The properties of globular clusters in dwarf galaxies are key to understanding the formation of globular cluster systems , and in particular in verifying scenarios in which globular cluster systems of larger galaxies formed ( at least partly ) from the accretion of dwarf galaxies .
Here , we revisit the globular cluster system of the dE , N galaxy NGC 3115 DW1 – a companion of the nearby S0 galaxy NGC 3115 – adding Keck/LRIS spectroscopy and HST/WFPC2 imaging to previous ground-based photometry .
Spectra for seven globular clusters reveal normal abundance ratios with respect to the Milky Way and M31 clusters , as well as a relatively high mean metallicity ( [ Fe/H ] \approx - 1.0 \pm 0.1 dex ) .
Crude kinematics indicate a high velocity dispersion within 10 kpc which could either be caused by dark matter dominated outer regions , or by the stripping of outer globular clusters by the nearby giant galaxy NGC 3115 .
The total galaxy mass out to 3 and 10 kpc lies between 1 \cdot 10 ^ { 10 } and 1 \cdot 10 ^ { 11 } M _ { \odot } and 2 \cdot 10 ^ { 10 } and 4 \cdot 10 ^ { 11 } M _ { \odot } , respectively , depending on the mass estimator used and the assumptions on cluster orbits and systemic velocity .
The HST imaging allows measurement of sizes for two clusters , returning core radii around 2.0 pc , similar to the sizes observed in other galaxies .
Spectroscopy allows an estimate of the degree of contamination by foreground stars or background galaxies for the previous ground-based photometry , but does not require a revision of previous results : NGC 3115 DW1 hosts around N _ { GC } = 60 \pm 20 clusters which corresponds to a specific frequency of S _ { N } = 4.9 \pm 1.9 , on the high end for massive dEs .
Given its absolute magnitude ( M _ { V } = -17.7 mag ) and the properties of its cluster system , NGC 3115 DW1 appears to be a transition between a luminous dE and low-luminosity E galaxy .