An improved formalism for measuring the dark matter subhalos mass by its gravitational wake

TL;DR

This work extends wake-based measurements of dark matter subhalo mass by incorporating a nonuniform Milky Way background and multiple subhalo density profiles. The authors derive an improved unbinned likelihood and distribution function, with and without the host halo potential, and test the framework on Gaia DR3 data and on simulated galaxies, including Auriga systems. They find that including the MW potential substantially improves mass inferences and that, while the data do not strongly distinguish between perturber density profiles, the NFW-like profiles are generally favored when combined with external constraints like circular velocity curves. The method shows promise for measuring the masses of smaller subhalos and potentially detecting dark subhalos through their gravitational wakes in the stellar halo, especially for subhalos closer to the host.

Abstract

We reexamined the framework used to determine the dark matter mass of a subhalo using the gravitational effects of its passage upon the stellar halo of a host. In particular, we aim to include different density distribution functions for the perturber and a non homogeneous background due to the host's halo gravitational potential. We have used a sample of K giant and RRLyrae stars based on Gaia DR3 data and two different set of simulations, to test the new formalism. From our analysis, we found that the inclusion of a nonhomogeneous background improves substantially the estimation of the subhalo dark matter mass. The methodology is not sufficiently sensitive to discriminate between different density distribution functions for the perturber, however, in the case of the observational data, the inclussion of the cloud's circular velocity is a fundamental tool to complement the analysis. The results obtained including the host halo potential agree with the independent previous measurements or with the reported value for the subhalo dark matter mass in the simulations. These results show that it is possible to measure the mass of smaller subhalos through their gravitational wake, even for subhalos closer to their host, with distances lower than 30 kpc.

Figures (6)

• Figure 1: Schematic relationship between the perturber ($p$) and the host ($H$) coordinate systems. The solid gray line represents the past orbit of the perturber. The star indicates the position of a generic star inside the ROI.
• Figure 2: Mollweide projection in galactic coordinates. The panels correspond to different distance from the CM of the MC. Green dotted line: region of the global wake; blue dashed line: region of the local wake.
• Figure 3: Best-fit values for the LMC dark matter subhalo mass in units of $10^{11} M_{\sun }$. The colors represent the models used for the MW halo potential, red: no MW halo; green: Model 1; violet: Model 2; cyan: Model 3; blue: Model 4. The black-dashed line stands for the weighted mean value of the reported LMC dark matter subhalo mass in the literature, along with it $1\sigma$ and $3\sigma$ confidence levels.
• Figure 4: Generic NFW parameters obtained form the best-fit values for the LMC dark matter subhalo mass. The colors represent the models used for the MW halo potential as in Fig. \ref{['result-fig']}. Left panel: $\alpha$; middle panel: $\beta$; right panel: $\gamma$.
• Figure 5: Subhalo rotation curve for the best-fit masses obtained with Model 1. Cyan region: envelope of circular velocities obtained from literature; dot with the error bar: circular velocity of the LMC at $8.7$ kpc.