DO NUCLEAR STARBURSTS OBSCURE THE X-RAY-BACKGROUND

We propose a model for the source of the X-ray background (XRB) in whi ch low-luminosity active nuclei (L similar to 10(43) erg s(-1)) are ob scured (N similar to 10(23) cm(-2)) by nuclear starbursts within the i nner similar to 100 pc. The obscuring material covers most of the sky as seen from the central source, rather than being distributed in a to roidal structure, and hardens the averaged X-ray spectrum. by photoele ctric absorption. The gas is turbulent with velocity dispersion simila r to few x 100 km s(-1) and cloud-cloud collisions lead to copious sta r formation. Although supernovae tend to produce outflows, most of the gas is trapped in the gravity field of the star-forming cluster itsel f and the central black hole. A hot (T similar to 10(6)-10(7) K) viria lized phase of this gas, comprising a few per cent of the total obscur ing material, feeds the central engine of similar to 10(7) M-. through Bondi accretion, at a sub-Eddington rate appropriate for the luminosi ty of these objects. If starburst-obscured objects give rise to the re sidual XRB, then only 10 per cent of the accretion in active galaxies occurs close to the Eddington limit in unabsorbed objects.