Ultradense Gas at the Dusty Torus Scale in a Partially Obscured Quasar

We present detailed studies of the partially obscured quasar 2MASS J151653.23+190048.2 with continuous broadband spectrophotometry from near-infrared (NIR) through optical to ultraviolet (UV). The NIR and optical spectra show strong broad emission lines, while the UV spectrum is dominated by a set of rich intermediate-width emission lines (IELs). These IELs, unshifted with respect to the quasar systemic velocity measured by narrow emission lines, share a common profile of about 1900 $\mathrm{km}\,{{\rm{s}}}^{-1}$ in FWHM, in contrast to the Balmer and Paschen broad emission lines of FWHM ∼6300 $\mathrm{km}\,{{\rm{s}}}^{-1}$ observed in the optical and NIR. The intermediate width of these lines indicates that the emitting gas may come from the dusty torus region. However, the observed peculiar IEL intensity ratios, such as N V λ1240/Lyα, indicate that the emitting gas has a very high density, up to $\sim {10}^{13}\,{\mathrm{cm}}^{-3}$ . Such a high density is unusual for gas around the dusty torus region, except that we consider mechanisms such as shocks that can produce local ultradense gas. We speculate that these emission lines could originate from the shock region, possibly induced by the quasar outflow colliding with the inner wall of the dusty torus. If true, this may give us an opportunity to peep at the quasar outflows at the scale of the dusty torus that have so far been elusive due to the limited resolving powers of existing facilities.