The X-ray luminosity function of local galaxies

We present an estimate of the local X-ray luminosity function and emissivity for different subsamples of galaxies namely Seyferts, LINERS, star-forming and passive (no-emission-line) galaxies. This is performed by convolving their optical luminosity function, as derived from the Ho et al. spectroscopic sample of nearby galaxies with the corresponding L_x/L_B relation. The local galaxy emissivity is about 1.6 X 10^{39} h erg/sec Mpc^3 in agreement with the results of Lahav et al. derived from cross-correlation techniques of the X-ray background with optical and infrared galaxy catalogues. From our analysis, it becomes evident that the largest fraction of the galaxy emissivity comes from galaxies associated with AGN (Seyferts but also LINERS) while the contribution of star-forming and passive galaxies is small. This independently supports the view that most of the yet unidentified X-ray sources in deep \rosat fields which are associated with faint optical galaxies, do harbour an AGN.