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		| Paper: | 
		Discovery of an Evolved Galaxy Cluster at z > 2 | 
	 
	
		| Volume: | 
		399, Panoramic Views of Galaxy Formation and Evolution | 
	 
	
		| Page: | 
		363 | 
	 
	
		| Authors: | 
		Onodera, M.; Daddi, E.; Kong, X.; Arimoto, N.; Renzini, A.; Brusa, M.; Finoguenov, A. | 
	 
	
	
		| Abstract: | 
		Over a 1,000-arcmin2 field imaged with the Spitzer/IRAC, we have discovered a candidate galaxy cluster at z > 2 with extremely red, evolved galaxies concentrated within an area of only 30 arcsec in diameter. The cluster candidate shows an extended x-ray emission with LX(0.1 − 2.4keV) ≃ 1044 erg s−1 likely to be associated with cluster potential. Among the galaxies with meaningful photometric redshifts, 20 galaxies in this region are consistent with photometric redshift of zphot = 2.15 ± 0.2. Their rest-frame optical colors are consistent with those of red-sequence galaxies with 1–3 Gyr stellar populations, reaching (z −K)AB ≃ 4. Compared with the passively evolving field galaxies at similar redshifts, these colors are typically ≃ 1 magnitude redder, indicating the presence of a strong environmental effect on the evolution of stellar populations at high redshift. | 
	 
	
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