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(Reference retrieved automatically from Web of Science through information on FAPESP grant and its corresponding number as mentioned in the publication by the authors.)


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de Oliveira, R. Lopes [1] ; Carrasco, E. R. [2] ; de Oliveira, C. Mendes [1] ; Bortoletto, D. R. [1, 3] ; Cypriano, E. [1] ; Sodre, Jr., L. [1] ; Lima Neto, G. B. [1]
Total Authors: 7
[1] Univ Sao Paulo, Dept Astron, Inst Astron Geofis & Ciencias Atmosfericas, BR-05508090 Sao Paulo - Brazil
[2] AURA, So Operat Ctr, Gemini Observ, La Serena - Chile
[3] Lab Nacl Astrofis, Itajuba - Brazil
Total Affiliations: 3
Document type: Journal article
Source: ASTRONOMICAL JOURNAL; v. 139, n. 1, p. 216-227, JAN 2010.
Web of Science Citations: 7

We present a new insight on NGC 6034 and UGC 842, two groups of galaxies previously reported in the literature as being fossil groups. The study is based on optical photometry and spectroscopy obtained with the CTIO Blanco telescope and Sloan Digital Sky Survey archival data. We find that NGC 6034 is embedded in a large structure, dominated by three rich clusters and other small groups. Its first and next four ranked galaxies have magnitude differences in the r band and projected distances which violate the optical criteria to classify it as a fossil group. We confirm that the UGC 842 group is a fossil group, but with about half the velocity dispersion that is reported in previous works. The velocity distribution of its galaxies reveals the existence of two structures in its line of sight, one with sigma(nu) similar to 223 km s(-1) and another with sigma(nu) similar to 235 km s(-1), with a difference in velocity of similar to 820 km s(-1). The main structure is dominated by passive galaxies, while these represent similar to 60% of the second structure. The X-ray temperature for the intragroup medium of a group with such a velocity dispersion is expected to be kT similar to 0.5-1 keV, against the observed value of kT similar to 1.9 keV reported in the literature. This result makes UGC 842 a special case among fossil groups because (1) it represents more likely the interaction between two small groups, which warms the intragroup medium and/or (2) it could constitute evidence that member galaxies lost energy in the process of spiraling toward the group center, and decreased the velocity dispersion of the system. As far as we know, UGC 842 is the first low-mass fossil group studied in detail. (AU)

FAPESP's process: 07/04710-1 - Nature and properties of fossil groups
Grantee:Raimundo Lopes de Oliveira Filho
Support type: Scholarships in Brazil - Post-Doctorate