1997/11/07 by Fábio Natali, F. Natali, E. Giallongo +2 · 55 citations
Physics and Astronomy · #Astronomy #Astronomy and Astrophysical Research #Astrophysics #Emission spectrum #Galaxies: Formation, Evolution, Phenomena #Galaxy #Optics #Physics #Power law #QSOS #Redshift #Rest frame #Spectral index #Spectral line #Spectral shape analysis #Statistics #Stellar, planetary, and galactic studies #Ultraviolet #Wavelength #astro-ph
paper · pdf · doi:10.1086/300211
published in The Astronomical Journal 115(2), 397-404 (Institute of Physics) · 12 pages. To appear in the Astronomical Journal
arxiv created 1997/11/07 · openalex publication_date 1998/02/01 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/06
The average optical-UV continuum shape of QSOs is investigated, using spectra of 62 QSOs that have good relative photometric calibrations. The QSO spectra were extracted from two complete colorselected samples in the magnitude interval m B ≈ 15–20. The analysis is performed by fitting power-law continua f ν ∝ ν α in well-defined rest-frame wavelength intervals after removing regions of the spectrum affected by strong emission lines or weak emission bumps. The average slope in the rest-frame optical-UV region 1200–5500 Å shows a rapid change around the 3000 Å emission bump, with α ≃ 0.15 longward of it and α ≃ -0.65 at shorter wavelengths. Although these average slopes were obtained using spectra of QSOs with different luminosities and redshifts, there are no significant correlations of the average spectral index with these quantities. For a few QSOs in the sample, we were able to measure the same softening of the spectral shape within the individual spectrum. These results have significant consequences on the estimate of the cosmological evolution of the optically selected QSOs, as they affect, for instance, the k -corrections. New k -corrections in the BVR and Gunn r bands are computed. The derived average spectral shape in the optical-UV band places interesting constraints on the expected emission mechanisms.