Star Clusters in the Tidal Tails of Interacting Galaxies: Cluster Populations Across a Variety of Tail Environments

We have searched for compact stellar structures within 17 tidal tails in 13 different interacting galaxies using F606W- and F814W-band images from the Wide Field Planetary Camera 2 on the Hubble Space Telescope. The sample of tidal tails includes a diverse population of optical properties, merging galaxy mass ratios, H i content, and ages. Combining our tail sample with Knierman et al., we find evidence of star clusters formed in situ with MV < −8.5 and V − I < 2.0 in 10 of 23 tidal tails; we are able to identify cluster candidates to MV = −6.5 in the closest tails. Three tails offer clear examples of “beads on a string” star formation morphology in V − I color maps. Two tails present both tidal dwarf galaxy candidates and cluster candidates. Statistical diagnostics indicate that clusters in tidal tails may be drawn from the same power-law luminosity functions (with logarithmic slopes ≈−2 to −2.5) found in quiescent spiral galaxies and interiors of interacting systems. We find that the tail regions with the largest number of observable clusters are relatively young (≲250 Myr old) and bright (V ≲ 24 mag arcsec−2), probably attributed to the strong bursts of star formation in interacting systems soon after periapse. Otherwise, we find no statistical difference between cluster-rich and cluster-poor tails in terms of many observable characteristics, though this analysis suffers from complex, unresolved gas dynamics and projection effects.