EDP Sciences
Free access
Volume 399, Number 1, February III 2003
Page(s) 9 - 17
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20021738

A&A 399, 9-17 (2003)
DOI: 10.1051/0004-6361:20021738

Starburst galaxies and the X-ray background

M. Persic1 and Y. Rephaeli2, 3

1  INAF/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

(Received 5 September 2002 / Accepted 14 November 2002 )

Integrated X-ray spectra of an evolving population of starburst galaxies (SBGs) are determined based on the observed spectra of local SBGs. In addition to emission from hot gas and binary systems, our model SBG spectrum includes a nonthermal component from Compton scattering of relativistic electrons by the intense ambient far-IR and the (steeply evolving) CMB radiation fields. We use these integrated spectra to calculate the levels of contribution of SBGs to the cosmic X-ray background assuming that their density evolves as (1+z)q up to a maximal redshift of 5. We find that at energies $\epsilon\la10$ keV this contribution is at a level of few percent for $q \leq 3$, and in the range of $5\%{-}15\%$ for $q \simeq 4.5$. The Compton component is predicted to be the main SBG emission at high energies, and its relative contribution gets progressively higher for increasing redshift.

Key words: X-ray: galaxies -- galaxies: spiral -- stars: formation

Offprint request: M. Persic, persic@ts.astro.it

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