OBSCURED STAR FORMATION IN INTERMEDIATE-DENSITY ENVIRONMENTS: ASPITZERSTUDY OF THE ABELL 901/902 SUPERCLUSTER

Abstract

We explore the amount of obscured star-formation as a function of environment in the A901/902 supercluster at z = 0.165 in conjunction with a field sample drawn from the A901 and CDFS fields, imaged with HST as part of the STAGES and GEMS surveys. We combine the COMBO-17 near-UV/optical SED with Spitzer 24µm photometry to estimate both the unobscured and obscured star formation in galaxies with M * > 10 10 M ⊙ . We find that the star formation activity in massive galaxies is suppressed in dense environments, in agreement with previous studies. Yet, nearly 40% of the star-forming galaxies have red optical colors at intermediate and high densities. These red systems are not starbursting; they have star formation rates per unit stellar mass similar to or lower than blue starforming galaxies. More than half of the red star-forming galaxies have low IR-to-UV luminosity ratios, relatively high Sersic indices and they are equally abundant at all densities. They might be gradually quenching their starformation, possibly but not necessarily under the influence of gas-removing environmental processes. The other 40% of the red star-forming galaxies have high IR-to-UV luminosity ratios, indicative of high dust obscuration. They have relatively high specific star formation rates and are more abundant at intermediate densities.Our results indicate that while there is an overall suppression in the star-forming galaxy fraction with density, the small amount of star formation surviving the cluster environment is to a large extent obscured, suggesting that environmental interactions trigger a phase of obscured star formation, before complete quenching.

LoCuSS: Shedding new light on the massive lensing cluster Abell 1689 – the view fromHerschel

“…1; top right). This is consistent with the findings of STAGES that the dusty red galaxies prefer the intermediate-density environment of cluster infall regions (Gallazzi et al 2009;Wolf et al 2009), and morphologically they found ∼70% to be Sa/Sb spirals with a bright nucleus or inner bar/disk, as well as a few cases of interactions or merger remnants, suggestive of galaxy harassment, interactions or mergers for their origin.…”

Ram pressure and dusty red galaxies – key factors in the evolution of the multiple cluster system Abell 901/902

“…It is therefore an interesting laboratory to investigate the interplay between galaxy evolution and environment. Gallazzi et al (2009) demonstrate the general suppression of star formation at higher galaxy number densities in the STAGES system, and find that a high fraction of the remaining star formation in the cluster is either obscured or dominated by old stellar populations. Therefore dusty star-forming galaxies are predominant at intermediate densities.…”

Hidden starbursts and active galactic nuclei at 0 < z < 4 from theHerschel-VVDS-CFHTLS-D1 field: Inferences on coevolution and feedback

“…Though galaxies undergoing a starburst event are commonly associated with a late-type morphology (i.e., spiral, irregular, or chaotic), a non-negligible fraction of starbursts are, surprisingly, associated with early-types (Mobasher et al 2004;Poggianti et al 2009;Abramson et al 2013). Additionally, starbursts are observed in hosts that span a wide range of stellar masses (e.g., Lehnert & Heckman 1996;Elbaz et al 2011, Hilton et al 2012Ibar et al 2013), color properties (e.g., Kartaltepe et al 2010b;Kocevski et al 2011a), and environments (e.g., Marcillac et al 2008;Gallazzi et al 2009;Hwang et al 2010a;Lemaux et al 2012;Dressler et al 2013). And though some starbursting populations show morphologies indicative of a recent merging or tidal interactions, others appear primarily as undisturbed, grand-design spirals, with little evidence of recent interactions with their surroundings (see, e.g., Ravindranath et al 2006;Kocevski et al 2011a;Tadhunter et al 2011).…”