Normal galaxies in the XMM-Newton fields^*

X-rays as a star formation indicator

¹ Max Planck Institut für extraterrestrische Physik, Giessenbachstraße, 85748, Garching, Germany e-mail: erovilos@mpe.mpg.de
² Institute for Astronomy and Astrophysics, National Observatory of Athens, I. Metaxa & V. Pavlou str, Palaia Penteli, 15236, Greece
³ Astronomical Laboratory, Department of Physics, University of Patras, 26500, Rio-Patras, Greece
⁴ Laboratory for X-ray Astrophysics, NASA Goddard Space Flight Center, Mail Code 662, Greenbelt, MD 20771, USA
⁵ Department of Physics and Astronomy, The Johns Hopkins University, 366 Bloomberg Center, 3400 N. Charles street, Baltimore, MD 21218, USA
⁶ Research School of Astronomy and Astrophysics, Mount Stromlo Observatory, Cotter Rd, Weston, ACT 2611, Australia
⁷ Australia Telescope National Facility, PO Box 76, Epping, NSW 1710, Australia
⁸ School of Physics, University of New South Wales, Sydney NSW 2052, Australia
⁹ Dept. of Physics & Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver B.C., V6T 1Z1, Canada

Received: 12 March 2009
Accepted: 18 May 2009

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 < -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.