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A. M. Gilbert (UC Berkeley)
Starbursts preferentially form stars in super star clusters (SSCs) whose sizes and masses are comparable to those of globular clusters (GCs). Thus SSCs may be young GCs. Establishing any relationship between SSCs and GCs requires examining both the photometric and kinematic properties of individual SSCs and the entire population, which is the goal of this study of two nearby starbursts, the dwarf irregular NGC 1569 and the young merger NGC 4038/39 (the Antennae).
Near-IR spectroscopy and population synthesis modeling of the handful of SSCs in NGC 1569 reveals supergiant-dominated stellar populations and permits measurement of their ages and internal velocity dispersions, and hence their masses and initial mass functions (IMFs). The IMF is critical in comparing SSCs and GCs since the latter are comprised solely of low-mass stars, while SSCs are viewed via massive stars. Although a range of IMFs is inferred for SSCs in the Antennae and a few other galaxies, the brightest NGC 1569 SSCs have normal IMFs, so they can evolve into GCs.
The Antennae have formed a large population of SSCs, the youngest of which are embedded in gas and dust. Their ionizing and FUV radiation powers giant compact HII regions and dissociates the surrounding molecular gas. The faintest SSCs resemble their most massive local analog, 30 Doradus, while the brightest are 100 times more powerful. Near-IR spectroscopy and population synthesis modeling reveal SSC ages and massive stellar content as well as their kinematics and interaction with surrounding gas. The youngest SSCs drive supersonic outflows detected via broad Brackett \gamma lines (FWHM 60-100 km/s) that efficiently entrain gas, and they are dubbed Emission-Line Clusters (ELCs). Their radial velocity dispersion is typical of a galactic stellar disk, so the ELC population must evolve further dynamically if it is to attain the kinematic distribution of a halo GC population.
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.