A normal abundance of faint satellites in the fossil group NGC 6482

Lieder, Stefan; Mieske, S.; Sánchéz-Janssen, R.; Hilker, M.; Lisker, Thorsten; Tanaka, Masayuki

doi:10.1051/0004-6361/201321288

Cited by 15 publications

(27 citation statements)

References 61 publications

(111 reference statements)

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“…For z 0.2, the mean number of faint galaxies in fossil systems grows to finally reach the values observed in control groups at z = 0. This later result agrees with the observational work of Lieder et al (2013), who found a normal abundance of faint satellites in the NGC 6482 fossil group. This rapid growth in the number of faint galaxies could be a consequence of a smaller number of missing galaxies in fossils.…”

Section: Discussionsupporting

confidence: 92%

“…Using this definition, it is assumed that galaxies within half the virial radius have had time to merge within a Hubble time, and also that normal elliptical galaxies that are not located at the centre of the groups will not be chosen as potential fossil groups (Lieder et al 2013). In addition to the conventional criteria, there exists an alternative criterion developed by Dariush et al (2010).…”

Section: Fossil Groupsmentioning

confidence: 99%

“…Nevertheless, most of these works agree that the faint galaxy population is represented by galaxies mainly down to −17 absolute magnitudes, hence, a wide range of faint galaxies are out of their analysis. More recently, an observational work of Lieder et al (2013) has attempted to gather information about a fainter population of galaxies. These authors analysed the faint galaxy population of a fossil system down to an absolute magnitude of −10.5 in the R-band.…”

Section: Introductionmentioning

confidence: 99%

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Fossil groups in the Millennium simulation

Kanagusuku

Díaz-Giménez

Zandivarez

2016

A&A

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Aims. We investigate the evolution of bright and faint galaxies in fossil and non-fossil groups. Methods. We used mock galaxies constructed based on the Millennium run simulation II. We identified fossil groups at redshift zero according to two different selection criteria, and then built reliable control samples of non-fossil groups that reproduce the fossil virial mass and assembly time distributions. The faint galaxies were defined as having r-band absolute magnitudes in the range [−16, −11]. We analysed the properties of the bright and faint galaxies in fossil and non-fossil groups during the past 8 Gyr.Results. We observed that the brightest galaxy in fossil groups is typically brighter and more massive than their counterparts in control groups. Fossil groups developed their large magnitude gap between the brightest galaxies around 3.5 Gyr ago. The brightest galaxy stellar masses of all groups show a notorious increment at that time. By analysing the behaviour of the magnitude gap between the first and the second, third, and fourth ranked galaxies, we found that at earlier times, fossil groups comprised two large brightest galaxies with similar magnitudes surrounded by much fainter galaxies, while in control groups these magnitude gaps were never as large as in fossils. At early times, fossil groups in the faint population were denser than non-fossil groups, then this trend reversed, and finally they became similar at the present day. The mean number of faint galaxies in non-fossil systems increases in an almost constant rate towards later times, while this number in fossil groups reaches a plateau at z ∼ 0.6 that lasts ∼2 Gyr, and then starts growing again more rapidly. Conclusions. The formation of fossil groups is defined at the very beginning of the groups according to their galaxy luminosity sampling, which could be determined by their merging rate at early times.

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Section: Discussionsupporting

confidence: 92%

Section: Fossil Groupsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Fossil groups in the Millennium simulation

Kanagusuku

Díaz-Giménez

Zandivarez

2016

A&A

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“…This agrees with our general result that the faint-end slope increases with the gap in magnitude. In a recent work, Lieder et al (2013) analyzed the FG NGC 6482. They present a deep spectroscopic LF, down to M r = −10.5.…”

Section: Comparison With the Literaturementioning

confidence: 99%

Fossil group origins

Zarattini

Aguerri

Sánchéz-Janssen

et al. 2015

A&A

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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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“…They found that the LF of these objects are well fitted by single Schechter function, but there is a large variety of values in the faint-end slope (α) of the LFs of FGs. In particular, the values of α measured goes from −1.6 to −0.6 (see Cypriano et al 2006; Khosroshahi et al 2006;Mendes de Oliveira et al 2006Zibetti et al 2009;Aguerri et al 2011;Lieder et al 2013). Unfortunately, all these studies were performed on single FGs or very small samples, and a systematic study of LFs of statistically meaningful samples of FGs remains to be done.…”

Section: Introductionmentioning

confidence: 98%

Fossil group origins

Zarattini¹,

Barrena²,

Girardi³

et al. 2014

A&A

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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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A normal abundance of faint satellites in the fossil group NGC 6482

Cited by 15 publications

References 61 publications

Fossil groups in the Millennium simulation

Fossil groups in the Millennium simulation

Fossil group origins

Fossil group origins

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