Kinematic Masses of Super-Star Clusters in M82 from High-Resolution Near-Infrared Spectroscopy

By N. McCrady, A. Gilbert, J. Graham. 2003

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Using high-resolution (R ~ 22,000) near-infrared (1.51-1.75 μm) spectra from Keck Observatory, we measure the kinematic masses of two super-star clusters in M82. Cross-correlation of the spectra with template spectra of cool evolved stars gives stellar velocity dispersions of σr = 15.9 ± 0.8 km s-1 for J0955505+694045 (MGG-9) and σr = 11.4 ± 0.8 km s-1 for J0955502+694045 (MGG-11). The cluster spectra are dominated by the light of red supergiants and correlate most closely with template supergiants of spectral types M0 and M4.5. King model fits to the observed profiles of the clusters in archival Hubble Space Telescope/Near-Infrared Camera and Multi-Object Spectometer images give half-light radii of rhp = 2.6 ± 0.4 pc for MGG-9 and rhp = 1.2 ± 0.17 pc for MGG-11. Applying the virial theorem, we determine masses of 1.5 ± 0.3 × 106 M☉ for MGG-9 and 3.5 ± 0.7 × 105 M☉ for MGG-11 (where the quoted errors include σr, rhp, and the distance). Population synthesis modeling suggests that MGG-9 is consistent with a standard initial mass function (IMF), whereas MGG-11 appears to be deficient in low-mass stars relative to a standard IMF. There is, however, evidence of mass segregation in the clusters, in which case the virial mass estimates would represent lower limits.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/79b3f213cfe3fb20f0e3a4b28ad2f5892ef16967

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Citations in the corpus

The evolution of runaway stellar collision products (2009, background): “For example, for the cluster MGG-11 in the starburst galaxy M 82 (M = 3.5 × 105 M , r = 1.2 pc McCrady et al. 2003), which was studied by Portegies Zwart et al. (2004), this leads to a central density ρc 108 M /pc3.”
A Universal Stellar Initial Mass Function? A critical look at variations in extreme environments (2010, result): “More worrisome is that some of these results have been derived within the same galaxy (e.g. M82, McCrady et al. 2003).”
Stellar Populations in the Nuclei of Late-Type Spiral Galaxies (2006, result): “Star formation rates in late-type disks are in no way comparable to those of starburst galaxies like M82, where the formation of massive clusters has been observed (e.g. McCrady et al. 2003).”
THE DISRUPTION OF GIANT MOLECULAR CLOUDS BY RADIATION PRESSURE & THE EFFICIENCY OF STAR FORMATION IN GALAXIES (2009, background): “30Myr) and old (& 30Myr) clusters in M51 with masses in the range 103 − 106M⊙ (Scheepmaker et al. 2007), for super star clusters in M82 withMcl = 105 − 4× 106M⊙ (McCrady et al. 2003; McCrady & Graham 2007), and in globular clusters with masses∼ 105 − 106M⊙ (Harris 1996).”
MAXIMALLY STAR-FORMING GALACTIC DISKS. I. STARBURST REGULATION VIA FEEDBACK-DRIVEN TURBULENCE (2011, background): “…near a central stellar cluster and the efficiency is high (see Appendix A), so that the value of p∗/m∗ will be comparable to the escape speed from the (super)cluster that forms – up to ∼ 100 km s−1 for the most extreme clusters (McCrady et al. 2003; Maraston et al. 2004; Overzier et al. 2009).”
Hubble Space Telescope STIS Spectra of Nuclear Star Clusters in Spiral Galaxies: Dependence of Age and Mass on Hubble Type (2006, background): “The most massive star clusters in M82 have typical masses of 5.54 ≤ logM ≤ 6.18 (McCrady et al. 2003).”
Runaway collisions in young star clusters - II. Numerical results (2005, result): “Following McCrady et al. (2003), they assume for MGG-9 an initial mass of 1.8 × 106 M⊙ and a half-mass radius of 2.6 pc. Unlike the case of MGG-11 for which there are indications of a lower cut-off of the IMF at ∼ 1M⊙ (which yields 〈M∗〉 ≃ 3M⊙), the observational data for MGG-9 is compatible with a…”
Disruption time scales of star clusters in different galaxies (2004, background): “Such a lower mass cut-off for the initial mass function is controversial, but is suggested in young star clusters like MGG-11 (McCrady et al. 2003) and MGG-F, both in M82 (Smith and Gallagher 2001) and in several of the young star clusters in the Antennae galaxies (Mengel et al. 2002).”
Massive Black Holes in Star Clusters. II. Realistic Cluster Models (2004, methodology): “Portegies Zwart et al. (2004) have performed N -body simulations of several star clusters in M82, using the cluster parameters determined by McCrady et al. (2003).”
Ultraluminous X-ray sources in the Chandra and XMM-Newton era (2011, background): “1 Myr (Pakull & Grisé 2008).”