The orbital velocity anisotropy of cluster galaxies: evolution

et al. 2016

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Aims. Our study is meant to extend our knowledge of the galaxy color and luminosity segregation in velocity space (VCS and VLS, respectively), to clusters at intermediate and high redshift. Methods. Our sample is a collection of 41 clusters in the 0.4 < ∼ z < ∼ 1.5 redshift range for a total of 4172 galaxies, 1674 of which are member galaxies of the clusters within 2R 200 with photometric or spectroscopic information, as taken from the literature. We perform homogeneous procedures to select cluster members, compute global cluster properties, in particular the line-of-sight (LOS) velocity dispersion σ V , and separate blue from red galaxies. Results. We find evidence of VCS in clusters out to z 0.8 (at the 97−99.99% confidence level, depending on the test), in the sense that the blue galaxy population has a 10−20% larger σ V than the red galaxy population. Poor or no VCS is found in the high-z sample at z ≥ 0.8. For the first time, we detect VLS in non-local clusters and confirm that VLS only affects the very luminous galaxies; brighter galaxies have lower velocities. The threshold magnitude of VLS is ∼m 3 + 0.5, where m 3 is the magnitude of the third brightest cluster galaxy. Current data suggest that the threshold value moves to fainter magnitudes at higher redshift. We also detect (marginal) evidence of VLS for blue galaxies. Conclusions. We conclude that segregation effects can be important tracers of the galaxy evolution and cluster assembly when they are studied up to distant clusters. We also discuss the evidence of VCS at high redshift, which is poor or absent.

Section: Discussionsupporting

confidence: 88%

Section: Introductionmentioning

confidence: 99%

Velocity segregation effects in galaxy clusters at 0.4 ≲z≲ 1.5

Barsanti

Girardi

et al. 2016

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“…This shape is as predicted for a cosmological halo evolving through an initial phase of fast collapse and a subsequent slow phase of inside-out growth by accretion of field material (Lapi & Cavaliere 2011). The z ∼ 1 cluster β(r) is also similar to the β(r) found for cluster galaxies at intermediate-z (Biviano & Poggianti 2009;Biviano et al 2013;Annunziatella et al 2016). Both at z ∼ 1 and at intermediate-z PG and SFG have similar β(r).…”

Section: The Velocity Anisotropy Profilessupporting

confidence: 77%

The dynamics ofz~ 1 clusters of galaxies from the GCLASS survey

Burg

Muzzin

et al. 2016

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Context. The dynamics of clusters of galaxies and its evolution provide information on their formation and growth, on the nature of dark matter and on the evolution of the baryonic components. Poor observational constraints exist so far on the dynamics of clusters at redshift z > 0.8. Aims. We aim to constrain the internal dynamics of clusters of galaxies at redshift z ∼ 1, namely their mass profile M(r), velocity anisotropy profile β(r), and pseudo-phase-space density profiles Q(r) and Q r (r), obtained from the ratio between the mass density profile and the third power of the (total and, respectively, radial) velocity dispersion profiles of cluster galaxies. Methods. We used the spectroscopic and photometric data-set of 10 clusters at 0.87 < z < 1.34 from the Gemini Cluster Astrophysics Spectroscopic Survey (GCLASS). We determined the individual cluster masses from their velocity dispersions, then stack the clusters in projected phase-space. We investigated the internal dynamics of this stack cluster, using the spatial and velocity distribution of its member galaxies. We determined the stack cluster M(r) using the MAMPOSSt method, and its β(r) by direct inversion of the Jeans equation. The procedures used to determine the two aforementioned profiles also allowed us to determine Q(r) and Q r (r). Results. Several M(r) models are statistically acceptable for the stack cluster (Burkert, Einasto, Hernquist, NFW). The stack cluster total mass concentration, c ≡ r 200 /r −2 = 4.0 +1.0 −0.6 , is in agreement with theoretical expectations. The total mass distribution is less concentrated than both the cluster stellar-mass and the cluster galaxies distributions. The stack cluster β(r) indicates that galaxy orbits are isotropic near the cluster center and become increasingly radially elongated with increasing cluster-centric distance. Passive and star-forming galaxies have similar β(r). The observed β(r) is similar to that of dark matter particles in simulated cosmological halos. Q(r) and Q r (r) are almost power-law relations with slopes similar to those predicted from numerical simulations of dark matter halos. Conclusions. Comparing our results with those obtained for lower-redshift clusters, we conclude that the evolution of the concentration-total mass relation and pseudo-phase-space density profiles agree with the expectations from ΛCDM cosmological simulations. The fact that Q(r) and Q r (r) already follow the theoretical expectations in z ∼ 1 clusters suggest these profiles are the result of rapid dynamical relaxation processes, such as violent relaxation. The different concentrations of the total and stellar mass distribution, and their subsequent evolution, can be explained by merging processes of central galaxies leading to the formation of the brightest cluster galaxy. The orbits of passive cluster galaxies appear to become more isotropic with time, while those of starforming galaxies do not evolve, presumably because star-formation is quenched on a shorter timescale than that required for orbital is...

“…Biviano & Girardi 2003;Katgert et al 2004). On the other hand, Biviano & Poggianti (2009) found in the ENACS clusters that the red galaxy population has a concentration that is as much as 1.7 times lower for the total matter density profile. Here, we find that the scale radius for the RED galaxy number density profile (0.95 Mpc) is 1.8 times greater than for the total mass density profile from our combined model, which agrees with the ENACS result.…”

Section: Mass Density Profilementioning

confidence: 92%

Mass, velocity anisotropy, and pseudo phase-space density profiles of Abell 2142

Munari

Mamon

2014

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Aims. We aim to compute the mass and velocity anisotropy profiles of Abell 2142 and, from there, the pseudo phase-space density profile Q(r) and the density slope − velocity anisotropy β − γ relation, and then to compare them with theoretical expectations. Methods. The mass profiles were obtained by using three techniques based on member galaxy kinematics, namely the caustic method, the method of dispersion-kurtosis, and MAMPOSSt. Through the inversion of the Jeans equation, it was possible to compute the velocity anisotropy profiles. Results. The mass profiles, as well as the virial values of mass and radius, computed with the different techniques agree with one another and with the estimates coming from X-ray and weak lensing studies. A combined mass profile is obtained by averaging the lensing, X-ray, and kinematics determinations. The cluster mass profile is well fitted by an NFW profile with c = 4.0 ± 0.5. The population of red and blue galaxies appear to have a different velocity anisotropy configuration, since red galaxies are almost isotropic, while blue galaxies are radially anisotropic, with a weak dependence on radius. The Q(r) profile for the red galaxy population agrees with the theoretical results found in cosmological simulations, suggesting that any bias, relative to the dark matter particles, in velocity dispersion of the red component is independent of radius. The β − γ relation for red galaxies matches the theoretical relation only in the inner region. The deviations might be due to the use of galaxies as tracers of the gravitational potential, unlike the non-collisional tracer used in the theoretical relation.