POSSIBLE SIGNATURES OF A COLD-FLOW DISK FROM MUSE USING A z ∼ 1 GALAXY–QUASAR PAIR TOWARD SDSS J1422−0001* * Based on observations made at the ESO telescopes under program 080.A-0364 (SINFONI), 079.A-0600 (UVES), and as part of MUSE commissioning (ESO program 060.A-9100). Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program ID 12522.
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 × R1/2). We estimate the mass accretion rate Ṁin 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 NH I/cm-2 ≃ 20.4 obtained from a Hubble Space Telescope/COS near-UV spectrum. From a detailed analysis of the lowionization 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.
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