Dynamical analysis of the cluster pair: A3407 + A3408

Abstract

We carried out a dynamical study of the galaxy cluster pair A3407 & A3408 based on a spectroscopic survey obtained with the 4 meter Blanco telescope at the CTIO, plus 6dF data, and ROSAT All-Sky-Survey. The sample consists of 122 member galaxies brighter than m R = 20. Our main goal is to probe the galaxy dynamics in this field and verify if the sample constitutes a single galaxy system or corresponds to an ongoing merging process. Statistical tests were applied to clusters members showing that both the composite system A3407 + A3408 as well as each individual cluster have Gaussian velocity distribution. A velocity gradient of ∼ 847 ± 114 km s −1 was identified around the principal axis of the projected distribution of galaxies, indicating that the global field may be rotating. Applying the KMM algorithm to the distribution of galaxies we found that the solution with two clusters is better than the single unit solution at the 99% c.l. This is consistent with the X-ray distribution around this field, which shows no common X-ray halo involving A3407 and A3408. We also estimated virial masses and applied a two-body model to probe the dynamics of the pair. The more likely scenario is that in which the pair is gravitationally bound and probably experiences a collapse phase, with the cluster cores crossing in less than ∼1 h −1 Gyr, a pre-merger scenario. The complex X-ray morphology, the gas temperature, and some signs of galaxy evolution in A3408 suggests a post-merger scenario, with cores having crossed each other ∼ 1.65h −1 Gyr ago, as an alternative solution.

eROSITA spectro-imaging analysis of the Abell 3408 galaxy cluster

“…Furthermore, the cluster properties r 500 , r 200 , and r 100 are consistent with the results of Nascimento et al (2016). In their dynamical analysis of 122 member galaxies of A3407 and A3408, the authors found galaxy velocity dispersions of σ A3407 = 718 +93 −48 km s −1 and σ A3408 = 573 +82 −59 km s −1 and corresponding virial masses of log(M V ) A3407 = 14.59 +0.46 −0.42 h −1 M and log(M V ) A3408 = 14.26 +0.55 −0.46 h −1 M .…”

“…Chow-Martínez et al ( 2014) classified A3408 and A3407 as a supercluster based on the small distance between the two neighboring clusters. Furthermore, there seems to be an indication that A3408 is interacting with A3407 (Nascimento et al 2016). Based on a dynamical study of 122 member galaxies, Nascimento et al concluded that A3408 and A3407 could be in a pre-merger scenario and might cross each other in less than ∼1 h −1 Gyr, or they might be in a post-merger scenario and might have crossed each other ∼1.65h −1 Gyr ago.…”

The SAMI Galaxy Survey: the cluster redshift survey, target selection and cluster properties

“…Galaxies identified as non-members using this method are shown in Figure 8 as black open circles. We note that the choice of σ200 as the maximum allowed gap is somewhat arbitrary, although it was found to produce good results here (see Figure 8), and in other clusters (e.g., Zabludoff et al 1990;Owers et al 2009aOwers et al ,b, 2011aNascimento et al 2016).…”

Analysis of candidates for interacting galaxy clusters

“…With the obtained lensing masses, this method allows us to estimate the probability that (1) the system is bound but still expanding, (2) the system is collapsing, or (3) the two structures are not bound to each other but are merely close together on the sky. It is important to highlight that this model does not consider the angular moment of the system, the distribution of matter inside each cluster, or the gravitational interaction of the infalling matter outside the cluster pair, since it is assumed that the masses are constant since their formation time (Nascimento et al 2016). Nevertheless, this model puts another constraint on the dynamical state and the evolution of the systems.…”