Matthew W. Auger

The Initial Mass Function of Early-Type Galaxies

We determine an absolute calibration of the initial mass function (IMF) of early-type galaxies, by studying a sample of 56 gravitational lenses identified by the SLACS Survey. Under the assumption of standard Navarro, Frenk & White dark matter halos, a combination of lensing, dynamical, and stellar population synthesis models is used to disentangle the stellar and dark matter contribution for each lens. We define an “IMF mismatch” parameter α ≡M ∗,Ein/M SPS ∗,Einas the ratio of stellar mass inferred by a joint lensing and dynamical models (M ∗,Ein) to the current stellar mass inferred from stellar populations synthesis models (M ∗,Ein). We find that a Salpeter IMF provides stellar masses in agreement with those inferred by lensing and dynamical models (〈log α〉 = 0.00 ± 0.03 ± 0.02), while a Chabrier IMF underestimates them (〈log α〉 = 0.25± 0.03± 0.02). A tentative trend is found, in the sense that α appears to increase with galaxy velocity dispersion. Taken at face value, this result would imply a non universal IMF, perhaps dependent on metallicity, age, or abundance ratios of the stellar populations. Alternatively, the observed trend may imply non-universal dark matter halos with inner density slope increasing with velocity dispersion. While the degeneracy between the two interpretations cannot be broken without additional information, the data imply that massive early-type galaxies cannot have both a universal IMF and universal dark matter halos. Subject headings: gravitational lensing — galaxies: elliptical and lenticular, cD — galaxies: evolution — galaxies: formation — galaxies: structure

The Structure and Dynamics of Massive Early-Type Galaxies: On Homology, Isothermality, and Isotropy Inside One Effective Radius

Based on 58 SLACS strong-lens early-type galaxies (ETGs) with direct total-mass and stellar-velocity dispersion measurements, we find that inside one effective radius massive elliptical galaxies with Meff 3 × 10 10 M� are well approximated by a power-law ellipsoid, with an average logarithmic density slope of � γ � LD �≡ −d log(ρtot)/d log(r) = 2.085 +0.025 −0.018 (random error on mean) for isotropic orbits with βr = 0, ±0.1 (syst.) and σγ � 0.20 +0.04 −0.02 intrinsic scatter (all errors indicate the 68% CL). We find no correlation of γ � LD with galaxy mass (Meff), rescaled radius (i.e., Reinst/Reff) or redshift, despite intrinsic differences in density-slope between galaxies. Based on scaling relations, the average logarithmic density slope can be derived in an alternative manner, fully independent from dynamics, yielding � γ � SR �= 1.959 ± 0.077. Agreement between the two values is reached for � βr �= 0.45 ± 0.25, consistent with mild radial anisotropy. This agreement supports the robustness of our results, despite the increase in mass-to-light ratio with total galaxy mass: Meff ∝ L 1.363±0.056 V, eff . We conclude that massive ETGs are structurally close to homologous with close to isothermal total density profiles (10% intrinsic scatter) and have at most some mild radial anisotropy. Our results provide new observational limits on galaxy formation and evolution scenarios, covering 4 Gyr look-back time.

DARK MATTER CONTRACTION AND THE STELLAR CONTENT OF MASSIVE EARLY-TYPE GALAXIES: DISFAVORING 'LIGHT' INITIAL MASS FUNCTIONS

We use stellar dynamics, strong lensing, stellar population synthesis models, and weak lensing shear measurements to constrain the dark matter (DM) profile and stellar mass in a sample of 53 massive early-type galaxies. We explore three DM halo models (unperturbed Navarro, Frenk, and White (NFW) halos and the adiabatic contraction models of Blumenthal and Gnedin) and impose a model for the relationship between the stellar and virial mass (i.e., a relationship for the star formation efficiency as a function of halo mass). We show that, given our model assumptions, the data clearly prefer a Salpeter-like initial mass function (IMF) over a lighter IMF (e.g., Chabrier or Kroupa), irrespective of the choice of DM halo. In addition, we find that the data prefer at most a moderate amount of adiabatic contraction (Blumenthal adiabatic contraction is strongly disfavored) and are only consistent with no adiabatic contraction (i.e., an NFW halo) if a mass-dependent IMF is assumed, in the sense of a more massive normalization of the IMF for more massive halos.

Gravitational detection of a low-mass dark satellite galaxy at cosmological distance

The mass function of dwarf satellite galaxies that are observed around Local Group galaxies differs substantially from simulations based on cold dark matter: the simulations predict many more dwarf galaxies than are seen. The Local Group, however, may be anomalous in this regard. A massive dark satellite in an early-type lens galaxy at a redshift of 0.222 was recently found using a method based on gravitational lensing, suggesting that the mass fraction contained in substructure could be higher than is predicted from simulations. The lack of very low-mass detections, however, prohibited any constraint on their mass function. Here we report the presence of a (1.9 ± 0.1) × 108 dark satellite galaxy in the Einstein ring system JVAS B1938+666 (ref. 11) at a redshift of 0.881, where denotes the solar mass. This satellite galaxy has a mass similar to that of the Sagittarius galaxy, which is a satellite of the Milky Way. We determine the logarithmic slope of the mass function for substructure beyond the local Universe to be , with an average mass fraction of per cent, by combining data on both of these recently discovered galaxies. Our results are consistent with the predictions from cold dark matter simulations at the 95 per cent confidence level, and therefore agree with the view that galaxies formed hierarchically in a Universe composed of cold dark matter.

THE RELATION BETWEEN BLACK HOLE MASS AND HOST SPHEROID STELLAR MASS OUT TO z ∼ 2

We combine Hubble Space Telescope images from the Great Observatories Origins Deep Survey with archival Very Large Telescope and Keck spectra of a sample of 11 X-ray-selected broad-line active galactic nuclei in the redshift range 1 < z < 2 to study the black-hole-mass-stellar-mass relation out to a look-back time of 10Gyr. Stellar masses of the spheroidal component (M sph,*) are derived from multi-filter surface photometry. Black hole masses (MBH) are estimated from the width of the broad MgII emission line and the 3000 A nuclear luminosity. Comparing with a uniformly measured local sample and taking into account selection effects, we find evolution in the form MBH/Msph,*(1 + z) 1.96 ± 0.55, in agreement with our earlier studies based on spheroid luminosity. However, this result is more accurate because it does not require a correction for luminosity evolution and therefore avoids the related and dominant systematic uncertainty. We also measure total stellar masses (Mhost,*). Combining our sample with data from the literature, we find M BH/Mhost,*(1 + z) 1.15 ±0.15, consistent with the hypothesis that black holes (in the range MBH ∼108-9 M⊙) pre-date the formation of their host galaxies. Roughly, one-third of our objects reside in spiral galaxies; none of the host galaxies reveal signs of interaction or major merger activity. Combined with the slower evolution in host stellar masses compared to spheroid stellar masses, our results indicate that secular evolution or minor mergers play a non-negligible role in growing both BHs and spheroids.

H0LiCOW - V. New COSMOGRAIL time delays of HE 0435-1223: H0 to 3.8 per cent precision from strong lensing in a flat ΛCDM model

We present a new measurement of the Hubble Constant H-0 and other cosmological parameters based on the joint analysis of three multiply imaged quasar systems with measured gravitational time delays. First, we measure the time delay of HE 0435-1223 from 13-yr light curves obtained as part of the COSMOGRAIL project. Companion papers detail the modelling of the main deflectors and line-of-sight effects, and how these data are combined to determine the time-delay distance of HE 0435-1223. Crucially, the measurements are carried out blindly with respect to cosmological parameters in order to avoid confirmation bias. We then combine the time-delay distance of HE 0435-1223 with previous measurements from systems B1608+656 and RXJ1131-1231 to create a Time Delay Strong Lensing probe (IDSL). In flat A cold dark matter (ACDM) with free matter and energy density, we find H-0 = 71.9(-3.0)(+2.4) km s(-1) Mpc(-1) and Omega(Lambda) = 0.62(-0.35)(+0.24) This measurement is completely independent of, and in agreement with, the local distance ladder measurements of H-0. We explore more general cosmological models combining TDSL with other probes, illustrating its power to break degeneracies inherent to other methods. The joint constraints from IDSL and Planck are H-0 = 69.2(-2.2)(+1.4) km s(-1) Mpc(-1), Omega(Lambda) = 0.70(-0.01)(+0.01) and Omega(k) = 0.003(-0.006)(+0.004) in open ACDM and H-0 = 79.0(-4.2)(+4.4) km s(-1) Mpc(-1), Omega(de) = 0.77(-0.03)(+0.02) and w = -1.38(-0.16)(+0.14) in flat wCDM. In combination with Planck and baryon acoustic oscillation data, when relaxing the constraints on the numbers of relativistic species we find N-eff = 3.34(-0.21)(+0.21) in N-eff Lambda CDM and when relaxing the total mass of neutrinos we find Sigma rn(nu) <= 0.182 eV in m(nu) Lambda CDM. Finally, in an open wCDM in combination with Planck and cosmic microwave background lensing, we find H-0 = 77.9(-4.2)(+5.0) km s(-1) Mpc(-1), Omega(de) = 0.77(-0.03)(+0.03), Omega(k) = -0.003(-0.004)(+0.004) and w = -1.37(-0.23)(+0.18).

COSMIC EVOLUTION OF BLACK HOLES AND SPHEROIDS. IV. THE M BH-L sph RELATION

From high-resolution images of 23 Seyfert-1 galaxies at z = 0.36 and z = 0.57 obtained with the Near-Infrared Camera and Multi-Object Spectrometer on board the Hubble Space Telescope (HST), we determine host-galaxy morphology, nuclear luminosity, total host-galaxy luminosity, and spheroid luminosity. Keck spectroscopy is used to estimate black hole mass (M BH). We study the cosmic evolution of the M BH-spheroid luminosity (L sph) relation. In combination with our previous work, totaling 40 Seyfert-1 galaxies, the covered range in BH mass is substantially increased, allowing us to determine for the first time intrinsic scatter and correct evolutionary trends for selection effects. We re-analyze archival HST images of 19 local reverberation-mapped active galaxies to match the procedure adopted at intermediate redshift. Correcting spheroid luminosity for passive luminosity evolution and taking into account selection effects, we determine that at fixed present-day V-band spheroid luminosity, M BH/L sph?(1 + z)2.8? 1.2. When including a sample of 44 quasars out to z = 4.5 taken from the literature, with luminosity and BH mass corrected to a self-consistent calibration, we extend the BH mass range to over 2 orders of magnitude, resulting in M BH/L sph (1 + z)1.4? 0.2. The intrinsic scatter of the relation, assumed constant with redshift, is 0.3?? 0.1 dex (<0.6 dex at 95% CL). The evolutionary trend suggests that BH growth precedes spheroid assembly. Interestingly, the M BH-total-host-galaxy-luminosity relation is apparently non-evolving. It hints at either a more fundamental relation or that the spheroid grows by a redistribution of stars. However, the high-z sample does not follow this relation, indicating that major mergers may play the dominant role in growing spheroids above z 1.

CAN DRY MERGING EXPLAIN THE SIZE EVOLUTION OF EARLY-TYPE GALAXIES?

The characteristic size of early-type galaxies (ETGs) of given stellar mass is observed to increase significantly with cosmic time, from redshift z 2 to the present. A popular explanation for this size evolution is that ETGs grow through dissipationless (dry) mergers, thus becoming less compact. Combining N-body simulations with up-to-date scaling relations of local ETGs, we show that such an explanation is problematic, because dry mergers do not decrease the galaxy stellar-mass surface density enough to explain the observed size evolution, and also introduce substantial scatter in the scaling relations. Based on our set of simulations, we estimate that major and minor dry mergers increase half-light radius and projected velocity dispersion with stellar mass as R e M 1.09 ± 0.29 * and σe2 M 0.07 ± 0.11 *, respectively. This implies that: (1) if the high-z ETGs are indeed as dense as estimated, they cannot evolve into present-day ETGs via dry mergers; (2) present-day ETGs cannot have assembled more than ~45% of their stellar mass via dry mergers. Alternatively, dry mergers could be reconciled with the observations if there was extreme fine tuning between merger history and galaxy properties, at variance with our assumptions. Full cosmological simulations will be needed to evaluate whether this fine-tuned solution is acceptable.

DISENTANGLING BARYONS AND DARK MATTER IN THE SPIRAL GRAVITATIONAL LENS B1933+503

Measuring the relative mass contributions of luminous and dark matter in spiral galaxies is important for understanding their formation and evolution. The combination of a galaxy rotation curve and strong lensing is a powerful way to break the disk-halo degeneracy that is inherent in each of the methods individually. We present an analysis of the 10 image radio spiral lens B1933+503 at zl = 0.755, incorporating (1) new global very long baseline interferometry observations, (2) new adaptive-optics-assisted K-band imaging, and (3) new spectroscopic observations for the lens galaxy rotation curve and the source redshift. We construct a three-dimensionally axisymmetric mass distribution with three components: an exponential profile for the disk, a point mass for the bulge, and a Navarro-Frenk-White (NFW) profile for the halo. The mass model is simultaneously fitted to the kinematics and the lensing data. The NFW halo needs to be oblate with a flattening of a/c = 0.33^(+0.07)_(–0.05) to be consistent with the radio data. This suggests that baryons are effective at making the halos oblate near the center. The lensing and kinematics analysis probe the inner ~10 kpc of the galaxy, and we obtain a lower limit on the halo scale radius of 16 kpc (95% credible intervals). The dark matter mass fraction inside a sphere with a radius of 2.2 disk scale lengths is f_(DM, 2.2) = 0.43+0.10 –0.09. The contribution of the disk to the total circular velocity at 2.2 disk scale lengths is 0.76^(+0.05)_(–0.06), suggesting that the disk is marginally submaximal. The stellar mass of the disk from our modeling is log10(M_*/M_☉) = 11.06^(+0.09)_(–0.11) assuming that the cold gas contributes ~20% to the total disk mass. In comparison to the stellar masses estimated from stellar population synthesis models, the stellar initial mass function of Chabrier is preferred to that of Salpeter by a probability factor of 7.2.

Size and velocity-dispersion evolution of early-type galaxies in a Λ cold dark matter universe

Early-type galaxies (ETGs) are observed to be more compact at z≳ 2 than in the local Universe. Remarkably, much of this size evolution appears to take place in a short ∼1.8 Gyr time span between z∼ 2.2 and 1.3, which poses a serious challenge to hierarchical galaxy formation models where mergers occurring on a similar time-scale are the main mechanism for galaxy growth. We compute the merger-driven redshift evolution of stellar mass M_* ∝ (1+z)^(a_M), half-mass radius inline image and velocity dispersion M_* ∝ (1+z)^(a_R) predicted by concordance Λ cold dark matter for a typical massive ETG in the redshift range z∼ 1.3–2.2. Neglecting dissipative processes, and thus maximizing evolution in surface density, we find −1.5 ≲a_M≲−0.6, −1.9 ≲a_R≲−0.7 and 0.06 ≲a_σ≲ 0.22, under the assumption that the accreted satellites are spheroids. It follows that the predicted z ∼ 2.2 progenitors of z ∼ 1.3 ETGs are significantly less compact (on average a factor of ∼2 larger R_e at given M*) than the quiescent galaxies observed at z≳ 2. Furthermore, we find that the scatter introduced in the size–mass correlation by the predicted merger-driven growth is difficult to reconcile with the tightness of the observed scaling law. We conclude that – barring unknown systematics or selection biases in the current measurements – minor and major mergers with spheroids are not sufficient to explain the observed size growth of ETGs within the standard model.