By observing the dust and gas at the center of NGC 1266, a team of astronomers led by Dr Katherine Alatalo of the California Institute of Technology in Pasadena has detected a ‘perfect storm’ of turbulence that is squelching star formation in a region that would otherwise be an ideal star factory.
This Hubble/ALMA composite image shows the nearby lenticular galaxy NGC 1266; ALMA data are orange. Image credit: NASA / ESA / Hubble / ALMA / NRAO / ESO / NAOJ.
High-energy jets powered by supermassive black holes can blast away a galaxy’s star-forming fuel, resulting in so-called ‘red and dead’ galaxies. Using the Atacama Large Millimeter/submillimeter Array (ALMA), the astronomers have discovered that black holes don’t have to be nearly so powerful to shut down star formation in their host galaxies.
The turbulence detected in NGC 1266 is stirred up by jets from the galaxy’s central black hole slamming into an incredibly dense envelope of gas.
This dense region, which may be the result of a recent merger with another smaller galaxy, blocks nearly 98 % of material propelled by the jets from escaping the galactic center.
NGC 1266 is a lenticular galaxy located in the constellation Eridanus, about 100 million light-years away. Leticular galaxies are spiral galaxies, like our own Milky Way, but they have little interstellar gas available to form new stars.
Previous observations of the galaxy revealed a broad outflow of gas from the galactic center traveling up to 400 km per second.
Dr Alatalo’s team estimates that this outflow is as forceful as the simultaneous supernova explosion of 10,000 stars.
The jets, though powerful enough to stir the gas, are not powerful enough to give it the velocity it needs to escape from the system.
The region observed by the astronomers contains about 400 million times the mass of our Sun in star-forming gas, which is 100 times more than is found in giant star-forming molecular clouds in our own Milky Way.
Normally, gas this concentrated should be producing stars at a rate at least 50 times faster than the astronomers observe in NGC 1266.
Previously, astronomers believed that only extremely powerful quasars and radio galaxies contained black holes that were powerful enough to serve as a star-forming on/off switch.
“The usual assumption in the past has been that the jets needed to be powerful enough to eject the gas from the galaxy completely in order to be effective at stopping start formation,” said Dr Mark Lacy of National Radio Astronomy Observatory, who is a co-author of the paper published in the Astrophysical Journal (arXiv.org preprint).
To make this discovery, Dr Alatalo, Dr Lacy and their colleagues first pinpointed the location of the far-infrared light being emitted by the galaxy.
Normally, this light is associated with star formation and enables astronomers to detect regions where new stars are forming.
In the case of NGC 1266, however, this light was coming from an extremely confined region at the center of the galaxy.
“This very small area was almost too small for the infrared light to be coming from star formation,” Dr Alatalo said.
With ALMA, the astronomers were then able to trace the location of the very dense molecular gas at the galactic center. They found that the gas is surrounding this compact source of far-infrared light.
Under normal conditions, this gas would be forming stars at a very high rate. The dust embedded within it would then be heated by young stars and seen as a bright and extended source of infrared light.
The small size and faintness of the infrared source in NGC 1266 suggests that it’s instead choking on its own fuel, seemingly in defiance of the rules of star formation.
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Katherine Alatalo et al. 2015. Suppression of Star Formation in NGC 1266. ApJ 798, 31; doi: 10.1088/0004-637X/798/1/31
