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 H i extent of NGC 3109 as derived by Jobin & Carignan ( 1990 ) with the VLA .
For 10 of these we can determine accurate hardness ratios \delta H R 2 \leq 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′ \times 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 4.3 10 ^ { 20 } cm ^ { -2 } we derive from the X-ray spectral fit , assuming reduced metallicities ( \sim 0.2 solar ) , a hydrogen column density due to NGC 3109 of 11 \pm ^ { 7 } _ { 5 } 10 ^ { 20 } cm ^ { -2 } .
This value is slightly larger than the hydrogen column density derived from the 21-cm observations of \sim 8 10 ^ { 20 } cm ^ { -2 } .
We estimate that the molecular mass fraction of the gas is not larger than \sim 60 % .