The turnover , or peak , magnitude in a galaxy ’ s globular cluster luminosity function ( GCLF ) may provide a standard candle for an independent distance estimator .
Here we examine the GCLF of the giant elliptical NGC 4365 using photometry of \sim 350 globular clusters from the Hubble Space Telescope ’ s Wide Field and Planetary Camera 2 ( WFPC2 ) .
The WFPC2 data have several advantages over equivalent ground–based imaging .
The membership of NGC 4365 in the Virgo cluster has been the subject of recent debate .
We have fit a Gaussian and t _ { 5 } profile to the luminosity function and find that it can be well represented by a turnover magnitude of m _ { V } ^ { 0 } = 24.2 \pm 0.3 and a dispersion \sigma = 1.28 \pm 0.15 .
After applying a small metallicity correction to the ‘ universal ’ globular cluster turnover magnitude , we derive a distance modulus of ( m – M ) = 31.6 \pm 0.3 which is in reasonable agreement with that from surface brightness fluctuation measurements .
This result places NGC 4365 about 6 Mpc beyond the Virgo cluster core .
For a V _ { CMB } = 1592 \pm 24 km s ^ { -1 } the Hubble constant is H _ { \circ } = 72 _ { -12 } ^ { +10 } km s ^ { -1 } Mpc ^ { -1 } .
We also describe our method for estimating a local specific frequency for the GC system within the central 5 h ^ { -1 } kpc which has fewer uncertain corrections than a total estimate .
The resulting value of 6.4 \pm 1.5 indicates that NGC 4365 has a GC richness similar to other early type galaxies .