Near-infrared integral-field spectroscopy of violent starburst environments


Richard de Grijs


Near-infrared (NIR) integral-field spectroscopy (IFS) of violent starburst environments at high spatial resolution has the potential to revolutionise our ideas regarding the local interactions between the newly-formed massive stars and the interstellar medium of their host galaxies. To illustrate this point, I will present our NIR IFS analysis of the central starburst region of NGC 1140, obtained with CIRPASS on Gemini-South, and planned GNIRS observations of the same system. While strong [Fe II] emission, thought to originate in the thermal shocks associated with supernova remnants, is found throughout the galaxy, higher-order Brackett emission is predominantly associated with the northern starburst region. The Brackett lines originate from recombination processes occurring on smaller scales in (young) HII regions. The time-scale associated with strong [Fe II] line emission implies that most of the recent star-formation activity in NGC 1140 was induced in the past ~(35-55) Myr. Based on the spatial distributions of the [Fe II] versus Brackett line emission, we conclude that a galaxy-wide starburst was induced several tens of Myr ago, with more recent starburst activity concentrated around the northern starburst region. This scenario is confirmed by our analysis of the spectral energy distributions of the compact, young massive star clusters (YMCs) detected in new and archival broad-band Hubble Space Telescope images. Our photometric mass estimates of the NGC 1140 YMCs, likely upper limits, are comparable to those of the highest-mass Galactic globular clusters and to spectroscopically confirmed masses of (compact) YMCs in other starburst galaxies. Our detection of similarly massive YMCs in NGC 1140 supports the scenario that such objects form preferentially in the extreme environments of interacting and starburst galaxies. I will argue that IFS at higher spatial resolution would allow us trace (i) the massive outflows ("superwinds") expected to originate in the dense YMCs, and (ii) their impact on the galaxy's ISM.