Journal Article

Do the spectral energy distributions of type 1 active galactic nuclei show diversity?

A. E. Scott and G. C. Stewart

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 438, issue 3, pages 2253-2266
Published in print March 2014 | ISSN: 0035-8711
Published online January 2014 | e-ISSN: 1365-2966 | DOI:
Do the spectral energy distributions of type 1 active galactic nuclei show diversity?

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We create broad-band spectral energy distributions (SEDs) of 761 type 1 active galactic nuclei (AGN). The Scott et al. sample, created by a cross-correlation of the optical Sloan Digital Sky Survey Data Release 5 quasar catalogue and the 2XMMi catalogue of serendipitous X-ray sources, is further matched with the Faint Images of the Radio Sky at Twenty-cm catalogue of radio sources, the mid-infrared (MIR) Wide-field Infrared Survey Explorer all-sky data release, the Two Micron All Sky Survey near-infrared point source catalogue, the UKIRT Infrared Deep Sky Survey Data Release 9 Large Area Survey and the Galaxy Evolution Explorer all-sky and medium ultraviolet (UV) imaging surveys. This allows broad-band SEDs including up to 19 flux measurements covering log ν ∼ 9.2–18.1 to be created. We investigate variations in the SED shape by binning a subsample of 237 AGN with the best quality SEDs according to their X-ray spectral parameters, their quasar subtype and physical parameters such as luminosity, black hole mass and Eddington ratio. The AGN subpopulations show some significant differences in their SEDs; X-ray absorbed AGN show a deficit of emission at X-ray/UV frequencies and an excess in the MIR consistent with absorption and re-emission, radio-loud AGN show increased radio and X-ray emission consistent with the presence of a jet component in addition to the emission seen from radio-quiet AGN and the SEDs of narrow-line Seyfert 1s only differ from other type 1s in the X-ray regime, suggesting any physical differences are limited to their X-ray emitting region. Binning the AGN according to underlying physical parameters reveals more subtle differences in the SEDs. The X-ray spectral slope does not appear to have any influence or dependence on the multiwavelength emission in the rest of the SED. The contribution of X-rays to the bolometric luminosity is lower in higher luminosity sources, and relatively more emission in the optical/UV is seen in AGN with higher X-ray luminosities. Variations in the relative flux and peak frequency of the big blue bump are observed and may suggest higher inner disc temperatures with increasing accretion rates. Overall, we find that the diversity in the SED shapes is relatively small, and we find no apparent single driver for the variations.

Keywords: accretion, accretion discs; galaxies: active; quasars: general; infrared: galaxies; ultraviolet: galaxies; X-rays: galaxies

Journal Article.  11668 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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