Feeding the Accretion Disk from the Dusty Torus in a Reddened Quasar

Abstract

We present here a detailed analysis of an unusual absorption line system in the quasar SDSS J122826.79+100532.2. The absorption lines in the system have a common redshifted velocity structure starting from $v\sim 0$ and extending to $\sim 1,000{\mathrm{km}\mathrm{s}}^{-1}$, and are clearly detected in hydrogen Balmer series up to H$\iota$, in metastable neutral helium triplet, and in optical lines of excited states of single ionized iron. We estimated that the absorber has a density $n_{\mathrm{H}}\approx 10^{8.4}{\mathrm{cm}}^{-3}$ and an ionization parameter $U\approx 10^{-1.2}$, thereupon located it at $r_{\mathrm{abs}}\approx 1.5$ pc from the central supermassive black hole. The inferred distance is remarkably similar to the evaporation radius for dust grains $r_{\mathrm{evap}}\approx 1$ pc in the quasar. Thus the absorber may be a probe of an inflow starting from the dusty torus and feeding the accretion disk. Both the featureless continuum and the broad emission lines are heavily reddened with $E(B-V)\approx 0.66$, in contrast to the narrow emission lines whose reddening is negligible. The dusty medium could be located in between the broad and narrow emission line regions, and possibly be associated with a 'cold' narrow absorption line system detected in \ion{Ca}{2} and \ion{Na}{1} doublets nearly unshifted from the quasar systemic velocity. SDSS J122826.79+100532.2 might represent such a rare case that both the inflow and the torus could be tracked by absorption lines.

Published in ApJ (2021, 919, 86)

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