POSSIBLE SIGNATURES OF A COLD-FLOW DISK FROM MUSE USING A z ∼ 1 GALAXY–QUASAR PAIR TOWARD SDSS J1422−0001*

Abstract

ABSTRACT We use a background quasar to detect the presence of circumgalactic gas around a z = 0.91 ?> low-mass star-forming galaxy. Data from the new Multi Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope show that the galaxy has a dust-corrected star formation rate (SFR) of 4.7 ± 2.0 M ⊙ yr−1, with no companion down to 0.22 M ⊙ yr−1 (5σ) within 240 h − 1 ?> kpc (“30”). Using a high-resolution spectrum 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 × R 1 / 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 H i column density of log N H I ?> / cm - 2 ?> ≃ 20.4 obtained from a Hubble Space Telescope/COS near-UV spectrum. From a detailed analysis of the low-ionization lines (e.g., Zn ii, Cr ii, Ti ii, Mn ii, Si ii), the accreting material appears to be enriched to about 0.4 Z ⊙ ?> (albeit with large uncertainties: log Z / Z ⊙ = − 0.4 ± 0.4 ?> ), which is comparable to the galaxy metallicity (12 + log O/H = 8.7 ± 0.2), implying a large recycling fraction from past outflows. Blueshifted Mg ii and Fe ii absorptions in the galaxy spectrum from the MUSE data reveal the presence of an outflow. The Mg ii and Fe ii absorption line ratios indicate emission infilling due to scattering processes, but the MUSE data do not show any signs of fluorescent Fe ii* emission.