2008/12/01 by P. Marziani, J. W. Sulentic, G. M. Stirpe +2 · 2 citations
Mathematics · Physics and Astronomy · #Astronomy #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Astrophysics #Emission spectrum #Equivalent width #Full width at half maximum #Galaxies: Formation, Evolution, Phenomena #Galaxy #Line (geometry) #Luminosity #Luminosity function #Mathematics #Optics #Physics #Population #Quasar #Redshift #Spectral line #astro-ph
paper · pdf · doi:10.1051/0004-6361:200810764
Accepted for publication in Astronomy and Astrophysics
arxiv created 2008/12/01 · openalex publication_date 2009/01/14 · arxiv updated 2009/12/01 · openalex created_date 2022/08/13 · openalex updated_date 2026/07/31
<i>Aims. <i/>We present new VLT ISAAC spectra for 30 quasars, which we combine with previous data to yield a sample of 53 intermediate-redshift (<i>z<i/> <i>≈<i/> 0.9–3.0) sources. The sample is used to explore properties of prominent lines in the h<i>β<i/> spectral region of these very luminous quasars.<i>Methods. <i/>We compare this data with two large low-redshift () samples in a search for trends over almost 6dex in source luminosity.<i>Results. <i/>We find two major trends: (1) a systematic increase in minimum <i>FWHM<i/> h<i>β<i/> with luminosity (discussed in a previous paper). This lower <i>FWHM<i/> envelope is best fit by assuming that the narrowest sources radiate near the Eddington limit, show line emission from a virialized cloud distribution, and obey a well-defined broad line region size vs. luminosity relation. (2) A systematic decrease in equivalent width of [oiii]4959, 5007 (from <i>W<i/> <i>≈<i/> 15 to ~1 Å) with increasing source bolometric luminosity (from 43 to 49). Other identified trends require differntiating between so-called Population A and Bsources. We generate median composite spectra in six luminosity bins to maximize . Population A sources show reasonably symmetric Lorentzian h<i>β<i/> profiles at all luminosities, while Pop. B sources require two component fits involving an unshifted broad and a redshifted very broad component. Very broad h<i>β<i/> increases in strength with increasing , while the broad component remains constant, resulting in an apparent “Baldwin effect” with equivalent width decreasing from <i>W<i/> ~ 80 to ~20 Å over our sample luminosity range. The roughly constant equivalent width shown by the h<i>β<i/> very broad component implies production in optically-thick, photoionized gas. The onset of the redshifted very broad component appears to be a critical change that occurs near the Pop. A–B boundary at <i>FWHM<i/> h<i>β<i/> <i>≈<i/> 4000 km s<sup>-1<sup/>, which we relate to a critical Eddington ratio (<i>≈<i/> 0.2<i>±<i/>0.1).