The Extraordinary Infrared Spectrum of NGC 1222 (Mkn 603)

Abstract

The infrared spectra of starburst galaxies are dominated by the low-excitation lines of [NeII] and [SIII], and the stellar populations deduced from these spectra appear to lack stars larger than about 35 Msun. The only exceptions to this result until now were low metallicity dwarf galaxies. We report our analysis of the mid-infrared spectra obtained with IRS on Spitzer of the starburst galaxy NGC 1222 (Mkn 603). NGC 1222 is a large spheroidal galaxy with a starburst nucleus that is a compact radio and infrared source, and its infrared emission is dominated by the [NeIII] line. This is the first starburst of solar or near-solar metallicity, known to us, which is dominated by the high-excitation lines and which is a likely host of high mass stars. We model the emission with several different assumptions as to the spatial distibution of the high- and low-excitation lines and find that the upper mass cutoff in this galaxy is 40-100 Msun.

arXiv commentaccepted, Astronomical Journal. 29 pp, 4 figures. In replacement version an acknowledgment to NRAO is added

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• Far-infrared line spectra of active galaxies from the Herschel/PACS Spectrometer: the complete database
• The Atlas3D project -- XXXI. Nuclear radio emission in nearby early-type galaxies
• The MASSIVE survey - XI. What drives the molecular gas properties of early-type galaxies
• Probing the Excitation of Extreme Starbursts: High Resolution Mid-IR Spectroscopy of Blue Compact Dwarfs
• Radio continuum observations of local star-forming galaxies using the Caltech Continuum Backend on the Green Bank Telescope
• Extreme Star Formation