The Mid-Infrared and Near-Ultraviolet Excess Emissions of Quiescent Galaxies on the Red Sequence

Abstract

We study the mid-infrared (IR) and near-ultraviolet (UV) excess emissions of spectroscopically selected quiescent galaxies on the optical red sequence. We use the Wide-field Infrared Survey Explorer mid-IR and Galaxy Evolution Explorer near-UV data for a spectroscopic sample of galaxies in the Sloan Digital Sky Survey Data Release 7 to study the possible connection between quiescent red-sequence galaxies with and without mid-IR/near-UV excess. Among 648 12 μm detected quiescent red-sequence galaxies without Hα emission, 26% and 55% show near-UV and mid-IR excess emissions, respectively. When we consider only bright (M r < −21.5) galaxies with an early-type morphology, the fraction of galaxies with recent star formation is still 39%. The quiescent red-sequence galaxies with mid-IR and near-UV excess emissions are optically fainter and have slightly smaller D n 4000 than those without mid-IR and near-UV excess emissions. We also find that mid-IR weighted mean stellar ages of quiescent red-sequence galaxies with mid-IR excess are larger than those with near-UV excess, and smaller than those without mid-IR and near-UV excess. The environmental dependence of the fraction of quiescent red-sequence galaxies with mid-IR and near-UV excess seems strong even though the trends of quiescent red-sequence galaxies with near-UV excess differ from those with mid-IR excess. These results indicate that the recent star formation traced by near-UV ( 1 Gyr) and mid-IR ( 2 Gyr) excess is not negligible among nearby, quiescent, red, early-type galaxies. We suggest a possible evolutionary scenario of quiescent red-sequence galaxies from quiescent red-sequence galaxies with near-UV excess to those with mid-IR excess to those without near-UV and mid-IR excess.

SHOCKED POSTSTARBURST GALAXY SURVEY. II. THE MOLECULAR GAS CONTENT AND PROPERTIES OF A SUBSET OF SPOGs

“…Alatalo et al (2014a) presented theexistence of a prominent bifurcation between star-forming spiral galaxies and quiescent early-type galaxies in the WISE [4.6]- [12] μm bands, deeming this the "Infrared Transition Zone" (IRTZ). Early-type galaxies that were within this IRTZ were found to have red optical colors (also described in Ko et al 2013;Yesuf et al 2014), indicating that galaxies must traverse the optical green valley before the IRTZ.…”

Star Formation Activity of Barred Spiral Galaxies

“…The optical g − r color is a good tracer of star formation activity in galaxies (e.g., Strateva et al 2001;Blanton et al 2003). The NUV−r and [3.4]−[12] colors are good indicators of recent star formation activity of galaxies with slightly different timescales (e.g., Ko et al 2013Ko et al , 2016Lee et al 2015Lee et al , 2017; both NUV and mid-infrared are sensitive to very recent (< 1 Gyr) star formation, but only the mid-infrared is sensitive to star formation over longer (up to ∼ 2 Gyr) timescales. The flux ratio between Hα and Hβ (i.e., Balmer decrement) is a measure of dust extinction.…”

The Dependence of Cluster Galaxy Properties on the Central Entropy of Their Host Cluster

“…For instance, Ko et al (2013Ko et al ( , 2016 point out that recent star formation traced by near-UV and mid-IR excess is not negligible in nearby, quiescent early-type galaxies on the tight RS. …”