My Research: Dark Clouds and Bright Young Stars

I am now at Boston University as a Post-Doc with Jim Jackson working on Infrared-Dark Clouds (IRDCs).

I was previously a Ph.D. student working as part of the COMPLETE Survey of Star forming clouds. Our goal is to observe nearby star-forming regions in a variety of ways to learn about (1) how well different methods of studying clouds agree and (2) how stars form.

By "clouds" I mean the great collections of dust and gas which form stars. They look somewhat similar to earthly clouds, but are much more tenuous than anything here on earth. By "nearby", I mean clouds between 500 and 1000 light-years away, so far away that we're seeing light that left these stars during the Middle Ages -- but this is still closer than many of the objects astronomers study.

My advisor was Alyssa Goodman and I studied the density structure of molecular clouds. I took deep near-infrared images and used them to make high-resolution extinction maps of parts of these star forming regions. Extinction mapping is simply measuring how much dust there is in the cloud by observing how light from background stars is made red as the dust scatters blue (shorter wavelength) light. We could then estimate the total mass of the cloud-- most of the mass is in essentially invisible hydrogen molecules, but there is normally a constant ratio between the amount of dust and the amount of hydrogen.

Studying Dense Cores with Ammonia

Ammonia, the common household chemical, is formed in the dense cores of gas where stars form. The structure of this molecule allows us to use various features of its spectra to measure the temperature of these very cold (~ 10 K, only a few degrees above absolute zero) dense cores. This temperature is key to deriving all sorts of other physical properties of the core; in combination with dust emission maps we can learn about a core's mass, its chemistry, and how turbulent it is. With the help of the Spitzer Space Telescope we are able to categorize cores based on whether they contain a young star and whether they are in a cluster of stars and study the physical properties of these different groups. Read my paper on the ammonia Properties of Dense Cores.

Hunting Galaxies to (and for) Extinction

In deep near-infrared images we see many objects which are not background stars. Instead, they are galaxies composed of billions of stars. Nearby galaxies look very different from stars, but more distant ones can sometimes be difficult to identify. If we want to study young stars galaxies can be a problem, as their colors mimic the colors of young stars at many infrared wavelengths. If we want to figure out where the dust is from the colors of background stars, galaxies are a potential contaminant, since their intrinsic colors are redder than most stars. However, if we can identify them robustly we can use them as extra background sources to make our maps better. Read my paper on Hunting Galaxies.

Cloudshine

In the course of obtaining very long exposure images of clouds in the near-infrared, we were very surprised to see the clouds themselves glowing. We named the effect cloudshine and modeled it as ambient starlight from many nearby stars reflecting off dust in the clouds. The pictures provide a beautiful qualitative picture of where the mass is in the clouds and how the wispy and condensed structures in molecular clouds exist together. It will also provide an important way to check simulations of what molecular clouds look like, and hopefully a direct measure of the column density of the cloud. Read more about cloudshine.