Tidal features around simulated groups and cluster galaxies: Enhancement and suppression of merger events through environment in LSST-like mock observations

TL;DR

This study investigates how environment shapes the presence of tidal features around satellite galaxies in groups and clusters by analyzing LSST-like mock observations drawn from three cosmological-hydrodynamical simulations (EAGLE, IllustrisTNG, Magneticum). By projecting galaxies into velocity-radius phase-space and classifying tidal features, the authors show a suppression of tidal features in cluster centers (high velocities and reduced satellite masses) while recent infallers and outskirts maintain a roughly constant feature fraction around ~0.2. The peak in tidal-feature incidence at intermediate halo masses is driven primarily by ancient infallers, with pre-processing in infalling groups contributing to the outskirts signal. A simple toy model suggests that group accretion can transport tidal features into higher-mass halos, and the lifetime of tidal features in clusters is constrained to about $3\pm2$ Gyr, offering testable predictions for LSST observations and informing our understanding of merger histories in dense environments.

Abstract

Generally, merger likelihood increases in denser environments; however, the large relative velocities at the centres of dense clusters are expected to reduce the likelihood of mergers for satellite galaxies. Tidal features probe the recent merger histories of galaxies. The Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) will produce an unprecedented sample of tidal features around millions of galaxies. We use LSST-like mock observations of galaxies at $z\sim0$ from the EAGLE, IllustrisTNG and Magneticum Pathfinder cosmological-hydrodynamical simulations to predict the occurrence rates of tidal features around satellite galaxies across group and cluster environments in the velocity-radius projected phase-space diagram to investigate the impact of these environments on tidal feature occurrence. We find that ancient infallers in the projected phase-space exhibit a decreasing tidal feature fraction with increasing halo mass, whereas recent infallers in the projected phase-space show unchanging tidal feature fractions with halo mass. Our results show, for the first time in cosmological simulations, a suppression of tidal feature fractions in the central regions of galaxy clusters, indicating a reduced merger rate due to higher cluster-centric velocities and lower galaxy total masses in the cluster centres. Using a toy model, we show that the presence of more tidal features in the recent infaller zone and cluster outskirts suggests that tidal features occur in interactions within infalling groups and dissipate by the time they are ancient infallers, indicating a $\lesssim3\pm2$ Gyr survival time of tidal features within clusters.

Figures (13)

• Figure 1: The cumulative distribution functions for satellite stellar mass computed for 3 different halo mass bins. The red lines show the distribution for $10^{12}<M_{\mathrm{200,\:crit}}/\mathrm{M}_{\odot}<10^{13}$, the green lines show the distribution for $10^{13}<M_{\mathrm{200,\:crit}}/\mathrm{M}_{\odot}<10^{14}$ and the blue line shows the distribution for $M_{\mathrm{200,\:crit}}\geq10^{14}\mathrm{\:M}_{\odot}$. Stellar mass is measured using a 30 pkpc spherical aperture. We see across all simulations that the stellar mass distributions for the intermediate and highest halo mass bins are shifted to higher stellar masses than the distributions for the lowest halo mass bin.
• Figure 2: The mean completeness of each FOF group in our sample, as a function of the mean halo mass for EAGLE (orange), TNG (pink) and Magneticum (purple). The points and uncertainties show the median and $1\sigma$ confidence levels for each value measured by bootstrapping. The completeness decreases with increasing halo mass. The sample for Magneticum is the most complete, followed by EAGLE, then TNG.
• Figure 3: The projected phase-space for satellite galaxies in a range of different halo masses for EAGLE, TNG and Magneticum. The red points represent galaxies without tidal features, and the blue crosses represent galaxies with tidal features. The curves show the zones for ancient infallers ($p\leq2$) and recent infallers ($p\geq5$ and $R_\mathrm{proj}\leq R_\mathrm{200,\:crit}$). The dashed line shows $R=R_{\mathrm{200,\:crit}}$, the group/cluster outskirts are defined as the region $1\:R_\mathrm{200,\:crit}<R_\mathrm{proj}\leq3\:R_\mathrm{200,\:crt}$. The tidal feature fractions for each zone are provided along with the $1\sigma$ binomial uncertainties. The tidal feature fraction within the ancient infaller zone appears to systematically decrease with increasing halo mass. The tidal feature fraction for recent infallers remains relatively unchanged for all halo masses across all simulations. The ancient infaller fractions for TNG are systematically higher than the ancient infaller fractions for EAGLE and Magneticum for our range of $M_\mathrm{200,\:crit}$.
• Figure 4: The projected phase-space diagram for the combined sample of satellite galaxies from EAGLE, TNG and Magneticum, across three halo mass bins $\log_{10}(M_{\mathrm{200,\:crit}}/$M$_{\odot})=[12,\:13,\:14,\:14.7]$. Galaxies hosting tidal features are plotted with blue crosses, whereas galaxies without tidal features are plotted with red circles. The green line shows the median cluster-centric line-of-sight velocities of the galaxies in 9 radial bins equally spaced between 0 and 1.2 $R_{\mathrm{200,\:crit}}$, and the shaded green region shows the $16^\mathrm{th}$ and $84^\mathrm{th}$ percentiles. We plot the grey curves corresponding to the ancient infaller and recent infaller zones, the dashed line shows $R_{\mathrm{200,\:crit}}$. There are statistically significant differences between ancient and recent infallers as a function of halo mass. In the lowest halo mass bin, ancient infallers have higher fractions, whereas recent infallers have lower fractions. With increasing halo mass, the ancient infaller fractions decrease while the recent infaller fractions remain the same.
• Figure 5: The tidal feature fraction as a function of the group/cluster halo mass for satellite galaxies, separated into the zones for recent (blue downward pointing triangle), ancient (red upward pointing triangle) infallers, centrals (yellow circle), outskirt galaxies with $R_\mathrm{200,\:crit}<R_\mathrm{proj}<3\:R_\mathrm{200,\:crit}$ (black points). We also provide the fraction of galaxies with tidal features for $M_\mathrm{200,\:crit}\leq10^{12}\:\mathrm{M}_\odot$, as an estimate for the field fraction (purple hexagon). The galaxies are binned by halo mass, with bin edges $\log_{10}(M_{\mathrm{200,\:crit}}/\mathrm{M}_{\odot})=[12,\:13,\:14,\:14.7]$. We plot the median halo mass and 1 $\sigma$ binomial confidence levels for the tidal feature fractions in these bins. The semi-filled yellow point indicates that the point is based on a single central galaxy. The ancient infallers have a maximum tidal feature fraction at $\log_{10}(M_{\mathrm{200,\:crit}}/\mathrm{M}_{\odot})\sim12.5$ and decline beyond this, whereas the recent infallers and outskirts galaxies have fractions that remain roughly consistent with $f_{\mathrm{Tidal}}\sim0.2\pm0.1$ for all halo masses.