| Abstract | We have detected 21 cm emission from the "Sombrero" galaxy, NGC 4594. For an assumed distance of 18.6 Mpc, the hydrogen mass is 8.7 + 2.6 x 108 M0, and the ratio MHIILpg is 0.0069 + 0.0021 in solar units. The gas is probably distributed in a ring and exhibits a classic, double-peaked line profile typical of later-type disk galaxies. Based on the rotational motions in the gas, corroborated by velocities measured from the stellar absorption lines, we have estimated the mass and mass-to-light ratio. The total mass within a radius of 3' (16.2 kpc) is 4.3 + 0.4 x 1011 M0, and an upper limit to MILE for the spheroidal component is 3-4. This low value indicates that MiL does not significantly increase away from the nucleus out to a distance of 3'. Since the bulge of NGC 4594 resembles an ordinary elliptical galaxy in many respects, this result may have significant implications for the behavior of MiL in the outer regions of elliptical galaxies as well. It suggests that large increases in MiL for ellipticals, if they occur at all, must take place far out in the halos, where the surface brightness is very low and where the effect will be extremely difficult to measure directly. A very rough estimate for the amount of H I expected on the basis of the dust content is 2.2 x l0 M0, a factor of 2.5 greater than the observed value. If this additional hydrogen were in molecular form and associated with dense clouds emitting CO, the predicted CO signal would be below our recently determined upper limit of 0.1 K. Subject headings: galaxies: individual - galaxies: internal motions - galaxies: stellar content - radio sources: 21 cm radiation |
