MusE GAs FLOw and Wind (MEGAFLOW) V. The dust/metallicity-anisotropy of the Circum-Galactic Medium
Résumé
Based on 13 galaxy-MgII absorber pairs (9 - 81 kpc distance) from the MusE GAs FLOw and Wind (MEGAFLOW) survey at 0.4 < z < 1.4, 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. The galaxy properties and orientation are determined from the Multi Unit Spectroscopic Explorer (MUSE) and the dust content in the CGM is obtained from [Zn/Fe] using Ultraviolet and Visual Echelle Spectrograph (UVES) data. When a direct measurement of [Zn/Fe] is unavailable, we estimate the dust depletion from a method which consists in solving for the depletion from multiple singly ionized ions (e.g. MnII, CrII, ZnII) 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. Given that [Zn/Fe] is a good proxy for metallicity, these results suggest that the CGM along the minor axis is on average more metal enriched (by ~ 1dex) than the gas located along the major axis of galaxies - consistent with outflow and accretion models. Our results suggest a metallicity anisotropy of the CGM provided there is a constant dust-to-metal ratio.
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