Uncovering the origin of complex velocity distributions in edge-on disc galaxies

Townson, S, Martig, M ORCID: 0000-0001-5454-1492, Grand, RJJ ORCID: 0000-0001-9667-1340, Jethwa, P, Falcón-Barroso, J and Davis, TA (2026) Uncovering the origin of complex velocity distributions in edge-on disc galaxies. Monthly Notices of the Royal Astronomical Society, 552 (4). ISSN 0035-8711

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Abstract

Stellar line-of-sight velocity distributions are a powerful tool for studying galaxy kinematics and formation history, with multiple-peaked line-of-sight velocity distributions (LOSVDs) often indicating the presence of complex kinematic components. We extract stellar LOSVDs across the disc of a simulated spiral galaxy viewed edge-on, and study how often and why we see multiple-peaked LOSVDs. We find that the multiple-peaked LOSVDs are mainly found close to the mid-plane because they result from the presence of spiral arms. This is not because the spiral arms have significantly different kinematics to the disc, but because they correspond to overdensities. Variations in the number of arms present along a line of sight create variations in the number of peaks in LOSVDs. This can be used to quantify the strength of the spiral arms above the mid-plane, and how the thickness of spiral arms varies across the disc. We find that the commonly used fourth-order Gauss–Hermite moment, (Formula presented), is negative in the regions where there are multiple-peaked LOSVDs, and hence traces spiral arms. Finally, we discuss the observability of the multiple-peaked regions and their associated (Formula presented) measurements with current integral field spectrographs. We find that the spectral resolution of MUSE might not be high enough to uncover multiple peaks in LOSVDs when they result from spiral arms, but should allow for identification of the regions of negative (Formula presented). On the other hand, higher resolution spectrographs like KOALA and WEAVE may be able to recover multiple peaks in LOSVDs, representing a promising avenue for characterizing spiral arms in edge-on disc galaxies.

Item Type:	Article
Uncontrolled Keywords:	methods: numerical; galaxies: kinematics and dynamics; galaxies: spiral; 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 Q Science > QC Physics
Divisions:	Astrophysics Research Institute
Publisher:	Oxford University Press
Date of acceptance:	1 October 2026
Date of first compliant Open Access:	5 November 2026
Date Deposited:	05 Nov 2026 15:33
Last Modified:	05 Nov 2026 15:33
DOI or ID number:	10.1093/mnras/stag1885
URI:	https://researchonline.ljmu.ac.uk/id/eprint/29834

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