Ultimate age-dating method for galaxy groups; clues from the Millennium Simulations

Raouf, Mojtaba; Khosroshahi, Habib G.; Ponman, T. J.; Dariush, A.; Molaeinezhad, Alireza; Tavasoli, Saeed

doi:10.1093/mnras/stu963

Cited by 45 publications

(80 citation statements)

References 67 publications

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“…The conventional argument for the formation of fossil groups is based on a scenario in which a massive galaxy forms via cannibalizing its surrounding galaxies through dynamical friction, which requires several Gyr (Jones et al 2000). A number of studies using cosmological simulations have shown that fossil galaxy group halos form relatively earlier than halos with a small luminosity gap (e.g., Δm 12 0.5) and the results are consistent between hydrodynamical approaches (D 'Onghia et al 2005;Cui et al 2011;Raouf et al 2016) and semi-analytical models for galaxies (Dariush et al 2007Sales et al 2007;Díaz-Giménez et al 2008;Raouf et al 2014). The observational findings appear to be consistent with the broad picture that groups with a large luminosity gap have an earlier formation epoch than those with a small luminosity gap (Khosroshahi et al 2006Smith et al 2010).…”

Section: Introductionmentioning

confidence: 63%

Galaxy And Mass Assembly (GAMA): A “No Smoking” Zone for Giant Elliptical Galaxies?

Khosroshahi

Raouf

Miraghaei

et al. 2017

ApJ

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We study the radio emission of the most massive galaxies in a sample of dynamically relaxed and unrelaxed galaxy groups from the Galaxy and Mass Assembly survey. The dynamical state of the group is defined by the stellar dominance of the brightest group galaxy (BGG), e.g., the luminosity gap between the two most luminous members, and the offset between the position of the BGG and the luminosity centroid of the group. We find that the radio luminosity of the largest galaxy in the group strongly depends on its environment, such that the BGGs in dynamically young (evolving) groups are an order of magnitude more luminous in the radio than those with a similar stellar mass but residing in dynamically old (relaxed) groups. This observation has been successfully reproduced by a newly developed semi-analytic model that allows us to explore the various causes of these findings. We find that the fraction of radio-loud BGGs in the observed dynamically young groups is ∼2 times that of the dynamically old groups. We discuss the implications of this observational constraint on the central galaxy properties in the context of galaxy mergers and the super massive black hole accretion rate.

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Section: Introductionmentioning

confidence: 63%

Galaxy And Mass Assembly (GAMA): A “No Smoking” Zone for Giant Elliptical Galaxies?

Khosroshahi

Raouf

Miraghaei

et al. 2017

ApJ

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“…However, it is not clear whether the magnitude gap of these systems was formed at high redshift or more recently (Díaz-Giménez et al 2008). In fact, Raouf et al (2014) suggest that Δm 12 alone is not a good age indicator. They claim that there is a trend in age from groups to clusters, where the former are, on average, older than the latter.…”

Section: Implications For Formation Scenariosmentioning

confidence: 96%

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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“…We show that the galaxy luminosity gap combined with the luminosity of the brightest group galaxy for all halo masses over 10 13 M /h is successful in identifying old groups with a probability of 61 percent and young galaxy groups with a probability of 92 per cent (Raouf et al, 2014). In addition, we estimate the halo concentration as the ratio between R 200 and the half-mass radius for all candidates for old and young systems (Ludlow et al, 2012).…”

Section: Age-dating Based On Multi-dimensional Approachesmentioning

confidence: 84%

“…Using this multi-dimensional parameter space we are able to achieve a very high probability in statistical identification of the evolved, old and evolving, and young galaxy groups using purely optical observations (Raouf et al, 2014). These parameters can be obtained from the optical observations of galaxies alone which are now available from various imaging/spectroscopic surveys.…”

Section: Resultsmentioning

confidence: 99%

Age Dating Galaxy Groups in the Millennium Simulation

Raouf

Khosroshahi

2015

Publications of The Korean Astronomical Society

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We study galaxies drawn from the semi-analytic models of Guo et al. (2011) based on the Millennium Simulation. We establish a set of four observationally measurable parameters which can be used in combination to identify a subset of galaxy groups which are old, with a very high probability. We therefore argue that a sample of fossil groups selected based on the luminosity gap will result in a contaminated sample of old galaxy groups. By adding constraints on the luminosity of the brightest galaxy, and its offset from the group luminosity centroid, we can considerably improve the age-dating.

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Ultimate age-dating method for galaxy groups; clues from the Millennium Simulations

Cited by 45 publications

References 67 publications

Galaxy And Mass Assembly (GAMA): A “No Smoking” Zone for Giant Elliptical Galaxies?

Galaxy And Mass Assembly (GAMA): A “No Smoking” Zone for Giant Elliptical Galaxies?

Fossil group origins

Age Dating Galaxy Groups in the Millennium Simulation

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