Star formation activity in cores within infrared dark clouds
Abstract
In this dissertation, I probe the star formation activity of cores within infrared dark clouds (IRDCs). IRDCs are identified as extinction features against the bright Galactic plane at infrared wavelengths. They are dense, cold, and massive, conditions expected for clouds that host the elusive earliest stages of high-mass star formation. A sample of 38 IRDCs was mapped in 1.2 mm continuum emission using the Institut de Radioastronomie Millimétrique (IRAM) 30m Telescope. These data show that each IRDC contains at least one compact, dense core, and most IRDCs contain several cores. This dissertation focuses on a sample of 190 cores found within these 38 IRDCs.
Some cores within IRDCs display several indicators of star formation. Among these signatures are extended, enhanced 4.5 mm emission, which I call 'green fuzzies,' and 24 mm point sources. I have identified green fuzzies within the sample of 190 IRDC cores and subsequently correlated the green fuzzies with 24 mm point sources. I call cores within IRDCs that contain a green fuzzy coincident with a 24 mm point source 'active,' and I call cores within IRDCs that contain neither star formation indicator 'quiescent.' I also find additional cores that are dominated by 8 mm emission, which I call 'red.' I hypothesize that quiescent, active, and red cores form a star-forming evolutionary sequence within IRDCs. I test this evolutionary sequence by comparing the sizes, densities, maser activity, and temperatures of the sample of 190 cores. I find that active cores are smaller and denser than quiescent cores, as expected if quiescent cores collapse to form active cores. I find that active and red cores are more likely to contain H 2 O and CH 3 OH masers (well-known signposts for star formation) than quiescent cores. Finally, I find that red cores are warmer than active cores, and that active cores are warmer than quiescent cores. Together, these results support the hypothesis that quiescent, active, and red cores form a star-forming evolutionary sequence within IRDCs.- Publication:
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Ph.D. Thesis
- Pub Date:
- 2010
- Bibcode:
- 2010PhDT.........2C
- Keywords:
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- Star formation;
- Infrared dark clouds;
- Active cores