MusE GAs FLOw and Wind (MEGAFLOW) IV: A two sightline tomography of a galactic wind

TL;DR

This study uses two sightlines to analyze a galactic wind at z=0.7, revealing anisotropic outflow characteristics and velocity shifts consistent with a bi-conical wind model, advancing understanding of galaxy feedback mechanisms.

Contribution

First direct two-sightline measurement of a galactic outflow at intermediate redshift, providing new insights into wind geometry and kinematics.

Findings

Detected significant velocity shift between two sightlines.

Observed outflow consistent with bi-conical wind model.

Measured outflow velocity of approximately 84 km/s.

Abstract

Galactic outflows are thought to eject baryons back out to the circum-galactic medium (CGM). Studies based on metal absorption lines (MgII in particular) in the spectra of background quasars indicate that the gas is ejected anisotropically, with galactic winds likely leaving the host in a bi-conical flow perpendicular to the galaxy disk. In this paper, we present a detailed analysis of an outflow from a z = 0.7 "green-valley" galaxy (log($M_*$/$\mathrm{M}_\odot$) = 9.9; SFR = 0.5 $\mathrm{M}_\odot\,\mathrm{yr}^{-1}$) probed by two background sources part of the MUSE Gas Flow and Wind (MEGAFLOW) survey. Thanks to a fortuitous configuration with a background quasar (SDSSJ1358+1145) and a bright background galaxy at $z = 1.4$, both at impact parameters of $\approx 15\,\mathrm{kpc}$, we can - for the first time - probe both the receding and approaching components of a putative galactic outflow around a distant galaxy. We measure a significant velocity shift between the MgII absorption from the two sightlines ($84\pm17\,\mathrm{km}\,\mathrm{s}^{-1}$), which is consistent with the expectation from our simple fiducial wind model, possibly combined with an extended disk contribution.