A Quasar without Broad Lyα Emission


Hall PB, Snedden SA, Niederste-Ostholt M, Eisenstein DJ, Strauss MA, York DG, Schneider DP. A Quasar without Broad Lyα Emission. The Astronomical Journal. 2004;128 :534-543.

Date Published:

August 1, 2004


The z=3.02 quasar SDSS J095253.83+011421.9 exhibits broad metal-lineemission (C IV FWHM~=9000 km s-1), but broad Lyαemission is not present. Instead, only a narrow Lyα line isobserved (FWHM~=1140 km s-1). The large CIV/Lyα ratioin the broad-line region (BLR) emission from this object can be matchedmost closely by a BLR dominated by gas at very high densities(1015 cm-3), which suppresses the Lyαemission, and illuminated by an incident power law extending to ~200μm, which yields increased emission from purely collisionally excitedcoolant lines (such as C IV, N V, and O VI) but not from recombinationlines like Lyα. However, the strong C III emission predicted bythis model is not observed, and the observed broad C III] emission mustcome from a lower density BLR component and should be accompanied bybroad Lyα emission, which is not observed. The least unlikelyexplanation for this spectrum seems to be that any intrinsic broadLyα emission is removed by smooth N V absorption in the red wingof the Lyα emission line and by smooth Lyα absorption in theblue wing of the Lyα emission line. This postulated smoothabsorption would be in addition to the strong, associated, narrowabsorption seen in numerous ions. Smooth absorption in Lyα, N V,and O VI, but not in C IV, would be unusual, but not impossible,although it is suspicious that the postulated absorption must almostexactly cancel the postulated intrinsic broad emission. We conclude thatthe spectrum of SDSS J0952+0114 appears unique (among ~=3600 SDSSspectra of quasars at z>2.12) because of some combination of unusualparameters, and we discuss possible observations to determine thecombination of circumstances responsible for the spectrum.