Normal galaxies in the XMM-Newton fields X-rays as a star formation indicator

Context. We use the first XMM serendipitous source catalogue (IXMM) to compile a sample of normal X-ray galaxies. Aims. We seek to expand the database of X-ray selected normal galaxies at intermediate redshifts and examine the relation between X-ray emission and star formation for late-type systems. Methods. The candidates are selected based on their X-ray (soft spectra), X-ray to optical (log(f_x/f_o) < -2) and optical (extended sources) properties. 44 candidates are found and 35 are spectroscopically observed with the Australian National University's 2.3 m telescope to examine their nature. Results. Of the 35 sources observed, 2 are AGN, 11 emission line galaxies, 12 absoiption line galaxies, 6 have featureless spectra while 4 are associated, with Galactic stars. We combine our emission line sample with earlier works forming the most comprehensive X-ray selected galaxy sample for the study of the X-ray luminosity to the Ha luminosity - a well-calibrated star-formation indicator - relation. Conclusions. We find that the X-ray luminosity strongly correlates with the Ha luminosity, suggesting that the X-rays efficiently trace the star-formation.