Possible Signatures of a Cold-Flow Disk from MUSE using a z=1 galaxy--quasar pair towards SDSSJ1422-0001

Original · EN

We use a background quasar to detect the presence of circum-galactic gas around a z=0.91 low-mass star forming galaxy. Data from the new Multi Unit Spectroscopic Explorer (MUSE) on the VLT show that the host galaxy has a dust-corrected star-formation rate (SFR) of 4.7±0.2 Msun/yr, with no companion down to 0.22 Msun/yr (5 σ) within 240 kpc (30"). Using a high-resolution spectrum (UVES) of the background quasar, which is fortuitously aligned with the galaxy major axis (with an azimuth angle α of only 15∘), we find, in the gas kinematics traced by low-ionization lines, distinct signatures consistent with those expected for a "cold flow disk" extending at least 12 kpc (3× R₁/₂). We estimate the mass accretion rate M in to be at least two to three times larger than the SFR, using the geometric constraints from the IFU data and the HI column density of N HI ≃ 20.4 obtained from a HST/COS NUV spectrum. From a detailed analysis of the low-ionization lines (e.g. ZnII, CrII, TiII, MnII, SiII), the accreting material appears to be enriched to about 0.4 Z (albeit with large uncertainties: Z/Z=-0.4 ± 0.4), which is comparable to the galaxy metallicity (12+ O/H=8.7±0.2), implying a large recycling fraction from past outflows. Blue-shifted MgII and FeII absorptions in the galaxy spectrum from the MUSE data reveal the presence of an outflow. The MgII and FeII doublet ratios indicate emission infilling due to scattering processes, but the MUSE data do not show any signs of fluorescent FeII* emission.