Showing papers by "Tommaso Treu published in 2008"

The Sloan Lens ACS Survey. V. The Full ACS Strong-Lens Sample

Abstract: We present the definitive data for the full sample of 131 strong gravitational lens candidates observed with the Advanced Camera for Surveys (ACS) aboard the Hubble Space Telescope by the Sloan Lens ACS (SLACS) Survey. All targets were selected for higher redshift emission lines and lower redshift continuum in a single Sloan Digital Sky Survey (SDSS) spectrum. The foreground galaxies are primarily of early-type morphology, with redshifts from z similar or equal to 0.05 to 0.5 and velocity dispersions from sigma similar or equal to 160 to 400 km s(-1); the faint background emission-line galaxies have redshifts ranging from z similar or equal to 0.2 to 1.2. We confirm 70 systems showing clear evidence of multiple imaging of the background galaxy by the foreground galaxy, as well as an additional 19 systems with probable multiple imaging. For 63 clear lensing systems, we present singular isothermal ellipsoid and light-traces-mass gravitational lens models fitted to the ACS imaging data. These strong-lensing mass measurements are supplemented by magnitudes and effective radii measured from ACS surface brightness photometry and redshifts and velocity dispersions measured from SDSS spectroscopy. These data constitute a unique resource for the quantitative study of the interrelations between mass, light, and kinematics in massive early-type galaxies. We show that the SLACS lens sample is statistically consistent with being drawn at random from a parent sample of SDSS galaxies with comparable spectroscopic parameters and effective radii, suggesting that the results of SLACS analyses can be generalized to the massive early-type population.

Revealing the properties of dark matter in the merging cluster MACSJ0025.4-1222

Abstract: We constrain the physical nature of dark matter using the newly identified massive merging galaxy cluster MACSJ0025.4-1222. As was previously shown by the example of the Bullet Cluster (1E0657-56), such systems are ideal laboratories for detecting isolated dark matter, and distinguishing between cold dark matter (CDM) and other scenarios (e.g. self-interacting dark matter, alternative gravity theories). MACSJ0025.4-1222 consists of two merging subclusters of similar richness at z=0.586. We measure the distribution of X-ray emitting gas from Chandra X-ray data and find it to be clearly displaced from the distribution of galaxies. A strong (information from highly distorted arcs) and weak (using weakly distorted background galaxies) gravitational lensing analysis based on Hubble Space Telescope observations and Keck arc spectroscopy confirms that the subclusters have near-equal mass. The total mass distribution in each of the subclusters is clearly offset (at >4sigma significance) from the peak of the hot X-ray emitting gas (the main baryonic component), but aligned with the distribution of galaxies. We measure the fractions of mass in hot gas (0.09^{+0.07}_{-0.03}) and stars (0.010^{+0.007}_{-0.004}), consistent with those of typical clusters, finding that dark matter is the dominant contributor to the gravitational field. Under the assumption that the subclusters experienced a head-on collision in the plane of the sky, we obtain an order-of-magnitude estimate of the dark matter self-interaction cross-section of sigma/m < 4cm^2/g, re-affirming the results from the Bullet Cluster on the collisionless nature of dark matter.

Revealing the Properties of Dark Matter in the Merging Cluster MACS J0025.4–1222

Abstract: We constrain the physical nature of dark matter using the newly identified massive merging galaxy cluster MACS J0025.4–1222. As was previously shown by the example of the Bullet Cluster (1E 0657–56), such systems are ideal laboratories for detecting isolated dark matter and distinguishing between cold dark matter (CDM) and other scenarios (e.g., self-interacting dark matter, alternative gravity theories). MACS J0025.4–1222 consists of two merging subclusters of similar richness at z = 0.586. We measure the distribution of X-ray-emitting gas from Chandra X-ray data and find it to be clearly displaced from the distribution of galaxies. A strong (information from highly distorted arcs) and weak (using weakly distorted background galaxies) gravitational lensing analysis based on Hubble Space Telescope observations and Keck arc spectroscopy confirms that the subclusters have near-equal mass. The total mass distribution in each of the subclusters is clearly offset (at >4 σ significance) from the peak of the hot X-ray-emitting gas (the main baryonic component) but aligned with the distribution of galaxies. We measure the fractions of mass in hot gas (0.09+ 0.07−0.03) and stars (0.010+ 0.007−0.004), consistent with those of typical clusters, finding that dark matter is the dominant contributor to the gravitational field. Under the assumption that the subclusters experienced a head-on collision in the plane of the sky, we obtain an order-of-magnitude estimate of the dark matter self-interaction cross section of σ/m < 4 cm 2 g−1, reaffirming the results from the Bullet Cluster on the collisionless nature of dark matter.

The Sloan Lens ACS Survey. V. The Full ACS Strong-Lens Sample

Abstract: We present the definitive data for the full sample of 131 strong gravitational lens candidates observed with the Advanced Camera for Surveys (ACS) aboard the Hubble Space Telescope by the Sloan Lens ACS (SLACS) Survey. All targets were selected for higher-redshift emission lines and lower-redshift continuum in a single Sloan Digital Sky Survey (SDSS) spectrum. The foreground galaxies are primarily of early-type morphology, with redshifts from approximately 0.05 to 0.5 and velocity dispersions from 160 km/s to 400 km/s; the faint background emission-line galaxies have redshifts ranging from about 0.2 to 1.2. We confirm 70 systems showing clear evidence of multiple imaging of the background galaxy by the foreground galaxy, as well as an additional 19 systems with probable multiple imaging. For 63 clear lensing systems, we present singular isothermal ellipsoid and light-traces-mass gravitational lens models fitted to the ACS imaging data. These strong-lensing mass measurements are supplemented by magnitudes and effective radii measured from ACS surface-brightness photometry and redshifts and velocity dispersions measured from SDSS spectroscopy. These data constitute a unique resource for the quantitative study of the inter-relations between mass, light, and kinematics in massive early-type galaxies. We show that the SLACS lens sample is statistically consistent with being drawn at random from a parent sample of SDSS galaxies with comparable spectroscopic parameters and effective radii, suggesting that the results of SLACS analyses can be generalized to the massive early-type population.

The Sloan Lens ACS Survey. VII. Elliptical Galaxy Scaling Laws from Direct Observational Mass Measurements

Abstract: We use a sample of 53 massive early-type strong gravitational lens galaxies with well-measured redshifts (ranging from z = 0.06 to 0.36) and stellar velocity dispersions (between 175 and 400 km s−1) from the Sloan Lens ACS (SLACS) Survey to derive numerous empirical scaling relations. The ratio between central stellar velocity dispersion and isothermal lens-model velocity dispersion is nearly unity within errors. The SLACS lenses define a fundamental plane (FP) that is consistent with the FP of the general population of early-type galaxies. We measure the relationship between strong-lensing mass Mlens within one-half effective radius (Re/2) and the dimensional mass variable Mdim ≡ G−1σe22(Re/2) to be log (Mlens/1011 M☉) = (1.03 ± 0.04) log (Mdim/1011 M☉) + (0.54 ± 0.02) (where σe2 is the projected stellar velocity dispersion within Re/2). The near-unity slope indicates that the mass-dynamical structure of massive elliptical galaxies is independent of mass and that the "tilt" of the SLACS FP is due entirely to variation in total (luminous plus dark) mass-to-light ratio with mass. Our results imply that dynamical masses serve as a good proxies for true masses in massive elliptical galaxies. Regarding the SLACS lenses as a homologous population, we find that the average enclosed two-dimensional (2D) mass profile goes as log [M(< R)/Mdim] = (1.10 ± 0.09) log (R/Re) + (0.85 ± 0.03) , consistent with an isothermal (flat rotation curve) model when deprojected into three dimensions (3D). This measurement is inconsistent with the slope of the average projected aperture luminosity profile at a confidence level greater than 99.9%, implying a minimum dark matter fraction of fDM = 0.38 ± 0.07 within 1 effective radius. We also present an analysis of the angular mass structure of the lens galaxies, which further supports the need for dark matter inside one effective radius.

Cosmic Evolution of Black Holes and Spheroids. III. The MBH-σ* Relation in the Last Six Billion Years

Abstract: We measure the evolution of the correlation between black hole mass and host spheroid velocity dispersion (MBH-σ*) over the last 6 billion years, by studying three carefully selected samples of active galaxies at z = 0.57, z = 0.36 and z < 0.1. For all three samples, virial black hole masses are consistently estimated using the line dispersion of Hβ and the continuum luminosity at 5100 A or Hα line luminosity, based on our cross calibration of the broad-line region size-luminosity relation. For the z = 0.57 sample, new stellar velocity dispersions are measured from high signal-to-noise ratio spectra obtained at the Keck Telescope, while for the two lower redshift samples they are compiled from previous works. Extending our previous result at z = 0.36, we find an offset from the local relation, suggesting that for fixed MBH, distant spheroids have on average smaller velocity dispersions than local ones. The measured offset at z = 0.57 is Δ log σ* = 0.12 ± 0.05 ± 0.06 (or Δ log MBH = 0.50 ± 0.22 ± 0.25), i.e., Δ log M BH = (3.1 ± 1.5) log (1 + z) + 0.05 ± 0.21. This is inconsistent with a tight and nonevolving universal M BH-σ* relation at the 95% CL. © 2008. The American Astronomical Society. All rights reserved.

Comparing and Calibrating Black Hole Mass Estimators for Distant Active Galactic Nuclei

Abstract: Black hole mass (MBH) is a fundamental property of active galactic nuclei (AGNs). In the distant universe, MBHis commonly estimated using the Mg II, Hβ, or Hα 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 MBHestimators for a sample of 19 AGNs at this redshift. We compare popular recipes available from the literature, finding that MBHestimates 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 MBHfrom 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 MBHestimators. © 2008. The American Astronomical Society. All rights reserved.

Cosmic Evolution of Black Holes and Spheroids. III. The M-sigma relation in the last six billion years

Abstract: We measure the evolution of the correlation between black hole mass and host spheroid velocity dispersion over the last 6 billion years, by studying three carefully selected samples of active galaxies at z=0.57, z=0.36 and z<0.1. For all three samples, virial black hole masses are consistently estimated using the line dispersion of H$\beta$ and the continuum luminosity at 5100A or Halpha line luminosity, based on our cross calibration of the broad line region size-luminosity relation. For the z=0.57 sample, new stellar velocity dispersions are measured from high signal-to-noise ratio spectra obtained at the Keck Telescope, while for the two lower redshift samples they are compiled from previous works. Extending our previous result at z=0.36, we find an offset from the local relation, suggesting that for fixed M_{BH}, distant spheroids have on average smaller velocity dispersions than local ones. The measured offset at z=0.57 is d log sigma_{*}=0.12 \pm 0.05\pm 0.06 (or d log M_{BH}=0.50 \pm 0.22\pm 0.25), i.e. d log M_{BH} = (3.1\pm1.5)\log (1+z) + 0.05\pm0.21. This is inconsistent with a tight and non-evolving universal M-sigma relation at the 95%CL

The sloan lens ACS survey. VI. Discovery and analysis of a double Einstein ring

Abstract: We report the discovery of two concentric partial Einstein rings around the gravitational lens SDSSJ0946+1006, as part of the Sloan Lens ACS Survey. The main lens is at redshift zl = 0.222, while the inner ring (1) is at redshift zs1 = 0.609 and Einstein radius REin1 = 1.43 ± 0.01 00 . The wider image separation (REin2 = 2.07±0.02 00 ) of the outer ring (2) implies that it is at higher redshift than Ring 1. Although no spectroscopic feature was detected in » 9 hours of spectroscopy at the Keck I Telescope, the detection of Ring 2 in the F814W ACS filter implies an upper limit on the redshift of zs2 . 6.9. The lens configuration can be well described by a power law total mass density profile for the main lens ‰tot / r i∞ 0 with logarithmic slope ∞ 0 = 2.00±0.03 (i.e. close to isothermal), velocity dispersion aeSIE = 287 ± 5kms i1 (in good agreement with the stellar velocity dispersion aev,⁄ = 284 ± 24kms i1 ) with little dependence upon cosmological parameters or the redshift of Ring 2. Using strong lensing constraints only we show that the enclosed mass to light ratio increases as a function of radius, inconsistent with mass following light. Adopting a prior on the stellar mass to light ratio from previous SLACS work we infer that 73 ± 9% of the mass is in form of dark matter within the cylinder of radius equal to the eective radius of the lens. We consider whether the double source plane configuration can be used to constrain cosmological parameters exploiting the ratios of angular distance ratios entering the set of lens equations. We find that constraints for SDSSJ0946+1006 are uninteresting due to the sub-optimal lens and source redshifts for this application. We then consider the perturbing eect of the mass associated with Ring 1 (modeled as a singular isothermal sphere) building a double lens plane compound lens model. This introduces minor changes to the mass of the main lens, allows to estimate the redshift of the Ring 2 (zs2 = 3.1 +2.0 i1.0 ), and the mass of the source responsible for Ring 1 (aeSIE,s1 = 94 +2747 kms i1 ). We conclude by examining the prospects of doing cosmography with a sample of 50 double source plane gravitational lenses, expected from future space based surveys such as DUNE or JDEM. Taking full account of the uncertainty in the mass density profile of the main lens, and of the eect of the perturber, and assuming known redshifts for both sources, we find that such a sample could be used to measure ›m and w with 10% accuracy, assuming a flat cosmological model. Subject headings: Gravitational lensing ‐ galaxies : Ellipticals and lenticulars, cD ‐ galaxies: structure ‐ galaxies: halos ‐ cosmology: dark matter ‐ cosmology: cosmological parameters

Separating baryons and dark matter in cluster cores : a full two-dimensional lensing and dynamic analysis of abell 383 and ms 2137-23

Abstract: We utilize existing data for the galaxy clusters MS 2137–23 and Abell 383 to present improved measures of the distribution of dark and baryonic material in the clusters' central regions. Our method, based on the combination of gravitational lensing and dynamical data, is uniquely capable of separating the distribution of dark and baryonic components at scales below 100 kpc. Our mass models include pseudoelliptical generalized NFW profiles for constraining the inner dark matter slope. We find that a variety of strong-lensing models fit the available data, including some with dark matter profiles as steep as expected from recent simulations. However, when combined with stellar velocity dispersion data for the brightest member, shallower inner slopes than predicted by numerical simulations are preferred, in general agreement with our earlier work in these clusters. For Abell 383, the preferred shallow inner slopes are statistically a good fit only when the multiple-image position uncertainties associated with our lens model are assumed to be 0.5", to account for unknown substructure. No statistically satisfactory fit was obtained matching both the multiple-image lensing data and the velocity dispersion profile of the brightest cluster galaxy in MS 2137–23. This suggests that the mass model we are using, which comprises a pseudoelliptical generalized NFW profile and a brightest cluster galaxy component, may inadequately represent the inner cluster regions. This may arise due to halo triaxiality or by the gravitational interaction of baryons and dark matter in cluster cores. The progress made via this detailed study highlights the key role that complementary observations of lensed features and stellar dynamics offer in understanding the interaction between dark and baryonic matter on nonlinear scales in the central regions of clusters.

AMUSE-Virgo. I. Supermassive Black Holes in Low-Mass Spheroids

Abstract: We present the first results from the AGN Multiwavelength Survey of Early-Type Galaxies in the Virgo Cluster (AMUSE-Virgo). This large program targets 100 early-type galaxies with the Advanced CCD Imaging Spectrometer on board the Chandra X-Ray Observatory and the Multiband Imaging Photometer on board the Spitzer Space Telescope, with the aim of providing an unbiased census of low-level supermassive black hole activity in the local universe. Here we report on the Chandra observations of the first 16 targets, and combine them with results from archival data of another, typically more massive, 16 targets. Pointlike X-ray emission from a position coincident with the optical nucleus is detected in 50% of the galaxies (down to our completeness limit of ~4 × 1038 ergs s−1). Two of the X-ray nuclei are hosted by galaxies (VCC 1178 [N4464] and VCC 1297 [N4486B]) with absolute B magnitudes fainter than –18, where nuclear star clusters are known to become increasingly common. After carefully accounting for possible contamination from low-mass X-ray binaries, we argue that the detected nuclear X-ray sources are most likely powered by low-level accretion on to a supermassive black hole, with a 11% chance contamination in VCC 1178, where a star cluster is barely resolvable in archival Hubble Space Telescope images. Based on black hole mass estimates from the global properties of the host galaxies, all the detected nuclei are highly sub-Eddington, with luminosities in the range –8.4 < log (L0.3–10 keV/LEdd) < − 5.9. The incidence of nuclear X-ray activity increases with the stellar mass M of the host galaxy: only between 3% and 44% of the galaxies with M < 1010 M☉ harbor an X-ray active supermassive black hole. The fraction rises to between 49% and 87% in galaxies with stellar mass above 1010 M☉ (at the 95% confidence level).

Dark matter and baryons in the most x-ray luminous and merging galaxy cluster rx j1347.5−1145 *

Abstract: The galaxy cluster RX J1347.5−1145 is one of the most X-ray luminous and most massive clusters known. Its extreme mass makes it a prime target for studying issues addressing cluster formation and cosmology. Despite the naive expectation that mass estimation for this cluster should be straightforward (high mass and favorable redshift make it an efficient lens, and in addition it is bright in X-rays and appears to be in a fairly relaxed state), some studies have reported very discrepant mass estimates from X-ray, dynamical and gravitational lensing. In this paper we present new high-resolution HST/ACS and Chandra X-ray data. The high resolution and sensitivity of ACS enabled us to detect and quantify several new multiply imaged sources, we now use a total of eight for the strong lensing analysis. Combining this information with shape measurements of weak lensing sources in the central regions of the cluster, we derive a high-resolution, absolutely-calibrated mass map. This map provides the best available quantification of the total mass of the central part of the cluster to date. We compare the reconstructed mass with that inferred from the new Chandra X-ray data, and conclude that both mass estimates agree extremely well in the observed region, namely within 400h −1 70 kpc of the cluster center. In addition we study the major baryonic components (gas and stars) and hence derive the dark matter distribution in the center of the cluster. We find that the dark matter and baryons are both centered on the BCG within the uncertainties (alignment is better than < 10 kpc). We measure the corresponding 1-D profiles and find that dark matter distribution is consistent with both NFW and cored profiles, indicating that a more extended radial analysis is needed to pinpoint the concentration parameter, and hence the inner slope of the dark matter profile. Subject headings: cosmology: dark matter – gravitational lensing – galaxies:clusters:individual:RX J1347.5-1145

Dark Matter and Baryons in the X-Ray Luminous Merging Galaxy Cluster RX J1347.5–1145*

Abstract: The galaxy cluster RX J1347.5–1145 is one of the most X-ray luminous and most massive clusters known. This makes it a prime target for studying issues addressing cluster formation and cosmology. Despite the naive expectation that mass estimation for this cluster should be straightforward (high mass and favorable redshift make it an efficient lens; it is bright in X-rays and appears to be fairly relaxed), some studies have reported very discrepant mass estimates. In this paper we present new high-resolution HST ACS and Chandra X-ray data. The high resolution and sensitivity of ACS enabled us to detect and quantify several new multiple images; we use a total of eight for the strong-lensing analysis. Combining it with shape measurements of weak-lensing sources in the central regions of the cluster, we derive a high-resolution, absolutely calibrated mass map. This map provides the best available quantification of the total mass of the central part of the cluster to date. We compare the reconstructed mass with that inferred from the new Chandra X-ray data. Both mass estimates agree extremely well in the observed region (within 400 -->h−170 kpc of the cluster center). In addition we study the major baryonic components (gas and stars) and hence derive the dark matter distribution in the center of the cluster. We find that the dark matter and baryons are both centered on the BCG within the uncertainties (alignment is better <10 kpc). We measure the corresponding dark matter profile and find it consistent with both NFW and cored profiles, indicating that a more extended radial analysis is needed to pinpoint the concentration parameter, and hence the inner slope of the dark matter profile.

The Sloan Lens ACS Survey. VIII. The relation between environment and internal structure of early-type galaxies

Abstract: We study the relation between the internal structure of early-type galaxies and their environment using 70 strong gravitational lenses from the Sloan ACS Lens Survey. The Sloan database is used to determine two measures of overdensity of galaxies around each lens: the projected number density of galaxies inside the tenth nearest neighbor (\Sigma_{10}) and within a cone of radius one h^{-1} Mpc (D_1). Our main results are: 1) The average overdensity is somewhat larger than unity, consistent with lenses preferring overdense environments as expected for massive early-type galaxies (12/70 lenses are in known groups/clusters). 2) The distribution of overdensities is indistinguishable from that of "twin" non-lens galaxies selected from SDSS to have the same redshift and stellar velocity dispersion \sigma_*. Thus, within our errors, lens galaxies are an unbiased population, and the SLACS results can be generalized to the overall population of early-type galaxies. 3) Typical contributions from external mass distribution are no more than a few per cent, reaching 10-20% (~0.05-0.10 external convergence) only in the most extreme overdensities. 4) No significant correlation between overdensity and slope of the mass density profile of the lens is found. 5) Satellite galaxies (those with a more luminous companion) have marginally steeper mass density profiles than central galaxies (those without). This result suggests that tidal stripping may affect the mass structure of early-type galaxies down to kpc scales probed by strong lensing, when they fall into larger structures [ABRIDGED].

First results from the lick AGN monitoring project: The mass of the black hole in ARP 151

Abstract: We have recently completed a 64 night spectroscopic monitoring campaign at the Lick Observatory 3 m Shane telescope with the aim of measuring the masses of the black holes in 13 nearby (z < 0.05) Seyfert 1 galaxies with expected masses in the range ~106-107 M☉. We present here the first results from this project—the mass of the central black hole in Arp 151. Strong variability throughout the campaign led to an exceptionally clean Hβ lag measurement in this object of 4.25−0.66+0.68 days in the observed frame. Coupled with the width of the Hβ emission line in the variable spectrum, we determine a black hole mass of (7.1 ± 1.2) × 106 M☉, assuming the Onken et al. normalization for reverberation-based virial masses. We also find velocity-resolved lag information within the Hβ emission line which clearly shows infalling gas in the Hβ-emitting region. Further detailed analysis may lead to a full model of the geometry and kinematics of broad line region gas around the central black hole in Arp 151.

Two-dimensional kinematics of SLACS lenses – I. Phase-space analysis of the early-type galaxy SDSS J2321−097 at z≈ 0.1

Abstract: We present the first results of a combined VLT VIMOS integral-field unit and Hubble Space Telescope (HST)/ACS study of the early-type lens galaxy SDSS J2321-097 at z = 0.0819, extending kinematic studies to a look-back time of 1 Gyr. This system, discovered in the Sloan Lens ACS Survey, has been observed as part of a VLT Large Programme with the goal of obtaining two-dimensional stellar kinematics of 17 early-type galaxies to z approximate to 0.35 and Keck spectroscopy of an additional dozen lens systems. Bayesian modelling of both the surface brightness distribution of the lensed source and the two-dimensional measurements of velocity and velocity dispersion has allowed us, under the only assumptions of axisymmetry and a two-integral stellar distribution function (DF) for the lens galaxy, to dissect this galaxy in three dimensions and break the classical mass-anisotropy, mass-sheet and inclination-oblateness degeneracies. Our main results are that the galaxy (i) has a total density profile well described by a single power law p alpha r(-gamma') with gamma' = 2.06(-0.06)(+0.03); (ii) is a very slow rotator (specific stellar angular momentum parameter lambda(R) = 0.075); (iii) shows only mild anisotropy (delta approximate to 0.15); and (iv) has a dark matter contribution of similar to 30 per cent inside the effective radius. Our first results from this large combined imaging and spectroscopic effort with the VLT, Keck and HST show that the structure of massive early-type galaxies beyond the local Universe can now be studied in great detail using the combination of stellar kinematics and gravitational lensing. Extending these studies to look-back times where evolutionary effects become measurable holds great promise for the understanding of formation and evolution of early-type galaxies.

Late-time observations of SN 2006gy: Still going strong

Abstract: Owing to its extremely high luminosity and long duration, supernova (SN) 2006gy radiated more energy in visual light than any other known SN. Two hypotheses to explain its high luminosity at early times - that it was powered by shock interaction with circumstellar material (CSM) as implied by its Type IIn spectrum, or that it was fueled by radioactive decay from a large mass of 56Ni synthesized in a pair-instability SN-predicted different late-time properties. Here we present observations of SN 2006gy obtained more than a year after discovery. We were unable to detect it at visual wavelengths, but clear near-infrared (IR) K′ and H-band detections show that it is still at least as luminous as the peak of a normal Type II SN. We also present spectra giving an upper limit to the late-time Ha luminosity of ≲S10 39 erg s-1. Based on the weak late-time Ha, X-ray, and radio emission, combined with the difficulty of explaining the shift to IR wavelengths, we can rule out ongoing CSM interaction as the primary late-time power source of SN 2006gy. Instead, we propose that the evolution of SN 2006gy is consistent with one of two possible scenarios: (1)apairinstability SN plus modest CSM interaction, where the radioactive decay luminosity shifts to the IR because of dust formation; or (2) an IR echo, where radiation emitted during peak luminosity heats a pre-existing dust shell at radii near 1 light year, requiring the progenitor star to have ejected another shell of ∼10 M ⊙ about 1500 yr before the SN. © 2008. The American Astronomical Society. All rights reserved.

First Results from the Lick AGN Monitoring Project: The Mass of the Black Hole in Arp 151

Abstract: We have recently completed a 64-night spectroscopic monitoring campaign at the Lick Observatory 3-m Shane telescope with the aim of measuring the masses of the black holes in 13 nearby (z < 0.05) Seyfert 1 galaxies with expected masses in the range ~10^6-10^7 M_sun. We present here the first results from this project -- the mass of the central black hole in Arp 151. Strong variability throughout the campaign led to an exceptionally clean Hbeta lag measurement in this object of 4.25(+0.68/-0.66) days in the observed frame. Coupled with the width of the Hbeta emission line in the variable spectrum, we determine a black hole mass of (7.1 +/- 1.2)x10^6 M_sun, assuming the Onken et al. normalization for reverberation-based virial masses. We also find velocity-resolved lag information within the Hbeta emission line which clearly shows infalling gas in the Hbeta-emitting region. Further detailed analysis may lead to a full model of the geometry and kinematics of broad line region gas around the central black hole in Arp 151.

Late-time observations of SN2006gy: Still Going Strong

Abstract: Owing to its extremely high luminosity and long duration, SN2006gy radiated more energy in visual light than any other known SN. Two hypotheses to explain its high luminosity -- that it was powered by shock interaction with CSM as implied by its Type IIn spectrum, or that it was fueled by radioactive decay from a large mass of 56Ni synthesized in a pair-instability SN -- predicted different late-time properties. Here we present observations of SN2006gy obtained more than a year after discovery. We were unable to detect it at visual wavelengths, but clear near-IR K and H-band detections show that it is still at least as luminous as the peak of a normal SN II. We also present spectra giving an upper limit to the late-time Ha luminosity of about 1e39 erg/s. Based on the weak late-time Ha, X-ray, and radio emission, combined with the difficulty of explaining the shift to IR wavelengths, we can rule out ongoing CSM interaction as the primary late-time power source. Instead, we propose that the evolution of SN2006gy is consistent with one of two possible scenarios: (1) A pair-instability SN plus modest CSM interaction, where the radioactive decay luminosity shifts to the IR because of dust formation. (2) An IR echo, where radiation emitted during peak luminosity heats a pre-existing dust shell at radii near 1 light year, requiring the progenitor star to have ejected another 10 Msun shell about 1500 yr before the SN.

The evolutionary history of galactic bulges : photometric and spectroscopic studies of distant spheroids in the GOODS fields

Abstract: Wereportonthefirstresultsof anewstudyaimedatunderstandingthediversityandevolutionaryhistoryof distant galactic bulges in the context of now well-established trends for pure spheroidal galaxies. To this end, bulges have been isolated for a sample of 137 spiral galaxies within the redshift range 0:1 0.2showsimilarpatternsof evolutiontothoseseenforpurespheroidalssuchthatthestellarpopu

Mass distribution and orbital anisotropy of early‐type galaxies: constraints from the mass plane

Abstract: Massive early-type galaxies are observed to lie on the mass plane (MP), a two-dimensional manifold in the space of effective radius Re, projected mass M p (measured via strong gravitational lensing) and projected stellar velocity dispersion σ e2 withinRe/2. The MP is less ‘tilted’ than the traditional Fundamental Plane, and the two have comparable associated scatter. This means that the dimensionless structure parameter ce2 = 2GM p /(Reσ 2 ) is a nearly universal constant in the range σ e2 = 175–400 km s −1 . This finding can be used to constrain the mass distribution and internal dynamics of early-type galaxies: in particular, we explore the dependence of ce2 on light profile, dark matter distribution, and orbital anisotropy for several families of spherical galaxy models. We find that a relatively wide class of models has values of ce2 in the observed range, because ce2 is not very strongly sensitive to the mass distribution and orbital anisotropy. The degree of fine-tuning required to match the small intrinsic scatter of ce2 depends on the considered family of models: if the total mass distribution is isothermal (∝ r −2 ), a broad range of stellar luminosity profile and anisotropy is consistent with the observations, while Navarro, Frenk & White dark matter haloes require more fine-tuning of the stellar mass fraction, luminosity profile and anisotropy. If future data can cover a broader range of masses, the MP could be seen to be tilted by the known non-homology of the luminosity profiles of early-type galaxies, and the value of any such tilt would provide a discriminant between models for the total mass–density profile of the galaxies.

Direct observation of cosmic strings via their strong gravitational lensing effect – I. Predictions for high-resolution imaging surveys

Abstract: We use current theoretical estimates for the density of long cosmic strings to predict the number of strong gravitational lensing events in astronomical imaging surveys as a function of angular resolution and survey area. We show that angular resolution is the single most important factor, and that interesting limits on the dimensionless string tension G{mu}/c{sup 2} can be obtained by existing and planned surveys. At the resolution of the Hubble Space Telescope (0'.14), it is sufficient to survey of order a square degree -- well within reach of the current HST archive -- to probe the regime G{mu}/c{sup 2} {approx} 10{sup -8}. If lensing by cosmic strings is not detected, such a survey would improve the limit on the string tension by an order of magnitude on that available from the cosmic microwave background. At the resolution (0'.028) attainable with the next generation of large ground based instruments, both in the radio and the infra-red with adaptive optics, surveying a sky area of order ten square degrees will allow us to probe the G{mu}/c{sup 2} {approx} 10{sup -9} regime. These limits will not be improved significantly by increasing the solid angle of the survey.

The Sloan Lens ACS Survey. VI: Discovery and analysis of a double Einstein ring

Abstract: We report the discovery of two concentric Einstein rings around the gravitational lens SDSSJ0946+1006, as part of the Sloan Lens ACS Survey. The main lens is at redshift zl=0.222, while the inner ring (1) is at zs1=0.609 and Einstein radius $Re_1=1.43\pm0.01"$. The wider image separation ($Re_2=2.07\pm 0.02"$) of the outer ring (2) implies that it is at higher redshift. Its detection in the F814W filter implies zs2<6.9. The configuration can be well described by a total density profile $\rho_{tot} ~ r^-g'$ with $g'=2.00\pm0.03$ and velocity dispersion $\sigma_{SIE}=287\pm5\kms$. [...] We consider whether this configuration can be used to constrain cosmological parameters exploiting angular distance ratios entering the lens equations. Constraints for SDSSJ0946+1006, are uninteresting due to the sub-optimal lens and source redshifts. We then consider the perturbing effect of the mass associated with Ring 1 building a double lens plane compound lens model. This introduces minor changes to the mass of the main lens and allows to estimate the mass of Ring 1 $(\sigma_{SIE,s1}=94\pm30\kms)$. We examine the prospects of doing cosmography with a sample of 50 double lenses, expected from future space based surveys such as DUNE or JDEM. Taking full account of the model uncertainties, such a sample could be used to measure $\Omega_m$ and $w$ with 10% accuracy, for a flat cosmology.

Dissecting the Gravitational Lens B1608+656. I. Lens Potential Reconstruction

Abstract: Strong gravitational lensing is a powerful technique for probing galaxy mass distributions and for measuring cosmological parameters. We present a pixelated approach to modeling simultaneously the lens potential and source intensity of strong gravitational lens systems with extended source-intensity distributions. For systems with sources of sufficient extent such that the separate lensed images are connected by intensity measurements, the accuracy in the reconstructed potential is solely limited by the quality of the data. We apply this potential reconstruction technique to deep HST observations of B1608+656, a four-image gravitational lens system formed by a pair of interacting lens galaxies. We present a comprehensive Bayesian analysis of the system that takes into account the extended source-intensity distribution, dust extinction, and the interacting lens galaxies. Our approach allows us to compare various models of the components of the lens system, which include the point-spread function (PSF), dust, lens galaxy light, source-intensity distribution, and lens potential. Using optimal combinations of the PSF, dust, and lens galaxy light models, we successfully reconstruct both the lens potential and the extended source-intensity distribution of B1608+656. The resulting reconstruction can be used as the basis of a measurement of the Hubble constant. We use our reconstruction of the gravitational potential to study the relative distribution of mass and light in the lensing galaxies. We find that the mass-to-light ratio for the primary lens galaxy is (2.0+/-0.2)h M_{\sun} L_{B,\sun}^{-1} within the Einstein radius 3.9 h^{-1} kpc, in agreement with what is found for noninteracting lens galaxies at the same scales. (Abridged)

The Sloan Lens ACS Survey. VII. Elliptical Galaxy Scaling Laws from Direct Observational Mass Measurements

Abstract: We use a sample of 53 massive early-type strong gravitational lens galaxies with well-measured redshifts (ranging from z=0.06 to 0.36) and stellar velocity dispersions (between 175 and 400 km/s) from the Sloan Lens ACS (SLACS) Survey to derive numerous empirical scaling relations. The ratio between central stellar velocity dispersion and isothermal lens-model velocity dispersion is nearly unity within errors. The SLACS lenses define a fundamental plane (FP) that is consistent with the FP of the general population of early-type galaxies. We measure the relationship between strong-lensing mass M_lens within one-half effective radius (R_e/2) and the dimensional mass variable M_dim = G^-1 sigma_e2^2 R_e/2 to be log_10 [M_lens/10^11 M_Sun] = (1.03 +/- 0.04) log_10 [M_dim/10^11 M_Sun] + (0.54 +/- 0.02) (where sigma_e2 is the projected stellar velocity dispersion within R_e/2). The near-unity slope indicates that the mass-dynamical structure of massive elliptical galaxies is independent of mass, and that the "tilt" of the SLACS FP is due entirely to variation in total (luminous plus dark) mass-to-light ratio with mass. Our results imply that dynamical masses serve as a good proxies for true masses in massive elliptical galaxies. Regarding the SLACS lenses as a homologous population, we find that the average enclosed 2D mass profile goes as log_10 [M(

Stars and dark matter in the spiral gravitational lens 2237+0305

Abstract: We construct a mass model for the spiral lens galaxy 2237+0305, at redshift z_l=0.04, based on gravitational-lensing constraints, HI rotation, and new stellar-kinematic information, based on data taken with the ESI spectrograph on the 10m Keck-II Telescope. High resolution rotation curves and velocity dispersion profiles along two perpendicular directions, close to the major and minor axes of the lens galaxy, were obtained by fitting the Mgb-Fe absorption line region. The stellar rotation curve rises slowly and flattens at r~1.5" (~1.1 kpc). The velocity dispersion profile is approximately flat. A combination of photometric, kinematic and lensing information is used to construct a mass model for the four major mass components of the system -- the dark matter halo, disc, bulge, and bar. The best-fitting solution has a dark matter halo with a logarithmic inner density slope of gamma=0.9+/-0.3 for rho_DM propto r^-gamma, a bulge with M/L_B=6.6+/-0.3 Upsilon_odot, and a disc with M/L_B =1.2+/-0.3 Upsilon_odot, in agreement with measurements of late-type spirals. The bulge dominates support in the inner regions where the multiple images are located and is therefore tightly constrained by the observations. The disc is sub-maximal and contributes 45+/-11 per cent of the rotational support of the galaxy at 2.2r_d. The halo mass is (2.0+/-0.6) x 10^12 M_odot, and the stellar to virial mass ratio is 7.0+/-2.3 per cent, consistent with typical galaxies of the same mass.

Enhanced lensing rate by clustering of massive galaxies: newly discovered systems in the SLACS fields

Abstract: [Abridged] We exploit the clustering of massive galaxies to perform a high efficiency imaging search for gravitational lenses. Our dataset comprises 44 fields imaged by the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS), each of which is centered on a lens discovered by the Strong Lens ACS Survey (SLACS). We compare four different search methods: 1) automated detection with the HST Archive Galaxy-scale Gravitational Lens Survey (HAGGLeS) robot, 2) examining cutout images of bright galaxies (BGs) after subtraction of a smooth galaxy light distribution, 3) examining the unsubtracted BG cutouts, and 4) performing a full-frame visual inspection of the ACS images. We compute purity and completeness and consider investigator time for the four algorithms, using the main SLACS lenses as a testbed. The first and second algorithms perform the best. We present the four new lens systems discovered during this comprehensive search, as well as one other likely candidate. For each new lens we use the fundamental plane to estimate the lens velocity dispersion and predict, from the resulting lens geometry, the redshifts of the lensed sources. Two of these new systems are found in galaxy clusters, which include the SLACS lenses in the two respective fields. Overall we find that the enhanced lens abundance (30^{+24}_{-8} lenses/degree^2) is higher than expected for random fields (12^{+4}_{-2} lenses/degree^2 for the COSMOS survey). Additionally, we find that the gravitational lenses we detect are qualitatively different from those in the parent SLACS sample: this imaging survey is largely probing higher-redshift, and lower-mass, early-type galaxies.

Mass distribution and orbital anisotropy of early-type galaxies: constraints from the Mass Plane

Abstract: Massive early-type galaxies are observed to lie on the Mass Plane (MP), a two-dimensional manifold in the space of effective radius R_e, projected mass M_p (measured via strong gravitational lensing) and projected velocity dispersion sigma within R_e/2. The MP is less `tilted' than the Fundamental Plane, and the two have comparable associated scatter. This means that c_e2=2*G*M_p/(R_e*sigma^2) is a nearly universal constant in the range sigma=175-400 km/s. This finding can be used to constrain the mass distribution and internal dynamics of early-type galaxies. We find that a relatively wide class of spherical galaxy models has values of c_e2 in the observed range, because c_e2 is not very strongly sensitive to the mass distribution and orbital anisotropy. If the total mass distribution is isothermal, a broad range of stellar luminosity profile and anisotropy is consistent with the observations, while NFW dark-matter halos require more fine tuning of the stellar mass fraction, luminosity profile and anisotropy. If future data can cover a broader range of masses, the MP could be seen to be tilted and the value of any such tilt would provide a discriminant between models for the total mass-density profile of the galaxies. [Abridged]

The nature of dusty starburst galaxies in a rich cluster at z=0.4: the progenitors of lenticulars?

Abstract: We present the results of a Spitzer Infrared Spectrograph (IRS) survey of 24um-selected luminous infrared galaxies (LIRGs, L_IR > 10^11 L_sun) in the rich cluster Cl0024+16 at z=0.4. Optically, these LIRGs resemble unremarkable spiral galaxies with e(a)/e(c) spectral classifications and [Oii]-derived star formation rates (SFRs) of <2 M_sun/yr, generally indistinguishable from the 'quiescent' star forming population in the cluster. Our IRS spectra show that the majority of the 24um-detected galaxies exhibit polycyclic aromatic hydrocarbon (PAH) emission with implied SFRs ~30-60 M_sun/yr, with only one (<10%) of the sample displaying unambiguous evidence of an active galactic nucleus in the mid-infrared. This confirms the presence of a large population of obscured starburst galaxies in distant clusters, which comprise the bulk of the star formation occurring in these environments at z~0.5. We suggest that, although several mechanisms could be at play, these dusty starbursts could be the signature of an important evolutionary transition converting gas-rich spiral galaxies in distant clusters into the passive, bulge-dominated lenticular galaxies that become increasingly abundant in the cores of rich clusters in the ~4Gyr to the present day.