Abstract
The MATLAS deep imaging survey has uncovered a plethora of dwarf galaxies in the low density environment it has mapped. A fraction of them are unusually extended and have low surface brightness. Among these so-called ultra-diffuse galaxies, a few seem to host an excess of globular clusters (GCs). With the integral field unit spectrograph MUSE we have observed one of these galaxies – MATLAS J15052031+0148447 (MATLAS-2019) – located toward the nearby group NGC 5846 and measured its systemic velocity, age, and metallicity, and that of its GC candidates. For the stellar body of MATLAS-2019 we derive a metallicity of −1.33−0.01+0.19 dex and an age of 11.2−0.8+1.8 Gyr. For some of the individual GCs and the stacked GC population, we derive consistent ages and metallicities. From the 11 confirmed GCs and using a Markov Chain Monte Carlo approach we derived a dynamical mass-to-light ratio of 4.2−3.4+8.6 M⊙/L⊙. This is at the lower end of the luminosity-mass scaling relation defined by the Local Group dwarf galaxies. Furthermore, we could not confirm or reject the possibility of a rotational component in the GC system. If present, this would further modify the inferred mass. Follow-up observations of the GC population and of the stellar body of the galaxy are needed to assess whether this galaxy lacks dark matter, as was suggested for the pair of dwarf galaxies in the field of NGC 1052, or if this is a misinterpretation arising from systematic uncertainties of the method commonly used for these systems and the large uncertainties of the individual GC velocities.
Highlights
The Mass Assembly of early Type gaLAxies with their fine Structures (MATLAS) survey is a large observing program designed to study low surface brightness features in the outskirts of nearby massive elliptical galaxies
We present a spectroscopic analysis of the ultra-diffuse galaxies (UDGs) candidate MATLAS-2019 and its rich globular clusters (GCs) population
With MUSE we have followed up the dwarf galaxy MATLAS J15052031+0148447 (MATLAS-2019), which has a rich globular cluster system and is located in the NGC 5846 group of galaxies
Summary
The Mass Assembly of early Type gaLAxies with their fine Structures (MATLAS) survey is a large observing program designed to study low surface brightness features in the outskirts of nearby massive elliptical galaxies. To test whether we could boost the signal, we weighted the pixels according to the Sérsic profile of the galaxy with the optimal extraction algorithm (Horne 1986) of MUSE Python Data Analysis Framework (MPDAF, Bacon et al 2016), giving more weight to the pixels near the center and less to the pixels in the outskirts, where fewer photons arrive This led to a minimal change in the velocity estimation, due to the fact that the stellar profile is considerably flat – one of the key properties of UDGs. The uncertainties of the velocities are derived via a wild bootstrap approach, such as we have taken in Emsellem et al (2019).
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