On Relaxation Processes in Collisionless Mergers

Valluri, Monica; Vass, Ileana M.; Kazantzidis, Stelios; Kravtsov, Andrey V.; Bohn, C.L.

doi:10.1086/511298

Cited by 38 publications

(47 citation statements)

References 62 publications

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“…In addition, the process of mixing does not seem to depend on the initial orbital geometry but it is generic to the merging process itself and leads to rather similar metallicity gradients. This implies that mixing is mostly driven by the progenitor structure that (at least partially) survives the merging process (see also White 1980;Barnes 1996;Valluri et al 2007). As a consequence, our simulations indicate that it is not possible to disentangle the orbits of the parent galaxies by using the metallicity distribution of the remnant if the analysis is restricted to the central region of the galaxy (i.e., inside the half-mass radius).…”

Section: Core-halo Differentiation and Phase-space Mixingmentioning

confidence: 86%

On the survival of metallicity gradients to major dry-mergers

Matteo¹,

Pipino

Lehnert³

et al. 2009

A&A

114

121

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Using a large suite of galaxies with a variety of concentrations and metallicity gradients, we study the evolution of non-dissipative ("dry") equal mass mergers. Our purpose in generating these simulations is to explore how the metallicity gradient in dry mergers depends on the structure and metallicity gradients of the galaxies involved in the merger. Specifically, we would like to answer: Could dry mergers lead to metallicity gradients as observed in elliptical galaxies in the local Universe? Do dry mergers always lead to a flattening of the initial (i.e., pre-merger) gradient? From this modeling, we conclude that: The ratio of the remnant and the initial galaxy slopes span a wide range of values, up to values greater than 1 (with values greater than one resulting only when companions have gradients twice the progenitor). For a merger between two ellipticals having identical initial metallicity slopes (i.e., equal companion and galaxy slopes), the metallicity profile of the remnant flattens, with a final gradient about 0.6 times the initial one. Ellipticals can maintain their original pre-merger metallicity gradient if the companion slope is sufficiently steep. The amount of flattening neither depends on the characteristics of the orbit of the progenitors or on their initial concentration. Given the diversity in outcomes of the mergers, we conclude that dry mergers do not violate any observational constraints on the systematic characteristics of metallicity gradients in local ellipticals. In fact, dry mergers may be important within the context of the results of our simulations and may explain the large scatter in gradients for massive ellipticals and the relative paucity of massive ellipticals with no or shallow metallicity gradients.

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Section: Core-halo Differentiation and Phase-space Mixingmentioning

confidence: 86%

On the survival of metallicity gradients to major dry-mergers

Matteo¹,

Pipino

Lehnert³

et al. 2009

A&A

114

121

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“…However, the relevance of maximum entropy principle for collisionless systems under gravity is not well understood at present. Perhaps the dynamical mixing/relaxation may be responsible for the universality (see, e.g., Valluri et al 2007).…”

Section: Discussionmentioning

confidence: 99%

A Universal Power-Law Profile of Pseudo-Phase-Space Density-Like Quantities in Elliptical Galaxies

Chae

2014

ApJ

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We study profiles of mass density, velocity dispersion (VD), and a combination of both using ∼2000 nearly spherical and rotation-free Sloan Digital Sky Survey galaxies. For observational stellar mass density ρ (r), we consider a range of dark matter (DM) distribution ρ DM (r) and VD anisotropy β(r) to investigate radial stellar VD σ r (r) using the spherical Jeans equation. While mass and VD profiles vary appreciably depending on DM distribution and anisotropy, the pseudo-phase-space density-like combination ρ(r)/σ 3 r (r) with total density ρ(r) = ρ (r) + ρ DM (r) is nearly universal. In the optical region, the negative logarithmic slope has a mean value of χ ≈ 1.86-1.90 with a galaxy-to-galaxy rms scatter of ≈0.04-0.06, which is a few times smaller than that of ρ(r) profiles. The scatter of χ can be increased by invoking wildly varying anisotropies that are, however, less likely because they would produce too large a scatter of line of sight VD profiles. As an independent check of this universality, we analyze stellar orbit-based dynamical models of 15 early-type galaxies (ETGs) of the Coma cluster provided by J. Thomas. Coma ETGs, with σ r (r) replaced by the rms velocity of stars v rms (r) including net rotation, exhibit a similar universality with a slope of χ = 1.93 ± 0.06. Remarkably, the inferred values of χ for ETGs match well the slope ≈1.9 predicted by N-body simulations of DM halos. We argue that the inferred universal nature of ρ(r)/σ 3 r (r) cannot be fully explained by equilibrium alone, implying that some astrophysical factors conspire and/or it reflects a fundamental principle in collisionless formation processes.

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“…According to theoretical models, the growth of halo masses occurs in two phases, an initial, fast accretion phase, followed by a slower, smoother accretion phase (Lapi & Cavaliere 2009). During the fast accretion phase clusters undergo major mergers that can induce rapid changes in the cluster gravitational potential (Manrique et al 2003;Peirani et al 2006;Valluri et al 2007), causing energy and angular momentum mixing in the galaxy distributions, and thereby isotropization of galaxy orbits (Hénon 1964;Lynden-Bell 1967;Kandrup & Siopis 2003;Merritt 2005;Lapi & Cavaliere 2009). …”

Section: Summary and Discussionmentioning

confidence: 99%

The orbital velocity anisotropy of cluster galaxies: evolution

Biviano

Poggianti

2009

A&A

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Context. In nearby clusters early-type galaxies follow isotropic orbits. The orbits of late-type galaxies are instead characterized by slightly radial anisotropy. Little is known about the orbits of the different populations of cluster galaxies at redshift z > 0.3. Aims. We investigate the redshift evolution of the orbits of cluster galaxies. Methods. We use two samples of galaxy clusters spanning similar (evolutionary corrected) mass ranges at different redshifts. The sample of low-redshift (z ∼ 0.0−0.1) clusters is extracted from the ESO Nearby Abell Cluster Survey (ENACS) catalog. The sample of high-redshift (z ∼ 0.4−0.8) clusters is mostly made of clusters from the ESO Distant Cluster Survey (EDisCS). For each of these samples, we solve the Jeans equation for hydrostatic equilibrium separately for two cluster galaxy populations, characterized by the presence and, respectively, absence of emission-lines in their spectra ("ELGs" and "nELGs" hereafter). Using two tracers of the gravitational potential allows to partially break the mass-anisotropy degeneracy which plagues these kinds of analyses. Results. We confirm earlier results for the nearby cluster sample. The mass profile is well fitted by a Navarro, Frenk & White (NFW) profile with concentration c = 4. The mass profile of the distant cluster sample is also well fitted by a NFW profile, but with a slightly lower concentration, as predicted by cosmological simulations of cluster-sized halos. While the mass density profile becomes less concentrated with redshift, the number density profile of nELGs becomes more concentrated with redshift. In nearby clusters, the velocity anisotropy profile of nELGs is close to isotropic, while that of ELGs is increasingly radial with clustercentric radius. In distant clusters the projected phase-space distributions of both nELGs and ELGs are best-fitted by models with radial velocity anisotropy. Conclusions. No significant evolution is detected for the orbits of ELGs, while the orbits of nELGs evolve from radial to isotropic with time. We speculate that this evolution may be driven by the secular mass growth of galaxy clusters during their fast accretion phase. Cluster mass density profiles and their evolution with redshift are consistent with predictions for cluster-sized halos in Λ Cold Dark Matter cosmological simulations. The evolution of the nELG number density profile is opposite to that of the mass density profile, becoming less concentrated with time, probably a result of the transformation of ELGs into nELGs.

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On Relaxation Processes in Collisionless Mergers

Cited by 38 publications

References 62 publications

On the survival of metallicity gradients to major dry-mergers

On the survival of metallicity gradients to major dry-mergers

A Universal Power-Law Profile of Pseudo-Phase-Space Density-Like Quantities in Elliptical Galaxies

The orbital velocity anisotropy of cluster galaxies: evolution

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