The Discovery of 1000 km/s Outflows in Massive Post-starburst Galaxies at z=0.6

TL;DR

This study provides observational evidence of high-velocity galactic outflows in post-starburst galaxies at z=0.6, supporting the role of AGN feedback in quenching star formation.

Contribution

First detection of 1000 km/s outflows in post-starburst galaxies at intermediate redshift, linking AGN activity to galaxy evolution.

Findings

10 out of 14 galaxies show blueshifted Mg II absorption lines

Median outflow velocity of 1140 km/s observed

Outflows are intermediate between starburst and quasar winds

Abstract

Numerical simulations suggest that active galactic nuclei (AGNs) play an important role in the formation of early-type galaxies by expelling gas and dust in powerful galactic winds and quenching star formation. However, the existence of AGN feedback capable of halting galaxy-wide star formation has yet to be observationally confirmed. To investigate this question, we have obtained spectra of 14 post-starburst galaxies at z~0.6 to search for evidence of galactic winds. In 10/14 galaxies we detect Mg II 2796,2803 absorption lines which are blueshifted by 490 - 2020 km/s with respect to the stars. The median blueshift is 1140 km/s. We hypothesize that the outflowing gas represents a fossil galactic wind launched near the peak of the galaxy's activity, a few 100 Myr ago. The velocities we measure are intermediate between those of luminous starbursts and broad absorption line quasars, which suggests that feedback from an AGN may have played a role in expelling cool gas and shutting down star formation.