Observational signatures of a warped disk associated with cold-flow accretion

We present MUSE observations of the field of the quasar Q0152-020, whose spectrum shows a Lyman limit system (LLS) at redshift z(abs) = 0.38, with a metallicity Z greater than or similar to 0.06 Z(circle dot). The low-ionization metal lines associated with the LLS present two narrow distinct absorption components with a velocity separation of 26 km s(-1). We detect six galaxies within 600 km s(-1) from the absorption redshift; their projected distances from the quasar sightline range from 60 to 200 kpc. The optical spectra of five of these galaxies exhibit prominent nebular emission lines, from which we deduce extinction-corrected star formation rates in the range SFR = 0.06-1.3 M-circle dot yr(-1), and metallicities between 0.2 Z(circle dot) and Z(circle dot). The sixth galaxy is only detected in the stellar continuum. By combining our data with archival Keck/HIRES spectroscopy of the quasar and Hubble Space Telescope/Wide Field Planetary Camera 2 imaging of the field, we can relate absorption line and galaxy kinematics; we conclude that the LLS is most likely associated with the galaxy closest to the quasar sightline (galaxy 'a'). Our morphokinematic analysis of galaxy 'a' combined with the absorption line kinematics supports the interpretation that one of the absorption components originates from an extension of the stellar disk of galaxy 'a', while the other component may arise in accreting gas in a warped disk with specific angular momentum similar to 3 times larger than the specific angular momentum of the galaxy halo. Such warped disks are common features in hydrodynamical simulations of cold-flow accretion on to galaxies; the data presented here provide observational evidence in favour of this scenario.