CONFIRMING THE EXISTENCE OF A QUIESCENT GALAXY POPULATION OUT TO z = 3: A STACKING ANALYSIS OF MID-, FAR-INFRARED, AND RADIO DATA

Abstract

We performed a comprehensive stacking analysis on ∼14,200 quiescent galaxy (QG) candidates at z=0-3 across mid-, far-infrared (MIR and FIR), and radio wavelengths. Identified via their rest-frame NUV−r and r−J colors, the QG candidates (M M 10 9.8 12.2 - =  ) have drastically different IR and radio properties depending on their 24 μm emission strength. The fraction of QG candidates with strong 24 μm emission (equivalent to inferred star formation rates SFR M yr 100, hereafter "IR-bright") increases with redshift and peaks at 15%, and their stacked MIPS 24 μm, Herschel (PACS and SPIRE) and VLA emissions are consistent with being starforming galaxies (SFGs). In contrast, the majority of QG candidates are faint or undetected at 24 μm individually (i.e., SFR 24 <100 M e yr −1 , hereafter "IR-faint"). Their low dust-obscured SFRs derived from Herschel stacking (SFR H  3, 15, 50 M e yr −1 out to z∼1, 2, 3) are >2.5-12.5×lower than compared to SFGs. This is consistent with the quiescence, as expected from their low unobscured SFRs, as inferred from modeling their ultraviolet-to-NIR photometry. The discrepancy between the L IR derived from stacking Herschel and 24 μm indicates that IRfaint QGs have dust SEDs that are different from those of SFGs. For the most massive (M M 10 11    ) IR-faint QGs at z<1.5, the stacked 1.4 GHz emission is in excess of that expected from other SFR indicators, suggesting a widespread presence of low-luminosity active galactic nuclei. Our results reaffirm the existence of a significant population of QGs out to z=3, thus corroborating the need to quench star formation in galaxies at early epochs.

Stellar Mass Function of Active and Quiescent Galaxies via the Continuity Equation

“…Afterwards, the SFR is quenched by feedbacks and the galaxy will then evolve passively to become a local early-type; then it will populate a region of the SFR versus stellar mass diagram substantially below the main sequence. These loci of 'red and dead' galaxies are indeed observed locally (see Renzini & Peng 2015), and start to be pinpointed even at high redshift (see Man et al 2016). …”

Molecular Gas Contents and Scaling Relations for Massive, Passive Galaxies at Intermediate Redshifts from the LEGA-C Survey

“…Several authors have noted that the IR luminosity (or observed-frame 24 µm luminosity, generally the only available tracer of dust emission at low SFR and high redshift) can overestimate the obscured SFR of quiescent galaxies, in some cases quite severely (e.g., Salim et al 2009;Hayward et al 2014;Utomo et al 2014;Man et al 2016). This can be due to several effects, including the fact that the IR luminosity is a long-lived tracer compared to the instantaneous SFR, and 24 µm emission can be boosted by dust heating unrelated to star formation, including circumstellar dust heated by intermediate-age AGB stars, extended cirrus dust heated by old stellar populations, or weak nuclear activity.…”

“Super-deblended” Dust Emission in Galaxies. I. The GOODS-North Catalog and the Cosmic Star Formation Rate Density out to Redshift 6

“…In practice, passive sources that might be discarded in this way amount only to a small fraction (of order 10%-15%) of the total. This classification as passive is not always fully reliable, and in some cases galaxies classified as such might actually have positive IR emission (Man et al 2016;Gobat et al 2017). By discarding passive galaxy candidates, we could erroneously miss some genuine FIR-emitting galaxies in trade for a fairly small benefit.…”