Simulations of collision and sloshing in the galaxy group NGC 5098/5096

TL;DR

This work addresses gas sloshing in the NGC 5098/5096 galaxy-group system through tailored hydrodynamical N-body simulations, aiming to reproduce Chandra X-ray morphologies. It systematically explores initial-condition parameters (infall velocity, impact parameter, and incidence angle) and uses pyXSIM to generate realistic Chandra-like mock images for direct comparison with observations, achieving quantitative agreement in key features. The best-fitting scenario identifies NGC 5096 as the perturber, with a small impact parameter and a near-line-of-sight orientation, yielding $v_{\mathrm{los}} \approx 716$ km s$^{-1}$ and $d_{\mathrm{proj}} \approx 160$ kpc, and reproducing the northeastern edge at $r \approx 93$ kpc. Even without AGN feedback, the simulated SW surface-brightness profile aligns with data within uncertainties, and a correlation between residual dark matter and intragroup light supports a DM–IGL connection in this interacting system. Overall, the study demonstrates that a relatively modest merger can generate observable sloshing in an intermediate-mass galaxy group and provides a framework for inferring dynamical histories in similar systems.

Abstract

The study of galaxy groups is essential to understanding the evolutionary history of large-scale structures in the Universe. These dense environments have a significant impact on galaxy evolution, influencing their gas content, morphology, and star formation activity. In this work we analyse in detail the system NGC~5098$/$5096 composed of two galaxy groups. We performed hydrodynamical $N$-body simulations of a galaxy group collision aimed at reproducing the gas sloshing and surface brightness distribution observed in X-ray data. We conducted a detailed X-ray analysis and generated mock image \textit{Chandra} observations from our simulations. The resulting corrected mock image surface brightness profiles show good agreement with the observed data. The relative line-of-sight velocity between NGC~5098 and NGC~5096 is $v_{\mathrm{los}} = 700$ km s$^{-1}$, with a projected separation of $d_{\mathrm{proj}} = 155$ kpc, suggesting that the collision occurs nearly in the line-of-sight. Our simulations were performed with an inclination angle of $80^\circ$ in order to reproduce the dynamical constraints. We also find a correlation between the dark matter and intragroup light distributions when comparing the residual dark matter map with the intragroup light morphology. Our best-fitting model is consistent with these observational constraints and provides a plausible dynamical scenario for the current state of the NGC~5098 group interaction with NGC 5096.

Figures (9)

• Figure 1: Schematic representation of the collision in the orbital plane. Here, $v_{\mathrm{sub}}$ denotes the initial velocity of NGC 5096, and $i$ is the angle of incidence between the line joining the two galaxy groups and the direction of the initial velocity vector.
• Figure 2: Time evolution of the corrected mock Chandra X-ray emissivity in the 0.5 -- 7.0 keV band for the interaction between NGC 5098 and NGC 5096. TSP refers to the time since pericentre passage. In the final frame, the circle indicates the position of the NGC 5096 galaxy group.
• Figure 3: Left: Smoothed, exposure-map corrected image of the combined Chandra observations in the 0.5--7.0 keV band. The surface brightness edges identified by Randall09 are marked in white. Right: Smoothed, corrected mock Chandra image in the same energy band, generated from the best-matching snapshot of our simulation. The simulated image successfully reproduces the main morphological features observed in the X-ray data, including the northeastern edge-like discontinuity associated with gas sloshing.
• Figure 4: Regions used to measure the X-ray surface brightness overlaid on the exposure-corrected Chandra image. Each sector is centred on NGC 5098a and subdivided into 12 bins with logarithmic radial spacing. Source regions were masked out to extract only the diffuse gas surface brightness radial profile.
• Figure 5: Top panel: Surface brightness profile extracted from the northeastern sector for both the X-ray observations and the corrected mock Chandra image. The vertical dashed line indicates the position of the surface brightness discontinuity reported by Randall09 at $r = 56$ kpc, as highlighted in Fig. \ref{['obs_mock_comp']}. The same extraction sector is applied over an extended radial range. Bottom panel: Same as the top panel, but for the southwestern sector. In this case, the vertical dashed line marks a radius of $r = 31$ kpc. The orange shaded area indicates the $1 \sigma$ confidence interval.