An X-Ray Detected Group of Quiescent Early-Type Galaxies atz= 1.6 in the Chandra Deep Field South

Masayuki Tanaka, Finoguenov Alexis, Mohammad Mirkazemi, David J. Wilman, John S. Mulchaey, Yoshihiro Ueda, Yongquan Xue, William N. Brandt, Nico Cappelluti
2013 Nippon Tenmon Gakkai obun kenkyu hokoku  
(Abridged) We report the discovery of an X-ray group of galaxies located at a high redshift of z=1.61 in the Chandra Deep Field South. The group is first identified as an extended X-ray source. We use a wealth of deep multi-wavelength data to identify the optical counterpart -- our red sequence finder detects a significant over-density of galaxies at z 1.6 and the brightest group galaxy is spectroscopically confirmed at z=1.61. We measure an X-ray luminosity of L_0.1-2.4 keV= 1.8±0.6 × 10^43
more » ... /s, which then translates into a group mass of 3.2±0.8 × 10^13 M_sun. This is the lowest mass group ever confirmed at z>1.5. The deep optical-nearIR images from CANDELS reveal that the group exhibits a surprisingly prominent red sequence. A detailed analysis of the spectral energy distributions of the group member candidates confirms that most of them are indeed passive galaxies. Furthermore, their structural parameters measured from the near-IR CANDELS images show that they are morphologically early-type. The newly identified group at z=1.61 is dominated by quiescent early-type galaxies and the group appears similar to those in the local Universe. One possible difference is the high fraction of AGN (38^+23_-20 statistical sample of high-z groups is needed to draw a general picture of groups at this redshift. Such a sample will hopefully be available in near future surveys.
doi:10.1093/pasj/65.1.17 fatcat:aquf6d4hprfhhgxyyzyvpffpdu