Accreted stars and stellar haloes of simulated galaxies in TNG50

Bruno M. Celiz; Julio F. Navarro; Mario G. Abadi

doi:10.1051/0004-6361/202556633

paper

Accreted stars and stellar haloes of simulated galaxies in TNG50

arXiv:2510.18971 · doi:10.1051/0004-6361/202556633

Abstract

We use the TNG50 cosmological hydrodynamic simulation to study the accreted stellar component and stellar haloes of isolated galaxies spanning a wide range of masses ( $1 0^{8} < M_{*} / M_{⊙} < 1 0^{11}$ ). We find that stars formed in the main progenitor (i.e., in-situ stars) typically dominate the inner regions as far as $\sim$ 10 half-light radii from the centre, implying that detecting uncontrovertible evidence for the presence of an accreted stellar halo requires probing the far outskirts of a galaxy. Stars from accreted, disrupted satellites (i.e., ex-situ stars) dominate beyond that radius (roughly $25%$ of the virial radius, $r_{200}$ ), which we identify as the inner boundary of the outer stellar halo. The fraction of accreted stars decreases monotonically with decreasing galaxy mass, $M_{*}$ , from $\sim$ $20%$ on average in $\sim$ $2 \times 1 0^{12} M_{⊙}$ haloes ( $M_{*} \sim$ $1 0^{11} M_{⊙}$ ) to $2$ - $3%$ in $\sim$ $2 \times 1 0^{10} M_{⊙}$ haloes ( $M_{*} \sim$ $1 0^{8} M_{⊙}$ ). The outer halo has a mass comparable to roughly $10%$ of all accreted stars. Fewer than $\sim$ $30%$ of stars in the outer halo are in-situ stars, many of which originate from star-forming satellites during the late stages of disruption, especially in low-mass systems. Accreted stars are systematically more metal poor in less massive systems, which makes the outer haloes of dwarf galaxies a fertile hunting ground for extremely metal-poor stars. At given galaxy mass, the more massive stellar haloes are systematically more concentrated (smaller $R_{eff}$ ) and have steeper density profiles (larger $n$ ). Our results provide a blueprint for interpreting observations of the outskirts of isolated galaxies in terms of their assembly histories.

arXiv comment10 pages, 9 figures. Accepted for publication in Astronomy & Astrophysics (A&A)

Accreted stars and stellar haloes of simulated galaxies in TNG50

Abstract

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