Probing the circumnuclear stellar populations of Starburst galaxies in the near-infrared

Abstract

We employ the NASA Infrared Telescope Facility’s near-infrared spectrograph SpeX at 0.8– 2.4 μm to investigate the spatial distribution of the stellar populations (SPs) in the four well-known starburst galaxies: NGC 34, NGC 1614, NGC 3310 and NGC 7714. We use the STARLIGHT code updated with the synthetic simple SPs models computed by Maraston. Our main results are that the near-infrared light in the nuclear surroundings of the galaxies is dominated by young-/intermediate-age SPs (t ≤ 2 × 109 yr), summing from ~40 up to 100 per cent of the light contribution. In the nuclear aperture of two sources (NGC 1614 and NGC 3310), we detected a predominant old SP component (t > 2 × 10⁹ yr), while for NGC 34 and NGC 7714 the younger component prevails. Furthermore, we found evidence of a circumnuclear star formation ring-like structure and a secondary nucleus in NGC 1614, in agreement with previous studies. We also suggest that the merger/interaction experienced by three of the galaxies studied, NGC 1614, NGC 3310 and NGC 7714, can explain the lower metallicity values derived for the young SP component of these sources. In this scenario, the fresh unprocessed metal poorer gas from the destroyed/interacting companion galaxy is driven to the centre of the galaxies and mixed with the central region gas, before star formation takes place. In order to deepen our analysis, we performed the same procedure of SP synthesis using the Maraston & Strömbäck evolutionary population synthesis models. Our results show that the newer and higher resolution M11 models tend to enhance the old-/intermediate-age SP contribution over the younger ages.