Are Dusty Galaxies Blue? Insights on Uv Attenuation From Dust-Selected Galaxies

Abstract

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 selected at rest-frame ultraviolet wavelengths, locally and at high-z, here we investigate attenuation in dusty, star-forming galaxies (DSFGs) selected at farinfrared wavelengths. By combining multiwavelength coverage across 0.15-500 µm in the COSMOS field, in particular making use of Herschel imaging, and a rich dataset on local galaxies, we find a empirical variation in the relationship between rest-frame UV slope (β) and ratio of infrared-toultraviolet emission (L IR /L UV ≡IRX) as a function of infrared luminosity, or total star formation rate, SFR. Both locally and at high-z, galaxies above SFR > ∼ 50 M yr −1 deviate from the nominal IRX-β 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 1% at z < ∼ 4 − 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 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 z ∼ 2 exhibit steady-state star formation in secular disks.

Mapping the Lyα Emission around a z ∼ 6.6 QSO with MUSE: Extended Emission and a Companion at a Close Separation

“…However, UV radiation is able to leak through small openings in the dust cocoon. These leakages may be associated with short and extreme bursts of star formation that have been proposed to explain the intrinsically blue rest-frame UV slope observed in dusty, star-forming galaxies (SFR>50 M e yr −1 ) up to z∼5 (e.g., Casey et al 2014). A similar scenario was also proposed by Decarli et al (2012) to explain the lack of extended Lyα emission from the host galaxy of the two highly star-forming z>6 QSOs: SDSSJ1030+0524 and SDSSJ1148+5251 (see also Mechtley et al 2012).…”

Dust Properties of C ii Detected z ∼ 5.5 Galaxies: New HST/WFC3 Near-IR Observations

“…11 It is therefore a valid tool to study the ISM column density of galaxies (Meurer et al 1999;Kong et al 2004;Casey et al 2014). Furthermore, β is the only estimate of the dust content available for the vast majority of galaxies at z>3 due to the relative insensitivity of contemporary optical and IR surveys.…”

Dissecting the IRX–β dust attenuation relation: exploring the physical origin of observed variations in galaxies

“…There are many other works that have explored variations in the IRX -β relation and their physical cause in local galaxies (e.g., Burgarella, Buat & Iglesias-Páramo 2005;Seibert et al 2005;Cortese et al 2006;Gil de Paz et al 2007;Johnson et al 2007;Panuzzo et al 2007;Cortese et al 2008;Siana et al 2008;Boquien et al 2009;Muñoz-Mateos et al 2009;Wijesinghe et al 2011;Boquien et al 2012;Ye et al 2016). High-redshift observations have demonstrated that dusty star-forming galaxies (DSFGs) have bluer UV continuum slopes for a given IRX (increasingly deviating from the Meurer et al relation as a function of IR luminosity, e.g., Oteo et al 2013;Casey et al 2014;Bourne et al 2017). High-redshift Lyman Break Galaxies are observed to have redder UV continuum slopes β for a given IRX value, more consistent with a Small Magellanic Cloud (SMC) or Large Magellanic Cloud (LMC) attenuation curve than the canonical Meurer, Heckman & Calzetti (1999) relation (e.g., Capak et al 2015;Bouwens et al 2016;Koprowski et al 2016;Pope et al 2017;Smit et al 2017).…”