We present an astrometry and photometry catalogue of globular cluster ( GC ) candidates detected with HST WFPC2 in a sample of 19 early-type galaxies , appropriate for comparison to the low-mass X-ray binary ( LMXB ) populations observed with Chandra .
In a companion paper , we present the Chandra data and investigate the relation between these populations .
We demonstrate that , although there is little evidence of a colour-magnitude correlation for the GCs , after estimating mass and metallicity from the photometry , under the assumption of a single age simple stellar population , there is a significant positive correlation between mass and metallicity .
We constrained { [ Z / H ] = ( -2.1 \pm 0.2 ) + ( 0.25 \pm 0.04 ) log _ { 10 } M } , with a 1- \sigma intrinsic scatter of 0.62 dex in metallicity .
If GCs are bimodal in metallicity this relation is consistent with recent suggestions of a mass-metallicity relation only for metal-poor clusters .
Adopting a new technique to fit the GC luminosity function ( GCLF ) accounting for incompleteness and the Eddington bias , we compute the V-band local GC specific frequency ( { S _ { N } } ) and specific luminosity ( { S _ { L } } ) of each galaxy .
We show that { S _ { L } } is the more robust measure of the richness of a GC population where a significant fraction is undetected due to source detection incompleteness .
We find that the absolute magnitude of the GCLF turnover exhibits intrinsic scatter from galaxy to galaxy of \sim 0.3 mag ( 1- \sigma ) , limiting its accuracy as a standard distance measure .