Globular Cluster Luminosity Functions and the Hubble Constant from WFPC2 Imaging: The Dominant Group Elliptical NGC 5846

Duncan A. Forbes
Lick Observatory, University of California, Santa Cruz
Jean P. Brodie
Lick Observatory, University of California, Santa Cruz
John Huchra
Center for Astrophysics, Harvard--Smithsonian, Cambridge

Abstract: The Hubble Space Telescope's Wide Field and Planetary Camera 2 (WFPC2) has several advantages over ground--based observations for the study of globular cluster luminosity functions (GCLFs) and distance determination. Here we present WFPC2 data on the globular clusters associated with NGC 5846. This giant elliptical is the dominant galaxy in a small, compact group located ~ 13 Mpc beyond the Virgo cluster. We have detected over 1200 globular clusters in three (central, north and south) separate pointings. %This is the first time a globular cluster system has been studied with %the WFPC2 over three pointings. The luminosity function in each of these pointings are statistically the same, indicating that the mean luminosity (mass) does not vary between ~ 3 and 30 kpc from the galaxy center. This suggests that dynamical friction and bulge shocking destruction processes are insignificant. We have fit a Gaussian and t_5 profile to the GCLF (of the combined pointings) and find that it is well represented by a turnover magnitude of m^0_V = 25.05 +/- 0.10 and a dispersion of sigma = 1.34 +/- 0.06. Our 50% completeness level is ~ 1 mag fainter than the turnover. After applying a metallicity correction to the `universal' GCLF turnover magnitude, we derive a distance modulus of (m--M) = 32.32 +/- 0.23. For a group velocity V_{CMB} = 1883 +/- 28 km s^{-1}, the Hubble constant is H_o = 65 +/- 8 km s^{-1} Mpc^{-1}.

Pick up:

The whole paper


Duncan A. Forbes
Lick Observatory
University of California, Santa Cruz
Santa Cruz CA 95064
forbes@lick.ucsc.edu