Search for Lyman Limit Absorption Edge in Quasar Continuum

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Session 91 -- Radio Galaxies and Lyman Continuum Absorption
Oral presentation, Friday, January 14, 10:15-11:45, Salon V Room (Crystal Gateway)

[91.05] Search for Lyman Limit Absorption Edge in Quasar Continuum

W.-H. Sun (National Central University), M.A. Malkan (UCLA), Thomas H.W. Chang (National Central University)

We examine the low resolution UV spectra of the 37 quasars in HST Key Project to search for intrinsic Lyman absorption edge which may be a signature of thermal accretion disks. Only 28 QSOs have proper redshifts to place the region of interest in the G160L window.

We fit the $L_{\beta}$ with two gaussians to remove the line. We then avoid 20 and 50\AA~on the blue and red sides of 912\AA~in the rest frame, and take 80\AA~bins (rest frame) on both sides but further out for analysis. We compare the single power-law fitting (to the entire range across the edge), with the two power-law fitting to blue and red bands. We also measure the percentage drop of flux over the Lyman limit. There are 7 objects with intrinsically noisy spectra, which were presumably caused by intervening Lyman absorption systems. Applying the two methods on the rest 21 objects, we found {24\%} candidates to have possible rest frame Lyman limit absorption edges. Same analyses have also been performed on optical spectra of medium- to high-redshift QSOs from Lick Observatory and Hale Observatory. Similar results were also found.

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