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Astron. Astrophys. 361, 491-499 (2000)


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Probing the gas content of the dwarf galaxy NGC 3109 with background X-ray sources *

P. Kahabka 1, T.H. Puzia 1 and W. Pietsch 2

1 Sternwarte, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
2 Max-Planck-Institut für Extraterrestrische Physik, 85740 Garching bei München, Germany

Received 6 April 2000 / Accepted 19 May 2000

Abstract

We established the catalog of X-ray point sources in the field of the Magellanic-type spiral galaxy NGC 3109 (DDO 236) from two ROSAT PSPC observations. Of the 91 X-ray sources 26 are contained within the HI extent of NGC 3109 as derived by Jobin & Carignan (1990) with the VLA. For 10 of these we can determine accurate hardness ratios [FORMULA]0.2. We find 3 candidate AGN, 2 candidate X-ray binaries and one source which may belong to either class. We also find 2 candidate foreground stars. In a field of 8´ [FORMULA] 8´ observed with the NTT in the I-band and centered on the nucleus of NGC 3109 we determine candidates for optical counterparts in the X-ray error circle of 7 ROSAT PSPC sources. We apply a spectral fit to the ROSAT spectrum of the X-ray brightest absorbed candidate AGN behind NGC 3109, RX J1003.2-2607. Assuming a galactic foreground hydrogen column density of [FORMULA] we derive from the X-ray spectral fit, assuming reduced metallicities ([FORMULA]0.2 solar), a hydrogen column density due to NGC 3109 of [FORMULA]. This value is slightly larger than the hydrogen column density derived from the 21-cm observations of [FORMULA]. We estimate that the molecular mass fraction of the gas is not larger than [FORMULA]%.

Key words: catalogs – galaxies: individual: NGC 3109 – galaxies: active – galaxies: ISM – radio continuum: galaxies – X-rays: galaxies

Table 6 and Fig. 8 are only available electronically here with the On-Line publication

Send offprint requests to: pkahabka@astro.uni-bonn.de

© European Southern Observatory (ESO) 2000

Online publication: October 2, 2000

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