Search

We present a spectroscopic survey of 21 young massive clusters and complexes and one tidal dwarf galaxy (TDG) candidate in Stephan's Quintet, an interacting compact group of galaxies. All of the selected targets lie outside the main galaxies of the system and are associated with tidal debris. We find clusters with ages between a few and 125 Myr and confirm the ages estimated through Hubble Space Telescope photometry by Fedotov et al., as well as their modeled interaction history of the Quintet. Many of the clusters are found to be relatively long-lived, given their spectrosopically derived ages, while their high masses suggest that they will likely evolve to eventually become intergalactic clusters. One cluster, T118, is particularly interesting, given its age (~125 Myr), high mass (~2 x 106 M☉), and position in the extreme outer end of the young tidal tail. This cluster appears to be quite extended (Reff ~ 12-15 pc) compared to clusters observed in galaxy disks (Reff ~ 3-4 pc), which confirms an effect we previously found in the tidal tails of NGC 3256, where clusters are similarly extended. We find that star and cluster formation can proceed at a continuous pace for at least ~150 Myr within the tidal debris of interacting galaxies. The spectrum of the TDG candidate is dominated by a young population (~7 Myr), and, assuming a single age for the entire region, has a mass of at least 106 M☉. [ABSTRACT FROM AUTHOR]

The post-starburst region B in M82 and its massive star cluster component have been the focus of multiple studies, with reports that there is a large population of coeval clusters of age ∼1 Gyr, which were created with a Gaussian initial mass distribution. This is in disagreement with other studies of young star clusters, which invariably find a featureless power-law mass distribution. Here, we present Gemini-North optical spectra of seven star clusters in M82-B and show that their ages are all between 10 and 300 Myr (a factor of 3–100 younger than previous photometric results) and that their extinctions range between near zero and 4 mag ( A V). Using new HST ACS-HRC U-band observations we age date an additional ∼30 clusters whose ages/extinctions agree well with those determined from spectroscopy. Completeness tests show that the reported ‘turn-over’ in the luminosity/mass distributions is most likely an artefact, due to the resolved nature of the clusters. We also show that the radial velocities of the clusters are inconsistent with them belonging to a bound region. [ABSTRACT FROM AUTHOR]