A multiwavelength study of the young star clusters and interstellar medium in the antennae galaxies

We report on a multiwavelength study of the relationship between young star clusters in the Antennae galaxies (NGC 4038/9) and their interstellar environment, with the goal of understanding the formation and feedback effects of star clusters in merging galaxies. This is possible for the first time because various new observations (from X-rays to radio wavelengths) have become available in the past several years. Quantitative comparisons are made between the positions of the star clusters (broken into three age groups) and the properties of the interstellar medium by calculating the two-point correlation functions. We find that young star clusters are distributed in a clustered fashion, demonstrated by power-law angular autocorrelation functions with slopes in the range -0.8 to -1.0. The young embedded clusters (ages similar to5 Myr) are found to be more associated with long-wavelength radiation (mid-infrared and longer), while clusters with ages similar to 10 Myr or older are more associated with short-wavelength radiation (e.g., far-UV and X-ray). The youngest star clusters are associated with molecular cloud complexes with characteristic radii of about 1 kpc. In addition, there is a weak tendency for them to be found in regions with higher H I velocity dispersions. There is some evidence that both cloud-cloud collisions and shocks from recent star formation can trigger star cluster formation, but no dominant triggering mechanism is identified for the majority of the clusters in the Antennae. Feedback from young bright cluster complexes reveals itself in the form of large Ha bubbles and Ha velocity gradients in shells around the complexes. We estimate the current star formation rate to be approximate to 20 M-circle dot yr(-1) and the gas consumption timescale to be similar to 700 Myr. The latter is comparable to the merging timescale and indicates that star formation has been enhanced by the merger event. Finally, we find that the Schmidt law, with index N approximate to -1.4, is also a good description of the cluster formation triggered by merging in the Antennae. There is some evidence that feedback effects may modify the Schmidt law at scales below 1 kpc.