X-ray spectral components of starburst galaxies

¹ Osservatorio Astronomico di Trieste, via G. B. Tiepolo 11, 34131 Trieste, Italy
² School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel
³ CASS, University of California, San Diego, La Jolla, CA 92093, USA

Corresponding author: M. Persic, persic@ts.astro.it

Received: 31 July 2001
Accepted: 21 November 2001

Abstract

X-ray emission processes in starburst galaxies (SBGs) are assessed, with the aim of identifying and characterizing the main spectral components. Our survey of spectral properties, complemented with a model for the evolution of galactic stellar populations, leads to the prediction of a complex spectrum. Comparing the predicted spectral properties with current X-ray measurements of the nearby SBGs M 82 and N253, we draw the following tentative conclusions: 1) X-ray binaries with accreting neutron stars are the main contributors in the 2–15 keV band, and could be responsible for the yet uninterpreted hard component required to fit the observed 0.5–10 keV spectra of SBGs; 2) diffuse thermal plasma contributes at energies 1 keV; 3) nonthermal emission, from Compton scattering of FIR and CMB radiation fields photons off supernova-accelerated relativistic electrons, and AGN-like emission, are likely be the dominant emission at energies 30 keV; 4) supernova remnants make a relatively minor contribution to the X-ray continuum but may contribute appreciably to the Fe-K emission at 6.7 keV.