Parent Galaxy Research Articles

Compact nuclear objects and properties of their parent galaxies

AbstractWe consider the relationship between the masses of the compact nuclear objects in the centers of disky galaxies – supermassive black holes (SMBHs) or nuclear star clusters (NCs) – and such parameters as the maximal velocity of rotation Vmax, obtained from the rotation curves, indicative dynamical mass M25, and the color index (B−V) of their parent galaxies. It was found that the mass of nuclear clusters Mnc correlates more closely with the velocity of rotation and total mass of galaxies than the mass of supermassive black holes Mbh. The dependence of masses of the central objects on the color index is bimodal: galaxies of the red group (red-sequence), which have (B−V) > 0.6−0.7, differ from bluer galaxies, by higher values of Mbh for similar host-galaxy parameters. In contrast, in the diagrams for nuclear clusters the “blue” and “red” galaxies form unified sequences. It agrees with scenarios in which most red-group galaxies form as a result of loss of interstellar gas in a stage of high nuclear activity in galaxies whose central black-hole masses are high, exceeding 106 − 107M⊙ (depending on the total mass of the galaxy). The active growth of nuclear star clusters possibly begun after the violent AGN activity.

Clustering at high redshift: the connection between Lyman α emitters and Lyman break galaxies

We present a physically motivated semi-analytic model to understand the clustering of high redshift Lyman Alpha Emitters (LAEs). We show that the model parameters constrained by the observed luminosity functions, can be used to predict large scale bias and angular correlation function of LAEs. These predictions are shown to reproduce the observations remarkably well. We find that average masses of dark matter halos hosting LAEs brighter than threshold narrow band magnitude ~ 25 are ~ 10^11 M_\odot. These are smaller than that of typical Lyman Break Galaxies (LBGs) brighter than similar threshold continuum magnitude by a factor ~ 10. This results in a smaller clustering strength of LAEs compared to LBGs. However, using the observed relationship between UV continuum and Lyman-alpha luminosity of LAEs, we show that both LAEs and LBGs belong to the same parent galaxy population with narrow band techniques having greater efficiency in picking up galaxies with low UV luminosity. We also show that the lack of evidence for the presence of the one halo term in the observed LAE angular correlation functions can be attributed to sub-Poisson distribution of LAEs in dark matter halos as a result of their low halo occupations.

Study of Possible Local Quasars and Search for a Quasar-Stellar Connection. III. A Sample of 341 QSOs

A new sample of 341 possible local QSOs are presented, which are in the vicinity of low redshift galaxies. Physical characteristics of the sample quasars are determined and previously reported relations are confirmed: density - redshift, abso- lute mag - radius, absolute mag - mass, mass - radius, mass - luminosity, and mass - density. These relations seem to sup- port the basic assumptions that quasars are single, compact objects, with dimensions close to their respective gravitational ra- dius. Redshifts of quasars are dominated by a gravitational redshift component, and the gravitational redshifts seem to be quantized according to the Karlsson - sequence. Evidence is found in favour of the Arp's evolutionary scenario: QSOs are ejected from their respective parent galaxy and evolve as they recede, building new small mass companion galaxies. Evidence is found that in the course of evolution the quasar density and redshift decrease, while dimensions and luminosity increase. Relation luminosity - density is found in the sense that more dense quasars are less luminous. Simple linear density equation is found, which seems to apply to quasars, but also to stars and may be even to planets, providing a possible link between these seemingly very different structures in the Universe. Evidence is found of possible increase of quasar mass and luminosity with increasing distance to about z=0.03. The physics behind all these processes and relations remain unclear, but a revival of the old Ambartsumian's hypotheses seems possible, suggesting disintegra- tion of an unknown primordial dense matter. The properties of quasars may invoke the need for deeper changes in our cur- rent theories. Most fascinating seems the possibility that a link may exist between quasars and stars.

ON THE ORIGIN OF LOPSIDEDNESS IN GALAXIES AS DETERMINED FROM THE SPITZER SURVEY OF STELLAR STRUCTURE IN GALAXIES (S4G)

We study the m=1 distortions (lopsidedness) in the stellar components of 167 nearby galaxies that span a wide range of morphologies and luminosities. We confirm the previous findings of 1) a high incidence of lopsidedness in the stellar distributions, 2) increasing lopsidedness as a function of radius out to at least 3.5 exponential scale lengths, and 3) greater lopsidedness, over these radii, for galaxies of later type and lower surface brightness. Additionally, the magnitude of the lopsidedness 1) correlates with the character of the spiral arms (stronger arm patterns occur in galaxies with less lopsidedness), 2) is not correlated with the presence or absence of a bar, or the strength of the bar when one is present, 3) is inversely correlated to the stellar mass fraction, f_*, within one radial scale length, and 4) correlates directly with f_* measured within the radial range over which we measure lopsidedness. We interpret these findings to mean that lopsidedness is a generic feature of galaxies and does not, generally, depend on a rare event, such as a direct accretion of a satellite galaxy onto the disk of the parent galaxy. While lopsidedness may be caused by several phenomena, moderate lopsidedness (<A_1>_i + <A_1>_o)/2 < 0.3) is likely to reflect halo asymmetries to which the disk responds or a gravitationally self-generated mode . We hypothesize that the magnitude of the stellar response depends both on how centrally concentrated the stars are with respect to the dark matter and whether there are enough stars in the region of the lopsidedness that self-gravity is dynamically important.

Low-mass X-ray binary populations in galaxy outskirts: Globular clusters and supernova kicks

For the first time, we have systematically explored the population of discrete X-ray sources in the outskirts of early-type galaxies. Based on a broad sample of 20 galaxies observed with Chandra we detected overdensity of X-ray sources in their outskirts. The overdensity appears as halos of resolved sources around the galaxies. These halos are broader than the stellar light, extending out to at least ~ 10 Re (Re is the effective radius). These halos are composed of sources fainter than ~5E38 erg/s, whereas the more luminous sources appear to follow the distribution of the stellar light, suggesting that the excess source population consists of neutron star binaries. Dividing the galaxy sample into four groups according to their stellar mass and specific frequency of globular clusters, we find that the extended halos are present in all groups except for the low-mass galaxies with low globular cluster content. We propose that the extended halos may be comprised of two independent components, low-mass X-ray binaries (LMXBs) located in globular clusters (GCs), which are known to have a wider distribution than the stellar light, and neutron star (NS) LMXBs kicked out of the main body of the parent galaxy by supernova explosions. The available deep optical and X-ray data of NGC 4365 support this conclusion. For this galaxy we identified 60.1+/-10.8 excess sources in the 4-10 Re region of which ~ 40% are located in GCs, whereas ~ 60% are field LMXBs. We interpret the latter as kicked NS LMXBs. We discuss the implications of these results for the natal kick distributions of black holes and neutron stars.

The effect of many minor mergers on the size growth of compact quiescent galaxies

Massive galaxies with a half-mass radius <~ 1kpc are observed in the early universe (z~>2), but not in the local universe. In the local universe similar-mass (within a factor of two) galaxies tend to be a factor of 4 to 5 larger. Dry minor mergers are known to drive the evolution of the size of a galaxy without much increasing the mass, but it is unclear if the growth in size is sufficient to explain the observations. We test the hypothesis that galaxies grow through dry minor mergers by simulating merging galaxies with mass ratios of q=1:1 (equal mass) to q=1:160. In our N-body simulations the total mass of the parent galaxy doubles. We confirm that major mergers do not cause a sufficient growth in size. The observation can be explained with mergers with a mass ratio of q=1:5--1:10. Smaller mass ratios cause a more dramatic growth in size, up to a factor of ~17 for mergers with a mass ratio of 1:80. For relatively massive minor mergers q ~> 1:20 the mass of the incoming child galaxies tend to settle in the halo of the parent galaxy. This is caused by the tidal stripping of the child galaxies by the time they enter the central portion of the parent. When the accretion of minor galaxies becomes more continuous, when q <~ 1:40, the foreign mass tends to concentrate more in the central region of the parent galaxy. We speculate that this is caused by dynamic interactions between the child galaxies inside the merger remnant and the longer merging times when the difference in mass is larger. These interactions cause dynamical heating which results in accretion of mass inside the galaxy core and a reduction of the parent's circular velocity and density.

CHARACTERIZING THE CIRCUMGALACTIC MEDIUM OF NEARBY GALAXIES WITHHST/COS ANDHST/STIS ABSORPTION-LINE SPECTROSCOPY

The Circumgalactic Medium (CGM) of late-type galaxies is characterized using UV spectroscopy of 11 targeted QSO/galaxy pairs at z < 0.02 with the Hubble Space Telescope Cosmic Origins Spectrograph and ~60 serendipitous absorber/galaxy pairs at z < 0.2 with the Space Telescope Imaging Spectrograph. CGM warm cloud properties are derived, including volume filling factors of 3-5%, cloud sizes of 0.1-30 kpc, masses of 10-1e8 solar masses and metallicities of 0.1-1 times solar. Almost all warm CGM clouds within 0.5 virial radii are metal-bearing and many have velocities consistent with being bound, "galactic fountain" clouds. For galaxies with L > 0.1 L*, the total mass in these warm CGM clouds approaches 1e10 solar masses, ~10-15% of the total baryons in massive spirals and comparable to the baryons in their parent galaxy disks. This leaves >50% of massive spiral-galaxy baryons "missing". Dwarfs (<0.1 L*) have smaller area covering factors and warm CGM masses (<5% baryon fraction), suggesting that many of their warm clouds escape. Constant warm cloud internal pressures as a function of impact parameter ($P/k ~ 10 cm^{-3} K) support the inference that previous COS detections of broad, shallow O VI and Ly-alpha absorptions are of an extensive (~400-600 kpc), hot (T ~ 1e6 K) intra-cloud gas which is very massive (>1e11 solar masses). While the warm CGM clouds cannot account for all the "missing baryons" in spirals, the hot intra-group gas can, and could account for ~20% of the cosmic baryon census at z ~ 0 if this hot gas is ubiquitous among spiral groups.

The multi-band study of the environment of the RC J0311+0507 radio galaxy: a step forward to understand massive stellar system formation at Z&gt; 4

The radio galaxy RC J0311+0507 was investigated in the “Big Trio” project, which aims to search for distant radio galaxies. Optical spectroscopy performed at the 6-m telescope measured its redshift as 4.514. The source is one of the most luminous objects in the high redshift Universe having L ≈ 3 × 1029 W Hz-1 at 500 MHz, that suggests the presence of a super massive black hole with a mass of about 1010 M ⊙ inside the parent galaxy. Mechanisms of the formation of galaxies with black holes of such masses in the early stage of the Universe is not yet clear. Based on a collection of deep images taken in 10 optical and infrared bands we started a photometric study of the environment of this radio galaxy to detect possible neighborhood.

THE OPTICAL COLORS OF GIANT ELLIPTICAL GALAXIES AND THEIR METAL-RICH GLOBULAR CLUSTERS INDICATE A BOTTOM-HEAVY INITIAL MASS FUNCTION

We report a systematic and statistically significant offset between the optical (g-z or B-I) colors of seven massive elliptical galaxies and the mean colors of their associated massive metal-rich globular clusters (GCs) in the sense that the parent galaxies are redder by 0.12-0.20 mag at a given galactocentric distance. However, spectroscopic indices in the blue indicate that the luminosity-weighted ages and metallicities of such galaxies are equal to that of their averaged massive metal-rich GCs at a given galactocentric distance, to within small uncertainties. The observed color differences between the red GC systems and their parent galaxies cannot be explained by the presence of multiple stellar generations in massive metal-rich GCs, as the impact of the latter to the populations' integrated g-z or B-I colors is found to be negligible. However, we show that this paradox can be explained if the stellar initial mass function (IMF) in these massive elliptical galaxies was significantly steeper at subsolar masses than canonical IMFs derived from star counts in the solar neighborhood, with the GC colors having become bluer due to dynamical evolution, causing a significant flattening of the stellar MF of the average surviving GC.

THE METALLICITY BIMODALITY OF GLOBULAR CLUSTER SYSTEMS: A TEST OF GALAXY ASSEMBLY AND OF THE EVOLUTION OF THE GALAXY MASS-METALLICITY RELATION

(Abridged) We build a theoretical model to study the origin of the globular cluster metallicity bimodality in the hierarchical galaxy assembly scenario, based on the observed galaxy mass-[O/H] relation and the galaxy stellar mass function up to z ~4, and on theoretical merger rates. We derive a new galaxy [Fe/H]-M(star) relation as a function of z, and by assuming that GCs share the metallicity of their parent galaxy when they form, we populate the merger tree with GCs. We perform a series of Monte-Carlo simulations of the galaxy assembly, and study the properties of the final GC population as a function of galaxy mass, assembly and star formation history, and under different assumptions for the evolution of the galaxy mass-[Fe/H] relation. The main results are: 1) The hierarchical clustering scenario naturally predicts a metallicity bimodality in the galaxy GC population: the metal-rich GCs are formed in the galaxy main progenitor around z~2, and the metal-poor GCs are accreted from satellites and formed at z~3-4. 2) The model reproduces the observed relations for the metallicity of the metal-rich and metal-poor GCs as a function of galaxy mass. The positions of the metal-poor and metal-rich peaks depend exclusively on the evolution of the galaxy mass-[Fe/H] relation and the [O/Fe], both of which can be constrained by this method. We find that the galaxy [O/Fe] evolves linearly with z from a value of ~0.5 at z~4 to a value of ~0.1 at z=0. 3) Given a galaxy mass, the relative strength of the metal-rich and metal-poor peaks depends exclusively on the galaxy assembly and star formation history: galaxies in denser environments and/or early types galaxies show a larger fraction of metal-poor GCs, while galaxies with a sparse merger history and/or late type galaxies are dominated by metal-rich GCs. 4) The GC metallicity bimodality disappears for galaxy masses below M(star)~1e9, and for z>2.

Quasar feedback: accelerated star formation and chaotic accretion

Growing supermassive black holes (SMBHs) are believed to influence their parent galaxies in a negative way, terminating their growth by ejecting gas before it can turn into stars. Here we present some of the most sophisticated SMBH feedback simulations to date, showing that the effects of quasars on galaxies are not always negative. We find that when the ambient shocked gas cools rapidly, the shocked gas is compressed into thin cold dense shells, filaments and clumps. Driving these high-density features out is much more difficult than analytical models predict. However, in this regime quasars have another way of affecting the host – by triggering a massive star-formation burst in the cold gas by overpressurizing it. Under these conditions SMBHs actually accelerate star formation in the host, having a positive rather than negative effect on their host galaxies. The relationship between SMBHs and galaxies is thus even more complex and symbiotic than currently believed. We also suggest that the instabilities found here may encourage a chaotic active galactic nucleus feeding mode.

Infrared light from wandering stars

An explanation has been proposed for the observed excess of cosmic light at infrared wavelengths. It invokes stars that are cast into the dark-matter haloes of their parent galaxies during powerful galaxy collisions. See Letter p.514 During the past two decades, space telescopes have detected variations in the near-infrared background radiation that cannot be explained by emissions from known galaxies. Suggested sources for this excess radiation have included contributions from the earliest galaxies during the epoch of reionization, and faint, dwarf galaxies at intermediate redshifts. These sources would leave characteristic imprints on the spatial variation of the near-infrared background, but previous measurements have not sampled at sufficiently large spatial scales to distinguish these signatures. Asantha Cooray et al. now report measurements from the Spitzer telescope that sample at angular scales of as much as one degree, and find that the previously suggested sources do not explain the data. Rather, they suggest that the fluctuations arise from intrahalo stars that were stripped from their host galaxies during galactic collisions and have migrated to distant orbits in the galaxies' dark-matter haloes.

Star formation in H itails: HCG 92, HCG 100 and six interacting systems

We present new Gemini spectra of 14 new objects found within the HI tails of Hickson Compact Groups 92 and 100. Nine of them are GALEX Far-UV (FUV) and Near-UV (NUV) sources. The spectra confirm that these objects are members of the compact groups and have metallicities close to solar, with an average value of 12+log(O/H)~8.5. They have average FUV luminosities 7 x 10^40 erg/s, very young ages (< 100 Myr) and two of them resemble tidal dwarf galaxies (TDGs) candidates. We suggest that they were created within gas clouds that were ejected during galaxy-galaxy interactions into the intergalactic medium, which would explain the high metallicities of the objects, inherited from the parent galaxies from which the gas originated. We conduct a search for similar objects in 6 interacting systems with extended HI tails, NGC 2623, NGC 3079, NGC 3359, NGC 3627, NGC 3718, NGC 4656. We found 35 UV sources with ages < 100 Myr, however most of them are on average less luminous/massive than the UV sources found around HCG 92 and 100. We speculate that this might be an environmental effect and that compact groups of galaxies are more favorable to TDG formation than other interacting systems.

BVRI lightcurves of supernovae SN 2011fe in M101, SN 2012aw in M95, and SN 2012cg in NGC 4424

Accurate and densely populated BVRCIC lightcurves of supernovae SN 2011fe in M101, SN 2012aw in M95 and SN 2012cg in NGC 4424 are presented and discussed. The SN 2011fe lightcurves span a total range of 342days, from 17days pre- to 325days post-maximum. The observations of both SN 2012aw and SN 2012cg were stopped by solar conjunction, when the objects were still bright. The lightcurve for SN 2012aw covers 92days, that of SN 2012cg spans 44days. Time and brightness of maxima are measured, and from the lightcurve shapes and decline rates the absolute magnitudes are obtained, and the derived distances are compared to that of the parent galaxies. The color evolution and the bolometric lightcurves are evaluated in comparison with those of other well observed supernovae, showing no significant deviations.

THE 2dF REDSHIFT SURVEY. I. PHYSICAL ASSOCIATION AND PERIODICITY IN QUASAR FAMILIES

We have tested for physical association of candidate companion quasars with putative parent galaxies by virtue of Karlsson periodicity in quasar redshifts. We examined galaxies from the 2dF Galaxy Redshift Survey (2dFGRS) and quasars from the 2dF Quasar Redshift Survey (2QZ) in the two declination strips (at declinations 0° and –30°) covered by the 2QZ, first filtering out galaxies and quasars using the respective survey masks and observation qualities as described, and using only quasars with z ≥ 0.5 to avoid the redshift region of mixed galaxies and quasars. Around each galaxy, quasars are detected as physically associated with a putative parent galaxy if their respective redshifts conform to empirically derived constraints based on an ejection hypothesis. We ran Monte Carlo control trials against the pure physical associations by replacing the actual redshifts of the candidate companion quasars with quasar redshifts drawn randomly from each respective right ascension hour. The constraints are grouping of quasar redshifts and Karlsson periodicity of quasar redshifts.

The globular cluster system of NGC 1316

SH2 has been described as an isolated HII-region, located about 6.5 arcmin south of the nucleus of NGC 1316 (Fornax A), a merger remnant in the the outskirts of the Fornax cluster of galaxies. We give a first, preliminary description of the stellar content and environment of this remarkable object. We used photometric data in the Washington system and HST photometry from the Hubble Legacy Archive for a morphological description and preliminary aperture photometry. Low-resolution spectroscopy provides radial velocities of the brightest star cluster in SH2 and a nearby intermediate-age cluster. SH2 is not a normal HII-region, ionized by very young stars. It contains a multitude of star clusters with ages of approximately 0.1 Gyr. A ring-like morphology is striking. SH2 seems to be connected to an intermediate-age massive globular cluster with a similar radial velocity, which itself is the main object of a group of fainter clusters. Metallicity estimates from emission lines remain ambiguous. The present data do not yet allow firm conclusions about the nature or origin of SH2. It might be a dwarf galaxy that has experienced a burst of extremely clustered star formation. We may witness how globular clusters are donated to a parent galaxy.

QUANTIFYING THE BIASES OF SPECTROSCOPICALLY SELECTED GRAVITATIONAL LENSES

Spectroscopic selection has been the most productive technique for the selection of galaxy-scale strong gravitational lens systems with known redshifts. Statistically significant samples of strong lenses provide a powerful method for measuring the mass-density parameters of the lensing population, but results can only be generalized to the parent population if the lensing selection biases are sufficiently understood. We perform controlled Monte Carlo simulations of spectroscopic lens surveys in order to quantify the bias of lenses relative to parent galaxies in velocity dispersion, mass axis ratio, and mass density profile. For parameters typical of the SLACS and BELLS surveys, we find: (1) no significant mass axis ratio detection bias of lenses relative to parent galaxies; (2) a very small detection bias toward shallow mass density profiles, which is likely negligible compared to other sources of uncertainty in this parameter; (3) a detection bias towards smaller Einstein radius for systems drawn from parent populations with group- and cluster-scale lensing masses; and (4) a lens-modeling bias towards larger velocity dispersions for systems drawn from parent samples with sub-arcsecond mean Einstein radii. This last finding indicates that the incorporation of velocity-dispersion upper limits of \textit{non-lenses} is an important ingredient for unbiased analyses of spectroscopically selected lens samples. In general we find that the completeness of spectroscopic lens surveys in the plane of Einstein radius and mass-density profile power-law index is quite uniform, up to a sharp drop in the region of large Einstein radius and steep mass density profile, and hence that such surveys are ideally suited to the study of massive field galaxies.

NGC 4656UV: A UV-SELECTED TIDAL DWARF GALAXY CANDIDATE

We report the discovery of a UV-bright tidal dwarf galaxy candidate in the NGC 4631/4656 galaxy group, which we designate NGC 4656UV. Using survey and archival data spanning from 1.4 GHz to the ultraviolet we investigate the gas kinematics and stellar properties of this system. The HI morphologies of NGC 4656UV and its parent galaxy NGC 4656 are extremely disturbed, with significant amounts of counterrotating and extraplanar gas. From UV-FIR photometry, computed using a new method to correct for surface gradients on faint objects, we find that NGC 4656UV has no significant dust opacity and a blue spectral energy distribution. We compute a star formation rate of 0.027 M_sun yr^-1 from the FUV flux and measure a total HI mass of 3.8x10^8 M_sun for the object. Evolutionary synthesis modeling indicates that NGC 4656UV is a low metallicity system whose only major burst of star formation occurred within the last ~260-290 Myr. The age of the stellar population is consistent with a rough timescale for a recent tidal interaction between NGC 4656 and NGC 4631, although we discuss the true nature of the object--whether it is tidal or pre-existing in origin--in the context of its metallicity being a factor of ten lower than its parent galaxy. We estimate that NGC 4656UV is either marginally bound or unbound. If bound, it contains relatively low amounts of dark matter. The abundance of archival data allows for a deeper investigation into this dynamic system than is currently possible for most TDG candidates.

SHOCKING TAILS IN THE MAJOR MERGER ABELL 2744

We identify four rare "jellyfish" galaxies in Hubble Space Telescope imagery of the major merger cluster Abell 2744. These galaxies harbor trails of star-forming knots and filaments which have formed in-situ in gas tails stripped from the parent galaxies, indicating they are in the process of being transformed by the environment. Further evidence for rapid transformation in these galaxies comes from their optical spectra, which reveal starburst, poststarburst and AGN features. Most intriguingly, three of the jellyfish galaxies lie near ICM features associated with a merging "Bullet-like" subcluster and its shock front detected in Chandra X-ray images. We suggest that the high pressure merger environment may be responsible for the star formation in the gaseous tails. This provides observational evidence for the rapid transformation of galaxies during the violent core passage phase of a major cluster merger.

KINEMATICS AND EXCITATION OF THE RAM PRESSURE STRIPPED IONIZED GAS FILAMENTS IN THE COMA CLUSTER OF GALAXIES

We present the results of deep imaging and spectroscopic observations of very extended ionized gas (EIG) around four member galaxies of the Coma cluster of galaxies: RB199, IC4040, GMP2923 and GMP3071. The EIGs were serendipitously found in an H-alpha narrow band imaging survey of the central region of the Coma cluster. The relative radial velocities of the EIGs with respect to the systemic velocities of the parent galaxies from which they emanate increase almost monotonically with the distance from the nucleus of the respective galaxies, reaching -400 - -800 km/s at around 40 - 80 kpc from the galaxies. The one-sided morphologies and the velocity fields of the EIGs are consistent with the predictions of numerical simulations of ram pressure stripping. We found a very low-velocity filament (v_rel = -1300 km/s) at the southeastern edge of the disk of IC4040. Some bright compact knots in the EIGs of RB199 and IC4040 exhibit blue continuum and strong H-alpha emission. The equivalent widths of the H-alpha emission exceed 200 A, and are greater than 1000 A for some knots. The emission line intensity ratios of the knots are basically consistent with those of sub-solar abundance HII regions. These facts indicate that intensive star formation occurs in the knots. Some filaments, including the low velocity filament of the IC4040 EIG, exhibit shock-like emission line spectra, suggesting that shock heating plays an important role in ionization and excitation of the EIGs.