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Barbara Laskin
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Dr. Jekyll or Mr. Hyde?  A Nearby Extreme Galaxy
Macalester Professor’s discovery will aid understanding of how galaxies form and remain stable

John Cannon

St. Paul, Minn. - May 1, 2009 - Macalester College Professor John Cannon has discovered a very extreme galaxy: one where gas is distributed over an area much larger than researchers had expected to find. Compared to other systems investigated to date, this “giant disk” dwarf galaxy has the largest size difference between stars and gas of any known galaxy.  This result is important for furthering our understanding of how galaxies form and how they remain stable over time.

Cannon and collaborators made the discovery during recent astronomy research at Macalester, using data from the Very Large Array (VLA) telescope in New Mexico and from the Kitt Peak National Observatory (KPNO) in Arizona. 

The KPNO data show the stars in the galaxy; this is how the object would appear to our eyes.  Looking at this data, the galaxy has a very small and compact stellar component.  The VLA data, on the other hand, show the gaseous component of the galaxy—the material from which those stars form. 

“Because the stars are so compact, we expected to see a system that has a similarly compact gaseous disk,” said Cannon.  “To our surprise, the gaseous disk is enormous - some 44 times larger than the size of the galaxy as seen in stars.  This is certainly a little galaxy doing big things.”

This galaxy, named “ADBS1138,” is considered an “extreme galaxy” because instead of having stars distributed throughout the galaxy, it has a very dense center where all the stars congregate.  This suggests that most of the gas—the raw material for star formation– has not been used; no stars are seen in the outer regions of the gaseous disk. 

This discovery raises important questions about disk stability and the nature of the mysterious “dark matter” seen in most galaxies.  Why do many galaxies form stars throughout their disks, while ADBS 1138 has only formed stars in the very innermost region?  Is dark matter distributed throughout the gaseous disk, and thus very much larger than the size of the galaxy’s stellar component?

Cannon’s research about this curious galaxy will be published in the May 10, 2009, edition of The Astrophysical Journal. Co-investigators Jessica Rosenberg (George Mason University) and John Salzer (Indiana University) join him on the manuscript. 

Macalester College, founded in 1874, is a national liberal arts college with a full-time enrollment of 1,858 students. Macalester is nationally recognized for its long-standing commitment to academic excellence, internationalism, multiculturalism and civic engagement.