Astronomers Discover Nearly 200 Previously Unknown ‘Red’ Galaxies

John P. Millis, Ph.D. for – Your Universe Online
One of the greatest aspects of NASA’s astronomical research program is that the data accumulated from virtually all of the instruments – X-ray satellites, Infrared detectors, gamma-ray satellites – is available to the public. This means professional and amateur astronomers alike have the ability to make breakthrough discoveries.
For instance, in 2007 Dutch school teacher Hanny van Arkel discovered a peculiar blob in an image of the spiral galaxy IC 2497 while participating in the scientific crowd sourcing project Galaxy Zoo. Now known as Hanny’s Voorwerp (Dutch for Hanny’s object) the source of the radiation is a hot topic in the astronomical community.
But beyond citizen science, professionals are getting in on the action as well. Astronomers Ivana Damjanov, Margaret Geller, Ho Seong Hwang, and Igor Chilingarian of the Harvard-Smithsonian Center for Astrophysics (CfA), combed through archival data from the Sloan Digital Sky Survey, looking for dense red galaxies known in the scientific community as “red nuggets”.
These galaxies are characterized by masses some 10 times greater than that of the Milky Way, but have volumes 100 times smaller. They are also important to cosmology theories as well, because most models predict the early Universe would have been filled with these types of galaxies.
However, previous attempts to find examples of these galaxies in the nearby regions of the Universe yielded few results. This is puzzling because low-mass red stars – the types that would be abundant in these galaxies – are long-lived, even longer than the age of the Universe. So, if absent, theories of galaxy evolution would be in question.
The challenge is that in optical images these galaxies appear as red stars, making them difficult to pick out. “These red nugget galaxies were hiding in plain view, masquerading as stars,” says Damjanov. But, using the archival survey data, the team was able to identify candidate objects for their study.
Using various other telescopes – such as the Hubble Space Telescope and the Canada-France-Hawaii Telescope – the team then turned their attention to spectroscopically analyzing these candidates, which would assist them in determining which objects were stars and which were red nuggets. The study revealed about 200 of the objects were, in fact, the target galaxies.
This was an important confirmation of the particular abundance of these galaxies in our neighborhood of the Universe. “Now we know that many of these amazingly small, dense, but massive galaxies survive. They are a fascinating test of our understanding of the way galaxies form and evolve,” explains Geller.
This result can now be used to refine models of how galaxies in the Universe evolved, and how the cosmos itself may have progressed over billions of years. “Many processes work together to shape the rich landscape of galaxies we see in the nearby universe,” says Damjanov.
The research was presented on Wednesday, June 11 at a meeting of the Canadian Astronomical Society (CASCA) in Quebec, QC.

Image 2 (below): This series of photos shows three “red nugget” galaxies at a distance of about 4 billion light-years, and therefore seen as they were 4 billion years ago. At left, a lonely one without companion galaxies. The one in the middle is alone as well, although it appears to be next to a larger spiral galaxy. That blue spiral is actually much closer to us, only one billion light-years away. Finally, the red nugget on the right might have some companion galaxies residing nearby. Credit: Ivana Damjanov & CFHT MegaCam Team