Sarah Sweet , Rodrigo Carrasco , and Fernanda Urrutia
January 2017
Gemini South Explores the Growth of Massive Galaxy Clusters
Using high-angular-resolution images obtained at Gemini South , we have measured , for the first time , the stellar mass – size relation for 49 galaxies in a cluster environment at redshift z ~ 1 . Our data suggest that the most likely relationship between stellar mass and size has a constant slope over time . This finding leads us to conclude that the probable evolutionary course for the most massive spheroid-like galaxies since z ~ 1 is either from minor mergers ( i . e ., when a galaxy grows via accretion of small satellite galaxies ), or adiabatic processes ( such as outflows from active galactic nuclei ), or a combination of both .
The Evolution of Massive Galaxies Over Cosmic Time
During the past 20 years astronomers have developed a picture for the evolution of the size and structure of galaxies — from the formation of the first galaxies in the early Universe , to what we see today . One of the most important discoveries in the last decade is that the most massive spheroid-like galaxies ( i . e ., galaxies with masses > 10 11 M Sun
) in the distant Universe ( z > 1 ) are much smaller in physical size than those with the same stellar mass in the local Universe ; the effective radii of these massive galaxies at z ~ 1- 4 are observed to be , on average , a factor of 2-6 times more compact when compared with local systems with the same stellar mass . At z = 0 , massive compact galaxies are very rare ; only a few have been found to date . Presumably , the most massive high-redshift galaxies must evolve significantly in size to become present-day passive elliptical galaxies .
January 2017 | 2016 Year in Review GeminiFocus
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