Open AccessFitting the spectrum of the X‐ray background: the effects ofhigh‐metallicity absorption
Author(s) -
Wilman R. J.,
Fabian A. C.
Publication year - 1999
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.1999.02949.x
Subject(s) - physics , astrophysics , redshift , metallicity , galaxy , compton scattering , flux (metallurgy) , x ray background , spectral line , active galactic nucleus , absorption (acoustics) , universe , x ray , quasar , astronomy , scattering , optics , materials science , metallurgy
Recent work by Risaliti, Maiolino & Salvati suggests that more than half of all Seyfert 2 galaxies in the local Universe are Compton‐thick ( N H >10 24 cm −2 ). This has implications for AGN synthesis models for the X‐ray background, the flexibility of which for the inclusion of large numbers of high‐ z type 2 sources we examine here. We highlight the importance of Compton down‐scattering in determining the individual source spectra and the fit to the X‐ray background spectrum, and demonstrate how parameter space ‘opens up’ considerably if a super‐solar iron abundance is assumed for the absorbing material. This is illustrated with a model which satisfies the present constraints, but which predicts substantial numbers of type 2 sources at the faint flux levels soon to be probed for the first time by the Chandra and XMM missions. We demonstrate also how a strong negative K ‐correction facilitates the detection of sources with 10 ∼24 N H 10 25 cm −2 out to the highest redshifts at which they could plausibly exist.