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We use observations from the CASTLES survey of gravitational lenses to study extinction in 23 lens galaxies with $0 < z_l < 1$. The median differential extinction between lensed images is $Delta E(bv) = 0.05$ mag, and the directly measured extinctions agree with the amount needed to explain the differences between the statistics of radio and (optical) quasar lens surveys. We also measure the first extinction laws outside the local universe, including an $R_V=7.2$ curve for a molecular cloud at $z_l=0.68$ and an $R_V=1.5$ curve for the dust in a redshift $z_l=0.96$ elliptical galaxy.
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We determine 37 differential extinctions in 23 gravitational lens galaxies over the range 0 < z_l < 1. Only 7 of the 23 systems have spectral differences consistent with no differential extinction. The median differential extinction for the optically-selected (radio-selected) subsample is E(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 R_V=1.5+/-0.2 for a z_l=0.96 elliptical, to R_V=7.2+/-0.1 for a z_l=0.68 spiral. For the four radio lenses where we can construct non-parametric 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.
To study the properties of the interstellar medium in the prototypical merging system of the Antennae galaxies (NGC 4038 and NGC 4039), we have obtained CO(1-0), (2-1) and (3-2) line maps, as well as a map of the 870 micron continuum emission. Our results are analysed in conjunction with data from X-ray to radio wavelengths. In order to distinguish between exact coincidence and merely close correspondence of emission features, we compare the morphological structure of the different emission components at the highest available angular resolution. To constrain the physical state of the molecular gas, we apply models of photon dominated regions (PDRs) that allow us to fit CO and [CII] data, as well as other indicators of widespread PDRs in the Antennae system, particularly within the super giant molecular cloud (SGMC) complexes of the interaction region (IAR) between the two galaxies. The modeled clouds have cores with moderately high gas densities up to 4 10^4 / cm^3 and rather low kinetic temperatures <=25K). At present, all these clouds, including those near the galactic nuclei, show no signs of intense starburst activity. Thermal radio or mid-infrared emission are all observed to peak slightly offset from the molecular peaks. The total molecular gas mass of the Antennae system adds up to ~10^10 M_sun. In the vicinity of each galactic nucleus, the moleculargas mass, 1-2 10^9 M_sun, exceeds that of the Galactic centre region by a factorof almost 100. Furthermore, the gas does not seem to deviate much from the N_{H_2}/I_CO ratio typical of the disk of our Galaxy rather than our Galactic centre.
We study the structure of spatially resolved, line-of-sight velocity dispersion for galaxies in the Epoch of Reionization (EoR) traced by [CII] $158murm{m}$ line emission. Our laboratory is a simulated prototypical Lyman-break galaxy, Freesia, part of the SERRA suite. The analysis encompasses the redshift range 6 < z < 8, when Freesia is in a very active assembling phase. We build velocity dispersion maps for three dynamically distinct evolutionary stages (Spiral Disk at z=7.4, Merger at z=8.0, and Disturbed Disk at z=6.5) using [CII] hyperspectral data cubes. We find that, at a high spatial resolution of 0.005 ($simeq 30 pc$), the luminosity-weighted average velocity dispersion is $sigma_{rm{CII}}$~23-38 km/s with the highest value belonging to the highly-structured Disturbed Disk stage. Low resolution observations tend to overestimate $sigma_{rm CII}$ values due to beam smearing effects that depend on the specific galaxy structure. For an angular resolution of 0.02 (0.1), the average velocity dispersion is 16-34% (52-115%) larger than the actual one. The [CII] emitting gas in Freesia has a Toomre parameter $mathcal{Q}$~0.2 and a rotational-to-dispersion ratio of $v_{rm c}/sigma$~ 7 similar to that observed in z=2-3 galaxies. The primary energy source for the velocity dispersion is due to gravitational processes, such as merging/accretion events; energy input from stellar feedback is generally subdominant (< 10%). Finally, we find that the resolved $sigma_{rm{CII}} - {Sigma}_{rm SFR}$ relation is relatively flat for $0.02<{Sigma}_{rm SFR}/{{rm M}_{odot}} mathrm{yr}^{-1} {mathrm kpc}^{-2} < 30$, with the majority of data lying on the derived analytical relation $sigma propto Sigma_{rm SFR}^{5/7}$. At high SFR, the increased contribution from stellar feedback steepens the relation, and $sigma_{rm{CII}}$ rises slightly.
Thanks to their proximity, local starbursts are perfectly suited for high-resolution and sensitivity multiwavelength observations aimed to test our ideas about star formation, evolution of massive stars, physics and chemical evolution of the interstellar medium (ISM). High-resolution UV spectroscopy with FUSE and STIS has recently given the possibility to characterize in great detail the neutral ISM in local starbursts thanks to the presence in this spectral range of many absorption lines from ions of the most common heavy elements. Here we present the results for two nearby starburst galaxies, I Zw 18 and NGC 1705, and show how these results relate to the star-formation history and evolutionary state of these stellar systems.
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