ROSAT PSPC spectra of X-ray-selected narrow-emission-line galaxies

We analyse the ROSAT PSPC spectrum of 19 X-ray selected Narrow Emission LineGalaxies (NELGs) discovered during the optical identification of sources in theROSAT UK Deep Survey. Their properties are compared to those of broad lineActive Galactic Nuclei (AGN) in the same sample. Counts in three spectral bandshave been extracted for all the sources, and have been fitted with a power-lawmodel assuming the Galactic value for NH. The average slope of NELGs is\alpha=0.45+-0.09, whilst for the AGN it is \alpha=0.96+-0.03. The power-lawmodel is a good fit for ~90% of NELGs and ~75% of AGN. Recent work shows thatthe fractional surface density of NELGs increases with respect to AGN at faintfluxes. Thus they are expected to be an important component of the residualsoft (<2 keV) X--ray background. The slope of the X--ray background(\alpha~0.4, 1-10 keV) is harder than that of AGN (\alpha~1) but our resultsshow that it is consistent with the summed spectrum of the NELGs in the deepsurvey (\alpha~0.4). This may finally reconcile the spectrum of the backgroundwith the properties of the sources that constitute it.Comment: Uuencoded compressed LaTex file and three PS figures plus mn.sty. Accepted in MNRA