Jonathan Foster's Homepage

Astronomy compels the soul to look upwards and leads us from this world to another.

      ~ Plato, The Republic

My Research: Dark Clouds and Bright Young Stars

Me in the Fog

Less than photometric conditions at CTIO

I am currently a Post-Doctoral research associate with Jim Jackson working on Infrared-Dark Clouds (IRDCs), the MALT90 Survey and various other topics in high-mass star formation. IRDCs are dense clouds seen in extinction against the diffuse light of galaxy and are great places to look for the early stages of high-mass star formation.

As a Ph.D. student I worked as part of the COMPLETE Survey of Star forming clouds with my advisor, Alyssa Goodman. The COMPLETE survey focused on the Perseus, Ophiuchus, and Serpens molecular clouds, where low- to intermediate-mass star formation is happening.

This page provides little snapshots focusing on my recent research topics and publications. On this website you can also find my full publications list, my Curriculum Vitae and my contact information

Extinction Distances to Dark Clouds

We have completed a study comparing different methods of obtaining distances to dark, star-forming clouds. We chose a sample of clouds for which there is a direct parallax measurement of the distance to maser spots within the cloud. We compared those distances against kinematic distances (using our knowledge of the rotation of the galaxy to estimate where a cloud is based on how fast it is moving) and extinction distances (using the fact that dark clouds make background stars appear fainter and redder). The main comparison figure is shown above and you can read the full paper.

The MALT90 Pilot Survey

In preparation for the large multi-year Millimeter Astronomy Legacy Team 90 GHz (MALT90) Survey, we conducted a short pilot survey to figure out how best to choose our targets and verify that our mapping scheme worked well. MALT90 will survey thousands of dense molecular clumps associated with high-mass star formation in a variety of evolutionary stages (as pictured above). These clumps cover only a small fraction of the Galactic plane, so we needed to select the best way to identify where to look. On the basis of the Pilot Survey detection rates, we chose the ATLASGAL catalog as our input source list. You can see the full results of the Pilot Survey at the MALT90 Pilot Survey Webpage.

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.