The weak connection between the stellar haloes and merger histories of Milky Way-mass galaxies

Abstract

Stellar haloes form through the disruption of satellite galaxies over time, making them a promising observable for constraining galaxy merger histories. We use a dynamical decomposition technique to isolate the stellar haloes of Milky Way-mass galaxies in the $100\mathrm{Mpc}$ EAGLE simulation and study their relationship to the merger histories of their hosts. We define the stellar halo as the stellar mass that is bound to the central subhalo but not associated with the disc or bulge components of a galaxy, and we quantify their merger histories using the most significant merger since $z=1$. Surprisingly, we find that the fraction of a galaxy's total stellar mass in the stellar halo, $f_{\mathrm{SH}}$, is not a reliable indicator of its merger activity. Contrary to common assumptions, disc galaxies with low $f_{\mathrm{SH}}$ do not necessarily have quiescent merger histories. In fact, roughly one quarter experienced a merger at $z\le 1$ with a satellite whose stellar mass was at least 10 per cent of the host galaxy's stellar mass. These galaxies undergo mergers with satellites on circular orbits that are roughly co-planar with the pre-existing disc and thereby avoid contributing mass to the stellar halo. Instead, such mergers build thick, extended discs and supply fresh gas that often triggers a significant episode of star formation in the disc. Our results suggest that disc galaxies with low-mass stellar haloes, such as the Milky Way, can have varied and active merger histories, and that stellar haloes may not be a reliable tool for inferring galaxy merger histories.

12 pages, 8 figures. MNRAS published

References in corpus (37)

• The EAGLE project: Simulating the evolution and assembly of galaxies and their environments
• The hierarchical formation of the brightest cluster galaxies
• The EAGLE simulations of galaxy formation: calibration of subgrid physics and model variations
• Chemical enrichment in cosmological, smoothed particle hydrodynamics simulations
• The Auriga Project: the properties and formation mechanisms of disc galaxies across cosmic time
• The Dual Origin of Stellar Halos
• A chronicle of galaxy mass assembly in the EAGLE simulation
• Building Late-Type Spiral Galaxies by In-Situ and Ex-Situ Star Formation
• Angular momentum evolution of galaxies in EAGLE
• Halo Mass and Assembly History Exposed in the Faint Outskirts: the Stellar and Dark Matter Haloes of Illustris Galaxies
• Galaxy And Mass Assembly (GAMA): Galaxy close-pairs, mergers, and the future fate of stellar mass
• The Dragonfly Nearby Galaxies Survey. I. Substantial variation in the diffuse stellar halos around spiral galaxies
• Galaxy And Mass Assembly (GAMA): A forensic SED reconstruction of the cosmic star formation history and metallicity evolution by galaxy type
• On the formation of extended galactic disks by tidally disrupted dwarf galaxies
• A tale of two populations: surviving and destroyed dwarf galaxies and the build up of the Milky Way's stellar halo
• Spurious heating of stellar motions in simulated galactic disks by dark matter halo particles
• 4MOST Consortium Survey 7: Wide-Area VISTA Extragalactic Survey (WAVES)
• The merger and assembly histories of Milky Way- and M31-like galaxies with TNG50: disk survival through mergers
• The dependence of the galaxy stellar-to-halo mass relation on galaxy morphology
• Euclid preparation: XVI. Exploring the ultra low-surface brightness Universe with Euclid/VIS
• The Milky Way's Shell Structure Reveals the Time of a Radial Collision
• ERGO-ML I: Inferring the assembly histories of IllustrisTNG galaxies from integral observable properties via invertible neural networks
• The impact of spurious collisional heating on the morphological evolution of simulated galactic discs
• Convergence properties of halo merger trees; halo and substructure merger rates across cosmic history
• Formation of massive disk galaxies in the IllustrisTNG simulation
• ProFuse: Physical Multi-Band Structural Decomposition of Galaxies and the Mass-Size-Age Plane
• Tracing the anemic stellar halo of M101
• How cosmological merger histories shape the diversity of stellar haloes
• A Swing of the Pendulum: The Chemodynamics of the Local Stellar Halo Indicate Contributions from Several Radial Merger Events
• A stream come true: Connecting tidal tails, shells, streams, and planes with galaxy kinematics and formation history
• Characterising Tidal Features Around Galaxies in Cosmological Simulations
• The diversity of assembly histories leading to disc galaxy formation in a LambdaCDM model
• The evolutionary pathways of disk galaxies with different sizes
• The Physical Origin of the Mass-Size Relation and Its Scatter of Disk Galaxies
• Saying Hallo to M94's Stellar Halo: Investigating the Accretion History of the Largest Pseudobulge Host in the Local Universe
• Formation of super-thin galaxies in Illustris-TNG
• Gamma rays from dark matter spikes in EAGLE simulations

Cited by in corpus (2)

• Bulgeless Evolution And the Rise of Discs (BEARD) I. Physical drivers of the mass-size relation for Milky Way-like galaxies
• Accreted stars and stellar haloes of simulated galaxies in TNG50