Numerical effects on the stripping of dark matter and stars in IllustrisTNG galaxy groups and clusters

TL;DR

This work systematically quantifies how numerical resolution in the IllustrisTNG simulations affects the stripping of dark matter and stars from satellites, and the consequent growth of stellar haloes and intra-cluster light. Using nine resolution levels and a Lagrangian matching technique across volumes, the study finds DM stripping is largely resolution-insensitive except at very low resolution, while stellar stripping is significantly resolution-dependent, leading to longer stripping times and larger ex-situ stellar haloes at higher resolution. The results show that higher resolution increases central concentrations of both DM and stars, skewing halo profiles and boosting the ex-situ stellar mass deposited in hosts, though total stellar halo mass does not converge across resolutions. The authors provide public matching catalogs and emphasize that while stripping times can be robust, the total stellar halo mass and outer halo density depend sensitively on resolution, impacting comparisons with observational constraints on stellar haloes and intra-cluster light.

Abstract

The stellar haloes and intra-cluster light around galaxies are crucial test beds for dark matter (DM) physics and galaxy formation models. We consider the role that the numerical resolution plays in the modelling of these systems by studying the stripping of satellites in the IllustrisTNG cosmological simulations. We focus on host haloes of total halo mass $M_\mathrm{200c}=10^{12-15}M_{\odot}$ and satellites of stellar mass $>10^{7}$$M_{\odot}$, and compare stellar halo / satellite properties across 9 IllustrisTNG runs with baryonic particle mass resolution between $8.5\times10^4M_{\odot}$ and $7\times10^8$$M_{\odot}$, using a Lagrangian-region technique to identify counterpart satellites across different resolution simulations of the same volume. We publish the corresponding catalogues alongside this paper. We demonstrate that the stripping of DM from satellites that orbit in group- and cluster-mass hosts is largely independent of resolution at least until 90 per cent of their initial mass at infall has been stripped. We do not find evidence for spurious disruption of galaxies due to insufficient resolution for the satellite masses we consider. By contrast, the stripping of stellar mass is strongly resolution-dependent: each factor of 8 improvement in particle stellar mass typically adds 2~Gyr to the stripping time. Improved numerical resolution within the IllustrisTNG model generally results in more compact satellites with larger stellar masses, which in turn generate more centrally concentrated stellar haloes and intra-cluster mass profiles. However, the concomitant increase in stellar mass of both satellites and hosts may still be the cause for the overprediction of the stellar halo mass at large host radii relative to observations seen in some previous studies.

Figures (16)

• Figure 1: The baryonic particle mass and volume for each of the nine TNG simulations considered in this paper plus TNG50-4, as indicated in the box labels. The boxes are arranged such that the largest box -- TNG300 -- occupies the top row and the smallest box -- TNG50 -- occupies the bottom row. The colour of each box indicates the colour used to denote each data set throughout this paper. See Table\ref{['tab1']} and text for more details.
• Figure 2: Subhalo mass functions for six logarithmic bins in host halo mass across the TNG simulation suite at $z=0$. The definition of mass is the total mass bound to each subhalo, here referred to as the dynamical mass, $M_\rmn{dyn}$. Level-1 resolution simulations are shown with solid lines, level-2 with faded dashed lines, and level-3 with faded dot-dashed lines. TNG100, TNG300, and TNG50 results are shown in blue, orange, and magenta, respectively. The host halo masses increase across panels, from left to right and top to bottom; the host mass values are given in each panel legend.
• Figure 3: Satellite mass functions for hosts from $10^{12}$ to $10^{15}\,{\,\rm M_\odot}$ in host halo mass across the TNG simulation suite at $z=0$. The six left-hand panels use the total mass bound to each subhalo, $M_\rmn{dyn}$, to characterize the satellites, whereas the six right-hand panels use the stellar mass within twice the stellar half mass radius. Unlike Fig. \ref{['fig:submf']}, each satellite included here is required to have at least one star particle, the mass of which is given in the figure legend: i.e. we are only considering luminous satellites. Annotations and colours are as in Fig. \ref{['fig:submf']}.
• Figure 4: The stellar density profiles of central galaxies (left; median across galaxies) and the ratio of these profiles between pairs of simulations one step in resolution apart (right), across all TNG runs at $z=0$ (see colours). Each panel corresponds to a range of host halo $M_{\rm 200c}$ as indicated, shown as a pair of dashed vertical lines, if within the plotting range. On the right, for example, for the TNG300-1 curve we quantify the ratio to TNG100-1 and for TNG100-1 we compute the ratio to TNG50-1.
• Figure 5: The evolution with time of the DM mass in randomly-selected TNG example satellites, starting at infall. Columns (rows) denote bins in satellite stellar mass at infall (host halo mass at $z=0$). Here we show the evolution of satellite galaxies matched across runs at different resolution levels and selected in the highest one (L1, i.e. selected in TNG50-1, TNG100-1 and TNG300-1 as described in Section \ref{['sec:stripping_methods']}). Results from the L1, L2, and L3 runs are shown as solid, dashed and dot-dashed curves, respectively, with different colours denoting different simulated volumes. The smaller the resolution effects on the stripping of DM from satellites, the smaller is the distance among curves of the same colour.