MusE GAs FLOw and Wind (MEGAFLOW)

XIII. Cool gas traced by Mg II around isolated galaxies

¹ Univ Lyon1, Ens de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon (CRAL) UMR5574, F-69230 Saint- Genis-Laval, France
² Institute for Computational Astrophysics and Department of Astronomy & Physics, Saint Mary’s University, 923 Robie Street, Halifax, Nova Scotia B3H 3C3, Canada
³ Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, Centre National de la Recherche Scientifique, Centre National d’Etudes Spatiales, 31028 Toulouse, France
⁴ Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Str. 24/25, 14476 Potsdam, Germany
⁵ Centro de Astrobiologia (CAB), CSIC-INTA, Carretera de Ajalvir km 4, Torrejon de Ardoz, 28850 Madrid, Spain
⁶ Leiden Observatory, Leiden University, P.O. Box 9513 NL-2300 AA Leiden, The Netherlands
⁷ Leibniz-Institut for Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany

^⋆ Corresponding author; maxime.cherrey@univ-lyon1.fr

Received: 18 June 2024
Accepted: 28 November 2024

Abstract

Aims. The circumgalactic medium (CGM) is a key component in understanding the physical processes governing the flows of gas around galaxies. Quantifying its evolution and its dependence on galaxy properties is particularly important for our understanding of accretion and feedback mechanisms.

Methods. We selected a volume-selected sample of 66 isolated star-forming galaxies at 0.4 < z < 1.5 with log(M_⋆/M_⊙) > 9 from the MusE GAs FLOw and Wind (MEGAFLOW) survey. Using Mg IIλλ2796,2803 absorptions in background quasars, we measured the covering fraction, f_c, and quantified how the cool gas profile depends on galaxy properties (such as star formation rate (SFR), stellar mass (M_⋆) or azimuthal angle relative to the line of sight) and how these dependencies evolve with redshift.

Results. The Mg II covering fraction of isolated galaxies is a strong function of impact parameter and is steeper than previously reported. The impact parameter, b₅₀, at which f_c = 50% is b₅₀ = 50 ± 7 kpc for W_r²⁷⁹⁶ > 0.5 Å. It is weakly correlated with SFR (∝SFR^{0.08 ± 0.09}) and decreases with cosmic time (∝(1 + z)^{0.8 ± 0.7}), contrary to the expectation of increasingly larger halos with time. The covering fraction is also higher along the minor axis than along the major axis at the ≈2σ level.

Conclusions. The CGM traced by Mg II is similar across the isolated galaxy population. Indeed, among the isolated galaxies with an impact parameter below 55 kpc, all have associated Mg II absorption with W_r²⁷⁹⁶ > 0.3 Å, resulting in a steep covering fraction, f_c(b).