Star clusters in tidal debris

We present results of a Hubble Space Telescope (HST) UBVI-band study of star clusters in tidal tails, using new WFC3 and ACS imaging to complement existing WFPC2 data. We survey 12 tidal tails across seven merging systems, deriving ages and masses for 425 star cluster candidates (SCCs). The stacked mass distribution across all systems follows a power law of the form dN/dM proportional to M-beta, with beta = -2.02 +/- 0.15, consistent with what is seen in other star-forming environments. GALEX and Swift UV imaging provide star formation rates (SFRs) for our tidal tails, which when compared with ages and masses of our SCCs, allows for a determination of the cluster formation efficiency (CFE). We find the CFE increases with increasing SFR surface density, matching the theoretical model. We confirm this fit down at SFR densities lower than previously measured (log Sigma(SFR)(M(circle dot)yr(-1)kpc(-2)) approximate to -4.2), as related to the CFE. We determine the half-light radii for a refined sample of 57 SCCs with our HST WFC3 and ACS imaging, and calculate their dynamical age, finding the majority of them to be gravitationally bound. We also provide evidence of only low-mass (<10(4) M-circle dot) cluster formation in our nearest galaxy, NGC 1487, consistent with the theory that this system is a dwarf merger.

Automated summary

In this study, star clusters in tidal tails were investigated using the Hubble Space Telescope. The results provide insights into the ages, masses, and formation efficiency of these star clusters. The study also reveals a strong correlation between the star formation rate of the tidal tails and the cluster formation efficiency.