Tracing Recent Star Formation of Red Early-type Galaxies out to $z$ $\sim$ 1

TL;DR

This study investigates mid-infrared excess emission in red early-type galaxies up to redshift 1, revealing that recent star formation is common even among massive, quiescent galaxies, using multi-wavelength color diagnostics.

Contribution

It provides new evidence that recent star formation occurs frequently in red early-type galaxies at z<1, utilizing mid-IR data and color diagnostics to identify star-forming activity.

Findings

Over 18% of massive ETGs show mid-IR excess indicating recent star formation.

Mid-IR and UV color diagnostics effectively distinguish quiescent from star-forming galaxies.

Recent star formation is common among red ETGs up to z~1.

Abstract

We study the mid-infrared (IR) excess emission of early-type galaxies (ETGs) on the red-sequence at $z <$ 1 using a spectroscopic sample of galaxies in the fields of Great Observatories Origins Deep Survey (GOODS). In the mass-limited sample of 1025 galaxies with $M_{star}$ $>$ 10$^{10.5}$ $M_{\odot}$ and $0.4<z<1.05$, we identify 696 $Spitzer$ 24 $\mu$m detected (above the 5$\sigma$) galaxies and find them to have a wide range of NUV-$r$ and $r$-[12 $\mu$m] colors despite their red optical $u-r$ colors. Even in the sample of very massive ETGs on the red sequence with $M_{star}$ $>$ 10$^{11.2}$ $M_{\odot}$, more than 18% show excess emission over the photospheric emission in the mid-IR. The combination with the results of red ETGs in the local universe suggests that the recent star formation is not rare among quiescent, red ETGs at least out to $z \sim 1$ if the mid-IR excess emission results from intermediate-age stars or/and from low-level ongoing star formation. Our color$-$color diagram including near-UV and mid-IR emissions are efficient not only for identifying ETGs with recent star formation, but also for distinguishing quiescent galaxies from dusty star-forming galaxies.