Cosmological evolution of dark matter subhaloes under tidal stripping by growing Milky Way--like galaxies

Yudai Kazuno (University of Tsukuba, Graduate School of Pure and Applied Sciences)

Masao Mori (University of Tsukuba, CCS)

Yuka Kaneda (University of Tsukuba, Graduate School of Pure and Applied Sciences)

Koki Otaki (Dipartimento di Fisica, Sapienza Università di Roma)

Abstract

We present the findings of a comprehensive and detailed analysis of merger tree data from ultra-high-resolution cosmological $N$-body simulations. The analysis, conducted with a particle mass resolution of $5 \times 10^3 h^{-1} M_{\odot}$ and a halo mass resolution of $10^7 h^{-1} M_{\odot}$, provides sufficient accuracy to suppress numerical artefacts. This study elucidates the dynamical evolution of subhaloes associated with the Milky Way-like host haloes. Unlike more massive dark matter haloes, which have been extensively studied, these subhaloes follow a distinct mass evolution pattern: an initial accretion phase, followed by a tidal stripping phase where mass is lost due to the tidal forces of the host halo. The transition from accretion to stripping, where subhaloes reach their maximum mass, occurs around a redshift of $z\simeq1$. Smaller subhaloes reach this point earlier, while larger ones do so later. Our analysis reveals that over 80 per cent of subhaloes have experienced mass loss, underscoring the universality of tidal stripping in subhalo evolution. Additionally, we derived the eccentricities and pericentre distances of subhalo orbits from the simulations and compare them with those of nearby satellite galaxies observed by the Gaia satellite. The results demonstrate a significant alignment between the orbital elements predicted by the cold dark matter model and the observed data, providing robust support for the model as a credible candidate for dark matter.

Figure shows the correlation between the orbital parameters at $z=0$ of subhaloes with $M_0\geq 10^7\ h^{-1}M_{\odot}$. The centre panel illustrates the distribution of eccentricity and pericentre distance, normalised by the virial radius of their host halo at $z=0$. The colour scale indicates the number of subhaloes. Based on the Gaia eDR 3, the filled red circles represent the median values of the orbital parameters for 31 dwarf galaxies in and around the Milky Way under the Low Mass Milky Way model (Battaglia, et al. 2022). Error bars indicate the 68% scatter around the median. The right and top panels show histograms of eccentricity and pericentre distance, respectively. Three vertical dashed lines represent the tidal-destruction radii for dark matter subhaloes of $10^7\ h^{-1} M_{\odot}$ ($8.41$ kpc), $10^8\ h^{-1} M_{\odot}$ ($10.4$ kpc), and $10^9\ h^{-1} M_{\odot}$ ($13.0$ kpc), given by Miki, Mori and Kawaguchi (2021).

This paper has been published in "Kazuno, Mori, Kaneda, and Otaki (2024), Publications of the Astronomical Society of Japan, 76, L39". For more details, please refer to PASJ or arXiv.