Detailed characterization of H beta emission line profile in low-z SDSS quasars

作者：Zamfir S^*; Sulentic J W; Marziani P; Dultzin D

来源：Monthly Notices of the Royal Astronomical Society, 2010, 403(4): 1759-1786.

DOI：10.1111/j.1365-2966.2009.16236.x

• galaxies: active
• quasars: emission lines
• quasars: general

We explore the properties of the H beta emission line profile in a large, homogeneous and bright sample of N similar to 470 low-redshift quasars extracted from Sloan Digital Sky Survey (Data Release 5). We approach the investigation from two complementary directions: composite/median spectra and a set of line diagnostic measures (asymmetry index, centroid shift and kurtosis) in individual quasars. The project is developed and presented in the framework of the so-called 4D Eigenvector 1 (4DE1) parameter space, with a focus on its optical dimensions, full width at half-maximum of broad H beta [FWHM(H beta)] and the relative strength of optical Fe II [R(FeII) equivalent to W(Fe II4434-4684 angstrom)/W(H beta)]. We reenforce the conclusion that not all quasars are alike and spectroscopically they do not distribute randomly about an average typical optical spectrum. Our results give further support to the concept of two populations A and B [narrower and broader than 4000 km s(-1) FWHM(H beta), respectively] that emerged in the context of 4DE1 space. The broad H beta profiles in composite spectra of Population A sources are best described by a Lorentzian and in Population B by a double Gaussian model. Moreover, high-and low-accretion sources (an alternative view of the Population A/B concept) not only show significant differences in terms of black hole (BH) and Eddington ratio L(bol)/L(Edd), but they also show distinct properties in terms of line asymmetry, shift and shapes. We finally suggest that a potential refinement of the 4DE1 space can be provided by separating two populations of quasars at R(FeII) similar to 0.50 rather than at FWHM(H beta) = 4000 km s(-1). Concomitantly, the asymmetry and centroid shift profile measures at 1/4 fractional intensity can be reasonable surrogates for the FWHM(H beta) dimension of the current 4DE1.

• 出版日期2010-4-21