A WFC3 study of globular clusters in NGC 4150 : An early-type minor merger

Abstract

We combine near-ultraviolet (NUV; 2250 Å) and optical (U, B, V, I) imaging from the Wide Field Camera 3 (WFC3), on-board the Hubble Space Telescope (HST), to study the globular cluster (GC) population in NGC 4150, a sub-L* (M ~-18.48 mag) early-type minor-merger remnant in the Coma I cloud. We use broad-band NUV-optical photometry from the WFC3 to estimate individual ages, metallicities, masses and line-of-sight extinctions [E(B - V)] for 63 bright (M <-5 mag) GCs in this galaxy. In addition to a small GC population with ages greater than 10 Gyr, we find a dominant population of clusters with ages centred around 6 Gyr, consistent with the expected peak of stellar mass assembly in faint early types residing in lowdensity environments. The old and intermediate-age GCs in NGC 4150 are metal poor, with metallicities less than 0.1 Z, and reside in regions of low extinction [E(B - V) <0.05 mag]. We also find a population of young, metal-rich (Z > 0.3 Z) clusters that have formed within the last Gyr and reside in relatively dusty [E(B - V) > 0.3 mag] regions that are coincident with the part of the galaxy core that hosts significant recent star formation. Cluster disruption models (in which ~80-90 per cent of objects younger than a few ×10 yr dissolve every dex in time) suggest that the bulk of these young clusters are a transient population.