MusE GAs FLOw and Wind (MEGAFLOW)

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 9 from the MusE GAs FLOw and Wind (MEGAFLOW) survey. Using Mg II λλ 2796,2803 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, b 50 , at which f c = 50% is b 50 = 50 ± 7 kpc for W r 2796 > 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 ≈2 σ 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 r 2796 > 0.3 Å, resulting in a steep covering fraction, f c ( b ).