Gravitational Lensing Reveals Cool Gas within 10-20 kpc around a Quiescent Galaxy

TL;DR

This study uses gravitational lensing and integral-field spectroscopy to detect substantial amounts of cool gas within 10-20 kpc of a quiescent galaxy, challenging previous assumptions about the inner CGM of such galaxies.

Contribution

It introduces a novel method combining gravitational lensing with spectroscopy to directly observe the inner CGM of a quiescent galaxy, revealing significant cool gas presence.

Findings

Detection of large amounts of cool gas (MgII absorption) within 10-20 kpc of the galaxy.

Identification of a diffuse, asymmetric mass component consistent with the MgII absorption.

Demonstration of gravitational lensing as a tool to probe both gas and mass in galaxy halos.

Abstract

While quiescent galaxies have comparable amounts of cool gas in their outer circumgalactic medium (CGM) compared to star-forming galaxies, they have significantly less interstellar gas. However, open questions remain on the processes causing galaxies to stop forming stars and stay quiescent . Theories suggest dynamical interactions with the hot corona prevent cool gas from reaching the galaxy, therefore predicting the inner regions of quiescent galaxy CGMs are devoid of cool gas. However, there is a lack of understanding of the inner regions of CGMs due to the lack of spatial information in quasar-sightline methods. We present integral-field spectroscopy probing 10--20~kpc (2.4--4.8 R\textsubscript{e}) around a massive quiescent galaxy using a gravitationally lensed star-forming galaxy. We detect absorption from Magnesium (MgII) implying large amounts of cool atomic gas (10\textsuperscript{8.4} -- 10\textsuperscript{9.3} M\textsubscript{$\odot$} with T$\sim$10\textsuperscript{4} Kelvin), in comparable amounts to star-forming galaxies. Lens modeling of Hubble imaging also reveals a diffuse asymmetric component of significant mass consistent with the spatial extent of the MgII absorption, and offset from the galaxy light profile. This study demonstrates the power of galaxy-scale gravitational lenses to not only probe the gas around galaxies, but to also independently probe the mass of the CGM due to it's gravitational effect.