Dying of the Light: An X-ray Fading Cold Quasar at z ~ 0.405

TL;DR

This study characterizes a rare cold quasar at z ~ 0.405, revealing its starburst nature, gas richness, variable AGN luminosity, and potential feedback outflow, shedding light on early AGN evolution stages.

Contribution

It provides multi-wavelength observations of a cold quasar, highlighting its co-existence of active star formation, cold gas, and an evolving AGN, which is a novel insight into early AGN feedback.

Findings

High gas mass fraction (~50-70%) in the galaxy.

AGN bolometric luminosity varies with observation method.

Candidate outflow feature indicating energetic feedback.

Abstract

Cold quasars are a rare subpopulation observed to host unobscured, X-ray luminous active galactic nuclei (AGN) while also retaining a cold gas supply fueling high star formation rates. These objects are interpreted as AGN early in their evolution. We present new SOFIA HAWC+ far-infrared observations, FUV-FIR photometry, and optical spectroscopy to characterize the accretion and star formation behavior in a cold quasar at z ~ 0.405 (CQ 4479). CQ 4479 is a starburst galaxy with a predominantly young stellar population and a high gas mass fraction of ~50-70%. The AGN component has yet to become the dominant component of the FIR emission. We also find AGN bolometric luminosity that varies as a function of observation method and AGN region probed. Finally, we identify a candidate outflow feature corroborating the hypothesis that cold quasars have energetic feedback. This object presents an intriguing look into the early stages of AGN feedback and probes the rare phase where an AGN and cold gaseous component co-exist.