MHONGOOSE discovery of a gas-rich low surface brightness galaxy in the Dorado group

¹ ASTRON – Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
² INAF – Osservatorio Astronomico di Cagliari, via della Scienza 5, 09047 Selargius (CA), Italy
³ Dept. of Astronomy, Univ. of Cape Town, Private Bag X3, Rondebosch 7701, South Africa
⁴ Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands
⁵ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁶ INAF – Osservatorio Astronomico di Capodimonte, via Moiariello 16, Napoli 80131, Italy
⁷ Department of Astronomy, Case Western Reserve University, Cleveland, OH 44106, USA
⁸ Institute for Computational Cosmology, Durham University, South Road, Durham DH1 3LE, United Kingdom
⁹ Centre for Extragalactic Astronomy, Durham University, South Road, Durham DH1 3LE, United Kingdom
¹⁰ Department of Physics, Durham University, South Road, Durham DH1 3LE, United Kingdom
¹¹ Australia Telescope National Facility, CSIRO Astronomy and Space Science, PO Box 76, Epping, NSW 1710, Australia
¹² Western Sydney University, Locked Bag 1797, Penrith South, NSW 1797, Australia
¹³ Department of Astronomy and Space Science, Sejong University, Seoul 05006, Korea
¹⁴ Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
¹⁵ Argelander-Institut für Astronomie, Auf dem Hügel 71, 53121 Bonn, Germany
¹⁶ Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
¹⁷ Instituto de Astrofísica, Departamento de Ciencias Físicas, Universidad Andrés Bello, Fernandez Concha 700, Las Condes, Santiago, Chile
¹⁸ LERMA, Observatoire de Paris, PSL research Université, CNRS, Sorbonne Université, 75104 Paris, France
¹⁹ Collège de France, 11 Place Marcelin Berthelot, 75005 Paris, France
²⁰ E.A. Milne Centre for Astrophysics, University of Hull, Hull HU6 7RX, United Kingdom
²¹ University of Louisville, Department of Physics and Astronomy, 102 Natural Science Building, 40292 KY, Louisville, USA
²² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
²³ Department of Physics and Electronics, Rhodes University, PO Box 94, Makhanda 6140, South Africa
²⁴ Ruhr University Bochum, Faculty of Physics and Astronomy, Astronomical Institute (AIRUB), 44780 Bochum, Germany
²⁵ INAF – Padova Astronomical Observatory, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
²⁶ Department of Physics and Space Science, Royal Military College of Canada, PO Box 17000, Station Forces Kingston, ON K7K 7B4, Canada
²⁷ Department of Physics, Engineering Physics and Astronomy, Queen’s University, Kingston, ON K7L 3N6, Canada
²⁸ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
²⁹ Department of Physics and Astronomy, The University of Manchester, Manchester M13 9PL, UK

Received: 31 January 2024
Accepted: 23 May 2024

Abstract

We present the discovery of a low-mass, gas-rich low surface brightness galaxy in the Dorado group, at a distance of 17.7 Mpc. Combining deep MeerKAT 21-cm observations from the MeerKAT H I Observations of Nearby Galactic Objects: Observing Southern Emitters (MHONGOOSE) survey with deep photometric images from the VST Early-type Galaxy Survey (VEGAS) we find a stellar and neutral atomic hydrogen (H I) gas mass of M_⋆ = 2.23 × 10⁶ M_⊙ and M_H I = 1.68 × 10⁶ M_⊙, respectively. This low surface brightness galaxy is the lowest-mass H I detection found in a group beyond the local Universe (D ≳ 10 Mpc). The dwarf galaxy has the typical overall properties of gas-rich low surface brightness galaxies in the Local group, but with some striking differences. Namely, the MHONGOOSE observations reveal a very low column density (∼10^{18 − 19} cm⁻²) H I disk with asymmetrical morphology possibly supported by rotation and higher velocity dispersion in the centre. There, deep optical photometry and UV observations suggest a recent enhancement of the star formation. Found at galactocentric distances where in the Local Group dwarf galaxies are depleted of cold gas (at a projected distance of 390 kpc from the group centre), this galaxy is likely on its first orbit within the Dorado group. We discuss the possible environmental effects that may have caused the formation of the H I disk and the enhancement of star formation (SF), highlighting the short-lived phase (a few hundreds million years) of the gaseous disk, before either SF or hydrodynamical forces will deplete the gas of the galaxy.