The Sloan Lens ACS Survey. IX. Colors, Lensing and Stellar Masses of Early-type Galaxies

We present the current photometric dataset for the Sloan Lens ACS (SLACS) Survey, including HST photometry from ACS, WFPC2, and NICMOS. These data have enabled the confirmation of an additional 15 grade `A' (certain) lens systems, bringing the number of SLACS grade `A' lenses to 85; including 13 grade `B' (likely) systems, SLACS has identified nearly 100 lenses and lens candidates. Approximately 80% of the grade `A' systems have elliptical morphologies while ~10% show spiral structure; the remaining lenses have lenticular morphologies. Spectroscopic redshifts for the lens and source are available for every system, making SLACS the largest homogeneous dataset of galaxy-scale lenses to date. We have developed a novel Bayesian stellar population analysis code to determine robust stellar masses with accurate error estimates. We apply this code to deep, high-resolution HST imaging and determine stellar masses with typical statistical errors of 0.1 dex; we find that these stellar masses are unbiased compared to estimates obtained using SDSS photometry, provided that informative priors are used. The stellar masses range from 10^10.5 to 10^11.8 M$_\odot$ and the typical stellar mass fraction within the Einstein radius is 0.4, assuming a Chabrier IMF. The ensemble properties of the SLACS lens galaxies, e.g. stellar masses and projected ellipticities, appear to be indistinguishable from other SDSS galaxies with similar stellar velocity dispersions. This further supports that SLACS lenses are representative of the overall population of massive early-type galaxies with M* >~ 10^11 M$_\odot$, and are therefore an ideal dataset to investigate the kpc-scale distribution of luminous and dark matter in galaxies out to z ~ 0.5.Comment: 20 pages, 18 figures, 5 tables, published in Ap

Comparing and calibrating black hole mass estimators for distant active galactic nuclei

Black hole mass is a fundamental property of active galactic nuclei (AGNs). In the distant universe, black hole mass is commonly estimated using the MgII, Hbeta, or Halpha emission line widths and the optical/UV continuum or line luminosities, as proxies for the characteristic velocity and size of the broad-line region. Although they all have a common calibration in the local universe, a number of different recipes are currently used in the literature. It is important to verify the relative accuracy and consistency of the recipes, as systematic changes could mimic evolutionary trends when comparing various samples. At z=0.36, all three lines can be observed at optical wavelengths, providing a unique opportunity to compare different empirical recipes. We use spectra from the Keck Telescope and the Sloan Digital Sky Survey to compare black hole mass estimators for a sample of nineteen AGNs at this redshift. We compare popular recipes available from the literature, finding that mass estimates can differ up to 0.38+-0.05 dex in the mean (or 0.13+-0.05 dex, if the same virial coefficient is adopted). Finally, we provide a set of 30 internally self consistent recipes for determining black hole mass from a variety of observables. The intrinsic scatter between cross-calibrated recipes is in the range 0.1-0.3 dex. This should be considered as a lower limit to the uncertainty of the black hole mass estimators.Comment: ApJ in press, 11 pages, 10 figure

The Mass Assembly History of Spheroidal Galaxies: Did Newly-Formed Systems Arise Via Major Mergers?

We examine the properties of a morphologically-selected sample of 0.4<z<1.0 spheroidal galaxies in the GOODS fields in order to ascertain whether their increase in abundance with time arises primarily from mergers. To address this question we determine scaling relations between the dynamical mass determined from stellar velocity dispersions, and the stellar mass determined from optical and infrared photometry. We exploit these relations across the larger sample for which we have stellar masses in order to construct the first statistically robust estimate of the evolving dynamical mass function over 0<z<1. The trends observed match those seen in the stellar mass functions of Bundy et al. 2005 regarding the top-down growth in the abundance of spheroidal galaxies. By referencing our dynamical masses to the halo virial mass we compare the growth rate in the abundance of spheroidals to that predicted by the assembly of dark matter halos. Our comparisons demonstrate that major mergers do not fully account for the appearance of new spheroidals since z~1 and that additional mechanisms, such as morphological transformations, are required to drive the observed evolution.Comment: Accepted to ApJL; New version corrects the Millennium merger predictions--further details at http://www.astro.utoronto.ca/~bundy/millennium

Inference of the Cold Dark Matter substructure mass function at z=0.2 using strong gravitational lenses

We present the results of a search for galaxy substructures in a sample of 11 gravitational lens galaxies from the Sloan Lens ACS Survey. We find no significant detection of mass clumps, except for a luminous satellite in the system SDSS J0956+5110. We use these non-detections, in combination with a previous detection in the system SDSS J0946+1006, to derive constraints on the substructure mass function in massive early-type host galaxies with an average redshift z ~ 0.2 and an average velocity dispersion of 270 km/s. We perform a Bayesian inference on the substructure mass function, within a median region of about 32 kpc squared around the Einstein radius (~4.2 kpc). We infer a mean projected substructure mass fraction $f = 0.0076^{+0.0208}_{-0.0052}$ at the 68 percent confidence level and a substructure mass function slope $\alpha$ < 2.93 at the 95 percent confidence level for a uniform prior probability density on alpha. For a Gaussian prior based on Cold Dark Matter (CDM) simulations, we infer $f = 0 .0064^{+0.0080}_{-0.0042}$ and a slope of $\alpha$ = 1.90$^{+0.098}_{-0.098}$ at the 68 percent confidence level. Since only one substructure was detected in the full sample, we have little information on the mass function slope, which is therefore poorly constrained (i.e. the Bayes factor shows no positive preference for any of the two models).The inferred fraction is consistent with the expectations from CDM simulations and with inference from flux ratio anomalies at the 68 percent confidence level.Comment: Accepted for publication on MNRAS, some typos corrected and some important references adde

The Lenses Structure & Dynamics Survey: The internal structure and evolution of E/S0 galaxies and the determination of H_0 from time-delay systems

The Lenses Structure & Dynamics (LSD) Survey aims at studying the internal structure of luminous and dark matter - as well as their evolution - of field early-type (E/SO) galaxies to z~1. In particular, E/S0 lens galaxies are studied by combining gravitational lensing, photometric and kinematic data obtained with ground-based (VLA/Keck/VLT) and space-based telescopes (HST). Here, we report on preliminary results from the LSD Survey, in particular on (i) the constraints set on the luminous and dark-matter distributions in the inner several R_eff of E/S0 galaxies, (ii) the evolution of their stellar component and (iii) the constraints set on the value of H_0 from time-delay systems by combining lensing and kinematic data to break degeneracies in gravitational-lens models.Comment: 4 pages; Proceeding for the "Multi-Wavelength Cosmology" conference, Mykonos, Greece, June 17-20, 200

Lenses Structure & Dynamics Survey: The internal structure and evolution of E/S0 galaxies and the determination of H₀ from time-delay systems

The Lenses Structure & Dynamics (LSD) Survey aims at studying the internal structure of luminous and dark matter - as well as their evolution - of field earlytype (E/SO) galaxies to z ∼ 1. In particular, E/S0 lens galaxies are studied by combining gravitational lensing, photometric and kinematic data obtained with ground-based (VLA/Keck/VLT) and space-based telescopes (HST). Here, we report on preliminary results from the LSD Survey, in particular on (i) the constraints set on the luminous and dark-matter distributions in the inner several R_(eff) of E/S0 galaxies, (ii) the evolution of their stellar component and (iii) the constraints set on the value of H0 from time-delay systems by combining lensing and kinematic data to break degeneracies in gravitational-lens models

The Sloan Lens ACS Survey. X. Stellar, Dynamical, and Total Mass Correlations of Massive Early-type Galaxies

We use stellar masses, photometry, lensing, and velocity dispersions to investigate empirical correlations for the final sample of 73 early-type lens galaxies (ETGs) from the SLACS survey. The traditional correlations (Fundamental Plane [FP] and its projections) are consistent with those found for non-lens galaxies, supporting the thesis that SLACS lens galaxies are representative of massive ETGs. The addition of strong lensing estimates of the total mass allows us to gain further insights into their internal structure: i) the mean slope of the total mass density profile is = 2.078+/-0.027 with an intrinsic scatter of 0.16+/-0.02; ii) gamma' correlates with effective radius and central mass density, in the sense that denser galaxies have steeper profiles; iii) the dark matter fraction within reff/2 is a monotonically increasing function of galaxy mass and size; iv) the dimensional mass M_dim is proportional to the total mass, and both increase more rapidly than stellar mass M*; v) the Mass Plane (MP), obtained by replacing surface brightness with surface mass density in the FP, is found to be tighter and closer to the virial relation than the FP and the M*P, indicating that the scatter of those relations is dominated by stellar population effects; vi) we construct the Fundamental Hyper-Plane by adding stellar masses to the MP and find the M* coefficient to be consistent with zero and no residual intrinsic scatter. Our results demonstrate that the dynamical structure of ETGs is not scale invariant and that it is fully specified by the total mass, r_eff, and sigma. Although the basic trends can be explained qualitatively in terms of varying star formation efficiency as a function of halo mass and as the result of dry and wet mergers, reproducing quantitatively the observed correlations and their tightness may be a significant challenge for galaxy formation models.Comment: 16 pages, 9 figures; submitted to ApJ after responding to the referee comment

Constraints on the equation of state of dark energy and the Hubble constant from stellar ages and the CMB

We place tight constraints on the redshift-averaged, effective value of the equation of state of dark energy, w, using only the absolute ages of Galactic stars and the observed position of the first peak in the angular power spectrum of the CMB. We find w<-0.8 at the 68% confidence level. If we further consider that w > -1, this finding suggests that within our uncertainties, dark energy is indistinguishable from a classical vacuum energy term. We detect a correlation between the ages of the oldest galaxies and their redshift. This opens up the possibility of measuring w(z) by computing the relative ages of the oldest galaxies in the universe as a function of redshift, dz/dt. We show that this is a realistic possibility by computing dz/dt at z~0 from SDSS galaxies and obtain an independent estimate for the Hubble constant, H_0 = 69 \pm 12 km s-1 Mpc-1. The small number of galaxies considered at z>0.2 does not yield, currently, a precise determination of w(z), but shows that the age--redshift relation is consistent with a Standard LCDM universe with $w=-1$.Comment: Submitted to Ap

Genome sequence of Rhizobium sullae HCNT1 isolated from Hedysarum coronarium nodules and featuring peculiar denitrification phenotypes

The genome sequence of Rhizobium sullae strain HCNT1, isolated from root nodules of the legume Hedysarum coronarium growing in wild stands in Tuscany, Italy, is described here. Unlike other R. sullae strains, this isolate features a truncated denitrification pathway lacking NO/N2O reductase activity and displaying high sensitivity to nitrite under anaerobic conditions