Showing papers by "Ralf Bender published in 2005"

The Epochs of Early-Type Galaxy Formation as a Function of Environment

Abstract: The aim of this paper is to set constraints on the epochs of early-type galaxy formation through the archaeology of the stellar populations in local galaxies. Using our models of absorption-line indices that account for variable abundance ratios, we derive ages, total metallicities, and element ratios of 124 early-type galaxies in high- and low-density environments. The data are analyzed by comparison with mock galaxy samples created through Monte Carlo simulations taking the typical average observational errors into account, in order to eliminate artifacts caused by correlated errors. We find that all three parameters, age, metallicity, and ?/Fe ratio, are correlated with velocity dispersion. We show that these results are robust against recent revisions of the local abundance pattern at high metallicities. To recover the observed scatter we need to assume an intrinsic scatter of about 20% in age, 0.08?dex in [Z/H], and 0.05?dex in [?/Fe]. All low-mass objects with M* 1010 M? (? 130 km s-1) show evidence for the presence of intermediate-age stellar populations with low ?/Fe ratios. About 20% of the intermediate-mass objects with 1010 M*/M? 1011 [110 ?/(km s-1) 230; both elliptical and lenticular galaxies] must have either a young subpopulation or a blue horizontal branch. On the basis of the above relationships, valid for the bulk of the sample, we show that the Mg-? relation is mainly driven by metallicity, with similar contributions from the ?/Fe ratio (23%) and age (17%). We further find evidence for an influence of the environment on the stellar population properties. Massive early-type galaxies in low-density environments seem on average ~2?Gyr younger and slightly (~0.05-0.1?dex) more metal-rich than their counterparts in high-density environments. No offsets in the ?/Fe ratios are instead detected. With the aid of a simple chemical evolution model, we translate the derived ages and ?/Fe ratios into star formation histories. We show that most star formation activity in early-type galaxies is expected to have happened between redshifts ~3 and 5 in high-density environments and between redshifts 1 and 2 in low-density environments. We conclude that at least 50% of the total stellar mass density must have already formed at z ~ 1, in good agreement with observational estimates of the total stellar mass density as a function of redshift. Our results suggest that significant mass growth in the early-type galaxy population below z ~ 1 must be restricted to less massive objects, and a significant increase of the stellar mass density between redshifts 1 and 2 should be present, caused mainly by the field galaxy population. The results of this paper further imply the presence of vigorous star formation episodes in massive objects at z ~ 2-5 and evolved elliptical galaxies around z ~ 1, both observationally identified as SCUBA galaxies and extremely red objects, respectively.

The centers of early-type galaxies with hubble space telescope. v. new wfpc2 photometry

Abstract: We present observations of 77 early-type galaxies imaged with the PC1 CCD of the Hubble Space Telescope (HST) WFPC2. Nuker-law parametric fits to the surface brightness profiles are used to classify the central structure into core or power-law forms. Core galaxies are typically rounder than power-law galaxies. Nearly all power-law galaxies with central ellipticities ? 0.3 have stellar disks, implying that disks are present in power-law galaxies with < 0.3 but are not visible because of unfavorable geometry. A few low-luminosity flattened core galaxies also have disks; these may be transition forms from power-law galaxies to more luminous core galaxies, which lack disks. Several core galaxies have strong isophote twists interior to their break radii, although power-law galaxies have interior twists of similar physical significance when the photometric perturbations implied by the twists are evaluated. Central color gradients are typically consistent with the envelope gradients; core galaxies have somewhat weaker color gradients than power-law galaxies. Nuclei are found in 29% of the core galaxies and 60% of the power-law galaxies. Nuclei are typically bluer than the surrounding galaxy. While some nuclei are associated with active galactic nuclei (AGNs), just as many are not; conversely, not all galaxies known to have a low-level AGN exhibit detectable nuclei in the broadband filters. NGC 4073 and 4382 are found to have central minima in their intrinsic starlight distributions; NGC 4382 resembles the double nucleus of M31. In general, the peak brightness location is coincident with the photocenter of the core to a typical physical scale of <1 pc. Five galaxies, however, have centers significantly displaced from their surrounding cores; these may be unresolved asymmetric double nuclei. Finally, as noted by previous authors, central dust is visible in about half of the galaxies. The presence and strength of dust correlates with nuclear emission; thus, dust may outline gas that is falling into the central black hole. The prevalence of dust and its morphology suggest that dust clouds form, settle to the center, and disappear repeatedly on ~108 yr timescales. We discuss the hypothesis that cores are created by the decay of a massive black hole binary formed in a merger. Apart from their brightness profiles, there are no strong differences between core galaxies and power-law galaxies that demand this scenario; however, the rounder shapes of core, their lack of disks, and their reduced color gradients may be consistent with it.

The Stellar Mass Function of Galaxies to z ~ 5 in the FORS Deep and GOODS-South Fields

Abstract: We present a measurement of the evolution of the stellar mass function (MF) of galaxies and the evolution of the total stellar mass density at 0 1010 M☉, which are the likely progenitors of today's L > L* galaxies, are found in much smaller numbers above z ~ 2. However, we note that massive galaxies with M > 1011 M☉ are present even to the largest redshift we probe. Beyond z ~ 2, the evolution of the MF becomes more rapid. We find that the total stellar mass density at z = 1 is 50% of the local value. At z = 2, 25% of the local mass density is assembled, and at z = 3 and z = 5, we find that at least 15% and 5% of the mass in stars is in place, respectively. The number density of galaxies with M > 1011 M☉ evolves very similarly to the evolution at lower masses. It decreases by 0.4 dex to z ~ 1, by 0.6 dex to z ~ 2, and by 1 dex to z ~ 4.

VLT spectroscopy of globular cluster systems - II. Spectroscopic ages, metallicities and [α/Fe] ratios of globular clusters in early-type galaxies

Abstract: An analysis of ages, metallicities, and [α/Fe] ratios of globular cluster systems in early-type galaxies is presented, based on Lick index measurements summarized in Puzia et al. (2004, A&A, 415, 123, Paper I of this series). In the light of calibration and measurement uncertainties, age-metallicity degeneracy, and the relative dynamic range of Lick indices, as well as systematics introduced by abundance ratio variations (in particular variations of [α/Fe] ratios), we find that the most reliable age indicator for our dataset is a combination of the Lick Balmer-line indices HγA, Hβ, and HδA. [MgFe] is used as a spectroscopic metallicity indicator which is least affected by [α/Fe] variations. We introduce an interpolation routine to simultaneously derive ages, metallicities, and [α/Fe] ratios from diagnostic grids constructed from Lick indices. From a comparison of high-quality data with SSP model predictions, we find that ∼2/3 of the globular clusters in earlytype galaxies are older than 10 Gyr, up to 1/3 have ages in the range ∼5−10 Gyr, and only a few cluster are younger than ∼5 Gyr. Our sample of globular clusters covers metallicities from [Z/H] ≈ −1.3 up to ∼0.5 dex. We find that metal-rich globular clusters show on average a smaller mean age and a larger age scatter than their metal-poor counterparts. [α/Fe] diagnostic plots show that globular cluster systems in early-type galaxies have super-solar α/Fe abundance ratios with a mean [α/Fe] = 0.47 ± 0.06 dex and a dispersion of ∼0.3 dex. We find evidence for a correlation between [α/Fe] and metallicity, in the sense that more metal-rich clusters exhibit lower α-element enhancements. A discussion of systematics related to the Lick index system shows that the method suffers to some extent from uncertainties due to unknown horizontal branch morphologies at high metallicities. However, these systematics still allow us to make good qualitative statements. A detailed investigation of indices as a function of data quality reveals that the scatter in Balmer index values decreases for higher-quality data. In particular, extremely low Balmer index values that are lower than any SSP model prediction tend to disappear. Furthermore, we find that observed photometric colors are in good agreement with computed SSP colors using ages and metallicities as derived from the spectroscopic line indices.

VLT Spectroscopy of Globular Cluster Systems, II. Spectroscopic Ages, Metallicities, and [alpha/Fe] Ratios of Globular Clusters in Early-Type Galaxies

Abstract: An analysis of ages, metallicities, and [alpha/Fe] ratios of globular cluster systems in early-type galaxies is presented, based on Lick index measurements summarized in Puzia et al. (2004, Paper I of this series). In the light of calibration and measurement uncertainties, age-metallicity degeneracy, and the relative dynamic range of Lick indices, as well as systematics introduced by abundance ratio variations (in particular variations of [alpha/Fe] ratios), we find that the most reliable age indicator for our dataset is a combination of the Lick Balmer-line indices HgammaA, Hbeta, and HdeltaA. [MgFe]' is used as a spectroscopic metallicity indicator which is least affected by [alpha/Fe] variations. We introduce an interpolation routine to simultaneously derive ages, metallicities, and [alpha/Fe] ratios from diagnostic grids constructed from Lick indices. From a comparison of high-quality data with SSP model predictions, we find that ~2/3 of the globular clusters in early-type galaxies are older than 10 Gyr, up to 1/3 have ages in the range ~5-10 Gyr, and only a few cluster are younger than ~5 Gyr. Our sample of globular clusters covers metallicities from [Z/H] = -1.3 up to ~0.5 dex. We find that metal-rich globular clusters show on average a smaller mean age and a larger age scatter than their metal-poor counterparts. [alpha/Fe] diagnostic plots show that globular cluster systems in early-type galaxies have super-solar alpha/Fe abundance ratios with a mean [alpha/Fe] = 0.47+/-0.06 dex and a dispersion of about 0.3 dex. We find evidence for a correlation between [alpha/Fe] and metallicity, in the sense that more metal-rich clusters exhibit lower alpha-element enhancements. [abridged]

EDisCS - the ESO distant cluster survey. Sample definition and optical photometry

Abstract: We present the ESO Distant Cluster Survey (EDisCS), a survey of 20 fields containing distant galaxy clusters with redshifts ranging from 0.4 to almost 1.0. Candidate clusters were chosen from among the brightest objects identified in the Las Campanas Distant Cluster Survey, half with estimated redshift z est ∼ 0.5 and half with z est ∼ 0.8. They were confirmed by identifying red sequences in moderately deep two colour data from VLT/FORS2. For confirmed candidates we have assembled deep three-band optical photometry using VLT/FORS2, deep near-infrared photometry in one or two bands using NTT/SOFI, deep optical spectroscopy using VLT/FORS2, wide field imaging in two or three bands using the ESO Wide Field Imager, and HST/ACS mosaic images for 10 of the most distant clusters. This first paper presents our sample and the VLT photometry we have obtained. We present images, colour-magnitude diagrams and richness estimates for our clusters, as well as giving redshifts and positions for the brightest cluster members. Subsequent papers will present our infrared photometry, spectroscopy, HST and wide-field imaging, as well as a wealth of further analysis and science results. Our reduced data become publicly available as these papers are accepted.

Regularized orbit models unveiling the stellar structure and dark matter halo of the Coma elliptical NGC 4807

Abstract: This is the second in a series of papers dedicated to unveiling the mass structure and orbital content of a sample of flattened early-type galaxies in the Coma cluster. The ability of our orbit libraries to reconstruct internal stellar motions and the mass composition of a typical elliptical in the sample is investigated by means of Monte Carlo simulations of isotropic rotator models. The simulations allow a determination of the optimal amount of regularization needed in the orbit superpositions. It is shown that under realistic observational conditions and with the appropriate regularization, internal velocity moments can be reconstructed to an accuracy of ≈15 per cent; the same accuracy can be achieved for the circular velocity and dark matter fraction. In contrast, the flattening of the halo remains unconstrained. Regularized orbit superpositions are applied to a first galaxy in our sample, NGC 4807, for which stellar kinematical observations extend to 3 r eff. The galaxy seems dark-matter dominated outside r > 2 r eff. Logarithmic dark matter potentials are consistent with the data, as well as NFW profiles, mimicking logarithmic potentials over the observationally sampled radial range. In both cases, the derived stellar mass-to-light ratio ϒ agrees well with independently obtained mass-to-light ratios from stellar population analysis. The achieved accuracy is �ϒ ≈ 0.5. Kinematically, NGC 4807 is characterized by mild radial anisotropy outside r > 0.5 r eff, becoming isotropic towards the centre. Our orbit models hint at either a distinct stellar component or weak triaxiality in the outer parts of the galaxy. Ke yw ords: stellar dynamics ‐ galaxies: elliptical and lenticular, cD ‐ galaxies: kinematics and dynamics ‐ galaxies: structure.

The density of very massive evolved galaxies to z ≃ 1.7

Abstract: We spectroscopically identified seven massive, evolved galaxies with magnitudes 17.8 2 supporting a high efficiency in the accretion of the stellar mass in massive haloes in the early Universe.

VLT Spectroscopy of Globular Cluster Systems, I. The Photometric and Spectroscopic Dataset

Abstract: We present Lick line-index measurements of extragalactic globular clusters in seven early-type galaxies (NGC 1380, 2434, 3115, 3379, 3585, 5846, and 7192) with different morphological types (E-S0) located in field and group/cluster environments. High-quality spectra were taken with the FORS2 instrument at ESO's Very Large Telescope. About 50% of our data allow an age resolution dt/t ~ 0.3 and a metallicity resolution ~0.25-0.4 dex, depending on the absolute metallicity. Globular cluster candidates are selected from deep B, V, R, I, K FORS2/ISAAC photometry with 80-100% success rate inside one effective radius. Using combined optical/near-infrared colour-colour diagrams we present a method to efficiently reduce fore-/background contamination down to <10%. We find clear signs for bi-modality in the globular cluster colour distributions of NGC 1380, 3115, and 3585. The colour distributions of globular clusters in NGC 2434, 3379, 5846, and 7192 are consistent with a broad single-peak distribution. For the analysed globular cluster systems the slopes of projected radial surface density profiles, of the form Sigma(R) ~ R^-Gamma, vary between ~0.8 and 2.6. Using globular clusters as a tracer population we determine total dynamical masses of host galaxies out to large radii (~1.6 - 4.8 Reff). For the sample we find masses in the range ~8.8*10^10 Msolar up to ~1.2*10^12 Msolar. The line index data presented here will be used in accompanying papers of this series to derive ages, metallicities and abundance ratios. A compilation of currently available high-quality Lick index measurements for globular clusters in elliptical, lenticular, and late-type galaxies is provided and will serve to augment the current data set. [abridged]

Dating the stellar population in massive early-type galaxies at z∼ 1.5

Abstract: We present an analysis of 10 massive early-type galaxies at z ∼ 1.5. They have been identified by means of a near-infrared (near-IR) low-resolution spectroscopic follow-up of a complete sample of 36 bright (K' 5) selected from the Munich Near-IR Cluster Survey (MUNICS) of Drory et al. The low-resolution near-IR spectra constrain their redshift at 1.2 2 for all the galaxies and z f ≥ 4 for the oldest ones. The comparison of the 4000-A break and of the overall spectral shape of the average spectrum of the 10 galaxies at z ∼ 1.5 with those of their local counterparts confirms that field massive early-type galaxies formed the bulk of their stellar mass at 2 < z < 4, most likely over a short (<1 Gyr) star formation time-scale, consistently with the results derived from the analysis of their individual spectrophotometric properties.

Looking for obscured QSOs in the X-ray emitting ERO population

Abstract: We present XMM-Newton data centered on one of the MUNICS Near Infrared Cluster Survey fields (S2F1) and we discuss the X-ray properties of the 6 X-ray emitting EROs found. For one of them we have already obtained the redshift using near-infrared spectroscopic data, while for the remaining 5 EROs the analysis is based on photometric redshifts. We find evidence for the presence of an X-ray obscured QSO in at least 5 out of the 6 X-ray emitting EROs. For these 5 objects we derive intrinsic (2–10 keV) luminosities in excess of 1044 erg s−1 and intrinsic column densities higher than 1022 cm−2. These values have been obtained through a basic X-ray spectral analysis for the three brightest sources and through the analysis of the hardness ratios for the remaining two. All of these 5 X-ray emitting EROs appear extended in the optical/near-infrared bands indicating that the host galaxy emission dominates at these wavelengths. This suggests that the hosted AGNs are likely to be absorbed also in the optical/near-infrared bands: i.e. they are likely X-ray obscured possible type 2 QSOs. For the remaining ERO the presence of an AGN is suggested both by its high 0.5–2 keV luminosity (L0.5−2keV ∼ 1043 erg s−1) and by its X-rayto- optical flux ratio. In this case the quality of the present data prevents us from placing firm constraints on the AGN type hosted. Finally, the near-IR spectrum obtained for one of the 6 EROs classifies the host galaxy as an elliptical at z 1.7 with a stellar mass well in excess of 1011 M⊙. This result corroborates the possible link between the QSO activity and the formation of massive spheroids.

Kinematic and chemical evolution of early-type galaxies ,

Abstract: We investigate in detail 13 early-type field galaxies with 0.2 < z < 0.7 drawn from the F Deep Field. Since the majority (9 galaxies) is at z ≈ 0.4, we compare the field galaxies to 22 members of three rich clusters with z = 0.37 to explore possible variations caused by environmental effects. We exploit VLT/FORS spectra (R ≈ 1200) and HST/ACS imaging to deter- mine internal kinematics, structures and stellar population parameters. From the Faber-Jackson and Fundamental Plane scaling relations we deduce a modest luminosity evolution in the B-band of 0.3-0.5 mag for both samples. We compare measured Lick absorption line strengths (Hδ ,H γ ,H β ,M g b, and Fe 5335) with evolutionary stellar population models to derive light-averaged ages, metallicities and the element abundance ratios Mg/Fe. We find that these three stellar parameters of the distant galaxies obey a scaling with velocity dispersion (mass) which is consistent with that of local nearby galaxies. In particular, the distri- bution of Mg/Fe ratios of local galaxies is matched by the distant ones, and their derived mean offset in age corresponds to the average lookback time. This indicates that there was little chemical enrichment and no significant star formation within the last ∼5 Gyr. The calculated luminosity evolution of a simple stellar population model for the derived galaxy ages and lookback times is in most cases consistent with the mild brightening measured by the scaling relations.

The Wendelstein Calar Alto Pixellensing Project (WeCAPP): The M31 Variable Star Catalogue

Abstract: In this paper we present the WeCAPP variable star catalogue towards the bulge of M31. The observations of the WeCAPP microlensing survey (optical R and I bands) during three years (2000-2003) result in a database with unprecedented time coverage for an extragalactic variable star study. We detect 23781 variable sources in a 16.1' x 16.6' field centered on the nucleus of M31. The catalogue of variable stars contains the positions, the periods and the variations in the R and I bands. We classify the variables according to their position in the R-band period-amplitude plane. Three groups can be distinguished; while the first two groups can be mainly associated with Cepheid-like variables (population I Cepheids in group I, type II Cepheids and RV Tauri stars in group II), the third one consists of Long Period Variables (LPVs). We detect 37 RV Tauri stars and 11 RV Tauri candidates which is one of the largest collections of this class of stars to date. The classification scheme is supported by Fourier decomposition of the light curves. Our data shows a correlation of the low-order Fourier coefficients Phi_21 with Phi_31 for classical Cepheids, as well for type II Cepheids and RV Tauri stars. Correlating our sample of variable stars with the X-ray based catalogues of Kaaret (2002) and Kong et al. (2002) results in 23 and 31 coincidences, 8 of which are M31 globular clusters. The number density of detected variables is clearly not symmetric, which has to be included in the calculations of the expected microlensing event rate towards M31. This asymmetry is due to the enhanced extinction in the spiral arms superimposed on the bulge of M31 which reduces the number of sources to about 60%, if compared to areas of equivalent bulge brightness (without enhanced extinction being present).

Oxygen and neon abundances of planetary nebulae in the elliptical galaxy NGC 4697

Abstract: This paper presents deep spectra of 14 planetary nebulae (PNs) at a variety of angular distances from the center of the flattened elliptical galaxy NGC 4697, which is located at ~11 Mpc from us. Both near the center and among the most outlying PNs, we have found several examples of very strong [O III] λ5007, about 20 times brighter than Hβ. This, together with strong [Ne III] lines, implies a lower limit for O and Ne abundances near solar at the center and also at more than 2 effective radii from the center of NGC 4697. Thus we have found, for the first time from individual stars, direct evidence of the existence of a metal-rich population in elliptical galaxies, confirming metallicities derived from absorption-line indices and extending the information to angular distances where the stellar surface brightness is too low for absorption-line studies. A comparison with abundances obtained closer to the center of NGC 4697 from integrated absorption-line spectra indicates that the metallicity gradient, which is quite steep within 1 effective radius, becomes much less pronounced beyond 1 effective radius. The only alternative to this interpretation would be the presence of a very metal-poor PN population with [Z/H] below -1, which we cannot rule out, but it would require an extremely bimodal metallicity distribution with almost no intermediate metallicities.

Microlensing toward crowded fields: Theory and applications to M31

Abstract: We present a comprehensive treatment of the pixel-lensing theory and apply it to lensing experiments and their results toward M31. Using distribution functions for the distances, velocities, masses, and luminosities of stars, we derive lensing event rates as a function of the event observables. In contrast to the microlensing regime, in the pixel-lensing regime (crowded or unresolved sources) the observables are the maximum excess flux of the source above a background and the full width at half-maximum (FWHM) time of the event. To calculate lensing event distribution functions depending on these observables for the specific case of M31, we use data from the literature to construct a model of M31, reproducing consistently photometry, kinematics and stellar population. We predict the halo- and self-lensing event rates for bulge and disk stars in M31 and treat events with and without finite source signatures separately. We use the M31 photon noise profile and obtain the event rates as a function of position, field of view, and S/N threshold at maximum magnification. We calculate the expected rates for WeCAPP and for a potential Advanced Camera for Surveys (ACS) lensing campaign. The detection of two events with a peak signal-to-noise ratio larger than 10 and a timescale larger than 1 day in the WeCAPP 2000/2001 data is in good agreement with our theoretical calculations. We investigate the luminosity function of lensed stars for noise characteristics of WeCAPP and ACS. For the pixel-lensing regime, we derive the probability distribution for the lens masses in M31 as a function of the FWHM timescale, flux excess and color, including the errors of these observables.

A counter-rotating core in the dwarf elliptical galaxy VCC 510

Abstract: We present optical long-slit spectra of the Virgo dwarf elliptical galaxy VCC 510 at high spectral and spatial resolution. Heliocentric velocities and velocity dispersions as functions of galaxy radius are derived by deconvolving line-of-sight velocity distributions. A maximum rotation v_rot=8 km/s inside half the effective radius (re~20 arcsec) and a mean, radially flat velocity dispersion sigma=44 km/s are measured. The core extending over the inner 2 arcsec (~140 pc) is found to rotate in the opposite sense with v_rot(core) ~ -1/2 v_rot. VCC 510 (M_B ~ -15.7) is therefore by far the faintest and smallest galaxy with a counter-rotating core known. From the main body rotation and the velocity dispersion profile we deduce that VCC 510 is anisotropic and clearly not entirely supported by rotation. By comparison of Lick absorption-line indices with stellar population models we derive an old luminosity-weighted age (10 Gyr) and sub-solar metallicity ([Z/H]=-0.4) inside the effective radius. There is tentative evidence that the counter-rotating core might be younger and less alpha/Fe enhanced. From the stellar population parameters we obtain a total stellar mass-to-light ratio of ~3.6 (M/L_B)_sun which is significantly lower than a rough dynamical estimate obtained from the kinematics through the virial theorem (~15). This discrepancy hints toward the possible presence of dark matter in the centre of VCC 510. We discuss the origin of the counter-rotating core and exclude fly-by encounters as a viable possibility. Gas accretion or galaxy merging provide more likely explanations. VCC 510 is therefore the direct observational evidence that such processes do occur in cluster satellite galaxies on dwarf galaxy scales.

Surveying the high-redshift universe with KMOS

Abstract: Ray Sharples1 Ralf Bender 2,4 Richard Bennett 3 Keith Burch 3 Paul Carter 3 Mark Casali 6 Paul Clark1 Robert Content1 Richard Davies 4 Roger Davies 5 Marc Dubbeldam1 Gert Finger 6 Reinhard Genzel 4 Reinhold Hafner 2 Achim Hess 2 Markus Kissler-Patig 6 Ken Laidlaw 3 Matt Lehnert 4 Ian Lewis 5 Alan Moorwood 6 Bernard Muschielok 2 Natascha Forster Schreiber 4 Jeff Pirard 6 Suzie Ramsay Howat 3 Phil Rees 3 Josef Richter 2 David Robertson1 Ian Robson 3 Roberto Saglia 2 Matthias Tecza 5 Naranjan Thatte 5 Stephen Todd 3 Michael Wegner 2

Multiwavelength mapping of galaxy formation and evolution : proceedings of the ESO workshop held at Venice, Italy, 13-16 October 2003

Abstract: The Dawn of Galaxies.- Evolution of X-Ray Selected AGN.- Clustering of Submillimetre-Selected Galaxies.- Star-Forming Galaxies in the 'Redshift Desert'.- The Near-Infrared View of Galaxy Evolution.- Galaxy Formation and Evolution since z=1.- Exploring the Reionization Epoch with HST and JWST.- Chemo-Photometric Models of Ring Galaxies.- The Cosmic Evolution of Quasar Hosts.- Stellar Populations in Spiral Galaxies.- The Cosmological Evolution of Quasar Black-Hole Masses.- Radio Observations of the Subaru/XMM-Newton Deep Survey Field.

Stellar population models with variable element abundance ratios

Abstract: We present a comprehensive set of new generation stellar population models of Lick absorption line indices, which for the first time include element abundance ratios different from solar. We computed the 21 Lick indices CN 1 , CN 2 , Ca4227, G4300, Fe4383, Ca4455, Fe4531, C 2 4668, H β , Fe5015, Mg 1 , Mg 2 , Mg b , Fe5270, Fe5335, Fe5406, Fe5709, Fe5782, Na D, TiO 1 , and TiO 2 , in the wavelength range 4000 ≲ λ ≲ 6500 A. Models are provided with: [α/ Fe ] = 0.0, 0.3, 0.5, [α/ Ca ] = -0.1, 0.0, 0.2, 0.5, and [α/ N ] = −0.5, 0.0; ages from 1 to 15 Gyr; total metallicities from 1/200 to 3.5 solar (-2.25 ≤ [ Z / H ] ≤ 0.67).

Submillimeter galaxies as tracers of mass assembly at large M

Abstract: Luminous submillimeter galaxies (SMGs) have been known for some time to produce a substantial fraction of the far-IR/submillimeter background. New observations show that these systems are not only very luminous, but also very massive. Here we present results from (a) a survey of SMGs' molecular line emission, which has confirmed Keck optical redshifts and revealed their high gas and dynamical masses; and (b) a detailed case study of the rest-frame optical emission from one SMG, which has revealed its high metallicity and old stellar population. We infer a high z~2.7 comoving number density of galaxies with baryonic masses greater than 10^11 solar masses; this is not accounted for in current semi-analytic models of galaxy evolution.