The Nature of Fossil Galaxy Groups: Are They Really Fossils?

Barbera, F. La; Carvalho, R. R. de; Rosa, I. G. de la; Sorrentino, Giuseppe; Gal, R. R.; Kohl-Moreira, J. L.

doi:10.1088/0004-6256/137/4/3942

Cited by 52 publications

(87 citation statements)

References 65 publications

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“…The S07 identification of extended systems based only on the RASS-BSC and FSC definition of extended sources might not always be reliable. For instance, out of six fossil groups identified by La Barbera et al (2009) in a similar way, the following XMM X-ray data analysis shows that one does not have an extended emission, and another is at the border of a real extended system (La Barbera et al 2012). Alternatively, the rejected objects might simply be too poorly contrasted in the sky.…”

Section: Checking the 2d Galaxy Distribution Of S07 Objectsmentioning

confidence: 82%

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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Section: Checking the 2d Galaxy Distribution Of S07 Objectsmentioning

confidence: 82%

Fossil group origins

Girardi¹,

Aguerri²,

Grandi³

et al. 2014

A&A

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“…This can lead to isolated giant elliptical galaxies, embedded in X-ray haloes with luminosities characteristic for entire galaxy groups. Such objects exist in the Universe (Vikhlinin et al 1999), either isolated (Yoshioka et al 2004) or surrounded by groups of less luminous satellite galaxies (Jones et al 2003;Khosroshahi et al 2006b; La Barbera et al 2009). One of the first systems has been reported by Ponman et al (1994) coining the term "fossil group", and Jones et al (2003) have introduced general selection criteria.…”

Section: Fossil Groupsmentioning

confidence: 99%

J0454-0309: evidence of a strong lensing fossil group falling into a poor galaxy cluster

Schirmer¹,

Suyu²,

Schrabback

et al. 2010

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Aims. We have discovered a strong lensing fossil group (J0454) projected near the well-studied cluster MS0451-0305. Using the large amount of available archival data, we compare J0454 to normal groups and clusters. A highly asymmetric image configuration of the strong lens enables us to study the substructure of the system. Methods. We used multicolour Subaru/Suprime-Cam and CFHT/Megaprime imaging, together with Keck spectroscopy to identify member galaxies. A VLT/FORS2 spectrum was taken to determine the redshifts of the brightest elliptical and the lensed arc. Using HST/ACS images, we determined the group's weak lensing signal and modelled the strong lens system. This is the first time that a fossil group is analysed with lensing methods. The X-ray luminosity and temperature were derived from XMM-Newton data. Results. J0454 is located at z = 0.26, with a gap of 2.5 mag between the brightest and second brightest galaxies within half the virial radius. Outside a radius of 1.5 Mpc, we find two filaments extending over 4 Mpc, and within we identify 31 members spectroscopically and 33 via the red sequence with i < 22 mag. (BGG) is inconsistent with the dynamic centre of J0454. It strongly lenses a galaxy at z = 2.1 ± 0.3, and we model the lens with a pseudo-isothermal elliptical mass distribution. A high external shear, and a discrepancy between the Einstein radius and the weak lensing velocity dispersion requires that the BGG must be offset from J0454's dark halo centre by at least 90−130 kpc. The X-ray halo is offset by 24 ± 16 kpc from the BGG, shows no signs of a cooling flow and can be fit by a single β-model. With L X = (1.4 ± 0.2) × 10 43 erg s −1 J0454 falls onto standard cluster scaling relations, but appears cooler (T = 1.1 ± 0.1 keV) than expected (T ∼ 2.0 keV). Taken all together, these data indicate that J0454 consists of two systems, a sparse cluster and an infalling fossil group, where the latter seeds the brightest cluster galaxy. An alternative to the sparse cluster could be a filament projected along the line of sight mimicking a cluster, with galaxies streaming towards the fossil group.

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“…Some observations (Khosroshahi et al 2006) show that these objects are different from both isolated elliptical galaxies and central galaxies in non-fossil clusters in the sense that they have disky isophotes in the center and their luminosity correlates with velocity dispersion, while other authors (La Barbera et al 2009;Méndez-Abreu et al 2012) found no differences in isophotal shapes between fossil and non-fossil central galaxies. In Méndez-Abreu et al (2012) we analyzed deep K-band images of 20 BGGs in fossil and non-fossil systems and showed that these galaxies follow the tilted fundamental plane of normal ellipticals (see Bernardi et al 2011).…”

Section: Introductionmentioning

confidence: 96%

“…We infer that BGGs grew throughout dissipational mergers in an early stage of their evolution and then assembled the bulk of their mass through subsequent dry mergers. Nevertheless, stellar population studies of BGGs in fossil systems suggest that their age, metallicity, and α-enhancement are similar to those of bright ellipticals field galaxies (see La Barbera et al 2009;Eigenthaler & Zeilinger 2013).…”

Section: Introductionmentioning

confidence: 97%

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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The Nature of Fossil Galaxy Groups: Are They Really Fossils?

Cited by 52 publications

References 65 publications

Fossil group origins

Fossil group origins

J0454-0309: evidence of a strong lensing fossil group falling into a poor galaxy cluster

Fossil group origins

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