Age and metallicity of low-mass galaxies: From their centres to their stellar halos

Tau, EA, Monachesi, A, Gómez, FA, Grand, RJJ ORCID: 0000-0001-9667-1340, Pakmor, R, van de Voort, F, Marinacci, F and Bieri, R (2026) Age and metallicity of low-mass galaxies: From their centres to their stellar halos. Astronomy & Astrophysics, 710. A241-A241. ISSN 0004-6361

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Abstract

Aims. In this work we aim to analyse the metallicity and the ages of the stellar halos of low-mass galaxies (M* ≲ 1010 M⊙) to better understand their formation history.

Methods. We use a sample of 17 simulated central low-mass galaxies from the Auriga project with a stellar mass range from ∼3 × 108 M⊙ to ∼2 × 1010 M⊙. We analyse the metallicity and the ages of these galaxies and their stellar halos, as well as the relation between these two properties.

Results. We find that all galaxies have negative radial [Fe/H] gradients, ranging from −0.18 to −0.07 dex/Rh, and that the centres of less massive dwarfs (M* < 6.30 × 109 M⊙) are in general more metal-poor than those of more massive dwarfs. We find no correlation between the metallicity gradients of the galaxies in dex/Rh and their intrinsic properties, such as their stellar mass or their accreted stellar mass. This implies that the metallicity gradients may not be such a straightforward consequence of the evolution of galaxies in the low-mass regime. However, we find a mild correlation between the metallicity gradients of the galaxies computed in dex/kpc and the galaxies’ luminosities. We also find that the dispersion in the mass-metallicity relation found in the stellar halos of low-mass galaxies can be explained with the infall time of their most dominant satellite: at a fixed accreted stellar halo mass, dwarf galaxies that accreted this satellite at later times have more metal-rich accreted stellar halos. This is because satellites that were accreted at later times had more time to chemically evolve and enrich their stellar populations before being disrupted. Regarding the ages of the analysed galaxies, we find a prominent U shape in the radial mean age profiles of ∼65% of them, which is mainly driven by the in situ stellar material. This presence of a U shape in the age profiles is due to the combination of the cessation of recent star formation at large radial distances and the merger events these galaxies undergo, which redistribute the stellar material to their outer regions. When focusing on the ages of the stellar halos, we find that more massive ones are older than less massive ones. Additionally, we find a strong correlation between the age and the metallicity of the accreted stellar halos of the galaxies in our sample, such that the more metal-rich ones are younger than the more metal-poor.

Conclusions. Our results show a wide variety in ages and metallicities of low-mass galaxies and their stellar halos, reflecting the complex and non-uniform evolutionary pathways these systems can follow. They also emphasise the importance of studying the outskirts of the galaxies as well as the central regions in order to obtain a complete picture of their evolution histories.

Item Type:	Article
Uncontrolled Keywords:	galaxies: dwarf; galaxies: evolution; galaxies: star formation; galaxies: stellar content; 51 Physical Sciences; 5103 Classical Physics; 5101 Astronomical Sciences; 51 Physical Sciences; 0201 Astronomical and Space Sciences; Astronomy & Astrophysics; 5101 Astronomical sciences; 5107 Particle and high energy physics; 5109 Space sciences
Subjects:	Q Science > QB Astronomy
Divisions:	Astrophysics Research Institute
Publisher:	EDP Sciences
Date of acceptance:	7 May 2026
Date of first compliant Open Access:	17 July 2026
Date Deposited:	17 Jul 2026 14:25
Last Modified:	17 Jul 2026 14:25
DOI or ID number:	10.1051/0004-6361/202558261
URI:	https://researchonline.ljmu.ac.uk/id/eprint/29030

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