Normal galaxies in the XMM-Newton fields. X-rays as a star formation indicator
Georgantopoulos, I.; Rovilos, E.; Whiting, M.; Tzanavaris, P.; Woods, D.; Goudis, C.; Pracy, M.
Germany, Greece, United States, Australia, Canada
Abstract
Context: We use the first XMM serendipitous source catalogue (1XMM) 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 absorption 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 Hα luminosity - a well-calibrated star-formation indicator - relation.
Conclusions: We find that the X-ray luminosity strongly correlates with the Hα luminosity, suggesting that the X-rays efficiently trace the star-formation.