THE STELLAR HALO OF M104. I. A SURVEY FOR PLANETARY NEBULAE AND THE PLANETARY NEBULA LUMINOSITY FUNCTION DISTANCE

摘要

We used the CTIO 4 m telescope to make a complete and kinematically unbiased survey of M104 (NGC 4594; the Sombrero galaxy) for planetary nebulae (i.e., stars) out to 16 kpc. We present the positions and monochromatic [O III] λ5007 magnitudes of 294 planetaries, and use the observed planetary nebula luminosity function (PNLF) to measure a distance of 8.9 ± 0.6 Mpc to the galaxy. The luminosity-specific PN number α_(2.5) in the halo of M104 is approximately 21.7 x 10~(-9) solar luminosity, which for its color (B— V) = 0.95, is comparable to the values in other galaxies. We use the PNLF distance to M104 to compare its luminosity to the luminosities of the brightest galaxies in the Virgo Cluster, finding that if M104 were in the Virgo Cluster, it would be the third brightest galaxy. We combined the PNLF distance and the observed velocity corrected for Virgo infall to calculate a Hubble constant H_0 = 91 ± 8 km s~(-1) Mpc~(-1). We also used the PNLF distances to the NGC 1023 group, the Leo group, the Virgo Cluster, and the Fornax Cluster to derive Hubble constants corrected for Virgo infall. The values of H_0 for M104, the NGC 1023 group, the Virgo Cluster, and the Fornax Cluster are in excellent agreement, suggesting that the PNLF distances and Schechter's linear infall model provide a self-consistent representation of the Hubble expansion and Virgo infall within most regions of the local supercluster. The unweighted mean of the four values is H_0 = 84 ± 4. The value of H_0 derived for the Leo group differs by four standard deviations from the mean of the other four measurements. We conclude that there may be large peculiar motions in the spatially extended Leo spur.