We present optical spectroscopy of 16 star clusters in the merging galaxies NGC 4038/39 ("The Antennae") and supplement this dataset with HST imaging. The age and metallicity of each cluster is derived through a comparison between the observed Balmer and metal line strengths with simple stellar population models. We then estimate extinctions and masses using the photometry. We find that all but three clusters have ages between ∼ 3 − 200 Myr, consistent with the expected increase in the star-formation rate due to the merger. Most of the clusters have velocities in agreement with nearby molecular and Hi gas that has been previously shown to be rotating within the progenitor galaxies, hence star/cluster formation is still taking place within the galactic disks. However, three clusters have radial velocities that are inconsistent with being part of the rotating gas disks, which is surprising given their young (200 − 500 Myr) ages. Interestingly, we find a stellar association with the same colors (V-I) near one of these three clusters, suggesting that the cluster and association were formed concurrently and have remained spatially correlated. We find evidence for spatially distributed cluster formation throughout the duration of the merger. The impact of various assumptions about the star/cluster formation rate on the interpretation of the cluster age distribution are explored, and we do not find evidence for long term "infant mortality" as has been previously suggested. Models of galaxy mergers that include a prescription for star formation can provide an overall good fit to the observed cluster age distribution.

We present a spectroscopic study of the stellar cluster population of M82, the archetype starburst galaxy, based primarily on new Gemini-North multi-object spectroscopy of 49 star clusters. These observations constitute the largest to date spectroscopic dataset of extragalactic young clusters, giving virtually continuous coverage across the galaxy; we use these data to deduce information about the clusters as well as the M82 poststarburst disk and nuclear starburst environments. Spectroscopic age-dating places clusters in the nucleus and disk between (7, 15) and (30, 270) Myr, with distribution peaks at ∼ 10 and ∼ 140 Myr respectively. We find cluster radial velocities in the range v R ∈ (−160, 220) km s −1 (wrt the galaxy centre) and line of sight Na I D interstellar absorption line velocities v Na I D R ∈ (−75, 200) km s −1 , in many cases entirely decoupled from the clusters. As the disk cluster radial velocities lie on the flat part of the galaxy rotation curve, we conclude that they comprise a regularly orbiting system. Our observations suggest that the largest part of the population was created as a result of the close encounter with M81 ∼ 220 Myr ago. Clusters in the nucleus are found in solid body rotation on the bar. The possible detection of WR features in their spectra indicates that cluster formation continues in the central starburst zone. We also report the potential discovery of two old populous clusters in the halo of M82, aged 8 Gyr. Using these measurements and simple dynamical considerations, we derive a toy model for the invisible physical structure of the galaxy, and confirm the existence of two dominant spiral arms.

The observed properties of young star clusters, such as the core radius and luminosity profile, change rapidly during the early evolution of the clusters. Here we present observations of six young clusters in M51 where we derive their sizes using Hubble Space Telescope (HST) imaging and ages using deep Gemini‐North spectroscopy. We find evidence for a rapid expansion of the cluster cores during the first 20 Myr of their evolution. We confirm this trend by including data from the literature of both Galactic and extragalactic embedded and young clusters, and possible mechanisms (rapid gas removal, stellar evolutionary mass loss and internal dynamical heating) are discussed. We explore the implications of this result, focussing on the fact that clusters were more concentrated in the past, implying that their stellar densities were much higher and relaxation times (trelax) correspondingly shorter. Thus, when estimating if a particular cluster is dynamically relaxed (i.e. when determining if a cluster's mass segregation is due to primordial or dynamical processes), the current relaxation time is only an upper limit, with trelax likely being significantly shorter in the past.

The Gemini Multi-conjugate Adaptive Optics System -GeMS, a facility instrument mounted on the Gemini South telescope, delivers a uniform, near diffraction limited images at near infrared wavelengths (0.95 µm -2.5 µm) over a field of view of 120 . GeMS is the first sodium layer based multi laser guide star adaptive optics system used in astronomy. It uses five laser guide stars distributed on a 60 square constellation to measure for atmospheric distortions and two deformable mirrors to compensate for it. In this paper, the second devoted to describe the GeMS project, we present the commissioning, overall performance and operational scheme of GeMS. Performance of each sub-system is derived from the commissioning results. The typical image quality, expressed in full with half maximum, Strehl ratios and variations over the field delivered by the system are then described. A discussion of the main contributor to performance limitation is carried-out. Finally, overheads and future system upgrades are described.