Confirming the Quiescent Galaxy Population out to $z=3$: A Stacking Analysis of Mid-, Far-Infrared and Radio Data

TL;DR

This study uses stacking analysis of infrared and radio data to confirm the existence of a large population of quiescent galaxies up to redshift 3, showing they have extremely low star formation rates and possible widespread low-luminosity AGN activity.

Contribution

It provides the first comprehensive constraints on the average infrared and radio emissions of quiescent galaxies out to z=3, confirming their low star formation and potential AGN presence.

Findings

Quiescent galaxies have star formation rates less than 0.1-3 M_sun/yr at z ≤ 2.

Stacked radio signals suggest widespread low-luminosity AGN among quiescent galaxies.

Existence of a significant quiescent galaxy population up to z=3 confirmed.

Abstract

We present stringent constraints on the average mid-, far-infrared and radio emissions of $\sim$14200 quiescent galaxies (QGs), identified out to $z=3$ in the COSMOS field via their rest-frame NUV$-$r and r$-$J colors, and with stellar masses $M_{\star}=10^{9.8-12.2} \,M_{\odot} $. Stacking in deep Spitzer (MIPS $24\,\mu$m), Herschel (PACS and SPIRE), and VLA (1.4 GHz) maps reveals extremely low dust-obscured star formation rates for QGs (SFR $<0.1-3\,M_{\odot}$yr$^{-1}$ at $z \leqslant 2$ and $<6-18\,M_{\odot}$yr$^{-1}$ at $z > 2$), consistent with the low unobscured SFRs ($<0.01-1.2\,M_{\odot}$yr$^{-1}$) inferred from modeling their ultraviolet-to-near-infrared photometry. The average SFRs of QGs are $>10\times$ below those of star-forming galaxies (SFGs) within the $M_{\star}$- and $z$-ranges considered. The stacked 1.4 GHz signals (S/N $> 5$) are, if attributed solely to star formation, in excess of the total (obscured plus unobscured) SFR limits, suggestive of a widespread presence of low-luminosity active galactic nuclei (AGN) among QGs. Our results reaffirm the existence of a significant population QGs out to $z = 3$, thus corroborating the need for powerful quenching mechanism(s) to terminate star formation in galaxies at earlier epochs.