Partially Obscured Quasars in the Sloan Digital Sky Survey Early Data Release

• Published in: The Astrophysical journal 2005-02, Vol.620 (2), p.629-645
• Main Authors: Dong, Xiao-Bo, Zhou, Hong-Yan, Wang, Ting-Gui, Wang, Jun-Xian, Li, Cheng, Zhou, You-Yuan
• Format: Article
• Language: English
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1086/427174

We have compiled a sample of 21 low-redshift (z 0.3), luminous active galactic nuclei (AGNs) with large Balmer decrements (Ha/Hb > 7) using the galaxy and QSO catalogs of the Sloan Digital Sky Survey Early Data Release. Using this sample we attempt to determine the fraction of quasars with large internal absorption. We find that these AGNs have strong [O III] l5007 and broad Ha emission, and that starlight dominates the spectra in the blue band, suggesting that these objects are heavily reddened. Their narrow emission line ratios are similar to those of Seyfert 2 galaxies, yet the average [O III] l5007 emission is 610 times more luminous. Applying the empirical relation between the optical continuum and the Balmer line luminosity for blue quasars, we find that the intrinsic luminosities of these 21 objects are in the range for quasars. We propose that they are obscured, intermediate-type quasars analogous to type 1.8 and 1.9 Seyfert galaxies. The ratio of these optically selected, intermediate-type quasars to type 1 quasars is found to be around 1, similar to that for local Seyfert galaxies. Preliminary study indicates that most of these quasars are hosted in early-type galaxies.