C. S. Kochanek

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.

The castles project

We describe the goals of the CASTLES (CfA-Arizona-Space-Telescope-LEns-Survey) project including a sample of NICMOS images of gravitational lenses and a brief list of the preliminary findings.

Results from the CASTLES survey of gravitational lenses

We show that most gravitational lenses lie on the passively evolving fundamental plane for early-type galaxies. For burst star formation models (1 Gyr of star formation, then quiescence) in low Ω 0 cosmologies, the stellar populations of the lens galaxies must have formed at z f ≳2. Typical lens galaxies contain modest amounts of patchy extinction, with a median differential extinction for the optical (radio) selected lenses of ΔE(B−V)=0.04(0.07) mag . The dust can be used to determine both extinction laws and lens redshifts. For example, the z l =0.96 elliptical lens in MG 0414+0534 has an R V =1.7±0.1 mean extinction law. Arc and ring images of the quasar and AGN source host galaxies are commonly seen in NICMOS H band observations. The hosts are typically blue, L≲L * galaxies.

Hst 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.