Quasars and the Big Blue Bump

Abstract

We investigate the ultraviolet-to-optical spectral energy distributions (SEDs) of 17 active galactic nuclei (AGNs) using quasi-simultaneous spectrophotometry spanning 900-9000 Angstrom (rest frame). We employ data from the Far Ultraviolet Spectroscopic Explorer (FUSE), the Hubble Space Telescope (HST), and the 2.1-meter telescope at Kitt Peak National Observatory (KPNO). Taking advantage of the short-wavelength coverage, we are able to study the so-called "big blue bump," the region where the energy output peaks, in detail. Most objects exhibit a spectral break around 1100 Angstrom. Although this result is formally associated with large uncertainty for some objects, there is strong evidence in the data that the far-ultraviolet spectral region is below the extrapolation of the near-ultraviolet-optical slope, indicating a spectral break around 1100 Angstrom. We compare the behavior of our sample to those of non-LTE thin-disk models covering a range in black-hole mass, Eddington ratio, disk inclination, and other parameters. The distribution of ultraviolet-optical spectral indices redward of the break, and far-ultraviolet indices shortward of the break, are in rough agreement with the models. However, we do not see a correlation between the far-ultraviolet spectral index and the black hole mass, as seen in some accretion disk models. We argue that the observed spectral break is intrinsic to AGNs, although intrinsic reddening as well as Comptonization can strongly affect the far-ultraviolet spectral index. We make our data available online in digital format.Comment: 32 pages (10pt), 12 figures. Accepted for publication in Ap

Outflows and the Physical Properties of Quasars

“…12 of Richards et al 2006). We acknowledge here that other, and perhaps more refined, estimates of the bolometric correction (e.g., Vestergaard 2004;Shang et al 2005) exist. Use of these estimates would generally require an extrapolation of our power-law fit to another wavelength, which we wish to avoid.…”

Constraints on spin of a supermassive black hole in quasars with big blue bump

“…The special attention has been paid to subtracting the host galaxy contribution. The estimation of the host galaxy contribution is made by Shang et al (2005) and appeared to be less than 5% for all targets. Near UV spectra of these targets, covering a wavelength range of 1150-3150Å have been obtained from the HST spectroscopic survey.…”

“…Fig. 1 The relationship between the radiation efficiency ε and the spin a 3 Sample and data for determining SMBH spins Shang et al (2005) investigated the ultraviolet-tooptical spectral energy distributions of 17 AGNs using quasi-simultaneous spectrophotometry spanning 900-9000Å in rest frame system. They used the observational data from the Far Ultraviolet Spectroscopic Explorer (FUSE), the Hubble Space Telescope (HST) and the 2.1-m telescope at Kitt Peak National Observatory.…”

“…We presented the results of our determinations of the radiation efficiency of the accretion flow and values of the spins of SMBHs, that derives the coefficient of radiation efficiency. The majority of SMBHs of AGNs from Shang et al (2005) sample are to be the Kerr black holes with the high spin value. …”

Variability of QSOs with variable regions in broad absorption troughs from the Sloan Digital Sky Survey

“…Some authors also used two power-law functions to model the QSO continuum (e.g. Forster et al 2001;Shang et al 2005). For BAL QSOs, a polynomial function or a reddened power law was also used to fit the continuum in previous studies (Lundgren et al 2007;Gibson et al 2008Gibson et al , 2009).…”