The MUSE-Faint survey

Astronomy and Astrophysics, vol. 708, pp. A101

Abstract

Context. The Leo T dwarf galaxy, the faintest and least massive galaxy known to have recent star formation (≤1 Gyr), exhibits a high dynamical mass-to-light ratio (100 M ⊙ /L ⊙ ), based on its stellar velocity dispersion (7.07 +1.29 −1.12 km s −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 < 10 au) and repeated the analysis with a semi-amplitude threshold (≥10 km s −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 < 10 au) 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.

Authors 6

1. Daniel Vaz

   Universidade do Porto · Institute of Astrophysics and Space Sciences · Centro de Astrofísica da Universidade do Porto

   Affiliation as printed

   Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto

   Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP

2. J. Brinchmann Aachen Leiden Observatory

   Leiden University · Universidade do Porto · Institute of Astrophysics and Space Sciences · Centro de Astrofísica da Universidade do Porto · Leiden Observatory

   Affiliation as printed

   Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto

   Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP

   Leiden Observatory, Leiden University

3. Sebastian Kamann

   Liverpool John Moores University

   Affiliation as printed

   Astrophysics Research Institute, Liverpool John Moores University

4. Sara Saracino

   Arcetri Astrophysical Observatory · Liverpool John Moores University · National Institute for Astrophysics

   Affiliation as printed

   Astrophysics Research Institute, Liverpool John Moores University

   INAF – Osservatorio Astrofisico di Arcetri

5. P. A. C. Cunha

   Universidade do Porto · Institute of Astrophysics and Space Sciences · Centro de Astrofísica da Universidade do Porto

   Affiliation as printed

   Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto

   Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP

6. Mariana P. Júlio

   University of Potsdam · Leibniz Institute for Astrophysics Potsdam

   Affiliation as printed

   Institut für Physik und Astronomie, Universität Potsdam

   Leibniz-Institute for Astrophysics Potsdam (AIP)