2009ApJ...697.1180K

We present observations of a massive star cluster near the nuclear region of the nearby starburst galaxy NGC 253. The peak of near-infrared (IR) emission, which is spatially separated by 4'' from the kinematic center of the galaxy, is coincident with a super star cluster whose properties we examine with low-resolution (R ∼ 1200) infrared Cerro Tololo Inter-American Observatory spectroscopy and optical/near-IR Hubble Space Telescope imaging. Extinction, measured from Fe II lines, is estimated at A_V= 17.7±2.6. The age of the cluster is estimated at 5.7 Myr, based on Brγ equivalent width for an instantaneous burst using Starburst99 modeling. However, a complex star formation history is inferred from the presence of both recombination emission and photospheric CO absorption. The ionizing photon flux has a lower limit of 7.3±2.5x10⁵³/s, corrected for extinction. Assuming a Kroupa initial mass function, we estimate a cluster mass of ∼1.4^+0.4_–0.5x 10⁷ M_☉. We observe a strong Wolf-Rayet signature at 2.06 µm and report a weak feature at 2.19 µm which may be due to a massive stellar population, consistent with the derived mass and age of this cluster.