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The accretion of interstellar medium onto the central super massive blackholes is widely accepted as the source of the gigantic energy released by theactive galactic nuclei. But few pieces of observational evidence have beenconfirmed directly demonstrating the existence of the inflows. The absorptionline system in the spectra of quasar SDSS J112526.12+002901.3 presents aninteresting example, in which the rarely detected hydrogen Balmer andmetastable He I absorption lines are found redshifted to the quasar's restframe along with the low-ionization metal absorption lines Mg II, Fe II, etc.The repeated SDSS spectroscopic observations suggest a transverse velocitysmaller than the radial velocity. The motion of the absorbing medium is thusdominated by infall. The He I* lines present a powerful probe to the strengthof ionizing flux, while the Balmer lines imply a dense environment. With thehelp of photoionization simulations, we find the absorbing medium is exposed tothe radiation with ionization parameter $U\approx 10^{-1.8}$, and the densityis $n(\mathrm{H})\approx 10^9\ \mathrm{cm}^{-3}$. Thus the absorbing medium islocated $\sim 4\ \mathrm{pc}$ away from the central engine. According to thesimilarity in the distance and physical conditions between the absorbing mediumand the torus, we strongly propose the absorption line system as a candidatefor the accretion inflow which originates from the inner surface of the torus.

astrophysical journal/the astrophysical journal

The Redshifted Hydrogen Balmer and Metastable He I Absorption Line  System in Mini-FeLoBAL Quasar SDSS J112526.12+002901.3: A Parsec Scale  Accretion Inflow?