The UV spectrum of the narrow emission line X-ray emitting nucleus ofthe galaxy NGC 7582.

Abstract

UV spectra of the narrow emission line, X-ray emitting nucleus of the galaxy NGC 7582 obtained with the IUE instrument show a steep featureless continuum, obeying a power-law of spectral index 3.4 + or - 0.4, close to the value of Ward et al. (1978) for the visible spectrum (spectral index equal to 3). The visual extinction on the line-of-sight of the source of continuum was derived from the strength of the 2200 A feature, and is found to be much smaller than the one deduced for the emission-line region by Ward et al. (1980). The total energy distribution cannot be accounted for in terms of a hot star model, but is rather well represented by a power-law spectrum of spectral index 2.1 suffering a total absorption corresponding to a reddening of 0.45. From the presence of a jump in the continuum near 3600 A, it is estimated that hot stars must contribute approximately 30% of the flux at visible wavelengths. The column density of gas in front of the source of continuum is 2.5 + or - 1.7 x 10 to the 21st atom/sq cm, so that a low-energy cut-off in the X-ray spectrum should be observed around 0.75 keV. The absence of emission lines in the UV range is consistent with the high value of the extinction for the line-emitting region found by Ward et al. (1980).