A Quasar Without Broad Lyman-alpha Emission

Abstract

The z=3.02 quasar SDSS J095253.83+011421.9 exhibits broad metal-line emission (CIV FWHM=9000 km/s), but broad Ly-alpha emission is not present. Instead, only a narrow Ly-alpha line is observed (FWHM=1140 km/s). The large CIV/Ly-alpha ratio in the broad-line region (BLR) emission from this object can be matched most closely by a BLR dominated by gas at very high densities (10^15 cm^-3), which suppresses the Ly-alpha emission, and illuminated by an incident power-law extending to ~200 micron, which yields increased emission from purely collisionally excited coolant lines (such as CIV, NV and OVI) but not from recombination lines like Ly-alpha. However, the strong CIII emission predicted by this model is not observed, and the observed broad CIII] emission must come from a lower-density BLR component and should be accompanied by broad Ly-alpha emission which is not observed. The least unlikely explanation for this spectrum seems to be that any intrinsic broad Ly-alpha emission is removed by smooth NV absorption in the red wing of the Ly-alpha emission line and by smooth Ly-alpha absorption in the blue wing of the Ly-alpha emission line. This postulated smooth absorption would be in addition to the strong, associated, narrow absorption seen in numerous ions. Smooth absorption in Ly-alpha, NV and OVI but not in CIV would be unusual, but not impossible, although it is suspicious that the postulated absorption must almost exactly cancel the postulated intrinsic broad emission. We conclude that the spectrum of SDSS J0952+0114 appears unique (among ~3600 SDSS spectra of quasars at z>2.12) because of some_combination_ of unusual parameters, and we discuss possible observations to determine the combination of circumstances responsible for the spectrum.