From high resolution cosmological simulations of the Local Group in a realistic environment, namely HESTIA simulations, we study the position and kinematic deviations that may arise between the disc of a Milky Way (or Andromeda)-like galaxy and its halo. We focus on the three-dimensional analysis of the centres of mass (COM). The study presents two parts. We first consider individual particles to track down the nature and amplitude of the physical deviations of the COM with respect to the distance from the disc centre. Dark matter dominates the behaviour of the COM of all particles at all distances. But the total COM is also very close to the COM of stars. In the absence of a significant merger, the velocity offsets are marginal (10 km s-1) but the positional shifts can be important compared to the disc characteristics (>10 kpc). In the event of a massive accretion, discrepancies are of the same order as the recent finding for the MW under the Magellanic Clouds influence. In a second part, the accent is put on the study of various populations of subhaloes and satellites. We show that satellites properly represent the entire subhalo population. There exists strong mismatch in phase space between the satellites' COM and the host disc. Moreover, the results are highly inhomogeneous between the simulations and thus, between the accretion histories. Finally, we point out that these shifts are mainly due to a few of the most massive objects.
Newton, O., Di Cintio, A., Cardona–Barrero, S., Libeskind, N. I., Hoffman, Y., Knebe, A., Sorce, J. G., Steinmetz, M., Tempel, E., 2023, The Astrophysical Journal
, 946, 2 , L37 Published: April 2023
Ultradiffuse galaxies (UDGs) are attractive candidates to probe cosmological models and test theories of galaxy formation at low masses; however, they are difficult to detect because of their low surface brightness. In the Local Group a handful of UDGs have been found to date, most of which are satellites of the Milky Way and M31, and only two are isolated galaxies. It is unclear whether so few UDGs are expected. We address this by studying the population of UDGs formed in hydrodynamic constrained simulations of the Local Group from the HESTIA suite. For a Local Group with a total enclosed mass M LG( < 2.5 Mpc) = 8 × 1012 M☉, we predict that there are 12 ± 3 isolated UDGs (68% confidence) with stellar masses 106 ≤ M */M☉ < 109, and effective radii R e ≥ 1.5 kpc, within 2.5 Mpc of the Local Group, of which ${2}_{-1}^{+2}$ (68% confidence) are detectable in the footprint of the Sloan Digital Sky Survey (SDSS). Accounting for survey incompleteness, we find that almost the entire population of UDGs in the Local Group field would be observable in a future all-sky survey with a depth similar to the SDSS, the Dark Energy Survey, or the Legacy Survey of Space and Time. Our results suggest that there is a population of UDGs in the Local Group awaiting discovery.
Biaus, L., Nuza, S. E., Richter, P., Sparre, M., Scannapieco, C., Damle, M., Sorce, J. G., Grand, R. J. J., Tempel, E., Libeskind, N. I., Hani, M. H., 2022, Monthly Notices of the Royal Astronomical Society
, 517, 4 , 6170 Published: December 2022
We investigate the kinematic properties of gas and galaxies in the Local Group (LG) using high-resolution simulations performed by the HESTIA (High-resolution Environmental Simulations of The Immediate Area) collaboration. Our simulations include the correct cosmography surrounding LG-like regions consisting of two main spiral galaxies of ~1012 M⊙, their satellites and minor isolated galaxies, all sharing the same large-scale motion within a volume of a few Mpc. We characterize the gas and galaxy kinematics within the simulated LGs, from the perspective of the Sun, to compare with observed trends from recent HST/COS absorption-line observations and LG galaxy data. To analyse the velocity pattern of LG gas and galaxies seen in the observational data, we build sky maps from the local standard of rest, and the Galactic and LG barycentre frames. Our findings show that the establishment of a radial velocity dipole at low/high latitudes, near the preferred barycentre direction, is a natural outcome of simulation kinematics for material outside the Milky Way virial radius after removing Galaxy rotation when the two main LG galaxies are approaching. Our results favour a scenario where gas and galaxies stream towards the LG barycentre producing a velocity dipole resembling observations. While our study shows in a qualitative way the global matter kinematics in the LG as part of its ongoing assembly, quantitative estimates of gas-flow rates and physical conditions of the LG gas have to await a more detailed modelling of the ionization conditions, which will be presented in a follow-up paper.
Dupuy, A., Libeskind, N. I., Hoffman, Y., Courtois, H. M., Gottlöber, S., Grand, R. J. J., Knebe, A., Sorce, J. G., Tempel, E., Tully, R. B., Vogelsberger, M., Wang, P., 2022, Monthly Notices of the Royal Astronomical Society
, 516, 3 , 4576 Published: November 2022
How the cosmic web feeds haloes, and fuels galaxy formation is an open question with wide implications. This study explores the mass assembly in the Local Group (LG) within the context of the local cosmography by employing simulations whose initial conditions have been constrained to reproduce the local environment. The goal of this study is to inspect whether the direction of accretion of satellites on to the Milky Way and Andromeda galaxies is related to the cosmic web. The analysis considers the three high-resolution simulations available in the HESTIA simulation suite, as well as the derived velocity shear and tidal tensors. We notice two eras in the LG accretion history, delimited by an epoch around z ≈ 0.7. We also find that satellites can travel up to ~4 Mpc, relative to their parent halo before crossing its viral radius R200. Finally, we observe a strong alignment of the infall direction with the axis of slowest collapse $\boldsymbol{e}_{3}$ of both tidal and shear tensors, implying satellites of the LG originated from one particular region of the cosmic web and were channeled towards us via the process of accretion.This alignment is dominated by the satellites that enter during the early infall era, i.e. z > 0.7.
Damle, M., Sparre, M., Richter, P., Hani, M. H., Nuza, S. E., Pfrommer, C., Grand, R. J. J., Hoffman, Y., Libeskind, N., Sorce, J. G., Steinmetz, M., Tempel, E., Vogelsberger, M., Wang, P., 2022, Monthly Notices of the Royal Astronomical Society
, 512, 3 , 3717 Published: May 2022
Recent observations have revealed remarkable insights into the gas reservoir in the circumgalactic medium (CGM) of galaxy haloes. In this paper, we characterize the gas in the vicinity of Milky Way and Andromeda analogues in the HESTIA (High resolution Environmental Simulations of The Immediate Area) suite of constrained Local Group (LG) simulations. The HESTIA suite comprise of a set of three high-resolution AREPO-based simulations of the LG, run using the Auriga galaxy formation model. For this paper, we focus only on the z = 0 simulation data sets and generate mock skymaps along with a power spectrum analysis to show that the distributions of ions tracing low-temperature gas (H I and Si III) are more clumpy in comparison to warmer gas tracers (O VI, O VII, and O VIII). We compare to the spectroscopic CGM observations of M31 and low-redshift galaxies. HESTIA underproduces the column densities of the M31 observations, but the simulations are consistent with the observations of low-redshift galaxies. A possible explanation for these findings is that the spectroscopic observations of M31 are contaminated by gas residing in the CGM of the Milky Way.
