Galaxies rest-frame ultraviolet (UV) properties are often used to directly infer the degree to which dust obscuration affects the measurement of star formation rates. While much recent work has focused on calibrating dust attenuation in galaxies sele
cted at rest-frame ultraviolet wavelengths, locally and at high-$z$, here we investigate attenuation in dusty, star-forming galaxies (DSFGs) selected at far-infrared wavelengths. By combining multiwavelength coverage across 0.15--500,$mu$m in the COSMOS field, in particular making use of {it Herschel} imaging, and a rich dataset on local galaxies, we find a empirical variation in the relationship between rest-frame UV slope ($beta$) and ratio of infrared-to-ultraviolet emission ($L_{rm IR}/L_{rm UV}equiv,IRX$) as a function of infrared luminosity, or total star formation rate, SFR. Both locally and at high-$z$, galaxies above SFR$gt$50,M$_odot$,yr$^{-1}$ deviate from the nominal $IRX-beta$ relation towards bluer colors by a factor proportional to their increasing IR luminosity. We also estimate contamination rates of DSFGs on high-$z$ dropout searches of $ll1$% at $zlt4-10$, providing independent verification that contamination from very dusty foreground galaxies is low in LBG searches. Overall, our results are consistent with the physical interpretation that DSFGs, e.g. galaxies with $>50$,M$_odot$,yr$^{-1}$, are dominated at all epochs by short-lived, extreme burst events, producing many young O and B stars that are primarily, yet not entirely, enshrouded in thick dust cocoons. The blue rest-frame UV slopes of DSFGs are inconsistent with the suggestion that most DSFGs at $zsim2$ exhibit steady-state star formation in secular disks.
We present X-ray data for a complete sample of 44 luminous infrared galaxies (LIRGs), obtained with the Chandra X-ray Observatory. These are the X-ray observations of the high luminosity portion of the Great Observatory All-sky LIRG Survey (GOALS), w
hich includes the most luminous infrared selected galaxies, log (Lir/Lsun) > 11.73, in the local universe, z < 0.088. X-rays were detected from 43 out of 44 objects, and their arcsec-resolution images, spectra, and radial brightness distributions are presented. With a selection by hard X-ray colour and the 6.4 keV iron line, AGN are found in 37% of the objects, with higher luminosity sources more likely to contain an AGN. These AGN also tend to be found in late-stage mergers. The AGN fraction would increase to 48% if objects with mid-IR [Ne V] detection are included. Double AGN are clearly detected only in NGC 6240 among 24 double/triple systems. Other AGN are found either in single nucleus objects or in one of the double nuclei at similar rates. Objects without conventional X-ray signatures of AGN appear to be hard X-ray quiet, relative to the X-ray to far-IR correlation for starburst galaxies, as discussed elsewhere. Most objects also show extended soft X-ray emission, which is likely related to an outflow from the nuclear region, with a metal abundance pattern suggesting enrichment by core collapse supernovae, as expected for a starburst.
