The circumgalactic medium of eBOSS emission line galaxies: signatures of galactic outflows in gas distribution and kinematics

TL;DR

This study analyzes the distribution and motion of cool gas around emission line galaxies, revealing outflows driven by star formation that shape the gas's density and kinematic properties.

Contribution

It provides the first large-scale comparison of CGM properties between ELGs and LRGs, highlighting outflow signatures and differences in gas kinematics.

Findings

Stronger metal absorption around ELGs on small scales.

Anisotropic absorption indicating outflows along minor axes.

Velocity dispersion ratios suggest active outflows in ELGs.

Abstract

We study the distribution and kinematics of the cool circumgalactic medium (CGM) of emission line galaxies (ELGs) traced by metal absorption lines. Using about 200,000 ELGs from SDSS-IV eBOSS and half a million background quasars from SDSS, we measure the median absorption strength of MgII and FeII lines in quasar spectra for impact parameters ranging from 10 kpc to 1 Mpc. For comparison we measure the same quantity around luminous red galaxies (LRGs). On scales greater than 100 kpc both ELGs and LRGs exhibit similar absorption profiles. However, metal absorption is 5-10 times stronger around ELGs on smaller scales. The metal absorption strength is anisotropic, with an excess along the minor-axis of the galaxies, indicating an outflow origin of the absorbing gas. The ratio between the velocity dispersion of the cool CGM and that of its host dark matter halo is about one for ELGs but about half for LRGs. These results show that the dichotomy of galaxy types is reflected in both the density distribution and kinematics of the CGM traced by metal absorption lines. Our results provide strong evidence that the CGM of ELGs is enriched by gas outflows generated by star formation.