Progenitor Diversity in the Accreted Stellar Halos of Milky Way-like Galaxies

Pu, SY ORCID: 0009-0000-3146-7154, Cooper, AP ORCID: 0000-0001-8274-158X, Grand, RJJ ORCID: 0000-0001-9667-1340, Gómez, FA ORCID: 0000-0002-1947-333X and Monachesi, A ORCID: 0000-0003-2325-9616 (2025) Progenitor Diversity in the Accreted Stellar Halos of Milky Way-like Galaxies. The Astrophysical Journal, 980 (1). ISSN 0004-637X

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Abstract

Ongoing large stellar spectroscopic surveys of the Milky Way seek to reconstruct the major events in the assembly history of the Galaxy. Chemical and kinematic observations can be used to separate the contributions of different progenitor galaxies to the present-day stellar halo. Here, we compute the number of progenitors that contribute to the accreted stellar halos of simulated Milky Way-like galaxies as a function of radius (the radial diversity) in three suites of models: Bullock & Johnston, Aquarius, and Auriga. We show that there are significant differences between the predictions of these three models, beyond the halo-to-halo scatter expected in ΛCDM. Predictions of diversity from numerical simulations are sensitive to model-dependent assumptions regarding the efficiency of star formation in dwarf galaxies. We compare, at face value, to current constraints on the radial diversity of the Milky Way's accreted halo. These constraints imply that the halo of our Galaxy is dominated by ∼2 progenitors in the range 8-45 kpc, in contrast to averages of 7 progenitors in the Bullock & Johnston models, 3.5 in Aquarius, and 4.2 in Auriga over the same region. We additionally find that the models with radial diversity most similar to that of the Milky Way are predominantly those with ongoing merger events. The Milky Way therefore appears unusual in having an accreted stellar halo dominated by a small number of progenitors accreted at very early times.

Item Type:	Article
Uncontrolled Keywords:	5101 Astronomical Sciences; 51 Physical Sciences; Stem Cell Research; Stem Cell Research - Nonembryonic - Non-Human; 5101 Astronomical Sciences; 51 Physical Sciences; Stem Cell Research - Nonembryonic - Non-Human; Stem Cell Research; 0201 Astronomical and Space Sciences; 0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics; 0306 Physical Chemistry (incl. Structural); Astronomy & Astrophysics; 5101 Astronomical sciences; 5107 Particle and high energy physics; 5109 Space sciences
Subjects:	Q Science > QB Astronomy
Divisions:	Astrophysics Research Institute
Publisher:	American Astronomical Society
Date of acceptance:	18 December 2024
Date of first compliant Open Access:	8 June 2026
Date Deposited:	08 Jun 2026 15:16
Last Modified:	08 Jun 2026 15:16
DOI or ID number:	10.3847/1538-4357/ada382
URI:	https://researchonline.ljmu.ac.uk/id/eprint/28780

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