The stellar halo in Local Group Hestia simulations I. The in-situ component and the effect of mergers

Abstract

Theory suggests that mergers play an important role in shaping galactic discs and stellar haloes, which was observationally confirmed in the MW thanks to Gaia data. In this work, aiming to probe the contribution of mergers to the in situ stellar halo formation, we analyse six M31/MW analogues from the HESTIA suite of cosmological hydrodynamical zoom-in simulations of the LG. We found that all the HESTIA galaxies experience between one to four mergers with stellar mass ratios between 0.2 and 1 relative to the host at the time of the merger. These significant mergers, with a single exception, happened 7-11Gyr ago. The overall impact of the most massive mergers in HESTIA is clearly seen as a sharp increase in the orbital eccentricity (and a corresponding decrease in the rotational velocity Vphi of pre-existing disc stars of the main progenitor, thus nicely reproducing the Splash-, Plume-like feature that was discovered in the MW. We do find a correlation between mergers and close pericentric passages of massive satellites and bursts of star formation in the in situ component. Massive mergers sharply increase the disc velocity dispersion of the in situ stars; however, the latest significant merger often heats up the disc up to the numbers when the contribution of the previous ones is less prominent in the age-velocity dispersion relation. In HESTIA galaxies, the in situ halo is an important component of the inner stellar halo where its fraction is about 30-40%, while in the outer parts it typically does not exceed ~5% beyond 15 kpc. The simulations suggest that this component of the stellar haloes continues to grow well after mergers conclude; however, the most significant contribution comes from stars that formed recently before the merger. The orbital analysis of the HESTIA galaxies suggests that wedges in Rmax-Zmax space are mainly populated by the stars born between significant mergers.

Paper I in a series of III, 17 pages, 15 figures, A&A in press

References in corpus (37)

• The NumPy array: a structure for efficient numerical computation
• The EAGLE project: Simulating the evolution and assembly of galaxies and their environments
• Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties
• Cold streams in early massive hot haloes as the main mode of galaxy formation
• Star formation efficiency in galaxy interactions and mergers: a statistical study
• The accretion origin of the Milky Way's stellar halo
• Evidence from the H3 Survey that the Stellar Halo is Entirely Comprised of Substructure
• The Atlas3D project -- XXIX. The new look of early-type galaxies and surrounding fields disclosed by extremely deep optical images
• The Dual Origin of Stellar Halos
• On the frequency, intensity and duration of starburst episodes triggered by galaxy interactions and mergers
• A time-resolved picture of our Milky Way's early formation history
• On the Formation of Galactic Thick Disks
• Building Late-Type Spiral Galaxies by In-Situ and Ex-Situ Star Formation
• Gaia early DR3 systemic motions of Local Group dwarf galaxies and orbital properties with a massive Large Magellanic Cloud
• The total stellar halo mass of the Milky Way
• High-redshift major mergers weakly enhance star formation
• The Hestia project: simulations of the Local Group
• Gas accretion and galactic fountain flows in the Auriga cosmological simulations: angular momentum and metal re-distribution
• Weighing the stellar constituents of the Galactic halo with APOGEE red giant stars
• Dissecting simulated disc galaxies II: the age-velocity relation
• A radial age gradient in the geometrically thick disk of the Milky Way
• Measuring the Milky Way mass distribution in the presence of the LMC
• The relationship between mono-abundance and mono-age stellar populations in the Milky Way disk
• Exploring the origin of low-metallicity stars in Milky Way-like galaxies with the NIHAO-UHD simulations
• Triggering of merger-induced starbursts by the tidal field of galaxy groups and clusters
• Merger-induced galaxy transformations in the ARTEMIS simulations
• Chasing the impact of the Gaia-Sausage-Enceladus merger on the formation of the Milky Way thick disc
• Minimization of Biases in Galaxy Peculiar Velocity Catalogs
• The distribution of globular clusters in kinematic spaces does not trace the accretion history of the host galaxy
• Pericentric passage-driven star formation in satellite galaxies and their hosts: CLUES from Local Group simulations
• Reading the CARDs: the Imprint of Accretion History in the Chemical Abundances of the Milky Way's Stellar Halo
• The stellar halo in Local Group Hestia simulations I. The in-situ component and the effect of mergers
• Gaia EDR3 proper motions of Milky Way dwarfs. II: Velocities, Total Energy and Angular Momentum
• On the Flaring of Thick Disc of Galaxies: Insights from Simulations
• Frequencies, chaos and resonances: a study of orbital parameters of nearby thick disc and halo stars
• Anisotropic satellite accretion onto the Local Group with HESTIA
• The survey of Planetary Nebulae in Andromeda (M31): I. Imaging the disk and halo with MegaCam@CFHT

Cited by in corpus (16)

• Galactic Archaeology with Gaia
• The Three-Phase Evolution of the Milky Way
• The stellar halo in Local Group Hestia simulations I. The in-situ component and the effect of mergers
• Metallicity distributions of halo stars: do they trace the Galactic accretion history?
• The stellar halo in Local Group Hestia simulations II. The accreted component
• The stellar halo in Local Group Hestia simulations III. Chemical abundance relations for accreted and in-situ stars
• Abundance ties: Nephele and the globular cluster population accreted with $\omega$ Cen. Based on APOGEE DR17 and Gaia EDR3
• Empirical derivation of the metallicity evolution with time and radius using TNG50 Milky Way/Andromeda analogues
• Recent star formation episodes in the Galaxy: impact on its chemical properties and the evolution of its abundance gradient
• Chronology of our Galaxy from Gaia colour-magnitude diagram fitting (ChronoGal) -- III. Age and metallicity distribution of Gaia-Sausage-Enceladus stars near the Sun
• The Pristine Survey -- XXVII. Journey to the Galactic outskirts -- Mapping the outer halo red giant stars down to the very metal-poor end
• Nearby stellar substructures in the Galactic halo from DESI Milky Way Survey Year 1 Data Release
• The Nephele ecosystem: stars, globular clusters, and stellar streams associated with the progenitor galaxy of $\omega$ Centauri
• Deciphering the Milky Way's star formation at cosmic noon with high proper-motion stars: A precursor to the merger-driven starburst
• Two faces of Gaia-Sausage-Enceladus: Mining the chemical abundance space with graph attention networks
• The chemodynamical memory of a major merger in a NIHAO-UHD Milky Way analogue -- I. A golden thread through time and space