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

¹ Dipartimento di Fisica, Università degli Studi di Trieste, via Tiepolo 11, 34143 Trieste, Italy
e-mail: stefania.jess@gmail.com
² INAF–Osservatorio Astronomico di Trieste, via G. B. Tiepolo 11, 34133 Trieste, Italy
³ INFN–Sezione di Trieste, via Valerio 2, 34127 Trieste, Italy

Received: 27 May 2016
Accepted: 11 August 2016

Abstract

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 2R₂₀₀ 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 ~ m₃ + 0.5, where m₃ 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.