Toward an unbiased sample of X-ray selected normal galaxies outside the local Universe

Abstract

This paper shows that our understanding of the statistical properties of X-ray selected normal galaxies (e.g. X-ray luminosity function) can be significantly improved by combining a wide-area XMM-Newton survey with the moderare resolution and high S/N optical spectroscopy of the SDSS. Such a combined dataset has the potential to minimise uncertainties that affect existing normal galaxy samples at X-rays, such as small number statistics, cosmic variance, AGN contamination and incompleteness at bright X-ray luminosities. It is demonstrated that a 100 deg² XMM-Newton survey in the SDSS area to the limit f_X ( 0.5-2 keV) ≈ 5 × 10^-15 erg cm^-2 s^-1 will detect over 400 X-ray selected normal galaxies with excellent control over systematic biases, thereby providing tight contraints on the X-ray luminosity function at z ≈ 0.1.