ADS: Spilker et al. 2015
ArXiv: Spilker et al. 2015
Stars are born from giant clouds of gas made mostly of molecular hydrogen. One of the best ways to observe this gas indirectly is to use the carbon monoxide (CO) molecule. It’s even better if you can observe it at high resolution – this can tell you about, for example, the relative distribution of stars, dust, gas, etc. within a galaxy. Unfortunately, CO is very faint in distant galaxies, so there haven’t been very many high-resolution observations of it. I was able to take advantage of a gravitational lens modeling code I wrote to figure out what the CO-emitting gas in two very distant galaxies looked like. In both cases, the gas was more spatially extended than the dust (which tells you where stars are actively being born). This might mean that, even though these galaxies are building new stars hundreds of times faster than our own Milky Way galaxy, they’re still only being born in relatively small parts of the galaxy.
Since we had high resolution, I was able to calculate the conversion factor between the observed CO brightness and an actual molecular gas mass in three independent ways – fortunately they all agreed pretty well. Having high resolution images of both the dust (aka star formation) and CO (aka molecular gas fuel) lets us put these galaxies on one of the most famous relationships about star formation. As it turns out, the difference in size between these two tracers causes a noticeable shift in the relationship compared to a case where you only know the size of the galaxy from one tracer. This just means we need to be more careful when making the star formation relation.