Joseph A. Muñoz

Dust and Extinction Curves in Galaxies with z > 0: The Interstellar Medium of Gravitational Lens Galaxies*

We determine 37 differential extinctions in 23 gravitational lens galaxies over the range 0 zl 1. Only seven of the 23 systems have spectral differences consistent with no differential extinction. The median differential extinction for the optically selected (radio-selected) subsample is ΔE(B-V) = 0.04 (0.06) mag. The extinction is patchy and shows no correlation with impact parameter. The median total extinction of the bluest images is E(B-V) = 0.08 mag, although the total extinction distribution is dominated by the uncertainties in the intrinsic colors of quasars. The directly measured extinction distributions are consistent with the mean extinction estimated by comparing the statistics of quasar and radio lens surveys, thereby confirming the need for extinction corrections when using the statistics of lensed quasars to estimate the cosmological model. A disjoint subsample of two face-on, radio-selected spiral lenses shows both high differential and total extinctions, but standard dust-to-gas ratios combined with the observed molecular gas column densities overpredict the amount of extinction by factors of 2-5. For several systems we can estimate the extinction law, ranging from RV = 1.5 ± 0.2 for a zl = 0.96 elliptical, to RV = 7.2 ± 0.1 for a zl = 0.68 spiral. For the four radio lenses where we can construct nonparametric extinction curves, we find no evidence for gray dust over the IR-UV wavelength range. The dust can be used to estimate lens redshifts with reasonable accuracy, although we sometimes find two degenerate redshift solutions.

The Fundamental Plane of Gravitational Lens Galaxies and The Evolution of Early-Type Galaxies in Low-Density Environments

Most gravitational lenses are early-type galaxies in relatively low density environments—a field rather than a cluster population. Their average properties are the mass-averaged properties of all early-type galaxies. We show that field early-type galaxies with 0 < z < 1, as represented by the lens galaxies, lie on the same fundamental plane as those in rich clusters at similar redshifts. We then use the fundamental plane to measure the combined evolutionary and K-corrections for early-type galaxies in the V, I, and H bands. Only for passively evolving stellar populations formed at zf 2 (H0 = 65 km s-1 Mpc-1, Ω0 = 0.3, λ0 = 0.7) can the lens galaxies be matched to the local fundamental plane. The high formation epoch and the lack of significant differences between the field and cluster populations contradict many current models of the formation history of early-type galaxies. Lens galaxy colors and the fundamental plane provide good photometric redshift estimates with an empirical accuracy of zFP - zl = -0.04 ± 0.09 for the 20 lenses with known redshifts. A mass model dominated by dark matter is more consistent with the data than either an isotropic or radially anisotropic constant M/L mass model, and a radially anisotropic model is better than an isotropic model.

Hubble Space Telescope Observations of 10 Two-Image Gravitational Lenses

We report on a program to obtain HST observations of galaxy-mass gravitational lens systems at optical and infrared wavelengths. Here we discuss the properties of 10 two-image gravitational lens systems (Q0142-100=UM673, B0218+357, SBS0909+532, BRI0952-0115, LBQS1009-0252, Q1017-207=J03.13, B1030+074, HE1104-1805, Q1208+1011, and PKS1830-211). We grouped these 10 systems because they have limited lens model constraints and often show poor contrast between the images and the lens galaxy. Of the 10 lens galaxies, 7 are probably early-type galaxies, 2 are probably late-type galaxies (B0218+357 and PKS1830-211), and one was not detected (Q1208+1011). We detect the host galaxies of the z_s=4.50 lensed quasar in BRI0952-0115, the z_s=2.32 lensed quasar in HE1104-1805, and the unlensed z=1.63 quasar near LBQS1009-0252. We fit a set of four standard lens models to each lens that had sufficient constraints to compare isothermal dark matter and constant mass-to-light lens models, and to explore the effects of local tidal shears.We report on a program to obtain HST observations of galaxy-mass gravitational lens systems at optical and infrared wavelengths. Here we discuss the properties of 10 two-image gravitational lens systems (Q0142-100=UM673, B0218+357, SBS0909+532, BRI0952-0115, LBQS1009-0252, Q1017-207=J03.13, B1030+074, HE1104-1805, Q1208+1011, and PKS1830-211). We grouped these 10 systems because they have limited lens model constraints and often show poor contrast between the images and the lens galaxy. Of the 10 lens galaxies, 7 are probably early-type galaxies, 2 are probably late-type galaxies (B0218+357 and PKS1830-211), and one was not detected (Q1208+1011). We detect the host galaxies of the z_s=4.50 lensed quasar in BRI0952-0115, the z_s=2.32 lensed quasar in HE1104-1805, and the unlensed z=1.63 quasar near LBQS1009-0252. We fit a set of four standard lens models to each lens that had sufficient constraints to compare isothermal dark matter and constant mass-to-light lens models, and to explore the effects of local tidal shears.

Constraining the Minimum Mass of High-redshift Galaxies and their Contribution to the Ionization State of the Intergalactic Medium

We model the latest HST WFPC3/IR observations of 100 galaxies at redshifts z = 7-8 in terms of a hierarchical galaxy formation model with starburst activity. Our model provides a distribution of UV luminosities per dark matter halo of a given mass and a natural explanation for the fraction of halos hosting galaxies. The observed luminosity function is best fit with a minimum halo mass per galaxy of , corresponding to a virial temperature of . Extrapolating to faint, undetected galaxies, the total production rate of ionizing radiation depends critically on this minimum mass. Future measurements with JWST should determine whether the entire galaxy population can comfortably account for the UV background required to keep the intergalactic medium ionized.

Probing the epoch of reionization with Milky Way satellites

While the connection between high-redshift star formation and the local Universe has recently been used to understand the observed population of faint dwarf galaxies in the Milky Way (MW) halo, we explore how well these nearby objects can probe the epoch of first light. We construct a detailed, physically motivated model for the MW satellites based on the state-of-the-art Via Lactea II dark-matter simulations. Our model incorporates molecular hydrogen (H 2 ) cooling in low-mass systems and inhomogeneous photoheating feedback during the internal reionization of our own Galaxy. We find that the existence of MW satellites fainter than M V ≈ -5 is strong evidence for H 2 cooling in low-mass haloes, while satellites with ―5 > M v > -9 were affected by hydrogen cooling and photoheating feedback. The age of stars in very low-luminosity systems and the minimum luminosity of these satellites are key predictions of our model. Most of the stars populating the brightest MW satellites could have formed after the epoch of reionization. Our models also predict a significantly larger dispersion in M 300 values than observed and a number of luminous satellites with M 300 as low as 10 6 M ⊙ .

OVERDENSITIES OF Y-DROPOUT GALAXIES FROM THE BRIGHTEST-OF-REIONIZING GALAXIES SURVEY: A CANDIDATE PROTOCLUSTER AT REDSHIFT z ≈ 8*

Theoretical and numerical modeling of the assembly of dark-matter halos predicts that the most massive and luminous galaxies at high redshift are surrounded by overdensities of fainter companions. We test this prediction with Hubble Space Telescope observations acquired by our Brightest of Reionizing Galaxies (BoRG) survey, which identified four very bright z ∼ 8 candidates as Y098-dropout sources in four of the 23 non-contiguous WFC3 fields observed. We extend here the search for Y098dropouts to fainter luminosities (M∗ galaxies with MAB ∼ −20), with detections at > 5� confidence (compared to the 8� confidence threshold adopted earlier) identifying 17 new candidates. We demonstrate that there is a correlation between number counts of faint and bright Y098-dropouts at > 99.84% confidence. Field BoRG58, which contains the best bright z ∼ 8 candidate (MAB = −21.3), has the most significant overdensity of faint Y098-dropouts. Four new sources are located within 70 ′′ (corresponding to 3.1 comoving Mpc at z = 8) from the previously known brighter z ∼ 8 candidate. The overdensity of Y098-dropouts in this field has a physical origin to very high confidence (p > 99.975%), independent of completeness and contamination rate of the Y098-dropout selection. We modeled the overdensity by means of cosmological simulations and estimate that the principal dark matter halo has mass Mh ≈ (4−7)×10 11 M⊙ (∼ 5� density peak) and is surrounded by several Mh ≈ 10 11 M⊙ halos which could host the fainter dropouts. In this scenario, we predict that all halos will eventually merge into a Mh > 2 × 10 14 M⊙ galaxy cluster by z = 0. Follow-up observations with ground and space

The host haloes of O I absorbers in the reionization epoch

We use a radiation hydrodynamic simulation of the hydrogen reionization epoch to study OI absorbers at z � 6. The intergalactic medium (IGM) is reionized before it is enriched, hence OI absorption originates within dark matter halos. The predicted abundance of OI absorbers is in reasonable agreement with observations. At z = 10, � 70% of sightlines through atomically-cooled halos encounter a visible (NOI > 10 14 cm −2 ) column. Reionization ionizes and removes gas from halos less massive than 10 8.4 M⊙, but 20% of sightlines through more massive halos encounter visible columns even at z = 5. The mass scale of absorber host halos is 10-100× smaller than the halos of Lyman break galaxies and Lyman-� emitters, hence absorption probes the dominant ionizing sources more directly. OI absorbers have neutral hydrogen columns of 10 19 -10 21 cm −2 , suggesting a close resemblance between objects selected in OI and HI absorption. Finally, the absorption in the foreground of the z = 7.085 quasar ULASJ1120+0641 cannot originate in a dark matter halo because halo gas at the observed HI column density is enriched enough to violate the upper limits on the OI column. By contrast, gas at less than one third the cosmic mean density satisfies the constraints. Hence the foreground absorption likely originates in the IGM.

The Infrared Einstein Ring in the Gravitational Lens MG J1131+0456 and the Death of the Dusty Lens Hypothesis*

We have obtained and modeled NICMOS images of the Einstein ring lens system MG J1131+0456, which show that its lens galaxy is an H = 18.6 mag, transparent, early-type galaxy at a redshift of zl 0.84; it has a major axis effective radius Re = 07 ? 01, projected axis ratio b/a = 0.6 ? 0.1, and major axis P.A. = 55? ? 9?. The lens is the brightest member of a group of at least seven galaxies with similar R-I and I-H colors, and the two closest group members produce sufficient tidal perturbations to explain the shape of the ring. The host galaxy of the MG J1131+0456 source is a zs 2 extremely red object (ERO) that is lensed into optical and infrared rings of dramatically different morphologies. These differences imply a strongly wavelength-dependent source morphology that could be explained by embedding the host in a larger, dusty disk. At 1.6 ?m (H), the ring is spectacularly luminous, with a total observed flux of H = 17.4 mag and a demagnified flux of 19.3 mag, corresponding to a 1-2 L* galaxy at the probable source redshift of zs 2. Thus, it is primarily the stellar emission of the radio source host galaxy that produces the overall colors of two of the reddest radio lenses, MG J1131+0456 and JVAS B1938+666, aided by the suppression of optical active galactic nucleus emission by dust in the source galaxy. The dusty lens hypothesis ? that many massive early-type galaxies with 0 zl 1 have large, uniform dust opacities ? is ruled out.

Multifrequency Analysis of the New Wide-Separation Gravitational Lens Candidate RX J0921+4529* **

We report the discovery of a new two-image gravitational lens candidate. The system RX J0921+4529 contains two zs = 1.66 quasars separated by 693 with an H-band magnitude difference of Δm = 1.39. The HST NIC2 H-band images reveal an H = 18.2 spiral galaxy between the quasar images, which is probably a member of a zl = 0.32 X-ray cluster centered on the field. We detect an extended source near the fainter quasar image but not in the brighter image. If this extended source is the host galaxy of the fainter quasar, then the system is a binary quasar rather than a gravitational lens. VLA observations at 3.6 cm reveal emission from the lens galaxy at the flux level of 1 mJy and a marginal detection of the brighter quasar.

The density contrast of the Shapley supercluster

We calculate the density contrast of the Shapley supercluster (SSC) based on the enhanced abundance of X-ray clusters in it using the extended Press-Schechter formalism. We derive a total SSC mass of M tot = (4.4 ± 0.44) x 10 16 M ⊙ within a sphere of 50 Mpc centred at a distance of about 160 Mpc. The non-linear fractional density contrast of the sphere is (1 + δ) = 1.76 ± 0.17 relative to the mean matter density in the Universe, but the contrast increases in the interior of the SSC. Including the cosmological constant, the SSC region is found to be gravitationally unbound. The SSC contributes only a minor portion (9.0 ±2.1 per cent) of the peculiar velocity of the Local Group.