Title: A hard X-ray investigation of Bright IR galaxies


Proposal ID: 0120068
Subject category: Extragalactic Object
Principal investigator: Della-Ceca
Institute: Osservatorio Astronomico di Brera

Abstract

We propose here to exploit the unique hard (E > 10 keV) X-ray imaging and spectroscopic capabilities of INTEGRAL to investigate the relative contribution and occurrence of AGN and starburst activity in a flux limited sample of 22 infrared galaxies having a 60micron flux greater than 50 Jy. After excluding the sources already observed with the BeppoSAX PDS, those not visible during AO1 and those at low (|b| < 13) galactic latitude (they will enter anyway in the INTEGRAL public archive since they are in the region covered by the ``INTEGRAL Low Galactic Latitude Core Program") we are left with 5 objects. We ask for INTEGRAL pointing observations of 100 ksec for each of these sources (priorities are specified). Measuring the hard (E > 10 keV) X-ray flux yields reliable indication of the presence of an optically-hidden AGN, absorbed in soft X-rays (N_H > 10^{24} cm^{-2}), potentially contributing for most of the emitted bolometric luminosity. It has been shown in the last few years (mainly using the BeppoSAX PDS instrument) that the hard X-ray regime is the best energy range to investigate the occurrence of AGN activity. INTEGRAL will allow such a detailed investigation only on local objects, but an improved physical knowledge of such sources and a measure of the relative contributions of stars and the AGN to the bolometric emission would be crucially informative about the nature of their distant, high-z counterparts. We stress that measuring the hard X-ray emission for a well defined flux-limited sample, will put this investigation on firm and solid statistical ground. We can reach this goal by combining INTEGRAL data of the proposed objects with archive data (BeppoSAX and INTEGRAL). With such an extended sample, our aim is to attempt, through a combination of hard X-ray and IR data, to quantify for the first time the relative weights of the AGN and starburst emission in the bolometric budget.