Investigating the H  I distribution and kinematics of ESO444-G084 and [KKS2000]23: New insights from the MHONGOOSE survey

¹ Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
² Wits Centre for Astrophysics, School of Physics, University of the Witwatersrand, 1 Jan Smuts Avenue, 2000, South Africa
³ Australia Telescope National Facility, CSIRO, Space and Astronomy, PO Box 76, NSW 1710, Epping, Australia
⁴ Western Sydney University, Locked Bag 1797, Penrith, NSW 2751, Australia
⁵ Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
⁶ Department of Astronomy, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa
⁷ Département de physique, Université de Montréal, Complexe des sciences MIL, 1375 Avenue Thérèse-Lavoie-Roux, & Montréal, QC H2V 0B3, Canada
⁸ Observatoire d’Astrophysique de l’Université Ouaga I Pr Joseph Ki-Zerbo (ODAUO), BP 7021, Ouaga 03, Burkina Faso
⁹ Max-Planck Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
¹⁰ Department of Physics and Electronics, Rhodes University, PO Box 94, Makhanda 6140, South Africa
¹¹ Ruhr University Bochum, Faculty of Physics and Astronomy, Astronomical Institute (AIRUB), 44780 Bochum, Germany
¹² Department of Physics, University of Pretoria, Hatfield, Pretoria, 0028, South Africa
¹³ Astrophysics Research Centre, University of KwaZulu-Natal, Durban, 3696, South Africa
¹⁴ School of Mathematics, Statistics & Computer Science, University of KwaZulu-Natal, Westville Campus, Durban 4041, South Africa
¹⁵ Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield, AL10 9AB, UK
¹⁶ Université de Strasbourg, CNRS, Observatoire astronomique de Strasbourg, UMR 7550, 67000 Strasbourg, France
¹⁷ Instituto de Astrofísica, Departamento de Ciencias Físicas, Universidad Andrés Bello, Fernández Concha 700, Las Condes, Santiago, Chile
¹⁸ Observatoire de Paris, Collège de France, Université PSL, Sorbonne Université, CNRS, LERMA, Paris, France
¹⁹ Netherlands Institute for Radio Astronomy (ASTRON), Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
²⁰ Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands
²¹ Department of Physics, Engineering Physics and Astronomy, Queen's University, Kingston, ON K7L 3N6, Canada
²² Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada
²³ Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK
²⁴ United Kingdom SKA Regional Centre (UKSRC), UK
²⁵ INAF – Padova Astronomical Observatory, Vicolo dell’Osservatorio 5, I-35122 Padova, Italy
²⁶ Department of Astronomy, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
²⁷ Institute for Computational Cosmology, Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
²⁸ Centre for Extragalactic Astronomy, Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
²⁹ Department of Physics, Engineering Physics and Astronomy, Queen's University, Kingston, ON K7L 3N6, Canada
³⁰ CSIRO, Space & Astronomy, PO Box 1130, Bentley WA 6102, Australia
³¹ International Centre for Radio Astronomy Research, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia

^⋆ Corresponding author.

Received: 6 March 2025
Accepted: 1 June 2025

Abstract

We present the neutral atomic hydrogen (H I) distribution, kinematics, mass modelling, and gravitational stability of the dwarf irregular galaxies ESO444–G084 and [KKS2000]23 using high spatial, spectral, and column density sensitivity data from the MeerKAT H I observations of nearby galactic objects: Observing Southern Emitters (MHONGOOSE) survey obtained with MeerKAT. ESO444–G084 exhibits centrally concentrated H I emission, while [KKS2000]23 has irregularly distributed high-density pockets. The total H I fluxes measured down to column density thresholds of 10¹⁹ cm⁻² and 10¹⁸ cm⁻² are nearly the same, suggesting that the increase in the H I diameter at lower column densities is primarily due to the larger beam size, and that no significant additional emission is detected. The total H I masses are (1.1±0.1)×10⁸ M_⊙ for ESO444–G084 and (6.1±0.3)×10⁸ M_⊙ for [KKS2000]23. We derived rotation curves using 3D kinematic modelling tools Python fully automated TiRiFiC (PyFAT) and tilted ring fitting code (TiRiFiC), which allow us to fully capture the gas kinematics. Both galaxies exhibit disk-like rotation, with ESO444–G084 showing a kinematic warp beyond ∼1.8 kpc. Its relatively fast-rising rotation curve suggests a more centrally concentrated dark matter distribution, whereas [KKS2000]23's more gradual rise indicates a more extended mass distribution. Mass modelling with an isothermal halo and stellar mass-to-light ratio (M/L)_3.μm^*=0.20 for ESO444–G084 and 0.18 for [KKS2000]23 yields physically consistent results. We further analyse disk stability using spatially resolved maps of the Toomre Q parameter and Σ_gas/Σ_crit, linking these with recent star formation traced by hydrogen-alpha (Hα) and far-ultraviolet (FUV) emission. ESO444–G084 supports localised star formation despite global stability, while [KKS2000]23 is gravitationally unstable yet lacks strong Hα emission, suggesting that turbulence, gas depletion, or past feedback suppresses star formation. The absence of detectable inflows or outflows implies that internal processes regulate star formation. This study highlights the interplay between H I morphology, kinematics, dark matter distribution, and disk stability, demonstrating how internal mechanisms shape dwarf galaxy evolution.