Receiver Arrays

For the Interested Reader
Here I describe a little more about how we get our data and what exactly those data are. In this project we want to map the farthest extent of emission in a galaxy. Unfortunately making big maps usually takes a lot of time, and observatories don't just give it away.

Why do we bother? The light we look at comes from molecules. Giant clouds of molecular gas and dust are where stars form, so we learn about the environment in these mysterious regions.

Mapmaker, Mapmaker, Make me a Map...
Normally you make a map by looking at one spot and then calibrating by looking at blank sky at another spot. You build a map point by point, and it is very slow. A simple way to map faster is to look at a lot of positions at the same time.

To look at many points at once we use receiver arrays. This is a grid of receivers, rather than just one, placed at the focus of the telescope. Film and CCD cameras work the same way only they use silver atoms and microchips as the array elements. Radio receivers are much harder to make so we have much fewer pixels. One of the most successful array receivers, which I used for my Ph.D. thesis, is QUARRY, recently retired from the FCRAO. Its replacement is SEQUOIA, which eventually will have more than twice the pixels as QUARRY, and will work faster.

Maps of What?
Star formation occurs solely in molecular clouds. We want to understand

We specifically are looking at the molecular gas in other galaxies. From our vantage point, we can see the galaxy rotate and find where the stars are most likely forming. We can trace large patterns like spiral arms, bars and rings, and compare them to the gas motions to figure out why those structures are there.