The Compact Star-Forming Complex at the Heart of NGC 253

We discuss integral field spectra of the compact star-forming complex that is the brightest near-infrared (NIR) source in the central regions of the starburst galaxy NGC 253. The spectra cover the H and K passbands and were recorded with the Gemini NIR Spectrograph during sub-arcsec seeing conditions. Absorption features in the spectrum of the star-forming complex are weaker than in the surroundings. An absorption feature is found near 1.78um that coincides with the location of a C2 bandhead. Emission lines of Brgamma, [FeII], and HeI2.06um do not track the NIR continuum light. Pockets of star-forming activity that do not have associated concentrations of red supergiants, and so likely have ages < 8 Myr, are found along the western edge of the complex, and there is evidence that one such pocket contains a rich population of Wolf-Rayet stars. Unless the star-forming complex is significantly more metal-poor than the surroundings, then a significant fraction of its total mass is in stars with ages < 8 Myr. If the present-day star formation rate is maintained then the time scale to double its stellar mass ranges from a few Myr to a few tens of Myr, depending on the contribution made by stars older than ~ 8 Myr. If -- as suggested by some studies -- the star-forming complex is centered on the galaxy nucleus, then the nucleus of NGC 253 is currently experiencing a phase of rapid growth in its stellar mass.

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