A systematic study of the soft X-ray emission properties of starburst galaxies
Session 77 -- Starbursts
Display presentation, Friday, January 14, 9:30-6:45, Salons I/II Room (Crystal Gateway)

## [77.07] A systematic study of the soft X-ray emission properties of starburst galaxies

M. Dahlem (STScI), T.M. Heckman (JHU), C. Leitherer (STScI)

We are undertaking a systematic study of the soft X-ray emission properties of starburst galaxies. Our sample consists of about 50 far-infrared selected galaxies, with 60$\mu$m fluxes $\geq$30~Jy and FIR colours f(60$\mu$m)/f(100$\mu$m)~$\geq$~0.4. For 38 of these galaxies ROSAT pointed observations are (or will be) available.

Based on the quality of the existing data, we take different approaches at the data analysis. In case of unresolved sources with low photon numbers ($<400$) we only otbain a rough spectral fit to derive the integrated flux. For sources with higher photon numbers, most of which are, however, spatially unresolved, we do a more sophisticated spectral fitting in order to distinguish between different possible emission mechanisms, i.e. contributions of supernovae, X-ray binaries, or diffuse ionized gas. In cases of spatially resolved emission we conduct both a detailed and a global spectral analysis. This yields information on the emission mechanisms of individual sources in the galaxies and an integrated spectrum which can be compared to the lower quality data.

Up to now, only a few galaxies in our sample have soft X-ray spectra that cannot be fitted with a single emission component. Their spectra show ''high energy wings'' in addition to the emission that is also found in all other spectra, peaking in the range from 0.4 to 1~keV.

Presently, the best-studied galaxy in our sample is NGC~1808, where strong emission from the star-forming regions in the circumnuclear starburst could be resolved with the ROSAT HRI (Dahlem et al.; in prep.). In addition, we found weak soft X-ray emission from the diffuse hot ionized gas associated with the outflow from the nucleus into the galaxy halo. The PSPC spectrum is best fit by a Raymond-Smith spectrum with a temperature of about 0.5~keV (Junkes et al.; in prep.).