Age and metallicity gradients in fossil ellipticals

Eigenthaler, Paul; Zeilinger, W. W.

doi:10.1051/0004-6361/201321078

Cited by 31 publications

(47 citation statements)

References 79 publications

(110 reference statements)

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“…Recent studies of the stellar population of BGGs seem to indicate that their age, metallicity, and α enhancement are similar to those of central galaxies in non-fossil systems (La Barbera et al 2009). Moreover, the absence of large gradients in the metallicity radial profiles rules out the hypothesis of the monolithic collapse for BGGs in FGs (Eigenthaler & Zeilinger 2013). In summary, these observational properties indicate that BGGs in fossil and nonfossil systems show similar properties.…”

Section: Introductionsupporting

confidence: 58%

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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Section: Introductionsupporting

confidence: 58%

Fossil group origins

Zarattini

Aguerri

Sánchéz-Janssen

et al. 2015

A&A

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“…For example, the monolithic formation of elliptical galaxies predicts strong metallicity gradients, whereas the stellar population gradients are erased by mergers. In this context, Eigenthaler & Zeilinger (2013) find flat age and metallicity gradients for a sample of central galaxies in fossil systems,which are not compatible with the failed group scenario. Moreover, the bend observed at high masses in the scaling relations of early-type galaxies also suggests that fossil systems were formed by mergers (see Bernardi et al 2011).…”

Section: Formation Scenarios For Fossil Systemsmentioning

confidence: 67%

“…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: 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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“…Supporting this suggestion, we show that some fossil groups in our XMM-CFHTLS galaxy groups catalogue at 0.6 < z < 1.2 include few galaxies A&A 571, A49 (2014) outside the 0.5R 200 , which are brighter than the second brightest galaxy used for magnitude gap calculation . Eigenthaler & Zeilinger (2013) determined flat metallicity gradients for six fossil galaxies, in contrast to the steep slope predicted by a monolithic collapse, suggesting multiple mergers of galaxies for the formation of fossil groups. Recently, following the fossil group origins project, Aguerri et al (2011), Zarattini et al (2014, and Girardi et al (2014) carried out a multi-wavelength study of a sample of 34 fossil group candidates, revealing that the brightest group galaxy (BGG) in a fossil group forms from the merger/cannibalism of the L * galaxies and the large magnitude gap in fossil groups is the result of an evolutionary effect and the extreme merger ratio of galaxies within these systems.…”

Section: Introductionmentioning

confidence: 76%

Evolution of the galaxy luminosity function in progenitors of fossil groups

Gozaliasl

Khosroshahi

Dariush

et al. 2014

A&A

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Using the semi-analytic models based on the Millennium simulation, we trace back the evolution of the luminosity function of galaxies residing in progenitors of groups classified by the magnitude gap at redshift zero. We determine the luminosity function of galaxies within 0.25 R 200 , 0.5 R 200 , and R 200 for galaxy groups/clusters. The bright end of the galaxy luminosity function of fossil groups shows a significant evolution with redshift, with changes in M * by ∼1−2 mag between z ∼ 0.5 and z = 0 (for the central 0.5 R 200 ), suggesting that the formation of the most luminous galaxy in a fossil group has had a significant impact on the M * galaxies e.g. it is formed as a result of multiple mergers of M * galaxies within the last 5 Gyr. In contrast, the slope of the faint end, α, of the luminosity function shows no considerable redshift evolution and the number of dwarf galaxies in the fossil groups exhibits no evolution, unlike in non-fossil groups where it grows by ∼25−42% towards low redshifts. In agreement with previous studies, we also show that fossil groups accumulate most of their halo mass earlier than non-fossil groups. Selecting the fossils at a redshift of 1 and tracing them to a redshift 0, we show that 80% of the fossil groups (10 13 M h −1 < M 200 < 10 14 M h −1 ) will lose their large magnitude gap. However, about 40% of fossil clusters (M 200 > 10 14 M h −1 ) will retain their large gaps.

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Age and metallicity gradients in fossil ellipticals

Cited by 31 publications

References 79 publications

Fossil group origins

Fossil group origins

Fossil group origins

Evolution of the galaxy luminosity function in progenitors of fossil groups

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