Fossil group origins

Girardi, M.; Aguerri, J. A. L.; Grandi, S. De; D’Onghia, Elena; Barrena, R.; Boschin, W.; Méndez-Abreu, J.; Sánchéz-Janssen, R.; Zarattini, S.; Biviano, A.; Castro-Rodríguez, N.; Corsini, E. M.; Burgo, C. del; Iglésias-Páramo, J.

doi:10.1051/0004-6361/201323311

Cited by 38 publications

(56 citation statements)

References 62 publications

(63 reference statements)

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“…We used an iterative procedure based on PIMMS 5 (Mukai 1993). Details of the procedure are available in Girardi et al (2014).…”

Section: Cluster Global Propertiesmentioning

confidence: 99%

“…Thus, uncertainties in the R 200 determination reflect in uncertainties in the fossil classification. Therefore, we computed the variation in the number of fossil systems considering a 25% uncertainty in R 200 in agreement with Girardi et al (2014). The number of fossil systems is 15 +8 −4 .…”

Section: Fossilness Determinationmentioning

confidence: 99%

“…The structural properties of the BGGs in fossil and non-fossil systems were shown in the second paper (Méndez-Abreu et al 2012). The L X −L opt relations of fossil and normal systems are analyzed in Girardi et al (2014), the third paper. This is the fourth paper in the series, and it is devoted to characterizing the sample.…”

Section: Introductionmentioning

confidence: 99%

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Fossil group origins

Zarattini¹,

Barrena²,

Girardi³

et al. 2014

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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 ∼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 (Δm 12 ) and the first and fourth ranked galaxies (Δm 14 ) within 0.5 R 200 . We consider fossil systems to be those with Δm 12 ≥ 2 mag or Δm 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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“…We used an iterative procedure based on PIMMS 5 (Mukai 1993). Details of the procedure are available in Girardi et al (2014).…”

Section: Cluster Global Propertiesmentioning

confidence: 99%

Section: Fossilness Determinationmentioning

confidence: 99%

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Fossil group origins

Zarattini¹,

Barrena²,

Girardi³

et al. 2014

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“…These differences between FS and non-FS were also reported in scaling relations combining optical and X-ray quantities, such as the L X − L opt or L X − σ relations (e.g., Proctor et al 2011;Khosroshahi et al 2014); they were interpreted as an indication that the halos of FSs formed early in the high redshift Universe. Nevertheless, larger samples of FSs and non-FSs have obtained that those differences do not exist, indicating that according to the global scaling relations, fossil and non-fossil halos are similar (e.g., Harrison et al 2012;Girardi et al 2014;Kundert et al 2015).…”

Section: Introductionmentioning

confidence: 99%

Fossil group origins

Aguerri

Longobardi

Zarattini

et al. 2018

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Context. It is thought that fossil systems are relics of structure formation in the primitive Universe. They are galaxy aggregations that have assembled their mass at high redshift with few or no subsequent accretion. Observationally these systems are selected by large magnitude gaps between their 1st and 2nd ranked galaxies (∆m 12 ). Nevertheless, there is still debate over whether or not this observational criterium selects dynamically evolved ancient systems. Aims. We have studied the properties of the nearby fossil group RXJ075243.6+455653 in order to understand the mass assembly of this system. Methods. Deep spectroscopic observations allow us to construct the galaxy luminosity function (LF) of RXJ075243.6+455653 down to M * r + 6. The analysis of the faint-end of the LF in groups and clusters provides valuable information about the mass assembly of the system. In addition, we have analyzed the nearby large-scale structure around this group. The LF of the group shows a flat faint-end slope (α = −1.08 ± 0.33). This low density of dwarf galaxies is confirmed by the low value of the dwarf-to-giant ratio (DGR = 0.99 ± 0.49) for this system. Both the lack of dwarf galaxies and the low luminosity of the BGG suggests that RXJ075243.6+455653 still has to accrete mass from its nearby environment. This mass accretion will be achieved because it is the dominant structure of a rich environment formed by several groups of galaxies (15) within ∼ 7 Mpc from the group center and with ±1000 km s −1 . Conclusions. RXJ075243.6+455653 is a group of galaxies that has not yet completed the process of its mass assembly. This new mass accretion will change the fossil state of the group. This group is an example of a galaxy aggregation selected by a large magnitude gap but still in the process of the accretion of its mass.

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“…However, these differences can be attributed to observational biases (see Voevodkin et al 2010;Harrison et al 2012). Recently, Girardi et al (2014) have analyzed a sample of 15 spectroscopically confirmed FGs, finding no significant differences in the L X − L opt relation. Particular attention was paid to the homogeneity of the data set and the analysis process in this work.…”

Section: Introductionmentioning

confidence: 99%

Fossil group origins

Zarattini

Aguerri

Sánchéz-Janssen

et al. 2015

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Context. In nature we observe galaxy aggregations that span a wide range of magnitude gaps between the two first-ranked galaxies of a system (Δm 12 ). Thus, there are systems with gaps close to zero (e.g., the Coma cluster), and at the other extreme of the distribution, the largest gaps are found among the so-called fossil systems. The observed distribution of magnitude gaps is thought to be a consequence of the orbital decay of M * galaxies in massive halos and the associated growth of the central object. As a result, to first order the amplitude of this gap is a good statistical proxy for the dynamical age of a system of galaxies. Fossil and non-fossil systems could therefore have different galaxy populations that should be reflected in their luminosity functions. Aims. In this work we study, for the first time, the dependence of the luminosity function parameters on Δm 12 using data obtained by the fossil group origins (FOGO) project. Methods. We constructed a hybrid luminosity function for 102 groups and clusters at z ≤ 0.25 using both photometric data from the SDSS-DR7 and redshifts from the DR7 and the FOGO surveys. The latter consists of ∼1200 new redshifts in 34 fossil system candidates. We stacked all the individual luminosity functions, dividing them into bins of Δm 12 , and studied their best-fit Schechter parameters. We additionally computed a "relative" luminosity function, expressed as a function of the central galaxy luminosity, which boosts our capacity to detect differences -especially at the bright end. Results. We find trends as a function of Δm 12 at both the bright and faint ends of the luminosity function. In particular, at the bright end, the larger the magnitude gap, the fainter the characteristic magnitude M * . The characteristic luminosity in systems with negligible gaps is more than a factor three brighter than in fossil-like ones. Remarkably, we also find differences at the faint end. In this region, the larger the gap, the flatter the faint-end slope α. Conclusions. The differences found at the bright end support a dissipationless, dynamical friction-driven merging model for the growth of the central galaxy in group-and cluster-sized halos. The differences in the faint end cannot be explained by this mechanism. Other processes -such as enhanced tidal disruption due to early infall and/or prevalence of eccentric orbits -may play a role. However, a larger sample of systems with Δm 12 > 1.5 is needed to establish the differences at the faint end.

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Fossil group origins

Cited by 38 publications

References 62 publications

Fossil group origins

Fossil group origins

Fossil group origins

Fossil group origins

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