Transition of Quasar Broad Emission Line Profiles from Double to Single Peaked: Signature of the Effects of an Accretion Disk Wind

The quasar J1258+3519 (J1258) exhibited a dramatic change in it’s broad Balmer line emission spectrum, transitioning from a double-peaked to single-peaked profile that coincided with a large increase in optical luminosity. We present a model for the Balmer broad line region (BLR) emission in J1258 as arising in the outer layers of the accretion disk, in which complex direction-dependent radiative transfer effects produced by velocity gradients lead to the particular shape of the observed line profiles, building on previous studies. A key feature of this model is the effect of an accretion disk wind in producing single-peaked lines. We show the transition from double to single peak lines in J1258 is consistent with the effects of a disk wind that increases in strength as the luminosity increases, generally consistent with predictions from dynamical models. The change in the observed Balmer decrement between the two states supports this model. We determine constraints on the physical parameters in J1258 (black hole mass, accretion rate, dimensions of the line-emission disk region, wind parameters) in the context of this model. Using our results for J1258 and from a sample of quasars with double-peaked BLR profiles, we discuss the parameters that are expected to be linked to double peaked BLRs generally.