A Multiwavelength view of IC 860: What Is in Action inside Quenching Galaxies

TL;DR

This study investigates the complex processes in the post-starburst galaxy IC 860, revealing multiphase outflows, a recent merger, and a buried AGN, which collectively influence its transition from star-forming to quiescent.

Contribution

It provides a detailed multiwavelength analysis of IC 860, highlighting the role of outflows, mergers, and AGN activity in galaxy quenching, with new insights into gas dynamics and star formation suppression.

Findings

Multiphase outflows are present but unlikely to escape the galaxy.

A recent merger is evidenced by optical and CO data.

The galaxy's gas depletion time is about 7 Gyr, indicating slow quenching.

Abstract

We present a multiwavelength study of IC 860, a nearby post-starburst galaxy at the early stage of transitioning from blue and star-forming to red and quiescent. Optical images reveal a galaxy-wide, dusty outflow originating from a compact core. We find evidence for a multiphase outflow in the molecular and neutral gas phase from the CO position-velocity diagram and NaD absorption features. We constrain the neutral mass outflow rate to be ~0.5 M$_{\odot}/$yr, and the total hydrogen mass outflow rate to be ~12 M$_{\odot}$/yr. Neither outflow component seems able to escape the galaxy. We also find evidence for a recent merger in the optical images, CO spatial distribution, and kinematics, and evidence for a buried AGN in the optical emission line ratios, mid-IR properties, and radio spectral shape. The depletion time of the molecular gas reservoir under the current star formation rate is ~7 Gyr, indicating that the galaxy could stay at the intermediate stage between the blue and red sequence for a long time. Thus the timescales for a significant decline in star formation rate ("quenching") and gas depletion are not necessarily the same. Our analysis supports the quenching picture where outflows help suppress star formation by disturbing rather than expelling the gas and shed light on possible ongoing activities in similar quenching galaxies.