低电离铁离子宽吸收线类星体SDSS J112526.12+002901.3的红移的巴尔默线和亚稳态$m He ~I$ 吸收线系统: 秒差距尺度的吸积流？

he accretion of interstellar medium onto the central super massive black holes is widely accepted as the source of the gigantic energy released by the active galactic nuclei. But few observational evidence has been confirmed directly demonstrating the existence of the inflows. The absorption system in the spectra of quasar SDSS J112526.12+002901.3 presents an interesting example, in which the rarely detected features hydrogen Balmer and metastable hei absorption lines are found redshifted to the quasar's rest frame along with the low-ionization metal absorption lines mgii, Feii, extit{et al.}. The repeated SDSS spectroscopic observations suggest a transverse velocity smaller than the radial velocity. The motion of the absorbing medium is dominated by infall. The hei lines present a direct indicator to the strength of ionizing flux, while the Balmer lines imply a dense environment. With the help of photoionization simulations, we find the absorbing medium is exposed to the radiation with $U≈10^{-1.8}$, and the density is $n(mathrm{H})≈ 10^9 mathrm{cm}^{-3}$. Thus the absorbing medium is located $sim 4 mathrm{pc}$ away from the central engine. According to the similarity in the distance and physical conditions between the absorbing medium and the clumpy torus, the absorption system is strongly proposed as a candidate for the accretion inflow which originates from the inner surface of the torus.