We present a study of globular clusters ( GCs ) in 17 relatively nearby early-type galaxies , based on deep F555W and F814W images from the Wide Field / Planetary Camera 2 ( WFPC2 ) on board the Hubble Space Telescope ( HST ) .
A detailed analysis of color distributions , cluster sizes and luminosity functions is performed and compared with GCs in the Milky Way .
In nearly all cases , a KMM test returns a high confidence level for the hypothesis that a sum of two Gaussians provides a better fit to the observed color distribution than a single Gaussian , although histograms of the ( V - I ) _ { 0 } distribution are not always obviously bimodal .
The blue and red peak colors returned by the KMM test are both found to correlate with absolute host galaxy B band magnitude and central velocity dispersion ( at about the 2 - 3 \sigma level ) , but we see no clear correlation with host galaxy V - I or J - K color .
Red GCs are generally smaller than blue GCs by about 20 % .
The size difference is seen at all radii and within sub-bins in ( V - I ) _ { 0 } color , and exists also in the Milky Way and Sombrero ( M104 ) spiral galaxies .
Fitting t _ { 5 } functions to the luminosity functions of blue and red GC populations separately , we find that the V -band turn-over of the blue GCs is brighter than that of the red ones by about 0.3 mag on the average , as expected if the two GC populations have similar ages and mass distributions but different metallicities .
Brighter than the “ turn-over ” at M _ { V } \sim - 7.5 , the luminosity functions ( LFs ) are well approximated by power-laws with an exponent of about -1.75 .
This is similar to the LF for young star clusters , suggesting that young and old globular clusters form by the same basic mechanism .
We discuss scenarios for GC formation and conclude that our data appear to favor “ in-situ ” models in which all GCs in a galaxy formed after the main body of the proto-galaxy had assembled into a single potential well .