We present results from a pilot HST ACS deep imaging study in broad-band V of five low-redshift QSO host galaxies classified in the literature as ellipticals. The aim of our study is to determine whether these early-type hosts formed at high redshift and have since evolved passively, or whether they have undergone relatively recent mergers that may be related to the triggering of the nuclear activity. We perform two-dimensional modeling of the light distributions to analyze the host galaxies' morphology. We find that, while each host galaxy is reasonably well fitted by a de Vaucouleurs profile, the majority of them (4/5) reveal significant fine structure such as shells and tidal tails. These structures contribute between ~5% and 10% to the total V-band luminosity of each host galaxy within a region of r ~ 3 r_eff and are indicative of merger events that occurred between a few hundred Myr and a Gyr ago. These timescales are comparable to starburst ages in the QSO hosts previously inferred from Keck spectroscopy. Our results thus support a consistent scenario in which most of the QSO host galaxies suffered mergers with accompanying starbursts that likely also triggered the QSO activity in some way, but we are also left with considerable uncertainty on physical mechanisms that might have delayed this triggering for several hundred Myr after the merger.
We report -as a part of a long-term study of mergers and IR QSOs- detailed spectroscopic evidences for outflow (OF) and/or Wolf Rayet features in: (i) low velocity OF in the ongoing mergers NGC 4038/39 and IRAS 23128-5919; (ii) extreme velocity OF (EVOF) in the QSOs IRAS 01003-2238 and IRAS 13218+0552; (iii) OF and EVOF in a complete sample of ultra-luminous IR galaxies/QSOs ("The IRAS 1 Jy MKO-KPNO Survey", of 118 objects). We found EVOF in IRAS 11119+3257, 14394+5332, 15130+1958 and 15462-0450. The OF components detected in these objects were mainly associated to starburst processes: i.e., t…
Ground-based high spatial-resolution optical and near-IR imaging at BIHK' is presented for a complete sample of optically selected Palomar-Green QSOs which have infrared excesses at least as great as those of "warm" AGN-like ultraluminous infrared galaxies. In all cases, the host galaxies of the QSOs were detected and most have considerable two-dimensional structure. One-half of the QSOs occur in spiral hosts while an additional one-quarter show extended merger-induced tidal tails suggestive of mergers between similar-sized disk galaxies. Eleven percent more are in elliptical hosts, and the re…
A study of morphology, kinematics and ionization structure of the IR merger NGC 5514, is presented. This study is based mainly on Integral 2D spectroscopy obtained on 4.2 m William Herschel Telescope (La Palma, Spain) and data from CASLEO (Argentina). Clear evidence of two extra-nuclear starbursts with young outflows and LINER activity are reported. One of these outflow generate a supergiant bubble, where the emission lines and kinematics maps show 4 extended ejections. These results suggest that the bubble is in the rupture phase.
To study the relevance of mergers for the fueling of QSOs, we are currently conducting an HST imaging campaign of a sample of QSO host galaxies classified as ellipticals in the literature. Here, we present results from a study of the first five QSO host galaxies imaged with HST/ACS. For the majority of objects, strong signs of interactions such as tidal tails, shells, and other fine structure are revealed. We estimate the nature and age of the merger by comparing the images with numerical simulations. The merger ages range between a few hundred Myr up to a Gyr. These timescales are comparable …
A study of outflow (OF) and BAL systems in Mrk 231 (and in similar IR QSOs) is presented. This study is based mainly on 1D and 2D spectroscopy (obtained at La Palma/WHT, HST, IUE, ESO/NTT, KPNO, APO and CASLEO observatories) plus HST images. For Mrk 231 we report evidence that the extreme nuclear OF process has at least 3 main components, which are probably associated with: (i) the radio jet, at pc scale, and (ii(the extreme starburst at pc and kpc scale. This OF has generate 4 or more concentric expanding bubbles and the BAL systems. The variability of the short lived BAL-III system was studi…
We test the hypothesis that QSOs are formed via strong tidal interactions or mergers, initially going through an ultraluminous infrared phase, by looking for traces to this phase in the host galaxies of QSOs. We present a systematic spectroscopic and imaging study of a sample of QSOs that may be in a transitionary stage. By modeling the spectra, we obtain ages for the recent starburst events in the host galaxies and interacting companions. We have discussed in detail the first 5 objects in the sample in previous publications; here we present results for the remaining 4 objects, and discuss the…
A growing body of observational evidence suggests that the luminosity, photometric shape and amount of rotational or anisotropical support in elliptical galaxies may provide vital clues to how they formed. Elliptical galaxies appear to fall into two distinct categories based on these parameters: bright, boxy shaped, with little or no rotation, and less luminous, disky shaped with significant rotation. One viable formation scenario is the ``Merger hypothesis,'' in which two disk galaxies merge to form a new elliptical galaxy. A comparison of the luminosity, photometric shape, and amount of rota…
This work presents high $S/N$ spectroscopic observations of a sample of six suspected merger remnants, selected primarily on the basis of H{\sc i} tidal debris detections. Single stellar population analysis of these galaxies indicates that their ages, metallicities, and $α$-enhancement ratios are consistent with those of a representative sample of nearby elliptical galaxies. The expected stellar population of a recent merger remnant, young age combined with low [$α$/Fe], is not seen in any H{\sc i}-selected galaxy. However, one galaxy (NGC~2534), is found to deviate from the $Z$-plane in the s…
We use numerical simulations to study the kinematic structure of remnants formed from mergers of equal-mass disk galaxies. In particular, we show that remnants of dissipational mergers, which include the radiative cooling of gas, star formation, feedback from supernovae, and the growth of supermassive black holes, are smaller, rounder, have, on average, a larger central velocity dispersion, and show significant rotation compared to remnants of dissipationless mergers. The increased rotation speed of dissipational remnants owes its origin to star formation that occurs in the central regions dur…
We investigate the long-term evolution and observability of remnants originating from the merger of compact binary systems and discuss the differences to supernova remnants. Compact binary mergers expel much smaller amounts of mass at much higher velocities, as compared to supernovae, which will affect the dynamical evolution of their remnants. The ejecta of mergers consist of very neutron rich nuclei. Some of these neutron rich nuclei will produce observational signatures in form of gamma ray lines during their decay. The composition of the ejecta might even give interesting constraints about…
Merger remnants of small groups of galaxies are contrasted with relics of mergers of pairs of galaxies to determine which process produces objects that best compare to real ellipticals. In both cases, the progenitors consist of self-gravitating disks, halos, and, sometimes, bulges. Pairs of galaxies merge from orbits that initially have zero--energy. The systems that produce multiple merger remnants are dense, six--member groups in virial equilibrium with low velocity dispersions. Multiple and pair mergers produce remnants which differ in both their spatial and kinematic properties. Multiple m…
We use numerical models which include star formation to analyze the mass profiles of remnants formed by mergers of disk galaxies. During a merger, dissipation in gas and ensuing star formation leave behind a dense stellar core in the remnant. Rather than joining smoothly onto a de Vaucouleurs profile, the starburst population leads to a sharp break in the surface density profile at a few percent the effective radius. While our results are preliminary, the lack of such signatures in most elliptical galaxies suggests that mergers of gas-rich disk galaxies may not have contributed greatly to the …
We use Gauss-Hermite functions to study the line of sight velocity distributions in simulated merger remnants. Our sample contains sixteen remnants; eight produced by mergers between disk galaxies of equal mass and eight produced by mergers between disk galaxies with mass ratios of 3:1. The equal-mass mergers display a wide range of kinematic features, including counterrotation at large radii, orthogonally rotating cores, and misaligned rotational axes. Most of the unequal-mass remnants exhibit fairly regular disk-like kinematics, although two have kinematics more typical of the equal-mass rem…
We present preliminary results of an HST/NICMOS program to image merger remnants in the J, H and K bands. The nuclear brightness profiles for most sample galaxies are similar to those typical for elliptical galaxies, but some (including the well-studied NGC 3921 and 7252) have an unusually high luminosity density at small radii. This is consistent with the prediction of N-body simulations that gas flows to the center during a merger and forms new stars.
We study galaxy mergers with various mass ratios using N-body simulations, with an emphasis on the unequal-mass mergers in the relatively unexplored range of mass-ratios 4:1-10:1. Our recent work (Bournaud et al. 2004) shows that the above range of mass ratio results in hybrid systems with spiral-like luminosity profiles but with elliptical-like kinematics, as observed in the data analysis for a sample of mergers by Jog & Chitre (2002). In this paper, we study the merger-remnants for mass ratios from 1:1 to 10:1 while systematically covering the parameter space. We obtain the morphological and…
We present a large set of merger simulations of early-type disc galaxies with mass ratios of 1:1 and 3:1 and 10% of the total disc mass in gas. In contrast to the collisionless case equal-mass mergers with gas do not result in very boxy remnants which is caused by the suppression of box orbits and the change of the projected shape of minor-axis tube orbits in the more axisymmetric remnants. The isophotal shape of 3:1 remnants and the global kinematic properties of 1:1 and 3:1 remnants are only weakly affected by the presence of gas. 1:1 remnants are slowly rotating whereas 3:1 remnants are fas…
We perform a large parameter survey of 112 collisionless N-body simulations of binary mergers of disk-galaxies with mass ratios of 1:1, 2:1, 3:1, and 4:1 using the special purpose hardware GRAPE. The basic properties of the remnants correlate with the mass ratio of the progenitor disks. We find that about 80% of the equal-mass merger simulations lead to slowly rotating remnants with significant minor-axis rotation. One half of all projected 1:1 remnants shows boxy and the other half shows disky isophotes. Remnants with mass ratios of 3:1 and 4:1 all rotate fast and show a small amount of minor…
The giant early-type merger remnant galaxy NGC 1316 is an ideal probe for studying the long-term effects of a major merger on its globular cluster (GC) system, given its spectroscopically derived merger age of 3 Gyr which we reported in a recent paper. Here we report several pieces of photometric evidence showing that the second-generation GCs in NGC 1316 are at an evolutionary phase in between that of luminous GCs found in younger merger remnants such as (e.g.) NGC 7252 and that of `red' GCs found in `normal, old' ellipticals. The observation that massive, second-generation GCs formed during …
We present a two-dimensional kinematic analysis for a sample of simulated binary disc merger remnants with mass ratios 1:1 and 3:1. For the progenitor discs we used pure stellar models as well as models with 10% of their mass in gas. A multitude of phenomena also observed in real galaxies are found in the simulations. These include misaligned rotation, embedded discs, gas rings, counter-rotating cores and kinematic misaligned discs. Using the 2D maps we illustrate projection effects and the change in properties of a merger remnant when gas is included in the merger. We find that kinematic pecu…
We construct a physically motivated model for predicting the properties of the remnants of gaseous galaxy mergers, given the properties of the progenitors and the orbit. The model is calibrated using a large suite of SPH merger simulations. It implements generalized energy conservation while accounting for dissipative energy losses and star formation. The dissipative effects are evaluated from the initial gas fractions and from the orbital parameters via an "impulse" parameter, which characterizes the strength of the encounter. Given the progenitor properties, the model predicts the remnant st…
We investigate the long-term evolution and observability of remnants originating from the merger of compact binary systems and discuss the differences to supernova remnants. Compact binary mergers expel much smaller amounts of mass at much higher velocities, as compared to supernovae and therefore the free expansion phase of the remnant will be short (~ 1 - 10 yr). In general the remnants will be observable for a considerable time (~ 10^6 - 10^7 yr). Events releasing large amounts of kinetic energy may be responsible for a subsample of observed giant HI holes of unknown origin as compact binar…
We use two-dimensional kinematic maps of simulated binary disc mergers to investigate the $λ_R$-parameter, which is a luminosity weighted measure of projected angular momentum per unit mass. This parameter was introduced to subdivide the SAURON sample of early type galaxies in so called fast $λ_R > 0.1$ and slow rotators $λ_R < 0.1$. Tests on merger remnants reveal that $λ_R$ is a robust indicator of the true angular momentum content in elliptical galaxies. We find the same range of $λ_R$ values in our merger remnants as in the SAURON galaxies. The merger mass ratio is decisive in creating a s…
We test the formation of low-luminosity elliptical galaxies through collisionless mergers of unequal-mass disk galaxies. The kinematic properties of a small survey of simulated merger end-products with initial disk mass ratios of 3:1 is compared to a sample of seven low-luminosity galaxies observed by Rix et al. that were chosen photometrically to be "ellipticals". In this paper, we go beyond a comparison in terms of global properties (using one number to characterize a model or a galaxy e.g. <a4>, ellipticity at some fixed radius or central velocity dispersion) and examine the detailed kinema…
Recent observations of globular clusters in intermediate-age (2-4 Gyr old) merger remnants have provided the hitherto `missing link' between between young merger remnants and normal elliptical galaxies. The luminosity functions (LFs) of the `blue' globular clusters exhibit a Gaussian shape centered on M_V ~ -7.2 as found for giant ellipticals, while the `red' clusters exhibit LFs that are more extended towards both the bright and faint ends, as expected for a cluster population of intermediate age. Specific frequencies for these systems have been calculated by evolving both the LF of the `red'…
This review focus on some issues which seem relevant to recent discussions: (1) how halo structure influences tail length, (2) the fate of power-law density cusps, (3) the results of unequal-mass disk galaxy mergers, and (4) the behavior of hot and cold gas in merging disk galaxies.
Recent observations of globular clusters (GCs) in intermediate-age (2-4 Gyr old), early-type merger remnants have provided the hitherto `missing link' between young merger remnants and `normal' elliptical galaxies in the form of a GC subsystem with colors and luminosities consistent with population synthesis model predictions for those ages and ~solar metallicity. Here we present new, deep observations of the GC system of the intermediate-age merger remnant NGC 1316, using the ACS camera aboard Hubble Space Telescope, which allowed us to create luminosity functions (LFs) as a function of galac…
We present a detailed surface density analysis of a large sample of simulated collisionless mergers of disc galaxies with bulges (mass ratios 1:1, 2:1, 3:1, 4:1, and 6:1) and without bulges (mass ratios 1:1 and 3:1). They were classified, according to their bulge--to--total ($B/T$) ratio, either as a one-component system or as a two-component systems. In general projection effects change the classification of a remnant. Only merger remnants of discs with bulges show properties similar to observed early--type galaxies. Their B/T ratios are in the range $0.2<B/T<1$. Surprisingly, the initial mas…
We study the observational constraints on the growth of massive black holes (BHs) in galactic nuclei. We use the velocity dispersions of early-type galaxies obtained by the SDSS and the relation between BH mass and velocity dispersion to estimate the local BH mass density to be 2.5x10^5 Msun/Mpc^3. We also use the QSO luminosity function from the 2dF Redshift Survey to estimate the BH mass density accreted during optically bright QSO phases. The local BH mass density is consistent with the density accreted during optically bright QSO phases if QSOs have an efficiency 0.1. By studying the conti…
We report the results from a deep HST NICMOS H-band imaging survey of a carefully selected sample of 33 luminous, late-stage galactic mergers at z < 0.3. Signs of a recent galactic interaction are seen in all of the objects in the HST sample, including all 7 IR-excess Palomar-Green (PG) QSOs in the sample. Unsuspected double nuclei are detected in 5 ULIRGs. A detailed two-dimensional analysis of the surface brightness distributions in these objects indicates that the great majority (81%) of the single-nucleus systems show a prominent early-type morphology. However, low-surface-brightness expon…
We study the properties of infrared-selected QSOs (IR QSOs), optically-selected QSOs (PG QSOs) and Narrow Line Seyfert 1 galaxies (NLS1s). We compare their properties from the infrared to the optical and examine various correlations among the black hole mass, accretion rate, star formation rate and optical and infrared luminosities. We find that the infrared excess in IR QSOs is mostly in the far infrared, and their infrared spectral indices suggest that the excess emission is from low temperature dust heated by starbursts rather than AGNs. The infrared excess is therefore a useful criterion t…
We perform collisionless N-body simulations of 1:1 galaxy mergers, using models which include a galaxy halo, disc and bulge, focusing on the behaviour of the halo component. The galaxy models are constructed without recourse to a Maxwellian approximation. We investigate the effect of varying the galaxies' orientation, their mutual orbit, and the initial velocity anisotropy or cusp strength of the haloes upon the remnant halo density profiles and shape, as well as on the kinematics. We observe that the halo density profile (determined as a spherical average, an approximation we find appropriate…
Low-ionization broad absorption line (BAL) QSOs present properties that cannot generally be explained by simple orientation effects. We have conducted a deep spectroscopic and imaging study of the host galaxies of the only four BAL QSOs that are currently known at z < 0.4, and found that all four objects reside in dusty, starburst or post-starburst, merging systems. The starburst ages derived from modeling the stellar populations are in every case a few hundred million years or younger. There is strong evidence that the ongoing mergers triggered both the starbursts and the nuclear activity, th…
We present a detailed investigation of the relation between the orbital content of merger remnants and observable properties of elliptical and S0 galaxies. Our analysis is based on the statistical sample of collisionless mergers of disk galaxies with different mass ratios and orbital parameters, published by Naab & Burkert. We use the spectral method by Carpintero & Aguilar to determine the orbital content of every remnant and correlate it with its intrinsic shape, and its projected kinematic and photometric properties. We discuss the influence of the bulge component and varying pericenter dis…
Millimeter-wave (CO) observations of optically-selected QSOs are potentially a powerful tool for studying the properties of both the QSOs and their host galaxies. We summarize here a recent molecular gas survey of z<0.17 optical QSOs with infrared (IR) excess, L_IR (8-1000 um) / L_bbb (0.1-1.0 um) > 0.36. Eight of these QSOs have been detected to date in CO(1-0), and the derived molecular gas masses are in the range 1.7-35x10^9 M_sun. The high L_IR / L'_CO of QSOs relative to the bulk of the local (z<0.2) IR luminous galaxy merger population is indicative of significant heating of dust (L_IR) …
Elliptical galaxies formed in a major merger tend to become more nearly spherical with time, thanks to the gravitational effect of their central black hole (or black holes). Observational results indicate that elliptical galaxies with older stellar populations (t > 7.5 Gyr) have rounder central isophotes than ellipticals with younger stellar populations. In addition, older ellipticals tend to have core profiles, while younger ellipticals tend to have power-law profiles. Numerical simulations of galaxy mergers indicate that if one or both of the progenitors have a central black hole with a mass…
Many of the conditions that are necessary for starbursts appear to be important in the triggering of QSOs. However, it is still debatable whether starbursts are ubiquitously present in galaxies harboring QSOs. In this paper we review our current knowledge from observations of the role of starbursts in different types of QSOs. Post-starburst stellar populations are potentially present in the majority of QSO hosts. QSOs with far-infrared colors similar to those of ultraluminous infrared galaxies invariably reside in merging galaxies that have interaction-induced starbursts of a few hundred Myr o…
It is generally believed that major galaxy mergers with mass ratios in the range 1:1-3:1 result in remnants that have properties similar to elliptical galaxies, and minor mergers below 10:1 result in disturbed spiral galaxies. The intermediate range of mass ratios 4:1-10:1 has not been studied so far. Using N-body simulations, we show that such mergers can result in very peculiar systems, that have the morphology of a disk galaxy with an exponential profile, but whose kinematics is closer to that of elliptical systems. These objects are similar to those recently observed by Jog & Chitre (2002)…
Using published luminosity and molecular gas profiles of the late-stage mergers NGC 3921, NGC 7252 and Arp 220, we examine the expected luminosity profiles of the evolved merger remnants, especially in light of the massive CO complexes that are observed in their nuclei. For NGC 3921 and NGC 7252 we predict that the resulting luminosity profiles will be characterized by an r^{1/4} law. In view of previous optical work on these systems, it seems likely that they will evolve into normal ellipticals as regards their optical properties. Due to a much higher central molecular column density, Arp 220…
Using high-resolution N-body simulations, we examine whether a major dry merger mitigates the difference in the radial density distributions between red and blue globular clusters (GCs). To this end, we study the relation between the density slope of the GCs in merger progenitors and that in a merger remnant, when the density distribution is described by $n_{\rm GC}\propto r^{-α}$. We also study how our results depend on the merger orbit and the size of the core radius of the initial GC density distribution. We find that a major dry merger makes the GC profile flatter, and the steeper initial …
Observations with the PC2 CCD of the Hubble Space Telescope are described of two bright QSOs of redshift ~0.3. 1403+434 is IR-bright and radio-quiet, and 2201+315 is radio-loud with extended structure. Exposures were taken with the F702W and F555W filters. The images are deconvolved on their own and combined with 0.5 arcsec ground-based images. Both host galaxies have the form and luminosity of bright ellipticals, with nuclei of 1-2 times higher luminosity. 1403+434 is strongly interacting while 2201+315 may be in later stages of a merger, both with a smaller companion. Both host galaxies have…
We present results from our VLT Large Program to study the dynamical evolution of Ultraluminous Infrared Galaxies (ULIRGs). We have so far obtained near-infrared high-resolution ISAAC spectra of 53 local ULIRGs at several merger timescales and 12 Palomar-Green QSOs (more than half of which are IR-bright sources). We have extracted the stellar velocity dispersion and rotational velocity along our slits to derive the kinematics of the merging galaxies. These quantities enable us to answer the following questions about the evolution of ULIRGs: 1) What are the progenitor mass ratios?, 2) How do th…
We apply the observed optical/X-ray spectral states of the Galactic black hole candidates (GBHCs) to the cosmological QSO luminosity evolution under the assumptions that QSOs and GBHCs are powered by similar accretion processes and that their emission mechanisms are also similar. The QSO luminosity function (LF) evolution in various energy bands is strongly affected by the spectral evolution which is tightly correlated with the luminosity evolution. We generate a random sample of QSOs born nearly synchronously by allowing the QSOs to have redshifts in a narrow range around an initial high reds…
NGC 6240 is a rare object in the local universe: an active merger remnant viewed at the point of merging where two active galactic nuclei are visible. We present IRAC data of this object, providing high sensitivity maps of the stellar and PAH distribution in this complicated system. We use photometry to analyze the variation in these distributions with radius and provide an SED in the four IRAC bands: 3.6 microns, 4.5 microns, 5.8 microns and 8.0 microns. We fit the radial profiles of the 3.6 micron band to r^.25 and exponential profiles to evaluate the structure of the remnant. Finally, we co…
We systematically explore the evolution of the merger of two carbon-oxygen (CO) white dwarfs. The dynamical evolution of a 0.9 Msun + 0.6 Msun CO white dwarf merger is followed by a three-dimensional SPH simulation. We use an elaborate prescription in which artificial viscosity is essentially absent, unless a shock is detected, and a much larger number of SPH particles than earlier calculations. Based on this simulation, we suggest that the central region of the merger remnant can, once it has reached quasi-static equilibrium, be approximated as a differentially rotating CO star, which consist…
We study the origin and properties of 'extra' or 'excess' central light in the surface brightness profiles of gas-rich merger remnants. Combining a large set of hydrodynamical simulations with data on observed mergers (spanning a broad range of profiles at various masses and degrees of relaxation), we show how to robustly separate the physically meaningful extra light -- stellar populations formed in a compact central starburst during a gas-rich merger -- from the outer profile established by violent relaxation acting on stars already present in the progenitors prior to the final merger. This …
This paper is the second in a series exploring the properties of 51 {\it optically} selected, single-nuclei merger remnants. Spectroscopic data have been obtained for a sub-sample of 38 mergers and combined with previously obtained infrared photometry to test whether mergers exhibit the same correlations as elliptical galaxies among parameters such as stellar luminosity and distribution, central stellar velocity dispersion ($σ$$_{\circ}$), and metallicity. Paramount to the study is to test whether mergers lie on the Fundamental Plane. Measurements of $σ$$_{\circ}$ have been made using the Ca t…
We model mock observations of collisionless N-body disc-disc mergers with an axisymmetric orbit superposition program that has been used to model Coma ellipticals. The remnants sample representatively the shapes of disc-disc mergers including prolate, triaxial and oblate objects. The aim is to better understand how the assumption of axial symmetry affects reconstructed masses and stellar motions of systems which are intrinsically not axisymmetric, whether it leads to a bias and how such a potential bias can be recognised in models of real galaxies. The mass recovery at the half-light radius de…
We present scaling relations between the virial velocity (V) and the one-dimensional central velocity dispersion (Sig0); the gravitational radius (Rv) and the effective radius (Re); and the total mass (M) and the luminous mass (ML) found in N-body simulations of binary mergers of spiral galaxies. These scalings are of the form V^2 ~ Sig0^alpha, Rv ~ Re^beta and M ~ ML^gamma. The particlar values obtained for (alpha,beta,gamma) depend on the method of fitting used [ordinary least-squares (ols) or orthogonal distance regression (odr)], the assumed profile [de Vaucouleurs (deV) or Sersic (S)], an…
