DISCOVERY OF A PROTOCLUSTER AT z similar to 6

作者：Toshikawa Jun^*; Kashikawa Nobunari; Ota Kazuaki; Morokuma Tomoki; Shibuya Takatoshi; Hayashi Masao; Nagao Tohru; Jiang Linhua; Malkan Matthew A; Egami Eiichi; Shimasaku Kazuhiro; Motohara Kentaro; Ishizaki Yoshifumi

来源：Astrophysical Journal, 2012, 750(2): 137.

DOI：10.1088/0004-637X/750/2/137

• early Universe
• galaxies: clusters: general
• galaxies: high-redshift
• large-scale structure of Universe

We report the discovery of a protocluster at z similar to 6 containing at least eight cluster member galaxies with spectroscopic confirmations in the wide-field image of the Subaru Deep Field (SDF). The overdensity of the protocluster is significant at the 6 sigma level, based on the surface number density of i%26apos;-dropout galaxies. The overdense region covers similar to 6%26apos; x 6%26apos; (14 Mpc x 14 Mpc in comoving units at z = 6) and includes 30 i%26apos;-dropout galaxies. Follow-up spectroscopy revealed that 15 of these are real z similar to 6 galaxies (5.7 %26lt; z %26lt; 6.3). Of these 15, 8 are clustering in a narrow redshift range (Delta z %26lt; 0.05 centered at z = 6.01), corresponding to a seven-fold increase in number density over the average in redshift space. We found no significant difference in the observed properties, such as Ly alpha luminosities and UV continuum magnitudes, between the eight protocluster members and the seven non-members. The velocity dispersion of the eight protocluster members is 647 +/- 124 km s(-1), which is about three times higher than that predicted by the standard cold dark matter model. This discrepancy could be attributed to the distinguishing three-dimensional distribution of the eight protocluster members. We discuss two possible explanations for this discrepancy: either the protocluster is already mature, with old galaxies at the center, or it is still immature and composed of three subgroups merging to become a larger cluster. In either case, this concentration of z = 6.01 galaxies in the SDF may be one of the first sites of formation of a galaxy cluster in the universe.

• 出版日期2012-5-10
• 单位中国科学院国家天文台