The Lyman edge test of the quasar emission mechanism

Abstract

This is a study of the Lyman edge region in the spectra of 11 high-redshift quasars. We present large-aperture, low-resolution data designed to detect broadened Lyman edge absorption predicted by thermal models of the " big blue bump " continuum component, especially thin accretion disks. We also present high-resolution data on the edge regions and the Lyman a emission lines for nine of the objects. Three objects have broadened, partial edges near the systemic redshifts, as expected for thermal models. However, in two cases we can identify narrow Lyman lines with the edge absorption, ruling out the disk interpretation. (In the third case there are no high-resolution data available for this test.) Therefore, our data are negative for thermal models, at least for opaque thin accretion disks. Our spectra show five complete intervening Lyman limit system edges, and they generally appear to be quite broad. The broadening can perhaps be explained by overlapping high-w absorption lines if the systems are clustered over a range of a few hundred kilometers per second in velocity.