The MUSE-Faint survey V. The binary fraction of Leo T

Vaz, D, Brinchmann, J, Kamann, S ORCID: 0000-0001-6604-0505, Saracino, S, Cunha, PAC and Julio, MP (2026) The MUSE-Faint survey V. The binary fraction of Leo T. Astronomy and Astrophysics, 708. pp. 1-15. ISSN 0004-6361

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Abstract

Context. The Leo T dwarf galaxy, the faintest and least massive galaxy known to have recent star formation ( 1Gyr), exhibits a high dynamical mass-to-light ratio 100 M LV , based on its stellar velocity dispersion 707+129 112 kms 1 , indicating extreme dark matter dominance. Aims. We present the first measurement of the binary fraction of Leo T using MUSE-Faint multi-epoch spectroscopy. We also determine the binary fraction for both young and old stellar populations separately and gain insights into binary properties in more metal-poor environments than the Milky Way or Magellanic Clouds. Finally, we investigate the potential impact of binaries on the inferred stellar velocity dispersion. Methods. We employed a forward model methodology combining empirical scaling relations to predict stellar velocity variations and a constrained binary distribution from the literature. To estimate the close binary fraction, we limited the maximum semi-major axis (a < 10au) and repeated the analysis with a semi-amplitude threshold ( 10kms 1) to check the impact on the inferred stellar velocity dispersion. Results. The overall binary fraction of Leo T is estimated to be 55+40 9 %, consistent with similar systems. The close binary fraction (a < 10au) is 30+34 9 %, which is aligned with low-metallicity environments. We found a lower binary fraction for the older stellar population 15+43 15 %when compared to the younger population 35+40 6 %. Finally, we found no significant inflation of the velocity dispersion estimate due to binary motions when compared to the dispersion inferred from the co-added spectra. This suggests that the co-added spectra effectively provide period-averaged velocities of the stars, thus mitigating the impact of binaries on the overall velocity dispersion measurement.

Item Type:	Article
Uncontrolled Keywords:	binaries: spectroscopic; galaxies: dwarf; galaxies: individual: Leo T; galaxies: kinematics and dynamics; Local Group; galaxies: stellar content; 5101 Astronomical Sciences; 51 Physical Sciences; 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:	EDP Sciences
Date of acceptance:	13 February 2026
Date of first compliant Open Access:	30 April 2026
Date Deposited:	30 Apr 2026 13:59
Last Modified:	30 Apr 2026 13:59
DOI or ID number:	10.1051/0004-6361/202555752
URI:	https://researchonline.ljmu.ac.uk/id/eprint/28508

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