Aims. To conduct an intensive study of the rich, X-ray luminous galaxy cluster Abell 773 at z = 0... more Aims. To conduct an intensive study of the rich, X-ray luminous galaxy cluster Abell 773 at z = 0.22 containing a diffuse radio halo to determine its dynamical status. Methods. Our analysis is based on new spectroscopic data obtained at the TNG telescope for 107 galaxies, 37 spectra recovered from the CFHT archive and new photometric data obtained at the Isaac Newton Telescope. We use statistical tools to select 100 cluster members (out to ∼1.8 h −1 70 Mpc from the cluster centre), to analyse the kinematics of cluster galaxies and to determine the cluster structure. Our analysis is also performed by using X-ray data stored in the Chandra archive. Results. The 2D distribution shows two significant peaks separated by ∼2 in the EW direction with the main western one closely located at the position of the two dominant galaxies and the X-ray peak. The velocity distribution of cluster galaxies shows two peaks at v ∼ 65 000 and ∼67 500 km s −1 , corresponding to the velocities of the two dominant galaxies. The low velocity structure has a high velocity dispersion-σ v = 800−1100 km s −1-and its galaxies are centred on the western 2D peak. The high velocity structure has intermediate velocity dispersion-σ v ∼ 500 km s −1-and is characterized by a complex 2D structure with a component centred on the western 2D peak and a component centred on the eastern 2D peak, these components probably being two independent groups. We estimate a cluster mass within 1 h −1 70 Mpc of 6−11 ×10 14 h −1 70 M. Our analysis of Chandra data shows the presence of two very close peaks in the core and the elongation of the X-ray emission in the NEE-SWW direction. Conclusions. Our results suggest we are looking at probably two groups in an advanced stage of merging with a main cluster and having an impact velocity ∆v rf ∼ 2300 km s −1. In particular, the radio halo seems to be related to the merger of the eastern group.
Context. Virialized halos grow by the accretion of smaller ones in the cold dark matter scenario.... more 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 at least two magnitude 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 telescope for ∼ 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 (∆m 12 ) and the first and fourth ranked galaxies (∆m 14 ) within 0.5 R 200 . We consider fossil systems those with ∆m 12 ≥ 2 mag or ∆m 14 ≥ 2.5 mag within the errors. Results. We find that 15 candidates turned out to be fossil systems. Their observational properties are in agreement 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 nonfossil 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 due to 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 candidates in our sample could represent a transitional fossil stage. This system could have been fossil in the past, but not now due to the recent accretion of another group of galaxies.
Optical imaging of RX J105453.3+552102 was carried out at the 2.5m NOT telescope in March 2008. O... more Optical imaging of RX J105453.3+552102 was carried out at the 2.5m NOT telescope in March 2008. Optical deep images were used for studying the properties of the brightest group galaxy and for computing the photometric luminosity function of the group. We have also performed a detail dynamical analysis of the system based on redshift data for 116 galaxies. Combining galaxy
Aims. To conduct an intensive study of the rich, X-ray luminous galaxy cluster Abell 773 at z = 0... more Aims. To conduct an intensive study of the rich, X-ray luminous galaxy cluster Abell 773 at z = 0.22 containing a diffuse radio halo to determine its dynamical status. Methods. Our analysis is based on new spectroscopic data obtained at the TNG telescope for 107 galaxies, 37 spectra recovered from the CFHT archive and new photometric data obtained at the Isaac Newton Telescope. We use statistical tools to select 100 cluster members (out to ∼1.8 h −1 70 Mpc from the cluster centre), to analyse the kinematics of cluster galaxies and to determine the cluster structure. Our analysis is also performed by using X-ray data stored in the Chandra archive. Results. The 2D distribution shows two significant peaks separated by ∼2 in the EW direction with the main western one closely located at the position of the two dominant galaxies and the X-ray peak. The velocity distribution of cluster galaxies shows two peaks at v ∼ 65 000 and ∼67 500 km s −1 , corresponding to the velocities of the two dominant galaxies. The low velocity structure has a high velocity dispersion-σ v = 800−1100 km s −1-and its galaxies are centred on the western 2D peak. The high velocity structure has intermediate velocity dispersion-σ v ∼ 500 km s −1-and is characterized by a complex 2D structure with a component centred on the western 2D peak and a component centred on the eastern 2D peak, these components probably being two independent groups. We estimate a cluster mass within 1 h −1 70 Mpc of 6−11 ×10 14 h −1 70 M. Our analysis of Chandra data shows the presence of two very close peaks in the core and the elongation of the X-ray emission in the NEE-SWW direction. Conclusions. Our results suggest we are looking at probably two groups in an advanced stage of merging with a main cluster and having an impact velocity ∆v rf ∼ 2300 km s −1. In particular, the radio halo seems to be related to the merger of the eastern group.
Context. Virialized halos grow by the accretion of smaller ones in the cold dark matter scenario.... more 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 at least two magnitude 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 telescope for ∼ 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 (∆m 12 ) and the first and fourth ranked galaxies (∆m 14 ) within 0.5 R 200 . We consider fossil systems those with ∆m 12 ≥ 2 mag or ∆m 14 ≥ 2.5 mag within the errors. Results. We find that 15 candidates turned out to be fossil systems. Their observational properties are in agreement 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 nonfossil 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 due to 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 candidates in our sample could represent a transitional fossil stage. This system could have been fossil in the past, but not now due to the recent accretion of another group of galaxies.
Optical imaging of RX J105453.3+552102 was carried out at the 2.5m NOT telescope in March 2008. O... more Optical imaging of RX J105453.3+552102 was carried out at the 2.5m NOT telescope in March 2008. Optical deep images were used for studying the properties of the brightest group galaxy and for computing the photometric luminosity function of the group. We have also performed a detail dynamical analysis of the system based on redshift data for 116 galaxies. Combining galaxy
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Papers by Rafael Barrena