The velocity field of the Lyra complex

Abstract

Context. The formation of cosmic structure culminates with the assembly of galaxy clusters, a process quite different from cluster to cluster. Aims. We present the study of the structure and dynamics of the Lyra complex formed of the two clusters RXC J1825.3+3026 and CIZA J1824.1+3029, very recently studied using both X-ray and radio data. Methods. This is the first analysis based on kinematics of member galaxies. New spectroscopic data for 285 galaxies were acquired at the Italian Telescopio Nazionale Galileo and used in combination with PanSTARRS photometry. The result of our member selection is a sample of 198 galaxies. Results. For RXCJ1825 and CIZAJ1824 we report the redshifts, z = 0.0645 and z = 0.0708, the first estimates of velocity dispersion, σ v = 995 +131 −125 km s −1 and σ v = 700 ± 50 km s −1 , and dynamical mass, M 200 = 1.1 ± 0.4 ×10 15 M ⊙ and M 200 = 4 ± 0.1 ×10 14 M ⊙ . The past assembly of RXCJ1825 is traced by the two dominant galaxies, both aligned with the major axis of the galaxy distribution along the East-West direction, and by a minor North-East substructure. We also detect a quite peculiar high velocity field in the South-West region of the Lyra complex. This feature is likely related to a high velocity, very luminous galaxy, suggested to be the central galaxy of a group in interaction with RXCJ1825 by very recent studies based on X-ray and radio data. The redshift of the whole Lyra complex is z = 0.067. Assuming that the redshift difference between RXCJ1825 and CIZAJ1824 is due to the relative kinematics, the projected distance between the cluster centers is D ∼ 1.3 Mpc and the line-of-sight velocity difference is ∼ 1750 km s −1 . A dynamical analysis of the system shows that the two clusters are likely to be gravitationally bound, in a pre-merger phase, with CIZAJ1824 in front of RXCJ1825 and going toward it. Conclusions. Our results corroborate a picture where the Lyra region is the place of a very complex scenario of cluster assembly.

A Robust Model for Flux Density Calculations of Radio Halos in Galaxy Clusters: Halo-FDCA

“…The radio halo in Abell 2744 was first identified by Giovannini et al (1999) and the flux density has been estimated by Pearce et al (2017) using 1.5 GHz VLA images. RXC J1825.3+3026 is a cluster at = 0.065 with a 500 mass of 4.08±0.13 M ⊙ belonging to the Lyra complex (Clav-ico et al, 2019;Girardi et al, 2020). The flux density has been estimated by Botteon et al (2019) using 144 MHz LO-FAR observations.…”