Evidence of role played by colossal black holes in ending star formation in galaxies obtained

June 5th, 2008 - 12:00 pm ICT by ANI  

Washington, June 5 (ANI): Astronomers have obtained unprecedented observational evidence of the role that supermassive black holes play in ending star formation in galaxies.

Dr Sugata Kaviraj of Oxford University, UK, has presented the report of these observations.

The team used ultraviolet light to provide solid observational evidence that the stormy centres of galaxies powered by supermassive black holes - ‘Active Galactic Nuclei’ (AGN) - take over from exploding stars (supernovae) as the main mechanism by which the gas that fuels star formation is dispersed, as galaxies reach a critical size of 10 billion times the mass of the Sun.

Our models of galaxy formation are all based on the notion that Active Galactic Nuclei are involved in snuffing out - quenching - star formation in galaxies which are too large for mechanisms based on supernovae to explain, said Dr Kaviraj.

According to Kaviraj, astronomers believe that the jets produced by the AGN are powerful enough to blow away star-forming gas from even the largest galaxies. But up until now, astronomers have not had solid observational evidence to back this up.

Our study indicates, for the first time from a purely observational viewpoint, the relationship between the mass of a galaxy and whether supernovae or AGN play a dominant role in quenching star formation, she said.

The scientific team from Oxford University, UK and the University of Hertfordshire, UK studied a special class of post-starburst galaxies, which lack ongoing star formation but whose spectra indicate that they formed a substantial fraction of their stellar mass in the very recent past.

A vigorous period of recent star formation in these galaxies has therefore been rapidly quenched, making these objects perfect test-beds to probe the quenching process.

The galaxies studied in this work are, by cosmological standards, nearby, at distances of 1.5 billion light-years or less.

Using a novel combination of ultraviolet data from the Galaxy Evolution Explorer (an orbiting space telescope launched by NASA in 2003) and optical data from the Sloan Digital Sky Survey, the scientists were able to measure the efficiency with which quenching takes place in individual galaxies with unprecedented accuracy.

According to co-author Joe Silk, who has pioneered the use of black holes in models of galaxy formation, Some form of feedback is slowing down and quenching star formation in both nearby galaxies and the distant Universe.

These results point to the likely culprit being a combination of the effects of exploding stars and supermassive black holes, with black holes dominating in the massive galaxies, as envisaged in contemporary galaxy formation models. (ANI)

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