MusE GAs FLOw and Wind V. The dust/metallicity-anisotropy of the circum-galactic medium

Abstract

ABSTRACT We investigate whether the dust content of the circum-galactic medium (CGM) depends on the location of the quasar sightline with respect to the galaxy major-axis using 13 galaxy-Mg ii absorber pairs (9–81 kpc distance) from the MusE GAs FLOw and Wind (MEGAFLOW) survey at 0.4 < z < 1.4. The dust content of the CGM is obtained from [Zn/Fe] using ultraviolet and visual echelle spectrograph data. When a direct measurement of [Zn/Fe] is unavailable, we estimate the dust depletion from a method that consists in solving for the depletion from multiple singly ionized ions (e.g. Mn ii, Cr ii, and Zn ii) since each ion depletes on dust grains at different rates. We find a positive correlation between the azimuthal angle and [Zn/Fe] with a Pearson’s r = 0.70 ± 0.14. The sightlines along the major axis show [Zn/Fe] < 0.5, whereas the [Zn/Fe] is > 0.8 along the minor axis. These results suggest that the CGM along the minor axis is on average more metal enriched (by ≈ 1 dex) than the gas located along the major axis of galaxies provided that dust depletion is a proxy for metallicity. This anisotropic distribution is consistent with recent results on outflow and accretion in hydro-dynamical simulations.