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.
