SLOW IV: Not all that is Close will Merge in the End. Superclusters and their Lagrangian collapse regions

TL;DR

This study leverages the SLOW constrained simulations of the local universe to identify and analyze local superclusters, assessing how well the constraints reproduce observed structures and using forward N-body evolution (Clairvoyant) to determine which member clusters become gravitationally bound. By cross-matching simulated counterparts to observed members across six regions and evaluating the likelihood of these configurations against random realizations, the work provides robust, morphology-consistent targets for future high-resolution zoom-ins and multi-wavelength studies. The Clairvoyant forward runs reveal that many clusters in these regions have largely finished their evolution by the present epoch, while some undergo significant late-time mergers, with notable mass-loss events and eventual freeze-out in co-moving space. The results reinforce the validity of spherical-collapse-based expectations for collapse regions, quantify the boundness and mass evolution of local structures, and establish a framework for connecting cluster-scale zoom-ins to their large-scale environments in the local universe.

Abstract

Superclusters are the most massive structures in the universe. To what degree they are actually bound against an accelerating expansion of the background is of significant cosmological and astrophysical interest. In this study, we introduce a cross matched set of superclusters from the SLOW constrained simulations of the local (z<0.05) universe. Identifying the superclusters provides estimates on the efficacy of the constraints in reproducing the local large-scale structure accurately. The simulated counterparts can help identifying possible future observational targets containing interesting features such as bridges between pre-merging and merging galaxy clusters and collapsing filaments and provide comparisons for current observations. By determining the collapse volumes for the superclusters we further elucidate the dynamics of cluster-cluster interactions in those regions. Using catalogs of local superclusters and the most massive simulated clusters, we search for counterparts of supercluster members of six regions. We evaluate the significance of these detections by comparing their geometries to supercluster regions in random simulations. We then run an N-body version of the simulation into the far future and determine which of the member clusters are gravitationally bound to the host superclusters. Furthermore we compute masses and density contrasts for the collapse regions. We demonstrate the SLOW simulation of the local universe to accurately reproduce local supercluster regions in mass of their members and three-dimensional geometrical arrangement. We furthermore find the bound regions of the local superclusters consistent in size and density contrast with previous theoretical studies. This will allow to connect future numerical zoom-in studies of the clusters to the large scale environments and specifically the supercluster environments these local galaxy clusters evolve in.

Figures (20)

• Figure 1: Schematic of how the two-point significances are estimated based on the radial ($dr$) and angular ($d\Omega$) separation of the simulated secondary cluster $M_2$ to the expected position ($x_{2,\mathrm{exp}}$). The red color indicates the part of the cone that is used as a "significance volume" to compute the probability of obtaining the geometric arrangement randomly.
• Figure 2: Simulated mock Compton-$y$ map from SLOW (left) and observed Compton-$y$ map (right) from Planck ade2014. SLOW cross identified supercluster members compared to selected observationally obtained supercluster regions using the catalogues from boehringer2021boehringer2021aproust2006monteiro-oliveira2022. The different colors indicate the regions: C=Centaurus, CO=Coma, H=Hercules, PP=Perseus-Pisces, SH=Shapley, V=Virgo (Local supercluster)
• Figure 3: Top left: Shapley supercluster region in the SLOW simulation with the cross identified counterparts: 1:A3558, 2:A3571, 3:A1736, 4: A3560, 5:A3532, 6:A3559. The white bar indicates 10 Mpc at the distance of the main cluster. The white contours show the 2D gas overdensity levels of $[1.25,10]*\bar{\rho_{\mathrm{image}}}$. Top right: The same FOV as viewed by ROSAT. Bottom left: Supercluster core region (black) according to the Clairvoyant N-Body forward simulation in the initial conditions ($z=120$) with the member clusters from \ref{['membertable']} overplotted as colored dots. Bottom right: The collapse region (red) and its environment at $z=0$.
• Figure 4: Two-point probabilities for the Shapley member clusters as a function of the opening angle $\sqrt{\Omega}$ of the cone spanned by the observed and simulated relative position of the secondary cluster to the main. The grey shaded regions reflect the mass uncertainty of the secondary halo. The red vertical line indicates the deviation angle measured in the SLOW simulation. The x value of the intersect of this line with the angular probability function gives the probability of finding the secondary within the deviation cone in a random simulation.
• Figure 5: The Perseus-Pisces supercluster region in the SLOW simulation with the cross-identified counterparts: 1: Perseus (A426), 2: AWM 7, 3: UGC2562, 4: 3C129, 5: A262, 6: CIZAJ0300.7+4427, 7: NGC507, 8: UGC3355. The white contours show the 2D gas overdensity levels of $[1.25,10]*\bar{\rho_{\mathrm{image}}}$. Top right: The same region as viewed by ROSAT. Bottom left: Supercluster core region according to the Clairvoyant N-Body forward simulation in the initial conditions ($z=120$).Bottom right: The collapse region (red) and its environment at $z=0$.