The Formation of Fossil Galaxy Groups in the Hierarchical Universe

D’Onghia, Elena; Sommer–Larsen, Jesper; Romeo, A. D.; Burkert, Andreas; Pedersen, Kim Steenstrup; Portinari, L.; Rasmussen, Jesper

doi:10.1086/491651

Cited by 155 publications

(186 citation statements)

References 18 publications

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“…It is possible that merging might lead to this anti-correlation: mergers between satellite galaxies and the central galaxy will increase the central galaxy luminosity and decrease the cluster richness. In fact, examples of the extreme cases of such a correlation have been well studied and are known as "fossil groups" (e.g, Jones et al 2003;D'Onghia et al 2005;Zentner et al 2005). However, further investigation will be necessary in order to confirm if this correlation may be strong enough to fully explain our results.…”

Section: Discussionmentioning

confidence: 85%

Luminous red galaxies in clusters: central occupation, spatial distributions and miscentring

Hoshino

Leauthaud

Lackner

et al. 2015

Mon. Not. R. Astron. Soc.

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Luminous Red Galaxies (LRG) from the Sloan Digital Sky Survey are considered among the best understood samples of galaxies, and they are employed in a broad range of cosmological studies. Because they form a relatively homogeneous population, with high stellar masses and red colors, they are expected to occupy halos in a relatively simple way. In this paper, we study how LRGs occupy massive halos via direct counts in clusters and we reveal several unexpected trends suggesting that the connection between LRGs and dark matter halos may not be straightforward. Using the redMaPPer cluster catalog, we derive the central occupation of LRGs as a function richness, N cen (λ). Assuming no correlation between cluster mass and central galaxy luminosity at fixed richness, we show that clusters contain a significantly lower fraction of central LRGs than predicted from the two-point correlation function. At halo masses of 10 14.5 M , we find N cen = 0.73, compared to N cen of 0.89 from correlation studies. Our central occupation function for LRGs converges to 0.95 at large halo masses. A strong anti-correlation between central luminosity and cluster mass at fixed richness is required to reconcile our results with those based on clustering studies. We also derive P BNC , the probability that the brightest cluster member is not the central galaxy. We find P BNC ≈ 20 − 30% which is a factor of ∼ 2 lower than the value found by Skibba et al. (2011). Finally, we study the radial offsets of bright non-central LRGs from cluster centers and show that bright noncentral LRGs follow a different radial distribution compared to red cluster members, which follow a Navarro-Frank-White profile. This work demonstrates that even the most massive clusters do not always have an LRG at the center, and that the brightest galaxy in a cluster is not always the central galaxy.

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Section: Discussionmentioning

confidence: 85%

Luminous red galaxies in clusters: central occupation, spatial distributions and miscentring

Hoshino

Leauthaud

Lackner

et al. 2015

Mon. Not. R. Astron. Soc.

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“…From the observational point of view, these are defined as galaxy systems with a magnitude difference of at least two magnitudes -in the R-band -between the brightest group/cluster galaxy (BCG) and the second-brightest galaxy within half the virial radius R 200 1 and an extended thermal X-ray halo with A&A 565, A115 (2014) and temperature (T X ) of fossil systems with respect to those of normal systems with comparable optical luminosity (L opt ) or comparable velocity dispersion (σ v ; six fossil groups in Jones et al 2003; seven in Khosroshahi et al 2007) and some evidence of a high centrally concentrated dark matter halo (Khosroshahi et al 2006). The above differences with normal systems have been generally interpreted as due to an early formation epoch of fossil groups as suggested by numerical simulations (e.g., D'Onghia et al 2005). Accordingly, the BCGs of fossil groups should contain a fossil relic of the structure formation in the high-redshift Universe.…”

Section: Introductionmentioning

confidence: 90%

Fossil group origins

Girardi¹,

Aguerri²,

Grandi³

et al. 2014

A&A

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Aims. This study is part of the Fossil group origins (FOGO) project which aims to carry out a systematic and multiwavelength study of a large sample of fossil systems. Here we focus on the relation between the optical luminosity (L opt ) and X-ray luminosity (L X ). Methods. Out of a total sample of 28 candidate fossil systems, we consider a sample of 12 systems whose fossil classification has been confirmed by a companion study. They are compared with the complementary sample of 16 systems whose fossil nature has not been confirmed and with a subsample of 102 galaxy systems from the RASS-SDSS galaxy cluster survey. Fossil and normal systems span the same redshift range 0 < z < 0.5 and have the same L X distribution. For each fossil system, the L X in the 0.1−2.4 keV band is computed using data from the ROSAT All Sky Survey to be comparable to the estimates of the comparison sample. For each fossil and normal system we homogeneously compute L opt in the r-band within the characteristic cluster radius, using data from the Sloan Digital Sky Survey Data Release 7. Results. We sample the L X -L opt relation over two orders of magnitude in L X . Our analysis shows that fossil systems are not statistically distinguishable from the normal systems through the 2D Kolmogorov-Smirnov test nor the fit of the L X -L opt relation. Thus, the optical luminosity of the galaxy system does strongly correlate with the X-ray luminosity of the hot gas component, independently of whether the system is fossil or not. We discuss our results in comparison with previous literature. Conclusions. We conclude that our results are consistent with the classical merging scenario of the brightest galaxy formed via merger/cannibalism of other group galaxies with conservation of the optical light. We find no evidence for a peculiar state of the hot intracluster medium.

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“…According to simulations, they accreted the majority of their mass at high A&A 559, A76 (2013) redshifts (e.g., 50% at z > 1; D'Onghia et al 2005;Dariush et al 2007;Díaz-Giménez et al 2008). Fossil groups would therefore constitute the top end of the hierarchical evolution of galaxies on group scales.…”

Section: Introductionmentioning

confidence: 99%

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

Lieder¹,

Mieske²,

Sánchéz-Janssen³

et al. 2013

A&A

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A fossil group is considered the end product in a galaxy group's evolution. It is a massive central galaxy that dominates the luminosity budget of the group, and is the outcome of efficient merging between intermediate-luminosity members. Little is known, however, about the faint satellite systems of fossil groups. Here we present a Subaru/Suprime-Cam wide-field, deep imaging study in the B− and R−bands of the nearest fossil group NGC 6482 (M tot ∼ 4 × 10 12 M ), covering the virial radius out to 310 kpc. We performed detailed completeness estimations and selected group member candidates by a combination of automated object detection and visual inspection. A fiducial sample of 48 member candidates down to M R ∼ −10.5 mag is detected, making this study the deepest of a fossil group to now. We investigate the photometric scaling relations, the color-magnitude relation, and the luminosity function of our galaxy sample. We find evidence of recent and ongoing merger events among bright group galaxies. The color-magnitude relation is comparable to that of nearby galaxy clusters, and it exhibits significant scatter at the faintest luminosities. The completeness-corrected luminosity function is dominated by early-type dwarfs and is characterized by a faint end slope α = −1.32 ± 0.05. We conclude that the NGC 6482 fossil group shows photometric properties consistent with those of regular galaxy clusters and groups, including a normal abundance of faint satellites.

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The Formation of Fossil Galaxy Groups in the Hierarchical Universe

Cited by 155 publications

References 18 publications

Luminous red galaxies in clusters: central occupation, spatial distributions and miscentring

Luminous red galaxies in clusters: central occupation, spatial distributions and miscentring

Fossil group origins

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

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