arXiv subjects

Tommaso Treu

Publications and source records attributed to Tommaso Treu.

At least 361 records · Page 20Linked to original sources

arXiv2008

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

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.

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arXiv2008

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

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.

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arXiv2008

Late-time observations of SN2006gy: Still Going Strong

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.

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arXiv2008

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

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.

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arXiv2008

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

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(<R)/M_dim] = (1.10 +/- 0.09) log_10 [R/R_e] + (0.85 +/- 0.03), consistent with an isothermal (flat rotation curve) model when de-projected into 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 f_DM = 0.38 +/- 0.07 within one effective radius. (abridged)

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arXiv2008

Dark Matter and Baryons in the Most X-ray Luminous and Merging Galaxy Cluster RX J1347.5-1145

The galaxy cluster RX J1347-1145 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. 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 400 / h_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.

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arXiv2008

AMUSE-Virgo I. Super-massive black holes in low-mass spheroids

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 Multi-band Imaging Photometer on board the Spitzer Space Telescope, with the aim of providing an unbiased census of low-level super-massive black hole (SMBH) 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. Point-like X-ray emission from a position coincident with the optical nucleus is detected in 50% of the galaxies (down to our completeness limit of ~4E+38 erg/sec). Two of the X-ray nuclei are hosted by galaxies (VCC1178=N4464 and VCC1297=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 SMBH, with a <11% chance contamination in VCC1178, 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(L_0.3-10keV/L_Edd)<-5.9. The incidence of nuclear X-ray activity increases with the stellar mass M_star of the host galaxy: only between 3-44% of the galaxies with M_star<1E+10 M_Sun harbor an X-ray active SMBH. The fraction rises to between 49-87% in galaxies with stellar mass above 1E+10 M_Sun (at the 95% confidence level).

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arXiv2008

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

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 $ρ_{tot} ~ r^-g'$ with $g'=2.00\pm0.03$ and velocity dispersion $σ_{SIE}=287\pm5\kms$. [...] 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 $(σ_{SIE,s1}=94\pm30\kms)$. 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 $Ω_m$ and $w$ with 10% accuracy, for a flat cosmology.

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arXiv2008

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

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 (SLACS), 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~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 rho propto r^{-gamma'} with gamma'=2.06^{+0.03}_{-0.06}; (ii) is a very slow rotator (specific stellar angular momentum parameter lambda_R = 0.075); (iii) shows only mild anisotropy (delta ~ 0.15); and (iv) has a dark matter contribution of ~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.

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arXiv2007

Direct Observation of Cosmic Strings via their Strong Gravitational Lensing Effect: I. Predictions for High Resolution Imaging Surveys

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 most important factor, and that interesting limits on the dimensionless string tension Gmu/c^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 few square degrees -- well within reach of the current HST archive -- to probe the regime Gmu/c^2 ~ 10^{-7}. If lensing by cosmic strings is not detected, such a survey would improve the limit on the string tension by a factor of two over that available from the cosmic microwave background. Future high resolution imaging surveys, covering a few hundred square degrees or more, either from space in the optical or from large-format radio telescopes on the ground, would be able to further lower this limit to Gmu/c^2 < 10^{-8}.

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arXiv2007

The Evolutionary History of Galactic Bulges: Photometric and Spectroscopic Studies of Distant Spheroids in the GOODS Fields

We report on the first results of a new study aimed at understanding the diversity and evolutionary history of 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 0.2 show very similar patterns of evolution to those seen for pure spheroidals such that the stellar populations of all spheroids with M>10^{11}Msun are homogeneously old, consistent with a single major burst of star formation at high redshift (z_f<~2), while bulges with M<10^{11}Msun must have had more recent stellar mass growth (~10% in mass since z~1). Although further data spanning a wider range of redshift and mass is desirable, the striking similarity between the assembly histories of bulges and low mass spheroidals is difficult to reconcile with the picture whereby the majority of large bulges form primarily via secular processes within spiral galaxies.

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arXiv2007

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.

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arXiv2007

The Fundamental Plane of Bulges at Intermediate Redshift

We report on a new study aimed at understanding the diversity and evolutionary properties of distant galactic bulges in the context of well-established trends for pure spheroidal galaxies. Bulges have been isolated for a sample of 137 spiral galaxies in the GOODS fields within the redshift range 0.1 < z < 1.2. Using proven photometric techniques we determine for each galaxy the characteristic parameters (size, surface brightness, profile shape) in the 4 GOODS-ACS imaging bands of both the disk and bulge components. Using the DEIMOS spectrograph on Keck, precision stellar velocity dispersions were secured for a sizeable fraction of the bulges. This has enabled us to compare the Fundamental Plane of our distant bulges with that of field spheroidal galaxies in a similar redshift range. Bulges in spiral galaxies with a bulge-to-total luminosity ratio (B/T) > 0.2 show very similar patterns of evolution to those seen for low luminosity spheroidals. To first order, their recent mass assembly histories are equivalent.

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arXiv2007

A Wide-field Survey of Two Z~0.5 Galaxy Clusters: Identifying the Physical Processes Responsible for the Observed Transformation of Spirals into S0s

We present new results from our comprehensive comparative survey of two massive, intermediate redshift galaxy clusters, Cl0024+17 (z=0.39) and MS0451-03 (z=0.54). We identify and study several key classes of `transition objects' whose stellar populations or dynamical states indicate a recent or ongoing change in morphology and star formation rate. For the first time, we have been able to conclusively identify spiral galaxies in the process of transforming into S0 galaxies. This has been accomplished by locating both spirals whose star formation is being quenched as well as their eventual successors, the recently created S0s. Differences between the two clusters in both the timescales and spatial location of this conversion process allow us to evaluate the relative importance of several proposed physical mechanisms that could be responsible for the transformation. Combined with other diagnostics that are sensitive to either ICM-driven galaxy evolution or galaxy-galaxy interactions, we describe a self-consistent picture of galaxy evolution in clusters. We find that spiral galaxies within infalling groups have already begun a slow process of conversion into S0s primarily via gentle galaxy-galaxy interactions. The fates of spirals upon reaching the core of the cluster depend heavily on the cluster ICM, with rapid conversion of all remaining spirals into S0s via ram-pressure stripping in clusters where the ICM is dense. In the presence of a less-dense ICM, the conversion continues at a slower pace, with galaxy-galaxy interactions continuing to play a role along with `starvation' by the ICM. We conclude that the buildup of the local S0 population through the transformation of spiral galaxies is a heterogeneous process that nevertheless proceeds robustly across a variety of different environments.

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arXiv2007

A More Fundamental Plane

We combine strong-lensing masses with SDSS stellar velocity dispersions and HST-ACS effective (half-light) radii for 36 lens galaxies from the Sloan Lens ACS (SLACS) Survey to study the mass dependence of mass-dynamical structure in early-type galaxies. We find that over a 180--390 km/s range in velocity dispersion, structure is independent of lensing mass to within 5%. This result suggests a systematic variation in the total (i.e., luminous plus dark matter) mass-to-light ratio as the origin of the tilt of the fundamental plane (FP) scaling relationship between galaxy size, velocity dispersion, and surface brightness. We construct the FP of the lens sample, which we find to be consistent with the FP of the parent SDSS early-type galaxy population, and present the first observational correlation between mass-to-light ratio and residuals about the FP. Finally, we re-formulate the FP in terms of surface mass density rather than surface brightness. By removing the complexities of stellar-population effects, this mass-plane formulation will facilitate comparison to numerical simulations and possible use as a cosmological distance indicator.

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arXiv2007

Cosmic Evolution of Black Holes and Spheroids. II: Scaling Relations at z=0.36

We combine Hubble Space Telescope images of a sample of 20 Seyfert galaxies at z=0.36 with spectroscopic information from the Keck Telescope to determine the black hole mass - spheroid luminosity relation (M-L), the Fundamental Plane (FP) of the host galaxies and the M-sigma relation. Assuming pure luminosity evolution, we find that the host spheroids had smaller luminosity and stellar velocity dispersion than today for a fixed M. The offsets correspond to Delta log L_B,0=0.40+-0.11+-0.15 (Delta log M = 0.51+-0.14+-0.19) and Delta log sigma = 0.13+-0.03+-0.05 (Delta log M = 0.54+-0.12+-0.21), respectively for the M-L and M-sigma relation. A detailed analysis of known systematic errors and selection effects shows that they cannot account for the observed offset. The data are inconsistent with pure luminosity evolution and the existence of universal and tight scaling relations. To obey the three local scaling relations by z=0 the distant spheroids have to grow their stellar mass by approximately 60% (Δlog M_sph=0.20+-0.14) in the next 4 billion years. The measured evolution can be expressed as M/ M_sph ~ (1+z)^{1.5+-1.0}. Based on the disturbed morphologies of a fraction of the sample (6/20) we suggest collisional mergers with disk-dominated systems as evolutionary mechanism.

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arXiv2007

The Dynamical Distinction between Elliptical and Lenticular Galaxies in Distant Clusters: Further Evidence for the Recent Origin of S0 Galaxies

We examine resolved spectroscopic data obtained with the Keck II telescope for 44 spheroidal galaxies in the fields of two rich clusters, Cl0024+16 (z=0.40) and MS0451-03 (z=0.54), and contrast this with similar data for 23 galaxies within the redshift interval 0.3<z<0.65 in the GOODS northern field. For each galaxy we examine the case for systemic rotation, derive central stellar velocity dispersions sigma and photometric ellipticities, epsilon. Using morphological classifications obtained via Hubble Space Telescope imaging as the basis, we explore the utility of our kinematic quantities in distinguishing between pressure-supported ellipticals and rotationally-supported lenticulars (S0s). We demonstrate the reliability of using the v/(1-epsilon) vs sigma and v/sigma vs epsilon distributions as discriminators, finding that the two criteria correctly identify 63%+-3% and 80%+-2% of S0s at z~0.5, respectively, along with 76%+8-3% and 79%+-2% of ellipticals. We test these diagnostics using equivalent local data in the Coma cluster, and find that the diagnostics are similarly accurate at z=0. Our measured accuracies are comparable to the accuracy of visual classification of morphologies, but avoid the band-shifting and surface brightness effects that hinder visual classification at high redshifts. As an example application of our kinematic discriminators, we then examine the morphology-density relation for elliptical and S0 galaxies separately at z~0.5. We confirm, from kinematic data alone, the recent growth of rotationally-supported spheroidals. We discuss the feasibility of extending the method to a more comprehensive study of cluster and field galaxies to z~1, in order to verify in detail the recent density-dependent growth of S0 galaxies.

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arXiv2007

The Sloan Lens ACS Survey. IV: the mass density profile of early-type galaxies out to 100 effective radii

We present a weak gravitational lensing analysis of 22 early-type strong lens galaxies, based on deep HST images obtained as part of the Sloan Lens ACS Survey. Using the most advanced techniques to control systematic uncertainties related to the variable PSF and charge transfer efficiency of the ACS, we detect weak lensing signal out to 300 kpc/h. We analyze blank control fields from the COSMOS survey in the same manner, inferring that the residual systematic uncertainty in the tangential shear is <0.3%. A joint strong and weak lensing analysis shows that the average total mass density profile is consistent with isothermal over two decades in radius (3-300 kpc/h, approximately 1-100 Reff). This finding extends by over an order of magnitude in radius previous results, based on strong lensing and/or stellar dynamics, that luminous and dark component ``conspire'' to form an isothermal mass distribution. In order to disentangle the contributions of luminous and dark matter, we fit a two-component mass model (R^1/4 + NFW) to the weak and strong lensing constraints. It provides a good fit to the data with only two free parameters; i) the average stellar mass-to-light ratio M_*/L_V=4.48 +- 0.46 hMo/Lo, in agreement with that expected for an old stellar population; ii) the average virial mass-to-light ratio M_vir/L_V = 246+101-87 hMo/Lo. [abridged]

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