[en] We constrain the post-Newtonian gravity parameter γ on kiloparsec scales by comparing the masses of 15 elliptical lensing galaxies from the Sloan Lens ACS Survey as determined in two independent ways. The first method assumes only that Newtonian gravity is correct and is independent of γ, while the second uses gravitational lensing which depends on γ. More specifically, we combine Einstein radii and radial surface-brightness gradient measurements of the lens galaxies with empirical distributions for the mass concentration and velocity anisotropy of elliptical galaxies in the local universe to predict γ-dependent probability distributions for the lens-galaxy velocity dispersions. By comparing with observed velocity dispersions, we derive a maximum-likelihood value of γ=0.98±0.07 (68% confidence). This result is in excellent agreement with the prediction of general relativity that γ=1, which has previously been verified to this accuracy only on solar-system length scales

[en] We present the observational results of a survey for strong gravitational lens systems consisting of extended emission-line galaxies lensed by intervening early-type galaxies, conducted using integral field units (IFUs) of the Magellan IMACS and Gemini GMOS-N spectrographs. These data are highly valuable for corroborating the lensing interpretation of Hubble Space Telescope imaging data. We show that in many cases, ground-based IFU spectroscopy is in fact competitive with space-based imaging for the measurement of the mass model parameters of the lensing galaxy. We demonstrate a novel technique of three-dimensional gravitational lens modeling for a single lens system with a resolved lensed rotation curve. We also describe the details of our custom IFU data analysis software, which performs optimal multi-fiber extraction, relative and absolute wavelength calibration to a few hundredths of a pixel RMS and nearly Poisson-limited sky subtraction

[en] Using big bang nucleosynthesis and present, high-precision measurements of light element abundances, we constrain the self-gravity of radiation pressure in the early universe. The self-gravity of pressure is strictly non-Newtonian, and thus the constraints we set provide a direct test of this prediction of general relativity and of the standard, Friedmann-Robertson-Walker cosmology

[en] We present the large-scale correlation function measured from a spectroscopic sample of 46,748 luminous red galaxies from the Sloan Digital Sky Survey. The survey region covers 0.72h^-3 Gpc³ over 3816 square degrees and 0.16 < z < 0.47, making it the best sample yet for the study of large-scale structure. We find a well-detected peak in the correlation function at 100h^-1 Mpc separation that is an excellent match to the predicted shape and location of the imprint of the recombination-epoch acoustic oscillations on the low-redshift clustering of matter. This detection demonstrates the linear growth of structure by gravitational instability between z ∼ 1000 and the present and confirms a firm prediction of the standard cosmological theory. The acoustic peak provides a standard ruler by which we can measure the ratio of the distances to z = 0.35 and z = 1089 to 4% fractional accuracy and the absolute distance to z = 0.35 to 5% accuracy. From the overall shape of the correlation function, we measure the matter density (Omega)_mh² to 8% and find agreement with the value from cosmic microwave background (CMB) anisotropies. Independent of the constraints provided by the CMB acoustic scale, we find (Omega)_m = 0.273 ± 0.025 + 0.123(1 + w₀) + 0.137(Omega)_K. Including the CMB acoustic scale, we find that the spatial curvature is (Omega)_K = -0.010 ± 0.009 if the dark energy is a cosmological constant. More generally, our results provide a measurement of cosmological distance, and hence an argument for dark energy, based on a geometric method with the same simple physics as the microwave background anisotropies. The standard cosmological model convincingly passes these new and robust tests of its fundamental properties

[en] We present an absorption line analysis of the Lyman limit system (LLS) at z ∼ 3.55 in our Magellan/MIKE spectrum of PKS2000 - 330. Our analysis of the Lyman limit and full H I Lyman series constrains the total H I column density of the LLS (N_HI = 10^18.0±0.25 cm^-2 for b_HI ≥ 20 km s^-1) and also the N_HI values of the velocity subsystems comprising the absorber. We measure ionic column densities for metal-line transitions associated with the subsystems and use these values to constrain the ionization state (>90% ionized) and relative abundances of the gas. We find an order of magnitude dispersion in the metallicities of the subsystems, marking the first detailed analysis of metallicity variations in an optically thick absorber. The results indicate that metals are not well mixed within the gas surrounding high z galaxies. Assuming a single-phase photoionization model, we also derive an N_H-weighted metallicity, ([Si/H]) = -1.66 ± 0.25, which matches the mean metallicity in the neutral interstellar medium in high z damped Lyα systems (DLAs). Because the line density of LLSs is over 10x higher than the DLAs, we propose that the former dominate the metal mass-density at z ∼ 3 and that these metals reside in the galaxy/intergalactic medium interface. Considerations of a multi-phase model do not qualitatively change these conclusions. Finally, we comment on an anomalously large O⁰/Si⁺ ratio in the LLS that suggests an ionizing radiation field dominated by soft UV sources (e.g., a starburst galaxy). Additional abundance analysis is performed on the super-LLS systems at z ∼ 3.19.

[en] We present an absorption-line survey of optically thick gas clouds—Lyman Limit Systems (LLSs)—observed at high dispersion with spectrometers on the Keck and Magellan telescopes. We measure column densities of neutral hydrogen $N_{\mathrm{H}\mathrm{I}}$ and associated metal-line transitions for 157 LLSs at $z_{\mathrm{L}\mathrm{L}\mathrm{S}}=1.76-<!--\; ???\; -->4.39$ restricted to ${10}^{17.3}{\mathrm{c}\mathrm{m}}^{-<!--\; ???\; -->2}⩽<!--\; ???\; -->N_{\mathrm{H}\mathrm{I}}<<!--\; <\; -->{10}^{20.3}{\mathrm{c}\mathrm{m}}^{-<!--\; ???\; -->2}.$ An empirical analysis of ionic ratios indicates an increasing ionization state of the gas with decreasing $N_{\mathrm{H}\mathrm{I}}$ and that the majority of LLSs are highly ionized, confirming previous expectations. The Si⁺/H⁰ ratio spans nearly four orders of magnitude, implying a large dispersion in the gas metallicity. Fewer than 5% of these LLSs have no positive detection of a metal transition; by $z\sim <!--\; ???\; -->3,$ nearly all gas that is dense enough to exhibit a very high Lyman limit opacity has previously been polluted by heavy elements. We add new measurements to the small subset of LLS (≈5%–10%) that may have super-solar abundances. High Si⁺/Fe⁺ ratios suggest an α-enhanced medium, whereas the Si⁺/C⁺ ratios do not exhibit the super-solar enhancement inferred previously for the Lyα forest.

[en] We report the discovery of significant mass/light offsets in the strong gravitational lensing system SDSS J1011+0143. We use the high-resolution Hubble Space Telescope (HST) F555W- and F814W-band imaging and Sloan Digital Sky Survey (SDSS) spectroscopy of this system, which consists of a close galaxy pair with a projected separation of $\approx <!--\; ???\; -->4.2\mathrm{k}\mathrm{p}\mathrm{c}$ at z_lens ∼ 0.331 lensing an Lyα emitter (LAE) at z_source = 2.701. Comparisons between the mass peaks inferred from lens models and light peaks from HST imaging data reveal significant spatial mass/light offsets as large as 1.72 ± 0.24 ± 0.34 kpc in both filter bands. Such large mass/light offsets, not seen in isolated field lens galaxies and relaxed galaxy groups, may be related to the interactions between the two lens galaxies. The detected mass/light offsets can potentially serve as an important test for the self-interacting dark matter model. However, other mechanisms such as dynamical friction on spatially differently distributed dark matter and stars could produce similar offsets. Detailed hydrodynamical simulations of galaxy–galaxy interactions with self-interacting dark matter could accurately quantify the effects of different mechanisms. The background LAE is found to contain three distinct star-forming knots with characteristic sizes from 116 to 438 pc. It highlights the power of strong gravitational lensing in probing the otherwise too faint and unresolved structures of distance objects below subkiloparsec or even 100 pc scales through its magnification effect.

[en] We present evidence that the incidence of active galactic nuclei (AGNs) and the distribution of their accretion rates do not depend on the stellar masses of their host galaxies, contrary to previous studies. We use hard (2-10 keV) X-ray data from three extragalactic fields (XMM-LSS, COSMOS, and ELAIS-S1) with redshifts from the Prism Multi-object Survey to identify 242 AGNs with L_2-10keV = 10^42-44 erg s^–1 within a parent sample of ∼25,000 galaxies at 0.2 < z < 1.0 over ∼3.4 deg² and to i ∼ 23. We find that although the fraction of galaxies hosting an AGN at fixed X-ray luminosity rises strongly with stellar mass, the distribution of X-ray luminosities is independent of mass. Furthermore, we show that the probability that a galaxy will host an AGN can be defined by a universal Eddington ratio distribution that is independent of the host galaxy stellar mass and has a power-law shape with slope –0.65. These results demonstrate that AGNs are prevalent at all stellar masses in the range 9.5< log M_*/M_sun<12 and that the same physical processes regulate AGN activity in all galaxies in this stellar mass range. While a higher AGN fraction may be observed in massive galaxies, this is a selection effect related to the underlying Eddington ratio distribution. We also find that the AGN fraction drops rapidly between z ∼ 1 and the present day and is moderately enhanced (factor ∼2) in galaxies with blue or green optical colors. Consequently, while AGN activity and star formation appear to be globally correlated, we do not find evidence that the presence of an AGN is related to the quenching of star formation or the color transformation of galaxies.

[en] Tidal interactions between galaxies can trigger star formation, which contributes to the global star formation rate (SFR) density of the universe and could be a factor in the transformation of blue, star-forming galaxies to red, quiescent galaxies over cosmic time. We investigate tidally triggered star formation in isolated close galaxy pairs drawn from the Prism Multi-Object Survey (PRIMUS), a low-dispersion prism redshift survey that has measured ∼120,000 robust galaxy redshifts over 9.1 deg² out to z ∼ 1. We select a sample of galaxies in isolated galaxy pairs at redshifts 0.25 ≤ z ≤ 0.75, with no other objects within a projected separation of 300 h^-1 kpc and Δz/(1 + z) = 0.01, and compare them to a control sample of isolated galaxies to test for systematic differences in their rest-frame FUV - r and NUV - r colors as a proxy for relative specific star formation rates (SSFRs). We find that galaxies in r_p ≤ 50 h^-1 kpc pairs have bluer dust-corrected UV - r colors on average than the control galaxies by -0.134 ± 0.045 mag in FUV - r and -0.075 ± 0.038 mag in NUV - r, corresponding to an ∼15%-20% increase in SSFR. This indicates an enhancement in SSFR due to tidal interactions. We also find that this relative enhancement is greater for a subset of r_p ≤ 30 h^-1 kpc pair galaxies, for which the average color offsets are -0.193 ± 0.065 mag in FUV - r and -0.159 ± 0.048 mag in NUV - r, corresponding to an ∼25%-30% increase in SSFR. We test for evolution in the enhancement of tidally triggered star formation with redshift across our sample redshift range and find marginal evidence for a decrease in SSFR enhancement from 0.25 ≤ z ≤ 0.5 to 0.5 ≤ z ≤ 0.75. This indicates that a change in enhanced star formation triggered by tidal interactions in low-density environments is not a contributor to the decline in the global SFR density across this redshift range.

[en] We study the relation between the internal structure of early-type galaxies and their environment using 70 strong gravitational lenses from the SLACS Survey. The Sloan Digital Sky Survey (SDSS) 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 (Σ₁₀) and within a cone of radius one h^-1 Mpc (D ₁). Our main results are as follows. (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' nonlens galaxies selected from SDSS to have the same redshift and stellar velocity dispersion σ_*. 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 percent in local mass density, 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 galaxies is found. (5) Satellite galaxies (those with a more luminous companion) have marginally steeper mass-density profiles (as quantified by f _SIE = σ_*/σ_SIE = 1.12 ± 0.05 versus 1.01 ± 0.01) and smaller dynamically normalized mass enclosed within the Einstein radius (Δlog M _Ein/M _dim differs by -0.09 ± 0.03 dex) 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.