS)

Sultanova, Madina; Barkhouse, Wayne; Rude, Cody

2018-01-01

The classification of galaxies based on their morphology is a field in astrophysics that aims to understand galaxy formation and evolution based on their physical differences. Whether structural differences are due to internal factors or a result of local environment, the dominate mechanism that determines galaxy type needs to be robustly quantified in order to have a thorough grasp of the origin of the different types of galaxies. The main subject of my Ph.D. dissertation is to explore the use of computers to automatically classify and analyze large numbers of galaxies according to their morphology, and to analyze sub-samples of galaxies selected by type to understand galaxy formation in various environments. I have developed a computer code to classify galaxies by measuring five parameters from their images in FITS format. The code was trained and tested using visually classified SDSS galaxies from Galaxy Zoo and the EFIGI data set. I apply my morphology software to numerous galaxies from diverse data sets. Among the data analyzed are the 15 Abell galaxy clusters (0.03 < z < 0.184) from Rude et al. 2017 (in preparation), which were observed by the Canada-France-Hawaii Telescope. Additionally, I studied 57 galaxy clusters from Barkhouse et al. (2007), 77 clusters from the WINGS survey (Fasano et al. 2006), and the six Hubble Space Telescope (HST) Frontier Field galaxy clusters. The high resolution of HST allows me to compare distant clusters with those nearby to look for evolutionary changes in the galaxy cluster population. I use the results from the software to examine the properties (e.g. luminosity functions, radial dependencies, star formation rates) of selected galaxies. Due to the large amount of data that will be available from wide-area surveys in the future, the use of computer software to classify and analyze the morphology of galaxies will be extremely important in terms of efficiency. This research aims to contribute to the solution of this problem.

Simulating The Dynamical Evolution Of Galaxies In Group And Cluster Environments

NASA Astrophysics Data System (ADS)

Vijayaraghavan, Rukmani

2015-07-01

Galaxy clusters are harsh environments for their constituent galaxies. A variety of physical processes effective in these dense environments transform gas-rich, spiral, star-forming galaxies to elliptical or spheroidal galaxies with very little gas and therefore minimal star formation. The consequences of these processes are well understood observationally. Galaxies in progressively denser environments have systematically declining star formation rates and gas content. However, a theoretical understanding of of where, when, and how these processes act, and the interplay between the various galaxy transformation mechanisms in clusters remains elusive. In this dissertation, I use numerical simulations of cluster mergers as well as galaxies evolving in quiescent environments to develop a theoretical framework to understand some of the physics of galaxy transformation in cluster environments. Galaxies can be transformed in smaller groups before they are accreted by their eventual massive cluster environments, an effect termed `pre-processing'. Galaxy cluster mergers themselves can accelerate many galaxy transformation mechanisms, including tidal and ram pressure stripping of galaxies and galaxy-galaxy collisions and mergers that result in reassemblies of galaxies' stars and gas. Observationally, cluster mergers have distinct velocity and phase-space signatures depending on the observer's line of sight with respect to the merger direction. Using dark matter only as well as hydrodynamic simulations of cluster mergers with random ensembles of particles tagged with galaxy models, I quantify the effects of cluster mergers on galaxy evolution before, during, and after the mergers. Based on my theoretical predictions of the dynamical signatures of these mergers in combination with galaxy transformation signatures, one can observationally identify remnants of mergers and quantify the effect of the environment on galaxies in dense group and cluster environments. The presence of

Star Formation in Merging Galaxies Using FIRE

NASA Astrophysics Data System (ADS)

Perez, Adrianna; Hung, Chao-Ling; Naiman, Jill; Moreno, Jorge; Hopkins, Philip

2018-01-01

Galaxy interactions and mergers are efficient mechanisms to birth stars at rates that are significantly higher than found in our Milky Way galaxy. The Kennicut-Schmidt (KS) relation is an empirical relationship between the star-forming rate and gas surface densities of galaxies (Schmidt 1959; Kennicutt 1998). Although most galaxies follow the KS relation, the high levels of star formation in galaxy mergers places them outside of this otherwise tight relationship. The goal of this research is to analyze the gas content and star formation of simulated merging galaxies. Our work utilizes the Feedback In Realistic Environments (FIRE) model (Hopkins et al., 2014). The FIRE project is a high-resolution cosmological simulation that resolves star-forming regions and incorporates stellar feedback in a physically realistic way. In this work, we have noticed a significant increase in the star formation rate at first and second passage, when the two black holes of each galaxy approach one other. Next, we will analyze spatially resolved star-forming regions over the course of the interacting system. Then, we can study when and how the rates that gas converts into stars deviate from the standard KS. These analyses will provide important insights into the physical mechanisms that regulate star formation of normal and merging galaxies and valuable theoretical predictions that can be used to compare with current and future observations from ALMA or the James Webb Space Telescope.

The resolved history of galaxy evolution.

PubMed

Brinchmann, Jarle

2002-12-15

We briefly review the study of the evolution of galaxies from an observational point of view, with particular emphasis on the role of the Hubble Space Telescope in probing the evolution of the different morphological types of galaxy. We show how using the stellar mass of galaxies as a tracer of evolution can improve our understanding of the physical process taking place before turning our eyes towards the future and giving an overview of what we can expect from future advances in technology.

Modelling galaxy spectra in presence of interstellar dust - III. From nearby galaxies to the distant Universe

NASA Astrophysics Data System (ADS)

Cassarà, L. P.; Piovan, L.; Chiosi, C.

2015-07-01

Improving upon the standard evolutionary population synthesis technique, we present spectrophotometric models of galaxies with morphology going from spherical structures to discs, properly accounting for the effect of dust in the interstellar medium (ISM). The models contain three main physical components: the diffuse ISM made of gas and dust, the complexes of molecular clouds where active star formation occurs, and stars of any age and chemical composition. These models are based on robust evolutionary chemical description providing the total amount of gas and stars present at any age, and matching the properties of galaxies of different morphological types. We have considered the results obtained by Piovan et al. for the properties of the ISM, and those by Cassarà et al. for the spectral energy distribution (SED) of single stellar populations, both in presence of dust, to model the integral SEDs of galaxies of different morphological types, going from pure bulges to discs passing through a number of composite systems with different combinations of the two components. The first part of the paper is devoted to recall the technical details of the method and the basic relations driving the interaction between the physical components of the galaxy. Then, the main parameters are examined and their effects on the SED of three prototype galaxies are highlighted. The theoretical SEDs nicely match the observational ones both for nearby galaxies and those at high redshift.

Galaxy Zoo: secular evolution of barred galaxies from structural decomposition of multiband images

NASA Astrophysics Data System (ADS)

Kruk, Sandor J.; Lintott, Chris J.; Bamford, Steven P.; Masters, Karen L.; Simmons, Brooke D.; Häußler, Boris; Cardamone, Carolin N.; Hart, Ross E.; Kelvin, Lee; Schawinski, Kevin; Smethurst, Rebecca J.; Vika, Marina

2018-02-01

We present the results of two-component (disc+bar) and three-component (disc+bar+bulge) multiwavelength 2D photometric decompositions of barred galaxies in five Sloan Digital Sky Survey (SDSS) bands (ugriz). This sample of ∼3500 nearby (z < 0.06) galaxies with strong bars selected from the Galaxy Zoo citizen science project is the largest sample of barred galaxies to be studied using photometric decompositions that include a bar component. With detailed structural analysis, we obtain physical quantities such as the bar- and bulge-to-total luminosity ratios, effective radii, Sérsic indices and colours of the individual components. We observe a clear difference in the colours of the components, the discs being bluer than the bars and bulges. An overwhelming fraction of bulge components have Sérsic indices consistent with being pseudo-bulges. By comparing the barred galaxies with a mass-matched and volume-limited sample of unbarred galaxies, we examine the connection between the presence of a large-scale galactic bar and the properties of discs and bulges. We find that the discs of unbarred galaxies are significantly bluer compared to the discs of barred galaxies, while there is no significant difference in the colours of the bulges. We find possible evidence of secular evolution via bars that leads to the build-up of pseudo-bulges and to the quenching of star formation in the discs. We identify a subsample of unbarred galaxies with an inner lens/oval and find that their properties are similar to barred galaxies, consistent with an evolutionary scenario in which bars dissolve into lenses. This scenario deserves further investigation through both theoretical and observational work.

The dark side of galaxy colour

NASA Astrophysics Data System (ADS)

Hearin, Andrew P.; Watson, Douglas F.

2013-10-01

We present age distribution matching, a theoretical formalism for predicting how galaxies of luminosity L and colour C occupy dark matter haloes. Our model supposes that there are just two fundamental properties of a halo that determine the colour and brightness of the galaxy it hosts: the maximum circular velocity Vmax and the redshift zstarve that correlates with the epoch at which the star formation in the galaxy ceases. The halo property zstarve is intended to encompass physical characteristics of halo mass assembly that may deprive the galaxy of its cold gas supply and, ultimately, quench its star formation. The new, defining feature of the model is that, at fixed luminosity, galaxy colour is in monotonic correspondence with zstarve, with the larger values of zstarve being assigned redder colours. We populate an N-body simulation with a mock galaxy catalogue based on age distribution matching and show that the resulting mock galaxy distribution accurately describes a variety of galaxy statistics. Our model suggests that halo and galaxy assembly are indeed correlated. We make publicly available our low-redshift, Sloan Digital Sky Survey Mr < -19 mock galaxy catalogue, and main progenitor histories of all z = 0 haloes, at http://logrus.uchicago.edu/~aphearin

Suites of dwarfs around Nearby giant galaxies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karachentsev, Igor D.; Kaisina, Elena I.; Makarov, Dmitry I., E-mail: ikar@sao.ru, E-mail: kei@sao.ru, E-mail: dim@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}. Allmore » 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

The Co-Evolution of Galaxies, their ISM, and the ICM: The Hydrodynamics of Galaxy Transformation

NASA Astrophysics Data System (ADS)

Vijayaraghavan, Rukmani; Sarazin, Craig L.; Ricker, Paul M.

2017-01-01

Cluster of galaxies are hostile environments. Infalling cluster galaxies are stripped of their dark matter, stars, and hot and cold interstellar medium gas. The ISM, in addition to tidal and ram pressure stripping, can evaporate due to thermal conduction. Gas loss and the subsequent suppression of star formation is not straightforward: magnetic fields in the ISM and ICM shield galaxies and their stripped tails from shear instabilities and conduction, radiative cooling can inhibit gas loss, and feedback from stars and AGN can replenish the ISM. While there is observational evidence that these processes operate, a theoretical understanding of the physics controlling the energy cycle in cluster galaxies remains elusive. Additionally, galaxies have a significant impact on ICM evolution: orbiting galaxies stir up and stretch ICM magnetic field lines, inject turbulence into the ICM via their wakes and g-waves, and infuse metals into the ICM. Quantifying the balance between processes that remove, retain, and replenish the ISM, and the impact of galaxies on the ICM require specialized hydrodynamic simulations of the cluster environment and its galaxies. I will present results from some of these simulations that include ram pressure stripping of galaxies' hot ISM, the effect of magnetic fields on this process, and the effectiveness of isotropic and anisotropic thermal conduction in removing and retaining the ISM.

Why do Galaxies Stop Forming Stars? New Evidence for the Role of AGN-feedback in Driving Galaxy Bimodality

NASA Astrophysics Data System (ADS)

Bluck, Asa; Teimoorinia, Hossen; Ellison, Sara L.; Mendel, Trevor

2018-01-01

One of the most striking features of the population of local galaxies is that the distributions of several key galaxy properties are highly bimodal (e.g. color and star formation rate). In general, high mass galaxies in dense environments, with bulge-dominated morphologies and pressure supported kinematics are more frequently passive (non-star forming) than lower mass galaxies in low density environments, with disc-dominated morphologies and rotationally supported kinematics. Understanding which, if any, of these correlations is causally related to the ‘quenching’ of star formation in galaxies remains an active and hotly debated area of investigation in modern astrophysics.Theoretically, a wealth of physical processes have been evoked to account for central galaxy quenching, including halo mass quenching from virial shocks, feedback from active galactic nuclei (AGN; in either the quasar or radio mode), stabilizing torques from central mass concentrations, feedback from supernovae, or even magnetic fields interacting with the hot gas halo.I will present strong new statistical evidence which suggests that the quenched fraction of local central galaxies is primarily related to their central kinematics (Bluck et al. 2016; 2017 in prep.). I will show that this is broadly consistent with quenching from AGN feedback, through a detailed comparison with a semi-analytic model and a cosmological hydrodynamical simulation.Using a sample of over half a million local galaxies from the SDSS DR7, we go on to develop a number of sophisticated techniques, including machine learning with artificial neural networks, to rank the importance of galaxy properties to quenching (Teimoorinia, Bluck & Ellison 2016). We find that properties closely correlated with the central supermassive black hole are highly favoured statistically to predict whether a galaxy will be star forming or not. Perhaps surprisingly, stellar mass and halo mass have no impact on star formation activity in central

Modelling baryonic effects on galaxy cluster mass profiles

NASA Astrophysics Data System (ADS)

Shirasaki, Masato; Lau, Erwin T.; Nagai, Daisuke

2018-06-01

Gravitational lensing is a powerful probe of the mass distribution of galaxy clusters and cosmology. However, accurate measurements of the cluster mass profiles are limited by uncertainties in cluster astrophysics. In this work, we present a physically motivated model of baryonic effects on the cluster mass profiles, which self-consistently takes into account the impact of baryons on the concentration as well as mass accretion histories of galaxy clusters. We calibrate this model using the Omega500 hydrodynamical cosmological simulations of galaxy clusters with varying baryonic physics. Our model will enable us to simultaneously constrain cluster mass, concentration, and cosmological parameters using stacked weak lensing measurements from upcoming optical cluster surveys.

Annual and spatial variation in shoot demography associated with masting in Betula grossa: comparison between mature trees and saplings

PubMed Central

Ishihara, Masae Iwamoto; Kikuzawa, Kihachiro

2009-01-01

Backgrounds and Aims Shoot demography affects the growth of the tree crown and the number of leaves on a tree. Masting may cause inter-annual and spatial variation in shoot demography of mature trees, which may in turn affect the resource budget of the tree. The aim of this study was to evaluate the effect of masting on the temporal and spatial variations in shoot demography of mature Betula grossa. Methods The shoot demography was analysed in the upper and lower parts of the tree crown in mature trees and saplings over 7 years. Mature trees and saplings were compared to differentiate the effect of masting from the effect of exogenous environment on shoot demography. The fate of different shoot types (reproductive, vegetative, short, long), shoot length and leaf area were investigated by monitoring and by retrospective survey using morphological markers on branches. The effects of year and branch position on demographic parameters were evaluated. Key Results Shoot increase rate, production of long shoots, bud mortality, length of long shoots and leaf area of a branch fluctuated periodically from year to year in mature trees over 7 years, in which two masting events occurred. Branches within a crown showed synchronized annual variation, and the extent of fluctuation was larger in the upper branches than the lower branches. Vegetative shoots varied in their bud differentiation each year and contributed to the dynamic shoot demography as much as did reproductive shoots, suggesting physiological integration in shoot demography through hormonal regulation and resource allocation. Conclusions Masting caused periodic annual variation in shoot demography of the mature trees and the effect was spatially variable within a tree crown. Since masting is a common phenomenon among tree species, annual variation in shoot demography and leaf area should be incorporated into resource allocation models of mature masting trees. PMID:19734164

Studying AGN Activation in Galaxy Mergers

NASA Astrophysics Data System (ADS)

Negus, James; Blecha, Laura

2018-06-01

Simulations predict that galaxy mergers drive central gas inflows that result in a peak AGN fraction when the two galaxy bulges reach separations near 1 kpc. Moreover, observations have shown that the AGN fraction increases as the separation between two merging galaxies decreases from 100 kpc to 10 kpc; however, the trend has not yet been measured in the pivotal sub 10 kpc regime, where activity may drastically increase as the simulations suggest. We present a uniform sample of dual and offset AGN, which features AGN parameters (e.g., redshift, angular separation) and normalized cosmology-dependent parameters (e.g., physical separation, bolometric luminosity), using multi-wavelength observations (IR to X-ray) in this critical sub 10 kpc range. In addition, using galaxy merger simulations with GADGET-3, a smoothed particle hydrodynamics N-body code, we report how much time galaxy pairs spend at different separations during a merger. Using these results, we will discuss how galaxy bulge separation correlates to increases in the AGN fraction over varying timescales, and where AGN are primarily fueled during mergers with galaxy bulge separations < 10 kpc.

Fundamental tests of galaxy formation theory

NASA Technical Reports Server (NTRS)

Silk, J.

1982-01-01

The structure of the universe as an environment where traces exist of the seed fluctuations from which galaxies formed is studied. The evolution of the density fluctuation modes that led to the eventual formation of matter inhomogeneities is reviewed, How the resulting clumps developed into galaxies and galaxy clusters acquiring characteristic masses, velocity dispersions, and metallicities, is discussed. Tests are described that utilize the large scale structure of the universe, including the dynamics of the local supercluster, the large scale matter distribution, and the anisotropy of the cosmic background radiation, to probe the earliest accessible stages of evolution. Finally, the role of particle physics is described with regard to its observable implications for galaxy formation.

[Demography of aging in Spain].

PubMed

Rubio Herrera, R

1994-01-01

In this article, the demography of the elderly in Spain is scrutinized. The older population from 1960 to 1991 and their presumed development for the period from 2001-2020 is analyzed. According to these data, we attempt to determine the influence on life situation of older people according to several factors, such as changes of family structures and intergenerational relations as well as changes in social stereotypes, expected political and economical developments, and new concepts in medical care. In closing, we raise questions about the necessary future living structures in Spain.

Stellar feedback in galaxies and the origin of galaxy-scale winds

NASA Astrophysics Data System (ADS)

Hopkins, Philip F.; Quataert, Eliot; Murray, Norman

2012-04-01

Feedback from massive stars is believed to play a critical role in driving galactic super-winds that enrich the intergalactic medium and shape the galaxy mass function, mass-metallicity relation and other global galaxy properties. In previous papers, we have introduced new numerical methods for implementing stellar feedback on sub-giant molecular cloud (sub-GMC) through galactic scales in numerical simulations of galaxies; the key physical processes include radiation pressure in the ultraviolet through infrared, supernovae (Type I and Type II), stellar winds ('fast' O star through 'slow' asymptotic giant branch winds), and H II photoionization. Here, we show that these feedback mechanisms drive galactic winds with outflow rates as high as ˜10-20 times the galaxy star formation rate. The mass-loading efficiency (wind mass-loss rate divided by the star formation rate) scales roughly as ? (where Vc is the galaxy circular velocity), consistent with simple momentum-conservation expectations. We use our suite of simulations to study the relative contribution of each feedback mechanism to the generation of galactic winds in a range of galaxy models, from Small Magellanic Cloud like dwarfs and Milky Way (MW) analogues to z˜ 2 clumpy discs. In massive, gas-rich systems (local starbursts and high-z galaxies), radiation pressure dominates the wind generation. By contrast, for MW-like spirals and dwarf galaxies the gas densities are much lower and sources of shock-heated gas such as supernovae and stellar winds dominate the production of large-scale outflows. In all of our models, however, the winds have a complex multiphase structure that depends on the interaction between multiple feedback mechanisms operating on different spatial scales and time-scales: any single feedback mechanism fails to reproduce the winds observed. We use our simulations to provide fitting functions to the wind mass loading and velocities as a function of galaxy properties, for use in cosmological

COMPACT E+A GALAXIES AS A PROGENITOR OF MASSIVE COMPACT QUIESCENT GALAXIES AT 0.2 < z < 0.8

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zahid, H. Jabran; Hochmuth, Nicholas Baeza; Geller, Margaret J.

We search the Sloan Digital Sky Survey and the Baryon Oscillation Sky Survey to identify ∼5500 massive compact quiescent galaxy candidates at 0.2 < z < 0.8. We robustly classify a subsample of 438 E+A galaxies based on their spectral properties and make this catalog publicly available. We examine sizes, stellar population ages, and kinematics of galaxies in the sample and show that the physical properties of compact E+A galaxies suggest that they are a progenitor of massive compact quiescent galaxies. Thus, two classes of objects—compact E+A and compact quiescent galaxies—may be linked by a common formation scenario. The typicalmore » stellar population age of compact E+A galaxies is <1 Gyr. The existence of compact E+A galaxies with young stellar populations at 0.2 < z < 0.8 means that some compact quiescent galaxies first appear at intermediate redshifts. We derive a lower limit for the number density of compact E+A galaxies. Assuming passive evolution, we convert this number density into an appearance rate of new compact quiescent galaxies at 0.2 < z < 0.8. The lower limit number density of compact quiescent galaxies that may appear at z < 0.8 is comparable to the lower limit of the total number density of compact quiescent galaxies at these intermediate redshifts. Thus, a substantial fraction of the z < 0.8 massive compact quiescent galaxy population may descend from compact E+A galaxies at intermediate redshifts.« less

GASP. I. Gas Stripping Phenomena in Galaxies with MUSE

NASA Astrophysics Data System (ADS)

Poggianti, Bianca M.; Moretti, Alessia; Gullieuszik, Marco; Fritz, Jacopo; Jaffé, Yara; Bettoni, Daniela; Fasano, Giovanni; Bellhouse, Callum; Hau, George; Vulcani, Benedetta; Biviano, Andrea; Omizzolo, Alessandro; Paccagnella, Angela; D’Onofrio, Mauro; Cava, Antonio; Sheen, Y.-K.; Couch, Warrick; Owers, Matt

2017-07-01

GAs Stripping Phenomena in galaxies with MUSE (GASP) is a new integral-field spectroscopic survey with MUSE at the VLT aimed at studying gas removal processes in galaxies. We present an overview of the survey and show a first example of a galaxy undergoing strong gas stripping. GASP is obtaining deep MUSE data for 114 galaxies at z = 0.04–0.07 with stellar masses in the range {10}9.2{--}{10}11.5 {M}ȯ in different environments (galaxy clusters and groups over more than four orders of magnitude in halo mass). GASP targets galaxies with optical signatures of unilateral debris or tails reminiscent of gas-stripping processes (“jellyfish galaxies”), as well as a control sample of disk galaxies with no morphological anomalies. GASP is the only existing integral field unit (IFU) survey covering both the main galaxy body and the outskirts and surroundings, where the IFU data can reveal the presence and origin of the outer gas. To demonstrate GASP’s ability to probe the physics of gas and stars, we show the complete analysis of a textbook case of a jellyfish galaxy, JO206. This is a massive galaxy (9× {10}10 {M}ȯ ) in a low-mass cluster (σ ∼ 500 {km} {{{s}}}-1) at a small projected clustercentric radius and a high relative velocity, with ≥90 kpc long tentacles of ionized gas stripped away by ram pressure. We present the spatially resolved kinematics and physical properties of the gas and stars and depict the evolutionary history of this galaxy.

Reconstructing the historic demography of an endangered seabird

Treesearch

Steven R. Beissinger; Zachariah M. Peery

2007-01-01

Reducing extinction risk for threatened species requires determining which demographic parameters are depressed and causing population declines. Museum collections may constitute a unique, underutilized resource for measuring demographic changes over long time periods using age-ratio analysis. We reconstruct the historic demography of a U.S. federally endangered...

Demography, Identity and the 2016 Presidential Election

ERIC Educational Resources Information Center

Davidson, Fiona M.; Sours, Tad; Moll, Rebecca Luebker

2016-01-01

Demography is the study of human population statistics. The United States Census Bureau has measured the demographics of the U.S. population since 1790. Why? The main purpose was for division of representatives of the people in government and for taxes. As time has gone on, it gives us a better picture of who we are as a nation and how to better…

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.

How Galaxies Acquire their Gas: A Map of Multiphase Accretion and Feedback in Gaseous Galaxy Halos

NASA Astrophysics Data System (ADS)

Tumlinson, Jason

2009-07-01

We propose to address two of the biggest open questions in galaxy formation - how galaxies acquire their gas and how they return it to the IGM - with a concentrated COS survey of diffuse multiphase gas in the halos of SDSS galaxies at z = 0.15 - 0.35. Our chief science goal is to establish a basic set of observational facts about the physical state, metallicity, and kinematics of halo gas, including the sky covering fraction of hot and cold material, the metallicity of infall and outflow, and correlations with galaxy stellar mass, type, and color - all as a function of impact parameter from 10 - 150 kpc. Theory suggests that the bimodality of galaxy colors, the shape of the luminosity function, and the mass-metallicity relation are all influenced at a fundamental level by accretion and feedback, yet these gas processes are poorly understood and cannot be predicted robustly from first principles. We lack even a basic observational assessment of the multiphase gaseous content of galaxy halos on 100 kpc scales, and we do not know how these processes vary with galaxy properties. This ignorance is presently one of the key impediments to understanding galaxy formation in general. We propose to use the high-resolution gratings G130M and G160M on the Cosmic Origins Spectrograph to obtain sensitive column density measurements of a comprehensive suite of multiphase ions in the spectra of 43 z < 1 QSOs lying behind 43 galaxies selected from the Sloan Digital Sky Survey. In aggregate, these sightlines will constitute a statistically sound map of the physical state and metallicity of gaseous halos, and subsets of the data with cuts on galaxy mass, color, and SFR will seek out predicted variations of gas properties with galaxy properties. Our interpretation of these data will be aided by state-of-the-art hydrodynamic simulations of accretion and feedback, in turn providing information to refine and test such models. We will also use Keck, MMT, and Magellan {as needed} to obtain

Galaxy Zoo 1: data release of morphological classifications for nearly 900 000 galaxies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Linott, C.; Slosar, A.; Lintott, C.

Morphology is a powerful indicator of a galaxy's dynamical and merger history. It is strongly correlated with many physical parameters, including mass, star formation history and the distribution of mass. The Galaxy Zoo project collected simple morphological classifications of nearly 900,000 galaxies drawn from the Sloan Digital Sky Survey, contributed by hundreds of thousands of volunteers. This large number of classifications allows us to exclude classifier error, and measure the influence of subtle biases inherent in morphological classification. This paper presents the data collected by the project, alongside measures of classification accuracy and bias. The data are now publicly availablemore » and full catalogues can be downloaded in electronic format from http://data.galaxyzoo.org.« less

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.

Quenching or Bursting: Star Formation Acceleration—A New Methodology for Tracing Galaxy Evolution

NASA Astrophysics Data System (ADS)

Martin, D. Christopher; Gonçalves, Thiago S.; Darvish, Behnam; Seibert, Mark; Schiminovich, David

2017-06-01

We introduce a new methodology for the direct extraction of galaxy physical parameters from multiwavelength photometry and spectroscopy. We use semianalytic models that describe galaxy evolution in the context of large-scale cosmological simulation to provide a catalog of galaxies, star formation histories, and physical parameters. We then apply models of stellar population synthesis and a simple extinction model to calculate the observable broadband fluxes and spectral indices for these galaxies. We use a linear regression analysis to relate physical parameters to observed colors and spectral indices. The result is a set of coefficients that can be used to translate observed colors and indices into stellar mass, star formation rate, and many other parameters, including the instantaneous time derivative of the star formation rate, which we denote the Star Formation Acceleration (SFA), We apply the method to a test sample of galaxies with GALEX photometry and SDSS spectroscopy, deriving relationships between stellar mass, specific star formation rate, and SFA. We find evidence for a mass-dependent SFA in the green valley, with low-mass galaxies showing greater quenching and higher-mass galaxies greater bursting. We also find evidence for an increase in average quenching in galaxies hosting an active galactic nucleus. A simple scenario in which lower-mass galaxies accrete and become satellite galaxies, having their star-forming gas tidally and/or ram-pressure stripped, while higher-mass galaxies receive this gas and react with new star formation, can qualitatively explain our results.

Multi-wavelength observations of barred, flocculent galaxies

NASA Astrophysics Data System (ADS)

Ratay, Douglas Lee

Although it is generally accepted that large galaxies form through the assemblage of smaller objects, an explanation for the morphology of galaxies is not available. Any complete theory of galaxy morphology must include production and dissolution mechanisms for galactic bars, rings, nuclear bars, spiral arms, and companions. This theory does not exist because of the lack of detailed data from many types of galaxies in different environments. We have defined a new sample of galaxies which are simultaneously flocculent, barred, and isolated. We have performed optical, near-infrared, and radio (HI) observations of the galaxies in this sample. We measured properties of our galaxies including bar length, bar axis ratio, HI diameter, HI mass, and dynamical mass. We found that our sample group is heterogeneous, and compares well to a standard samples of galaxies. We found two of our galaxies to possess companions, and two others to show evidence of current interactions. This is consistent with other observations indicating that local isolated galaxies do not possess a large number of small companions. We cannot rule out the possibility of very small companions. We find that as a group our sample is slightly less luminous than normal galaxies and may be more likely to be involved in interactions. We conclude that the bar and spiral arm features in our sample are due to processes internal to the galaxies, likely involving the interaction between the galactic disk and halo. We defined a control sample of barred, grand design galaxies to further determine the acceptability of barred, flocculent galaxies as a physically meaningful subset of galaxies.

Galaxy Evolution

NASA Astrophysics Data System (ADS)

Matteucci, F.

We review both the observational and theoretical constraints on the evolution of the abundances of heavy elements in gas and stars in galaxies of different morphological type. The main aim of this work is to document the progress made in our understanding of the physical processes regulating the chemical evolution of galaxies during the last sixteen years since the appearance, in this same journal (volume 5, page 287), of the well know review of Beatrice Tinsley, to whom I dedicate this paper. Finally, this article is addressed particularly to readers who do not actively work on galactic chemical evolution and who might use it as a cook book where the main ingredients are discussed and useful recipes can be found.

Galaxy Clusters

NASA Astrophysics Data System (ADS)

Miller, Christopher J. Miller

2012-03-01

of galaxy clusters will be at locations of the peaks in the true underlying (mostly) dark matter density field. Kaiser (1984) [19] called this the high-peak model, which we demonstrate in Figure 16.1. We show a two-dimensional representation of a density field created by summing plane-waves with a predetermined power and with random wave-vector directions. In the left panel, we plot only the largest modes, where we see the density peaks (black) and valleys (white) in the combined field. In the right panel, we allow for smaller modes. You can see that the highest density peaks in the left panel contain smaller-scale, but still high-density peaks. These are the locations of future galaxy clusters. The bottom panel shows just these cluster-scale peaks. As you can see, the peaks themselves are clustered, and instead of just one large high-density peak in the original density field (see the left panel), the smaller modes show that six peaks are "born" within the broader, underlying large-scale density modes. This exemplifies the "bias" or amplified structure that is traced by galaxy clusters [19]. Clusters are rare, easy to find, and their member galaxies provide good distance estimates. In combination with their amplified clustering signal described above, galaxy clusters are considered an efficient and precise tracer of the large-scale matter density field in the Universe. Galaxy clusters can also be used to measure the baryon content of the Universe [43]. They can be used to identify gravitational lenses [38] and map the distribution of matter in clusters. The number and spatial distribution of galaxy clusters can be used to constrain cosmological parameters, like the fraction of the energy density in the Universe due to matter (Omega_matter) or the variation in the density field on fixed physical scales (sigma_8) [26,33]. The individual clusters act as “Island Universes” and as such are laboratories here we can study the evolution of the properties of the cluster

Star formation trends in high-redshift galaxy surveys: the elephant or the tail?

NASA Astrophysics Data System (ADS)

Stringer, Martin; Cole, Shaun; Frenk, Carlos S.; Stark, Daniel P.

2011-07-01

Star formation rate and accumulated stellar mass are two fundamental physical quantities that describe the evolutionary state of a forming galaxy. Two recent attempts to determine the relationship between these quantities, by interpreting a sample of star-forming galaxies at redshift of z˜ 4, have led to opposite conclusions. Using a model galaxy population, we investigate possible causes for this discrepancy and conclude that minor errors in the conversion from observables to physical quantities can lead to a major misrepresentation when applied without awareness of sample selection. We also investigate, in a general way, the physical origin of the correlation between star formation rate and stellar mass within the hierarchical galaxy formation theory.

Dust formation in a galaxy with primitive abundances.

PubMed

Sloan, G C; Matsuura, M; Zijlstra, A A; Lagadec, E; Groenewegen, M A T; Wood, P R; Szyszka, C; Bernard-Salas, J; van Loon, J Th

2009-01-16

Interstellar dust plays a crucial role in the evolution of galaxies. It governs the chemistry and physics of the interstellar medium. In the local universe, dust forms primarily in the ejecta from stars, but its composition and origin in galaxies at very early times remain controversial. We report observational evidence of dust forming around a carbon star in a nearby galaxy with a low abundance of heavy elements, 25 times lower than the solar abundance. The production of dust by a carbon star in a galaxy with such primitive abundances raises the possibility that carbon stars contributed carbonaceous dust in the early universe.

Near-Field Cosmology with Low-Mass Galaxies: Constraining the Escape of Radiation from the UV-slopes of Local Galaxies

NASA Astrophysics Data System (ADS)

Venkatesan, Aparna; Rosenberg, Jessica L.; Salzer, John Joseph; Gronke, Max; Cannon, John M.; Miller, Christopher J.; Dijkstra, Mark

2018-06-01

Low-mass galaxies are thought to play a large role in reionizing the Universe at redshifts, z > 6. However, due to limited UV data on low-mass galaxies, the models used to estimate the escape of radiation are poorly constrained. Using theoretical models of radiation transport in dusty galaxies with clumpy gas media, we translate measurements of the UV slopes of a sample of low-mass low-z KISSR galaxies to their escape fraction values in Ly-alpha radiation, fesc (LyA), and in the Ly-continuum, fesc (LyC). These low-mass starforming systems have potentially steep UV slopes, and could provide a much-needed relation between easily measured spectral properties such as UV slope or LyA line properties, and the escape of LyA/LyC radiation. Such a relation could advance studies of primordial star clusters and the underlying physical conditions characterizing early galaxies, one of the target observation goals of the soon to-be-launched James Webb Space Telescope. This work was supported by the University of San Francisco Faculty Development Fund, and NSF grant AST-1637339. We thank the Aspen Center for Physics, where some of this work was conducted, and which is supported by National Science Foundation grant PHY-1607611.

Physical conditions of the interstellar medium in high-redshift submillimetre bright galaxies

NASA Astrophysics Data System (ADS)

Yang, Chentao

2017-12-01

The discovery of a population of high- redshift dust-obscured submillimeter galaxies (SMGs) from ground-based submm cameras has revolutionised our understanding of galaxy evolution and star formation in extreme conditions. They are the strongest starbursts in the Universe approaching the Eddington limit and are believed to be the progenitors of the most massive galaxies today. However, theoretical models of galaxy evolution have even been challenged by a large number of detections of high-redshift SMGs. A very few among them are gravitationally lensed by an intervening galaxy. Recent wide-area extragalactic surveys have discovered hundreds of such strongly lensed SMGs, opening new exciting opportunities for observing the interstellar medium in these exceptional objects. We have thus carefully selected a sample of strongly gravitational lensed SMGs based on the submillimeter flux limit from the Herschel-ATLAS sample. Using IRAM telescopes, we have built a rich H2O-line-detected sample of 16 SMGs. We found a close-to-linear tight correlation between the H2O line and total infrared luminosity. This indicates the importance of far-IR pumping to the excitation of the H2O lines. Using a far-IR pumping model, we have derived the physical properties of the H2O gas and the dust. We showed that H2O lines trace a warm dense gas that may be closely related to the active star formation. Along with the H2O lines, several H2O+ lines have also been detected in three of our SMGs. We also find a tight correlation between the luminosity of the lines of H2O and H2O+ from local ULIRGs to high-redshift SMGs. The flux ratio between H2O+ and H2O suggests that cosmic rays from strong star forming activities are possibly driving the related oxygen chemistry. Another important common molecular gas tracer is the CO line. We have observed multiple transitions of the CO lines in each of our SMGs with IRAM 30m telescope. By analysing the CO line profile, we discovered a significant differential

Multiwavelength Search and Studies of Active Galaxies

NASA Astrophysics Data System (ADS)

Mickaelian, A. M.

2016-06-01

Since 1950s, Byurakan Astrophysical Observatory (BAO) has always been one of the centres for surveys and studies of active galaxies. Here I review our search and studies of active galaxies during last 30 years using various wavelength ranges, as well as some recent related works. These projects since late 1980s were focused on multiwavelength search and studies of AGN and Starbursts (SB). 1103 blue stellar objects (BSOs) on the basis of their UV-excess were selected using Markarian Survey (First Byurakan Survey, FBS) plates and Markarian's criteria used for the galaxies. Among many blue stars, QSOs and Seyfert galaxies were found by follow-up observations. 1577 IRAS point sources were optically identified using FBS low-dispersion spectra and many AGN, SB and high-luminosity IR galaxies (LIRG/ULIRG) were discovered. 32 extremely high IR/opt flux ratio galaxies were studies with Spitzer. 2791 ROSAT FSC sources were optically identified using Hamburg Quasar Survey (HQS) low-dispersion spectra and many AGN were discovered by follow-up observations. Fine analysis of emission line spectra was carried out using spectral line decomposition software to establish true profiles and calculate physical parameters for the emitting regions, as well as to study the spectral variability of these objects. X-ray and radio selection criteria were used to find new AGN and variable objects for further studies. Multiwavelength approach allowed revealing many new AGN and SB and obtaining a number of interesting relations using their observational characteristics and physical properties.

CLUMPY GALAXIES IN CANDELS. I. THE DEFINITION OF UV CLUMPS AND THE FRACTION OF CLUMPY GALAXIES AT 0.5 < z < 3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guo, Yicheng; Koo, David C.; Barro, Guillermo

Although giant clumps of stars are thought to be crucial to galaxy formation and evolution, the most basic demographics of clumps are still uncertain, mainly because the definition of clumps has not been thoroughly discussed. In this paper, we carry out a study of the basic demographics of clumps in star-forming galaxies at 0.5 < z < 3, using our proposed physical definition that UV-bright clumps are discrete star-forming regions that individually contribute more than 8% of the rest-frame UV light of their galaxies. Clumps defined this way are significantly brighter than the H II regions of nearby large spiral galaxies,more » either individually or blended, when physical spatial resolution and cosmological dimming are considered. Under this definition, we measure the fraction of star-forming galaxies that have at least one off-center clump (f {sub clumpy}) and the contributions of clumps to the rest-frame UV light and star formation rate (SFR) of star-forming galaxies in the CANDELS/GOODS-S and UDS fields, where our mass-complete sample consists of 3239 galaxies with axial ratio q > 0.5. The redshift evolution of f {sub clumpy} changes with the stellar mass (M {sub *}) of the galaxies. Low-mass (log (M {sub *}/M {sub ☉}) < 9.8) galaxies keep an almost constant f {sub clumpy} of ∼60% from z ∼ 3 to z ∼ 0.5. Intermediate-mass and massive galaxies drop their f {sub clumpy} from 55% at z ∼ 3 to 40% and 15%, respectively, at z ∼ 0.5. We find that (1) the trend of disk stabilization predicted by violent disk instability matches the f {sub clumpy} trend of massive galaxies; (2) minor mergers are a viable explanation of the f {sub clumpy} trend of intermediate-mass galaxies at z < 1.5, given a realistic observability timescale; and (3) major mergers are unlikely responsible for the f {sub clumpy} trend in all masses at z < 1.5. The clump contribution to the rest-frame UV light of star-forming galaxies shows a broad peak around galaxies with log (M {sub *}/M

Isolated Early-type Galaxies in the 2dFGRS

NASA Astrophysics Data System (ADS)

Fuse, Christopher R.; Lamir, C.

2014-01-01

Isolated galaxies are systems that have experienced limited external perturbations, thus the properties of these galaxies are largely due to internal processes. The features of isolated early-type galaxies (IEGs) provide a baseline from which to compare early-type systems residing in higher-density environments. We use the Two-Degree Field Galaxy Redshift Survey (2dFGRS) and the NASA Extragalactic Database (NED) to identify IEGs in the nearby universe. Search criteria in the 2dFGRS were chosen to insure that the IEGs have remained separated from neighboring galaxies for the majority of their lifetimes. Isolated galaxies are chosen utilizing a minimum projected physical separation of 1 Mpc from any neighboring non-dwarf galaxy brighter than Mb = -16.5 mags. A minimum redshift separation of 350 km/s between a candidate galaxy and a neighboring was imposed to further insure the candidate’s isolation. Early results of the search for isolated early-type galaxies in the southern sky are presented.

Influence of local demography on asymptotic and transient dynamics of a yellow-bellied marmot metapopulation.

PubMed

Ozgul, Arpat; Oli, Madan K; Armitage, Kenneth B; Blumstein, Daniel T; Van Vuren, Dirk H

2009-04-01

Despite recent advances in biodemography and metapopulation ecology, we still have limited understanding of how local demographic parameters influence short- and long-term metapopulation dynamics. We used long-term data from 17 local populations, along with the recently developed methods of matrix metapopulation modeling and transient sensitivity analysis, to investigate the influence of local demography on long-term (asymptotic) versus short-term (transient) dynamics of a yellow-bellied marmot metapopulation in Colorado. Both long- and short-term dynamics depended primarily on a few colony sites and were highly sensitive to changes in demography at these sites, particularly in survival of reproductive adult females. Interestingly, the relative importance of sites differed between long- and short-term dynamics; the spatial structure and local population sizes, while insignificant for asymptotic dynamics, were influential on transient dynamics. However, considering the spatial structure was uninformative about the relative influence of local demography on metapopulation dynamics. The vital rates that were the most influential on local dynamics were also the most influential on both long- and short-term metapopulation dynamics. Our results show that an explicit consideration of local demography is essential for a complete understanding of the dynamics and persistence of spatially structured populations.

MACS: The impact of environment on galaxy evolution at z>0.5

NASA Astrophysics Data System (ADS)

Ma, Cheng-Jiun

2010-08-01

In order to investigate galaxy evolution in environments of greatly varying density, we conduct an extensive spectroscopic survey of galaxies in eight X-ray luminous clusters at redshift higher than 0.5. Unlike most spectroscopic surveys of cluster galaxies, we sample the galaxy population beyond the virial radius of each cluster (out to ˜6 Mpc), thereby probing regions that differ by typically two orders of magnitude in galaxy density. Galaxies are classified by spectroscopic type into emission-line, absorption-line, post starburst (E+A), and starburst (e(a) and e(b)) galaxies, and the spatial distribution of each type is used as a diagnostic of the presence and efficiency of different physical mechanisms of galaxy evolution. Our analysis yields the perhaps strongest confirmation so far of the morphology-density relation for emission- and absorption-line galaxies. In addition, we find E+A galaxies to be exclusively located within the ram-pressure stripping radius of each cluster. Taking advantage of this largest sample of E+A galaxies in clusters compiled to date, the spatial profile of the distribution of E+A galaxies can be studied for the first time. We show that ram-pressure stripping is the dominant, and possibly only, physical mechanism to cause the post-starburst phase of cluster galaxies. In addition, two particular interesting clusters are studied individually. For MACS J0717.5+3745, a clear morphology-density correlation is observed for lenticular (S0) galaxies around this cluster, but becomes insignificant toward the center of cluster. We interpret this finding as evidence of the creation of S0s being triggered primarily in environments of low to intermediate density. In MACS J0025.4-1225, a cluster undergoing a major merger, all faint E+A galaxies are observed to lie near the peak of the X-ray surface brightness, strongly suggesting that starbursts are enhanced as well as terminated during cluster mergers. We conclude that ram-pressure stripping and

Quenching or Bursting: Star Formation Acceleration—A New Methodology for Tracing Galaxy Evolution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martin, D. Christopher; Darvish, Behnam; Seibert, Mark

We introduce a new methodology for the direct extraction of galaxy physical parameters from multiwavelength photometry and spectroscopy. We use semianalytic models that describe galaxy evolution in the context of large-scale cosmological simulation to provide a catalog of galaxies, star formation histories, and physical parameters. We then apply models of stellar population synthesis and a simple extinction model to calculate the observable broadband fluxes and spectral indices for these galaxies. We use a linear regression analysis to relate physical parameters to observed colors and spectral indices. The result is a set of coefficients that can be used to translate observedmore » colors and indices into stellar mass, star formation rate, and many other parameters, including the instantaneous time derivative of the star formation rate, which we denote the Star Formation Acceleration (SFA), We apply the method to a test sample of galaxies with GALEX photometry and SDSS spectroscopy, deriving relationships between stellar mass, specific star formation rate, and SFA. We find evidence for a mass-dependent SFA in the green valley, with low-mass galaxies showing greater quenching and higher-mass galaxies greater bursting. We also find evidence for an increase in average quenching in galaxies hosting an active galactic nucleus. A simple scenario in which lower-mass galaxies accrete and become satellite galaxies, having their star-forming gas tidally and/or ram-pressure stripped, while higher-mass galaxies receive this gas and react with new star formation, can qualitatively explain our results.« less

Cooling flows and X-ray emission in early-type galaxies

NASA Technical Reports Server (NTRS)

Sarazin, Craig L.

1990-01-01

The X-ray properties of normal early-type galaxies and the limited theoretical understanding of the physics of the hot interstellar medium in these galaxies are reviewed. A number of simple arguments about the physical state of the gas are given. Steady-state cooling flow models for these galaxies are presented, and their time-dependent evolution is discussed. The X-ray emission found in early-type galaxies indicates that they contain significant amounts of hot interstellar gas, and that they are not the gas-poor systems they were previously thought to be. In the brighter X-ray galaxies, the amounts of hot gas observed are consistent with those expected given the present rates of stellar mass loss. The required rates of heating of the gas are consistent with those expected from the motions of gas-losing stars and supernovae. The X-ray observations are generally more consistent with a lower rate of Type I supernovae than was previously thought.

Dust emission in simulated dwarf galaxies using GRASIL-3D

NASA Astrophysics Data System (ADS)

Santos-Santos, I. M.; Domínguez-Tenreiro, R.; Granato, G. L.; Brook, C. B.; Obreja, A.

2017-03-01

Recent Herschel observations of dwarf galaxies have shown a wide diversity in the shapes of their IR-submm spectral energy distributions as compared to more massive galaxies, presenting features that cannot be explained with the current models. In order to understand the physics driving these differences, we have computed the emission of a sample of simulated dwarf galaxies using the radiative transfer code GRASIL-3D. This code separately treats the radiative transfer in dust grains from molecular clouds and cirri. The simulated galaxies have masses ranging from 10^6-10^9 M_⊙ and have evolved within a Local Group environment by using CLUES initial conditions. We show that their IR band luminosities are in agreement with observations, with their SEDs reproducing naturally the particular spectral features observed. We conclude that the GRASIL-3D two-component model gives a physical interpretation to the emission of dwarf galaxies, with molecular clouds (cirri) as the warm (cold) dust components needed to recover observational data.

A catalog of galaxy morphology and photometric redshift

NASA Astrophysics Data System (ADS)

Paul, Nicholas; Shamir, Lior

2018-01-01

Morphology carries important information about the physical characteristics of a galaxy. Here we used machine learning to produce a catalog of ~3,000,000 SDSS galaxies classified by their broad morphology into spiral and elliptical galaxies. Comparison of the catalog to Galaxy Zooshows that the catalog contains a subset of 1.7*10^6 galaxies classified with the same level of consistency as the debiased “superclean” sub-sample. In addition to the morphology, we also computed the photometric redshifts of the galaxies. Several pattern recognition algorithms and variable selection strategies were tested, and the best accuracy of mean absolute error of ~0.0062 was achieved by using random forest with a combination of manually and automatically selected variables. The catalog shows that for redshift lower than 0.085 galaxies that visually look spiral become more prevalent as the redshift gets higher. For redshift greater than 0.085 galaxies thatvisually look elliptical become more prevalent. The catalog as well as the source code used to produce it is publicly available athttps://figshare.com/articles/Morphology_and_photometric_redshift_catalog/4833593 .

A detection of wobbling brightest cluster galaxies within massive galaxy clusters

NASA Astrophysics Data System (ADS)

Harvey, David; Courbin, F.; Kneib, J. P.; McCarthy, Ian G.

2017-12-01

A striking signal of dark matter beyond the standard model is the existence of cores in the centre of galaxy clusters. Recent simulations predict that a brightest cluster galaxy (BCG) inside a cored galaxy cluster will exhibit residual wobbling due to previous major mergers, long after the relaxation of the overall cluster. This phenomenon is absent with standard cold dark matter where a cuspy density profile keeps a BCG tightly bound at the centre. We test this hypothesis using cosmological simulations and deep observations of 10 galaxy clusters acting as strong gravitational lenses. Modelling the BCG wobble as a simple harmonic oscillator, we measure the wobble amplitude, Aw, in the BAHAMAS suite of cosmological hydrodynamical simulations, finding an upper limit for the cold dark matter paradigm of Aw < 2 kpc at the 95 per cent confidence limit. We carry out the same test on the data finding a non-zero amplitude of A_w=11.82^{+7.3}_{-3.0} kpc, with the observations dis-favouring Aw = 0 at the 3σ confidence level. This detection of BCG wobbling is evidence for a dark matter core at the heart of galaxy clusters. It also shows that strong lensing models of clusters cannot assume that the BCG is exactly coincident with the large-scale halo. While our small sample of galaxy clusters already indicates a non-zero Aw, with larger surveys, e.g. Euclid, we will be able to not only confirm the effect but also to use it to determine whether or not the wobbling finds its origin in new fundamental physics or astrophysical process.

The Physical Origin of Long Gas Depletion Times in Galaxies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Semenov, Vadim A.; Kravtsov, Andrey V.; Gnedin, Nickolay Y.

2017-08-18

We present a model that elucidates why gas depletion times in galaxies are long compared to the time scales of the processes driving the evolution of the interstellar medium. We show that global depletion times are not set by any "bottleneck" in the process of gas evolution towards the star-forming state. Instead, depletion times are long because star-forming gas converts only a small fraction of its mass into stars before it is dispersed by dynamical and feedback processes. Thus, complete depletion requires that gas transitions between star-forming and non-star-forming states multiple times. Our model does not rely on the assumption of equilibrium and can be used to interpret trends of depletion times with the properties of observed galaxies and the parameters of star formation and feedback recipes in galaxy simulations. In particular, the model explains the mechanism by which feedback self-regulates star formation rate in simulations and makes it insensitive to the local star formation efficiency. We illustrate our model using the results of an isolatedmore » $$L_*$$-sized disk galaxy simulation that reproduces the observed Kennicutt-Schmidt relation for both molecular and atomic gas. Interestingly, the relation for molecular gas is close to linear on kiloparsec scales, even though a non-linear relation is adopted in simulation cells. This difference is due to stellar feedback, which breaks the self-similar scaling of the gas density PDF with the average gas surface density.« less

The Physical Origin of Long Gas Depletion Times in Galaxies

NASA Astrophysics Data System (ADS)

Semenov, Vadim A.; Kravtsov, Andrey V.; Gnedin, Nickolay Y.

2017-08-01

We present a model that explains why galaxies form stars on a timescale significantly longer than the timescales of processes governing the evolution of interstellar gas. We show that gas evolves from a non-star-forming to a star-forming state on a relatively short timescale, and thus the rate of this evolution does not limit the star formation rate (SFR). Instead, the SFR is limited because only a small fraction of star-forming gas is converted into stars before star-forming regions are dispersed by feedback and dynamical processes. Thus, gas cycles into and out of a star-forming state multiple times, which results in a long timescale on which galaxies convert gas into stars. Our model does not rely on the assumption of equilibrium and can be used to interpret trends of depletion times with the properties of observed galaxies and the parameters of star formation and feedback recipes in simulations. In particular, the model explains how feedback self-regulates the SFR in simulations and makes it insensitive to the local star formation efficiency. We illustrate our model using the results of an isolated L *-sized galaxy simulation that reproduces the observed Kennicutt-Schmidt relation for both molecular and atomic gas. Interestingly, the relation for molecular gas is almost linear on kiloparsec scales, although a nonlinear relation is adopted in simulation cells. We discuss how a linear relation emerges from non-self-similar scaling of the gas density PDF with the average gas surface density.

Deep Chandra Observations of NGC 1404: Cluster Plasma Physics Revealed by an Infalling Early-type Galaxy

NASA Astrophysics Data System (ADS)

Su, Yuanyuan; Kraft, Ralph P.; Roediger, Elke; Nulsen, Paul; Forman, William R.; Churazov, Eugene; Randall, Scott W.; Jones, Christine; Machacek, Marie E.

2017-01-01

The intracluster medium (ICM), as a magnetized and highly ionized fluid, provides an ideal laboratory to study plasma physics under extreme conditions that cannot be achieved on Earth. NGC 1404 is a bright elliptical galaxy that is being gas stripped as it falls through the ICM of the Fornax Cluster. We use the new Chandra X-ray observations of NGC 1404 to study ICM microphysics. The interstellar medium of NGC 1404 is characterized by a sharp leading edge, 8 kpc from the Galaxy center, and a short downstream gaseous tail. Contact discontinuities are resolved on unprecedented spatial scales (0.″5 = 45 pc) due to the combination of the proximity of NGC 1404, the superb spatial resolution of Chandra, and the very deep (670 ks) exposure. At the leading edge, we observe sub-kiloparsec-scale eddies generated by Kelvin-Helmholtz instability (KHI) and put an upper limit of 5% Spitzer on the isotropic viscosity of the hot cluster plasma. We also observe mixing between the hot cluster gas and the cooler galaxy gas in the downstream stripped tail, which provides further evidence of a low viscosity plasma. The assumed ordered magnetic fields in the ICM ought to be smaller than 5 μG to allow KHI to develop. The lack of an evident magnetic draping layer just outside the contact edge is consistent with such an upper limit.

Galaxy and Mass Assembly (GAMA): the GAMA galaxy group catalogue (G3Cv1)

NASA Astrophysics Data System (ADS)

Robotham, A. S. G.; Norberg, P.; Driver, S. P.; Baldry, I. K.; Bamford, S. P.; Hopkins, A. M.; Liske, J.; Loveday, J.; Merson, A.; Peacock, J. A.; Brough, S.; Cameron, E.; Conselice, C. J.; Croom, S. M.; Frenk, C. S.; Gunawardhana, M.; Hill, D. T.; Jones, D. H.; Kelvin, L. S.; Kuijken, K.; Nichol, R. C.; Parkinson, H. R.; Pimbblet, K. A.; Phillipps, S.; Popescu, C. C.; Prescott, M.; Sharp, R. G.; Sutherland, W. J.; Taylor, E. N.; Thomas, D.; Tuffs, R. J.; van Kampen, E.; Wijesinghe, D.

2011-10-01

Using the complete Galaxy and Mass Assembly I (GAMA-I) survey covering ˜142 deg2 to rAB= 19.4, of which ˜47 deg2 is to rAB= 19.8, we create the GAMA-I galaxy group catalogue (G3Cv1), generated using a friends-of-friends (FoF) based grouping algorithm. Our algorithm has been tested extensively on one family of mock GAMA lightcones, constructed from Λ cold dark matter N-body simulations populated with semi-analytic galaxies. Recovered group properties are robust to the effects of interlopers and are median unbiased in the most important respects. G3Cv1 contains 14 388 galaxy groups (with multiplicity ≥2), including 44 186 galaxies out of a possible 110 192 galaxies, implying ˜40 per cent of all galaxies are assigned to a group. The similarities of the mock group catalogues and G3Cv1 are multiple: global characteristics are in general well recovered. However, we do find a noticeable deficit in the number of high multiplicity groups in GAMA compared to the mocks. Additionally, despite exceptionally good local spatial completeness, G3Cv1 contains significantly fewer compact groups with five or more members, this effect becoming most evident for high multiplicity systems. These two differences are most likely due to limitations in the physics included of the current GAMA lightcone mock. Further studies using a variety of galaxy formation models are required to confirm their exact origin. The G3Cv1 catalogue will be made publicly available as and when the relevant GAMA redshifts are made available at .

Mathematical demography of spotted owls in the Pacific Northwest

Treesearch

B.R. Noon; C.M. Biles

1990-01-01

We examined the mathematical demography of northern spotted owls (Strix occidentalis caurina) using simple deterministic population models. Our goals were to gain insights into the life history strategy, to determine demographic attributes most affecting changes in population size, and to provide guidelines for effective management of spotted owl...

Molecular gas content of galaxies in the Hydra-Centaurus supercluster

NASA Technical Reports Server (NTRS)

Huchtmeier, W. K.

1993-01-01

A survey of bright spiral galaxies in the Hydra-Centaurus supercluster for the CO(1-0) transition at 115 GHz was performed with the 15m Swedish-ESO submillimeter telescope (SEST). A total of 30 galaxies have been detected in the CO(1-0) transition out of 47 observed, which is a detection rate over 60%. Global physical parameters of these galaxies derived from optical, CO, HI, and IR measurements compare very well with properties of galaxies in the Virgo cluster.

Accelerated Evolution in the Death Galaxy

NASA Astrophysics Data System (ADS)

Austin, Robert; Tung, Chih-Kuan; Gong, Xiu-Quing; Lambert, Guillaume; Liao, David

2010-03-01

We recall 4 main guiding principles of evolution: 1) instability of defections, 2) stress induced non-random mutations, 3) genetic heterogeneity, and 4) fragmented populations. Our previous preliminary experiments have been relatively simple 1-D stress experiments. We are proceeding with 2-D experiments whose design is guided by these principles. Our new experiment we have dubbed the Death Galaxy because of it's use of these design principles. The ``galaxy'' name comes from the fact that the structure is designed as an interconnected array of micro-ecologies, these micro-ecologies are similar to the stars that comprise an astronomical galaxy, and provide the fragmented small populations. A gradient of the antibiotic Cipro is introduced across the galaxy, and we will present results which show how bacterial evolution resulting in resistance to Cipro is accelerated by the physics principles underlying the device.

On the galaxy-halo connection in the EAGLE simulation

NASA Astrophysics Data System (ADS)

Desmond, Harry; Mao, Yao-Yuan; Wechsler, Risa H.; Crain, Robert A.; Schaye, Joop

2017-10-01

Empirical models of galaxy formation require assumptions about the correlations between galaxy and halo properties. These may be calibrated against observations or inferred from physical models such as hydrodynamical simulations. In this Letter, we use the EAGLE simulation to investigate the correlation of galaxy size with halo properties. We motivate this analysis by noting that the common assumption of angular momentum partition between baryons and dark matter in rotationally supported galaxies overpredicts both the spread in the stellar mass-size relation and the anticorrelation of size and velocity residuals, indicating a problem with the galaxy-halo connection it implies. We find the EAGLE galaxy population to perform significantly better on both statistics, and trace this success to the weakness of the correlations of galaxy size with halo mass, concentration and spin at fixed stellar mass. Using these correlations in empirical models will enable fine-grained aspects of galaxy scalings to be matched.

Galactic rings revisited - I. CVRHS classifications of 3962 ringed galaxies from the Galaxy Zoo 2 Database

NASA Astrophysics Data System (ADS)

Buta, Ronald J.

2017-11-01

Rings are important and characteristic features of disc-shaped galaxies. This paper is the first in a series that re-visits galactic rings with the goals of further understanding the nature of the features and for examining their role in the secular evolution of galaxy structure. The series begins with a new sample of 3962 galaxies drawn from the Galaxy Zoo 2 citizen science data base, selected because zoo volunteers recognized a ring-shaped pattern in the morphology as seen in Sloan Digital Sky Survey colour images. The galaxies are classified within the framework of the Comprehensive de Vaucouleurs revised Hubble-Sandage system. It is found that zoo volunteers cued on the same kinds of ring-like features that were recognized in the 1995 Catalogue of Southern Ringed Galaxies. This paper presents the full catalogue of morphological classifications, comparisons with other sources of classifications and some histograms designed mainly to highlight the content of the catalogue. The advantages of the sample are its large size and the generally good quality of the images; the main disadvantage is the low physical resolution that limits the detectability of linearly small rings such as nuclear rings. The catalogue includes mainly inner and outer disc rings and lenses. Cataclysmic (`encounter-driven') rings (such as ring and polar ring galaxies) are recognized in less than 1 per cent of the sample.

Interactions of galaxies outside clusters and massive groups

NASA Astrophysics Data System (ADS)

Yadav, Jaswant K.; Chen, Xuelei

2018-06-01

We investigate the dependence of physical properties of galaxies on small- and large-scale density environment. The galaxy population consists of mainly passively evolving galaxies in comparatively low-density regions of Sloan Digital Sky Survey (SDSS). We adopt (i) local density, ρ _{20}, derived using adaptive smoothing kernel, (ii) projected distance, r_p, to the nearest neighbor galaxy and (iii) the morphology of the nearest neighbor galaxy as various definitions of environment parameters of every galaxy in our sample. In order to detect long-range interaction effects, we group galaxy interactions into four cases depending on morphology of the target and neighbor galaxies. This study builds upon an earlier study by Park and Choi (2009) by including improved definitions of target and neighbor galaxies, thus enabling us to better understand the effect of "the nearest neighbor" interaction on the galaxy. We report that the impact of interaction on galaxy properties is detectable at least up to the pair separation corresponding to the virial radius of (the neighbor) galaxies. This turns out to be mostly between 210 and 360 h^{-1}kpc for galaxies included in our study. We report that early type fraction for isolated galaxies with r_p > r_{vir,nei} is almost ignorant of the background density and has a very weak density dependence for closed pairs. Star formation activity of a galaxy is found to be crucially dependent on neighbor galaxy morphology. We find star formation activity parameters and structure parameters of galaxies to be independent of the large-scale background density. We also exhibit that changing the absolute magnitude of the neighbor galaxies does not affect significantly the star formation activity of those target galaxies whose morphology and luminosities are fixed.

H I-SELECTED GALAXIES IN THE SLOAN DIGITAL SKY SURVEY. II. THE COLORS OF GAS-RICH GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

West, Andrew A.; Garcia-Appadoo, Diego A.; Dalcanton, Julianne J.

2009-09-15

We utilize color information for an H I-selected sample of 195 galaxies to explore the star formation histories and physical conditions that produce the observed colors. We show that the H I selection creates a significant offset toward bluer colors that can be explained by enhanced recent bursts of star formation. There is also no obvious color bimodality, because the H I selection restricts the sample to bluer, actively star-forming systems, diminishing the importance of the red sequence. Rising star formation rates are still required to explain the colors of galaxies bluer than g - r< 0.3. We also demonstratemore » that the colors of the bluest galaxies in our sample are dominated by emission lines and that stellar population synthesis models alone (without emission lines) are not adequate for reproducing many of the galaxy colors. These emission lines produce large changes in the r - i colors but leave the g - r color largely unchanged. In addition, we find an increase in the dispersion of galaxy colors at low masses that may be the result of a change in the star formation process in low-mass galaxies.« less

The SAMI Galaxy Survey: can we trust aperture corrections to predict star formation?

NASA Astrophysics Data System (ADS)

Richards, S. N.; Bryant, J. J.; Croom, S. M.; Hopkins, A. M.; Schaefer, A. L.; Bland-Hawthorn, J.; Allen, J. T.; Brough, S.; Cecil, G.; Cortese, L.; Fogarty, L. M. R.; Gunawardhana, M. L. P.; Goodwin, M.; Green, A. W.; Ho, I.-T.; Kewley, L. J.; Konstantopoulos, I. S.; Lawrence, J. S.; Lorente, N. P. F.; Medling, A. M.; Owers, M. S.; Sharp, R.; Sweet, S. M.; Taylor, E. N.

2016-01-01

In the low-redshift Universe (z < 0.3), our view of galaxy evolution is primarily based on fibre optic spectroscopy surveys. Elaborate methods have been developed to address aperture effects when fixed aperture sizes only probe the inner regions for galaxies of ever decreasing redshift or increasing physical size. These aperture corrections rely on assumptions about the physical properties of galaxies. The adequacy of these aperture corrections can be tested with integral-field spectroscopic data. We use integral-field spectra drawn from 1212 galaxies observed as part of the SAMI Galaxy Survey to investigate the validity of two aperture correction methods that attempt to estimate a galaxy's total instantaneous star formation rate. We show that biases arise when assuming that instantaneous star formation is traced by broad-band imaging, and when the aperture correction is built only from spectra of the nuclear region of galaxies. These biases may be significant depending on the selection criteria of a survey sample. Understanding the sensitivities of these aperture corrections is essential for correct handling of systematic errors in galaxy evolution studies.

The Galaxy Evolution Probe

NASA Astrophysics Data System (ADS)

Glenn, Jason; Galaxy Evolution Probe Team

2018-01-01

The Galaxy Evolution Probe (GEP) is a concept for a far-infrared observatory to survey large regions of sky for star-forming galaxies from z = 0 to beyond z = 3. Our knowledge of galaxy formation is incomplete and requires uniform surveys over a large range of redshifts and environments to accurately describe mass assembly, star formation, supermassive black hole growth, interactions between these processes, and what led to their decline from z ~ 2 to the present day. Infrared observations are sensitive to dusty, star-forming galaxies, which have bright polycyclic aromatic hydrocarbon (PAH) emission features and warm dust continuum in the rest-frame mid infrared and cooler thermal dust emission in the far infrared. Unlike previous far-infrared continuum surveys, the GEP will measure photometric redshifts commensurate with galaxy detections from PAH emission and Si absorption features, without the need for obtaining spectroscopic redshifts of faint counterparts at other wavelengths.The GEP design includes a 2 m diameter telescope actively cooled to 4 K and two instruments: (1) An imager covering 10 to 300 um with 25 spectral resolution R ~ 8 bands (with lower R at the longest wavelengths) to detect star-forming galaxies and measure their redshifts photometrically. (2) A 23 – 190 um, R ~ 250 dispersive spectrometer for redshift confirmation and identification of obscured AGN using atomic fine-structure lines. Lines including [Ne V], [O IV], [O III], [O I], and [C II] will probe gas physical conditions, radiation field hardness, and metallicity. Notionally, the GEP will have a two-year mission: galaxy surveys with photometric redshifts in the first year and a second year devoted to follow-up spectroscopy. A comprehensive picture of star formation in galaxies over the last 10 billion years will be assembled from cosmologically relevant volumes, spanning environments from field galaxies and groups, to protoclusters, to dense galaxy clusters.Commissioned by NASA, the

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.

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.

JELLYFISH GALAXY CANDIDATES AT LOW REDSHIFT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Poggianti, B. M.; Fasano, G.; Omizzolo, A.

Galaxies that are being stripped of their gas can sometimes be recognized from their optical appearance. Extreme examples of stripped galaxies are the so-called “jellyfish galaxies” that exhibit tentacles of debris material with a characteristic jellyfish morphology. We have conducted the first systematic search for galaxies that are being stripped of their gas at low-z (z = 0.04−0.07) in different environments, selecting galaxies with varying degrees of morphological evidence for stripping. We have visually inspected B- and V-band images and identified 344 candidates in 71 galaxy clusters of the OMEGAWINGS+WINGS sample and 75 candidates in groups and lower mass structuresmore » in the PM2GC sample. We present the atlas of stripping candidates and a first analysis of their environment and their basic properties, such as morphologies, star formation rates and galaxy stellar masses. Candidates are found in all clusters and at all clustercentric radii, and their number does not correlate with the cluster velocity dispersion σ or X-ray luminosity L{sub X}. Interestingly, convincing cases of candidates are also found in groups and lower mass halos (10{sup 11}−10{sup 14}M{sub ⊙}), although the physical mechanism at work needs to be securely identified. All the candidates are disky, have stellar masses ranging from log M/M{sub ⊙} < 9 to > 11.5 and the majority of them form stars at a rate that is on average a factor of 2 higher (2.5σ) compared to non-stripped galaxies of similar mass. The few post-starburst and passive candidates have weak stripping evidence. We conclude that disturbed morphologies suggestive of stripping phenomena are ubiquitous in clusters and could be present even in groups and low mass halos. Further studies will reveal the physics of the gas stripping and clarify the mechanisms at work.« less

Dark-ages reionization and galaxy formation simulation - IV. UV luminosity functions of high-redshift galaxies

NASA Astrophysics Data System (ADS)

Liu, Chuanwu; Mutch, Simon J.; Angel, P. W.; Duffy, Alan R.; Geil, Paul M.; Poole, Gregory B.; Mesinger, Andrei; Wyithe, J. Stuart B.

2016-10-01

In this paper, we present calculations of the UV luminosity function (LF) from the Dark-ages Reionization And Galaxy-formation Observables from Numerical Simulations project, which combines N-body, semi-analytic and seminumerical modelling designed to study galaxy formation during the Epoch of Reionization. Using galaxy formation physics including supernova feedback, the model naturally reproduces the UV LFs for high-redshift star-forming galaxies from z ˜ 5 through to z ˜ 10. We investigate the luminosity-star formation rate (SFR) relation, finding that variable SFR histories of galaxies result in a scatter around the median relation of 0.1-0.3 dex depending on UV luminosity. We find close agreement between the model and observationally derived SFR functions. We use our calculated luminosities to investigate the LF below current detection limits, and the ionizing photon budget for reionization. We predict that the slope of the UV LF remains steep below current detection limits and becomes flat at MUV ≳ -14. We find that 48 (17) per cent of the total UV flux at z ˜ 6 (10) has been detected above an observational limit of MUV ˜ -17, and that galaxies fainter than MUV ˜ -17 are the main source of ionizing photons for reionization. We investigate the luminosity-stellar mass relation, and find a correlation for galaxies with MUV < -14 that has the form M_{ast } ∝ 10^{-0.47M_UV}, in good agreement with observations, but which flattens for fainter galaxies. We determine the luminosity-halo mass relation to be M_vir ∝ 10^{-0.35M_UV}, finding that galaxies with MUV = -20 reside in host dark matter haloes of 1011.0±0.1 M⊙ at z ˜ 6, and that this mass decreases towards high redshift.

Numerical simulation of the formation of a spiral galaxy

NASA Astrophysics Data System (ADS)

Williams, P. R.; Nelson, A. H.

2001-08-01

A simulation is described in which the numerical galaxy formed compares favourably in every measurable respect with contemporary bright spiral galaxies, including the formation of a distinct stellar bulge and large scale spiral arm shocks in the gas component. This is achieved in spite of the fact that only idealized proto-galactic initial conditions were used, and only simple phenomenological prescriptions for the physics of the interstellar medium (ISM) and star formation were implemented. In light of the emphasis in recent literature on the importance of the link between galaxy formation and models of the universe on cosmological scales, on the details of the physics of the ISM and star formation, and on apparent problems therein, the implications of this result are discussed.

Constraining Accreting Binary Populations in Normal Galaxies

NASA Astrophysics Data System (ADS)

Lehmer, Bret; Hornschemeier, A.; Basu-Zych, A.; Fragos, T.; Jenkins, L.; Kalogera, V.; Ptak, A.; Tzanavaris, P.; Zezas, A.

2011-01-01

X-ray emission from accreting binary systems (X-ray binaries) uniquely probe the binary phase of stellar evolution and the formation of compact objects such as neutron stars and black holes. A detailed understanding of X-ray binary systems is needed to provide physical insight into the formation and evolution of the stars involved, as well as the demographics of interesting binary remnants, such as millisecond pulsars and gravitational wave sources. Our program makes wide use of Chandra observations and complementary multiwavelength data sets (through, e.g., the Spitzer Infrared Nearby Galaxies Survey [SINGS] and the Great Observatories Origins Deep Survey [GOODS]), as well as super-computing facilities, to provide: (1) improved calibrations for correlations between X-ray binary emission and physical properties (e.g., star-formation rate and stellar mass) for galaxies in the local Universe; (2) new physical constraints on accreting binary processes (e.g., common-envelope phase and mass transfer) through the fitting of X-ray binary synthesis models to observed local galaxy X-ray binary luminosity functions; (3) observational and model constraints on the X-ray evolution of normal galaxies over the last 90% of cosmic history (since z 4) from the Chandra Deep Field surveys and accreting binary synthesis models; and (4) predictions for deeper observations from forthcoming generations of X-ray telesopes (e.g., IXO, WFXT, and Gen-X) to provide a science driver for these missions. In this talk, we highlight the details of our program and discuss recent results.

The AMIGA sample of isolated galaxies. IV. A catalogue of neighbours around isolated galaxies

NASA Astrophysics Data System (ADS)

Verley, S.; Odewahn, S. C.; Verdes-Montenegro, L.; Leon, S.; Combes, F.; Sulentic, J.; Bergond, G.; Espada, D.; García, E.; Lisenfeld, U.; Sabater, J.

2007-08-01

Context: Studies of the effects of environment on galaxy properties and evolution require well defined control samples. Such isolated galaxy samples have up to now been small or poorly defined. The AMIGA project (Analysis of the interstellar Medium of Isolated GAlaxies) represents an attempt to define a statistically useful sample of the most isolated galaxies in the local (z ≤ 0.05) Universe. Aims: A suitable large sample for the AMIGA project already exists, the Catalogue of Isolated Galaxies (CIG, Karachentseva, 1973, Astrofizicheskie Issledovaniia Izvestiya Spetsial'noj Astrofizicheskoj Observatorii, 8, 3; 1050 galaxies), and we use this sample as a starting point to refine and perform a better quantification of its isolation properties. Methods: Digitised POSS-I E images were analysed out to a minimum projected radius R ≥ 0.5 Mpc around 950 CIG galaxies (those within Vr = 1500 km s-1 were excluded). We identified all galaxy candidates in each field brighter than B = 17.5 with a high degree of confidence using the LMORPHO software. We generated a catalogue of approximately 54 000 potential neighbours (redshifts exist for ≈30% of this sample). Results: Six hundred sixty-six galaxies pass and two hundred eighty-four fail the original CIG isolation criterion. The available redshift data confirm that our catalogue involves a largely background population rather than physically associated neighbours. We find that the exclusion of neighbours within a factor of four in size around each CIG galaxy, employed in the original isolation criterion, corresponds to Δ Vr ≈ 18 000 km s-1 indicating that it was a conservative limit. Conclusions: Galaxies in the CIG have been found to show different degrees of isolation. We conclude that a quantitative measure of this is mandatory. It will be the subject of future work based on the catalogue of neighbours obtained here. Full Table [see full text] is only available in electronic form at the CDS via anonymous ftp to cdsarc

The ZEUS 1 & 2 INvestigated Galaxy Reference Sample (ZINGRS): A window into galaxies in the early Universe.

NASA Astrophysics Data System (ADS)

Ferkinhoff, Carl; Hershey, Deborah; Scrabeck, Alex; Higdon, Sarah; Higdon, James L.; Tidwell, Hannah; Lamarche, Cody; Vishwas, Amit; Nikola, Thomas; Stacey, Gordon J.; Brisbin, Drew

2018-06-01

Galaxies have evolved significantly from the early Universe until today. Star formation rates, stellar and molecular gas masses, sizes and metal enrichment of galaxies have all changed significantly from early epochs until the present. Probing the physical conditions of galaxy at high redshift is vital to understanding this evolution. ZINGRS, the ZEUS 1 and 2 INvestigated Galaxy Reference Sample, provides a unique and powerful window for this work. The sample consists of more than ~30 galaxies from z ~ 1 - 4.5 for which the far-IR fine-structure lines (e.g. [CII] 158 micron, [NII] 122micron, [OIII] 88 micron) have been observed with the ZEUS-1 and 2 instruments. These lines are ideal for studying high-z systems since they require low energies for excitation, are typically optically thin, and are not susceptible to extinction from dust. ZINGRS is the largest collection of far-IR fine-structure line detections at high-z. Here we describe the sample, including extensive multifrequency supporting observations like CO & radio continuum, and summarize what we have learned so far.

Reconstructing the galaxy density field with photometric redshifts - II. Environment-dependent galaxy evolution since z ≃ 3

NASA Astrophysics Data System (ADS)

Malavasi, Nicola; Pozzetti, Lucia; Cucciati, Olga; Bardelli, Sandro; Ilbert, Olivier; Cimatti, Andrea

2017-09-01

Although extensively investigated, the role of the environment in galaxy formation is still not well understood. In this context, the galaxy stellar mass function (GSMF) is a powerful tool to understand how environment relates to galaxy mass assembly and the quenching of star formation. In this work, we make use of the high-precision photometric redshifts of the UltraVISTA Survey to study the GSMF in different environments up to z ˜ 3, on physical scales from 0.3 to 2 Mpc, down to masses of M ˜ 1010 M⊙. We witness the appearance of environmental signatures for both quiescent and star-forming galaxies. We find that the shape of the GSMF of quiescent galaxies is different in high- and low-density environments up to z ˜ 2 with the high-mass end (M ≳ 1011 M⊙) being enhanced in high-density environments. On the contrary, for star-forming galaxies, a difference between the GSMF in high- and low-density environments is present for masses M ≲ 1011 M⊙. Star-forming galaxies in this mass range appear to be more frequent in low-density environments up to z < 1.5. Differences in the shape of the GSMF are not visible anymore at z > 2. Our results, in terms of general trends in the shape of the GSMF, are in agreement with a scenario in which galaxies are quenched when they enter hot gas-dominated massive haloes that are preferentially in high-density environments.

Demography and life history characteristics of two honey bee races (Apis mellifera).

PubMed

Winston, Mark L; Dropkin, Jennifer A; Taylor, Orley R

1981-03-01

Intra-colony demography and life history characteristics of neotropical Africanized and temperate European honey bearaces were compared under simulated feral conditions. Major differences in colony demography were found which nevertheless resulted in some similar reproductive characteristics. European colonies were larger than Africanized colonies, had more rapid initral growth rates of worker populations, showed better survivorship of brood and adult workers, and differed in patterns of worker age distribution. However, both races were similar in the brood and adult populations when colonies swarmed, the frequency and timing of swarming, and the number of workers in prime swarms. The factors most important in determining these colony growth and reproductive patterns were likely worker mortality rates, climate, and resource availability.

The galaxy-subhalo connection in low-redshift galaxy clusters from weak gravitational lensing

NASA Astrophysics Data System (ADS)

Sifón, Cristóbal; Herbonnet, Ricardo; Hoekstra, Henk; van der Burg, Remco F. J.; Viola, Massimo

2018-07-01

We measure the gravitational lensing signal around satellite galaxies in a sample of galaxy clusters at z < 0.15 by combining high-quality imaging data from the Canada-France-Hawaii Telescope with a large sample of spectroscopically confirmed cluster members. We use extensive image simulations to assess the accuracy of shape measurements of faint, background sources in the vicinity of bright satellite galaxies. We find a small but significant bias, as light from the lenses makes the shapes of background galaxies appear radially aligned with the lens. We account for this bias by applying a correction that depends on both lens size and magnitude. We also correct for contamination of the source sample by cluster members. We use a physically motivated definition of subhalo mass, namely the mass bound to the subhalo, mbg, similar to definitions used by common subhalo finders in numerical simulations. Binning the satellites by stellar mass we provide a direct measurement of the subhalo-to-stellar-mass relation, log mbg/M⊙ = (11.54 ± 0.05) + (0.95 ± 0.10)log [m⋆/(2 × 1010 M⊙)]. This best-fitting relation implies that, at a stellar mass m⋆ ˜ 3 × 1010 M⊙, subhalo masses are roughly 50 per cent of those of central galaxies, and this fraction decreases at higher stellar masses. We find some evidence for a sharp change in the total-to-stellar mass ratio around the clusters' scale radius, which could be interpreted as galaxies within the scale radius having suffered more strongly from tidal stripping, but remain cautious regarding this interpretation.

The galaxy-subhalo connection in low-redshift galaxy clusters from weak gravitational lensing

NASA Astrophysics Data System (ADS)

Sifón, Cristóbal; Herbonnet, Ricardo; Hoekstra, Henk; van der Burg, Remco F. J.; Viola, Massimo

2018-05-01

We measure the gravitational lensing signal around satellite galaxies in a sample of galaxy clusters at z < 0.15 by combining high-quality imaging data from the Canada-France-Hawaii Telescope with a large sample of spectroscopically-confirmed cluster members. We use extensive image simulations to assess the accuracy of shape measurements of faint, background sources in the vicinity of bright satellite galaxies. We find a small but significant bias, as light from the lenses makes the shapes of background galaxies appear radially aligned with the lens. We account for this bias by applying a correction that depends on both lens size and magnitude. We also correct for contamination of the source sample by cluster members. We use a physically-motivated definition of subhalo mass, namely the mass bound to the subhalo, mbg, similar to definitions used by common subhalo finders in numerical simulations. Binning the satellites by stellar mass we provide a direct measurement of the subhalo-to-stellar-mass relation, log mbg/M⊙ = (11.54 ± 0.05) + (0.95 ± 0.10)log [m⋆/(2 × 1010M⊙)]. This best-fitting relation implies that, at a stellar mass m⋆ ˜ 3 × 1010 M⊙, subhalo masses are roughly 50 per cent of those of central galaxies, and this fraction decreases at higher stellar masses. We find some evidence for a sharp change in the total-to-stellar mass ratio around the clusters' scale radius, which could be interpreted as galaxies within the scale radius having suffered more strongly from tidal stripping, but remain cautious regarding this interpretation.

Recovering Galaxy Properties Using Gaussian Process SED Fitting

NASA Astrophysics Data System (ADS)

Iyer, Kartheik; Awan, Humna

2018-01-01

Information about physical quantities like the stellar mass, star formation rates, and ages for distant galaxies is contained in their spectral energy distributions (SEDs), obtained through photometric surveys like SDSS, CANDELS, LSST etc. However, noise in the photometric observations often is a problem, and using naive machine learning methods to estimate physical quantities can result in overfitting the noise, or converging on solutions that lie outside the physical regime of parameter space.We use Gaussian Process regression trained on a sample of SEDs corresponding to galaxies from a Semi-Analytic model (Somerville+15a) to estimate their stellar masses, and compare its performance to a variety of different methods, including simple linear regression, Random Forests, and k-Nearest Neighbours. We find that the Gaussian Process method is robust to noise and predicts not only stellar masses but also their uncertainties. The method is also robust in the cases where the distribution of the training data is not identical to the target data, which can be extremely useful when generalized to more subtle galaxy properties.

Feedback Driven Chemical Evolution in Simulations of Low Mass Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Emerick, Andrew; Bryan, Greg; Mac Low, Mordecai-Mark

2018-06-01

Galaxy chemical properties place some of the best constraints on models of galaxy evolution. Both gas and stellar metal abundances in galaxies depend upon the integrated star formation history of the galaxy, gas accretion, outflows, and the effectiveness of metal mixing within the interstellar medium (ISM). Capturing the physics that governs these processes in detail, however, is challenging, in part due to the difficulty in self-consistently modelling stellar feedback physics that impacts each of these processes. Using high resolution hydrodynamics simulations of isolated dwarf galaxies where we follow stars as individual star particles, we examine the role of feedback in driving dwarf galaxy chemical evolution. This star-by-star method allows us to directly follow feedback from stellar winds from massive and AGB stars, stellar ionizing radiation and photoelectric heating, and supernovae. Additionally, we track 15 individual metal species yields from these stars as they pollute the ISM and enrich new stellar populations. I will present initial results from these simulations in the context of observational constraints on the retention/ejection of metals from Local Group dwarf galaxies. In addition, I will discuss the variations with which individual elements evolve in the various phases of the ISM, as they progress from hot, ionized gas down to cold, star forming regions. I will conclude by outlining the implications of these results on interpretations of observed chemical abundances in dwarf galaxies and on standard assumptions made in semi-analytic chemical evolution models of these galaxies.

Low-Surface-Brightness Galaxies: Hidden Galaxies Revealed

NASA Astrophysics Data System (ADS)

Bothun, G.; Impey, C.; McGaugh, S.

1997-07-01

In twenty years, low surface brightness (LSB) galaxies have evolved from being an idiosyncratic notion to being one of the major baryonic repositories in the Universe. The story of their discovery and the characterization of their properties is told here. Their recovery from the noise of the night sky background is a strong testament to the severity of surface brightness selection effects. LSB galaxies have a number of remarkable properties which distinguish them from the more familiar Hubble Sequence of spirals. The two most important are 1) they evolve at a significantly slower rate and may well experience star formation outside of the molecular cloud environment, 2) they are embedded in dark matter halos which are of lower density and more extended than the halos around high surface brightness (HSB) disk galaxies. Compared to HSB disks, LSB disks are strongly dark matter dominated at all radii and show a systematic increase in $M/L$ with decreasing central surface brightness. In addition, the recognition that large numbers of LSB galaxies actually exist has changed the form of the galaxy luminosity function and has clearly increased the space density of galaxies at z =0. Recent CCD surveys have uncovered a population of red LSB disks that may be related to the excess of faint blue galaxies detected at moderate redshifts. LSB galaxies offer us a new window into galaxy evolution and formation which is every bit as important as those processes which have produced easy to detect galaxies. Indeed, the apparent youth of some LSB galaxies suggest that galaxy formation is a greatly extended process. While the discovery of LSB galaxies have lead to new insights, it remains unwise to presume that we now have a representative sample which encompasses all galaxy types and forms. (SECTION: Invited Review Paper)

DEEP CHANDRA OBSERVATIONS OF NGC 1404: CLUSTER PLASMA PHYSICS REVEALED BY AN INFALLING EARLY-TYPE GALAXY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Su, Yuanyuan; Kraft, Ralph P.; Nulsen, Paul

The intracluster medium (ICM), as a magnetized and highly ionized fluid, provides an ideal laboratory to study plasma physics under extreme conditions that cannot be achieved on Earth. NGC 1404 is a bright elliptical galaxy that is being gas stripped as it falls through the ICM of the Fornax Cluster. We use the new Chandra X-ray observations of NGC 1404 to study ICM microphysics. The interstellar medium of NGC 1404 is characterized by a sharp leading edge, 8 kpc from the Galaxy center, and a short downstream gaseous tail. Contact discontinuities are resolved on unprecedented spatial scales (0.″5 = 45 pc)more » due to the combination of the proximity of NGC 1404, the superb spatial resolution of Chandra , and the very deep (670 ks) exposure. At the leading edge, we observe sub-kiloparsec-scale eddies generated by Kelvin–Helmholtz instability (KHI) and put an upper limit of 5% Spitzer on the isotropic viscosity of the hot cluster plasma. We also observe mixing between the hot cluster gas and the cooler galaxy gas in the downstream stripped tail, which provides further evidence of a low viscosity plasma. The assumed ordered magnetic fields in the ICM ought to be smaller than 5 μ G to allow KHI to develop. The lack of an evident magnetic draping layer just outside the contact edge is consistent with such an upper limit.« less

Galaxy bias from galaxy-galaxy lensing in the DES Science Verification Data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prat, J.; et al.

We present a measurement of galaxy-galaxy lensing around a magnitude-limited (more » $$i_{AB} < 22.5$$) sample of galaxies selected from the Dark Energy Survey Science Verification (DES-SV) data. We split these lenses into three photometric-redshift bins from 0.2 to 0.8, and determine the product of the galaxy bias $b$ and cross-correlation coefficient between the galaxy and dark matter overdensity fields $r$ in each bin, using scales above 4 Mpc/$h$ comoving, where we find the linear bias model to be valid given our current uncertainties. We compare our galaxy bias results from galaxy-galaxy lensing with those obtained from galaxy clustering (Crocce et al. 2016) and CMB lensing (Giannantonio et al. 2016) for the same sample of galaxies, and find our measurements to be in good agreement with those in Crocce et al. (2016), while, in the lowest redshift bin ($$z\\sim0.3$$), they show some tension with the findings in Giannantonio et al. (2016). Our results are found to be rather insensitive to a large range of systematic effects. We measure $$b\\cdot r$$ to be $$0.87\\pm 0.11$$, $$1.12 \\pm 0.16$$ and $$1.24\\pm 0.23$$, respectively for the three redshift bins of width $$\\Delta z = 0.2$$ in the range $0.2« less

Galaxy gas as obscurer - II. Separating the galaxy-scale and nuclear obscurers of active galactic nuclei

NASA Astrophysics Data System (ADS)

Buchner, Johannes; Bauer, Franz E.

2017-03-01

The 'torus' obscurer of active galactic nuclei (AGN) is poorly understood in terms of its density, sub-structure and physical mechanisms. Large X-ray surveys provide model boundary constraints, for both Compton-thin and Compton-thick levels of obscuration, as obscured fractions are mean covering factors fcov. However, a major remaining uncertainty is host-galaxy obscuration. In Paper I, we discovered a relation of {NH} ∝ M_{star }^{1/3} for the obscuration of galaxy-scale gas. Here, we apply this observational relation to the AGN population, and find that galaxy-scale gas is responsible for a luminosity-independent fraction of Compton-thin AGN, but does not produce Compton-thick columns. With the host-galaxy obscuration understood, we present a model of the remaining nuclear obscurer, which is consistent with a range of observations. Our radiation-lifted torus model consists of a Compton-thick component (fcov ∼ 35 per cent) and a Compton-thin component (fcov ∼ 40 per cent), which depends on both black hole mass and luminosity. This provides a useful summary of observational constraints for torus modellers who attempt to reproduce this behaviour. It can also be employed as a sub-grid recipe in cosmological simulations that do not resolve the torus. We also investigate host-galaxy X-ray obscuration inside cosmological, hydrodynamic simulations (Evolution and Assembly of Galaxies and their Environment; Illustris). The obscuration from ray-traced galaxy gas can agree with observations, but is highly sensitive to the chosen feedback assumptions.

An order statistics approach to the halo model for galaxies

NASA Astrophysics Data System (ADS)

Paul, Niladri; Paranjape, Aseem; Sheth, Ravi K.

2017-04-01

We use the halo model to explore the implications of assuming that galaxy luminosities in groups are randomly drawn from an underlying luminosity function. We show that even the simplest of such order statistics models - one in which this luminosity function p(L) is universal - naturally produces a number of features associated with previous analyses based on the 'central plus Poisson satellites' hypothesis. These include the monotonic relation of mean central luminosity with halo mass, the lognormal distribution around this mean and the tight relation between the central and satellite mass scales. In stark contrast to observations of galaxy clustering; however, this model predicts no luminosity dependence of large-scale clustering. We then show that an extended version of this model, based on the order statistics of a halo mass dependent luminosity function p(L|m), is in much better agreement with the clustering data as well as satellite luminosities, but systematically underpredicts central luminosities. This brings into focus the idea that central galaxies constitute a distinct population that is affected by different physical processes than are the satellites. We model this physical difference as a statistical brightening of the central luminosities, over and above the order statistics prediction. The magnitude gap between the brightest and second brightest group galaxy is predicted as a by-product, and is also in good agreement with observations. We propose that this order statistics framework provides a useful language in which to compare the halo model for galaxies with more physically motivated galaxy formation models.

Surface Photometric Properties of HII Galaxies

NASA Astrophysics Data System (ADS)

Vajgel, B.; Telles, E.

2009-05-01

HII galaxies are dwarf galaxies undergoing violent star formation. They were firstly selected by objective-prism spectroscopy and were object of extensive studies to characterize their physical conditions of the interstellar medium. Their SFR together with their low Z raised the question whether some of them can be truly ``young'' galaxies. To infer the SFH, one needs information in a large spectral range. We obtained images in the optical region of the spectrum with the 0.6 m B&C and the 1.6 m telescopes at the Laboratório Nacional de Astrofísica, for a sample of 50 objects in B, V, R and I, which combined with recent evolutionary models, enable us to deduce the stellar population content and its spatial distribution. These seem to be the nearest youngest galaxies that can be studied in detail, and their structural properties offer important indications about the evolutionary relation and the origin of dwarf galaxies in the universe. With this sample we built a morphological catalogue with broad-band photometry, including the structural analysis through the brightness profiles. The initial analysis suggests that the galaxies can be segregated in two broad classes, in agreement with what had already been proposed in the literature; Type I have irregular envelopes with signs of perturbation and turn out to the more luminous sub-sample; while Type II have regular external isophotes and are less luminous. The brightness profiles are well represented by exponential fits, as in irregular and elliptical dwarf galaxies. However, HII galaxies are more compact in comparison with their more diffuse counterparts. We study the behavior of the HII galaxies in the metallicity-luminosity plane. This relation, interpreted as a relation between the mass and the metallicity of dwarf galaxies of low surface brightness (dE and dIrr), has direct implications for their formation and evolution, and over the possible evolutionary links between HII galaxies and other types of dwarf

The Sensitive Side of Galaxy Formation: How sub-L* Galaxies Accrete, Form Stars, and Enrich the IGM

NASA Astrophysics Data System (ADS)

Oppenheimer, Benjamin

2012-10-01

We propose a series of cosmological zoom simulations specifically targeting the formation and evolution of dwarf and sub-L* galaxies living in halos of 10^11- 10^12 solar masses. The shallow potential wells and low-density environments of these halos provide uniquely sensitive laboratories to understand the physics of galactic feedback, as well as the thermal history of the intergalactic medium, from which these galaxies accrete. Given that 129 orbits of Cycle 18 COS data probing such halos is now being completed, combined with the insufficiency of current cosmological simulations to resolve these halos, the theory is lagging the data. We will remedy this by running zoom simulations of individual halos with 1000-10,000 times greater mass resolution than current cosmological simulations used for similar studies. We aim to resolve the sub-kpc scale of high-velocity cloud-like structures and <100 pc scales of the interstellar medium. We will simulate circumgalactic quasar absorption metal-line and H I statistics using our novel non-equilibrium ionization solver that follows individual ionic states. We will also investigate the delicate balance of accretion, star formation, and feedback required to reproduce the observed stellar properties of these small galaxies. In the spirit of transparency, we will make our simulation results available on a public website to encourage new projects and collaborations with observers and theorists understanding the physics regulating galaxy growth.

Physically detached 'compact groups'

NASA Technical Reports Server (NTRS)

Hernquist, Lars; Katz, Neal; Weinberg, David H.

1995-01-01

A small fraction of galaxies appear to reside in dense compact groups, whose inferred crossing times are much shorter than a Hubble time. These short crossing times have led to considerable disagreement among researchers attempting to deduce the dynamical state of these systems. In this paper, we suggest that many of the observed groups are not physically bound but are chance projections of galaxies well separated along the line of sight. Unlike earlier similar proposals, ours does not require that the galaxies in the compact group be members of a more diffuse, but physically bound entity. The probability of physically separated galaxies projecting into an apparent compact group is nonnegligible if most galaxies are distributed in thin filaments. We illustrate this general point with a specific example: a simulation of a cold dark matter universe, in which hydrodynamic effects are included to identify galaxies. The simulated galaxy distribution is filamentary and end-on views of these filaments produce apparent galaxy associations that have sizes and velocity dispersions similar to those of observed compact groups. The frequency of such projections is sufficient, in principle, to explain the observed space density of groups in the Hickson catalog. We discuss the implications of our proposal for the formation and evolution of groups and elliptical galaxies. The proposal can be tested by using redshift-independent distance estimators to measure the line-of-sight spatial extent of nearby compact groups.

CO excitation in four IR luminous galaxies

NASA Technical Reports Server (NTRS)

Radford, Simon J. E.; Solomon, P. M.; Downes, Dennis

1990-01-01

The correlation between the CO and far infrared luminosities of spiral galaxies is well established. The luminosity ration, L sub FIR/L sub CO in IR luminous active galaxies is, however, systematically five to ten times higher than in ordinary spirals and molecular clouds in our Galaxy. Furthermore, the masses of molecular hydrogen in luminous galaxies are large, M (H2) approx. equals 10(exp 10) solar magnitude, which indicates the observed luminosity ratios are due to an excess of infrared output, rather than a deficiency of molecular gas. These large amounts of molecular gas may fuel luminous galaxies through either star formation or nuclear activity. This interpretation rests on applying the M (H2)/L sub CO ratio calibrated in our Galaxy to galaxies with strikingly different luminosity ratios. But are the physical conditions of the molecular gas different in galaxies with different luminosity ratios. And, if so, does the proportionality between CO and H2 also vary among galaxies. To investigate these questions researchers observed CO (2 to 1) and (1 to 0) emission from four luminous galaxies with the Institute for Radio Astronomy in the Millimeter range (IRAM) 30 m telescope. Researchers conclude that most of the CO emission from these Arp 193, Arp 220, and Mrk 231 arises in regions with moderate ambient densities similar to the clouds in the Milky Way molecular ring. The emission is neither from dense hot cloud cores nor from the cold low density gas characteristic of the envelopes of dark clouds.

Understanding the dust properties in nearby galaxies

NASA Astrophysics Data System (ADS)

Decleir, Marjorie; Baes, Maarten; De Looze, Ilse; Camps, Peter

2018-04-01

Dust is a crucial component in the interstellar medium of galaxies. It regulates several physical and chemical processes. Dust grains are also efficient at absorbing and scattering ultraviolet/optical photons and then re-radiating the absorbed energy in the infrared/submm wavelength range. The spatial distribution and properties of dust in galaxies can hence be investigated in two complementary ways: by its attenuation effects at short wavelengths, and by its thermal emission at long wavelengths. Both approaches have their advantages and challenges. In this contribution, we discuss a number of recent interesting results on interstellar dust in nearby galaxies, obtained by our research group at Ghent University.

Manganese in Dwarf Galaxies as a Probe of Type Ia Supernovae

NASA Astrophysics Data System (ADS)

De Los Reyes, Mithi; Kirby, Evan N.

2018-06-01

Despite the importance of thermonuclear or Type Ia supernovae (SNe) as standard candles in astrophysics, the physical mechanisms behind Type Ia SNe are still poorly constrained. Theoretically, the nucleosynthetic yields from Type Ia SNe can distinguish among different models of Type Ia explosions. For example, neutron-rich elements such as manganese (Mn) are sensitive probes of the physics of Type Ia SNe because their abundances are correlated to the density of the progenitor white dwarf. Since dwarf galaxies' chemical evolution is dominated by Type Ia SNe at late times, Type Ia nucleosynthetic yields can be indirectly inferred from stellar abundances in dwarf galaxies. However, previous measurements of Mn in dwarf galaxies are too incomplete to draw definitive conclusions on the Type Ia explosion mechanism. In this work, we therefore use medium-resolution stellar spectroscopy from Keck/DEIMOS to measure Mn abundances in red giants in several Milky Way satellite galaxies. We report average Type Ia Mn yields computed from these abundances, and we discuss the implications for Type Ia supernova physics.

Deep spectroscopy of nearby galaxy clusters - IV. The quench of the star formation in galaxies in the infall region of Abell 85

NASA Astrophysics Data System (ADS)

Aguerri, J. A. L.; Agulli, I.; Méndez-Abreu, J.

2018-06-01

Our aim is to understand the role of the environment in the quenching of star formation of galaxies located in the infall cluster region of Abell 85 (A85). This is achieved by studying the post-starburst galaxy population as tracer of recent quenching. By measuring the equivalent width (EW) of the [O II] and Hδ spectral lines, we classify the galaxies into three groups: passive (PAS), emission line (EL), and post-starburst (PSB) galaxies. The PSB galaxy population represents ˜ 4.5 per cent of the full sample. Dwarf galaxies (Mr > -18.0) account for ˜ 70 - 80 per cent of PSBs, which indicates that most of the galaxies undergoing recent quenching are low-mass objects. Independently of the environment, PSB galaxies are disc-like objects with g - r colour between the blue ELs and the red PAS ones. The PSB and EL galaxies in low-density environments show similar luminosities and local galaxy densities. The dynamics and local galaxy density of the PSB population in high-density environments are shared with PAS galaxies. However, PSB galaxies inside A85 are at shorter clustercentric radius than PAS and EL ones. The value of the EW(Hδ) is larger for those PSBs closer to the cluster centre. We propose two different physical mechanisms producing PSB galaxies depending on the environment. In low-density environments, gas-rich minor mergers or accretions could produce the PSB galaxies. For high-density environments like A85, PSBs would be produced by the removal of the gas reservoirs of EL galaxies by ram-pressure stripping when they pass near the cluster centre.

Classifying galaxy spectra at 0.5 < z < 1 with self-organizing maps

NASA Astrophysics Data System (ADS)

Rahmani, S.; Teimoorinia, H.; Barmby, P.

2018-05-01

The spectrum of a galaxy contains information about its physical properties. Classifying spectra using templates helps elucidate the nature of a galaxy's energy sources. In this paper, we investigate the use of self-organizing maps in classifying galaxy spectra against templates. We trained semi-supervised self-organizing map networks using a set of templates covering the wavelength range from far ultraviolet to near infrared. The trained networks were used to classify the spectra of a sample of 142 galaxies with 0.5 < z < 1 and the results compared to classifications performed using K-means clustering, a supervised neural network, and chi-squared minimization. Spectra corresponding to quiescent galaxies were more likely to be classified similarly by all methods while starburst spectra showed more variability. Compared to classification using chi-squared minimization or the supervised neural network, the galaxies classed together by the self-organizing map had more similar spectra. The class ordering provided by the one-dimensional self-organizing maps corresponds to an ordering in physical properties, a potentially important feature for the exploration of large datasets.

IRAC Imaging of LSB Galaxies

NASA Astrophysics Data System (ADS)

Schombert, James; McGaugh, Stacy; Lelli, Federico

2017-04-01

We propose a program to observe a large sample of Low Surface Brightness (LSB) galaxies. Large galaxy surveys conducted with Spitzer suffer from the unavoidable selection bias against LSB systems (e.g., the S4G survey). Even those programs thathave specifically targeted LSB galaxies have usually been restricted objects of intermediate surface brightness (between 22 and 23 B mag/ []). Our sample is selected to be of a more extreme LSB nature (with central surface brightness fainter than 23 Bmag/[]). Even warm, Spitzer is the ideal instrument to image these low contrast targets in the near infrared: our sample goes a considerable way towards remedying this hole in the Spitzer legacy archive, also increasing coverage in terms of stellar mass, gas mass, and SFR. The sample will be used to address the newly discovered radial acceleration relation (RAR) in disk galaxies. While issues involving the connection between baryons and dark matter have been known since the development of the global baryonic Tully-Fisher (bTF) relation, it is only in the last six months that the particle physics and theoretical communities have recognized and responded to the local coupling between dark and baryonic matter represented by the RAR. This important new correlation is effectively a new natural law for galaxies. Spitzer photometry has been at the forefront of resolving the stellar mass component in galaxies that make-up the RAR and is the primary reason for the discovery of this new kinematic law.

Galaxy properties in clusters. II. Backsplash galaxies

NASA Astrophysics Data System (ADS)

Muriel, H.; Coenda, V.

2014-04-01

Aims: We explore the properties of galaxies on the outskirts of clusters and their dependence on recent dynamical history in order to understand the real impact that the cluster core has on the evolution of galaxies. Methods: We analyse the properties of more than 1000 galaxies brighter than M0.1r = - 19.6 on the outskirts of 90 clusters (1 < r/rvir < 2) in the redshift range 0.05 < z < 0.10. Using the line of sight velocity of galaxies relative to the cluster's mean, we selected low and high velocity subsamples. Theoretical predictions indicate that a significant fraction of the first subsample should be backsplash galaxies, that is, objects that have already orbited near the cluster centre. A significant proportion of the sample of high relative velocity (HV) galaxies seems to be composed of infalling objects. Results: Our results suggest that, at fixed stellar mass, late-type galaxies in the low-velocity (LV) sample are systematically older, redder, and have formed fewer stars during the last 3 Gyrs than galaxies in the HV sample. This result is consistent with models that assume that the central regions of clusters are effective in quenching the star formation by means of processes such as ram pressure stripping or strangulation. At fixed stellar mass, LV galaxies show some evidence of having higher surface brightness and smaller size than HV galaxies. These results are consistent with the scenario where galaxies that have orbited the central regions of clusters are more likely to suffer tidal effects, producing loss of mass as well as a re-distribution of matter towards more compact configurations. Finally, we found a higher fraction of ET galaxies in the LV sample, supporting the idea that the central region of clusters of galaxies may contribute to the transformation of morphological types towards earlier types.

Physical Properties of Massive, Star-Forming Galaxies When the Universe Was Only Two Billion Years Old

NASA Astrophysics Data System (ADS)

Fu, Nicole Christina

Due to the finite speed of light and a vast, expanding universe, telescopes are just now receiving the light emitted by galaxies as they were forming in the very early universe. The light from these galaxies has been redshifted (stretched to longer, redder wavelengths) as a result of its journey through expanding space. Using sophisticated techniques and exceptional multi-wavelength optical and infrared data, we isolate a population of 378 galaxies in the process of formation when the Universe was only two billion years old. By matching the distinctive properties of the light spectra of these galaxies to models, the redshift, age, dust content, star formation rate and total stellar mass of each galaxy are determined. Comparing our results to similar surveys of galaxy populations at other redshifts, a picture emerges of the growth and evolution of massive, star-forming galaxies over the course of billions of years.

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).

Ultraviolet Radiative Transfer Modeling of Nearby Galaxies with Extraplanar Dusts

NASA Astrophysics Data System (ADS)

Shinn, Jong-Ho; Seon, Kwang-Il

2015-12-01

In order to examine their relation to the host galaxy, the extraplanar dusts of six nearby galaxies are modeled, employing a three-dimensional Monte Carlo radiative transfer code. The targets are from the highly inclined galaxies that show dust-scattered ultraviolet halos, and the archival Galaxy Evolution Explorer FUV band images were fitted with the model. The observed images are generally well-reproduced by two dust layers and one light source layer, whose vertical and radial distributions have exponential profiles. We obtained several important physical parameters, such as star formation rate (SFRUV), face-on optical depth, and scale-heights. Three galaxies (NGC 891, NGC 3628, and UGC 11794) show clear evidence for the existence of an extraplanar dust layer. However, it is found that the remaining three targets (IC 5249, NGC 24, and NGC 4173) do not necessarily need a thick dust disk to model the ultraviolet (UV) halo, because its contribution is too small and the UV halo may be caused by the wing part of the GALEX point spread function. This indicates that the galaxy samples reported to have UV halos may be contaminated by galaxies with negligible extraplanar (halo) dust. The galaxies showing evidence of an extraplanar dust layer fall within a narrow range on the scatter plots between physical parameters such as SFRUV and extraplanar dust mass. Several mechanisms that could possibly produce the extraplanar dust are discussed. We also found a hint that the extraplanar dust scale-height might not be much different from the polycyclic aromatic hydrocarbon emission characteristic height.

Dark-ages reionization and galaxy formation simulation - III. Modelling galaxy formation and the epoch of reionization

NASA Astrophysics Data System (ADS)

Mutch, Simon J.; Geil, Paul M.; Poole, Gregory B.; Angel, Paul W.; Duffy, Alan R.; Mesinger, Andrei; Wyithe, J. Stuart B.

2016-10-01

We introduce MERAXES, a new, purpose-built semi-analytic galaxy formation model designed for studying galaxy growth during reionization. MERAXES is the first model of its type to include a temporally and spatially coupled treatment of reionization and is built upon a custom (100 Mpc)3 N-body simulation with high temporal and mass resolution, allowing us to resolve the galaxy and star formation physics relevant to early galaxy formation. Our fiducial model with supernova feedback reproduces the observed optical depth to electron scattering and evolution of the galaxy stellar mass function between z = 5 and 7, predicting that a broad range of halo masses contribute to reionization. Using a constant escape fraction and global recombination rate, our model is unable to simultaneously match the observed ionizing emissivity at z ≲ 6. However, the use of an evolving escape fraction of 0.05-0.1 at z ˜ 6, increasing towards higher redshift, is able to satisfy these three constraints. We also demonstrate that photoionization suppression of low-mass galaxy formation during reionization has only a small effect on the ionization history of the intergalactic medium. This lack of `self-regulation' arises due to the already efficient quenching of star formation by supernova feedback. It is only in models with gas supply-limited star formation that reionization feedback is effective at regulating galaxy growth. We similarly find that reionization has only a small effect on the stellar mass function, with no observationally detectable imprint at M* > 107.5 M⊙. However, patchy reionization has significant effects on individual galaxy masses, with variations of factors of 2-3 at z = 5 that correlate with environment.

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.

The Effects of Galaxy Interactions on Star Formation

NASA Astrophysics Data System (ADS)

Beverage, Aliza; Weiner, Aaron; Ramos Padilla, Andres; Ashby, Matthew; Smith, Howard A.

2018-01-01

Galaxy interactions are key events in galaxy evolution, and are widely thought to trigger significant increases in star formation. However, the mechanisms and timescales for these increases are still not well understood. In order to probe the effects of mergers, we undertook an investigation based on the Spitzer Interacting Galaxies Survey (SIGS), a sample of 102 nearby galaxies in 48 systems ranging from weakly interacting to near coalescence. Our study is unique in that we use both broadband photometry and a large sample of objects chosen to be statistically meaningful. Our data come from 32 broad bands ranging from the UV to far-IR, and we model spectral energy distributions (SEDs) using the Code for Investigating Galaxy Emission (CIGALE) to estimate physical characteristics for each galaxy. We find marginal statistical correlations between galaxy interaction strength and dust luminosity and the distribution of dust mass as a function of heating intensity. The specific star formation rates, however, do not show any enhancement across the interaction stages. This result challenges conventional wisdom that mergers induce star formation throughout galaxy interaction.The SAO REU program is funded in part by the National Science Foundation REU and Department of Defense ASSURE programs under NSF Grant no. 1262851, and by the Smithsonian Institution.

Classifying the Optical Morphology of Shocked POststarburst Galaxies

NASA Astrophysics Data System (ADS)

Stewart, Tess; SPOGs Team

2018-01-01

The Shocked POststarburst Galaxy Survey (SPOGS) is a sample of galaxies in transition from blue, star forming spirals to red, inactive ellipticals. These galaxies are earlier in the transition than classical poststarburst samples. We have classified the physical characteristics of the full sample of 1067 SPOGs in 7 categories, covering (1) their shape; (2) the relative prominence of their nuclei; (3) the uniformity of their optical color; (4) whether the outskirts of the galaxy were indicative of on-going star formation; (5) whether they are engaged in interactions with other galaxies, and if so, (6) the kinds of galaxies with which they are interacting; and (7) the presence of asymmetrical features, possibly indicative of recent interactions. We determined that a plurality of SPOGs are in elliptical galaxies, indicating morphological transformations may tend to conclude before other indicators of transitions have faded. Further, early-type SPOGs also tend to have the brightest optical nuclei. Most galaxies do not show signs of current or recent interactions. We used these classifications to search for correlations between qualitative and quantitative characteristics of SPOGs using Sloan Digital Sky Survey and Wide-field Infrared Survey Explorer magnitudes. We find that relative optical nuclear brightness is not a good indicator of the presence of an active galactic nuclei and that galaxies with visible indications of active star formation also cluster in optical color and diagnostic line ratios.

Galaxy bias from galaxy-galaxy lensing in the DES science verification data

NASA Astrophysics Data System (ADS)

Prat, J.; Sánchez, C.; Miquel, R.; Kwan, J.; Blazek, J.; Bonnett, C.; Amara, A.; Bridle, S. L.; Clampitt, J.; Crocce, M.; Fosalba, P.; Gaztanaga, E.; Giannantonio, T.; Hartley, W. G.; Jarvis, M.; MacCrann, N.; Percival, W. J.; Ross, A. J.; Sheldon, E.; Zuntz, J.; Abbott, T. M. C.; Abdalla, F. B.; Annis, J.; Benoit-Lévy, A.; Bertin, E.; Brooks, D.; Burke, D. L.; Carnero Rosell, A.; Carrasco Kind, M.; Carretero, J.; Castander, F. J.; da Costa, L. N.; DePoy, D. L.; Desai, S.; Diehl, H. T.; Doel, P.; Eifler, T. F.; Evrard, A. E.; Fausti Neto, A.; Flaugher, B.; Frieman, J.; Gerdes, D. W.; Goldstein, D. A.; Gruen, D.; Gruendl, R. A.; Gutierrez, G.; Honscheid, K.; James, D. J.; Kuehn, K.; Kuropatkin, N.; Lahav, O.; Lima, M.; Marshall, J. L.; Melchior, P.; Menanteau, F.; Nord, B.; Plazas, A. A.; Reil, K.; Romer, A. K.; Roodman, A.; Sanchez, E.; Scarpine, V.; Schubnell, M.; Sevilla-Noarbe, I.; Smith, R. C.; Soares-Santos, M.; Sobreira, F.; Suchyta, E.; Swanson, M. E. C.; Tarle, G.; Thomas, D.; Walker, A. R.

2018-01-01

We present a measurement of galaxy-galaxy lensing around a magnitude-limited (iAB < 22.5) sample of galaxies from the dark energy survey science verification (DES-SV) data. We split these lenses into three photometric-redshift bins from 0.2 to 0.8, and determine the product of the galaxy bias b and cross-correlation coefficient between the galaxy and dark matter overdensity fields r in each bin, using scales above 4 h-1 Mpc comoving, where we find the linear bias model to be valid given our current uncertainties. We compare our galaxy bias results from galaxy-galaxy lensing with those obtained from galaxy clustering and CMB lensing for the same sample of galaxies, and find our measurements to be in good agreement with those in Crocce et al., while, in the lowest redshift bin (z ∼ 0.3), they show some tension with the findings in Giannantonio et al. We measure b · r to be 0.87 ± 0.11, 1.12 ± 0.16 and 1.24 ± 0.23, respectively, for the three redshift bins of width Δz = 0.2 in the range 0.2 < z < 0.8, defined with the photometric-redshift algorithm BPZ. Using a different code to split the lens sample, TPZ, leads to changes in the measured biases at the 10-20 per cent level, but it does not alter the main conclusion of this work: when comparing with Crocce et al. we do not find strong evidence for a cross-correlation parameter significantly below one in this galaxy sample, except possibly at the lowest redshift bin (z ∼ 0.3), where we find r = 0.71 ± 0.11 when using TPZ, and 0.83 ± 0.12 with BPZ.

Chemically-Deduced Star Formation Histories Of Dwarf Galaxies Using Barium

NASA Astrophysics Data System (ADS)

Duggan, Gina; Kirby, Evan

2017-06-01

Dwarf galaxies offer a unique opportunity to study the competing forces of galaxy evolution. Their simpler history (i.e., small size, fewer major mergers, and lack of active galactic nuclei) enables us to isolate different physical mechanisms more easily. The effects of these mechanisms are imprinted on the galaxy's star formation history. Traditionally, star formation histories are determined from color-magnitude diagrams. However, chemical abundances can increase the precision of this measurement. Here we present a simplistic galactic chemical evolution model to infer the star formation history. Chemical abundances are measured from spectra obtained with Keck/DEIMOS medium-resolution spectroscopy for over a hundred red giant stars from several satellite dwarf spheroidal galaxies and globular clusters. We focus our work on iron and barium abundances because they predominantly trace Type Ia supernovae and asymptotic giant branch stars, respectively. The different timescales of these two nucleosynthetic sources can be used to measure a finely resolved star formation history, especially when combined with existing [α/Fe] measurements. These models will inform the details of early star formation in dwarf galaxies and how it is affected by various physical processes, such as reionization and tidal stripping.

On the importance of using appropriate spectral models to derive physical properties of galaxies at 0.7 < z < 2.8

NASA Astrophysics Data System (ADS)

Pacifici, Camilla; da Cunha, Elisabete; Charlot, Stéphane; Rix, Hans-Walter; Fumagalli, Mattia; Wel, Arjen van der; Franx, Marijn; Maseda, Michael V.; van Dokkum, Pieter G.; Brammer, Gabriel B.; Momcheva, Ivelina; Skelton, Rosalind E.; Whitaker, Katherine; Leja, Joel; Lundgren, Britt; Kassin, Susan A.; Yi, Sukyoung K.

2015-02-01

Interpreting observations of distant galaxies in terms of constraints on physical parameters - such as stellar mass (M★), star formation rate (SFR) and dust optical depth ({hat{τ}V}) - requires spectral synthesis modelling. We analyse the reliability of these physical parameters as determined under commonly adopted `classical' assumptions: star formation histories assumed to be exponentially declining functions of time, a simple dust law and no emission-line contribution. Improved modelling techniques and data quality now allow us to use a more sophisticated approach, including realistic star formation histories, combined with modern prescriptions for dust attenuation and nebular emission. We present a Bayesian analysis of the spectra and multiwavelength photometry of 1048 galaxies from the 3D-HST survey in the redshift range 0.7 < z < 2.8 and in the stellar mass range 9 ≲ log (M★/M⊙) ≲ 12. We find that, using the classical spectral library, stellar masses are systematically overestimated (˜0.1 dex) and SFRs are systematically underestimated (˜0.6 dex) relative to our more sophisticated approach. We also find that the simultaneous fit of photometric fluxes and emission-line equivalent widths helps break a degeneracy between SFR and {hat{τ}V}, reducing the uncertainties on these parameters. Finally, we show how the biases of classical approaches can affect the correlation between M★ and SFR for star-forming galaxies (the `star-formation main sequence'). We conclude that the normalization, slope and scatter of this relation strongly depend on the adopted approach and demonstrate that the classical, oversimplified approach cannot recover the true distribution of M★ and SFR.

The Arecibo Galaxy Environment Survey (AGES) - HI Observations of the Isolated Galaxy UGC 2082

NASA Astrophysics Data System (ADS)

Taber, Timothy M.; Minchin, R.; AGES

2011-01-01

The Arecibo Galactic Environment Survey (AGES) is a 21-cm neutral hydrogen survey utilizing the Arecibo L-band Feed Array on the 305-m radio telescope at Arecibo Observatory. AGES uses a bandwidth of 100 MHz, allowing the detection of galaxies out to heliocentric velocities of 20000 km/s. Many different galaxy environments are being examined in AGES including isolated galaxies, where one objective is to find possible low surface brightness companion galaxies. The field surrounding isolated galaxy UGC 2082 was examined for this project, and 90 possible sources were found in the data cube. Of these, 46 are regarded as definite detections; the others will be re-observed with the L-Band Wide receiver at Arecibo Observatory in order to confirm their reality. Using optical data from the Sloan Digital Sky Survey and SuperCOSMOS the most likely optical counterparts have been chosen for each 21-cm source. 24 of the detected HI sources have no clear optical counterpart, many of these being dubious detections. A very faint companion galaxy to UGC 2082 was found at a heliocentric velocity of 590 km/s. This source is located approximately 66.5 arcminutes north of UGC 2082 (which has a measured heliocentric velocity of 713 km/s). Using the published Tully-Fisher distance to UGC 2082 of 14.7 Mpc, the projected physical separation of the two galaxies is 284.4 kpc. Another objective of AGES is to gain insight on the HI mass function and the large-scale structure of the universe. All of the detected sources in this data were plotted by right ascension or declination versus heliocentric velocity. These plots showed noticeable structure at both 5500 km/s and 11000 km/s. The Arecibo Observatory is part of the National Astronomy and Ionosphere Center, which is operated by Cornell University under a cooperative agreement with the National Science Foundation.

A BIRD'S EYE VIEW OF A GALAXY COLLISION

NASA Technical Reports Server (NTRS)

2002-01-01

What appears as a bird's head, leaning over to snatch up a tasty meal, is a striking example of a galaxy collision in NGC 6745. A large spiral galaxy, with its nucleus still intact, peers at the smaller passing galaxy (nearly out of the field of view at lower right), while a bright blue beak and bright whitish-blue top feathers show the distinct path taken during the smaller galaxy's journey. These galaxies did not merely interact gravitationally as they passed one another, they actually collided. When galaxies collide, the stars that normally comprise the major portion of the luminous mass of each of the two galaxies will almost never collide with each other, but will pass rather freely between each other with little damage. This occurs because the physical size of individual stars is tiny compared to their typical separations, making the chance of physical encounter relatively small. In our own Milky Way galaxy, the space between our Sun and our nearest stellar neighbor, Proxima Centauri (part of the Alpha Centauri triple system), is a vast 4.3 light-years. However, the situation is quite different for the interstellar media in the above two galaxies - material consisting largely of clouds of atomic and molecular gases and of tiny particles of matter and dust, strongly coupled to the gas. Wherever the interstellar clouds of the two galaxies collide, they do not freely move past each other without interruption but, rather, suffer a damaging collision. High relative velocities cause ram pressures at the surface of contact between the interacting interstellar clouds. This pressure, in turn, produces material densities sufficiently extreme as to trigger star formation through gravitational collapse. The hot blue stars in this image are evidence of this star formation. This image was created by the Hubble Heritage Team using NASA Hubble Space Telescope archive data taken with the Wide Field Planetary Camera 2 in March 1996. Members of the science team, which include

Galaxy And Mass Assembly (GAMA): the effect of galaxy group environment on active galactic nuclei

NASA Astrophysics Data System (ADS)

Gordon, Yjan A.; Pimbblet, Kevin A.; Owers, Matt S.; Bland-Hawthorn, Joss; Brough, Sarah; Brown, Michael J. I.; Cluver, Michelle E.; Croom, Scott M.; Holwerda, Benne W.; Loveday, Jonathan; Mahajan, Smriti; Wang, Lingyu

2018-04-01

In galaxy clusters, efficiently accreting active galactic nuclei (AGNs) are preferentially located in the infall regions of the cluster projected phase-space, and are rarely found in the cluster core. This has been attributed to both an increase in triggering opportunities for infalling galaxies, and a reduction of those mechanisms in the hot, virialized, cluster core. Exploiting the depth and completeness (98 per cent at r < 19.8 mag) of the Galaxy And Mass Assembly survey (GAMA), we probe down the group halo mass function to assess whether AGNs are found in the same regions in groups as they are in clusters. We select 451 optical AGNs from 7498 galaxies with log10(M*/M⊙) > 9.9 in 695 groups with 11.53 ≤ log10(M200/M⊙) ≤ 14.56 at z < 0.15. By analysing the projected phase-space positions of these galaxies, we demonstrate that when split both radially, and into physically derived infalling and core populations, AGN position within group projected phase-space is dependent on halo mass. For groups with log10(M200/M⊙) > 13.5, AGNs are preferentially found in the infalling galaxy population with 3.6σ confidence. At lower halo masses, we observe no difference in AGN fraction between core and infalling galaxies. These observations support a model where a reduced number of low-speed interactions, ram pressure stripping and intra-group/cluster medium temperature, the dominance of which increase with halo mass, work to inhibit AGN in the cores of groups and clusters with log10(M200/M⊙) > 13.5, but do not significantly affect nuclear activity in cores of less massive structures.

Galaxies and Their Host Dark Matter Structures

NASA Astrophysics Data System (ADS)

Hahn, ChangHoon

Through their connection with dark matter structures, galaxies act as tracers of the underlying matter distribution in the Universe. Their observed spatial distribution allows us to precisely measure large scale structure and effectively test cosmological models that explain the content, geometry, and history of the Universe. Current observations from galaxy surveys such as the Baryon Oscillation Spectroscopic Survey have already probed vast cosmic volumes with millions of galaxies and ushered in an era of precision cosmology. The next surveys will probe over an order of magnitude more. With this unprecedented statistical power, the bottleneck of scientific discovery is in the methodology. In this dissertation, I address major methodological challenges in constraining cosmology with the large-scale distribution of galaxies. I develop a robust framework for treating systematic effects, which significantly bias galaxy clustering measurements. I apply new innovative approaches to probabilistic parameter inference that challenge and test the in- correct assumptions of the standard approach. Furthermore, I use precise predictions of structure formation from cosmology and observations of galaxies during the last eight billion years to develop detailed models of how galaxies are impacted by their host dark matter structures. These models provide key insight into the galaxy-halo connection, which bridges the gap between cosmology theory and observations. They also answer crucial questions of how galaxies form and evolve. The developments in this dissertation will help unlock the full potential of future observations and allow us to precisely test cosmological models, General Relativity and modified gravity scenarios, and even particle physics theory beyond the Standard Model.

A Spectroscopic Survey of Lensed Dwarf Galaxies at 1

NASA Astrophysics Data System (ADS)

Alavi, Anahita; Siana, Brian; gburek, Timothy; Richard, Johan; Teplitz, Harry; Rafelski, Marc; Stark, Daniel P.; Anahita Alavi

2018-01-01

High-redshift dwarf galaxies (M<109 M⊙) are one of the primary targets of the James Web Space Telescope. Recent studies have suggested that these galaxies are different than their bright counterparts, as they follow a divergent evolutionary history of star formation. In our previous study, utilizing the magnification from massive clusters of galaxies (Hubble Frontier Fields), we found a large sample of dwarf star-forming galaxies at the peak epoch of star formation (1physical properties are different than normal galaxies, we have conducted a spectroscopic survey of these lensed faint galaxies using the Multi-Object Near-IR Spectrograph (MOSFIRE) at the Keck observatory. In this talk, I will present their nebular dust attenuation measurements using the ratio of Balmer lines (i.e., Balmer decrement) and compare with their stellar dust attenuation (i.e., from UV spectral slopes). I will also show that these faint galaxies follow a steep dust extinction curve (i.e., SMC like).

Galaxy Formation from the Primordial Black Holes

NASA Astrophysics Data System (ADS)

Morikawa, Masahiro

2017-12-01

Supermassive black hole (SMBH) of size MBH = 106-10M⊙ is common in the Universe and it defines the center of the galaxy. A galaxy and the SMBH are generally thought to have co-evolved. However, the SMBH cannot evolve so fast as commonly observed even at redshift z > 6. Therefore, we explore a natural hypothesis that the SMBH has been already formed mature at z ⪆ 10 before stars and galaxies. The SMBH forms energetic jets and out-flows which trigger massive star formation in the ambient gas. They eventually construct globular clusters and classical bulge as well as the body of elliptical galaxies. We propose simple models which implement these processes. We point out that the globular clusters and classical bulges have a common origin but are in different phases. The same is true for the elliptical and spiral galaxies. Physics behind these phase division is the runaway star formation process with strong feedback to SMBH. This is similar to the forest-fire model that displays self-organized criticality.

Can Low-Luminosity Galaxies Reionize the Universe?

NASA Astrophysics Data System (ADS)

Ferguson, Harry

2017-08-01

The prevailing wisdom is that low-luminosity galaxies are responsible for cosmic reionization. If this is true, then low-luminosity galaxies at high redshift have to be different from most of the low-luminosity galaxies studied to date at low redshift, which absorb too much of their ionizing radiation. While it is possible that high-z dwarf galaxies have the same metallicity at fixed mass and star-formation rate as low-redshift galaxies, they are different in one key respect. At fixed dark-halo mass, they are probably much denser (having collapsed earlier). This could lead to higher star-formation surface densities more capable of creating cavities in the ISM. But the denser halos of surrounding gas could be harder to clear. There is a critical need for further observations to validate and test physical models for the trends of escaping ionizing continuum with redshift, luminosity, and surface density. JWST will not be able to measure ionizing radiation during the epoch of reionization because the IGM absorbs most of the photons. To prepare for JWST, we need to use the ultraviolet capabilities of HST to measure diverse samples of galaxies at z<3, where we can see the photons and quantify the trends with other galaxy properties. As a complement to other studies, we propose to constrain the Lyman-continuum emission from 8 relatively low-luminosity strongly-lensed galaxies at 1

Unbiased estimates of galaxy scaling relations from photometric redshift surveys

NASA Astrophysics Data System (ADS)

Rossi, Graziano; Sheth, Ravi K.

2008-06-01

Many physical properties of galaxies correlate with one another, and these correlations are often used to constrain galaxy formation models. Such correlations include the colour-magnitude relation, the luminosity-size relation, the fundamental plane, etc. However, the transformation from observable (e.g. angular size, apparent brightness) to physical quantity (physical size, luminosity) is often distance dependent. Noise in the distance estimate will lead to biased estimates of these correlations, thus compromising the ability of photometric redshift surveys to constrain galaxy formation models. We describe two methods which can remove this bias. One is a generalization of the Vmax method, and the other is a maximum-likelihood approach. We illustrate their effectiveness by studying the size-luminosity relation in a mock catalogue, although both methods can be applied to other scaling relations as well. We show that if one simply uses photometric redshifts one obtains a biased relation; our methods correct for this bias and recover the true relation.

Unstable Box Orbits in Cuspy Elliptical Galaxies

NASA Technical Reports Server (NTRS)

Hasan, H.; Pfenniger, D.

1996-01-01

The aim of this work is to gain physical insight into the role played by a concentrated central mass in affecting the shape of elliptical galaxies, by examining its effect on the stability of box orbits which are the backbone of triaxial elliptical galaxies. Ample observational evidence is now available for the existence of a central mass concentration or central cusps in galaxies. The central mass is expected to cause orbital stochasticity and chaotic mixing of orbits, which could have ramifications on galactic evolution. We investigate here the interplay between potential cuspiness and eccentricity on the stability of axial orbits in a scale-free potential in a simple, preliminary attempt to characterize this effect.

Multi-wavelength Searches for Massive Black Holes in Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Reines, Amy E.

2018-01-01

Contrary to conventional wisdom, low-mass, physically small dwarf galaxies can indeed host massive black holes (BHs). Moreover, the population and properties of BHs in nearby dwarf galaxies hold clues to the formation of the first seed BHs in the earlier Universe. Identifying BHs in dwarf galaxies, however, is challenging. AGNs powered by smaller BHs are less luminous and more difficult to detect than typical AGNs in more massive systems, and low-mass galaxies generally have ongoing star formation, gas and dust that can mimic or mask signatures of BH accretion. With these challenges in mind, I will present ongoing multi-wavelength searches for AGNs in dwarf galaxies, as well as follow-up studies of existing samples. I will also discuss how this work has implications for directly detecting BH activity in the first galaxies at high redshift.

Dust-obscured Galaxies in the Local Universe

NASA Astrophysics Data System (ADS)

Hwang, Ho Seong; Geller, Margaret J.

2013-06-01

We use Wide-field Infrared Survey Explorer (WISE), AKARI, and Galaxy Evolution Explorer (GALEX) data to select local analogs of high-redshift (z ~ 2) dust obscured galaxies (DOGs). We identify 47 local DOGs with S 12 μm/S 0.22 μm >= 892 and S 12 μm > 20 mJy at 0.05 < z < 0.08 in the Sloan Digital Sky Survey data release 7. The infrared (IR) luminosities of these DOGs are in the range 3.4 × 1010 (L ⊙) <~ L IR <~ 7.0 × 1011 (L ⊙) with a median L IR of 2.1 × 1011 (L ⊙). We compare the physical properties of local DOGs with a control sample of galaxies that have lower S 12 μm/S 0.22 μm but have similar redshift, IR luminosity, and stellar mass distributions. Both WISE 12 μm and GALEX near-ultraviolet (NUV) flux densities of DOGs differ from the control sample of galaxies, but the difference is much larger in the NUV. Among the 47 DOGs, 36% ± 7% have small axis ratios in the optical (i.e., b/a < 0.6), larger than the fraction among the control sample (17% ± 3%). There is no obvious sign of interaction for many local DOGs. No local DOGs have companions with comparable optical magnitudes closer than ~50 kpc. The large- and small-scale environments of DOGs are similar to the control sample. Many physical properties of local DOGs are similar to those of high-z DOGs, even though the IR luminosities of local objects are an order of magnitude lower than for the high-z objects: the presence of two classes (active galactic nuclei- and star formation-dominated) of DOGs, abnormal faintness in the UV rather than extreme brightness in the mid-IR, and diverse optical morphology. These results suggest a common underlying physical origin of local and high-z DOGs. Both seem to represent the high-end tail of the dust obscuration distribution resulting from various physical mechanisms rather than a unique phase of galaxy evolution.

Dust-obscured galaxies in the local universe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hwang, Ho Seong; Geller, Margaret J., E-mail: hhwang@cfa.harvard.edu, E-mail: mgeller@cfa.harvard.edu

We use Wide-field Infrared Survey Explorer (WISE), AKARI, and Galaxy Evolution Explorer (GALEX) data to select local analogs of high-redshift (z ∼ 2) dust obscured galaxies (DOGs). We identify 47 local DOGs with S {sub 12μm}/S {sub 0.22μm} ≥ 892 and S {sub 12μm} > 20 mJy at 0.05 < z < 0.08 in the Sloan Digital Sky Survey data release 7. The infrared (IR) luminosities of these DOGs are in the range 3.4 × 10{sup 10} (L {sub ☉}) ≲ L {sub IR} ≲ 7.0 × 10{sup 11} (L {sub ☉}) with a median L {sub IR} of 2.1more » × 10{sup 11} (L {sub ☉}). We compare the physical properties of local DOGs with a control sample of galaxies that have lower S {sub 12μm}/S {sub 0.22μm} but have similar redshift, IR luminosity, and stellar mass distributions. Both WISE 12 μm and GALEX near-ultraviolet (NUV) flux densities of DOGs differ from the control sample of galaxies, but the difference is much larger in the NUV. Among the 47 DOGs, 36% ± 7% have small axis ratios in the optical (i.e., b/a < 0.6), larger than the fraction among the control sample (17% ± 3%). There is no obvious sign of interaction for many local DOGs. No local DOGs have companions with comparable optical magnitudes closer than ∼50 kpc. The large- and small-scale environments of DOGs are similar to the control sample. Many physical properties of local DOGs are similar to those of high-z DOGs, even though the IR luminosities of local objects are an order of magnitude lower than for the high-z objects: the presence of two classes (active galactic nuclei- and star formation-dominated) of DOGs, abnormal faintness in the UV rather than extreme brightness in the mid-IR, and diverse optical morphology. These results suggest a common underlying physical origin of local and high-z DOGs. Both seem to represent the high-end tail of the dust obscuration distribution resulting from various physical mechanisms rather than a unique phase of galaxy evolution.« less

Seyfert Galaxies in the Infrared

NASA Astrophysics Data System (ADS)

Ruiz-Nishiky, Milagros

1997-10-01

This thesis contains complementary aspects of the Seyfert phenomenon, each of which is analysed to bring a better understanding of present unification theories. Observations of the nuclear regions of various types of Seyfert galaxies were mostly made at infrared wavelengths which allow the study of dusty environments and provide new information on the physical conditions of these objects. For example, near infrared spectroscopy of Seyfert 2 galaxies revealed that there is a subclass of type 2 Seyferts with hot IR excess at ~3μm with broad IR emission lines suggesting that some Seyfert 2s do in fact contain a hidden Seyfert 1 nucleus. Additional spectropolarimetry showed that the scattering screens, postulated in the standard model, are not always present in Seyfert 2s. At mid infrared wavelengths, it was found that the 10 μm nuclear emission of Seyferts with broad emission lines is intrinsically brighter than that of Seyferts with no broad lines. The extended 10μm emission shows that Seyfert 2 galaxies present enhanced star-formation when compared to Seyfert 1s. Both results pose obstacles for present unification ideas and I discuss possible interpretations to these observations. Seyfert galaxies were also observed at radio wavelengths to study their large scale emission of 1-0 CO. Surprisingly, this emission usually related with star formation activity was found to be similar in both types of Seyfert galaxies and therefore does not explain why Seyfert 2 galaxies have enhanced star formation as concluded in the 10μm study. A study of galaxy morphology and companions in this set of Seyferts shows at a significant statistical level that Seyfert 2s present a higher incidence of asymmetric morphologies compared to Seyfert 1s and field galaxies, and therefore are undergoing gravitational perturbations which may induce star formation. Near infrared spectroscopy of a large sample of Seyfert galaxies is analysed to study the excitation mechanisms of (FeII) and H2 lines

Wobbling The Galactic Disk with Bombardment of Satellite Galaxies

NASA Astrophysics Data System (ADS)

D'Onghia, Elena

We propose to assess the effect of impacts of large visible satellite galaxies on a disk, as well as the relevance of the continuing bombardment of the Galactic disk by dark matter clumps as predicted by the current cosmological framework that can wobble the disk, heating it and eventually exciting ragged spiral structures. In particular, we make detailed predictions for observable features such as spiral arms, rings and their associated stars in galactic disks and relate them to the physical processes that drive their formation and evolution in our Milky Way galaxy and nearby spirals. To do this, we will combine analytic methods and numerical simulations that allow us to calculate observables, which we will compare to present and forthcoming observations. Our methodology utilizes a combination of state of the art hydrodynamic simulations of galaxy evolution and multi- wavelength radiative transfer simulations. Our primary goals are: (1) To identify the physical processes that are responsible for spiral structure formation observed in our Milky Way and nearby disk galaxies, from the flocculent to grand- designed spiral galaxies and to provide observable signatures to be compared with data on nearby galaxies combining maps of 24 micron emission (Spitzer) and cold gas, CO (Heracles) and HI (THINGS). (2) To explore different morphologies of spiral galaxies: from the multi-armed galaxies to the Milky Way sized galaxies with few arms. (3) For a Milky Way disk we will assess the effect of impacts of substructures passing through the disk to origin the asymmetry in the number density of stars recently discovered from SDSS and SEGUE data and confirmed from RAVE data. We will also investigate the disk heating in the vertical plane due to the formation of vertical oscillations that are produced by the impact and migration of stars in the disk as consequence of the heating as compared to the classical stellar migration mechanism. (4) We will measure the spiral pattern speed

Galaxy Classification using Machine Learning

NASA Astrophysics Data System (ADS)

Fowler, Lucas; Schawinski, Kevin; Brandt, Ben-Elias; widmer, Nicole

2017-01-01

We present our current research into the use of machine learning to classify galaxy imaging data with various convolutional neural network configurations in TensorFlow. We are investigating how five-band Sloan Digital Sky Survey imaging data can be used to train on physical properties such as redshift, star formation rate, mass and morphology. We also investigate the performance of artificially redshifted images in recovering physical properties as image quality degrades.

The Origin of the Relation between Metallicity and Size in Star-forming Galaxies

NASA Astrophysics Data System (ADS)

Sánchez Almeida, J.; Dalla Vecchia, C.

2018-06-01

For the same stellar mass, physically smaller star-forming galaxies are also metal richer. What causes the relation remains unclear. The central star-forming galaxies in the EAGLE cosmological numerical simulation reproduce the observed trend. We use them to explore the origin of the relation assuming that the physical mechanism responsible for the anticorrelation between size and gas-phase metallicity is the same in the simulated and the observed galaxies. We consider the three most likely causes: (1) metal-poor gas inflows feeding the star formation (SF) process, (2) metal-rich gas outflows particularly efficient in shallow gravitational potentials, and (3) enhanced efficiency of the SF process in compact galaxies. Outflows (cause 2) and enhanced SF efficiency (cause 3) can be discarded. Metal-poor gas inflows (cause 1) produce the correlation in the simulated galaxies. Galaxies grow in size with time, so those that receive gas later are both metal poorer and larger, giving rise to the observed anticorrelation. As expected within this explanation, larger galaxies have younger stellar populations. We explore the variation with redshift of the relation, which is maintained up to, at least, redshift 8.

Dynamical Constraints On The Galaxy-Halo Connection

NASA Astrophysics Data System (ADS)

Desmond, Harry

2017-07-01

galaxy datasets become larger and more precise in the future, we may expect these methods to continue providing insight into the relation between the visible and dark matter content of the universe and the physical processes that underlie it.

The Universe's Most Extreme Star-forming Galaxies

NASA Astrophysics Data System (ADS)

Casey, Caitlin

2017-06-01

Dusty star-forming galaxies host the most intense stellar nurseries in the Universe. Their unusual characteristics (SFRs=200-2000Msun/yr, Mstar>1010 Msun) pose a unique challenge for cosmological simulations and galaxy formation theory, particularly at early times. Although rare today, they were factors of 1000 times more prevalent at z~2-5, contributing significantly to the buildup of the Universe's stellar mass and the formation of high-mass galaxies. At even earlier times (within 1Gyr post Big Bang) they could have played a pivotal role in enriching the IGM. However, an ongoing debate lingers as to their evolutionary origins at high-redshift, whether or not they are triggered by major mergers of gas-rich disk galaxies, or if they are solitary galaxies continually fed pristine gas from the intergalactic medium. Furthermore, their presence in early protoclusters, only revealed quite recently, pose intriguing questions regarding the collapse of large scale structure. I will discuss some of the latest observational programs dedicated to understanding dust-obscuration in and gas content of the early Universe, their context in the cosmic web, and future long-term observing campaigns that may reveal their relationship to `normal’ galaxies, thus teaching us valuable lessons on the physical mechanisms of galaxy growth and the collapse of large scale structure in an evolving Universe.

Velocity field and physical conditions in the active lenticular galaxy NGC 3998

NASA Technical Reports Server (NTRS)

Blackman, C. P.; Wilson, A. S.; Ward, M. J.

1983-01-01

A rotating and expanding flattened distribution of gas is suggested by measurements of the emission line velocity field for the line elliptical/lenticular galaxy NGC 3998, using seven long slit spectrograms in five position angles. Expanding material kinetic energy values of 10 to the 53rd to 10 to the 54th ergs, together with the flat spectrum radio source and nucleus X-ray emission, indicate pronounced nuclear activity. Spectrophotometry of the galactic nucleus shows emission line strengths typical of shocks rather than of photoionization, and line ratios indicate a postshock temperature of 60,000 K and a preshock density of 25 particles/cu cm. Both the stars and the ionized gas of the galaxy have central velocity dispersions of 260 km/s. In view of the high rotational velocity of the stars, NGC 3998 is a lenticular rather than elliptical galaxy.

Active Galactic Nucleus Feedback in an Elliptical Galaxy with the Most Updated AGN Physics. I. Low Angular Momentum Case

NASA Astrophysics Data System (ADS)

Yuan, Feng; Yoon, DooSoo; Li, Ya-Ping; Gan, Zhao-Ming; Ho, Luis C.; Guo, Fulai

2018-04-01

We investigate the effects of AGN feedback on the cosmological evolution of an isolated elliptical galaxy by performing two-dimensional high-resolution hydrodynamical numerical simulations. The inner boundary of the simulation is chosen so that the Bondi radius is resolved. Compared to previous works, the two accretion modes—namely, hot and cold, which correspond to different accretion rates and have different radiation and wind outputs—are carefully discriminated, and the feedback effects by radiation and wind in each mode are taken into account. The most updated AGN physics, including the descriptions of radiation and wind from the hot accretion flows and wind from cold accretion disks, are adopted. Physical processes like star formation and SNe Ia and II are taken into account. We study the AGN light curve, typical AGN lifetime, growth of the black hole mass, AGN duty cycle, star formation, and X-ray surface brightness of the galaxy. We compare our simulation results with observations and find general consistency. Comparisons with previous simulation works find significant differences, indicating the importance of AGN physics. The respective roles of radiation and wind feedback are examined, and it is found that they are different for different problems of interest, such as AGN luminosity and star formation. We find that it is hard to neglect any of them, so we suggest using the names “cold feedback mode” and “hot feedback mode” to replace the currently used ones.

Hubble Space Telescope Imaging of Brightest Cluster Galaxies

NASA Astrophysics Data System (ADS)

Laine, Seppo; van der Marel, Roeland P.; Lauer, Tod R.; Postman, Marc; O'Dea, Christopher P.; Owen, Frazer N.

2003-02-01

We used the Hubble Space Telescope Wide Field Planetary Camera 2 to obtain I-band images of the centers of 81 brightest cluster galaxies (BCGs), drawn from a volume-limited sample of nearby BCGs. The images show a rich variety of morphological features, including multiple or double nuclei, dust, stellar disks, point-source nuclei, and central surface brightness depressions. High-resolution surface brightness profiles could be inferred for 60 galaxies. Of those, 88% have well-resolved cores. The relationship between core size and galaxy luminosity for BCGs is indistinguishable from that of Faber et al. (published in 1997, hereafter F97) for galaxies within the same luminosity range. However, the core sizes of the most luminous BCGs fall below the extrapolation of the F97 relationship rb~L1.15V. A shallower relationship, rb~L0.72V, fits both the BCGs and the core galaxies presented in F97. Twelve percent of the BCG sample lacks a well-resolved core; all but one of these BCGs have ``power law'' profiles. Some of these galaxies have higher luminosities than any power-law galaxy identified by F97 and have physical upper limits on rb well below the values observed for core galaxies of the same luminosity. These results support the idea that the central structure of early-type galaxies is bimodal in its physical properties but also suggest that there exist high-luminosity galaxies with power-law profiles (or unusually small cores). The BCGs in the latter category tend to fall at the low end of the BCG luminosity function and tend to have low values of the quantity α (the logarithmic slope of the metric luminosity as a function of radius, at 10 kpc). Since theoretical calculations have shown that the luminosities and α-values of BCGs grow with time as a result of accretion, this suggests a scenario in which elliptical galaxies evolve from power-law profiles to core profiles through accretion and merging. This is consistent with theoretical scenarios that invoke the

Gas Dynamics in Galaxy Clusters

NASA Astrophysics Data System (ADS)

McCourt, Michael Kingsley, Jr.

develop significant anisotropies with respect to the local magnetic field. This interesting regime is one of the frontiers in theoretical studies of fluid dynamics. Unlike other astrophysical environments of similar collisionality (e. g. accretion disk coronae), galaxy clusters are optically thin and subtend large angles on the sky. Thus, they are easily observed in the x-ray (to constrain thermal processes) and in the radio (to constrain non-thermal processes) and provide a wonderful environment to develop our understanding of dilute plasmas. This thesis studies the dynamics of the hot gas in galaxy clusters, which touches on all three of the above topics. Chapter 2 shows that galaxy clusters are likely to be unstable to a new, vigorous form of convection. As a dynamical process which involves thermodynamic and magnetic properties of the gas, this convection bears directly on our understanding of the physics of dilute plas- mas. Furthermore, by moving metals and thermal energy through the cluster, convection may change the cooling rate of the gas and thus significantly impact the process of galaxy formation. Cluster convection also impacts the use of clusters as cosmological probes. Convection may drive turbulence in clusters with mean Mach numbers of order-unity. This changes the force balance in clusters, decreasing the thermal energy of a cluster of a given mass. Current methods for using clusters to constrain dark energy rely on observational probes of the thermal energy as a proxy for total mass. The accuracy of these methods depends on how vigorous cluster convection is. Chapter 3 studies thermal instability in galaxy clusters. I argue that clusters are all likely to be thermally unstable, but that this instability only grows to large amplitude in a subset of systems. Later studies have applied this result to galaxy formation in clusters and shown that one can reproduce some features of the well-known non-self-similarity at the high mass end of the galaxy

Identifying Nearby Galaxy Outliers Using Neutral Hydrogen Scaling Relations

NASA Astrophysics Data System (ADS)

Mohammed, Steven; Schiminovich, D.

2013-01-01

Galaxies appear to be divided into two distinct families: blue, star-forming, gas-rich, spiral galaxies and red, gas-deficient, elliptical galaxies. However, the transition between these two families is not well understood. A galaxy's gas content could be a good indicator of processes that affect this transition. We assembled a catalog of physical properties for 535 nearby massive galaxies (redshifts 0.025 < z < 0.05; stellar masses M* > 108 solar masses) from various existing surveys to examine their neutral hydrogen (HI) gas content. We obtained HI data (e.g., HI masses and HI radii) from several surveys; other properties (e.g., stellar masses, light radii and star formation rates) were derived from the Sloan Digital Sky Survey (SDSS) and the Galaxy Evolution Explorer (GALEX). Our goal is to identify any outliers from scaling relations derived from galaxies in the GALEX Arecibo SDSS Survey (GASS) in hope that these outliers can provide us with insight into processes relevant to the blue-to-red-galaxy transition. Results indicate that our heterogeneous selection yields a sample that shows similar scaling relations as the GASS galaxies. For example, the atomic HI gas fraction (MHI/M*) decreases strongly as both stellar mass and stellar mass surface density increase. Here, we show recent work that investigates the HI distribution maps of our galaxies to identify environmental effects that might cause outliers to exist.

Feeding, Feedback and the Growth of Galaxies - Molecules as Tools for Probing Galaxy Evolution

NASA Astrophysics Data System (ADS)

Aalto, Susanne

2017-06-01

Cold gas plays a central role in feeding and regulating star formation and growth of supermassive black holes (SMBH) in galaxy nuclei. Particularly powerful activity occurs when interactions of gas-rich galaxies funnel large amounts of gas and dust into nuclei of luminous and ultra luminous infrared galaxies (LIRGs/ULIRGs). These dusty objects are of key importance to galaxy mass assembly over cosmic time. Some (U)LIRGS have deeply embedded galaxy nuclei that harbour a very active evolutionary stage of AGNs and/or starbursts. The nuclear activity will often drive mechanical feedback in the form of molecular winds, jets and outflows. This feedback can for example remove baryons from low-mass galaxies, prevent overgrowth of galaxies, be linked to the M_{BH}-σ relation, and explain "red-and dead" properties of local ellipticals. With the ALMA and NOEMA telescopes we can use molecules as diagnostic tools to probe the properties of dust-enshrouded galaxy nuclei and their associated cold winds and outflows. Their morphology, velocity structure, physical conditions and even chemistry can be studied at unprecedented sensitivity and resolution, opening new avenues to further our understanding of the growth of galaxies. I will give a brief review of the ALMA/NOEMA view of AGN and starburst radiative and mechanical feedback, and how it is linked to the properties of the nuclear power source. I will discuss the use of molecules (e.g. H_2O, H_3O^{+}, HCN, HCO^+, H_2S) for studying dusty nuclei and the nature of the embedded activity. We can, for example, investigate ionization rates and the impact of cosmic ray-, X-ray- and PDR-chemistry and the onset of outflows and winds. Interestingly, in some deeply obscured nuclei the chemistry shows strong similarities to that of Galactic hot cores. Finally I will show peculiar molecular jets and very recent ALMA observations at resolutions of tens of milli-arcseconds (few pc) of vibrationally excited HCN in opaque nuclei. These regions

Insights on star-formation histories and physical properties of 1.2 ≤z ≲ 4 Herschel-detected galaxies

NASA Astrophysics Data System (ADS)

Sklias, P.; Schaerer, D.; Elbaz, D.; Pannella, M.; Schreiber, C.; Cava, A.

2017-09-01

Aims: We aim to test the impact of using variable star-forming histories (SFHs) and the IR luminosity as a constrain on the physical parameters of high redshift dusty star-forming galaxies. We explore in particular the properties (SFHs, ages, timescales) of galaxies depending on their belonging to the "main sequence" of star-forming galaxies (MS). Methods: We performed spectral energy distribution (SED) fitting of the UV-to-NIR and FIR emissions of a moderately large sample of GOODS-Herschel galaxies, for which rich multi-wavelength, optical to IR observations are available. We tested different SFHs and the impact of imposing energy conservation in the SED fitting process, to help with issues like the age-extinction degeneracy and produce SEDs consistent with observations. Results: Our simple models produce well constrained SEDs for the broad majority of the sample (84%), with the notable exception of the very high LIR end, for which we have indications that the energy conservation hypothesis cannot hold true for a single component population approach. We observe trends in the preferences in SFHs among our sources depending on stellar mass M⋆ and z. Trends also emerge in the characteristic timescales of the SED models depending on the location on the SFR - M⋆ diagram. We show that whilst using the same available observational data, we can produce galaxies less star-forming than classically inferred, if we allow rapidly declining SFHs, while properly reproducing their observables. These sources, representing 7% of the sample, can be post-starbursts undergoing quenching, and their SFRs are potentially overestimated if inferred from their LIR. Based on the trends observed in the rising SFH fits we explore a simple evolution model for stellar mass build-up over the considered time period. Conclusions: Our approach successfully breaks the age-extinction degeneracy, and enables to evaluate properly the SFRs of the sources in the SED fitting process. Fitting without

Weak-Lensing Determination of the Mass in Galaxy Halos

NASA Astrophysics Data System (ADS)

Smith, D. R.; Bernstein, G. M.; Fischer, P.; Jarvis, M.

2001-04-01

We detect the weak gravitational lensing distortion of 450,000 background galaxies (20galaxies (R<18) selected from the Las Campanas Redshift Survey (LCRS). This is the first detection of weak lensing by field galaxies of known redshift, and as such permits us to reconstruct the shear profile of the typical field galaxy halo in absolute physical units (modulo H0), and to investigate the dependence of halo mass upon galaxy luminosity. This is also the first galaxy-galaxy lensing study for which the calibration errors due to uncertainty in the background galaxy redshift distribution and the seeing correction are negligible. Within a projected radius of 200 h-1 kpc, the shear profile is consistent with an isothermal profile with circular velocity vc=164+/-20 km s-1 for an L* galaxy, consistent with the typical circular velocity for the disks of spirals at this luminosity. This halo mass normalization, combined with the halo profile derived by Fischer and coworkers from a galaxy-galaxy lensing analysis of the Sloan Digital Sky Survey, places a lower limit of (2.7+/-0.6)×1012 h-1 Msolar on the mass of an L* galaxy halo, in good agreement with the satellite galaxy studies of Zaritsky et al. Given the known luminosity function of LCRS galaxies, and assuming that M~Lβ for galaxies, we determine that the mass within 260 h-1 kpc of normal galaxies contributes Ω=0.16+/-0.03 to the density of the universe (for β=1) or Ω=0.24+/-0.06 for β=0.5. These lensing data suggest that 0.6<β<2.4 (95% confidence level), only marginally in agreement with the usual β~0.5 Faber-Jackson or Tully-Fisher scaling. This is the most complete direct inventory of the matter content of the universe to date.

Report on the ESO and Excellence Cluster Universe Workshop "Galaxy Ecosystem: Flow of Baryons through Galaxies"

NASA Astrophysics Data System (ADS)

Mainieri, V.; Popesso, P.

2017-12-01

This conference focussed on the "baryon cycle", namely the flow of baryons through galaxies. The following aspects were discussed: a) the gas inflow into systems through streams of pristine gas or as drizzles of recycled material; b) the conversion of this gas into stars; and c) the ejection of gas enriched with heavy elements through powerful outflows. Understanding these different but mutually connected phases is of fundamental importance when studying the details of galaxy formation and evolution through cosmic time. This conference was held following the month-long workshop of the Munich Institute for Astro- and Particle Physics (MIAPP) entitled: "In & out: What rules the galaxy baryon cycle?" It therefore provided an opportunity to share the main outcomes of the MIAPP workshop with a larger audience, including many young outstanding scientists who could not attend the MIAPP workshop.

Angular momentum of dwarf galaxies

NASA Astrophysics Data System (ADS)

Kurapati, Sushma; Chengalur, Jayaram N.; Pustilnik, Simon; Kamphuis, Peter

2018-05-01

Mass and specific angular momentum are two fundamental physical parameters of galaxies. We present measurements of the baryonic mass and specific angular momentum of 11 void dwarf galaxies derived from neutral hydrogen (HI) synthesis data. Rotation curves were measured using 3D and 2D tilted ring fitting routines, and the derived curves generally overlap within the error bars, except in the central regions where, as expected, the 3D routines give steeper curves. The specific angular momentum of void dwarfs is found to be high compared to an extrapolation of the trends seen for higher mass bulge-less spirals, but comparable to that of other dwarf irregular galaxies that lie outside of voids. As such, our data show no evidence for a dependence of the specific angular momentum on the large scale environment. Combining our data with the data from the literature, we find a baryonic threshold of ˜109.1 M⊙ for this increase in specific angular momentum. Interestingly, this threshold is very similar to the mass threshold below which the galaxy discs start to become systematically thicker. This provides qualitative support to the suggestion that the thickening of the discs, as well as the increase in specific angular momentum, are both results of a common physical mechanism, such as feedback from star formation. Quantitatively, however, the amount of star formation observed in our dwarfs appears insufficient to produce the observed increase in specific angular momentum. It is hence likely that other processes, such as cold accretion of high angular momentum gas, also play a role in increasing the specific angular momentum.

SPECTROSCOPY OF LUMINOUS COMPACT BLUE GALAXIES IN DISTANT CLUSTERS. II. PHYSICAL PROPERTIES OF dE PROGENITOR CANDIDATES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Crawford, S. M.; Wirth, Gregory D.; Bershady, M. A.

2016-02-01

Luminous Compact Blue Galaxies (LCBGs) are an extreme star-bursting population of galaxies that were far more common at earlier epochs than today. Based on spectroscopic and photometric measurements of LCBGs in massive (M > 10{sup 15} M{sub ⊙}), intermediate redshift (0.5 < z < 0.9) galaxy clusters, we present their rest-frame properties including star formation rate, dynamical mass, size, luminosity, and metallicity. The appearance of these small, compact galaxies in clusters at intermediate redshift helps explain the observed redshift evolution in the size–luminosity relationship among cluster galaxies. In addition, we find the rest-frame properties of LCBGs appearing in galaxy clusters are indistinguishable from field LCBGs atmore » the same redshift. Up to 35% of the LCBGs show significant discrepancies between optical and infrared indicators of star formation, suggesting that star formation occurs in obscured regions. Nonetheless, the star formation for LCBGs shows a decrease toward the center of the galaxy clusters. Based on their position and velocity, we estimate that up to 10% of cluster LCBGs are likely to merge with another cluster galaxy. Finally, the observed properties and distributions of the LCBGs in these clusters lead us to conclude that we are witnessing the quenching of the progenitors of dwarf elliptical galaxies that dominate the number density of present-epoch galaxy clusters.« less

Galaxy Morphology Revealed By SDSS: Blue Elliptical Galaxies

NASA Astrophysics Data System (ADS)

Ann, Hong Bae

The Sloan Digital Sky Survey (SDSS) reveals many new features of galaxy morphologies. Among others, the discovery of blue elliptical galaxies provides some insights into the formation and evolution of galaxies. There seems to be two types of blue elliptical galaxies. One type shows globally blue colors suggesting star formations over the entire galaxy whereas the other type shows blue core that indicates enhanced star formation in the nuclear regions. The former seems to be currently forming galaxies, while the latter is thought to be in transition stage from the blue cloud to the red sequence due to AGN feedback.

Balance of dark and luminous mass in rotating galaxies.

PubMed

McGaugh, Stacy S

2005-10-21

A fine balance between dark and baryonic mass is observed in spiral galaxies. As the contribution of the baryons to the total rotation velocity increases, the contribution of the dark matter decreases by a compensating amount. This poses a fine-tuning problem for galaxy formation models, and may point to new physics for dark matter particles or even a modification of gravity.

Dark-ages reionization and galaxy formation simulation V: morphology and statistical signatures of reionization

NASA Astrophysics Data System (ADS)

Geil, Paul M.; Mutch, Simon J.; Poole, Gregory B.; Angel, Paul W.; Duffy, Alan R.; Mesinger, Andrei; Wyithe, J. Stuart B.

2016-10-01

We use the Dark-ages, Reionization And Galaxy formation Observables from Numerical Simulations (DRAGONS) framework to investigate the effect of galaxy formation physics on the morphology and statistics of ionized hydrogen (H II) regions during the Epoch of Reioinization (EoR). DRAGONS self-consistently couples a semi-analytic galaxy formation model with the inhomogeneous ionizing UV background, and can therefore be used to study the dependence of morphology and statistics of reionization on feedback phenomena of the ionizing source galaxy population. Changes in galaxy formation physics modify the sizes of H II regions and the amplitude and shape of 21-cm power spectra. Of the galaxy physics investigated, we find that supernova feedback plays the most important role in reionization, with H II regions up to ≈20 per cent smaller and a fractional difference in the amplitude of power spectra of up to ≈17 per cent at fixed ionized fraction in the absence of this feedback. We compare our galaxy formation-based reionization models with past calculations that assume constant stellar-to-halo mass ratios and find that with the correct choice of minimum halo mass, such models can mimic the predicted reionization morphology. Reionization morphology at fixed neutral fraction is therefore not uniquely determined by the details of galaxy formation, but is sensitive to the mass of the haloes hosting the bulk of the ionizing sources. Simple EoR parametrizations are therefore accurate predictors of reionization statistics. However, a complete understanding of reionization using future 21-cm observations will require interpretation with realistic galaxy formation models, in combination with other observations.

SIDM on FIRE: hydrodynamical self-interacting dark matter simulations of low-mass dwarf galaxies

NASA Astrophysics Data System (ADS)

Robles, Victor H.; Bullock, James S.; Elbert, Oliver D.; Fitts, Alex; González-Samaniego, Alejandro; Boylan-Kolchin, Michael; Hopkins, Philip F.; Faucher-Giguère, Claude-André; Kereš, Dušan; Hayward, Christopher C.

2017-12-01

We compare a suite of four simulated dwarf galaxies formed in 1010 M⊙ haloes of collisionless cold dark matter (CDM) with galaxies simulated in the same haloes with an identical galaxy formation model but a non-zero cross-section for DM self-interactions. These cosmological zoom-in simulations are part of the Feedback In Realistic Environments (FIRE) project and utilize the FIRE-2 model for hydrodynamics and galaxy formation physics. We find the stellar masses of the galaxies formed in self-interacting dark matter (SIDM) with σ/m = 1 cm2 g-1 are very similar to those in CDM (spanning M⋆ ≈ 105.7-7.0M⊙) and all runs lie on a similar stellar mass-size relation. The logarithmic DM density slope (α = d log ρ/d log r) in the central 250-500 pc remains steeper than α = -0.8 for the CDM-Hydro simulations with stellar mass M⋆ ∼ 106.6 M⊙ and core-like in the most massive galaxy. In contrast, every SIDM hydrodynamic simulation yields a flatter profile, with α > -0.4. Moreover, the central density profiles predicted in SIDM runs without baryons are similar to the SIDM runs that include FIRE-2 baryonic physics. Thus, SIDM appears to be much more robust to the inclusion of (potentially uncertain) baryonic physics than CDM on this mass scale, suggesting that SIDM will be easier to falsify than CDM using low-mass galaxies. Our FIRE simulations predict that galaxies less massive than M⋆ ≲ 3 × 106 M⊙ provide potentially ideal targets for discriminating models, with SIDM producing substantial cores in such tiny galaxies and CDM producing cusps.

Polar ring galaxies in the Galaxy Zoo

NASA Astrophysics Data System (ADS)

Finkelman, Ido; Funes, José G.; Brosch, Noah

2012-05-01

We report observations of 16 candidate polar-ring galaxies (PRGs) identified by the Galaxy Zoo project in the Sloan Digital Sky Survey (SDSS) data base. Deep images of five galaxies are available in the SDSS Stripe82 data base, while to reach similar depth we observed the remaining galaxies with the 1.8-m Vatican Advanced Technology Telescope. We derive integrated magnitudes and u-r colours for the host and ring components and show continuum-subtracted Hα+[N II] images for seven objects. We present a basic morphological and environmental analysis of the galaxies and discuss their properties in comparison with other types of early-type galaxies. Follow-up photometric and spectroscopic observations will allow a kinematic confirmation of the nature of these systems and a more detailed analysis of their stellar populations.

Mosfire Spectroscopy Of Galaxies In Cosmic Noon

NASA Astrophysics Data System (ADS)

Nanayakkara, Themiya

2017-07-01

�-EW distribution is much broader (10-500˚A) than can be explained by a simple monotonic SFH with a standard Salpeter-slope IMF. This result is robust against uncertainties in dust correction and observational bias, and no single IMF (i.e. non-Salpeter slope) can explain the distribution. Starburst models cannot explain the Hα-EW distribution because: 1) spectral stacking still shows an excess Hα-EW in composite populations and 2) Monte Carlo burst models show that the timescale for high Hα-EW is too short to explain their abundance in the ZFIRE sample. Other possible physical mechanisms that could produce excess ionising photons for a given star-formation rate, and hence high equivalent widths, including models with variations in stellar rotation, binary star evolution, metallicity, and upper mass cutoff of the IMF are investigated and ruled out. IMF variation is one possible explanation for the high Hα-EWs. However, the highest Hα-EW values would require very shallow slopes (Γ > -1.0) and no single IMF change can explain the large variation in Hα-EWs. Instead the IMF would have to vary stochastically. Therefore, currently there is no simple physical model to explain the large variation in Hα-EWs at z ˜ 2, but the distinct differences of the z ˜ 2 sample with that of local galaxies are found to be intriguing. Further study is required to fully constrain the stellar population parameters of actively star-forming galaxies at the epoch of maximum star-formation. Probing multiple rest-frame UV and optical features of galaxies simultaneously along with galaxy dynamical studies via integral field spectroscopy will be vital to understand stellar and ionized gas properties of these galaxies. Furthermore, low-z analogues of galaxies at z ˜ 2 will provide vital clues to constrain galaxy evolution models aided by the ability to probe galaxies in high resolution to low surface brightness limits.

Resolved Star Formation in Galaxies Using Slitless Spectroscopy

NASA Astrophysics Data System (ADS)

Pirzkal, Norbert; Finkelstein, Steven L.; Larson, Rebecca L.; Malhotra, Sangeeta; Rhoads, James E.; Ryan, Russell E.; Tilvi, Vithal; FIGS Team

2018-06-01

The ability to spatially resolve individual star-formation regions in distant galaxies and simultaneously extract their physical properties via emission lines is a critical step forward in studying the evolution of galaxies. While efficient, deep slitless spectroscopic observations offer a blurry view of the summed properties of galaxies. We present our studies of resolved star formation over a wide range of redshifts, including high redshift Ly-a sources. The unique capabilities of the WFC3 IR Grism and our two-dimensional emission line method (EM2D) allows us to accurately identify the specific spatial origin of emission lines in galaxies, thus creating a spatial map of star-formation sites in any given galaxy. This method requires the use of multiple position angles on the sky to accurately derive both the location and the observed wavelengths of these emission lines. This has the added benefit of producing better defined redshifts for these sources. Building on our success in applying the EM2D method towards galaxies with [OII]. [OIII], and Ha emission lines, we have also applied EM2D to high redshift (z>6) Ly-a emitting galaxies. We are also able to produce accurate 2D emission line maps (MAP2D) of the Ly-a emission in WFC3 IR grism observations, looking for evidence that a significant amount of resonant scattering is taking place in high redshift galaxies such as in a newly identified z=7.5 Faint Infrared Galaxy Survey (FIGS) Ly-a galaxy.

Properties of Narrow line Seyfert 1 galaxies

NASA Astrophysics Data System (ADS)

Rakshit, Suvendu; Stalin, Chelliah Subramonian; Chand, Hum; Zhang, Xue-Guang

2018-04-01

Narrow line Seyfert 1 (NLSy1) galaxies constitute a class of active galactic nuclei characterized by the full width at half maximum (FWHM) of the Hα broad emission line <2000 km s-1 and the flux ratio of [O III] to Hα <3. Their properties are not well understood since only a few NLSy1 galaxies were known earlier. We have studied various properties of NLSy1 galaxies using an enlarged sample and compared them with the conventional broad-line Seyfert 1 (BLSy1) galaxies. Both the sample of sources have z˜ 0.8 and their optical spectra from SDSS-DR12 that are used to derive various physical parameters have a median signal to noise (S/N) ratio >10 pixel-1. A strong correlation between the Hα and Hα emission lines is found both in the FWHM and flux. The nuclear continuum luminosity is found to be strongly correlated with the luminosity of Hα, Hα and [O III] emission lines. The black hole mass in NLSy1 galaxies is lower compared to their broad line counterparts. Compared to BLSy1 galaxies, NLSy1 galaxies have a stronger FeII emission and a higher Eddington ratio that place them in the extreme upper right corner of the R4570 - λEdd diagram. The distribution of the radio-loudness parameter (R) in NLSy1 galaxies drops rapidly at R>10 compared to the BLSy1 galaxies that have powerful radio jets. The soft X-ray photon index in NLSy1 galaxies is on average higher (2.9 ± 0.9) than BLSy1 galaxies (2.4 ± 0.8). It is anti-correlated with the Hα width but correlated with the FeII strength. NLSy1 galaxies on average have a lower amplitude of optical variability compared to their broad lines counterparts. These results suggest Eddington ratio as the main parameter that drives optical variability in these sources.

Blue diffuse dwarf galaxies: a clearer picture

NASA Astrophysics Data System (ADS)

James, Bethan L.; Koposov, Sergey E.; Stark, Daniel P.; Belokurov, Vasily; Pettini, Max; Olszewski, Edward W.; McQuinn, Kristen B. W.

2017-03-01

The search for chemically unevolved galaxies remains prevalent in the nearby Universe, mostly because these systems provide excellent proxies for exploring in detail the physics of high-z systems. The most promising candidates are extremely metal-poor galaxies (XMPs), I.e. galaxies with <1/10 solar metallicity. However, due to the bright emission-line-based search criteria traditionally used to find XMPs, we may not be sampling the full XMP population. In 2014, we reoriented this search using only morphological properties and uncovered a population of ˜150 'blue diffuse dwarf (BDD) galaxies', and published a sub-sample of 12 BDD spectra. Here, we present optical spectroscopic observations of a larger sample of 51 BDDs, along with their Sloan Digital Sky Survey (SDSS) photometric properties. With our improved statistics, we use direct-method abundances to confirm that BDDs are chemically unevolved (7.43 < 12 + log(O/H) < 8.01), with ˜20 per cent of our sample classified as being XMP galaxies, and find that they are actively forming stars at rates of ˜1-33 × 10-2 M⊙ yr-1 in H II regions randomly embedded in a blue, low-surface-brightness continuum. Stellar masses are calculated from population synthesis models and estimated to be in the range log (M*/M⊙) ≃ 5-9. Unlike other low-metallicity star-forming galaxies, BDDs are in agreement with the mass-metallicity relation at low masses, suggesting that they are not accreting large amounts of pristine gas relative to their stellar mass. BDD galaxies appear to be a population of actively star-forming dwarf irregular (dIrr) galaxies which fall within the class of low-surface-brightness dIrr galaxies. Their ongoing star formation and irregular morphology make them excellent analogues for galaxies in the early Universe.

Hidden interaction in SBO galaxies

NASA Technical Reports Server (NTRS)

Galletta, G.; Bettoni, D.; Oosterloo, T.; Fasano, G.

1990-01-01

Galaxies, like plants, show a large variety of grafts: an individual of some type connects physically with a neighborhood of same or different type. The effects of these interactions between galaxies have a broad range of morphologies depending, among other quantities, on the distance of the closest approach between systems and the relative size of the two galaxies. A sketch of the possible situations is shown in tabular form. This botanical classification is just indicative, because the effects of interactions can be notable also at relatively large separations, when additional conditions are met, as for example low density of the interacting systems or the presence of intra-cluster gas. In spite of the large variety of encounters and effects, in the literature the same terms are often used to refer to different types of interactions. Analysis indicates that only few of the situations show evident signs of interaction. They appear to be most relevant when the size of the two galaxies is comparable. Bridges and tails, like the well known case of NGC 4038/39, the Antennae, are only observed for a very low percentage of all galaxies (approx. 0.38 percent, Arp and Madore 1977). In most cases of gravitational bond between two galaxies, the effects of interactions are not relevant or evident. For instance, the detection of stellar shells (Malin and Carter 1983), which have been attributed to the accretion of gas stripped from another galaxy or to the capture and disruption of a small stellar system (Quinn 1984), requires particular observing and reduction techniques. Besides these difficulties of detection, time plays an important role in erasing, within a massive galaxy, the effects of interactions with smaller objects. This can happen on a timescale shorter than the Hubble time, so the number of systems now showing signs of interaction suggests lower limits to the true frequency of interactions in the life-time of a stellar system.

The Emission of Galaxies over the Whole Electromagnetic Spectrum

NASA Astrophysics Data System (ADS)

Burgarella, Denis; Boquien, Médéric; Roehlly, Yannick; Ciesla, Laure; Buat, Véronique

2017-08-01

The emission of galaxies is not limited to the usual optical range but extends to a wider spectral range with, most notably, emission in the X-ray, ultraviolet, infrared and radio ranges. Their detection and study brings a lot of information to the astrophysics because the physical phenomena at the origin of the various emissions are different. Each of them allows analysis of a different facet of the physics of galaxies: gas, stars, dust, Active Galactic Nuclei (AGN). However, gathering this multi-wavelength information is not an easy task as some of them do not reach ground-based telescopes and we have to design and launch space telescopes to catch and collect the relevant photons. This paper will present the tools that are available to the astrophysicist to decipher the message sent by local, distant or even the most remote galaxies observed in the universe.

Adding Spice to Vanilla LCDM simulations: From Alternative Cosmologies to Lighting up Galaxies

NASA Astrophysics Data System (ADS)

Jahan Elahi, Pascal

2015-08-01

Cold Dark Matter simulations have formed the backbone of our theoretical understanding of cosmological structure formation. Predictions from the Lambda Cold Dark Matter (LCDM) cosmology, in which the Universe contains two major dark components, namely Dark Matter and Dark Energy, are in excellent agreement with the Large-Scale Structures observed, i.e., the distribution of galaxies across cosmic time. However, this paradigm is in tension with observations at small-scales, from the number and properties of satellite galaxies around galaxies such as the Milky Way and Andromeda, to the lensing statistics of massive galaxy clusters. I will present several alternative models of cosmology (from Warm Dark Matter to coupled Dark Matter-Dark Energy models) and how they compare to vanilla LCDM by studying formation of groups and clusters dark matter only and adiabatic hydrodynamical zoom simulations. I will show how modifications to the dark sector can lead to some surprising results. For example, Warm Dark Matter, so often examined on small satellite galaxies scales, can be probed observationally using weak lensing at cluster scales. Coupled dark sectors, where dark matter decays into dark energy and experiences an effective gravitational potential that differs from that experienced by normal matter, is effectively hidden away from direct observations of galaxies. Studies like these are vital if we are to pinpoint observations which can look for unique signatures of the physics that governs the hidden Universe. Of course, all of these predictions are unfortunately affected by uncertain galaxy formation physics. I will end by presenting results from a comparison study of numerous hydrodynamical codes, the nIFTY cluster comparison project, and how even how purely adiabatic simulations run with different codes give in quite different galaxy populations. The galaxies that form in these simulations, which all attempt to reproduce the observed galaxy population via not

Star formation quenching in green valley galaxies at 0.5 ≲ z ≲ 1.0 and constraints with galaxy morphologies

NASA Astrophysics Data System (ADS)

Nogueira-Cavalcante, J. P.; Gonçalves, T. S.; Menéndez-Delmestre, K.; Sheth, K.

2018-01-01

We calculate the star formation quenching time-scales in green valley galaxies at intermediate redshifts (z ∼ 0.5-1) using stacked zCOSMOS spectra of different galaxy morphological types: spheroidal, disc-like, irregular and merger, dividing disc-like galaxies further into unbarred, weakly barred and strongly barred, assuming a simple exponentially decaying star formation history model and based on the H δ absorption feature and the 4000 Å break. We find that different morphological types present different star formation quenching time-scales, reinforcing the idea that the galaxy morphology is strongly correlated with the physical processes responsible for quenching star formation. Our quantification of the star formation quenching time-scale indicates that discs have typical time-scales 60 per cent to five times longer than that of galaxies presenting spheroidal, irregular or merger morphologies. Barred galaxies, in particular, present the slowest transition time-scales through the green valley. This suggests that although secular evolution may ultimately lead to gas exhaustion in the host galaxy via bar-induced gas inflows that trigger star formation activity, secular agents are not major contributors in the rapid quenching of galaxies at these redshifts. Galaxy interaction, associated with the elliptical, irregular and merger morphologies, contributes, to a more significant degree, to the fast transition through the green valley at these redshifts. In light of previous works suggesting that both secular and merger processes are responsible for the star formation quenching at low redshifts, our results provide an explanation to the recent findings that star formation quenching happened at a faster pace at z ∼ 0.8.

Quasar Feedback at the Peak of Galaxy Formation Epoch

NASA Astrophysics Data System (ADS)

Liu, Guilin; Zakamska, Nadia L.; Strauss, Michael A.; Greene, Jenny E.; Alexandroff, Rachael

2013-02-01

The correlations between properties of supermassive black holes and stellar spheroids in galaxies imply a physical connection between these two components in spite of their vastly different masses and physical scales. Using Gemini GMOS IFU, we demonstrated that powerful ionized gas winds are a ubiquitous feature in luminous radio-quiet obscured z 0.5 quasars. We now plan to extend this discovery to the era of peak galaxy formation and quasar activity - to the epoch when feedback was most prominent and the galaxy vs. black hole correlations were established. We propose a GMOS IFU survey to map the spatial distribution and the kinematics of Ly(alpha) and N sc v 1240Å emission around 5 obscured quasars at z=3-3.4. We will use Ly(alpha) observations to directly probe the effects of ionizing radiation of obscured quasars on their large-scale environments and N sc v observations to look for signatures of unbound quasar-driven outflows. We will observe in the g-band on sub-galactic and galaxy- wide scales (spatial resolution 3-6 kpc, field of view 40times50 kpc^2 at z=3). Obscured quasars likely constitute the majority of the quasar population and may represent the relatively early enshrouded phase of black hole growth; thus, luminous obscured quasars are the most likely sites of quasar ionization- and wind-feedback, as we found at low redshifts. Our proposed GMOS observations will provide a definitive probe of the effects of quasars on their galaxy-wide and large-scale environments close to the peak of galaxy formation epoch.

Search and Studies of Active Galaxies Using Multiwavelength Data

NASA Astrophysics Data System (ADS)

Mickaelian, A. M.; Gyulzadyan, M. V.; Abrahamyan, H. V.; Paronyan, G. M.; Mikayelyan, G. A.

2017-07-01

The Byurakan Astrophysical Observatory (BAO) during its history has always been one of the centres for surveys and studies of active galaxies. Here we review our search and studies of active galaxies during last 30 years using various wavelength ranges, as well as some recent related works. These projects since late 1980s were focused on multiwavelength search and studies of AGN and Starbursts. 1103 blue stellar objects (BSOs) on the basis of their UV-excess were selected using Markarian Survey (First Byurakan Survey, FBS) plates and Markarian's criteria used for the galaxies. 1577 IRAS point sources were optically identified using FBS low-dispersion spectra and many AGN, SB and high-luminosity IR galaxies (LIRG/ULIRG) were discovered. 2791 ROSAT FSC sources were optically identified using Hamburg Quasar Survey (HQS) low-dispersion spectra and many AGN were discovered by follow-up observations. Fine analysis of emission line spectra was carried out using spectral line decomposition software to establish true profiles and calculate physical parameters for the emitting regions. Multiwavelength approach allowed revealing many new AGN and SB and obtaining a number of interesting relations using their observational characteristics and physical properties.

Star Formation Histories of Dwarf Irregular Galaxies

NASA Astrophysics Data System (ADS)

Skillman, Evan

1995-07-01

We propose to obtain deep WFPC2 `BVI' color-magnitude diagrams {CMDs} for the dwarf irregular {dI} Local Group galaxies GR 8, Leo A, Pegasus, and Sextans A. In addition to resolved stars, we will use star clusters, and especially any globulars, to probe the history of intense star formation. These data will allow us to map the Pop I and Pop II stellar components, and thereby construct the first detailed star formation histories for non-interacting dI galaxies. Our results will bear on a variety of astrophysical problems, including the evolution of small galaxies, distances in the Local Group, age-metallicity distributions in small galaxies, ages of dIs, and the physics of star formation. The four target galaxies are typical dI systems in terms of luminosity, gas content, and H II region abundance, and represent a range in current star forming activity. They are sufficiently near to allow us to reach to stars at M_V = 0, have 0.1 of the luminosity of the SMC and 0.25 of its oxygen abundance. Unlike the SMC, these dIs are not near giant galaxies. This project will allow the extension of our knowledge of stellar populations in star forming galaxies from the spirals in the Local Group down to its smallest members. We plan to take maximum advantage of the unique data which this project will provide. Our investigator team brings extensive and varied experience in studies of dwarf galaxies, stellar populations, imaging photometry, and stellar evolution to this project.

Andromeda Galaxy

NASA Image and Video Library

2003-12-10

This image is from NASA Galaxy Evolution Explorer is an 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.

Far-infrared line images of dwarf galaxies

NASA Technical Reports Server (NTRS)

Poglitsch, A.; Geis, N.; Herrmann, F.; Madden, S. C.; Stacey, G. J.; Townes, C. H.; Genzel, R.

1993-01-01

Irregular dwarf galaxies are about ten times more widespread in the universe than regular spiral galaxies. They are characterized by a relatively low metallicity, i.e., lower abundance of the heavier elements (metals) with respect to hydrogen than in the solar neighborhood. These heavier elements in the form of molecules, atoms, or ions, which have radiative transitions in the infrared play a decisive role in the energy balance of the ISM and thereby for the formation of stars. Dwarf galaxies are thus model cases for the physical conditions in the early phase of the universe. Large Magellanic Cloud: 30 Doradus. The two nearest dwarf galaxies are the Magellanic clouds at a distance approximately 50 kpc. The LMC contains 30 Dor, a region with young, extremely massive stars which strongly interact with the surrounding ISM on account of their stellar winds and intense UV radiation. 30 Dor is the brightest object in the LMC at almost all wavelengths.

Galaxy and Mass Assembly (GAMA): ugriz galaxy luminosity functions

NASA Astrophysics Data System (ADS)

Loveday, J.; Norberg, P.; Baldry, I. K.; Driver, S. P.; Hopkins, A. M.; Peacock, J. A.; Bamford, S. P.; Liske, J.; Bland-Hawthorn, J.; Brough, S.; Brown, M. J. I.; Cameron, E.; Conselice, C. J.; Croom, S. M.; Frenk, C. S.; Gunawardhana, M.; Hill, D. T.; Jones, D. H.; Kelvin, L. S.; Kuijken, K.; Nichol, R. C.; Parkinson, H. R.; Phillipps, S.; Pimbblet, K. A.; Popescu, C. C.; Prescott, M.; Robotham, A. S. G.; Sharp, R. G.; Sutherland, W. J.; Taylor, E. N.; Thomas, D.; Tuffs, R. J.; van Kampen, E.; Wijesinghe, D.

2012-02-01

Galaxy and Mass Assembly (GAMA) is a project to study galaxy formation and evolution, combining imaging data from ultraviolet to radio with spectroscopic data from the AAOmega spectrograph on the Anglo-Australian Telescope. Using data from Phase 1 of GAMA, taken over three observing seasons, and correcting for various minor sources of incompleteness, we calculate galaxy luminosity functions (LFs) and their evolution in the ugriz passbands. At low redshift, z < 0.1, we find that blue galaxies, defined according to a magnitude-dependent but non-evolving colour cut, are reasonably well fitted over a range of more than 10 magnitudes by simple Schechter functions in all bands. Red galaxies, and the combined blue plus red sample, require double power-law Schechter functions to fit a dip in their LF faintwards of the characteristic magnitude M* before a steepening faint end. This upturn is at least partly due to dust-reddened disc galaxies. We measure the evolution of the galaxy LF over the redshift range 0.002 < z < 0.5 both by using a parametric fit and by measuring binned LFs in redshift slices. The characteristic luminosity L* is found to increase with redshift in all bands, with red galaxies showing stronger luminosity evolution than blue galaxies. The comoving number density of blue galaxies increases with redshift, while that of red galaxies decreases, consistent with prevailing movement from blue cloud to red sequence. As well as being more numerous at higher redshift, blue galaxies also dominate the overall luminosity density beyond redshifts z≃ 0.2. At lower redshifts, the luminosity density is dominated by red galaxies in the riz bands, and by blue galaxies in u and g.

Properties of galaxies reproduced by a hydrodynamic simulation

NASA Astrophysics Data System (ADS)

Vogelsberger, M.; Genel, S.; Springel, V.; Torrey, P.; Sijacki, D.; Xu, D.; Snyder, G.; Bird, S.; Nelson, D.; Hernquist, L.

2014-05-01

Previous simulations of the growth of cosmic structures have broadly reproduced the `cosmic web' of galaxies that we see in the Universe, but failed to create a mixed population of elliptical and spiral galaxies, because of numerical inaccuracies and incomplete physical models. Moreover, they were unable to track the small-scale evolution of gas and stars to the present epoch within a representative portion of the Universe. Here we report a simulation that starts 12 million years after the Big Bang, and traces 13 billion years of cosmic evolution with 12 billion resolution elements in a cube of 106.5 megaparsecs a side. It yields a reasonable population of ellipticals and spirals, reproduces the observed distribution of galaxies in clusters and characteristics of hydrogen on large scales, and at the same time matches the `metal' and hydrogen content of galaxies on small scales.

Women, Demography, and Politics: How Lower Fertility Rates Lead to Democracy.

PubMed

Sommer, Udi

2018-04-01

Where connections between demography and politics are examined in the literature, it is largely in the context of the effects of male aspects of demography on phenomena such as political violence. This project aims to place the study of demographic variables' influence on politics, particularly on democracy, squarely within the scope of political and social sciences, and to focus on the effects of woman-related demographics-namely, fertility rate. I test the hypothesis that demographic variables-female-related predictors, in particular-have an independent effect on political structure. Comparing countries over time, this study finds a growth in democracy when fertility rates decline. In the theoretical framework developed, it is family structure as well as the economic and political status of women that account for this change at the macro and micro levels. Findings based on data for more than 140 countries over three decades are robust when controlling not only for alternative effects but also for reverse causality and data limitations.

The Taxonomy of Blue Amorphous Galaxies. I. Hα and UBVI Data

NASA Astrophysics Data System (ADS)

Marlowe, Amanda T.; Meurer, Gerhardt R.; Heckman, Timothy M.; Schommer, Robert

1997-10-01

Dwarf galaxies play an important role in our understanding of galaxy formation and evolution. We have embarked on a systematic study of 12 nearby dwarf galaxies (most of which have been classified as amorphous) selected preferentially by their blue colors. The properties of the galaxies in the sample suggest that they are in a burst or postburst state. It seems likely that these amorphous galaxies are closely related to other ``starburst'' dwarfs such as blue compact dwarfs (BCDs) and H II galaxies but are considerably closer and therefore easier to study. If so, these galaxies may offer important insights into dwarf galaxy evolution. In an effort to clarify the role of starbursts in evolutionary scenarios for dwarf galaxies, we present Hα and UBVI data for our sample. Blue amorphous galaxies, like BCDs and H II galaxies, have surface brightness profiles that are exponential in the outer regions (r >~ 1.5re) but have a predominantly blue central excess, which suggests a young burst in an older, redder galaxy. Seven of the galaxies have the bubble or filamentary Hα morphology and double-peaked emission lines that are the signature of superbubbles or superwind activity. These galaxies are typically the ones with the strongest central excesses. The underlying exponential galaxies are very similar to those found in BCDs and H II galaxies. How amorphous galaxies fit into the dwarf irregular-``starburst dwarf''-dwarf elliptical evolutionary debate is less clear. In this paper, we present our data and make some preliminary comparisons between amorphous galaxies and other classes of dwarf galaxies. In a future companion paper, we will compare this sample more quantitatively with other dwarf galaxy samples in an effort to determine if amorphous galaxies are a physically different class of object from other starburst dwarfs such as BCDs and H II galaxies and also investigate their place in dwarf galaxy evolution scenarios.

Observational Searches for Star-Forming Galaxies at z > 6

NASA Astrophysics Data System (ADS)

Finkelstein, Steven L.

2016-08-01

Although the universe at redshifts greater than six represents only the first one billion years (< 10%) of cosmic time, the dense nature of the early universe led to vigorous galaxy formation and evolution activity which we are only now starting to piece together. Technological improvements have, over only the past decade, allowed large samples of galaxies at such high redshifts to be collected, providing a glimpse into the epoch of formation of the first stars and galaxies. A wide variety of observational techniques have led to the discovery of thousands of galaxy candidates at z > 6, with spectroscopically confirmed galaxies out to nearly z = 9. Using these large samples, we have begun to gain a physical insight into the processes inherent in galaxy evolution at early times. In this review, I will discuss (i) the selection techniques for finding distant galaxies, including a summary of previous and ongoing ground and space-based searches, and spectroscopic follow-up efforts, (ii) insights into galaxy evolution gleaned from measures such as the rest-frame ultraviolet luminosity function, the stellar mass function, and galaxy star-formation rates, and (iii) the effect of galaxies on their surrounding environment, including the chemical enrichment of the universe, and the reionisation of the intergalactic medium. Finally, I conclude with prospects for future observational study of the distant universe, using a bevy of new state-of-the-art facilities coming online over the next decade and beyond.

Fast Outflow of Molecular Gas in the Seyfert Galaxy IC 5063

NASA Astrophysics Data System (ADS)

Morganti, Raffaella; Oosterloo, T.; Oonk, R.; Tadhunter, C.

2017-11-01

AGN-driven gas outflows may play an important role in the evolution of galaxies, as they impact on the growth on the central supermassive black hole as well on the star formation of the host galaxy. Much of the detailed physics of these gas outflows, and their actual impact on the host galaxy, is still not well understood. We present a detailed analysis, using ALMA observations, of the radio-jet driven outflow of molecular gas in the nearby radio-loud Seyfert galaxy IC 5063 which allows to derive important physical parameters of the gas and the outflow which, in turn, provide crucial input to numerical models. In recent years, a surprising result in the field of AGN-driven outflows has been that the cold phases of the gas (atomic and molecular) in some galaxies are the massive components of these outflows, despite the huge amounts of energy involved in driving these outflows. However, why most of the outflowing gas should be molecular/atomic, and in general, what are the physical conditions of the gas in the outflows and what really drives them, are still open questions. We present the results obtained from ALMA observations of multiple CO transitions and other molecules of what appears to be a textbook case of a jet-driven multi- phase outflow in the central regions of the Seyfert galaxy IC 5063. The data on multiple transitions allow us to derive the physical conditions in the different regions of the outflowing molecular gas. The signature of the impact of the radio jet is clearly seen in the spatial distribution of the excitation temperature and pressure of the outflowing gas, with the highest excitation and pressure found for the gas with the highest outflow velocities. We obtain a detailed three- dimensional picture of the outflow, and its kinematics, and find that outflowing molecular gas is present across the entire region co-spatial with the radio plasma, providing unambiguous evidence that the radio jets/cocoon are responsible for the outflow. The

Nebular Metallicities in Two Isolated Local Void Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Nicholls, David C.; Jerjen, Helmut; Dopita, Michael A.; Basurah, Hassan

2014-01-01

Isolated dwarf galaxies, especially those situated in voids, may provide insight into primordial conditions in the universe and the physical processes that govern star formation in undisturbed stellar systems. The metallicity of H II regions in such galaxies is key to investigating this possibility. From the SIGRID sample of isolated dwarf galaxies, we have identified two exceptionally isolated objects, the Local Void galaxy [KK98]246 (ESO 461-G036) and another somewhat larger dwarf irregular on the edge of the Local Void, MCG-01-41-006 (HIPASS J1609-04). We report our measurements of the nebular metallicities in these objects. The first object has a single low luminosity H II region, while the second is in a more vigorous star forming phase with several bright H II regions. We find that the metallicities in both galaxies are typical for galaxies of this size, and do not indicate the presence of any primordial gas, despite (for [KK98]246) the known surrounding large reservoir of neutral hydrogen.

On the unification of dwarf and giant elliptical galaxies

NASA Astrophysics Data System (ADS)

Graham, Alister W.; Guzman, Rafael

2004-01-01

The near orthogonal distributions of dwarf elliptical (dE) and giant elliptical (E) galaxies in the mue-M and mue-log(Re) diagrams have been interpreted as evidence for two distinct galaxy formation processes. However, continuous, linear relationships across the alleged dE/E boundary at MB = -18 mag - such as the relationships between central surface brightness (mu0) and: a) galaxy magnitude (M); and b) light-profile shape (n) --- suggest a similar initial formation mechanism. Here we explain how these latter two trends in fact necessitate a different behavior for dE and E galaxies, exactly as observed, in diagrams involving mue (and also e). Together with other linear trends across the alleged dE/E boundary, such as those between luminosity and color, metallicity, and velocity dispersion, it appears that the dEs form a continuous extension to the E galaxies. The presence of partially depleted cores in luminous (MB < -20.5 mag) Es does however signify the action of a different physical process at the centers (< ~300 pc) of these galaxies.

Evolution of Hot Gas in Elliptical Galaxies

NASA Technical Reports Server (NTRS)

Mathews, William G.

2004-01-01

This theory grant was awarded to study the curious nature, origin and evolution of hot gas in elliptical galaxies and their surrounding groups. Understanding the properties of this X-ray emitting gas has profound implications over the broad landscape of modern astrophysics: cosmology, galaxy formation, star formation, cosmic metal enrichment, galactic structure and dynamics, and the physics of hot gases containing dust and magnetic fields. One of our principal specific objectives was to interpret the marvelous new observations from the XMM and Chandru satellite X-ray telescopes.

Green valley galaxies as a transition population in different environments

NASA Astrophysics Data System (ADS)

Coenda, Valeria; Martínez, Héctor J.; Muriel, Hernán

2018-02-01

We present a comparative analysis of the properties of passive, star-forming and transition (green valley) galaxies in four discrete environments: field, groups, the outskirts and the core of X-ray clusters. We construct samples of galaxies from the Sloan Digital Sky Survey in these environments so that they are bound to have similar redshift distributions. The classification of galaxies into the three sequences is based on the UV-optical colour NUV - r. We study a number of galaxy properties: stellar mass, morphology, specific star formation rate and the history of star formation. The analysis of green valley (GV) galaxies reveals that the physical mechanisms responsible for external quenching become more efficient moving from the field to denser environments. We confirm previous findings that GV galaxies have intermediate morphologies; moreover, we find that this appears to be independent of the environment. Regarding the stellar mass of GV galaxies, we find that they tend to be more massive in the field than in denser environments. On average, GV galaxies account for ∼ 20 per cent of all galaxies in groups and X-ray clusters. We find evidence that the field environment is inefficient in transforming low-mass galaxies. GV galaxies have average star formation histories intermediate between passive and star-forming galaxies, and have a clear and consistent dependence on the environment: both, the quenching time and the amplitude of the star formation rate, decrease towards higher density environments.

Testing galaxy quenching theories with scatter in the stellar-to-halo mass relation

NASA Astrophysics Data System (ADS)

Tinker, Jeremy L.

2017-05-01

We use the scatter in the stellar-to-halo mass relation to constrain galaxy evolution models. If the efficiency of converting accreted baryons into stars varies with time, haloes of the same present-day mass but different formation histories will have different z = 0 galaxy stellar mass. This is one of the sources of scatter in stellar mass at fixed halo mass, σlog M*. For massive haloes that undergo rapid quenching of star formation at z ˜ 2, different mechanisms that trigger this quenching yield different values of σlog M*. We use this framework to test various models in which quenching begins after a galaxy crosses a threshold in one of the following physical quantities: redshift, halo mass, stellar mass and stellar-to-halo mass ratio. Our model is highly idealized, with other sources of scatter likely to arise as more physics is included. Thus, our test is whether a model can produce scatter lower than observational bounds, leaving room for other sources. Recent measurements find σlog M* = 0.16 dex for 1011 M⊙ galaxies. Under the assumption that the threshold is constant with time, such a low value of σlog M* rules out all of these models with the exception of quenching by a stellar mass threshold. Most physical quantities, such as metallicity, will increase scatter if they are uncorrelated with halo formation history. Thus, to decrease the scatter of a given model, galaxy properties would correlate tightly with formation history, creating testable predictions for their clustering. Understanding why σlog M* is so small may be key to understanding the physics of galaxy formation.

Exploring the Web : The Active Galaxy Population in the ORELSE Survey

NASA Astrophysics Data System (ADS)

Lubin, Lori

What are the physical processes that trigger starburst and nuclear activity in galaxies and drive galaxy evolution? Studies aimed at understanding this complex issue have largely focused on the cores of galaxy clusters or on field surveys, leaving underexplored intermediate-density regimes where rapid evolution occurs. As a result, we are conducting the ORELSE survey, a search for structure on scales > 10 Mpc around 18 clusters at 0.6 < z < 1.3. The survey covers 5 sq. deg., all targeted at high-density regions, making it comparable to field surveys such as DEEP2 and COSMOS. ORELSE is unmatched, with no other cluster survey having comparable breadth, depth, precision, and multi-band coverage. As such, ORELSE overcomes critical problems with previous high-redshift studies, including cosmic variance, restricted environmental ranges, sparse cluster samples, inconsistent star formation rate measures, and limited spectroscopy. From its initial spectral and photometric components, ORELSE already contains wellmeasured properties such as redshift, color, stellar mass, and star formation rate for a statistical sample of 7000 field+cluster galaxies. Because X-ray and mid-IR observations are crucial for a complete census of the active galaxy population, we propose to use the wealth of archival Chandra, Spitzer, and Herschel data in the ORELSE fields to map AGN and starburst galaxies over large scales. When complete, our sample will exceed by more than an order of magnitude the current samples of spectroscopically-confirmed active galaxies in high-redshift clusters and their environs. Combined with our numerical simulations plus galaxy formation models, we will provide a robust census of the active galaxy population in intermediate and high-density environments at z = 1, constrain the physical processes (e.g., merging, intracluster gas interactions, AGN feedback) responsible for triggering/quenching starburst and nuclear activity, and estimate their associated timescales.

Companions to isolated elliptical galaxies: revisiting the Bothun-Sullivan (1977) sample using the NASA/IPAC extragalactic database

NASA Technical Reports Server (NTRS)

Madore, B. F.; Freedman, W. L.; Bothun, G. D.

2002-01-01

We investigate the number of physical companion galaxies for a sample of relatively isolated elliptical galaxies. The NASA/IPAC Extragalactic Database (NED) has been usedto reinvestigate the incidence of satellite galaxies for a sample of 34 elliptical galaxies, firstinvestigated by Bothun & Sullivan (1977) using a visual inspection of Palomar Sky Survey prints out to a projected search radius of 75 kpc. We have repeated their original investigation usingdata cataloged data in NED. Nine of these ellipticals appear to be members of galaxy clusters:the remaining sample of 25 galaxies reveals an average of +1.0 f 0.5 apparent companions per galaxy within a projected search radius of 75 kpc, in excess of two equal-area comparisonregions displaced by 150-300 kpc. This is nearly an order of magnitude larger than the +0.12+/- 0.42 companions/galaxy found by Bothun & Sullivan for the identical sample. Making use of published radial velocities, mostly available since the completion of the Bothun-Sullivan study,identifies the physical companions and gives a somewhat lower estimate of +0.4 companions per elliptical. This is still a factor of 3x larger than the original statistical study, but giventhe incomplete and heterogeneous nature of the survey redshifts in NED, it still yields a firmlower limit on the number (and identity) of physical companions. An expansion of the searchradius out to 300 kpc, again restricted to sampling only those objects with known redshifts in NED, gives another lower limit of 4.3 physical companions per galaxy. (Excluding fiveelliptical galaxies in the Fornax cluster this average drops to 3.5 companions per elliptical.)These physical companions are individually identified and listed, and the ensemble-averagedradial density distribution of these associated galaxies is presented. For the ensemble, the radial density distribution is found to have a fall-off consistent with p c( R^-0.5 out to approximately150 kpc. For non-Fornax cluster companions the

BayeSED: A GENERAL APPROACH TO FITTING THE SPECTRAL ENERGY DISTRIBUTION OF GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Han, Yunkun; Han, Zhanwen, E-mail: hanyk@ynao.ac.cn, E-mail: zhanwenhan@ynao.ac.cn

2014-11-01

We present a newly developed version of BayeSED, a general Bayesian approach to the spectral energy distribution (SED) fitting of galaxies. The new BayeSED code has been systematically tested on a mock sample of galaxies. The comparison between the estimated and input values of the parameters shows that BayeSED can recover the physical parameters of galaxies reasonably well. We then applied BayeSED to interpret the SEDs of a large K{sub s} -selected sample of galaxies in the COSMOS/UltraVISTA field with stellar population synthesis models. Using the new BayeSED code, a Bayesian model comparison of stellar population synthesis models has beenmore » performed for the first time. We found that the 2003 model by Bruzual and Charlot, statistically speaking, has greater Bayesian evidence than the 2005 model by Maraston for the K{sub s} -selected sample. In addition, while setting the stellar metallicity as a free parameter obviously increases the Bayesian evidence of both models, varying the initial mass function has a notable effect only on the Maraston model. Meanwhile, the physical parameters estimated with BayeSED are found to be generally consistent with those obtained using the popular grid-based FAST code, while the former parameters exhibit more natural distributions. Based on the estimated physical parameters of the galaxies in the sample, we qualitatively classified the galaxies in the sample into five populations that may represent galaxies at different evolution stages or in different environments. We conclude that BayeSED could be a reliable and powerful tool for investigating the formation and evolution of galaxies from the rich multi-wavelength observations currently available. A binary version of the BayeSED code parallelized with Message Passing Interface is publicly available at https://bitbucket.org/hanyk/bayesed.« less

BayeSED: A General Approach to Fitting the Spectral Energy Distribution of Galaxies

NASA Astrophysics Data System (ADS)

Han, Yunkun; Han, Zhanwen

2014-11-01

We present a newly developed version of BayeSED, a general Bayesian approach to the spectral energy distribution (SED) fitting of galaxies. The new BayeSED code has been systematically tested on a mock sample of galaxies. The comparison between the estimated and input values of the parameters shows that BayeSED can recover the physical parameters of galaxies reasonably well. We then applied BayeSED to interpret the SEDs of a large Ks -selected sample of galaxies in the COSMOS/UltraVISTA field with stellar population synthesis models. Using the new BayeSED code, a Bayesian model comparison of stellar population synthesis models has been performed for the first time. We found that the 2003 model by Bruzual & Charlot, statistically speaking, has greater Bayesian evidence than the 2005 model by Maraston for the Ks -selected sample. In addition, while setting the stellar metallicity as a free parameter obviously increases the Bayesian evidence of both models, varying the initial mass function has a notable effect only on the Maraston model. Meanwhile, the physical parameters estimated with BayeSED are found to be generally consistent with those obtained using the popular grid-based FAST code, while the former parameters exhibit more natural distributions. Based on the estimated physical parameters of the galaxies in the sample, we qualitatively classified the galaxies in the sample into five populations that may represent galaxies at different evolution stages or in different environments. We conclude that BayeSED could be a reliable and powerful tool for investigating the formation and evolution of galaxies from the rich multi-wavelength observations currently available. A binary version of the BayeSED code parallelized with Message Passing Interface is publicly available at https://bitbucket.org/hanyk/bayesed.

From Galaxies to the Intergalactic Medium

NASA Astrophysics Data System (ADS)

Peeples, Molly S.

2010-07-01

Deep in dark matter halos, galaxies are large factories that convert gas into stars. Gas is accreted from the expansive intergalactic medium (IGM); stars process this gas by fusing lighter elements into heavier ones. In this Dissertation, I combine both observations and theories from a variety of subfields of astrophysics with analytic and numerical models in an aim for a comprehensive understanding of the underlying physics of star formation feedback, galaxy chemical evolution, and the IGM. The mass-metallicity relation is an observed tight correlation between the stellar masses and gas-phase oxygen abundances of star-forming galaxies. I show that while the intrinsic scatter in this relation is small, extreme outliers do exist; I argue that these outliers have unusual metallicities for their masses because they have unusual gas fractions for their masses. The low-mass high-metallicity galaxies appear to be nearing the end of their star formation, and thus should have abnormally small gas reservoirs with which to dilute their metals. On the other hand, the high-mass low-metallicity galaxies appear to be undergoing gas-rich galaxy mergers, implying that they have larger-than-normal amounts of gas diluting their metals. I then show through analytic arguments that while gas fractions can have a large impact on observed metallicities, the low-redshift mass-metallicity relation is dominated by outflow properties because typical galaxies have relatively small gas fractions. Specifically, the mass-metallicity relation implies that the efficiency with which galaxies expel metals should scale steeply with galaxy mass. Combining this model with reasonable models for star formation feedback, I show that the outflow metallicity should likewise vary with galaxy mass; future measurements of wind metallicity can therefore inform models of the physics underlying galaxy winds. The high-redshift IGM is primarily observed through the Lyman-alpha absorption of neutral hydrogen along

Astrophysical Magnetic Fields and Topics in Galaxy Formation

NASA Technical Reports Server (NTRS)

Field, George B.

1997-01-01

The grant was used to support theoretical research on a variety of astro-physical topics falling broadly into those described by the proposal: galaxy formation, astrophysical magnetic fields, magnetized accretion disks in AGN, new physics, and other astrophysical problems. Work accomplished; references are to work authored by project personel.

Long-term change in a behavioural trait: truncated spawning distribution and demography in Northeast Arctic cod

PubMed Central

Opdal, Anders Frugård; Jørgensen, Christian

2015-01-01

Harvesting may be a potent driver of demographic change and contemporary evolution, which both may have great impacts on animal populations. Research has focused on changes in phenotypic traits that are easily quantifiable and for which time series exist, such as size, age, sex, or gonad size, whereas potential changes in behavioural traits have been under-studied. Here, we analyse potential drivers of long-term changes in a behavioural trait for the Northeast Arctic stock of Atlantic cod Gadus morhua, namely choice of spawning location. For 104 years (1866–1969), commercial catches were recorded annually and reported by county along the Norwegian coast. During this time period, spawning ground distribution has fluctuated with a trend towards more northerly spawning. Spawning location is analysed against a suite of explanatory factors including climate, fishing pressure, density dependence, and demography. We find that demography (age or age at maturation) had the highest explanatory power for variation in spawning location, while climate had a limited effect below statistical significance. As to potential mechanisms, some effects of climate may act through demography, and explanatory variables for demography may also have absorbed direct evolutionary change in migration distance for which proxies were unavailable. Despite these caveats, we argue that fishing mortality, either through demographic or evolutionary change, has served as an effective driver for changing spawning locations in cod, and that additional explanatory factors related to climate add no significant information. PMID:25336028

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.

Atomic and molecular far-infrared lines from high redshift galaxies

NASA Astrophysics Data System (ADS)

Vallini, L.

2015-03-01

The advent of Atacama Large Millimeter-submillimeter Array (ALMA), with its unprecedented sensitivity, makes it possible the detection of far-infrared (FIR) metal cooling and molecular lines from the first galaxies that formed after the Big Bang. These lines represent a powerful tool to shed light on the physical properties of the interstellar medium (ISM) in high-redshift sources. In what follows we show the potential of a physically motivated theoretical approach that we developed to predict the ISM properties of high redshift galaxies. The model allows to infer, as a function of the metallicity, the luminosities of various FIR lines observable with ALMA. It is based on high resolution cosmological simulations of star-forming galaxies at the end of the Epoch of Reionization (z˜eq6) , further implemented with sub-grid physics describing the cooling and the heating processes that take place in the neutral diffuse ISM. Finally we show how a different approach based on semi-analytical calculations can allow to predict the CO flux function at z>6.

Spatial and kinematic distributions of transition populations in intermediate redshift galaxy clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Crawford, Steven M.; Wirth, Gregory D.; Bershady, Matthew A., E-mail: crawford@saao.ac.za, E-mail: wirth@keck.hawaii.edu, E-mail: mab@astro.wisc.edu

2014-05-01

We analyze the spatial and velocity distributions of confirmed members in five massive clusters of galaxies at intermediate redshift (0.5 < z < 0.9) to investigate the physical processes driving galaxy evolution. Based on spectral classifications derived from broad- and narrow-band photometry, we define four distinct galaxy populations representing different evolutionary stages: red sequence (RS) galaxies, blue cloud (BC) galaxies, green valley (GV) galaxies, and luminous compact blue galaxies (LCBGs). For each galaxy class, we derive the projected spatial and velocity distribution and characterize the degree of subclustering. We find that RS, BC, and GV galaxies in these clusters havemore » similar velocity distributions, but that BC and GV galaxies tend to avoid the core of the two z ≈ 0.55 clusters. GV galaxies exhibit subclustering properties similar to RS galaxies, but their radial velocity distribution is significantly platykurtic compared to the RS galaxies. The absence of GV galaxies in the cluster cores may explain their somewhat prolonged star-formation history. The LCBGs appear to have recently fallen into the cluster based on their larger velocity dispersion, absence from the cores of the clusters, and different radial velocity distribution than the RS galaxies. Both LCBG and BC galaxies show a high degree of subclustering on the smallest scales, leading us to conclude that star formation is likely triggered by galaxy-galaxy interactions during infall into the cluster.« less

Rearrangement of gas in disc galaxies

NASA Astrophysics Data System (ADS)

Piñol Ferrer, Núria

Active galactic nuclei and bursts of star formation are two distinct phenomena that amply change their host environments. They are present in a significant number of galaxies at all redshifts. In this thesis, we aim toward a better understanding of the physical processes that allow for the formation and maintenance of these two phenomena. We focus on the study of the physical conditions of the interstellar gas in the central kiloparsec region of the barred active galaxy NGC 1097 (Paper I). In Paper I we present different CO transitions and the consequent analysis realized in order to derive the molecular gas content together with the molecular mass inflow toward the centre of the galactic gravitational potential well. To completely understand the physical processes that drive such gas rearrangement, a coherent picture for a dynamical system has to be considered. We have developed a code, Paper II, in order to model the dynamics of a predominantly rotating system with an arbitrary mass distribution. The formalism we have used is based on analytical solutions of the first order approximation of the equations of motion of a smooth medium that may be subject to dissipation. The most important free parameter to constrain the boundary conditions of the model is the angular frequency of the perturbing pattern, which may be assumed virtually invariant over significant ranges of galactocentric radii. We constrain the pattern velocity using the Tremaine-Weinberg method (Paper III). Hence, we have prepared all procedures needed to comprehend the physical processes that sustain the nuclear activity and bursts of star formation: the amount of gas in the region and the dynamics of the system. In Paper IV, we model the neutral and ionized gas kinematics in NGC 1097 and apply a combination of the methods described in Paper II and Paper III to comprehend the rearrangement of gas in the galaxy. In order to observationally discern the gas inflow in the nuclear region at a higher

RELICS: A Candidate Galaxy Arc at z~10 and Other Brightly Lensed z>6 Galaxies

NASA Astrophysics Data System (ADS)

Salmon, Brett; Coe, Dan; Bradley, Larry; Bradac, Marusa; Huang, Kuang-Han; Oesch, Pascal; Brammer, Gabriel; Stark, Daniel P.; Sharon, Keren; Trenti, Michele; Avila, Roberto J.; Ogaz, Sara; Acebron, Ana; Andrade-Santos, Felipe; Carrasco, Daniela; Cerny, Catherine; Cibirka, Nathália; Dawson, William; Frye, Brenda; Hoag, Austin; Jones, Christine; Mainali, Ramesh; Ouchi, Masami; Paterno-Mahler, Rachel; Rodney, Steven; Umetsu, Keiichi; Zitrin, Adi; RELICS

2018-01-01

Massive foreground galaxy clusters magnify and distort the light of objects behind them, permitting a view into both the extremely distant and intrinsically faint galaxy populations. We present here some of the most brightly lensed z>6 galaxy candidates known from the Reionization Lensing Cluster Survey (RELICS) and the discovery of a particularly fortuitous z~10 galaxy candidate which has been arced by the effects of strong gravitational lensing. The z~10 candidate has a lensed H-band magnitude of 25.8 AB mag and a high lensing magnification (~4-7). The inferred upper limits on the stellar mass (log [M_star /M_Sun]=9.5) and star formation rate (log [SFR/(M_Sun/yr)]=1.5) indicate that this candidate is a typical star-forming galaxy on the z>6 SFR-M_star relation. We rule out the only low-z solution as unphysical based on the required stellar mass, dust attenuation, size, and [OIII] EW needed for a z~2 SED to match the data. Finally, we reconstruct the source-plane image and estimate the candidate's physical size at z~10, finding a half-light radius of r_e < 0.8 kpc that is in line with the sizes of other z>9 candidates. While the James Webb Space Telescope will detect z>10 with ease, this rare candidate offers the potential for unprecedented spatial resolution less than 500 Myr after the Big Bang.

Chemical abundances in low surface brightness galaxies: Implications for their evolution

NASA Technical Reports Server (NTRS)

Mcgaugh, S. S.; Bothun, G. D.

1993-01-01

Low Surface Brightness (LSB) galaxies are an important but often neglected part of the galaxy content of the universe. Their importance stems both from the selection effects which cause them to be under-represented in galaxy catalogs, and from what they can tell us about the physical processes of galaxy evolution that has resulted in something other than the traditional Hubble sequence of spirals. An important constraint for any evolutionary model is the present day chemical abundances of LSB disks. Towards this end, spectra for a sample of 75 H 2 regions distributed in 20 LSB disks galaxies were obtained. Structurally, this sample is defined as having B(0) fainter than 23.0 mag arcsec(sup -2) and scale lengths that cluster either around 3 kpc or 10 kpc. In fact, structurally, these galaxies are very similar to the high surface brightness spirals which define the Hubble sequence. Thus, our sample galaxies are not dwarf galaxies but instead have masses comparable to or in excess of the Milky Way. The basic results from these observations are summarized.

The Illustris simulation: supermassive black hole-galaxy connection beyond the bulge

NASA Astrophysics Data System (ADS)

Mutlu-Pakdil, Burçin; Seigar, Marc S.; Hewitt, Ian B.; Treuthardt, Patrick; Berrier, Joel C.; Koval, Lauren E.

2018-02-01

We study the spiral arm morphology of a sample of the local spiral galaxies in the Illustris simulation and explore the supermassive black hole-galaxy connection beyond the bulge (e.g. spiral arm pitch angle, total stellar mass, dark matter mass, and total halo mass), finding good agreement with other theoretical studies and observational constraints. It is important to study the properties of supermassive black holes and their host galaxies through both observations and simulations and compare their results in order to understand their physics and formative histories. We find that Illustris prediction for supermassive black hole mass relative to pitch angle is in rather good agreement with observations and that barred and non-barred galaxies follow similar scaling relations. Our work shows that Illustris presents very tight correlations between supermassive black hole mass and large-scale properties of the host galaxy, not only for early-type galaxies but also for low-mass, blue and star-forming galaxies. These tight relations beyond the bulge suggest that halo properties determine those of a disc galaxy and its supermassive black hole.

Probing The Stellar, Gaseous, And Dust Properties Of Galaxies Through Analysis Of Their Spectral Energy Distributions

NASA Astrophysics Data System (ADS)

Eufrasio, Rafael T.

The spectral energy distributions (SEDs) of galaxies are shaped by their physical properties and they are our primary source of information on galaxies stellar, gaseous, and dust content. Nearby galaxies (less than 100 Mpc away) are spatially resolved by current telescopes from the ultraviolet (UV) to radio wavelengths, allowing the study of the SEDs of subgalactic regions. Such studies are necessary for deriving maps and spatial trends of the physical properties across a galaxy. In principle, the complex history of the formation, growth, and evolution of a galaxy or a region of a galaxy can be inferred from its radiative output. In practice, this task is complicated by the fact that a significant fraction of the star formation activity takes place in dust obscured regions, in which a significant fraction of the stellar radiative output is absorbed, scattered, and reradiated by the gas and dust in the interstellar medium (ISM). This reprocessing of the stellar radiation takes place in ionized interstellar gas regions (H II regions) surrounding massive hot stars, in diffuse atomic gas (H I regions), and in dense molecular clouds. For this work, we have analyzed two galaxies in detail, NGC 6872 and NGC 6946, also known as Condor and Fireworks Galaxy, respectively. The Condor galaxy is the largest-known spiral galaxy. It is part a group of galaxies, the Pavo group, with 12 other galaxies. It has, however, interacted in the past ~150 Myr with a smaller companion, previously believed to have shaped the physical extent of the giant spiral. We have performed detailed SED fitting from the UV to mid-infrared (mid-IR) to obtain star formation histories of seventeen sub-galactic regions across the Condor. These regions are large enough to be galaxies themselves, with 32.3 million light-years in diameter. We find that the Condor was already very massive before this interaction and that it was much less affected by the passage of the companion than previously thought. We also

Observing Galaxy Mergers in Simulations

NASA Astrophysics Data System (ADS)

Snyder, Gregory

2018-01-01

I will describe results on mergers and morphology of distant galaxies. By mock-observing 3D cosmological simulations, we aim to contrast theory with data, design better diagnostics of physical processes, and examine unexpected signatures of galaxy formation. Recently, we conducted mock surveys of the Illustris Simulations to learn how mergers would appear in deep HST and JWST surveys. With this approach, we reconciled merger rates estimated using observed close galaxy pairs with intrinsic merger rates predicted by theory. This implies that the merger-pair observability time is probably shorter in the early universe, and therefore that major mergers are more common than implied by the simplest arguments. Further, we show that disturbance-based diagnostics of late-stage mergers can be improved significantly by combining multi-dimensional image information with simulated merger identifications to train automated classifiers. We then apply these classifiers to real measurements from the CANDELS fields, recovering a merger fraction increasing with redshift in broad agreement with pair fractions and simulations, and with statistical errors smaller by a factor of two than classical morphology estimators. This emphasizes the importance of using robust training sets, including cosmological simulations and multidimensional data, for interpreting observed processes in galaxy evolution.

Overdensity of galaxies in the environment of quasar pairs

NASA Astrophysics Data System (ADS)

Sandrinelli, A.; Falomo, R.; Treves, A.; Scarpa, R.; Uslenghi, M.

2018-03-01

We report on a study of the galaxy environments of low redshift physical quasars pairs. We selected 20 pairs having projected separation < 0.5 Mpc and difference of systemic velocity < 800 km s-1. Using Sloan Digital Sky Survey images, we evaluated the galaxy overdensity around these quasars in pairs and then compare it with that of a sample of isolated quasars with same redshift and luminosity. It is found that on average there is a systematic larger overdensity of galaxies around quasars in pairs with respect to that of isolated quasars. This may represent a significant link between nuclear activity and galaxy environment. However, at odds with that, the closest quasar pairs seem to inhabit poorer environments. Implications of present results and perspectives for future work are briefly discussed.

The effects of assembly bias on the inference of matter clustering from galaxy-galaxy lensing and galaxy clustering

NASA Astrophysics Data System (ADS)

McEwen, Joseph E.; Weinberg, David H.

2018-07-01

The combination of galaxy-galaxy lensing and galaxy clustering is a promising route to measuring the amplitude of matter clustering and testing modified gravity theories of cosmic acceleration. Halo occupation distribution (HOD) modelling can extend the approach down to non-linear scales, but galaxy assembly bias could introduce systematic errors by causing the HOD to vary with the large-scale environment at fixed halo mass. We investigate this problem using the mock galaxy catalogs created by Hearin & Watson (2013, HW13), which exhibit significant assembly bias because galaxy luminosity is tied to halo peak circular velocity and galaxy colour is tied to halo formation time. The preferential placement of galaxies (especially red galaxies) in older haloes affects the cutoff of the mean occupation function ⟨Ncen(Mmin)⟩ for central galaxies, with haloes in overdense regions more likely to host galaxies. The effect of assembly bias on the satellite galaxy HOD is minimal. We introduce an extended, environment-dependent HOD (EDHOD) prescription to describe these results and fit galaxy correlation measurements. Crucially, we find that the galaxy-matter cross-correlation coefficient, rgm(r) ≡ ξgm(r) . [ξmm(r)ξgg(r)]-1/2, is insensitive to assembly bias on scales r ≳ 1 h-1 Mpc, even though ξgm(r) and ξgg(r) are both affected individually. We can therefore recover the correct ξmm(r) from the HW13 galaxy-galaxy and galaxy-matter correlations using either a standard HOD or EDHOD fitting method. For Mr ≤ -19 or Mr ≤ -20 samples the recovery of ξmm(r) is accurate to 2 per cent or better. For a sample of red Mr ≤ -20 galaxies, we achieve 2 per cent recovery at r ≳ 2 h-1 Mpc with EDHOD modelling but lower accuracy at smaller scales or with a standard HOD fit. Most of our mock galaxy samples are consistent with rgm = 1 down to r = 1 h-1 Mpc, to within the uncertainties set by our finite simulation volume.

The effects of assembly bias on the inference of matter clustering from galaxy-galaxy lensing and galaxy clustering

NASA Astrophysics Data System (ADS)

McEwen, Joseph E.; Weinberg, David H.

2018-04-01

The combination of galaxy-galaxy lensing (GGL) and galaxy clustering is a promising route to measuring the amplitude of matter clustering and testing modified gravity theories of cosmic acceleration. Halo occupation distribution (HOD) modeling can extend the approach down to nonlinear scales, but galaxy assembly bias could introduce systematic errors by causing the HOD to vary with large scale environment at fixed halo mass. We investigate this problem using the mock galaxy catalogs created by Hearin & Watson (2013, HW13), which exhibit significant assembly bias because galaxy luminosity is tied to halo peak circular velocity and galaxy colour is tied to halo formation time. The preferential placement of galaxies (especially red galaxies) in older halos affects the cutoff of the mean occupation function for central galaxies, with halos in overdense regions more likely to host galaxies. The effect of assembly bias on the satellite galaxy HOD is minimal. We introduce an extended, environment dependent HOD (EDHOD) prescription to describe these results and fit galaxy correlation measurements. Crucially, we find that the galaxy-matter cross-correlation coefficient, rgm(r) ≡ ξgm(r) . [ξmm(r)ξgg(r)]-1/2, is insensitive to assembly bias on scales r ≳ 1 h^{-1} Mpc, even though ξgm(r) and ξgg(r) are both affected individually. We can therefore recover the correct ξmm(r) from the HW13 galaxy-galaxy and galaxy-matter correlations using either a standard HOD or EDHOD fitting method. For Mr ≤ -19 or Mr ≤ -20 samples the recovery of ξmm(r) is accurate to 2% or better. For a sample of red Mr ≤ -20 galaxies we achieve 2% recovery at r ≳ 2 h^{-1} Mpc with EDHOD modeling but lower accuracy at smaller scales or with a standard HOD fit. Most of our mock galaxy samples are consistent with rgm = 1 down to r = 1h-1Mpc, to within the uncertainties set by our finite simulation volume.

The demography of extraterrestrial civilizations

NASA Technical Reports Server (NTRS)

Billingham, J.

1981-01-01

Studies carried out within the last ten years on the nature and distribution of extraterrestrial intelligent life are reviewed. Arguments for the absence of intelligent life in the Galaxy based on the assumption that at least some of these would have engaged in colonization and for the presence of colonies of extraterrestrials in some undiscovered location in the solar system are presented, and it is noted that both these views rest on the notion that interstellar travel can be achieved at high velocities in very large vehicles, which has been questioned. Alternative suggestions concerning interstellar exploration by automated probes and the possible extended time scale and motivation for galactic colonization are pointed out. Attention is then given to arguments for the extreme smallness of one of the factors in the Drake equation used to estimate the number of communicative extraterrestrial civilizations in the Galaxy, including the frequency of single stars, the likelihood that planets with the correct initial composition and conditions for life are at the proper distance from their stars, the probability of the formation of DNA and the origin of life, and the time for the evolution of intelligence. It is concluded that it seems likely that other civilizations exist in the Galaxy, although the number and distribution of such civilizations may only be determined by the detection of one or more examples.

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.

Kinematic Evolution of Simulated Star-Forming Galaxies

NASA Technical Reports Server (NTRS)

Kassin, Susan A.; Brooks, Alyson; Governato, Fabio; Weiner, Benjamin J.; Gardner, Jonathan P.

2014-01-01

Recent observations have shown that star-forming galaxies like our own Milky Way evolve kinematically into ordered thin disks over the last approximately 8 billion years since z = 1.2, undergoing a process of "disk settling." For the first time, we study the kinematic evolution of a suite of four state of the art "zoom in" hydrodynamic simulations of galaxy formation and evolution in a fully cosmological context and compare with these observations. Until now, robust measurements of the internal kinematics of simulated galaxies were lacking as the simulations suffered from low resolution, overproduction of stars, and overly massive bulges. The current generation of simulations has made great progress in overcoming these difficulties and is ready for a kinematic analysis. We show that simulated galaxies follow the same kinematic trends as real galaxies: they progressively decrease in disordered motions (sigma(sub g)) and increase in ordered rotation (V(sub rot)) with time. The slopes of the relations between both sigma(sub g) and V(sub rot) with redshift are consistent between the simulations and the observations. In addition, the morphologies of the simulated galaxies become less disturbed with time, also consistent with observations. This match between the simulated and observed trends is a significant success for the current generation of simulations, and a first step in determining the physical processes behind disk settling.

The galaxy clustering crisis in abundance matching

NASA Astrophysics Data System (ADS)

Campbell, Duncan; van den Bosch, Frank C.; Padmanabhan, Nikhil; Mao, Yao-Yuan; Zentner, Andrew R.; Lange, Johannes U.; Jiang, Fangzhou; Villarreal, Antonio

2018-06-01

Galaxy clustering on small scales is significantly underpredicted by sub-halo abundance matching (SHAM) models that populate (sub-)haloes with galaxies based on peak halo mass, Mpeak. SHAM models based on the peak maximum circular velocity, Vpeak, have had much better success. The primary reason for Mpeak-based models fail is the relatively low abundance of satellite galaxies produced in these models compared to those based on Vpeak. Despite success in predicting clustering, a simple Vpeak-based SHAM model results in predictions for galaxy growth that are at odds with observations. We evaluate three possible remedies that could `save' mass-based SHAM: (1) SHAM models require a significant population of `orphan' galaxies as a result of artificial disruption/merging of sub-haloes in modern high-resolution dark matter simulations; (2) satellites must grow significantly after their accretion; and (3) stellar mass is significantly affected by halo assembly history. No solution is entirely satisfactory. However, regardless of the particulars, we show that popular SHAM models based on Mpeak cannot be complete physical models as presented. Either Vpeak truly is a better predictor of stellar mass at z ˜ 0 and it remains to be seen how the correlation between stellar mass and Vpeak comes about, or SHAM models are missing vital component(s) that significantly affect galaxy clustering.

Relational demography in the workplace and health: an analysis of gender and the subordinate-superordinate role-set.

PubMed

Schieman, Scott; McMullen, Taralyn

2008-09-01

Using data from a 2005 national survey of working adults in the United States, we examine the effects of the gender composition of the superordinate-subordinate role-set on mental and physical health measures. Subordinates' and superordinates' genders are important determinants. Men who work in gender-mixed superordinate contexts (i.e., with one male and one female superior) report lower levels of distress and physical symptoms than men who work with one male superior. Women who work with one male superior report less distress and fewer physical symptoms compared to women who work with one female superior or in gender-mixed superordinate contexts. With a few exceptions, these observations generally hold net of occupation, job sector, and an array of work-related conditions. We discuss the implications of these findings in light of predictions derived from the similarity-attraction and role congruity theories. We also outline ways that theoretical development in relational demography can be refined by a more specific focus on the demographic characteristics--especially gender--of the superordinate-subordinate role-set.

Narrow-Line Seyfert 1 Galaxies

NASA Technical Reports Server (NTRS)

Leighly, Karen M.

2000-01-01

The primary work during this year has been the analysis and interpretation of our HST spectra from two extreme Narrow-line Seyfert 1 galaxies (NLS1s) Infrared Astronomy Satellite (IRAS) 13224-3809 and 1H 0707-495. This work has been presented as an invited talk at the workshop entitled "Observational and theoretical progress in the Study of Narrow-line Seyfert 1 Galaxies" held in Bad Honnef, Germany December 8-11, as a contributed talk at the January 2000 AAS meeting in Atlanta, Georgia, and as a contributed talk at the workshop "Probing the Physics of Active Galactic Nuclei by Multiwavelength Monitoring" held at Goddard Space Flight Center June 20-22, 2000.

Properties of galaxies reproduced by a hydrodynamic simulation.

PubMed

Vogelsberger, M; Genel, S; Springel, V; Torrey, P; Sijacki, D; Xu, D; Snyder, G; Bird, S; Nelson, D; Hernquist, L

2014-05-08

Previous simulations of the growth of cosmic structures have broadly reproduced the 'cosmic web' of galaxies that we see in the Universe, but failed to create a mixed population of elliptical and spiral galaxies, because of numerical inaccuracies and incomplete physical models. Moreover, they were unable to track the small-scale evolution of gas and stars to the present epoch within a representative portion of the Universe. Here we report a simulation that starts 12 million years after the Big Bang, and traces 13 billion years of cosmic evolution with 12 billion resolution elements in a cube of 106.5 megaparsecs a side. It yields a reasonable population of ellipticals and spirals, reproduces the observed distribution of galaxies in clusters and characteristics of hydrogen on large scales, and at the same time matches the 'metal' and hydrogen content of galaxies on small scales.

Mass and Environment as Drivers of Galaxy Evolution: Simplicity and its Consequences

NASA Astrophysics Data System (ADS)

Peng, Yingjie

2012-01-01

The galaxy population appears to be composed of infinitely complex different types and properties at first sight, however, when large samples of galaxies are studied, it appears that the vast majority of galaxies just follow simple scaling relations and similar evolutional modes while the outliers represent some minority. The underlying simplicities of the interrelationships among stellar mass, star formation rate and environment are seen in SDSS and zCOSMOS. We demonstrate that the differential effects of mass and environment are completely separable to z 1, indicating that two distinct physical processes are operating, namely the "mass quenching" and "environment quenching". These two simple quenching processes, plus some additional quenching due to merging, then naturally produce the Schechter form of the galaxy stellar mass functions and make quantitative predictions for the inter-relationships between the Schechter parameters of star-forming and passive galaxies in different environments. All of these detailed quantitative relationships are indeed seen, to very high precision, in SDSS, lending strong support to our simple empirically-based model. The model also offers qualitative explanations for the "anti-hierarchical" age-mass relation and the alpha-enrichment patterns for passive galaxies and makes some other testable predictions such as the mass function of the population of transitory objects that are in the process of being quenched, the galaxy major- and minor-merger rates, the galaxy stellar mass assembly history, star formation history and etc. Although still purely phenomenological, the model makes clear what the evolutionary characteristics of the relevant physical processes must in fact be.

Luminous Blue Compact Galaxies: Probes of galaxy assembly

NASA Astrophysics Data System (ADS)

Newton, Cassidy Louann

The life cycles of galaxies over cosmic time is yet to be fully understood. How did galaxies evolve from their formative stages to the structures we observe today? This dissertation details the identification and analysis of a sample of Luminous Blue Compact Galaxies (LBCGs), a class of galaxy in the local (z < 0.05) universe exhibiting blue colors, high surface brightness, and high star formation rates. These systems appear to be very similar in their global properties to the early evolutionary phases of most galaxies, however their locality permits detailed investigation over a broad range of the electromagnetic spectrum in contrast to the smaller angular sizes and extreme faintness of distant galaxies. We use a combination of optical, ultraviolet, and infrared data to investigate a sample of LBCGs utilizing space and ground-based data.

Galaxy NGC 55

NASA Image and Video Library

2003-12-10

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. http://photojournal.jpl.nasa.gov/catalog/PIA04923

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.

Galaxy bachelors, couples, spouses: Star formation in interacting galaxies

NASA Astrophysics Data System (ADS)

Sun, Jing; Barger, Kathleen; Richstein, Hannah; SDSS-IV/MaNGA

2017-01-01

We investigate the star formation activity in three galaxy systems in different stages of interaction to determine how the environment of galaxies affects their star forming ability and potential. These systems include an isolated galaxy, a pair of interacting galaxies, and a pair of merging galaxies. All of the target galaxies in these systems have similar stellar masses and similar radii and are at similar redshifts. We trace the star formation activity over the past 1-2 Gyr using spatially and kinematically resolved H-alpha emission, H-alpha equivalent width, and 4000-Angstrom break maps. This work is based on data from the fourth-generation Sloan Digital Sky Survey (SDSS-IV)/Mapping Nearby Galaxies at Apache Point Observatory (MaNGA), and is part of the Project No.0285 in SDSS-IV.

Galaxy pairs in the SDSS - XIII. The connection between enhanced star formation and molecular gas properties in galaxy mergers

NASA Astrophysics Data System (ADS)

Violino, Giulio; Ellison, Sara L.; Sargent, Mark; Coppin, Kristen E. K.; Scudder, Jillian M.; Mendel, Trevor J.; Saintonge, Amelie

2018-05-01

We investigate the connection between star formation and molecular gas properties in galaxy mergers at low redshift (z ≤ 0.06). The study we present is based on IRAM 30-m CO(1-0) observations of 11 galaxies with a close companion selected from the Sloan Digital Sky Survey (SDSS). The pairs have mass ratios ≤4, projected separations rp ≤ 30 kpc and velocity separations ΔV ≤ 300 km s-1, and have been selected to exhibit enhanced specific star formation rates (sSFRs). We calculate molecular gas (H2) masses, assigning to each galaxy a physically motivated conversion factor αCO, and we derive molecular gas fractions and depletion times. We compare these quantities with those of isolated galaxies from the extended CO Legacy Data base for the GALEX Arecibo SDSS Survey sample (xCOLDGASS; Saintonge et al.) with gas quantities computed in an identical way. Ours is the first study which directly compares the gas properties of galaxy pairs and those of a control sample of normal galaxies with rigorous control procedures and for which SFR and H2 masses have been estimated using the same method. We find that the galaxy pairs have shorter depletion times and an average molecular gas fraction enhancement of 0.4 dex compared to the mass matched control sample drawn from xCOLDGASS. However, the gas masses (and fractions) in galaxy pairs and their depletion times are consistent with those of non-mergers whose SFRs are similarly elevated. We conclude that both external interactions and internal processes may lead to molecular gas enhancement and decreased depletion times.

Astronomers Discover Spectacular Structure in Distant Galaxy

NASA Astrophysics Data System (ADS)

1999-01-01

Researchers using the National Science Foundation's Very Large Array (VLA) radio telescope have imaged a "spectacular and complex structure" in a galaxy 50 million light-years away. Their work both resolves a decades-old observational mystery and revises current theories about the origin of X-ray emission coming from gas surrounding the galaxy. The new VLA image is of the galaxy M87, which harbors at its core a supermassive black hole spewing out jets of subatomic particles at nearly the speed of light and also is the central galaxy of the Virgo Cluster of galaxies. The VLA image is the first to show detail of a larger structure that originally was detected by radio astronomers more than a half-century ago. Analysis of the new image indicates that astronomers will have to revise their ideas about the physics of what causes X-ray emission in the cores of many galaxy clusters. Frazer Owen of the National Radio Astronomy Observatory (NRAO) in Socorro, NM; Jean Eilek of the New Mexico Institute of Mining and Technology (NM Tech) in Socorro, NM; and Namir Kassim of the Naval Research Laboratory in Washington, DC, announced their discovery at the American Astronomical Society's meeting today in Austin, TX. The new observations show two large, bubble-like lobes, more than 200,000 light-years across, that emit radio waves. These lobes, which are intricately detailed, apparently are powered by gravitational energy released from the black hole at the galaxy's center. "We think that material is flowing outward from the galaxy's core into these large, bright, radio-emitting 'bubbles,'" Owen said. The newly-discovered "bubbles" sit inside a region of the galaxy known to be emitting X-rays. Theorists have speculated that this X-ray emission arises when gas that originally was part of the Virgo Cluster of galaxies, cools and falls inwards onto M87 itself, at the center of the cluster. Such "cooling flows" are commonly thought to be responsible for strong X-ray emission in many

The Hydrodynamics of Galaxy Transformation in Extreme Cluster Environments

NASA Astrophysics Data System (ADS)

Vijayaraghavan, Rukmani

2017-08-01

Cluster of galaxies are hostile environments. Infalling cluster galaxies are stripped of their dark matter, stars, and hot and cold interstellar medium gas. The ISM, in addition to tidal and ram pressure stripping, can evaporate due to thermal conduction. Gas loss and the subsequent suppression of star formation is not straightforward: magnetic fields in the ISM and ICM shield galaxies and their stripped tails from shear instabilities and conduction, radiative cooling can inhibit gas loss, and feedback from stars and AGN can replenish the ISM. While there is observational evidence that these processes operate, a theoretical understanding of the physics controlling the energy cycle in cluster galaxies remains elusive. Additionally, galaxies have a significant impact on ICM evolution: orbiting galaxies stir up and stretch ICM magnetic field lines, inject turbulence into the ICM via their wakes and g-waves, and infuse metals into the ICM. Quantifying the balance between processes that remove, retain, and replenish the ISM, and the impact of galaxies on the ICM require specialized hydrodynamic simulations of the cluster environment and its galaxies. I will present results from some of these simulations that include ram pressure stripping of galaxies' hot ISM, the effect of magnetic fields on this process, and the effectiveness of isotropic and anisotropic thermal conduction in removing and retaining the ISM. I will also quantify magnetic field amplification and turbulence injection due to orbiting galaxies, and implications for X-ray and radio observations and measurements of galactic coronae, tails, magnetic fields, and turbulence.

Moving-mesh cosmology: characteristics of galaxies and haloes

NASA Astrophysics Data System (ADS)

Kereš, Dušan; Vogelsberger, Mark; Sijacki, Debora; Springel, Volker; Hernquist, Lars

2012-09-01

We discuss cosmological hydrodynamic simulations of galaxy formation performed with the new moving-mesh code AREPO, which promises higher accuracy compared with the traditional smoothed particle hydrodynamics (SPH) technique that has been widely employed for this problem. In this exploratory study, we deliberately limit the complexity of the physical processes followed by the code for ease of comparison with previous calculations, and include only cooling of gas with a primordial composition, heating by a spatially uniform ultraviolet background, and a simple subresolution model for regulating star formation in the dense interstellar medium. We use an identical set of physics in corresponding simulations carried out with the well-tested SPH code GADGET, adopting also the same high-resolution gravity solver. We are thus able to compare both simulation sets on an object-by-object basis, allowing us to cleanly isolate the impact of different hydrodynamical methods on galaxy and halo properties. In accompanying papers, Vogelsberger et al. and Sijacki et al., we focus on an analysis of the global baryonic statistics predicted by the simulation codes, and complementary idealized simulations that highlight the differences between the hydrodynamical schemes. Here we investigate their influence on the baryonic properties of simulated galaxies and their surrounding haloes. We find that AREPO leads to significantly higher star formation rates for galaxies in massive haloes and to more extended gaseous discs in galaxies, which also feature a thinner and smoother morphology than their GADGET counterparts. Consequently, galaxies formed in AREPO have larger sizes and higher specific angular momentum than their SPH correspondents. Interestingly, the more efficient cooling flows in AREPO yield higher densities and lower entropies in halo centres compared to GADGET, whereas the opposite trend is found in halo outskirts. The cooling differences leading to higher star formation rates

Galaxy Zoo: Infrared and Optical Morphology

NASA Astrophysics Data System (ADS)

Carla Shanahan, Jesse; Lintott, Chris; Zoo, Galaxy

2018-01-01

We present the detailed, visual morphologies of approximately 60,000 galaxies observed by the UKIRT Infrared Deep Sky Survey and then classified by participants in the Galaxy Zoo project. Our sample is composed entirely of nearby objects with redshifts of z ≤ 0.3, which enables us to robustly analyze their morphological characteristics including smoothness, bulge properties, spiral structure, and evidence of bars or rings. The determination of these features is made via a consensus-based analysis of the Galaxy Zoo project data in which inconsistent and outlying classifications are statistically down-weighted. We then compare these classifications of infrared morphology to the objects’ optical classifications in the Galaxy Zoo 2 release (Willett et al. 2013). It is already known that morphology is an effective tool for uncovering a galaxy’s dynamical past, and previous studies have shown significant correlations with physical characteristics such as stellar mass distribution and star formation history. We show that majority of the sample has agreement or expected differences between the optical and infrared classifications, but also present a preliminary analysis of a subsample of objects with striking discrepancies.

A Bayesian Hierarchical Approach to Galaxy-Galaxy Lensing

NASA Astrophysics Data System (ADS)

Sonnenfeld, Alessandro; Leauthaud, Alexie

2018-04-01

We present a Bayesian hierarchical inference formalism to study the relation between the properties of dark matter halos and those of their central galaxies using weak gravitational lensing. Unlike traditional methods, this technique does not resort to stacking the weak lensing signal in bins, and thus allows for a more efficient use of the information content in the data. Our method is particularly useful for constraining scaling relations between two or more galaxy properties and dark matter halo mass, and can also be used to constrain the intrinsic scatter in these scaling relations. We show that, if observational scatter is not properly accounted for, the traditional stacking method can produce biased results when exploring correlations between multiple galaxy properties and halo mass. For example, this bias can affect studies of the joint correlation between galaxy mass, halo mass, and galaxy size, or galaxy colour. In contrast, our method easily and efficiently handles the intrinsic and observational scatter in multiple galaxy properties and halo mass. We test our method on mocks with varying degrees of complexity. We find that we can recover the mean halo mass and concentration, each with a 0.1 dex accuracy, and the intrinsic scatter in halo mass with a 0.05 dex accuracy. In its current version, our method will be most useful for studying the weak lensing signal around central galaxies in groups and clusters, as well as massive galaxies samples with log M* > 11, which have low satellite fractions.

A Bayesian hierarchical approach to galaxy-galaxy lensing

NASA Astrophysics Data System (ADS)

Sonnenfeld, Alessandro; Leauthaud, Alexie

2018-07-01

We present a Bayesian hierarchical inference formalism to study the relation between the properties of dark matter haloes and those of their central galaxies using weak gravitational lensing. Unlike traditional methods, this technique does not resort to stacking the weak lensing signal in bins, and thus allows for a more efficient use of the information content in the data. Our method is particularly useful for constraining scaling relations between two or more galaxy properties and dark matter halo mass, and can also be used to constrain the intrinsic scatter in these scaling relations. We show that, if observational scatter is not properly accounted for, the traditional stacking method can produce biased results when exploring correlations between multiple galaxy properties and halo mass. For example, this bias can affect studies of the joint correlation between galaxy mass, halo mass, and galaxy size, or galaxy colour. In contrast, our method easily and efficiently handles the intrinsic and observational scatter in multiple galaxy properties and halo mass. We test our method on mocks with varying degrees of complexity. We find that we can recover the mean halo mass and concentration, each with a 0.1 dex accuracy, and the intrinsic scatter in halo mass with a 0.05 dex accuracy. In its current version, our method will be most useful for studying the weak lensing signal around central galaxies in groups and clusters, as well as massive galaxies samples with log M* > 11, which have low satellite fractions.

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.

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.

The dwarf galaxy population of nearby galaxy clusters

NASA Astrophysics Data System (ADS)

Lisker, Thorsten; Wittmann, Carolin; Pak, Mina; Janz, Joachim; Bialas, Daniel; Peletier, Reynier; Grebel, Eva; Falcon Barroso, Jesus; Toloba, Elisa; Smakced Collaboration, Focus Collaboration

2015-01-01

The Fornax, Virgo, Ursa Major and Perseus galaxy clusters all have very different characteristics, in terms of their density, mass, and large-scale environment. We can regard these clusters as laboratories for studying environmental influence on galaxy evolution, using the sensitive low-mass galaxies as probes for external mechanisms. Here we report on recent and ongoing observational studies of the said clusters with imaging and spectroscopy, as well as on the interpretation of present-day cluster galaxy populations with the aid of cosmological simulations.Multicolor imaging data allow us to identify residual star formation in otherwise red early-type dwarf galaxies, which hold clues to the strength of gas stripping processes. Major-axis spectra and 2D kinematical maps provide insight regarding the amount of rotational support and how much dynamical heating a dwarf galaxy may have experienced. To this end, dedicated N-body simulations that follow the evolution of galaxies since early epochs reveal their path through parameter space, and can be compared to observations in order to understand the time-integrated effect of environmental influence.

Activity of the Seyfert galaxy neighbours

NASA Astrophysics Data System (ADS)

Koulouridis, E.; Plionis, M.; Chavushyan, V.; Dultzin, D.; Krongold, Y.; Georgantopoulos, I.; León-Tavares, J.

2013-04-01

We present a follow-up study of a series of papers concerning the role of close interactions as a possible triggering mechanism of AGN activity. We have already studied the close (≤100 h-1 kpc) and the large-scale (≤1 h-1 Mpc) environment of a local sample of Sy1, Sy2, and bright IRAS galaxies (BIRG) and of their respective control samples. The results led us to the conclusion that a close encounter appears capable of activating a sequence where an absorption line galaxy (ALG) galaxy first becomes a starburst, then a Sy2, and finally a Sy1. Here we investigate the activity of neighbouring galaxies of different types of AGN, since both galaxies of an interacting pair should be affected. To this end we present the optical spectroscopy and X-ray imaging of 30 neighbouring galaxies around two local (z ≲ 0.034) samples of 10 Sy1 and 13 Sy2 galaxies. Although this is a pilot study of a small sample, various interesting trends have been discovered that imply physical mechanisms that may lead to different Seyfert types. Based on the optical spectroscopy, we find that more than 70% of all neighbouring galaxies exhibit star forming and/or nuclear activity (namely recent star formation and/or AGN), while an additional X-ray analysis showed that this percentage might be significantly higher. Furthermore, we find a statistically significant correlation, at a 99.9% level, between the value of the neighbour's [OIII]/Hβ ratio and the activity type of the central active galaxy, i.e. the neighbours of Sy2 galaxies are systematically more ionized than the neighbours of Sy1s. This result, in combination with trends found using the Equivalent Width of the Hα emission line and the stellar population synthesis code STARLIGHT, indicate differences in the stellar mass, metallicity, and star formation history between the samples. Our results point towards a link between close galaxy interactions and activity and also provide more clues regarding the possible evolutionary sequence

X-ray Emission from Early Universe Analog Galaxies

NASA Astrophysics Data System (ADS)

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

2016-01-01

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

Fitting the spectral energy distributions of galaxies with CIGALE : Code Investigating GALaxy Emission

NASA Astrophysics Data System (ADS)

Giovannoli, E.; Buat, V.

2013-03-01

We use the code CIGALE (Code Investigating Galaxies Emission: Burgarella et al. 2005; Noll et al. 2009) which provides physical information about galaxies by fitting their UV (ultraviolet)-to-IR (infrared) spectral energy distribuition (SED). CIGALE is based on the use of a UV-optical stellar SED plus a dust IR-emitting component. We study a sample of 136 Luminous Infrared Galaxies (LIRGs) at z˜0.7 in the ECDF-S previously studied in Giovannoli et al. (2011). We focus on the way the empirical Dale & Helou (2002) templates reproduce the observed SEDs of the LIRGs. Fig. 1 shows the total infrared luminosity (L IR ) provided by CIGALE using the 64 templates (x axis) and using 2 templates (y axis) representative of the whole sample. Despite the larger dispersion when only 1 or 2 Herschel data are available, the agreement between both values is good with Δ log L IR = 0.0013 ± 0.045 dex. We conclude that 2 IR SEDs can be used alone to determine the L IR of LIRGs at z˜0.7 in an SED-fitting procedure.

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

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

Long-term change in a behavioural trait: truncated spawning distribution and demography in Northeast Arctic cod.

PubMed

Opdal, Anders Frugård; Jørgensen, Christian

2015-04-01

Harvesting may be a potent driver of demographic change and contemporary evolution, which both may have great impacts on animal populations. Research has focused on changes in phenotypic traits that are easily quantifiable and for which time series exist, such as size, age, sex, or gonad size, whereas potential changes in behavioural traits have been under-studied. Here, we analyse potential drivers of long-term changes in a behavioural trait for the Northeast Arctic stock of Atlantic cod Gadus morhua, namely choice of spawning location. For 104 years (1866-1969), commercial catches were recorded annually and reported by county along the Norwegian coast. During this time period, spawning ground distribution has fluctuated with a trend towards more northerly spawning. Spawning location is analysed against a suite of explanatory factors including climate, fishing pressure, density dependence, and demography. We find that demography (age or age at maturation) had the highest explanatory power for variation in spawning location, while climate had a limited effect below statistical significance. As to potential mechanisms, some effects of climate may act through demography, and explanatory variables for demography may also have absorbed direct evolutionary change in migration distance for which proxies were unavailable. Despite these caveats, we argue that fishing mortality, either through demographic or evolutionary change, has served as an effective driver for changing spawning locations in cod, and that additional explanatory factors related to climate add no significant information. © 2014 The Authors. Global Change Biology Published by John Wiley & Sons Ltd.

How to quench a galaxy

NASA Astrophysics Data System (ADS)

Pontzen, Andrew; Tremmel, Michael; Roth, Nina; Peiris, Hiranya V.; Saintonge, Amélie; Volonteri, Marta; Quinn, Tom; Governato, Fabio

2017-02-01

We show how the interplay between active galactic nuclei (AGNs) and merger history determines whether a galaxy quenches star formation (SF) at high redshift. We first simulate, in a full cosmological context, a galaxy of total dynamical mass Mvir = 1012 M⊙ at z = 2. Then we systematically alter the accretion history of the galaxy by minimally changing the linear overdensity in the initial conditions. This `genetic modification' approach allows the generation of three sets of Λ CDM initial conditions leading to maximum merger ratios of 1:10, 1:5 and 2:3, respectively. The changes leave the final halo mass, large-scale structure and local environment unchanged, providing a controlled numerical experiment. Interaction between the AGN physics and mergers in the three cases leads, respectively, to a star-forming, temporarily quenched and permanently quenched galaxy. However, the differences do not primarily lie in the black hole accretion rates, but in the kinetic effects of the merger: the galaxy is resilient against AGN feedback unless its gaseous disc is first disrupted. Typical accretion rates are comparable in the three cases, falling below 0.1 M⊙ yr-1, equivalent to around 2 per cent of the Eddington rate or 10-3 times the pre-quenching star formation rate, in agreement with observations. This low level of black hole accretion can be sustained even when there is insufficient dense cold gas for SF. Conversely, supernova feedback is too distributed to generate outflows in high-mass systems, and cannot maintain quenching over periods longer than the halo gas cooling time.

Physics of Galaxy Clusters and How it Affects Cosmological Tests

NASA Technical Reports Server (NTRS)

Vikhlinin, Alexey; Oliversen, Ronald J. (Technical Monitor)

2002-01-01

We have worked on the analysis of the Chandra observations of the nearby and distant clusters of galaxies, and on the expansion of the sample of distant X-ray clusters based on the archival ROSAT PSPC data. Some of the scientific results are discussed.

A class of compact dwarf galaxies from disruptive processes in galaxy clusters.

PubMed

Drinkwater, M J; Gregg, M D; Hilker, M; Bekki, K; Couch, W J; Ferguson, H C; Jones, J B; Phillipps, S

2003-05-29

Dwarf galaxies have attracted increased attention in recent years, because of their susceptibility to galaxy transformation processes within rich galaxy clusters. Direct evidence for these processes, however, has been difficult to obtain, with a small number of diffuse light trails and intra-cluster stars being the only signs of galaxy disruption. Furthermore, our current knowledge of dwarf galaxy populations may be very incomplete, because traditional galaxy surveys are insensitive to extremely diffuse or compact galaxies. Aware of these concerns, we recently undertook an all-object survey of the Fornax galaxy cluster. This revealed a new population of compact members, overlooked in previous conventional surveys. Here we demonstrate that these 'ultra-compact' dwarf galaxies are structurally and dynamically distinct from both globular star clusters and known types of dwarf galaxy, and thus represent a new class of dwarf galaxy. Our data are consistent with the interpretation that these are the remnant nuclei of disrupted dwarf galaxies, making them an easily observed tracer of galaxy disruption.

Galaxy NGC 247

NASA Technical Reports Server (NTRS)

2003-01-01

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

Angular Momentum and Galaxy Formation Revisited

NASA Astrophysics Data System (ADS)

Romanowsky, Aaron J.; Fall, S. Michael

2012-12-01

-M sstarf scaling relations. This provides a physical motivation for characterizing galaxies most basically with two parameters: mass and bulge-to-disk ratio. Next, in an approach complementary to numerical simulations, we construct idealized models of angular momentum content in a cosmological context, using estimates of dark matter halo spin and mass from theoretical and empirical studies. We find that the width of the halo spin distribution cannot account for the differences between spiral and elliptical j sstarf, but that the observations are reproduced well if these galaxies simply retained different fractions of their initial j complement (~60% and ~10%, respectively). We consider various physical mechanisms for the simultaneous evolution of j sstarf and M sstarf (including outflows, stripping, collapse bias, and merging), emphasizing that the vector sum of all such processes must produce the observed j sstarf-M sstarf relations. We suggest that a combination of early collapse and multiple mergers (major or minor) may account naturally for the trend for ellipticals. More generally, the observed variations in angular momentum represent simple but fundamental constraints for any model of galaxy formation.

ANGULAR MOMENTUM AND GALAXY FORMATION REVISITED

DOE Office of Scientific and Technical Information (OSTI.GOV)

Romanowsky, Aaron J.; Fall, S. Michael

2012-12-15

follow separate, fundamental j{sub *}-M{sub *} scaling relations. This provides a physical motivation for characterizing galaxies most basically with two parameters: mass and bulge-to-disk ratio. Next, in an approach complementary to numerical simulations, we construct idealized models of angular momentum content in a cosmological context, using estimates of dark matter halo spin and mass from theoretical and empirical studies. We find that the width of the halo spin distribution cannot account for the differences between spiral and elliptical j{sub *}, but that the observations are reproduced well if these galaxies simply retained different fractions of their initial j complement ({approx}60% and {approx}10%, respectively). We consider various physical mechanisms for the simultaneous evolution of j{sub *} and M{sub *} (including outflows, stripping, collapse bias, and merging), emphasizing that the vector sum of all such processes must produce the observed j{sub *}-M{sub *} relations. We suggest that a combination of early collapse and multiple mergers (major or minor) may account naturally for the trend for ellipticals. More generally, the observed variations in angular momentum represent simple but fundamental constraints for any model of galaxy formation.« less

Neutral hydrogen in the Fourcade-Figueroa galaxy (A 1332 - 45)

NASA Astrophysics Data System (ADS)

Colomb, F. R.; Loiseau, N.; Testori, J. C.

The H I 21-cm line has been observed around the Fourcade-Figueroa galaxy (A 1332 - 45), a late spiral-type galaxy seen edge-on, with a systematic velocity of 823 km/s. Its distance is estimated as 3.2 Mpc, and the mass and other parameters of the galaxy are derived from the observed 21-cm profiles. The distance given for A 1332 - 45 agrees with the one adopted by Dottori and Fourcade (1973), and is at variance with the distance estimated by other authors. The possibility of a physical association with the Centaurus Group is discussed.

Gas inflow patterns and nuclear rings in barred galaxies

NASA Astrophysics Data System (ADS)

Shen, Juntai; Li, Zhi

2017-06-01

Nuclear rings, dust lanes, and nuclear spirals are common structures in the inner region of barred galaxies, with their shapes and properties linked to the physical parameters of the galaxies. We use high-resolution hydrodynamical simulations to study gas inflow patterns in barred galaxies, with special attention on the nuclear rings. The location and thickness of nuclear ringsare tightly correlated with galactic properties, such as the bar pattern speed and bulge central density, within certain ranges. We identify the backbone of nuclear rings with a major orbital family of bars. The rings form exactly at the radius where the residual angular momentum of inflowing gas balances the centrifugal force. We propose a new simple method to predict the bar pattern speed for barred galaxies possessing a nuclear ring, without actually doing simulations. We apply this method to some real galaxies and find that our predicted bar pattern speed compare reasonably well with other estimates. Our study may have important implications for using nuclear ringsto measure the parameters of real barred galaxies with detailed gas kinematics. We have also extended current hydrodynamical simulations to model gas features in the Milky Way.

Star clusters in evolving galaxies

NASA Astrophysics Data System (ADS)

Renaud, Florent

2018-04-01

Their ubiquity and extreme densities make star clusters probes of prime importance of galaxy evolution. Old globular clusters keep imprints of the physical conditions of their assembly in the early Universe, and younger stellar objects, observationally resolved, tell us about the mechanisms at stake in their formation. Yet, we still do not understand the diversity involved: why is star cluster formation limited to 105M⊙ objects in the Milky Way, while some dwarf galaxies like NGC 1705 are able to produce clusters 10 times more massive? Why do dwarfs generally host a higher specific frequency of clusters than larger galaxies? How to connect the present-day, often resolved, stellar systems to the formation of globular clusters at high redshift? And how do these links depend on the galactic and cosmological environments of these clusters? In this review, I present recent advances on star cluster formation and evolution, in galactic and cosmological context. The emphasis is put on the theory, formation scenarios and the effects of the environment on the evolution of the global properties of clusters. A few open questions are identified.

Demography of Mexican spotted owls in the Sacramento Mountains, New Mexico

Treesearch

Joseph L. Ganey; Gary C. White; James P. Ward; Sean C. Kyle; Darrell L. Apprill; Todd A. Rawlinson; Ryan S. Jonnes

2014-01-01

Information on population dynamics is key to gauging the status of threatened or endangered species. We monitored demography of a population of threatened Mexican spotted owls (Strix occidentalis lucida) in the Sacramento Mountains, New Mexico from 2003 to 2011. We estimated reproductive output for territorial pairs of owls; used mark-recapture methodology and Pradel...

Clusters of Galaxies

NASA Astrophysics Data System (ADS)

Huchtmeier, W. K.; Richter, O. G.; Materne, J.

1981-09-01

The large-scale structure of the universe is dominated by clustering. Most galaxies seem to be members of pairs, groups, clusters, and superclusters. To that degree we are able to recognize a hierarchical structure of the universe. Our local group of galaxies (LG) is centred on two large spiral galaxies: the Andromeda nebula and our own galaxy. Three sr:naller galaxies - like M 33 - and at least 23 dwarf galaxies (KraanKorteweg and Tammann, 1979, Astronomische Nachrichten, 300, 181) can be found in the evironment of these two large galaxies. Neighbouring groups have comparable sizes (about 1 Mpc in extent) and comparable numbers of bright members. Small dwarf galaxies cannot at present be observed at great distances.

Panchromatic spectral energy distributions of simulated galaxies: results at redshift z = 0

NASA Astrophysics Data System (ADS)

Goz, David; Monaco, Pierluigi; Granato, Gian Luigi; Murante, Giuseppe; Domínguez-Tenreiro, Rosa; Obreja, Aura; Annunziatella, Marianna; Tescari, Edoardo

2017-08-01

We present predictions of spectral energy distributions (SEDs), from the UV to the FIR, of simulated galaxies at z = 0. These were obtained by post-processing the results of an N-body+hydro simulation of a cosmological box of side 25 Mpc, which uses the Multi-Phase Particle Integrator (MUPPI) for star formation and stellar feedback, with the grasil-3d radiative transfer code that includes reprocessing of UV light by dust. Physical properties of our sample of ˜500 galaxies resemble observed ones, though with some tension at small and large stellar masses. Comparing predicted SEDs of simulated galaxies with different samples of local galaxies, we find that these resemble observed ones, when normalized at 3.6 μm. A comparison with the Herschel Reference Survey shows that the average SEDs of galaxies, divided in bins of star formation rate (SFR), are reproduced in shape and absolute normalization to within a factor of ˜2, while average SEDs of galaxies divided in bins of stellar mass show tensions that are an effect of the difference of simulated and observed galaxies in the stellar mass-SFR plane. We use our sample to investigate the correlation of IR luminosity in Spitzer and Herschel bands with several galaxy properties. SFR is the quantity that best correlates with IR light up to 160 μm, while at longer wavelengths better correlations are found with molecular mass and, at 500 μm, with dust mass. However, using the position of the FIR peak as a proxy for cold dust temperature, we assess that heating of cold dust is mostly determined by SFR, with stellar mass giving only a minor contribution. We finally show how our sample of simulated galaxies can be used as a guide to understand the physical properties and selection biases of observed samples.

On the interdependence of galaxy morphology, star formation and environment in massive galaxies in the nearby Universe

NASA Astrophysics Data System (ADS)

Bait, Omkar; Barway, Sudhanshu; Wadadekar, Yogesh

2017-11-01

Using multiwavelength data, from ultraviolet to optical to near-infrared to mid-infrared, for ˜6000 galaxies in the local Universe, we study the dependence of star formation on the morphological T-types for massive galaxies (log M*/M⊙ ≥ 10). We find that, early-type spirals (Sa-Sbc) and S0s predominate in the green valley, which is a transition zone between the star forming and quenched regions. Within the early-type spirals, as we move from Sa to Sbc spirals the fraction of green valley and quenched galaxies decreases, indicating the important role of the bulge in the quenching of galaxies. The fraction of early-type spirals decreases as we enter the green valley from the blue cloud, which coincides with the increase in the fraction of S0s. These points towards the morphological transformation of early-type spiral galaxies into S0s, which can happen due to environmental effects such as ram-pressure stripping, galaxy harassment or tidal interactions. We also find a second population of S0s that are actively star forming and are present in all environments. Since morphological T-type, specific star formation rate (sSFR), and environmental density are all correlated with each other, we compute the partial correlation coefficient for each pair of parameters while keeping the third parameter as a control variable. We find that morphology most strongly correlates with sSFR, independent of the environment, while the other two correlations (morphology-density and sSFR-environment) are weaker. Thus, we conclude that, for massive galaxies in the local Universe, the physical processes that shape their morphology are also the ones that determine their star-forming state.

Unveiling Galaxy Bias via the Halo Model, KiDS and GAMA

NASA Astrophysics Data System (ADS)

Dvornik, Andrej; Hoekstra, Henk; Kuijken, Konrad; Schneider, Peter; Amon, Alexandra; Nakajima, Reiko; Viola, Massimo; Choi, Ami; Erben, Thomas; Farrow, Daniel J.; Heymans, Catherine; Hildebrandt, Hendrik; Sifón, Cristóbal; Wang, Lingyu

2018-06-01

We measure the projected galaxy clustering and galaxy-galaxy lensing signals using the Galaxy And Mass Assembly (GAMA) survey and Kilo-Degree Survey (KiDS) to study galaxy bias. We use the concept of non-linear and stochastic galaxy biasing in the framework of halo occupation statistics to constrain the parameters of the halo occupation statistics and to unveil the origin of galaxy biasing. The bias function Γgm(rp), where rp is the projected comoving separation, is evaluated using the analytical halo model from which the scale dependence of Γgm(rp), and the origin of the non-linearity and stochasticity in halo occupation models can be inferred. Our observations unveil the physical reason for the non-linearity and stochasticity, further explored using hydrodynamical simulations, with the stochasticity mostly originating from the non-Poissonian behaviour of satellite galaxies in the dark matter haloes and their spatial distribution, which does not follow the spatial distribution of dark matter in the halo. The observed non-linearity is mostly due to the presence of the central galaxies, as was noted from previous theoretical work on the same topic. We also see that overall, more massive galaxies reveal a stronger scale dependence, and out to a larger radius. Our results show that a wealth of information about galaxy bias is hidden in halo occupation models. These models should therefore be used to determine the influence of galaxy bias in cosmological studies.

Exploring the Surface Brightness Breaks and Star Formation in Disk Galaxies

NASA Astrophysics Data System (ADS)

Malko, Bradley Ann; Hunter, Deidre Ann

2018-06-01

Stellar surface brightness profiles of both spirals and dwarf irregular galaxies often show breaks in which the exponential fall-off abruptly changes slope. Most often the profile is down-bending (Type II) in the outer disk, but sometimes it is up-bending (Type III). Stellar disks extend a long ways beyond the profile breaks, but we do not understand what happens physically at the breaks. To explore this we are examining the star formation activity, as traced with FUV emission, interior to the break compared to that exterior to the break in both dwarf irregulars and spiral galaxies. We present the results for the spiral galaxy NGC 2500 and compare it to the LITTLE THINGS dwarf irregular galaxies.

Cosmic web and star formation activity in galaxies at z ∼ 1

DOE Office of Scientific and Technical Information (OSTI.GOV)

Darvish, B.; Mobasher, B.; Sales, L. V.

We investigate the role of the delineated cosmic web/filaments on star formation activity by exploring a sample of 425 narrow-band selected Hα emitters, as well as 2846 color-color selected underlying star-forming galaxies for a large-scale structure at z = 0.84 in the COSMOS field from the HiZELS survey. Using the scale-independent Multi-scale Morphology Filter algorithm, we are able to quantitatively describe the density field and disentangle it into its major components: fields, filaments, and clusters. We show that the observed median star formation rate (SFR), stellar mass, specific SFR, the mean SFR-mass relation, and its scatter for both Hα emittersmore » and underlying star-forming galaxies do not strongly depend on different classes of environment, in agreement with previous studies. However, the fraction of Hα emitters varies with environment and is enhanced in filamentary structures at z ∼ 1. We propose mild galaxy-galaxy interactions as the possible physical agent for the elevation of the fraction of Hα star-forming galaxies in filaments. Our results show that filaments are the likely physical environments that are often classed as the 'intermediate' densities and that the cosmic web likely plays a major role in galaxy formation and evolution which has so far been poorly investigated.« less

Host galaxies of type ia supernovae from the nearby supernova factory

NASA Astrophysics Data System (ADS)

Childress, Michael Joseph

Type Ia Supernovae (SNe Ia) are excellent distance indicators, yet the full details of the underlying physical mechanism giving rise to these dramatic stellar deaths remain unclear. As large samples of cosmological SNe Ia continue to be collected, the scatter in brightnesses of these events is equally affected by systematic errors as statistical. Thus we need to understand the physics of SNe Ia better, and in particular we must know more about the progenitors of these SNe so that we can derive better estimates for their true intrinsic brightnesses. The host galaxies of SNe Ia provide important indirect clues as to the nature of SN Ia progenitors. In this Thesis we utilize the host galaxies of SNe Ia discovered by the Nearby Supernova Factory (SNfactory) to pursue several key investigations into the nature of SN Ia progenitors and their effects on SN Ia brightnesses. We first examine the host galaxy of SN 2007if, an important member of the subclass of SNe Ia whose extreme brightnesses indicate a progenitor that exceeded the canonical Chandrasekhar-mass value presumed for normal SNe Ia, and show that the host galaxy of this SN is composed of very young stars and has extremely low metallicity, providing important constraints on progenitor scenarios for this SN. We then utilize the full sample of SNfactory host galaxy masses (measured from photometry) and metallicities (derived from optical spectroscopy) to examine several global properties of SN Ia progenitors: (i) we show that SN Ia hosts show tight agreement with the normal galaxy mass-metallicity relation; (ii) comparing the observed distribution of SN Ia host galaxy masses to a theoretical model that couples galaxy physics to the SN Ia delay time distribution (DTD), we show the power of the SN Ia host mass distribution in constraining the SN Ia DTD; and (iii) we show that the lack of ultra-low metallicities in the SNfactory SN Ia host sample gives provisional support for the theorized low-metallicity inhibition of

Dynamically hot galaxies. I - Structural properties

NASA Technical Reports Server (NTRS)

Bender, Ralf; Burstein, David; Faber, S. M.

1992-01-01

Results are reported from an analysis of the structural properties of dynamically hot galaxies which combines central velocity dispersion, effective surface brightness, and effective radius into a new 3-space (k), in which the axes are parameters that are physically meaningful. Hot galaxies are found to divide into groups in k-space that closely parallel conventional morphological classifications, namely, luminous ellipticals, compacts, bulges, bright dwarfs, and dwarf spheroidals. A major sequence is defined by luminous ellipticals, bulges, and most compacts, which together constitute a smooth continuum in k-space. Several properties vary smoothly with mass along this continuum, including bulge-to-disk ratio, radio properties, rotation, degree of velocity anisotropy, and 'unrelaxed'. A second major sequence is comprised of dwarf ellipticals and dwarf spheroidals. It is suggested that mass loss is a major factor in hot dwarf galaxies, but the dwarf sequence cannot be simply a mass-loss sequence, as it has the wrong direction in k-space.

Merging Galaxies Create a Binary Quasar

NASA Astrophysics Data System (ADS)

2010-02-01

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

Galaxy Transformation Under Extreme Conditions: The Evolution of Galaxies in the Largest Structures in the High Redshift Universe

NASA Astrophysics Data System (ADS)

Lemaux, Brian Clark

This dissertation describes research performed in the field of observational astrophysics as part of the Observations of Redshift Evolution in Large Scale Environment (ORELSE) survey. The general motivation of the research presented in this dissertation is to investigate the processes responsible for the evolution of galaxies in a wide range of physical conditions over cosmic time. Throughout this dissertation, galaxy populations will be considered in the very nearby universe (i.e., within one billion light years from Earth), the middle-aged universe (i.e., eight billion years ago), and in the very early universe (i.e., just one billion years after the beginning of the universe). In each chapter I present unique data from observations taken and analyzed specifically for the ORELSE survey. In the first part of this dissertation I describe the context, aims, and current state of the ORELSE survey. The studies presented in this dissertation span a large range of galaxy samples and investigate a variety of different astrophysical phenomena. As all of these studies fall under the context of galaxy evolution, these initial sections will set the framework for the variety of studies presented in this thesis. In the second part of this dissertation I present four studies undertaken to investigate various aspects of galaxy evolution. The first of these studies is an investigation of a large population of very distant galaxies detected in one of the ORELSE fields. The survey in this field represents the deepest survey of a particular kind of very distant galaxy population known as Lymanalpha Emitter (LAEs). The number of LAEs found in this survey far exceeded expectations for such galaxies and are shown to be in excess of every other survey of similar galaxies at similar distances. This result has important consequences for galaxy evolution studies, as it suggests that faint LAEs may be much more numerous than previously thought. This work also has important consequences for

Intrinsic alignments in redMaPPer clusters - I. Central galaxy alignments and angular segregation of satellites

NASA Astrophysics Data System (ADS)

Huang, Hung-Jin; Mandelbaum, Rachel; Freeman, Peter E.; Chen, Yen-Chi; Rozo, Eduardo; Rykoff, Eli; Baxter, Eric J.

2016-11-01

The shapes of cluster central galaxies are not randomly oriented, but rather exhibit coherent alignments with the shapes of their parent clusters as well as with the surrounding large-scale structures. In this work, we aim to identify the galaxy and cluster quantities that most strongly predict the central galaxy alignment phenomenon among a large parameter space with a sample of 8237 clusters and 94 817 members within 0.1 < z < 0.35, based on the red-sequence Matched-filter Probabilistic Percolation cluster catalogue constructed from the Sloan Digital Sky Survey. We first quantify the alignment between the projected central galaxy shapes and the distribution of member satellites, to understand what central galaxy and cluster properties most strongly correlate with these alignments. Next, we investigate the angular segregation of satellites with respect to their central galaxy major axis directions, to identify the satellite properties that most strongly predict their angular segregation. We find that central galaxies are more aligned with their member galaxy distributions in clusters that are more elongated and have higher richness, and for central galaxies with larger physical size, higher luminosity and centring probability, and redder colour. Satellites with redder colour, higher luminosity, located closer to the central galaxy, and with smaller ellipticity show a stronger angular segregation towards their central galaxy major axes. Finally, we provide physical explanations for some of the identified correlations, and discuss the connection to theories of central galaxy alignments, the impact of primordial alignments with tidal fields, and the importance of anisotropic accretion.

The Role of Hot ISM in Galaxy Formation and Evolution

NASA Astrophysics Data System (ADS)

Ostriker, Jeremiah

2014-08-01

The cooling rate for hot gas in and around galaxies has a critical importance both in physically setting the basic mass scale for these massive, self-gravitating systems and as an observational tool for assessing formation models, by enabling the comparison between predicted and observed X-ray luminosities. Three classic papers in 1977 showed that it would be difficult for galaxies above a certain mass to cool on a dynamical timescale. That mass scale, in terms of fundamental physics is as follows: M ≃ [({Gm_p^2}/{hbar c})^{-2}({e^2}/{hbar c})^5({m_p}/{m_e})^{1/2}]m_{p} or roughly 10^{12} solar masses. Galaxies above this mass tend to be enveloped in the hot, X-ray emitting, gaseous halos familiar to Chandra observers and their predecessors. The outer parts of these gaseous halos are easily kept hot by SNI, dynamical in-fall of satellites and other processes, but the inner parts will repeatedly collapse into cooling flows, starbursts and AGN flare-ups. The thermal X-ray emission will be highly variable with this providing an important diagnostic for these physical processes. Also, normal cosmological inflow of gas onto massive galaxies can be shown to produce (absent feedback) more X-rays emission than is observed - providing yet another argument for feedback processes, which would reduce the ambient hot gas density. Finally, several postulated physical scenarios, such as gas rich ("wet") binary spiral mergers or thermal AGN feedback would produce X-ray emission far in excess of observational limits, again showing the power of X-ray observations as a critical diagnostic tool.

Characterizing the Interstellar and Circumgalactic Medium in Star-forming Galaxies

NASA Astrophysics Data System (ADS)

Du, Xinnan; Shapley, Alice; Crystal Martin, Alison Coil, Charles Steidel, Tucker Jones, Daniel Stark, Allison Strom

2018-01-01

Rest-frame UV and optical spectroscopy provide valuable information on the physical properties of the neutral and ionized interstellar medium (ISM) in star-forming galaxies, including both the systemic interstellar component originating from HII regions, and the multi-phase outflowing component associated with star-formation feedback. My thesis focuses on both the systemic and outflowing ISM in star-forming galaxies at redshift z ~ 1-4. With an unprecedented sample at z~1 with the rest-frame near-UV coverage, we examined how the kinematics of the warm and cool phrases of gas, probed by the interstellar CIV and low-ionization features, respectively, relate to each other. The spectral properties of CIV strongly correlate with the current star-formation rate, indicating a distinct nature of highly-ionized outflowing gas being driven by massive star formation. Additionally, we used the same set of z~1 galaxies to study the properties of the systemic ISM in HII regions by analyzing the nebular CIII] emission. CIII] emission tends to be stronger in lower-mass, bluer, and fainter galaxies with lower metallicity, suggesting that the strong CIII] emitters at lower redshifts can be ideal analogs of young, bursty galaxies at z > 6, which are possibly responsible for reionizing the universe. We are currently investigating the redshift evolution of the neutral, circumgalactic gas in a sample of ~1100 Lyman Break Galaxies at z ~ 2-4. The negative correlation between Lya emission and low-ionization interstellar absorption line strengths appears to be universal across different redshifts, but the fine-structure line emitting regions are found to be more compact for higher-redshift galaxies. With the detailed observational constraints provided by the rest-UV and rest-optical spectroscopy, our study sheds light on how the interstellar and circumgalactic gas components and different phases of gas connect to each other, and therefore provides a comprehensive picture of the overall

Multiwavelength search and studies of active galaxies and quasars

NASA Astrophysics Data System (ADS)

Mickaelian, Areg M.

2017-12-01

The Byurakan Astrophysical Observatory (BAO) has always been one of the centres for surveys and studies of active galaxies. Here we review our search and studies of active galaxies during last 30 years using various wavelength ranges, as well as some recent related works. These projects since late 1980s were focused on multiwavelength search and studies of AGN and Starbursts (SB). 1103 blue stellar objects (BSOs) on the basis of their UV-excess were selected using Markarian Survey (First Byurakan Survey, FBS) plates and Markarian's criteria used for the galaxies. Among many blue stars, QSOs and Seyfert galaxies were found by follow-up observations. 1577 IRAS point sources were optically identified using FBS low-dispersion spectra and many AGN, SB and high-luminosity IR galaxies (LIRG/ULIRG) were discovered. 32 extremely high IR/opt flux ratio galaxies were studies with Spitzer. 2791 ROSAT FSC sources were optically identified using Hamburg Quasar Survey (HQS) low-dispersion spectra and many AGN were discovered by follow-up observations. Fine analysis of emission line spectra was carried out using spectral line decomposition software to establish true profiles and calculate physical parameters for the emitting regions, as well as to study the spectral variability of these objects. X-ray and radio selection criteria were used to find new AGN and variable objects for further studies. We have estimated AGN content of X-ray sources as 52.9%. We have also combined IRAS PSC and FSC catalogs and compiled its extragalactic sample, which allowed us to estimate AGN content among IR sources as 23.7%. Multiwavelength approach allowed revealing many new AGN and SB and obtaining a number of interesting relations using their observational characteristics and physical properties.

The Spatial Distribution of Resolved Young Stars in Blue Compact Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Murphy, K.; Crone, M. M.

2002-12-01

We present the first results from a survey of the distribution of resolved young stars in Blue Compact Dwarf Galaxies. In order to identify the dominant physical processes driving star formation in these puzzling galaxies, we use a multi-scale cluster-finding algorithm to quantify the characteristic scales and properties of star-forming regions, from sizes smaller than 10 pc up to the size of each entire galaxy. This project was partially funded by the Lubin Chair at Skidmore College.

A Bridge from Optical to Infrared Galaxies: Explaining Local Properties and Predicting Galaxy Counts and the Cosmic Background Radiation

NASA Astrophysics Data System (ADS)

Totani, Tomonori; Takeuchi, Tsutomu T.

2002-05-01

We give an explanation for the origin of various properties observed in local infrared galaxies and make predictions for galaxy counts and cosmic background radiation (CBR) using a new model extended from that for optical/near-infrared galaxies. Important new characteristics of this study are that (1) mass scale dependence of dust extinction is introduced based on the size-luminosity relation of optical galaxies and that (2) the large-grain dust temperature Tdust is calculated based on a physical consideration for energy balance rather than by using the empirical relation between Tdust and total infrared luminosity LIR found in local galaxies, which has been employed in most previous works. Consequently, the local properties of infrared galaxies, i.e., optical/infrared luminosity ratios, LIR-Tdust correlation, and infrared luminosity function are outputs predicted by the model, while these have been inputs in a number of previous models. Our model indeed reproduces these local properties reasonably well. Then we make predictions for faint infrared counts (in 15, 60, 90, 170, 450, and 850 μm) and CBR using this model. We found results considerably different from those of most previous works based on the empirical LIR-Tdust relation; especially, it is shown that the dust temperature of starbursting primordial elliptical galaxies is expected to be very high (40-80 K), as often seen in starburst galaxies or ultraluminous infrared galaxies in the local and high-z universe. This indicates that intense starbursts of forming elliptical galaxies should have occurred at z~2-3, in contrast to the previous results that significant starbursts beyond z~1 tend to overproduce the far-infrared (FIR) CBR detected by COBE/FIRAS. On the other hand, our model predicts that the mid-infrared (MIR) flux from warm/nonequilibrium dust is relatively weak in such galaxies making FIR CBR, and this effect reconciles the prima facie conflict between the upper limit on MIR CBR from TeV gamma

Galaxy NGC 247

NASA Image and Video Library

2003-12-10

This image of the dwarf spiral galaxy NGC 247 was taken by Galaxy Evolution Explorer on October 13, 2003, in a single orbit exposure of 1600 seconds. The region that looks like a "hole" in the upper part of the galaxy is a location with a deficit of gas and therefore a lower star formation rate and ultraviolet brightness. Optical images of this galaxy show a bright star on the southern edge. This star is faint and red in the Galaxy Evolution Explorer ultraviolet image, revealing that it is a foreground star in our Milky Way galaxy. The string of background galaxies to the North-East (upper left) of NGC 247 is 355 million light years from our Milky Way galaxy whereas NGC 247 is a mere 9 million light years away. The faint blue light that can be seen in the Galaxy Evolution Explorer image of the upper two of these background galaxies may indicate that they are in the process of merging together. http://photojournal.jpl.nasa.gov/catalog/PIA04922

Spatially resolved spectroscopy of lensed galaxies in the Frontier Fields

NASA Astrophysics Data System (ADS)

Jones, Tucker; Aff004

The Grism Lens-Amplified Survey from Space (GLASS) has obtained slitless near-infrared spectroscopy of 10 galaxy clusters selected for their strong lensing properties, including all six Hubble Frontier Fields. Slitless grism spectra are ideal for mapping emission lines such as [O ii], [O iii], and Hα at z=1-3. The combination of strong gravitational lensing and Hubble's diffraction limit provides excellent sensitivity with spatial resolution as fine as 100 pc for highly magnified sources, and ~500 pc for less magnified sources near the edge of the field of view. The GLASS survey represents the largest spectroscopic sample with such high resolution at z > 1. GLASS and Hubble Frontier Field data provide the distribution of stellar mass, star formation, gas-phase metallicity, and other aspects of the physical structure of high redshift galaxies, reaching stellar masses as low as ~107 M⊙ at z=2. I discuss precise measurements of these physical properties and implications for galaxy evolution.

Probing the Baryon Cycle of Galaxies with SPICA Mid- and Far-Infrared Observations

NASA Astrophysics Data System (ADS)

van der Tak, F. F. S.; Madden, S. C.; Roelfsema, P.; Armus, L.; Baes, M.; Bernard-Salas, J.; Bolatto, A.; Bontemps, S.; Bot, C.; Bradford, C. M.; Braine, J.; Ciesla, L.; Clements, D.; Cormier, D.; Fernández-Ontiveros, J. A.; Galliano, F.; Giard, M.; Gomez, H.; González-Alfonso, E.; Herpin, F.; Johnstone, D.; Jones, A.; Kaneda, H.; Kemper, F.; Lebouteiller, V.; De Looze, I.; Matsuura, M.; Nakagawa, T.; Onaka, T.; Pérez-González, P.; Shipman, R.; Spinoglio, L.

2018-01-01

The SPICA mid- and far-infrared telescope will address fundamental issues in our understanding of star formation and ISM physics in galaxies. A particular hallmark of SPICA is the outstanding sensitivity enabled by the cold telescope, optimised detectors, and wide instantaneous bandwidth throughout the mid- and far-infrared. The spectroscopic, imaging, and polarimetric observations that SPICA will be able to collect will help in clarifying the complex physical mechanisms which underlie the baryon cycle of galaxies. In particular, (i) the access to a large suite of atomic and ionic fine-structure lines for large samples of galaxies will shed light on the origin of the observed spread in star-formation rates within and between galaxies, (ii) observations of HD rotational lines (out to 10 Mpc) and fine structure lines such as [C ii] 158 μm (out to 100 Mpc) will clarify the main reservoirs of interstellar matter in galaxies, including phases where CO does not emit, (iii) far-infrared spectroscopy of dust and ice features will address uncertainties in the mass and composition of dust in galaxies, and the contributions of supernovae to the interstellar dust budget will be quantified by photometry and monitoring of supernova remnants in nearby galaxies, (iv) observations of far-infrared cooling lines such as [O i] 63 μm from star-forming molecular clouds in our Galaxy will evaluate the importance of shocks to dissipate turbulent energy. The paper concludes with requirements for the telescope and instruments, and recommendations for the observing strategy.

The Weak Lensing Masses of Filaments between Luminous Red Galaxies

NASA Astrophysics Data System (ADS)

Epps, Seth D.; Hudson, Michael J.

2017-07-01

In the standard model of non-linear structure formation, a cosmic web of dark-matter-dominated filaments connects dark matter haloes. In this paper, we stack the weak lensing signal of an ensemble of filaments between groups and clusters of galaxies. Specifically, we detect the weak lensing signal, using CFHTLenS galaxy ellipticities, from stacked filaments between Sloan Digital Sky Survey (SDSS)-III/Baryon Oscillation Spectroscopic Survey luminous red galaxies (LRGs). As a control, we compare the physical LRG pairs with projected LRG pairs that are more widely separated in redshift space. We detect the excess filament mass density in the projected pairs at the 5σ level, finding a mass of (1.6 ± 0.3) × 1013 M⊙ for a stacked filament region 7.1 h-1 Mpc long and 2.5 h-1 Mpc wide. This filament signal is compared with a model based on the three-point galaxy-galaxy-convergence correlation function, as developed in Clampitt et al., yielding reasonable agreement.

The formation and evolution of high-redshift dusty galaxies

NASA Astrophysics Data System (ADS)

Ma, Jingzhe; Gonzalez, Anthony H.; Ge, Jian; Vieira, Joaquin D.; Prochaska, Jason X.; Spilker, Justin; Strandet, Maria; Ashby, Matthew; Noterdaeme, Pasquier; Lundgren, Britt; Zhao, Yinan; Ji, Tuo; Zhang, Shaohua; Caucal, Paul; SPT SMG Collaboration

2017-01-01

Star formation and chemical evolution are among the biggest questions in galaxy formation and evolution. High-redshift dusty galaxies are the best sites to investigate mass assembly and growth, star formation rates, star formation history, chemical enrichment, and physical conditions. My thesis is based on two populations of high-redshift dusty galaxies, submillimeter galaxies (SMGs) and quasar 2175 Å dust absorbers, which are selected by dust emission and dust absorption, respectively.For the SMG sample, I have worked on the gravitationally lensed dusty, star-forming galaxies (DSFGs) at 2.8 < z < 5.7, which were first discovered by the South Pole Telescope (SPT) and further confirmed by ALMA. My thesis is focused on the stellar masses and star formation rates of these objects by means of multi-wavelength spectral energy distribution (SED) modelling. The data include HST/WFC3, Spitzer/IRAC, Herschel/PACS, Herschel/SPIRE, APEX/Laboca and SPT. Compared to the star-forming main sequence (MS), these DSFGs have specific SFRs that lie above the MS, suggesting that we are witnessing ongoing strong starburst events that may be driven by major mergers. SPT0346-52 at z = 5.7, the most extraordinary source in the SPT survey for which we obtained Chandra X-ray and ATCA radio data, was confirmed to have the highest star formation surface density of any known galaxy at high-z.The other half of my thesis is focused on a new population of quasar absorption line systems, 2175 Å dust absorbers, which are excellent probes of gas and dust properties, chemical evolution and physical conditions in the absorbing galaxies. This sample was selected from the SDSS and BOSS surveys and followed up with the Echelle Spectrographs and Imager on the Keck-II telescope, the Red & Blue Channel Spectrograph on the Multiple Mirror Telescope, and the Ultraviolet and Visible Echelle Spectrograph onboard the Very Large Telescope. We found a correlation between the presence of the 2175 Å bump and other

Demography of northern flying squirrels informs ecosystem management of western interior forests.

Treesearch

John F. Lehmkuhl; Keith D. Kistler; James S. Begley; John. Boulanger

2006-01-01

We studied northern flying squirrel (Glaucomys sabrinus) demography in the eastern Washington Cascade Range to test hypotheses about regional and local abundance patterns and to inform managers of the possible effects of fire and fuels management on flying squirrels. We quantified habitat characteristics and squirrel density, population trends, and...

Galaxy NGC 300

NASA Image and Video Library

2003-12-10

This image of the nearby spiral galaxy NGC 300 was taken by Galaxy Evolution Explorer in a single orbit exposure of 27 minutes on October 10, 2003. NGC 300 lies 7 million light years from our Milky Way galaxy and is one of a group of galaxies in the constellation Sculptor. NGC 300 is often used as a prototype of a spiral galaxy because in optical images it displays flowing spiral arms and a bright central region of older (and thus redder) stars. The Galaxy Evolution Explorer image taken in ultraviolet light shows us that NGC 300 is an efficient star-forming galaxy. The bright blue regions in the Galaxy Evolution Explorer image reveal new stars forming all the way into the nucleus of NGC 300. http://photojournal.jpl.nasa.gov/catalog/PIA04924

The Herschel Perspective on Nearby Galaxies

NASA Astrophysics Data System (ADS)

Smith, Matthew

2013-01-01

This thesis presents an investigation of local galaxies using new data from the Herschel Space Observatory. Herschel observes the entire far-infrared peak of galaxies, at higher sensitivities and angular resolution than previously possible, and can observe large samples of galaxies or areas of sky. I developed data reduction routines to optimise the data processing of SPIRE extragalactic fields, and found the best methods of flux extraction for galaxies and for fitting of spectral energy distributions. For all the objects I investigated, a single-temperature modified blackbody was a good fit to the global fluxes between 100–500 μm. Within an individual galaxy (i.e., M31, NGC4501 and NGC4567/8) the dust temperature varies between 15–30K. In M31 the dust emissivity index varies between 1.2–2.5 suggesting a change in the physical properties of the grains. The dust and gas are highly correlated in M31, with the gas-to-dust ratio varying from ˜20 in the centre to ˜200 at 18 kpc as expected from the metallicity gradient of the galaxy. By averaging the radial profiles of the late-type objects in the Herschel Reference Survey (HRS), I have shown that dust emission can be traced to at least twice the optical radius (R25) of the galaxy. Within the HRS, dust is detected in 24% of Ellipticals and 62% of S0s and has a mean temperature of 23.9 ± 0.8K for early-type galaxies, warmer than that found for other Herschel studies of late-type galaxies. The mean dust mass for the entire detected early-type sample is logMd = 6.1 ± 0.1M⊙ with a mean dust-to-stellar-mass ratio of log(Md/M∗) = ‑4.3 ± 0.1, a factor of ˜50 lower dust-to-stellar-mass ratio than for the spiral galaxies in the HRS. The wide range in the dust-to-stellar-mass ratio for ETGs and the lack of a correlation between dust mass and optical luminosity suggest that much of the dust in the ETGs detected by Herschel has been acquired as the result of interactions, although these are unlikely to have had a

The Dragonfly Nearby Galaxies Survey. II. Ultra-Diffuse Galaxies near the Elliptical Galaxy NGC 5485

NASA Astrophysics Data System (ADS)

Merritt, Allison; van Dokkum, Pieter; Danieli, Shany; Abraham, Roberto; Zhang, Jielai; Karachentsev, I. D.; Makarova, L. N.

2016-12-01

We present the unexpected discovery of four ultra-diffuse galaxies (UDGs) in a group environment. We recently identified seven extremely low surface brightness galaxies in the vicinity of the spiral galaxy M101, using data from the Dragonfly Telephoto Array. The galaxies have effective radii of 10″-38″ and central surface brightnesses of 25.6-27.7 mag arcsec-2 in the g-band. We subsequently obtained follow-up observations with HST to constrain the distances to these galaxies. Four remain persistently unresolved even with the spatial resolution of HST/ACS, which implies distances of D\\gt 17.5 Mpc. We show that the galaxies are most likely associated with a background group at ˜27 Mpc containing the massive ellipticals NGC 5485 and NGC 5473. At this distance, the galaxies have sizes of 2.6-4.9 kpc, and are classified as UDGs, similar to the populations that have been revealed in clusters such as Coma, Virgo, and Fornax, yet even more diffuse. The discovery of four UDGs in a galaxy group demonstrates that the UDG phenomenon is not exclusive to cluster environments. Furthermore, their morphologies seem less regular than those of the cluster populations, which may suggest a different formation mechanism or be indicative of a threshold in surface density below which UDGs are unable to maintain stability.

A New Approach for Simulating Galaxy Cluster Properties

NASA Astrophysics Data System (ADS)

Arieli, Y.; Rephaeli, Y.; Norman, M. L.

2008-08-01

We describe a subgrid model for including galaxies into hydrodynamical cosmological simulations of galaxy cluster evolution. Each galaxy construct—or galcon—is modeled as a physically extended object within which star formation, galactic winds, and ram pressure stripping of gas are modeled analytically. Galcons are initialized at high redshift (z ~ 3) after galaxy dark matter halos have formed but before the cluster has virialized. Each galcon moves self-consistently within the evolving cluster potential and injects mass, metals, and energy into intracluster (IC) gas through a well-resolved spherical interface layer. We have implemented galcons into the Enzo adaptive mesh refinement code and carried out a simulation of cluster formation in a ΛCDM universe. With our approach, we are able to economically follow the impact of a large number of galaxies on IC gas. We compare the results of the galcon simulation with a second, more standard simulation where star formation and feedback are treated using a popular heuristic prescription. One advantage of the galcon approach is explicit control over the star formation history of cluster galaxies. Using a galactic SFR derived from the cosmic star formation density, we find the galcon simulation produces a lower stellar fraction, a larger gas core radius, a more isothermal temperature profile, and a flatter metallicity gradient than the standard simulation, in better agreement with observations.

UV spectroscopy of the most metal-poor galaxies: clues for interpreting distant galaxy observations

NASA Astrophysics Data System (ADS)

Wofford, A.; Vidal-García, A.; Feltre, A.; Chevallard, J.; Herenz, E.; Charlot, S., Stark, D. P.; Hayes, M.

2017-11-01

Among the most metal-poor galaxies known, SBS 0335-052E is on one of the most well-studied. For this galaxy, we present Hubble Space Telescope (HST) / Cosmic Origins Spectrograph (COS) detections of the C IV λλ1549, 1551, He II λ1640, O III] λλ1661, 1666, [C III] λ1907, and C III] λ1909 UV emission lines; and a Very Large Telescope (VLT) / Multi Unit Spectroscopic Explorer (MUSE) spectrum covering from 4600 to 9400 Å, which is co-spatial with the UV data and integrated over the same area. Using these datasets we test: a) the latest Charlot & Bruzal spectral synthesis models with very massive (300 M_⊙) single non-rotating stars; b) the ability of the tool, BayEsian Analysis of GaLaxy sEds (BEAGLE) to reproduce the observed emission line fluxes; and c) the extent to which physical properties of the gas and dust derived independently from the UV and optical with BEAGLE are constrained. The UV observations are part of a pilot program where we also observed UGC 5340-1 and I Zw 18 SE, whose spectra we also present in this contribution.

Understanding Galaxy Shapes Across Cosmic Time Using The IllustrisTNG Simulation

NASA Astrophysics Data System (ADS)

Genel, Shy

2017-08-01

Legacy HST observations have enabled groundbreaking measurements of galaxy structure over cosmic time, measurements that still require theoretical interpretation in the context of a comprehensive galaxy evolution model. This proposed research aims at significantly promoting our understanding of the shapes of galaxies as quantified by their principal axes ratios. The main tool we propose to use is IllustrisTNG, a suite consisting of two of the largest cosmological hydrodynamical simulations run to date, which contain resolved galaxy populations (thousands of L* galaxies) that represent a state-of-the-art match to observed galaxies. In Part I of the program, we will use the simulations to create mock images and study the dependence of projected shape measurements on various factors: shape estimator, observed band, the presence of dust, radial and surface brightness cuts, and noise. We will then perform apples-to-apples comparison with observations (including HST), and provide predictions for archival as well as future observations. Further, we will quantify the intrinsic, three-dimensional, shape distribution of galaxies as a function of various galaxy parameters: redshift, mass, color, and size. In Part II of the program, we will develop theoretical insights into the physical mechanisms driving these results. We will study how galaxy shapes relate to angular momentum and merger history, and will follow the shape evolution of individual galaxies over time, looking for correlations to the evolution of other galaxy properties, e.g. size and SFR. We will also study galaxy shape relations to dark matter halo shape, thereby providing input for high-precision cosmic shear models.

THE ZURICH ENVIRONMENTAL STUDY OF GALAXIES IN GROUPS ALONG THE COSMIC WEB. I. WHICH ENVIRONMENT AFFECTS GALAXY EVOLUTION?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carollo, C. Marcella; Cibinel, Anna; Lilly, Simon J.

2013-10-20

The Zurich Environmental Study (ZENS) is based on a sample of ∼1500 galaxy members of 141 groups in the mass range ∼10{sup 12.5-14.5} M{sub ☉} within the narrow redshift range 0.05 < z < 0.0585. ZENS adopts novel approaches, described here, to quantify four different galactic environments, namely: (1) the mass of the host group halo; (2) the projected halo-centric distance; (3) the rank of galaxies as central or satellites within their group halos; and (4) the filamentary large-scale structure density. No self-consistent identification of a central galaxy is found in ∼40% of <10{sup 13.5} M{sub ☉} groups, from whichmore » we estimate that ∼15% of groups at these masses are dynamically unrelaxed systems. Central galaxies in relaxed and unrelaxed groups generally have similar properties, suggesting that centrals are regulated by their mass and not by their environment. Centrals in relaxed groups have, however, ∼30% larger sizes than in unrelaxed groups, possibly due to accretion of small satellites in virialized group halos. At M > 10{sup 10} M{sub ☉}, satellite galaxies in relaxed and unrelaxed groups have similar size, color, and (specific) star formation rate distributions; at lower galaxy masses, satellites are marginally redder in relaxed relative to unrelaxed groups, suggesting quenching of star formation in low-mass satellites by physical processes active in relaxed halos. Overall, relaxed and unrelaxed groups show similar stellar mass populations, likely indicating similar stellar mass conversion efficiencies. In the enclosed ZENS catalog, we publish all environmental diagnostics as well as the galaxy structural and photometric measurements described in companion ZENS papers II and III.« less

The Taxonomy of Blue Amorphous Galaxies. II. Structure and Evolution

NASA Astrophysics Data System (ADS)

Marlowe, Amanda T.; Meurer, Gerhardt R.; Heckman, Timothy M.

1999-09-01

Dwarf galaxies play an important role in our understanding of galaxy formation and evolution, and starbursts are believed to affect the structure and evolution of dwarf galaxies strongly. We have therefore embarked on a systematic study of 12 of the nearest dwarf galaxies thought to be undergoing bursts of star formation. These were selected primarily by their morphological type (blue ``amorphous'' galaxies). We show that these blue amorphous galaxies are not physically distinguishable from dwarfs selected as starbursting by other methods, such as blue compact dwarfs (BCDs) and H II galaxies. All these classes exhibit surface brightness profiles that are exponential in the outer regions (r>~1.5re) but often have a predominantly central blue excess, suggesting a young burst in an older, redder galaxy. Typically, the starbursting ``cores'' are young (~107-108 yr) events compared to the older (~109-1010 yr) underlying galaxy (the ``envelope''). The ratio of the core to envelope in blue light ranges from essentially zero to about 2. These starbursts are therefore modest events involving only a few percent of the stellar mass. The envelopes have surface brightnesses that are much higher than typical dwarf irregular (dI) galaxies, so it is unlikely that there is a straightforward evolutionary relation between typical dIs and dwarf starburst galaxies. Instead we suggest that amorphous galaxies may repeatedly cycle through starburst and quiescent phases, corresponding to the galaxies with strong and weak/absent cores, respectively. Once amorphous galaxies use up the available gas (either through star formation or galactic winds) so that star formation is shut off, the faded remnants would strongly resemble dwarf elliptical galaxies. However, in the current cosmological epoch, this is evidently a slow process that is the aftermath of a series of many weak, recurring bursts. Present-day dE's must have experienced more rapid and intense evolution than this in the distant past.

Galaxies Detected by the Dwingeloo Obscured Galaxies Survey

NASA Astrophysics Data System (ADS)

Rivers, A. J.; Henning, P. A.; Kraan-Korteweg, R. C.

1999-04-01

The Dwingeloo Obscured Galaxies Survey (DOGS) is a 21-cm blind survey for galaxies hidden in the northern `Zone of Avoidance' (ZOA): the portion of the optical extragalactic sky which is obscured by dust in the Milky Way. Like the Parkes southern hemisphere ZOA survey, the DOGS project is designed to reveal hidden dynamically important nearby galaxies and to help `fill in the blanks' in the local large scale structure. To date, 36 galaxies have been detected by the Dwingeloo survey; 23 of these were previously unknown [no corresponding sources recorded in the NASA Extragalactic Database (NED)]. Among the interesting detections are three nearby galaxies in the vicinity of NGC 6946 and 11 detections in the Supergalactic plane crossing region. VLA follow-up observations have been conducted for several of the DOGS detections.

Spitzer IRS Observations of Low-Mass Seyfert Galaxies

NASA Astrophysics Data System (ADS)

Thornton, Carol E.; Barth, A. J.; Ho, L. C.; Greene, J. E.

2010-01-01

We present results from Spitzer IRS observations of a sample of 41 Seyfert galaxies with estimated black hole masses below 106 solar masses, including objects from the SDSS-selected samples of Seyfert 1 galaxies from Greene & Ho (2004) and Seyfert 2 galaxies from Barth et al. (2008), as well as NGC 4395 and POX 52. We use the IDL code PAHFIT (Smith et al. 2007) to derive measurements of continuum shapes and narrow emission line and PAH luminosities from the low-resolution spectra in order to examine the dust emission properties of these objects and investigate the relationship between Type 1 and Type 2 AGNs at low luminosities and low masses, to search for evidence of star formation, and to use emission-line diagnostics to constrain physical conditions within the narrow-line regions.

On the dynamical basis of the classification of normal galaxies

PubMed Central

Haass, J.; Bertin, G.; Lin, C. C.

1982-01-01

Some realistic galaxy models have been found to support discrete unstable spiral modes. Here, through the study of the relevant physical mechanisms and an extensive numerical investigation of the properties of the dominant modes in a wide class of galactic equilibria, we show how spiral structures are excited with different morphological features, depending on the properties of the equilibrium model. We identify the basic dynamical parameters and mechanisms and compare the resulting morphology of spiral modes with the actual classification of galaxies. The present study suggests a dynamical basis for the transition among various types and subclasses of normal and barred spiral galaxies. Images PMID:16593200

The Subaru FMOS galaxy redshift survey (FastSound). V. Intrinsic alignments of emission-line galaxies at z ˜ 1.4

NASA Astrophysics Data System (ADS)

Tonegawa, Motonari; Okumura, Teppei; Totani, Tomonori; Dalton, Gavin; Glazebrook, Karl; Yabe, Kiyoto

2018-06-01

Intrinsic alignments (IA), the coherent alignment of intrinsic galaxy orientations, can be a source of a systematic error of weak lensing surveys. The redshift evolution of IA also contains information about the physics of galaxy formation and evolution. This paper presents the first measurement of IA at high redshift, z ˜ 1.4, using the spectroscopic catalog of blue star-forming galaxies of the FastSound redshift survey, with the galaxy shape information from the Canada-Hawaii-France telescope lensing survey. The IA signal is consistent with zero with power-law amplitudes fitted to the projected correlation functions for density-shape and shape-shape correlation components, Aδ+ = -0.0071 ± 0.1340 and A++ = -0.0505 ± 0.0848, respectively. These results are consistent with those obtained from blue galaxies at lower redshifts (e.g., A _{δ +}=0.0035_{-0.0389}^{+0.0387} and A_{++}=0.0045_{-0.0168}^{+0.0166} at z = 0.51 from the WiggleZ survey). The upper limit of the constrained IA amplitude corresponds to a few percent contamination to the weak-lensing shear power spectrum, resulting in systematic uncertainties on the cosmological parameter estimations by -0.052 < Δσ8 < 0.039 and -0.039 < ΔΩm < 0.030.

The Subaru FMOS galaxy redshift survey (FastSound). V. Intrinsic alignments of emission-line galaxies at z ˜ 1.4

NASA Astrophysics Data System (ADS)

Tonegawa, Motonari; Okumura, Teppei; Totani, Tomonori; Dalton, Gavin; Glazebrook, Karl; Yabe, Kiyoto

2018-04-01

Intrinsic alignments (IA), the coherent alignment of intrinsic galaxy orientations, can be a source of a systematic error of weak lensing surveys. The redshift evolution of IA also contains information about the physics of galaxy formation and evolution. This paper presents the first measurement of IA at high redshift, z ˜ 1.4, using the spectroscopic catalog of blue star-forming galaxies of the FastSound redshift survey, with the galaxy shape information from the Canada-Hawaii-France telescope lensing survey. The IA signal is consistent with zero with power-law amplitudes fitted to the projected correlation functions for density-shape and shape-shape correlation components, Aδ+ = -0.0071 ± 0.1340 and A++ = -0.0505 ± 0.0848, respectively. These results are consistent with those obtained from blue galaxies at lower redshifts (e.g., A _{δ +}=0.0035_{-0.0389}^{+0.0387} and A_{++}=0.0045_{-0.0168}^{+0.0166} at z = 0.51 from the WiggleZ survey). The upper limit of the constrained IA amplitude corresponds to a few percent contamination to the weak-lensing shear power spectrum, resulting in systematic uncertainties on the cosmological parameter estimations by -0.052 < Δσ8 < 0.039 and -0.039 < ΔΩm < 0.030.

Connections between Star Cluster Populations and Their Host Galaxy Nuclear Rings

NASA Astrophysics Data System (ADS)

Ma, Chao; de Grijs, Richard; Ho, Luis C.

2018-04-01

Nuclear rings are excellent laboratories for probing diverse phenomena such as the formation and evolution of young massive star clusters and nuclear starbursts, as well as the secular evolution and dynamics of their host galaxies. We have compiled a sample of 17 galaxies with nuclear rings, which are well resolved by high-resolution Hubble and Spitzer Space Telescope imaging. For each nuclear ring, we identified the ring star cluster population, along with their physical properties (ages, masses, and extinction values). We also determined the integrated ring properties, including the average age, total stellar mass, and current star formation rate (SFR). We find that Sb-type galaxies tend to have the highest ring stellar mass fraction with respect to the host galaxy, and this parameter is correlated with the ring’s SFR surface density. The ring SFRs are correlated with their stellar masses, which is reminiscent of the main sequence of star-forming galaxies. There are striking correlations between star-forming properties (i.e., SFR and SFR surface density) and nonaxisymmetric bar parameters, appearing to confirm previous inferences that strongly barred galaxies tend to have lower ring SFRs, although the ring star formation histories turn out to be significantly more complicated. Nuclear rings with higher stellar masses tend to be associated with lower cluster mass fractions, but there is no such relation for the ages of the rings. The two youngest nuclear rings in our sample, NGC 1512 and NGC 4314, which have the most extreme physical properties, represent the young extremity of the nuclear ring age distribution.

The Star Formation Demographics of Galaxies in the Local Volume

NASA Astrophysics Data System (ADS)

Lee, Janice C.; Kennicutt, Robert C.; Funes, S. J., José G.; Sakai, Shoko; Akiyama, Sanae

2007-12-01

We examine the connections between the current global star formation activity, luminosity, dynamical mass, and morphology of galaxies in the Local Volume, using Hα data from the 11 Mpc Hα and Ultraviolet Galaxy Survey (11HUGS). Taking the equivalent width (EW) of the Hα emission line as a tracer of the specific star formation rate, we analyze the distribution of galaxies in the MB-EW and rotational velocity (Vmax)-EW planes. Star-forming galaxies show two characteristic transitions in these planes. A narrowing of the galaxy locus occurs at MB~-15 and Vmax~50 km s-1, where the scatter in the logarithmic EWs drops by a factor of 2 as the luminosities/masses increase, and galaxy morphologies shift from predominately irregular to late-type spiral. Another transition occurs at MB~-19 and Vmax~120 km s-1, above which the sequence turns off toward lower EWs and becomes mostly populated by intermediate- and early-type bulge-prominent spirals. Between these two transitions, the mean logarithmic EW appears to remain constant at 30 Å. We comment on how these features reflect established empirical relationships, and provide clues for identifying the large-scale physical processes that both drive and regulate star formation, with emphasis on the low-mass galaxies which dominate our approximately volume-limited sample.

Galaxy Zoo: Major Galaxy Mergers Are Not a Significant Quenching Pathway

NASA Astrophysics Data System (ADS)

Weigel, Anna K.; Schawinski, Kevin; Caplar, Neven; Carpineti, Alfredo; Hart, Ross E.; Kaviraj, Sugata; Keel, William C.; Kruk, Sandor J.; Lintott, Chris J.; Nichol, Robert C.; Simmons, Brooke D.; Smethurst, Rebecca J.

2017-08-01

We use stellar mass functions to study the properties and the significance of quenching through major galaxy mergers. In addition to SDSS DR7 and Galaxy Zoo 1 data, we use samples of visually selected major galaxy mergers and post-merger galaxies. We determine the stellar mass functions of the stages that we would expect major-merger-quenched galaxies to pass through on their way from the blue cloud to the red sequence: (1) major merger, (2) post-merger, (3) blue early type, (4) green early type, and (5) red early type. Based on their similar mass function shapes, we conclude that major mergers are likely to form an evolutionary sequence from star formation to quiescence via quenching. Relative to all blue galaxies, the major-merger fraction increases as a function of stellar mass. Major-merger quenching is inconsistent with the mass and environment quenching model. At z˜ 0, major-merger-quenched galaxies are unlikely to constitute the majority of galaxies that transition through the green valley. Furthermore, between z˜ 0-0.5, major-merger-quenched galaxies account for 1%-5% of all quenched galaxies at a given stellar mass. Major galaxy mergers are therefore not a significant quenching pathway, neither at z˜ 0 nor within the last 5 Gyr. The majority of red galaxies must have been quenched through an alternative quenching mechanism that causes a slow blue to red evolution. .

Spectrophotometric Study of the Region of the Sky Around the Galaxies Markarian 261 and 262

NASA Astrophysics Data System (ADS)

Khachikian, E. Ye.; Sargsyan, L. A.

2005-10-01

Results are presented from a detailed spectrophotometric study of a unique system of physically coupled galaxies whose spectra contain identical emission lines. This system consists of four galaxies, three of which have a double or multiple structure in their central portions and are, by definition, galaxies with two or multiple nuclei. Two of these objects are the galaxies with an ultraviolet excess (UVE), Mark 261 and Mark 262, while one is a galaxy made up of two identical starlike nuclei that are referred to as the “twin objects.” In the DSS2 charts, the latter show up as two adjacent stars without any surroundings. However, there are two condensations between these starlike nuclei. The fourth object has a triplet structure. It is shown here that all these objects have the same emission (line) spectra and red shifts. All the physical characteristics that can be determined from the spectra are determined: red shifts, relative intensities of emission lines, their equivalent widths, distances to the galaxies, etc. It is concluded that the members of this system have a common origin, more or less consistent with Ambartsumyan's idea of the fragmentation of an isolated, high density body.

Correlations among Galaxy Properties from the Sloan Digital Sky Survey

NASA Astrophysics Data System (ADS)

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 *) = 4.31 - 0.30 M r for the stellar mass (log M *) and absolute magnitude (M r) of red galaxies. The median relationships between various parameter pairs are also presented for comparison.

A Bridge from Optical to Infrared Galaxies: Explaining Local Properties, Predicting Galaxy Counts and the Cosmic Background Radiation

NASA Astrophysics Data System (ADS)

Totani, T.; Takeuchi, T. T.

2001-12-01

A new model of infrared galaxy counts and the cosmic background radiation (CBR) is developed by extending a model for optical/near-infrared galaxies. Important new characteristics of this model are that mass scale dependence of dust extinction is introduced based on the size-luminosity relation of optical galaxies, and that the big grain dust temperature T dust is calculated based on a physical consideration for energy balance, rather than using the empirical relation between T dust and total infrared luminosity L IR found in local galaxies, which has been employed in most of previous works. Consequently, the local properties of infrared galaxies, i.e., optical/infrared luminosity ratios, L IR-T dust correlation, and infrared luminosity function are outputs predicted by the model, while these have been inputs in a number of previous models. Our model indeed reproduces these local properties reasonably well. Then we make predictions for faint infrared counts (in 15, 60, 90, 170, 450, and 850 μ m) and CBR by this model. We found considerably different results from most of previous works based on the empirical L IR-T dust relation; especially, it is shown that the dust temperature of starbursting primordial elliptical galaxies is expected to be very high (40--80K). This indicates that intense starbursts of forming elliptical galaxies should have occurred at z ~ 2--3, in contrast to the previous results that significant starbursts beyond z ~ 1 tend to overproduce the far-infrared (FIR) CBR detected by COBE/FIRAS. On the other hand, our model predicts that the mid-infrared (MIR) flux from warm/nonequilibrium dust is relatively weak in such galaxies making FIR CBR, and this effect reconciles the prima facie conflict between the upper limit on MIR CBR from TeV gamma-ray observations and the COBE\\ detections of FIR CBR. The authors thank the financial support by the Japan Society for Promotion of Science.

Intrinsic alignments in redMaPPer clusters – I. Central galaxy alignments and angular segregation of satellites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Hung -Jin; Mandelbaum, Rachel; Freeman, Peter E.

The shapes of cluster central galaxies are not randomly oriented, but rather exhibit coherent alignments with the shapes of their parent clusters as well as with the surrounding large-scale structures. In this work, we aim to identify the galaxy and cluster quantities that most strongly predict the central galaxy alignment phenomenon among a large parameter space with a sample of 8237 clusters and 94 817 members within 0.1 < z < 0.35, based on the red-sequence Matched-filter Probabilistic Percolation cluster catalogue constructed from the Sloan Digital Sky Survey. We first quantify the alignment between the projected central galaxy shapes andmore » the distribution of member satellites, to understand what central galaxy and cluster properties most strongly correlate with these alignments. Next, we investigate the angular segregation of satellites with respect to their central galaxy major axis directions, to identify the satellite properties that most strongly predict their angular segregation. We find that central galaxies are more aligned with their member galaxy distributions in clusters that are more elongated and have higher richness, and for central galaxies with larger physical size, higher luminosity and centring probability, and redder colour. Satellites with redder colour, higher luminosity, located closer to the central galaxy, and with smaller ellipticity show a stronger angular segregation towards their central galaxy major axes. Lastly, we provide physical explanations for some of the identified correlations, and discuss the connection to theories of central galaxy alignments, the impact of primordial alignments with tidal fields, and the importance of anisotropic accretion.« less

Intrinsic alignments in redMaPPer clusters – I. Central galaxy alignments and angular segregation of satellites

DOE PAGES

Huang, Hung -Jin; Mandelbaum, Rachel; Freeman, Peter E.; ...

2016-08-11

The shapes of cluster central galaxies are not randomly oriented, but rather exhibit coherent alignments with the shapes of their parent clusters as well as with the surrounding large-scale structures. In this work, we aim to identify the galaxy and cluster quantities that most strongly predict the central galaxy alignment phenomenon among a large parameter space with a sample of 8237 clusters and 94 817 members within 0.1 < z < 0.35, based on the red-sequence Matched-filter Probabilistic Percolation cluster catalogue constructed from the Sloan Digital Sky Survey. We first quantify the alignment between the projected central galaxy shapes andmore » the distribution of member satellites, to understand what central galaxy and cluster properties most strongly correlate with these alignments. Next, we investigate the angular segregation of satellites with respect to their central galaxy major axis directions, to identify the satellite properties that most strongly predict their angular segregation. We find that central galaxies are more aligned with their member galaxy distributions in clusters that are more elongated and have higher richness, and for central galaxies with larger physical size, higher luminosity and centring probability, and redder colour. Satellites with redder colour, higher luminosity, located closer to the central galaxy, and with smaller ellipticity show a stronger angular segregation towards their central galaxy major axes. Lastly, we provide physical explanations for some of the identified correlations, and discuss the connection to theories of central galaxy alignments, the impact of primordial alignments with tidal fields, and the importance of anisotropic accretion.« less

Properties of the X-ray emitting gas in early-type galaxies

NASA Technical Reports Server (NTRS)

Canizares, Claude R.; Fabbiano, Giuseppina; Trinchieri, Ginevra

1987-01-01

The properties of the X-ray emitting gas in a sample of 81 E and S0 galaxies observed with the Einstein Observatory are studied. Measured fluxes for 55 of the galaxies and upper limits for 26 of them are reported. An attempt is made to use consistent optical parameters for the galaxies, including a correction to the velocities for the Virgocentric flow. The sample is then used to explore the contribution from discrete sources, the global physical properties of the hot gas, and the implications for heating by supernovae and gravity. Finally, the question of the presence of heavy halos is addressed.

Associating Fast Radio Bursts with Their Host Galaxies

NASA Astrophysics Data System (ADS)

Eftekhari, T.; Berger, E.

2017-11-01

The first precise localization of a fast radio burst (FRB) sheds light on the nature of these mysterious bursts and the physical mechanisms that power them. Increasing the sample of FRBs with robust host galaxy associations is the key impetus behind ongoing and upcoming searches and facilities. Here, we quantify the robustness of FRB host galaxy associations as a function of localization area and galaxy apparent magnitude. We also explore the use of FRB dispersion measures to constrain the source redshift, thereby reducing the number of candidate hosts. We use these results to demonstrate that even in the absence of a unique association, a constraint can be placed on the maximum luminosity of a host galaxy as a function of localization and dispersion measure (DM). We find that localizations of ≲ 0.5\\text{'}\\text{'} are required for a chance coincidence probability of ≲ 1 % for dwarf galaxies at z≳ 0.1; if some hosts have luminosities of ˜ {L}\\ast , then localizations of up to ≈ 5\\prime\\prime may suffice at z˜ 0.1. Constraints on the redshift from the DM only marginally improve the association probability unless the DM is low, ≲ 400 pc cm-3. This approach also relies on the determination of galaxy redshifts, which is challenging at z≳ 0.5 if the hosts are dwarf galaxies. Finally, interesting limits on the maximum host luminosity require localizations of ≲ 5\\prime\\prime at z≳ 0.1. Even a few such localizations will explain the nature of FRB progenitors, their possible diversity, and their use as cosmological tools.

Galaxy-galaxy weak gravitational lensing in f(R) gravity

NASA Astrophysics Data System (ADS)

Li, Baojiu; Shirasaki, Masato

2018-03-01

We present an analysis of galaxy-galaxy weak gravitational lensing (GGL) in chameleon f(R) gravity - a leading candidate of non-standard gravity models. For the analysis, we have created mock galaxy catalogues based on dark matter haloes from two sets of numerical simulations, using a halo occupation distribution (HOD) prescription which allows a redshift dependence of galaxy number density. To make a fairer comparison between the f(R) and Λ cold dark matter (ΛCDM) models, their HOD parameters are tuned so that the galaxy two-point correlation functions in real space (and therefore the projected two-point correlation functions) match. While the f(R) model predicts an enhancement of the convergence power spectrum by up to ˜ 30 per cent compared to the standard ΛCDM model with the same parameters, the maximum enhancement of GGL is only half as large and less than 5 per cent on separations above ˜1-2 h-1 Mpc, because the latter is a cross-correlation of shear (or matter, which is more strongly affected by modified gravity) and galaxy (which is weakly affected given the good match between galaxy autocorrelations in the two models) fields. We also study the possibility of reconstructing the matter power spectrum by combination of GGL and galaxy clustering in f(R) gravity. We find that the galaxy-matter cross-correlation coefficient remains at unity down to ˜2-3 h-1 Mpc at relevant redshifts even in f(R) gravity, indicating joint analysis of GGL and galaxy clustering can be a powerful probe of matter density fluctuations in chameleon gravity. The scale dependence of the model differences in their predictions of GGL can potentially allows us to break the degeneracy between f(R) gravity and other cosmological parameters such as Ωm and σ8.

A Complete Library of Infrared Spectral Energy Distributions for z=0 Galaxies

NASA Astrophysics Data System (ADS)

Sandstrom, Karin

CONTEXT: Half of the light emitted by galaxies is starlight absorbed and reprocessed into the infrared by dust. The spectral energy distribution (SED) of this IR emission encodes information on the mass and properties of the dust, the radiation field heating it, and the bolometric luminosity of the region. This makes IR emission a main tool to estimate star formation rates (SFRs) and to trace the distribution of the interstellar medium (ISM) in galaxies. The dust itself also plays key roles in the physics of star formation, and thereby galaxy evolution. This critical information on dust and its dependence on environment can only be reliably measured when we have observations with full wavelength coverage of the IR SED that resolve galaxies. With no new IR imaging missions on the horizon, the remarkably thorough census conducted by Herschel, Spitzer, and WISE of the nearby (D < 50 Mpc) galaxy population is the definitive resource on dust at z=0 for the foreseeable future. Such observations allow us to understand the behavior of the IR SED and so inform observations from the major new facilities ALMA and JWST, which have amazing sensitivity and resolution but limited wavelength coverage. OBJECTIVES: We will create a library of matched resolution, uniformly processed IR SEDs for all 532 local galaxies with resolved mapping in the Herschel, Spitzer, and WISE archives. We will associate the SED measurements with rich "value added" data, including fits of physical models to the IR SED (yielding small grain fractions, temperature, and dust masses), host galaxy properties (e.g., stellar mass, SFR, morphology, inclination), and local conditions in the galaxy (SFR and stellar surface density, ISM gas mass and metallicity where available). The library will be created for a range of spatial and angular scales and served through IRSA/MAST, providing a major high level legacy resource that will be useful to a wide community. We will exploit this database to address three major

Simplified galaxy formation with mesh-less hydrodynamics

NASA Astrophysics Data System (ADS)

Lupi, Alessandro; Volonteri, Marta; Silk, Joseph

2017-09-01

Numerical simulations have become a necessary tool to describe the complex interactions among the different processes involved in galaxy formation and evolution, unfeasible via an analytic approach. The last decade has seen a great effort by the scientific community in improving the sub-grid physics modelling and the numerical techniques used to make numerical simulations more predictive. Although the recently publicly available code gizmo has proven to be successful in reproducing galaxy properties when coupled with the model of the MUFASA simulations and the more sophisticated prescriptions of the Feedback In Realistic Environment (FIRE) set-up, it has not been tested yet using delayed cooling supernova feedback, which still represent a reasonable approach for large cosmological simulations, for which detailed sub-grid models are prohibitive. In order to limit the computational cost and to be able to resolve the disc structure in the galaxies we perform a suite of zoom-in cosmological simulations with rather low resolution centred around a sub-L* galaxy with a halo mass of 3 × 1011 M⊙ at z = 0, to investigate the ability of this simple model, coupled with the new hydrodynamic method of gizmo, to reproduce observed galaxy scaling relations (stellar to halo mass, stellar and baryonic Tully-Fisher, stellar mass-metallicity and mass-size). We find that the results are in good agreement with the main scaling relations, except for the total stellar mass, larger than that predicted by the abundance matching technique, and the effective sizes for the most massive galaxies in the sample, which are too small.

Galaxy NGC5474

NASA Image and Video Library

2003-07-25

NASA 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. http://photojournal.jpl.nasa.gov/catalog/PIA04634

Distributions of Gas and Galaxies from Galaxy Clusters to Larger Scales

NASA Astrophysics Data System (ADS)

Patej, Anna

2017-01-01

We address the distributions of gas and galaxies on three scales: the outskirts of galaxy clusters, the clustering of galaxies on large scales, and the extremes of the galaxy distribution. In the outskirts of galaxy clusters, long-standing analytical models of structure formation and recent simulations predict the existence of density jumps in the gas and dark matter profiles. We use these features to derive models for the gas density profile, obtaining a simple fiducial model that is in agreement with both observations of cluster interiors and simulations of the outskirts. We next consider the galaxy density profiles of clusters; under the assumption that the galaxies in cluster outskirts follow similar collisionless dynamics as the dark matter, their distribution should show a steep jump as well. We examine the profiles of a low-redshift sample of clusters and groups, finding evidence for the jump in some of these clusters. Moving to larger scales where massive galaxies of different types are expected to trace the same large-scale structure, we present a test of this prediction by measuring the clustering of red and blue galaxies at z 0.6, finding low stochasticity between the two populations. These results address a key source of systematic uncertainty - understanding how target populations of galaxies trace large-scale structure - in galaxy redshift surveys. Such surveys use baryon acoustic oscillations (BAO) as a cosmological probe, but are limited by the expense of obtaining sufficiently dense spectroscopy. With the intention of leveraging upcoming deep imaging data, we develop a new method of detecting the BAO in sparse spectroscopic samples via cross-correlation with a dense photometric catalog. This method will permit the extension of BAO measurements to higher redshifts than possible with the existing spectroscopy alone. Lastly, we connect galaxies near and far: the Local Group dwarfs and the high redshift galaxies observed by Hubble and Spitzer. We

Scaling Relations between Gas and Star Formation in Nearby Galaxies

NASA Astrophysics Data System (ADS)

Bigiel, Frank; Leroy, Adam; Walter, Fabian

2011-04-01

High resolution, multi-wavelength maps of a sizeable set of nearby galaxies have made it possible to study how the surface densities of H i, H2 and star formation rate (ΣHI, ΣH2, ΣSFR) relate on scales of a few hundred parsecs. At these scales, individual galaxy disks are comfortably resolved, making it possible to assess gas-SFR relations with respect to environment within galaxies. ΣH2, traced by CO intensity, shows a strong correlation with ΣSFR and the ratio between these two quantities, the molecular gas depletion time, appears to be constant at about 2 Gyr in large spiral galaxies. Within the star-forming disks of galaxies, ΣSFR shows almost no correlation with ΣHI. In the outer parts of galaxies, however, ΣSFR does scale with ΣHI, though with large scatter. Combining data from these different environments yields a distribution with multiple regimes in Σgas - ΣSFR space. If the underlying assumptions to convert observables to physical quantities are matched, even combined datasets based on different SFR tracers, methodologies and spatial scales occupy a well define locus in Σgas - ΣSFR space.

SEMI-ANALYTIC GALAXY EVOLUTION (SAGE): MODEL CALIBRATION AND BASIC RESULTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Croton, Darren J.; Stevens, Adam R. H.; Tonini, Chiara

2016-02-15

This paper describes a new publicly available codebase for modeling galaxy formation in a cosmological context, the “Semi-Analytic Galaxy Evolution” model, or sage for short.{sup 5} sage is a significant update to the 2006 model of Croton et al. and has been rebuilt to be modular and customizable. The model will run on any N-body simulation whose trees are organized in a supported format and contain a minimum set of basic halo properties. In this work, we present the baryonic prescriptions implemented in sage to describe the formation and evolution of galaxies, and their calibration for three N-body simulations: Millennium,more » Bolshoi, and GiggleZ. Updated physics include the following: gas accretion, ejection due to feedback, and reincorporation via the galactic fountain; a new gas cooling–radio mode active galactic nucleus (AGN) heating cycle; AGN feedback in the quasar mode; a new treatment of gas in satellite galaxies; and galaxy mergers, disruption, and the build-up of intra-cluster stars. Throughout, we show the results of a common default parameterization on each simulation, with a focus on the local galaxy population.« less

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.

Simulating the assembly of galaxies at redshifts z = 6-12

NASA Astrophysics Data System (ADS)

Dayal, Pratika; Dunlop, James S.; Maio, Umberto; Ciardi, Benedetta

2013-09-01

We use state-of-the-art simulations to explore the physical evolution of galaxies in the first billion years of cosmic time. First, we demonstrate that our model reproduces the basic statistical properties of the observed Lyman-break galaxy (LBG) population at z = 6-8, including the evolving ultraviolet (UV) luminosity function (LF), the stellar mass density (SMD) and the average specific star-formation rates (sSFRs) of LBGs with MUV < -18 (AB mag). Encouraged by this success we present predictions for the behaviour of fainter LBGs extending down to MUV ≃ -15 (as will be probed with the James Webb Space Telescope) and have interrogated our simulations to try to gain insight into the physical drivers of the observed population evolution. We find that mass growth due to star formation in the mass-dominant progenitor builds up about 90 per cent of the total z ˜ 6 LBG stellar mass, dominating over the mass contributed by merging throughout this era. Our simulation suggests that the apparent `luminosity evolution' depends on the luminosity range probed: the steady brightening of the bright end of the LF is driven primarily by genuine physical luminosity evolution and arises due to a fairly steady increase in the UV luminosity (and hence star-formation rates) in the most massive LBGs; for example the progenitors of the z ≃ 6 galaxies with MUV < -18.5 comprised ≃90 per cent of the galaxies with MUV < -18 at z ≃ 7 and ≃75 per cent at z ≃ 8. However, at fainter luminosities the situation is more complex, due in part to the more stochastic star-formation histories of lower mass objects; the progenitors of a significant fraction of z ≃ 6 LBGs with MUV > -18 were in fact brighter at z ≃ 7 (and even at z ≃ 8) despite obviously being less massive at earlier times. At this end, the evolution of the UV LF involves a mix of positive and negative luminosity evolution (as low-mass galaxies temporarily brighten and then fade) coupled with both positive and negative

Galaxy redshift surveys with sparse sampling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chiang, Chi-Ting; Wullstein, Philipp; Komatsu, Eiichiro

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 bemore » 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.« less

Unravelling Galaxy Components

NASA Astrophysics Data System (ADS)

Kennedy, Rebecca

2017-06-01

This thesis aims to understand more about the developmental histories of galaxies and their internal components by studying the wavelength dependence of their spatial structure. I use a large sample of low-redshift galaxies with optical–near-IR imaging from the GAMA survey, which have been fitted with Sérsic and Sérsic + exponential functions in nine wavebands simultaneously, using software developed by the MegaMorph project. The first section of this thesis examines how the sizes and radial profiles of galaxies vary with wavelength. To quantify the wavelength dependence of effective radius I use the ratio, R, of measurements in two restframe bands. The dependence of Sérsic index on wavelength, N, is computed correspondingly. I show that accounting for different redshift and luminosity selections partly reconciles variations between several recent studies. Dividing galaxies by visual morphology confirms the behaviour inferred using morphological proxies, although our quantitative measurements allow me to study larger and fainter samples. I then demonstrate that varying dust opacity and disc inclination can account for features of the joint distribution of R and N for late-type galaxies. However, dust does not appear to explain the highest values of R and N. The bulge-disc nature of galaxies must also contribute to the wavelength-dependence of their structure. The second section of this thesis studies radial colour gradients across the galaxy population. I use the multi-wavelength information provided by MegaMorph analysis of galaxy light profiles to calculate intrinsic colour gradients, and divide into six subsamples split by overall Sérsic index (n) and galaxy colour. I find a bimodality in the colour gradients of high- and low-n galaxies in all wavebands which varies with overall galaxy luminosity. Global trends in colour gradients therefore result from combining the contrasting behaviour of a number of different galaxy populations. The ubiquity of strong

A Submillimeter Survey of Dust Continuum Emission in Local Dust-Obscured Galaxies

NASA Astrophysics Data System (ADS)

Lee, Jong Chul; Hwang, Ho Seong; Lee, Gwang-Ho

2015-08-01

Dusty star-forming galaxies are responsible for the bulk of cosmic star formation at 1galaxies is far from clear because of their extreme distances. The study of their local analogs helps us to improve understanding of the drivers of the intense star formation activity at high redshift. The submillimeter data on the 'Rayleigh-Jeans' side of the infrared spectral energy distributions (SEDs) of these galaxies are crucial for deriving the physical parameters of the dust content. We therefore conduct a submillimeter survey of local dust-obscured galaxies (DOGs) with the Caltech Submillimeter Observatory and the Submillimeter Array to study their dust properties. We determine the dust masses and temperatures for 16 local DOGs from the SED fit, and compare them with other dusty galaxies to understand a possible evolutionary link among them.

SDSS-IV MaNGA: Galaxy Pair Fraction and Correlated Active Galactic Nuclei

NASA Astrophysics Data System (ADS)

Fu, Hai; Steffen, Joshua L.; Gross, Arran C.; Dai, Y. Sophia; Isbell, Jacob W.; Lin, Lihwai; Wake, David; Xue, Rui; Bizyaev, Dmitry; Pan, Kaike

2018-04-01

We have identified 105 galaxy pairs at z ∼ 0.04 with the MaNGA integral-field spectroscopic data. The pairs have projected separations between 1 and 30 kpc, and are selected to have radial velocity offsets less than 600 km s‑1 and stellar mass ratio between 0.1 and 1. The pair fraction increases with both the physical size of the integral-field unit and the stellar mass, consistent with theoretical expectations. We provide the best-fit analytical function of the pair fraction and find that ∼3% of M* galaxies are in close pairs. For both isolated galaxies and paired galaxies, active galactic nuclei (AGNs) are selected using emission-line ratios and Hα equivalent widths measured inside apertures at a fixed physical size. We find AGNs in ∼24% of the paired galaxies and binary AGNs in ∼13% of the pairs. To account for the selection biases in both the pair sample and the MaNGA sample, we compare the AGN comoving volume densities with those expected from the mass- and redshift-dependent AGN fractions. We find a strong (∼5×) excess of binary AGNs over random pairing and a mild (∼20%) deficit of single AGNs. The binary AGN excess increases from ∼2× to ∼6× as the projected separation decreases from 10–30 to 1–10 kpc. Our results indicate that the pairing of galaxies preserves the AGN duty cycle in individual galaxies but increases the population of binary AGNs through correlated activities. We suggest tidally induced galactic-scale shocks and AGN cross-ionization as two plausible channels to produce low-luminosity narrow-line-selected binary AGNs.

Stellar Mass Function of Active and Quiescent Galaxies via the Continuity Equation

NASA Astrophysics Data System (ADS)

Lapi, A.; Mancuso, C.; Bressan, A.; Danese, L.

2017-09-01

The continuity equation is developed for the stellar mass content of galaxies and exploited to derive the stellar mass function of active and quiescent galaxies over the redshift range z˜ 0{--}8. The continuity equation requires two specific inputs gauged from observations: (I) the star formation rate functions determined on the basis of the latest UV+far-IR/submillimeter/radio measurements and (II) average star formation histories for individual galaxies, with different prescriptions for disks and spheroids. The continuity equation also includes a source term taking into account (dry) mergers, based on recent numerical simulations and consistent with observations. The stellar mass function derived from the continuity equation is coupled with the halo mass function and with the SFR functions to derive the star formation efficiency and the main sequence of star-forming galaxies via the abundance-matching technique. A remarkable agreement of the resulting stellar mass functions for active and quiescent galaxies of the galaxy main sequence, and of the star formation efficiency with current observations is found; the comparison with data also allows the characteristic timescales for star formation and quiescence of massive galaxies, the star formation history of their progenitors, and the amount of stellar mass added by in situ star formation versus that contributed by external merger events to be robustly constrained. The continuity equation is shown to yield quantitative outcomes that detailed physical models must comply with, that can provide a basis for improving the (subgrid) physical recipes implemented in theoretical approaches and numerical simulations, and that can offer a benchmark for forecasts on future observations with multiband coverage, as will become routinely achievable in the era of JWST.

wft4galaxy: a workflow testing tool for galaxy.

PubMed

Piras, Marco Enrico; Pireddu, Luca; Zanetti, Gianluigi

2017-12-01

Workflow managers for scientific analysis provide a high-level programming platform facilitating standardization, automation, collaboration and access to sophisticated computing resources. The Galaxy workflow manager provides a prime example of this type of platform. As compositions of simpler tools, workflows effectively comprise specialized computer programs implementing often very complex analysis procedures. To date, no simple way to automatically test Galaxy workflows and ensure their correctness has appeared in the literature. With wft4galaxy we offer a tool to bring automated testing to Galaxy workflows, making it feasible to bring continuous integration to their development and ensuring that defects are detected promptly. wft4galaxy can be easily installed as a regular Python program or launched directly as a Docker container-the latter reducing installation effort to a minimum. Available at https://github.com/phnmnl/wft4galaxy under the Academic Free License v3.0. marcoenrico.piras@crs4.it. © The Author 2017. Published by Oxford University Press.

Submillimeter Galaxy Number Counts and Magnification by Galaxy Clusters

NASA Astrophysics Data System (ADS)

Lima, Marcos; Jain, Bhuvnesh; Devlin, Mark; Aguirre, James

2010-07-01

We present an analytical model that reproduces measured galaxy number counts from surveys in the wavelength range of 500 μm-2 mm. The model involves a single high-redshift galaxy population with a Schechter luminosity function that has been gravitationally lensed by galaxy clusters in the mass range 1013-1015 M sun. This simple model reproduces both the low-flux and the high-flux end of the number counts reported by the BLAST, SCUBA, AzTEC, and South Pole Telescope (SPT) surveys. In particular, our model accounts for the most luminous galaxies detected by SPT as the result of high magnifications by galaxy clusters (magnification factors of 10-30). This interpretation implies that submillimeter (submm) and millimeter surveys of this population may prove to be a useful addition to ongoing cluster detection surveys. The model also implies that the bulk of submm galaxies detected at wavelengths larger than 500 μm lie at redshifts greater than 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

The host galaxy/AGN connection in nearby early-type galaxies. Is there a miniature radio-galaxy in every "core" galaxy?

NASA Astrophysics Data System (ADS)

Balmaverde, B.; Capetti, A.

2006-02-01

This is the second of a series of three papers exploring the connection between the multiwavelength properties of AGN in nearby early-type galaxies and the characteristics of their hosts. We selected two samples with 5 GHz VLA radio flux measurements down to 1 mJy, reaching levels of radio luminosity as low as 1036 erg s-1. In Paper I we presented a study of the surface brightness profiles for the 65 objects with available archival HST images out of the 116 radio-detected galaxies. We classified early-type galaxies into "core" and "power-law" galaxies, discriminating on the basis of the slope of their nuclear brightness profiles, following the Nukers scheme. Here we focus on the 29 core galaxies (hereafter CoreG). We used HST and Chandra data to isolate their optical and X-ray nuclear emission. The CoreG invariably host radio-loud nuclei, with an average radio-loudness parameter of Log R = L5 {GHz} / LB ˜ 3.6. The optical and X-ray nuclear luminosities correlate with the radio-core power, smoothly extending the analogous correlations already found for low luminosity radio-galaxies (LLRG) toward even lower power, by a factor of ˜ 1000, covering a combined range of 6 orders of magnitude. This supports the interpretation of a common non-thermal origin of the nuclear emission also for CoreG. The luminosities of the nuclear sources, most likely dominated by jet emission, set firm upper limits, as low as L/L_Edd ˜ 10-9 in both the optical and X-ray band, on any emission from the accretion process. The similarity of CoreG and LLRG when considering the distributions host galaxies luminosities and black hole masses, as well as of the surface brightness profiles, indicates that they are drawn from the same population of early-type galaxies. LLRG represent only the tip of the iceberg associated with (relatively) high activity levels, with CoreG forming the bulk of the population. We do not find any relationship between radio-power and black hole mass. A minimum black hole

The Physical Conditions, Metallicity and Metal Abundance Ratios in a Highly Magnified Galaxy at z = 3.6252

NASA Astrophysics Data System (ADS)

Bayliss, Matthew B.; Rigby, Jane R.; Sharon, Keren; Wuyts, Eva; Florian, Michael; Gladders, Michael D.; Johnson, Traci; Oguri, Masamune

2014-08-01

We present optical and near-IR imaging and spectroscopy of SGAS J105039.6+001730, a strongly lensed galaxy at z = 3.6252 magnified by >30×, and derive its physical properties. We measure a stellar mass of log(M */M ⊙) = 9.5 ± 0.35, star formation rates from [O II] λλ3727 and Hβ of 55 ± 25 and 84 ± 24 M ⊙ yr-1, respectively, an electron density of ne <= 103 cm-2, an electron temperature of Te <= 14,000 K, and a metallicity of 12 + log(O/H) = 8.3 ± 0.1. The strong C III] λλ1907,1909 emission and abundance ratios of C, N, O, and Si are consistent with well-studied starbursts at z ~ 0 with similar metallicities. Strong P Cygni lines and He II λ1640 emission indicate a significant population of Wolf-Rayet stars, but synthetic spectra of individual populations of young, hot stars do not reproduce the observed integrated P Cygni absorption features. The rest-frame UV spectral features are indicative of a young starburst with high ionization, implying either (1) an ionization parameter significantly higher than suggested by rest-frame optical nebular lines, or (2) differences in one or both of the initial mass function and the properties of ionizing spectra of massive stars. We argue that the observed features are likely the result of a superposition of star forming regions with different physical properties. These results demonstrate the complexity of star formation on scales smaller than individual galaxies, and highlight the importance of systematic effects that result from smearing together the signatures of individual star forming regions within galaxies. Based on observations from the Magellan Telescopes at Las Campanas Observatory, from 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 United States, Canada, Chile, Australia, Brazil and Argentina, with additional supporting data obtained at the Subaru telescope

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.

The IRX-β dust attenuation relation in cosmological galaxy formation simulations

NASA Astrophysics Data System (ADS)

Narayanan, Desika; Davé, Romeel; Johnson, Benjamin D.; Thompson, Robert; Conroy, Charlie; Geach, James

2018-02-01

We utilize a series of galaxy formation simulations to investigate the relationship between the ultraviolet (UV) slope, β, and the infrared excess (IRX) in the spectral energy distributions (SEDs) of galaxies. Our main goals are to understand the origin of and scatter in the IRX-β relation; to assess the efficacy of simplified stellar population synthesis screen models in capturing the essential physics in the IRX-β relation; and to understand systematic deviations from the canonical local IRX-β relations in particular populations of high-redshift galaxies. Our main results follow. Young galaxies with relatively cospatial UV and IR emitting regions and a Milky Way-like extinction curve fall on or near the standard Meurer relation. This behaviour is well captured by simplified screen models. Scatter in the IRX-β relation is dominated by three major effects: (i) older stellar populations drive galaxies below the relations defined for local starbursts due to a reddening of their intrinsic UV SEDs; (ii) complex geometries in high-z heavily star-forming galaxies drive galaxies towards blue UV slopes owing to optically thin UV sightlines; (iii) shallow extinction curves drive galaxies downwards in the IRX-β plane due to lowered near-ultraviolet/far-ultraviolet extinction ratios. We use these features of the UV slopes of galaxies to derive a fitting relation that reasonably collapses the scatter back towards the canonical local relation. Finally, we use these results to develop an understanding for the location of two particularly enigmatic populations of galaxies in the IRX-β plane: z ˜ 2-4 dusty star-forming galaxies and z > 5 star-forming galaxies.

Why do high-redshift galaxies show diverse gas-phase metallicity gradients?

NASA Astrophysics Data System (ADS)

Ma, Xiangcheng; Hopkins, Philip F.; Feldmann, Robert; Torrey, Paul; Faucher-Giguère, Claude-André; Kereš, Dušan

2017-04-01

Recent spatially resolved observations of galaxies at z ˜ 0.6-3 reveal that high-redshift galaxies show complex kinematics and a broad distribution of gas-phase metallicity gradients. To understand these results, we use a suite of high-resolution cosmological zoom-in simulations from the Feedback in Realistic Environments project, which include physically motivated models of the multiphase interstellar medium, star formation and stellar feedback. Our simulations reproduce the observed diversity of kinematic properties and metallicity gradients, broadly consistent with observations at z ˜ 0-3. Strong negative metallicity gradients only appear in galaxies with a rotating disc, but not all rotationally supported galaxies have significant gradients. Strongly perturbed galaxies with little rotation always have flat gradients. The kinematic properties and metallicity gradient of a high-redshift galaxy can vary significantly on short time-scales, associated with starburst episodes. Feedback from a starburst can destroy the gas disc, drive strong outflows and flatten a pre-existing negative metallicity gradient. The time variability of a single galaxy is statistically similar to the entire simulated sample, indicating that the observed metallicity gradients in high-redshift galaxies reflect the instantaneous state of the galaxy rather than the accretion and growth history on cosmological time-scales. We find weak dependence of metallicity gradient on stellar mass and specific star formation rate (sSFR). Low-mass galaxies and galaxies with high sSFR tend to have flat gradients, likely due to the fact that feedback is more efficient in these galaxies. We argue that it is important to resolve feedback on small scales in order to produce the diverse metallicity gradients observed.

Radio Galaxy Zoo: A Search for Hybrid Morphology Radio Galaxies

NASA Astrophysics Data System (ADS)

Kapińska, A. D.; Terentev, I.; Wong, O. I.; Shabala, S. S.; Andernach, H.; Rudnick, L.; Storer, L.; Banfield, J. K.; Willett, K. W.; de Gasperin, F.; Lintott, C. J.; López-Sánchez, Á. R.; Middelberg, E.; Norris, R. P.; Schawinski, K.; Seymour, N.; Simmons, B.

2017-12-01

Hybrid morphology radio sources (HyMoRS) are a rare type of radio galaxy that display different Fanaroff-Riley classes on opposite sides of their nuclei. To enhance the statistical analysis of HyMoRS, we embarked on a large-scale search of these sources within the international citizen science project, Radio Galaxy Zoo (RGZ). Here, we present 25 new candidate hybrid morphology radio galaxies. Our selected candidates are moderate power radio galaxies ({L}{median}=4.7× {10}24 W Hz-1 sr-1) at redshifts 0.14< z< 1.0. Hosts of nine candidates have spectroscopic observations, of which six are classified as quasars, one as high- and two as low-excitation galaxies. Two candidate HyMoRS are giant (> 1 Mpc) radio galaxies, one resides at the center of a galaxy cluster, and one is hosted by a rare green bean galaxy. Although the origin of the hybrid morphology radio galaxies is still unclear, this type of radio source starts depicting itself as a rather diverse class. We discuss hybrid radio morphology formation in terms of the radio source environment (nurture) and intrinsically occurring phenomena (nature; activity cessation and amplification), showing that these peculiar radio galaxies can be formed by both mechanisms. While high angular resolution follow-up observations are still necessary to confirm our candidates, we demonstrate the efficacy of the RGZ in the pre-selection of these sources from all-sky radio surveys, and report the reliability of citizen scientists in identifying and classifying complex radio sources.

The connection between dark and baryonic matter in the process of galaxy formation

NASA Astrophysics Data System (ADS)

Trujillo, Sebastian

2014-01-01

Current galaxy formation theory still struggles to explain many essential galaxy properties. This thesis addresses these problems in the context of the interplay between baryons and dark matter in the concordance cosmological model. In the first part, we investigate galaxy abundance and scaling relations using a compilation of observational data along with large-scale cosmological simulations of dark matter (DM). We find that the standard cosmological model, in conjunction with halo abundance matching (HAM) and simple dynamical corrections, fits all basic statistics of galaxies more massive than the Large Magellanic Cloud (LMC). This zero-parameter model predicts the observed luminosity-velocity relation of early-and late-type galaxies, as well as the clustering of bright galaxies and the observed abundance of galaxies as a function of circular velocity. However, we find that all DM halos more massive than the LMC are much more abundant than the galaxies they host. Motivated by the model's shortcomings, in the second part we study the effect of baryons on galaxy formation using numerical simulations that include gas physics. We implement a model of star formation (SF) and stellar feedback based directly on observations of star-forming regions, where stellar feedback from massive stars includes radiation pressure, photoheating, supernovae, and stellar winds. We find that stellar radiation has a strong effect at z > 1, where it efficiently suppresses SF by dispersing cold and dense gas, preventing runaway growth of the stellar component, and yielding rising SF histories that reproduce many observations. Stellar feedback produces bulgeless discs with rotation curves and baryon fractions in excellent agreement with data. Feedback-driven blowouts reduce the central DM density of a dwarf, relieving tension between ACDM and observations. Based on these results, we begin to characterize the baryon cycle of galaxies and its imprint on studies of the circumgalactic medium

Reconciling Dwarf Galaxies with ΛCDM Cosmology: Simulating a Realistic Population of Satellites around a Milky Way-mass Galaxy

NASA Astrophysics Data System (ADS)

Wetzel, Andrew R.; Hopkins, Philip F.; Kim, Ji-hoon; Faucher-Giguère, Claude-André; Kereš, Dušan; Quataert, Eliot

2016-08-01

Low-mass “dwarf” galaxies represent the most significant challenges to the cold dark matter (CDM) model of cosmological structure formation. Because these faint galaxies are (best) observed within the Local Group (LG) of the Milky Way (MW) and Andromeda (M31), understanding their formation in such an environment is critical. We present first results from the Latte Project: the Milky Way on Feedback in Realistic Environments (FIRE). This simulation models the formation of an MW-mass galaxy to z=0 within ΛCDM cosmology, including dark matter, gas, and stars at unprecedented resolution: baryon particle mass of 7070 {M}⊙ with gas kernel/softening that adapts down to 1 {pc} (with a median of 25{--}60 {pc} at z=0). Latte was simulated using the GIZMO code with a mesh-free method for accurate hydrodynamics and the FIRE-2 model for star formation and explicit feedback within a multi-phase interstellar medium. For the first time, Latte self-consistently resolves the spatial scales corresponding to half-light radii of dwarf galaxies that form around an MW-mass host down to {M}{star}≳ {10}5 {M}⊙ . Latte’s population of dwarf galaxies agrees with the LG across a broad range of properties: (1) distributions of stellar masses and stellar velocity dispersions (dynamical masses), including their joint relation; (2) the mass-metallicity relation; and (3) diverse range of star formation histories, including their mass dependence. Thus, Latte produces a realistic population of dwarf galaxies at {M}{star}≳ {10}5 {M}⊙ that does not suffer from the “missing satellites” or “too big to fail” problems of small-scale structure formation. We conclude that baryonic physics can reconcile observed dwarf galaxies with standard ΛCDM cosmology.

GLASS: spatially resolved spectroscopy of lensed galaxies in the Frontier Fields

NASA Astrophysics Data System (ADS)

Jones, Tucker; Treu, Tommaso; Brammer, Gabriel; Borello Schmidt, Kasper; Malkan, Matthew A.

2015-08-01

The Grism Lens-Amplified Survey from Space (GLASS) has obtained slitless near-IR spectroscopy of 10 galaxy clusters selected for their strong lensing properties, including all six Hubble Frontier Fields. Slitless grism spectra are ideal for mapping emission lines such as [O II], [O III], and H alpha at z=1-3. The combination of strong gravitational lensing and HST's diffraction limit provides excellent sensitivity with spatial resolution as fine as 100 pc for highly magnified sources, and ~500 pc for less magnified sources near the edge of the field of view. The GLASS survey represents the largest spectroscopic sample with such high resolution at z>1. GLASS and Hubble Frontier Field data provide the distribution of stellar mass, star formation, gas-phase metallicity, and other aspects of the physical structure of high redshift galaxies, reaching unprecedented stellar masses as low as ~10^7 Msun at z=2. I will discuss precise measurements of these physical properties and implications for galaxy evolution.

Cosmic evolution and metal aversion in superluminous supernova host galaxies

NASA Astrophysics Data System (ADS)

Schulze, S.; Krühler, T.; Leloudas, G.; Gorosabel, J.; Mehner, A.; Buchner, J.; Kim, S.; Ibar, E.; Amorín, R.; Herrero-Illana, R.; Anderson, J. P.; Bauer, F. E.; Christensen, L.; de Pasquale, M.; de Ugarte Postigo, A.; Gallazzi, A.; Hjorth, J.; Morrell, N.; Malesani, D.; Sparre, M.; Stalder, B.; Stark, A. A.; Thöne, C. C.; Wheeler, J. C.

2018-01-01

The SUperluminous Supernova Host galaxIES survey aims to provide strong new constraints on the progenitors of superluminous supernovae (SLSNe) by understanding the relationship to their host galaxies. We present the photometric properties of 53 H-poor and 16 H-rich SLSN host galaxies out to z ∼ 4. We model their spectral energy distributions to derive physical properties, which we compare with other galaxy populations. At low redshift, H-poor SLSNe are preferentially found in very blue, low-mass galaxies with high average specific star formation rates. As redshift increases, the host population follows the general evolution of star-forming galaxies towards more luminous galaxies. After accounting for secular evolution, we find evidence for differential evolution in galaxy mass, but not in the B band and the far-ultraviolet luminosity (3σ confidence). Most remarkable is the scarcity of hosts with stellar masses above 1010 M⊙ for both classes of SLSNe. In case of H-poor SLSNe, we attribute this to a stifled production efficiency above ∼0.4 solar metallicity. However, we argue that, in addition to low metallicity, a short-lived stellar population is also required to regulate the SLSN production. H-rich SLSNe are found in a very diverse population of star-forming galaxies. Still, the scarcity of massive hosts suggests a stifled production efficiency above ∼0.8 solar metallicity. The large dispersion of the H-rich SLSNe host properties is in stark contrast to those of gamma-ray burst, regular core-collapse SN, and H-poor SLSNe host galaxies. We propose that multiple progenitor channels give rise to this subclass.

The Nature of Accreting Black Holes in Nearby Galaxy Nuclei

NASA Astrophysics Data System (ADS)

Colbert, E. J. M.; Mushotzky, R. F.

1999-04-01

We have found compact X-ray sources in the center of 21 (54%) of 39 nearby face-on spiral and elliptical galaxies with available ROSAT HRI data. ROSAT X-ray luminosities (0.2 - 2.4 keV) of these compact X-ray sources are ~ 10(37) -10(40) erg s(-1) (with a mean of 3 x 10(39) erg s(-1) ). The mean displacement between the location of the compact X-ray source and the optical photometric center of the galaxy is ~ 390 pc. The fact that compact nuclear sources were found in nearly all (five of six) galaxies with previous evidence for a black hole or an AGN indicates that at least some of the X-ray sources are accreting supermassive black holes. ASCA spectra of six of the 21 galaxies show the presence of a hard component with relatively steep (Gamma ~ 2.5) spectral slope. A multicolor disk blackbody model fits the data from the spiral galaxies well, suggesting that the X-ray object in these galaxies may be similar to a Black Hole Candidate in its soft (high) state. ASCA data from the elliptical galaxies indicate that hot (kT ~ 0.7 keV) gas dominates the emission. The fact that (for both spiral and elliptical galaxies) the spectral slope is steeper than in normal type 1 AGNs and that relatively low absorbing columns (N_H ~ 10(21) cm(-2) ) were found to the power-law component indicates that these objects are somehow geometrically and/or physically different from AGNs in normal active galaxies. The X-ray sources in the spiral and elliptical galaxies may be black hole X-ray binaries, low-luminosity AGNs, or possibly young X-ray luminous supernovae. Assuming the sources in the spiral galaxies are accreting black holes in their soft state, we estimate black hole masses ~ 10(2) -10(4) M_sun.

The Nature of Accreting Black Holes in Nearby Galaxy Nuclei

NASA Astrophysics Data System (ADS)