ADS: Spilker et al. 2014
arXiv: Spilker et al. 2014
This was a paper I wrote for my second year project (sort of Arizona’s version of a MSc thesis). The idea was to take all of those beautiful ALMA spectra we used to figure out the redshifts of a couple dozen SPT galaxies and stack/combine them together to see if we could see any lines from molecules that are usually much, much fainter than CO. These other molecules, like HCN, HNC, HCO+, etc., tell you about gas that’s denser than what CO traces – the kind of gas that stars are actively forming out of, in other words. Knowing how bright these lines are on average also lets you predict how long you’d have to observe single objects in a more dedicated follow-up program.
We ended up detecting 9 lines total of 13CO, HCN, HNC, HCO+, and CN. These lines end up being about 10-30x fainter than CO, which makes them very hard to detect. In fact, they’ve only been seen in a handful of other galaxies at high redshift, and most of those are known to have strong AGN activity. This paper lays the groundwork for future programs looking to detect these kinds of lines in individual galaxies – with ALMA at full capability, a lot of previously-impossible science questions are well within the realm of possibility.