The extreme synchronicity of stellar ages of red galaxies in [...] (S. Andreon et al.)

Vol. 529
In section 1. Letters

The extreme synchronicity of stellar ages of red galaxies in the JKCS041 cluster at z=2.2

by S. Andreon, A&A 529, L5
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How fast did galaxies form? How fast did they form their stars? In the galaxy cluster JKCS041 at z=2.2 (one quarter of the age of the universe), red massive galaxies show a tight distribution in color, whose small scatter indicates a star formation history that is highly synchronized across galaxies. This can be interpreted as a spread in stellar age of 160+/-30 Myr, as if all stars in these galaxies were formed in a single event. This would not be expected in the hierachical scenario, where massive galaxies are progressively formed through merging episodes sometimes involving gas, hence star formation.