Astronomical instrumentation

Abstract:

The large populations of young star clusters observed in interacting galaxies like NGC4038 4039 ("The Antennae") are widely believed to be the progenitors of part of the globular cluster systems seen in local elliptical galaxies. For a comprehensive study of the young clusters in the Antennae we have obtained near infrared broad and narrow band images (SOFI on the NTT). integral field spectroscopy (MPE-3D at the AAT) and medium and high resolution spectroscopy (ISAAC VLT-UT1 and UVES VLT-UT2). We find that all of the bright star clusters are young (< 20 Myr), with the interaction region hosting the youngest clusters (similar to 5 Myr). The nuclear starbursts are older (similar to 65 Myr), but also show snore recent star formation activity. Age variations on small spatial scales are seen throughout the merger. Cluster masses range from 10(5) to a few x 10(6) M-circle dot. A comparison between dynamically determined masses and those estimated from photometry in combination with starburst models suggests variations in the IMF from cluster to cluster.

Abstract:

We performed near infrared integral field spectroscopy of several star clusters and the nuclei of the prototypical merger NGC 4038/39 ("The Antennae"). Near infrared (NIR) images covered both galaxies. The collision of the two gas-rich spiral galaxies has triggered a starburst obvious from a large number of young star clusters. ISO data suggest that the most active star formation occurs in the region where the two galaxy disks overlap. A significant fraction of the total bolometric luminosity of the system is produced there. Since this region is heavily extincted in the optical, the investigation was made in the NIR. Using Brgamma emission and CO absorption features as age indicators, we derive the ages and mass estimates of the star clusters from a comparison with stellar synthesis models. Extinction is calculated from the Brgamma/Halpha ratio. The young, bright star clusters have ages ranging from 4-12 Myrs, while the nuclear starbursts are much older (50-80 Myrs). The overlap region hosts most of the youngest star clusters below similar to8 Myrs, while the northwestern region is dominated by star clusters in the age range between 8 and 12 Myrs. Several regions, including the northern nucleus, show evidence for sequential star formation on small spatial scales (<100pc).