Why X-ray--Selected AGN Appear Optically Dull
摘要
We investigate why half of X-ray--selected active galactic nuclei (AGN) in deep surveys lack signs of accretion in their optical spectra. The majority of these ``optically--dull'' AGN are no more than 6 times fainter than their host galaxies in rest-frame R-band; as such, AGN lines are unlikely to be overwhelmed by stellar continuum in at least half the sample. We find that optically--dull AGN have the mid--infrared emission and L(x)/L(IR) ratios characteristic of local Seyferts, suggesting that the cause of optical dullness is not missing UV--optical continua. We compare the morphologies of 22 optically--dull and 9 optically--active AGN at 0.5<z<0.8, and find that optically--dull AGN show a wide range of axis ratio, but optically--active AGN have only very round axis ratios. We conclude that hard X-rays select AGN in host galaxies with a wide range of inclination angle, but only those AGN in the most face-on or spheroidal host galaxies show optical emission lines. Thus, extranuclear dust in the host galaxy plays an important role in hiding the emission lines of optically--dull AGN.
引用
@article{arxiv.astro-ph/0603313,
title = {Why X-ray--Selected AGN Appear Optically Dull},
author = {J. R. Rigby and G. H. Rieke and J. L. Donley and A. Alonso-Herrero and P. G. Pérez-González},
journal= {arXiv preprint arXiv:astro-ph/0603313},
year = {2011}
}
备注
Accepted for publication in The Astrophysical Journal; 20 pages High-res version here: http://satchmo.as.arizona.edu/~jrigby/optdull.ps