| Recent observations have revealed numerous young massive star clusters, often known as "young globular clusters". Their formation and evolution are important astrophysical processes and may potentially have cosmological implications. In this work, we focus on the star clusters in the nearest ongoing merger NGC 4038/9 (the "Antennae"). With the Hubble Space Telescope, we identify clusters with all ages, most of which are younger than 20 Myr. Our goal is to study their formation mechanisms, and the relation with the interstellar medium environment, and their evolutionary connection with old globular clusters.; We find that their luminosity function and mass function are best described as power laws with indices around -2. The masses of young star clusters cover the range 104 ≤ M ≤ 10 6 M⊙ . This result is distinctly different from that of old globular clusters that has a "preferred" scale at M ≈ 2 x 105 M⊙ . To understand the difference in MF between the young and old star clusters, we conduct a theoretical study on the effects of dynamical disruption of individual clusters on the mass function. We find that, for a wide variety of initial conditions, the mass function develops a characteristic scale, that is remarkably close to the observed one for globular clusters after 12 Gyr. In addition, we find that some radial anisotropy in the initial velocity distribution, especially when decreasing outward, is needed to account for the observed near-uniformity of the mass functions of globular clusters. This is consistent with the observed near-isotropy of the present velocity distributions because clusters on elongated orbits are preferentially destroyed.; In order to understand the formation and feedback effects of young star clusters, we have also conducted a multi-wavelength study on the association between young star clusters and their interstellar environment in the Antennae 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. We find that young star clusters are distributed in a clustered fashion. 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 steeper CO velocity gradients and higher HI velocity dispersions. We estimate the current star formation rate in the Antennae to be ≈20 M⊙ yr-1, and the gas consumption timescale to be ∼700 Myr. Finally, we find that the Schmidt law, with index N ≈ -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. |
