A Possible New Population of Sources with Extreme X-Ray / Optical Ratios
Abstract
We describe a possible new class of X-ray sources that have robust detections in ultra-deep Chandra data, yet have no detections at all in our deep multi-band GOODS Hubble Space Telescope (HST) ACS images, which represent the highest quality optical imaging obtained to date on these fields. These extreme X-ray / Optical ratio sources ("EXO"s) have values of Fx/Fopt at least an order of magnitude above those generally found for other AGN, even those that are harbored by reddened hosts. We thus infer two possible scenarios: (1) if these sources lie at redshifts z < 6, then their hosts need to be exceedingly underluminous, or more reddened, compared with other known sources; (2) if these sources lie above z ~ 6-7, such that even their Lyman-alpha emission is redshifted out of the bandpass of our ACS z(850) filter, then their optical and X-ray fluxes can be accounted for in terms of relatively normal L* hosts and moderate-luminosity AGN.
Cite
@article{arxiv.astro-ph/0306407,
title = {A Possible New Population of Sources with Extreme X-Ray / Optical Ratios},
author = {Anton M. Koekemoer and D. M. Alexander and F. E. Bauer and J. Bergeron and W. N. Brandt and E. Chatzichristou and S. Cristiani and S. M. Fall and N. A. Grogin and M. Livio and V. Mainieri and L. Moustakas and P. Padovani and P. Rosati and E. J. Schreier and C. M. Urry},
journal= {arXiv preprint arXiv:astro-ph/0306407},
year = {2009}
}
Comments
AASTEX-Latex, 12 pages, 3 figures, including 1 jpg figure. Accepted by the Astrophysical Journal Letters