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

We analyse the ROSAT PSPC spectra of 19 X-ray-selected narrow-emission-line galaxies (NELGs) discovered during the optical identification of sources in the ROSAT UK Deep Survey. Their properties are compared with those of broad-line active galactic nuclei (AGN) in the same sample. Counts in three spectral bands have been extracted for all the sources, and have been fitted with a power-law model assuming the Galactic value for NH. The average slope of the NELGs is α = 0.45±0.09, whilst for the AGN it is α = 0.96±0.03. The power-law model is a good fit for ∼ 90 per cent of NELGs and ∼ 75 per cent of AGN. Recent work shows that the fractional surface density of NELGs increases with respect to AGN at faint fluxes. Thus they are expected to be an important component of the residual soft (< 2 keV) X-ray background. The slope of the X-ray background (α ∼ 0.4, 1-10 keV) is harder than that of AGN (α ∼ 1) but our results show that it is consistent with the summed spectrum of the NELGs in the deep survey (α ∼ 0.4). This may finally reconcile the spectrum of the background with the properties of the sources that constitute it.