Fossil group origins IV. Characterization of the sample and observational properties of fossil systems



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Zarattini, S. and Barrena, R. and Girardi, M. and Castro Rodríguez, N. and Boschin, W. and Aguerri, J. A. L. and Mendéz Abreu, J. and Sánchez Janssen, R. and Catalán Torrecilla, Cristina and Corsini, E. M. and Burgo, C. del and D'Onghia, E. and Herrera Ruiz, N. and Iglesias Páramo, J. and Jiménez Bailón, E. and Lozada Muñoz, M. and Napolitano, N. and Vilchez, J. M. (2014) Fossil group origins IV. Characterization of the sample and observational properties of fossil systems. Astronomy & Astrophysics, 565 . ISSN 0004-6361

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Context. Virialized halos grow by the accretion of smaller ones in the cold dark matter scenario. The rate of accretion depends on the different properties of the host halo. Those halos for which this accretion rate was very fast and efficient resulted in systems dominated by a central galaxy surrounded by smaller galaxies that were at least two magnitudes fainter. These galaxy systems are called fossil systems, and they can be the fossil relics of ancient galaxy structures. Aims. We started an extensive observational program to characterize a sample of 34 fossil group candidates spanning a broad range of physical properties. Methods. Deep r-band images were obtained with the 2.5-m Isaac Newton Telescope and Nordic Optic Telescope. Optical spectroscopic observations were performed at the 3.5-m Telescopio Nazionale Galileo for similar to 1200 galaxies. This new dataset was completed with Sloan Digital Sky Survey Data Release 7 archival data to obtain robust cluster membership and global properties of each fossil group candidate. For each system, we recomputed the magnitude gaps between the two brightest galaxies (Delta m(12)) and the first and fourth ranked galaxies (Delta m(14)) within 0.5 R-200. We consider fossil systems to be those with Delta m(12) >= 2 mag or Delta m(14) >= 2.5 mag within the errors. Results. We find that 15 candidates turned out to be fossil systems. Their observational properties agree with those of non-fossil systems. Both follow the same correlations, but the fossil systems are always extreme cases. In particular, they host the brightest central galaxies, and the fraction of total galaxy light enclosed in the brightest group galaxy is larger in fossil than in non-fossil systems. Finally, we confirm the existence of genuine fossil clusters. Conclusions. Combining our results with others in the literature, we favor the merging scenario in which fossil systems formed from mergers of L* galaxies. The large magnitude gap is a consequence of the extreme merger ratio within fossil systems and therefore it is an evolutionary effect. Moreover, we suggest that at least one fossil group candidate in our sample could represent a transitional fossil stage. This system could have been a fossil in the past, but not now owing to the recent accretion of another group of galaxies.

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© ESO 2014. We would like to thank the anonymous referee for useful comments that helped us improve the paper. This work was partially funded by the Spanish MICINN (grant AYA2010-21887-C04-04), and the local Canarian Government (grant ProID20100140). This article is based on observations made with the Isaac Newton Telescope, Nordic Optical Telescope, and Telescope Nazionale Galileo operated on the island of La Palma by the Isaac Newton Group, the Nordic Optical Telescope Scientific Association, and the Fundacion Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica), respectively, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. E. D. gratefully acknowledges support from the Alfred P. Sloan Foundation. M. G. acknowledges financial support from the MIUR PRIN/2010-2011 (J91J12000450001). E. M. C. is supported by Padua University (grants 60A02-1283/10,5052/11, 4807/12). J.I.P. and J.V.M. acknowledge financial support from the Spanish MINECO under grant AYA2010-21887-C04-01, and from Junta de Andalucía Excellence Project PEX2011-FQM7058. J.M.A. acknowledges support from the European Research Council Starting Grant (SEDmorph; P.I. V. Wild).

Uncontrolled Keywords:Digital Sky Survey, Galaxy-Cluster-Survey, X-Ray Luminosity, Brightest Group Galaxies, Velocity Dispersions, Millennium Simulation, Internal Dynamics, Scaling Relations, Redshift Survey, Stellar Mass
Subjects:Sciences > Physics > Astrophysics
Sciences > Physics > Astronomy
Sciences > Physics > Atmospheric physics
ID Code:28177
Deposited On:06 Feb 2015 09:34
Last Modified:10 Dec 2018 15:05

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