Washington, Jan 12 (ANI): Young and active galaxies evolve into 'red and dead' elliptical galaxies as their central super massive black holes and their jets starve them of their star-forming gas, a new study has revealed.
For years, astronomers have been developing a picture of galaxy evolution in which mergers between spiral galaxies could explain why nearby large elliptical galaxies have so few young stars.
The theoretical picture is chaotic and violent: The merging galaxies knock gas and dust into clumps of rapid star formation, called starbursts, and down into the maws of the supermassive black hole growing in the merger's core.
As more and more matter heaves onto the black hole, powerful jets erupt, and the region around the black hole glows brilliantly as a quasar. The jets blowing out of the merger eventually plow out the galaxy's potential star-forming gas, ending the starbursts.
Until now, astronomers had never spotted enough mergers at this critical, jet-plowing stage to definitively link jet-driven outflows to the cessation of starburst activity.
During its Early Science observations in late 2011, however, ALMA became the first telescope to confirm nearly two dozen galaxies in this brief stage of galaxy evolution.
"Despite ALMA's great sensitiviy to detecting starbursts, we saw nothing, or next to nothing - which is exactly what we hoped it would see," said lead investigator Dr. Carol Lonsdale of the North American ALMA Science Center at the National Radio Astronomy Observatory (NRAO) in Charlottesville, Virginia.
For these observations, ALMA was tuned to look for dust warmed by active star-forming regions. However, half of Lonsdale's two dozen galaxies did not show up at all in ALMA's observations, and the other half were extremely dim, indicating that there was very little of the tell-tale dust present.
"ALMA's results reveal to us that there is little-to-no starbursting going on in these young, active galaxies. The galaxy evolution model says this is thanks to their central black holes whose jets are starving them of star-forming gas," Lonsdale said.
"On its first run out of the gate, ALMA confirmed a critical phase in the timeline of galaxy evolution," Lonsdale added.
Once their star-forming gas has been blown away, merging galaxies will be unable to make new stars.
As the last generation of massive and brilliant, but short-lived, blue stars dies out, the long-lived, lower mass, redder stars come to dominate the merger's star population, giving the gas-starved galaxy an overall reddish hue over time. (ANI)
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