We analyzed nine X-ray bright Virgo early-type galaxies observed by both the ASCA and ROSAT. In this paper we discuss the results of abundance determinations of Mg, Si and Fe. For galaxies with low metallicities, there is evidence for an overabundance of alpha-process elements relative to iron. Compared to the stars in our Galaxy, the combined results on Virgo early-types show a somewhat larger heavy element contribution from SNe~Ia at higher metallicities. We explain the observed trend by the metallicity dependence of SN~Ia metal production and present constraints on the available theoretical modeling for low-metallicity inhibition of SNe~Ia (Kobayashi et al. 1998). Our results imply a cut-off metallicity in the range 0.07-0.3 solar and require a lower limit of 0.3 solar on the Fe contribution of SN~Ia. We estimate a SN~Ia rate at the centers of the brightest galaxies in our sample of ~0.05h753 SNU. The rates inferred from optical searches values should be corrected for the presence of ``faint'' SN Ia events, since these release limited metals and therefore are not found through the X-ray emission. With this correction the present-day SN~Ia rate in early-type galaxies is 0.10+/-0.06 h752 SNU (Cappellaro et al. 1997) and is therefore comparable with the X-ray.
19th Texas Symposium on Relativistic Astrophysics and Cosmology
- Pub Date:
- December 1998