X-ray luminous IRAS galaxies

Abstract

A sample of 14708 extragalactic IRAS sources selected from the Point Source Catalog via statistical classification has been cross-correlated with the ROSAT All Sky Survey (Bolleret al., 1992). 244 galaxies emerge as being detected both by ROSAT and IRAS.

The most interesting point is the discovery of a dozen of “normal” spirals whose X-ray luminosities reach nearly 10⁴³ erg s⁻¹ (0.1–2.4 keV), higher than previous detection limits of a few 10⁴¹ erg s⁻¹ (Stockeet al. 1991; Green, Anderson and Ward, 1992). We obtained optical spectra for nine of them, showing Seyfert spectra for three of the objects (thus previous mis-classifications), spectra close to LINERs for two further objects and normal IRAS galaxy spectra for the last four.

In the case of “normal” galaxies, the source of energy is not clear yet and could be related to the high rate of star formation likely to occur in the central regions or also to a low level active nucleus. The study of these objects is of interest to the nature of LINERs and, more generally, to possible relations between AGN and starbursts (Sanderset al., 1988).