Showing papers by "Tommaso Treu published in 2006"

The Sloan Lens ACS Survey. III. The Structure and Formation of Early-Type Galaxies and Their Evolution since z ≈ 1

Abstract: We present a joint gravitational lensing and stellar-dynamical analysis of 15 massive field early-type galaxies selected from the Sloan Lens ACS (SLACS) Survey. The following numerical results are found: (1) A joint likelihood gives an average logarithmic density slope for the total mass density of = 2.01(-0.03)(+0.02) (68% CL; rho(tot) proportional to r(-gamma')) = 4.2 +/- 0.4 kpc (rms of 1.6 kpc) for isotropic models. The inferred intrinsic rms spread in logarithmic density slopes is sigma(gamma') = 0.12. (2) The average position-angle difference between the light distribution and the total mass distribution is found to be = 0 degrees +/- 3 degrees (rms of 10 degrees), setting an upper limit of less than or similar to 0.035 on the average external shear. The total mass has an average ellipticity = 0.78 +/- 0.03 (rms of 0.12), which correlates extremely well with the stellar ellipticity, q(*), resulting in = 0.99 +/- 0.03 (rms of 0.11) for sigma greater than or similar to 225 km s(-1) omitting three S0 lens galaxies. (3) The average projected dark matter mass fraction is inferred to be = 0.25 +/- 0.06 (rms of 0.22) inside , using the stellar mass-to-light ratios derived from the fundamental plane as priors. (4) Combined with results from the Lenses Structure and Dynamics (LSD) Survey at z greater than or similar to 0.3, we find no significant evolution of the total density slope inside one effective radius for galaxies with sigma(ap) >= 200 km s(-1): a linear fit gives alpha(gamma') equivalent to d / dz = 0.23 +/- 0.16 (1 sigma) for the range z = 0.08-1.01. The small scatter and absence of significant evolution in the inner density slopes suggest a collisional scenario in which gas and dark matter strongly couple during galaxy formation, leading to a total mass distribution that rapidly converges to dynamical isothermality.

The Sloan Lens ACS Survey. I. A large spectroscopically selected sample of massive early-type lens galaxies

Abstract: The Sloan Lens ACS (SLACS) Survey is an efficient Hubble Space Telescope (HST) Snapshot imaging survey for new galaxy-scale strong gravitational lenses. The targeted lens candidates are selected spectroscopically from the Sloan Digital Sky Survey (SDSS) database of galaxy spectra for having multiple nebular emission lines at a redshift significantly higher than that of the SDSS target galaxy. The SLACS survey is optimized to detect bright early-type lens galaxies with faint lensed sources in order to increase the sample of known gravitational lenses suitable for detailed lensing, photometric, and dynamical modeling. In this paper, the first in a series on the current results of our HST Cycle 13 imaging survey, we present a catalog of 19 newly discovered gravitational lenses, along with nine other observed candidate systems that are either possible lenses, nonlenses, or nondetections. The survey efficiency is thus >=68%. We also present Gemini 8 m and Magellan 6.5 m integral-field spectroscopic data for nine of the SLACS targets, which further support the lensing interpretation. A new method for the effective subtraction of foreground galaxy images to reveal faint background features is presented. We show that the SLACS lens galaxies have colors and ellipticities typical of the spectroscopic parent sample from which they are drawn (SDSS luminous red galaxies and quiescent MAIN sample galaxies), but are somewhat brighter and more centrally concentrated. Several explanations for the latter bias are suggested. The SLACS survey provides the first statistically significant and homogeneously selected sample of bright early-type lens galaxies, furnishing a powerful probe of the structure of early-type galaxies within the half-light radius. The high confirmation rate of lenses in the SLACS survey suggests consideration of spectroscopic lens discovery as an explicit science goal of future spectroscopic galaxy surveys.

The Sloan Lens ACS Survey. II. Stellar Populations and Internal Structure of Early-Type Lens Galaxies*

Abstract: We use HST images to derive effective radii and effective surface brightnesses of 15 early-type (E+S0) lens galaxies identified by the SLACS Survey. Our measurements are combined with stellar velocity dispersions from the SDSS database to investigate for the first time the distribution of lens galaxies in the fundamental plane (FP) space. Accounting for selection effects (top priority to the largest Einstein radii and thus approximately to the largest velocity dispersions, σ 240 km s-1) and for passive evolution, the distribution of the lens galaxies inside the FP is indistinguishable from that of the parent sample of SDSS galaxies. We conclude that SLACS lenses are a fair sample of high velocity dispersion E+S0s. By comparing the central stellar velocity dispersion (σ) with the velocity dispersion that best fits the lensing models (σSIE) we find fSIE ≡ σ/σSIE = 1.01 ± 0.02 with 0.065 rms scatter. We infer that within the Einstein radii (typically Re/2) the SLACS lenses are very well approximated by isothermal ellipsoids, requiring a fine tuning of the stellar and dark matter distribution (the bulge-halo ``conspiracy''). Interpreting the offset from the local FP in terms of evolution of the stellar mass-to-light ratio, we find d log(M/LB)/dz = -0.69 ± 0.08 (rms 0.11) consistent with the rate found for field E+S0s and with most of the stars being old (zf > 2) and less than ~10% of the stellar mass having formed below z = 1. We discuss our results in the context of formation mechanisms such as collisionless (``dry'') mergers.

Cosmic Evolution of Black Holes and Spheroids. I. The MBH-σ Relation at z = 0.36

Abstract: We test the evolution of the correlation between black hole mass and bulge velocity dispersion (MBH-σ), using a carefully selected sample of 14 Seyfert 1 galaxies at z = 0.36±0.01. We measure velocity dispersion from stellar absorption lines around Mg b (5175 A) and Fe (5270 A) using high-S/N Keck spectra and estimate black hole mass from the Hβ line width and the optical luminosity at 5100 A, based on the empirically calibrated photoionization method. We find a significant offset from the local relation, in the sense that velocity dispersions were smaller for given black hole masses at z = 0.36 than locally. We investigate various sources of systematic uncertainties and find that those cannot account for the observed offset. The measured offset is Δlog MBH = 0.62 ±0.10±0.25; i.e., Δlog σ = 0.15±0.03±0. 06, where the error bars include a random component and an upper limit to the systematics. At face value, this result implies a substantial growth of bulges in the last 4 Gyr, assuming that the local MBH-σ relation is the universal evolutionary endpoint. Along with two samples of active galaxies with consistently determined black hole mass and stellar velocity dispersion taken from the literature, we quantify the observed evolution with the best-fit linear relation: Δlog MBH = (1-66±0.43)z + (0.04±0.09) with respect to the local relationship of Tremaine and coworkers, and Δlog MBH = (1-55 ±0.46)z + (0.01 ±0.12) with respect to that of Ferrarese. This result is consistent with the growth of black holes predating the final growth of bulges at these mass scales (〈σ〉 = 170 km s-1). © 2006. The American Astronomical Society. All rights reserved.

Cosmic Evolution of Black Holes and Spheroids. I: The M_BH-sigma Relation at z=0.36

Abstract: We test the evolution of the correlation between black hole mass and bulge velocity dispersion (M$_{\rm BH}-\sigma$), using a carefully selected sample of 14 Seyfert 1 galaxies at $z=0.36\pm0.01$. We measure velocity dispersion from stellar absorption lines around Mgb (5175A) and Fe (5270A) using high S/N Keck spectra, and estimate black hole mass from the H$\beta$ line width and the optical luminosity at 5100A, based on the empirically calibrated photo-ionization method. We find a significant offset from the local relation, in the sense that velocity dispersions were smaller for given black hole masses at $z=0.36$ than locally. We investigate various sources of systematic uncertainties and find that those cannot account for the observed offset. The measured offset is $\Delta \log M_{\rm BH}=0.62 \pm 0.10 \pm 0.25$, i.e. $\Delta \log \sigma=0.15 \pm 0.03 \pm 0.06$, where the error bars include a random component and an upper limit to the systematics. At face value, this result implies a substantial growth of bulges in the last 4 Gyr, assuming that the local M$_{\rm BH}-\sigma$ relation is the universal evolutionary end-point. Along with two samples of active galaxies with consistently determined black hole mass and stellar velocity dispersion taken from the literature, we quantify the observed evolution with the best fit linear relation, $\Delta \log M_{\rm BH} = (1.66\pm0.43)z + (0.04\pm0.09)$ with respect to the local relationship of Tremaine et al. (2002), and $\Delta \log M_{\rm BH} = (1.55\pm0.46)z + (0.01\pm0.12)$ with respect to that of Ferrarese (2002). This result is consistent with the growth of black holes predating the final growth of bulges at these mass scales ($ $=170 km s$^{-1}$).

A Panoramic Mid-Infrared Survey of Two Distant Clusters

Abstract: We present panoramic Spitzer MIPS 24 μm observations, covering ~9 × 9 Mpc2 (25' × 25') fields around two massive clusters, Cl 0024+16 and MS 0451-03, at z = 0.39 and z = 0.55, respectively, reaching a 5 σ flux limit of ~200 μJy. Our observations cover a very wide range of environments within these clusters, from high-density regions around the cores out to the turnaround radius. Cross-correlating the mid-infrared catalogs with deep optical and near-infrared imaging of these fields, we investigate the optical/near-infrared colors of the mid-infrared sources. We find excesses of mid-infrared sources with the optical/near-infrared colors expected of cluster members in the two clusters and test this selection using spectroscopically confirmed 24 μm members. The much more significant excess is associated with Cl 0024+16, whereas MS 0451-03 has comparatively few mid-infrared sources. The mid-infrared galaxy population in Cl 0024+16 appears to be associated with dusty star-forming galaxies (typically redder than the general cluster population by up to AV ~ 1-2 mag) rather than emission from dusty tori around active galactic nuclei in early-type hosts. We compare the star formation rates derived from the total infrared (8-1000 μm) luminosities for the mid-infrared sources in Cl 0024+16 with those estimated from a published Hα survey, finding rates 5 times those found from Hα, indicating significant obscured activity in the cluster population. Compared to previous mid-infrared surveys of clusters from z ~ 0-0.5, we find evidence for strong evolution of the level of dust-obscured star formation in dense environments to z = 0.5, analogous to the rise in the fraction of optically selected star-forming galaxies seen in clusters and the field out to similar redshifts. However, there are clearly significant cluster-to-cluster variations in the populations of mid-infrared sources, probably reflecting differences in the intracluster media and recent dynamical evolution of these systems.

GALEX Observations of ``Passive Spirals'' in the Cluster Cl 0024+17: Clues to the Formation of S0 Galaxies

Abstract: We present new results from deep GALEX UV imaging of the cluster Cl 0024+17 at z ~ 0.4. Rest-frame far-UV emission is detected from a large fraction of so-called passive spiral galaxies—a significant population that exhibits spiral morphology with little or no spectroscopic evidence of ongoing star formation. This population is thought to represent infalling galaxies whose star formation has been somehow truncated by environmental processes, possibly in morphological transition to S0 galaxies. Compared to normal cluster spirals, we find that passive spirals are redder in FUV-optical color, while exhibiting much stronger UV emission than cluster E/S0 galaxies—as expected for recently truncated star formation. By modeling the different temporal sensitivities of UV and spectroscopic data to recent activity, we show that star formation in passive spirals decayed on timescales of less than 1 Gyr, consistent with "gas starvation"—a process where the cluster environment prevents cold gas from accreting onto the spiral disk. Intriguingly, the fraction of spirals currently observed in the passive phase is consistent with the longer period expected for the morphological transformation and the subsequent buildup of cluster S0 galaxies observed since z 0.4.

Cosmic Evolution of Black Holes And Spheroids. 1, the M(BH)-Sigma Relation at Z=0.36

Abstract: We test the evolution of the correlation between black hole mass and bulge velocity dispersion (M{sub BH} - {sigma}), using a carefully selected sample of 14 Seyfert 1 galaxies at z = 0.36 {+-} 0.01. We measure velocity dispersion from stellar absorption lines around Mgb (5175 {angstrom}) and Fe (5270 {angstrom}) using high S/N Keck spectra, and estimate black hole mass from the H{beta} line width and the optical luminosity at 5100 {angstrom}, based on the empirically calibrated photo-ionization method. We find a significant offset from the local relation, in the sense that velocity dispersions were smaller for given black hole masses at z = 0.36 than locally. We investigate various sources of systematic uncertainties and find that those cannot account for the observed offset. The measured offset is {Delta} log M{sub BH} = 0.62 {+-} 0.10 {+-} 0.25, i.e. {Delta} log {sigma} = 0.15 {+-} 0.03 {+-} 0.06, where the error bars include a random component and an upper limit to the systematics. At face value, this result implies a substantial growth of bulges in the last 4 Gyr, assuming that the local M{sub BH} - {sigma} relation is the universal evolutionary end-point. Along with two samples of activemore » galaxies with consistently determined black hole mass and stellar velocity dispersion taken from the literature, we quantify the observed evolution with the best fit linear relation, {Delta} log M{sub BH} = (1.66 {+-} 0.43)z + (0.04 {+-} 0.09) with respect to the local relationship of Tremaine et al. (2002), and {Delta} log M{sub BH} = (1.55 {+-} 0.46)z +(0.01 {+-} 0.12) with respect to that of Ferrarese (2002). This result is consistent with the growth of black holes predating the final growth of bulges at these mass scales ( = 170 km s{sup -1}).« less

The Sloan Lens ACS Survey. III - The Structure and Formation of Early-type Galaxies and their Evolution since z~1

Abstract: (Abridged) We present a joint gravitational lensing and stellar dynamical analysis of fifteen massive field early-type galaxies, selected from the Sloan Lens (SLACS) Survey. The following numerical results are found: (i) A joint-likelihood gives an average logarithmic density slope for the total mass density of 2.01 (+0.02/-0.03) (68 perecnt C.L). inside the Einstein radius. (ii) The average position-angle difference between the light distribution and the total mass distribution is found to be 0+-3 degrees, setting an upper limit of <= 0.035 on the average external shear. (iii) The average projected dark-matter mass fraction is inferred to be 0.25+-0.06 inside R_E, using the stellar mass-to-light ratios derived from the Fundamental Plane as priors. (iv) Combined with results from the LSD Survey, we find no significant evolution of the total density slope inside one effective radius: a linear fit gives d\gamma'/dz = 0.23+-0.16 (1-sigma) for the range z=0.08-1.01. The small scatter and absence of significant evolution in the inner density slopes suggest a collisional scenario where gas and dark matter strongly couple during galaxy formation, leading to a total mass distribution that rapidly converge to dynamical isothermality.

GALEX Observations of "Passive Spirals" in the Cluster Cl 0024+17: Clues to the Formation of S0 Galaxies

Abstract: We present new results from deep GALEX UV imaging of the cluster Cl 0024+17 at z~0.4. Rest-frame far UV emission is detected from a large fraction of so-called ``passive spiral galaxies'' -a significant population which exhibits spiral morphology with little or no spectroscopic evidence for ongoing star formation. This population is thought to represent infalling galaxies whose star formation has been somehow truncated by environmental processes, possibly in morphological transition to S0 galaxies. Compared to normal cluster spirals, we find that passive spirals are redder in FUV-optical color, while exhibiting much stronger UV emission than cluster E/S0s - as expected for recently-truncated star formation. By modeling the different temporal sensitivities of UV and spectroscopic data to recent activity, we show that star formation in passive spirals decayed on timescales of less than 1 Gyr, consistent with `gas starvation' - a process where the cluster environment prevents cold gas from accreting onto the spiral disk. Intriguingly, the fraction of spirals currently observed in the passive phase is consistent with the longer period expected for the morphological transformation and the subsequent build-up of cluster S0s observed since z=0.4.

Three Gravitational Lenses for the Price of One: Enhanced Strong Lensing Through Galaxy Clustering

Abstract: We report the serendipitous discovery of two strong gravitational lens candidates (ACS J160919+6532 and ACS J160910+6532) in deep images obtained with the Advanced Camera for Surveys on the Hubble Space Telescope, each less than 40'' from the previously known gravitational lens system CLASS B1608+656. The redshifts of both lens galaxies have been measured with Keck and Gemini: one is a member of a small galaxy group at z {approx} 0.63, which also includes the lensing galaxy in the B1608+656 system, and the second is a member of a foreground group at z {approx} 0.43. By measuring the effective radii and surface brightnesses of the two lens galaxies, we infer their velocity dispersions based on the passively evolving Fundamental Plane (FP) relation. Elliptical isothermal lens mass models are able to explain their image configurations within the lens hypothesis, with a velocity dispersion compatible with that estimated from the FP for a reasonable source-redshift range. Based on the large number of massive early-type galaxies in the field and the number-density of faint blue galaxies, the presence of two additional lens systems around CLASS B1608+656 is not unlikely in hindsight. Gravitational lens galaxies are predominantly early-type galaxies, which are clustered, and the lensedmore » quasar host galaxies are also clustered. Therefore, obtaining deep high-resolution images of the fields around known strong lens systems is an excellent method of enhancing the probability of finding additional strong gravitational lens systems.« less

Spheroids scaling relations over cosmic time

Abstract: I report on recent measurements of two scaling relations of spheroids in the distant universe: the Fundamental Plane, and the relation between lensing velocity dispersion and stellar velocity dispersion. The joint analysis of the two scaling relations indicates that the most massive (above 10^11.5 solar masses) spheroids are consistent with no evolution since z~1 both in terms of star formation and internal structure. Furthermore their total mass density profile is on average well described by an isothermal sphere with no evidence for redshift evolution. At smaller masses the picture appears to be substantially different, as indicated by evidence for substantial recent star formation (as much as 20-40% of stellar mass formed since z~1), and by hints of a reduced dark matter content at smaller masses. A larger sample of lenses extending to velocity dispersions below 200 km/s, and to redshifts above >0.5 is needed to verify these trends.

GALEX Observations of "Passive Spirals" in the Cluster Cl 0024+17: Clues to the Formation of S0 Galaxies

Abstract: We present new results from deep GALEX UV imaging of the cluster Cl 0024+17 at z~0.4. Rest-frame far UV emission is detected from a large fraction of so-called ``passive spiral galaxies'' -a significant population which exhibits spiral morphology with little or no spectroscopic evidence for ongoing star formation. This population is thought to represent infalling galaxies whose star formation has been somehow truncated by environmental processes, possibly in morphological transition to S0 galaxies. Compared to normal cluster spirals, we find that passive spirals are redder in FUV-optical color, while exhibiting much stronger UV emission than cluster E/S0s - as expected for recently-truncated star formation. By modeling the different temporal sensitivities of UV and spectroscopic data to recent activity, we show that star formation in passive spirals decayed on timescales of less than 1 Gyr, consistent with `gas starvation' - a process where the cluster environment prevents cold gas from accreting onto the spiral disk. Intriguingly, the fraction of spirals currently observed in the passive phase is consistent with the longer period expected for the morphological transformation and the subsequent build-up of cluster S0s observed since z=0.4.

Cosmic evolution of black holes and galaxies to z=0.4

Abstract: We test the evolution of the correlation between black hole mass and bulge properties, using a carefully selected sample of 20 Seyfert 1 galaxies at z =0.36 ±0.01. We estimate black hole mass from the Hβ line width and the optical luminosity at 5100 A, based on the empirically calibrated photo-ionization method. Velocity dispersion are measured from stellar absorption lines around Mgb (5175 A) and Fe (5270 A) using high S/N Keck spectra, and bulge properties (luminosity and effective radius) are measured from HST images by fitting surface brightness. We find a significant offset from the local relations, in the sense that bulge sizes were smaller for given black hole masses at z =0.36 than locally. The measured offset is Δ M •=0.62 ± 0.10, 0.45 ±0.13, 0.59 ±0.19, respectively for M •–σ, M •– L bulge , and M •– M bulge relations. At face value, this result implies a substantial growth of bulges in the last 4 Gyr, assuming that the local M •–bulge property relation is the universal evolutionary end-point. This result is consistent with the growth of black holes predating the final growth of bulges at these mass scales (〈σ〉=170 km s −1 ).

Spheroids scaling relations over cosmic time

Abstract: I report on recent measurements of two scaling relations of spheroids in the distant universe: the Fundamental Plane, and the relation between lensing velocity dispersion and stellar velocity dispersion. The joint analysis of the two scaling relations indicates that the most massive (above 10^11.5 solar masses) spheroids are consistent with no evolution since z~1 both in terms of star formation and internal structure. Furthermore their total mass density profile is on average well described by an isothermal sphere with no evidence for redshift evolution. At smaller masses the picture appears to be substantially different, as indicated by evidence for substantial recent star formation (as much as 20-40% of stellar mass formed since z~1), and by hints of a reduced dark matter content at smaller masses. A larger sample of lenses extending to velocity dispersions below 200 km/s, and to redshifts above >0.5 is needed to verify these trends.