Measuring and modelling the Splash with APOGEE/Gaia and ARTEMIS

Kisku, S ORCID: 0000-0002-2904-8206, Schiavon, RP ORCID: 0000-0002-2244-0897, Font, AS ORCID: 0000-0001-8405-9883, Mason, AC ORCID: 0000-0003-1502-2088, Horta, D ORCID: 0000-0003-1856-2151, Taylor, DJ ORCID: 0000-0002-0031-630X, Sante, A ORCID: 0009-0005-1823-8089, Fernández-Trincado, JG ORCID: 0000-0003-3526-5052 and Beers, TC (2025) Measuring and modelling the Splash with APOGEE/Gaia and ARTEMIS. Monthly Notices of the Royal Astronomical Society, 542 (1). pp. 76-95. ISSN 0035-8711

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Abstract

Using combined data from SDSS-IV/APOGEE and Gaia, we study the chemo-dynamical properties of the Splash population in comparison with those of the high- disc. We investigate a wide range of abundance ratios, finding that the Splash differs from the high- disc overall. However, these differences result from a smooth variation of chemical compositions as a function of orbital properties. The Splash occupies the high-, high-[Al,K/Fe], and low-[Mn/Fe] end of the high- disc population. In agreement with previous studies, we find that Splash stars are distributed over large heights from the Galactic mid-plane. To further elucidate the relation between the Splash and the high- disc, we turn to simulations. Using a sample of Milky Way-like galaxies with and without major accretion events from the ARTEMIS simulations, we find that Splash-like populations are ubiquitous, though not always resulting from major mergers. Lower mass progenitors can also generate Splash-like features, as long as they are on retrograde orbits. Moreover, we find a strong correlation between the mass fraction of Splash stars and the fraction of retrograde accreted stars in the disc. Some galaxies with minor (retrograde) mergers contain more pronounced Splash populations than others with major, but prograde, mergers. For stars in the high- discs, we also find a decrease in the [/Fe] with increasing orbital angular momentum. This trend is found in hosts with both major or minor mergers. Our results suggest that a number of relatively low-mass mergers on retrograde orbits could result in populations that are qualitatively similar to the Splash.

Item Type:	Article
Uncontrolled Keywords:	5109 Space 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 Q Science > QC Physics
Divisions:	Astrophysics Research Institute
Publisher:	Oxford University Press (OUP)
Date of acceptance:	25 June 2025
Date of first compliant Open Access:	20 January 2026
Date Deposited:	20 Jan 2026 13:41
Last Modified:	20 Jan 2026 13:41
DOI or ID number:	10.1093/mnras/staf1075
URI:	https://researchonline.ljmu.ac.uk/id/eprint/27942

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