Fossil Groups Origins III. Characterization of the sample and observational properties of fossil systems

Abstract

(Abridged) Fossil systems are group- or cluster-sized objects whose luminosity is dominated by a very massive central galaxy. In the current cold dark matter scenario, these objects formed hierarchically at an early epoch of the Universe and then slowly evolved until present day. That is the reason why they are called {\it fossils}. We started an extensive observational program to characterize a sample of 34 fossil group candidates spanning a broad range of physical properties. Deep $r-$band images were taken for each candidate and optical spectroscopic observations were obtained for $\sim$ 1200 galaxies. This new dataset was completed with SDSS DR7 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 those with $\Delta m_{12}\ge 2$ mag or $\Delta m_{14}\ge 2.5$ mag within the errors. 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 fossils are always extreme cases. In particular, they host the brightest central galaxies and the fraction of total galaxy light enclosed in the central galaxy is larger in fossil than in non-fossil systems. Finally, we confirm the existence of genuine fossil clusters. Combining our results with others in the literature, we favor the merging scenario in which fossil systems formed due to mergers of $L^{\ast }$ 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 candidate in our sample could represent a transitional fossil stage.

arXiv comment14 pages, 11 figures, accepted for publication in A&A

References in corpus (42)

• The Sixth Data Release of the Sloan Digital Sky Survey
• Spectroscopic Target Selection for the Sloan Digital Sky Survey: The Luminous Red Galaxy Sample
• The Fifth Data Release of the Sloan Digital Sky Survey
• The Average Mass-to-Light Profile of Galaxy Clusters
• The Northern ROSAT All-Sky (NORAS) Galaxy Cluster Survey I: X-ray Properties of Clusters Detected as Extended X-ray Sources
• Improved background subtraction for the Sloan Digital Sky Survey images
• K-band Properties of Galaxy Clusters and Groups: Brightest Cluster Galaxies and Intracluster Light
• Dynamical Friction and Galaxy Merging Timescales
• The structural and scaling properties of nearby galaxy clusters - II. The M-T relation
• Optical Mass Estimates of Galaxy Clusters
• The nature and space density of fossil groups of galaxies
• The Properties of Poor Groups of Galaxies: II. X-ray and Optical Comparisons
• The Representative XMM-Newton Cluster Structure Survey (REXCESS) of an X-ray Luminosity Selected Galaxy Cluster Sample
• The Lx-T, Lx-sigma and sigma-T relations for groups and clusters of galaxies
• WINGS: a WIde-field Nearby Galaxy-cluster Survey. I - Optical imaging
• The Isolated Elliptical NGC 1132: Evidence For a Merged Group of Galaxies?
• WINGS-SPE Spectroscopy in the WIde-field Nearby Galaxy-cluster Survey
• Evolution of the Internal Dynamics of Galaxy Clusters
• Scaling relations in fossil galaxy groups
• An old galaxy group: Chandra X-ray observations of the nearby fossil group NGC 6482
• The importance of major mergers in the build up of stellar mass in brightest cluster galaxies at z=1
• The Mass Assembly of Fossil Groups of Galaxies in the Millennium Simulation
• The Fossil Phase in the Life of a Galaxy Group
• The mass assembly of galaxy groups and the evolution of the magnitude gap
• Curvature in the color-magnitude relation but not in color-sigma: Major dry mergers at M* > 2 x 10^11 Msun?
• Study of the Core of the Shapley Concentration: I.the Sample
• The Shapley Supercluster. II. Spectroscopic observations in a wide area and general morphology
• Properties of Intra-group Stars and Galaxies in Galaxy Groups: "Normal" versus "Fossil" Groups
• ESO 3060170 -- a massive fossil galaxy group with a heated gas core?
• The XMM Cluster Survey: The Stellar Mass Assembly of Fossil Galaxies
• Velocity dispersion, mass and the luminosity function of the fossil cluster RX J1416.4+2315
• On the Nature of Fossil Galaxy Groups: Are they really fossils ?
• Evolution of BCGs structural parameters in the last $\sim$6 Gyr: feedback processes versus merger events
• The X-ray Luminosity - Velocity Dispersion relation in the REFLEX Cluster Survey
• Internal dynamics of the massive cluster Abell 697: a multiwavelength analysis
• Testing adiabatic contraction of dark matter in fossil group candidates
• Fossil Groups Origins III. The relation between optical and X-ray luminosities
• The statistical nature of the brightest group galaxies
• Age and metallicity gradients in fossil ellipticals
• An optical and X-ray study of the fossil group RX J1340.6+4018
• Are fossil groups a challenge of the Cold Dark Matter paradigm?
• The 2dF Galaxy Redshift Survey: correlation with the ROSAT-ESO Flux Limited X-ray (REFLEX) galaxy cluster survey

Cited by in corpus (8)

• The XXL Survey XX: The 365 cluster catalogue
• Fossil Groups Origins III. The relation between optical and X-ray luminosities
• Intracluster Light Properties in a Fossil Cluster at z=0.47
• Fossil group origins - VI. Global X-ray scaling relations of fossil galaxy clusters
• On Mass Concentrations & Magnitude Gaps of Galaxy Systems in the CS82 Survey
• Fossil group origins. XI. The dependence of galaxy orbits on the magnitude gap
• Fossil group origins X. Velocity segregation in fossil systems
• The lens SW05 J143454.4+522850: a fossil group at redshift 0.6?