July 24, 2013
Mystery Of Missing Massive Galaxies Gets Help From ALMA Telescope
[ Watch the Video: Three-Dimensional View of NGC 253 ]
Lee Rannals for redOrbit.com - Your Universe Online
Astronomers using the European Southern Observatory's (ESO) ALMA telescope in Chile say they have discovered how vigorous star formation in a galaxy can blast gas out of it and deprive future generations of stars of the fuel they need to form and grow. The scientists wrote in the journal Nature that these images help explain the strange paucity of very massive galaxies in the Universe.
"With ALMA's superb resolution and sensitivity, we can clearly see for the first time massive concentrations of cold gas being jettisoned by expanding shells of intense pressure created by young stars," said Alberto Bolatto of the University of Maryland, USA lead author of the paper.
"The amount of gas we measure gives us very good evidence that some growing galaxies spew out more gas than they take in. We may be seeing a present-day example of a very common occurrence in the early Universe."
Astronomers have been puzzled at finding so few high-mass galaxies in the universe. Computer models show that older, redder galaxies should have considerably more mass and a larger number of stars, but it seems that the galactic winds or outflow of gas are so strong that they deprive the galaxy of the fuel they need for the formation of the next generation of stars.
The team was studying the Sculptor Galaxy, or NGC 253, a spiral galaxy that sits about 11.5 million light-years away from our Solar System. NGC 253 is one of the closest starburst galaxies visible from the southern Hemisphere.
Gas can be removed from a galaxy in one of two ways. One way is through supermassive black holes, while the other is to potentially blow gas out of a galaxy through galactic winds generated by star formation. The second method has never been observed with enough resolution or sensitivity to measure the outflow of gas or its impact on star formation.
"These features trace an arc that is almost perfectly aligned with the edges of the previously observed hot, ionized gas outflow," said Fabian Walter, a lead investigator at the Max Planck Institute for Astronomy in Heidelberg, Germany, and a co-author of the paper. "We can now see the step-by-step progression of starburst to outflow."
The researchers say molecular gas in quantities nearly ten times the mass of our Sun were being ejected from the galaxy at about 25 to 155 miles per second. The total amount of gas ejected would add up to more gas than what helped form the galaxy's stars in the same time.
"For me, this is a prime example of how new instruments shape the future of astronomy. We have been studying the starburst region of NGC 253 and other nearby starburst galaxies for almost ten years," says Walter.
Adam Leroy with the National Radio Astronomy Observatory, a facility of the National Science Foundation (NSF), said more studies are needed to help figure out the ultimate fate of the gas that's being carried away by the cosmic wind. He said this will help us understand whether these starburst-driven winds simply recycle or truly remove star-forming material.
"Probably in a galaxy like this, the gas is pulled back into the heart of the galaxy, perhaps after several hundred million years. Star formation then takes off again and the whole process repeats itself," says Bolatto.