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Boltzmann-Poisson-like approach to simulating the galactic halo response to sate

Boltzmann-Poisson-like approach to simulating the galactic halo response to sate

Excluding Tax




Recent studies have reported the detection of the galactic stellar halo wake and dipole triggered by the Large Magellanic Cloud (LMC), mirroring the corresponding response from dark matter (DM). These studies open up the possibility of adding constraints on the global mass distribution of the Milky Way (MW), and even on the nature of DM itself, with current and upcoming stellar surveys reigniting the discussion on response modes in dynamical friction. However, the simulation of such features remains
computationally challenging. Aims. Using a continuous medium approach, we investigate the density and velocity response modes in simulations of Galactic-type DM halos accreting LMC-sized satellites, including the dependence on the halo density profile. Methods. We used, for the first time in the context of galactic dynamics, a collisionless Boltzmann equation (CBE)+Poisson solver based on an existing method from the literature. We studied the dynamical density and velocity response of halos to sinking perturbers. Results. We successfully captured both the local wake and the global over- and underdensity induced in the host halo. We also captured the velocity response. In line with previous studies, we find that the code can reproduce the core formation in the cuspy profile and the satellite core stalling. The angular power spectrum (APS) response is shown to be sensitive to each density profile. The
cored Plummer density profile seems the most responsive, displaying a richness of modes. At the end of the simulation, the central halo acquires cylindrical rotation. When present, a stellar component is expected to behave in a similar fashion. Conclusions. The CBE description makes it tenable to capture the response modes with a better handling of noise in comparison to traditional N-body simulations. Hence, given a certain noise level, BPM has a lower computational cost than N-body simulations,
making it feasible to explore large parameter sets. We anticipate that stellar spheroids in the MW or external galaxies could show central cylindrical rotation if they underwent a massive accretion event. The code can be adjusted to include a variety of DM physics.



The current paradigm assumed for cosmic structure formation is
the cold dark matter (CDM) model. This scenario encompasses
collisionless cold Dark Matter (DM) and a cosmological
constant (Planck Collaboration et al. 2020). The dark halo structure
of galaxies has been extensively studied in CDM-related
models, most frequently with rotation curves, disk dynamics, or
galaxy scaling relations (Rodríguez-Puebla et al. 2016; Aquino-
Ortíz et al. 2018). The dynamics of satellite galaxies are also
critical tests (Wang et al. 2018), particularly for nearby galaxies
(Cautun et al. 2020). Recent and upcoming surveys such
as GAIA (Gaia Collaboration et al. 2021), APOGEE (Majewski
et al. 2017; Fernández-Trincado et al. 2020), DESI (Cooper
2021), WEAVE (Dalton et al. 2012), and LSST (Rich 2018) will
produce an exquisite mapping of the Milky Way’s (MW) stellar
halo. In addition, these surveys will open up an opportunity
to track the subtle stellar response that is presumably paired with
the DM halo response, constraining such processes as dynamical
friction as well as the properties of halos, or even those of DM itself,
as recently shown via observations by Conroy et al. (2021).
Using high-resolution N-body simulations, Garavito-Camargo
et al. (2021) investigated the halo response modes to satellite accretion
following such pioneering studies asWeinberg (1989). In
addition, Ogiya & Burkert (2016); Tamfal et al. (2021) used super
high-resolution simulations to study the relative importance
of global mode and local wake in dynamical friction.
The recent studies mentioned above (Ogiya & Burkert 2016;
Garavito-Camargo et al. 2021; Tamfal et al. 2021) have revealed
a rich response mode population in fully self-consistent calculations
reaching particle numbers of around 108 􀀀 109 based on
large computational resources. However, exploring a large parameter
space using N-body simulations, while possible, may
prove challenging due to the large amount of computational resources
required. Therefore, devising an alternative technique
may be useful. In the field of numerical simulations, testing results
using dierent techniques consistently contributes to their
individual robustness. Additionally, a continuum medium approach
to dynamical problems is always interesting thanks to
shot-noise handling, which is critical when the main mechanism
we aim to capture is low-amplitude overdensities, as touched
upon in the discussion above.
In this work, we propose using a flexible alternative or complementary
strategy based on a continuous medium description
for matter density. Our code is based on recent Collisionless
Boltzmann Equation (CBE) solver implementations aimed at

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