Charting Stars and Gases in 40,000 Galaxies

Posted: May 22, 2009 at 10:32 am, Last Updated: May 28, 2009 at 12:22 pm

By Leah Kerkman Fogarty

Jessica Rosenberg, assistant professor of physics and astronomy

Jessica Rosenberg, assistant professor of physics and astronomy

Think back to your class trips to the planetarium. Remember the awe-inspiring view of all those stars and heavenly bodies projected onto the ceiling? Now imagine charting stars and celestial gases in about 40,000 nearby galaxies.

That’s the responsibility facing Mason astronomer Jessica Rosenberg. She’s been creating an enormous dataset — a huge extragalactic survey — which she and her colleagues will use to help answer fundamental questions facing astronomers today.

One the major questions in astronomy is how galaxies evolve, she says.

“These data will give us some of the pieces to that puzzle,” says Rosenberg, an assistant professor in Mason’s Department of Physics and Astronomy. “To do this, we need to move beyond looking at only the stars and study the gas and stars together.”

400 Million Light Years Away

Rosenberg’s finished product will combine these two elements to create a more complete set of data than if stars or gas were mapped independently.

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“The understanding of these components of galaxies allows us to test some of the theories of how the universe evolves,” she says.

The survey will look for galaxies out to 400 million light years from the Milky Way, which is “far away, but relatively close relative to the full scale of the universe,” says Rosenberg.

“Usually, when we look for galaxies, we look for them by their stars,” explains Rosenberg. “But there have been a few studies that have tried to look for galaxies by their gas.”

Rosenberg’s extragalactic study will be the first to combine optical (stars) and radio (gas) survey data. It focuses on matching data collected from the Arecibo Legacy Fast ALFA (ALFALFA) radio survey with optical data from the Sloan Digital Sky Survey (SDSS).

Rosenberg has been involved with the ALFALFA survey from its inception. She contributed to the survey planning, observed, worked on data reduction and wrote some analysis software.

The Primordial Element

The ALFALFA survey will have collected information on about 25,000 gas-rich galaxies when it is completed in early 2011.

Rosenberg will use a large cross-section of the information about these galaxies to compare against the additional 30,000 or so galaxies from the SDSS. She anticipates approximately 40,000 galaxies in the overlap region.

By combining the optical and radio data, astronomers will measure the fraction of mass in two of the major components of galaxies, which is the key to understanding how galaxies form and evolve.

“Hydrogen gas is the primordial element out of which everything in a galaxy was formed,” Rosenberg says. So by evaluating a galaxy’s stars and gas, she hopes to shed some light on the processes that govern galaxy evolution.

This article originally appeared in Mason Research 2009.

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