| Résumé | 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 subarcsecond seeing conditions. Absorption features in the
spectrum of the star-forming complex are weaker than in the surroundings. An absorption feature is found near
1.78 μm that coincides with the location of a C₂ bandhead. If this feature is due to C₂ then the star-forming
complex has been in place for at least a few hundred Myr. Emission lines of Brγ, [Fe II], and He I 2.06 μm 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 timescale 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’s nucleus, which presumably
contains a large population of old and intermediate-age stars, then the nucleus of NGC 253 is currently
experiencing a phase of rapid growth in its stellar mass |
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