Novel data has been obtained by the Hubble Cosmological Evolution Survey (COSMOS), suggesting the potential evolution of distant galaxies. Researchers have pondered over obscure findings that galaxies continue to demonstrate signs of expansion, even in the absence of star formation. At the point at which galaxies no longer manufacture new stars, they are classified “quenched galaxies”, and have also been whimsically christened “post-menopausal” galaxies.
Many theories have been proposed to explicate the difference in magnitude between quenched galaxies from long ago, relative to newly forming quenched galaxies. Simply stated, older galaxies that have ceased star production appear significantly smaller than today’s galaxies that have ceased star production. Discombobulated scientists were initially stumped as to how these “post-menopausal” galaxies, who were no longer pumping out star formations, were still growing. The dominant hypothesis revolved around the potential for two quenched galaxies to, essentially, amalgamate, explaining the perceived increase in size. These theories were dismissed as being improbable, since many smaller quenched galaxy stacks would need to be floating around together to cause such formations; scientists simply did not observe this phenomenon.
“The apparent puffing up of quenched galaxies has been one of the biggest puzzles about the galaxy evolution for many years,” Marcella Carollo of the Federal Institute of Technology University (ETH), based in Zurich, declared. Nick Scoville, from Caltech (Pasadena), discussed what lied at the heart of the problem, “No single collection of images has been large enough to enable us to study very large numbers of galaxies in exactly the same way until Hubble’s cosmos.”
Researchers decided further data was necessary to solve this cosmological mystery. Mapping an area of the sky, nine times larger than the moon, harnessing the power of the Canada-France-Hawaii Telescope and Subaru Telescope, they made their extensive findings from COSMOS.
The answer to the problem was elementary, according to experts. When peering back through time, looking at quenched galaxies that were in existence when the galaxy was half its current age, they established that they were smaller and more compact; it was concluded that these galaxy formations do not alter greatly in volume, definitively disproving the previous notion of galaxy mergers.
The next question was, why did it appear that the quenched galaxies were growing from one moment in time (e.g. when looking at formations close to us) to another (e.g. looking at formations at considerable distance from us)? Simon Lily of ETH provides the answer. “We found that a larger number of the galaxies instead switch off at later times, joining their smaller quenched siblings and giving the mistaken impression of individual galaxy growth over time.”
Alvio Renzini of the INAF Padua Observatory in Italy, sought to clarify, “It’s like saying that an increase in the average apartment size in a city is not due to the addition of new rooms to old buildings, but rather to the construction of new, larger apartments.”
So, all along, it seems that quenched galaxies do not increase in size and, quite simply, the size variations between quenched stars at different periods in time have been due to galaxies “switching off” at different times. In short, new galaxies, observed close to us, switch off star production later than old galaxies, observed far away.
Written By: James Fenner