The Bright Ultra-hard XMM-Newton Survey (BUXS) aimes at mapping obscured accretion in luminous AGN up to the cosmic epoch of the peak of Super Massive Black Holes (SMBH) growth and star formation activity. BUXS is the result of an intensive collaboration that has brought together leading experts around the world working on different aspects of AGN physics
BUXS is a sample of 258 X-ray bright AGN (flux4.5−10 keV > 6×10−14 erg s−1cm−2) detected over 44.43 deg2 of the northern sky with the XMM-Newton observatory. The AGN were selected at the highest energies at which the XMM-Newton X-ray detectors are sensitive, 4.5-10 keV. The selection of sources in the 4.5-10 keV energy band was motivated by the need to reduce the strong bias against heavily absorbed AGN affecting surveys conducted at softer energies. The AGN in BUXS have redshifts up to ~2, intrinsic (absorption-corrected) 2-10 keV X-ray luminosities between 1042 and 1046 erg s−1 and X-ray absorption in the Compton-thin regime (X-ray column densities NH<1.5×1024 cm-2).
BUXS is one of the largest complete samples of AGN at such hard X-ray energies sampling the fluxes where most of the Universe’s accretion power originates. BUXS will increase the number of uniformly selected highly luminous distant AGN identified at such high X-ray energies (>4.5 keV) by more than a factor of 4 from a redshift of 0.05 to ~2 (see Figure 1). From 2009 to 2012 the P.I. of this proposed project has coordinated an intensive follow-up program of UV/optical spectroscopic identification of the sources using instruments on many large-class ground-based telescopes (ESO’s NTT, VLT in Chile; GTC, WHT, TNG, NOT in La Palma). The program has been a success. We currently have optical spectroscopic classifications and accurate redshifts for ~99% of the sources.
