HI within and around observed and simulated galaxy discs

Comparing MeerKAT observations with mock data from TNG50 and FIRE-2

¹ INAF – Padova Astronomical Observatory, Vicolo dell’Osservatorio 5, I-35122 Padova, Italy
² The Netherlands Institute for Radio Astronomy (ASTRON), Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
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 INAF – Osservatorio Astronomico di Cagliari, Via della Scienza 5, 09047 Selargius, (CA), Italy
⁶ Institute for Computational Cosmology, Durham University, South Road, Durham DH1 3LE, UK
⁷ Centre for Extragalactic Astronomy, Durham University, South Road, Durham DH1 3LE, UK
⁸ Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
⁹ Observatoire de Paris, LERMA, Collège de France, CNRS, PSL University, Sorbonne University, 75014 Paris, France
¹⁰ Department of Astronomy, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
¹¹ Ruhr University Bochum, Faculty of Physics and Astronomy, Astronomical Institute (AIRUB), 44780 Bochum, Germany
¹² Department of Physics, Engineering Physics and Astronomy, Queen’s University, Kingston, ON K7L 3N6, Canada
¹³ Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
¹⁴ Universidad Andrés Bello, Facultad de Ciencias Exactas, Departamento de Ciencias Físicas – Instituto de Astrofísica, Fernandez Concha 700, Las Condes, Santiago, Chile
¹⁵ Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK

^⋆ Corresponding author: antonino.marasco@inaf.it

Received: 26 November 2024
Accepted: 3 March 2025

Abstract

Extragalactic gas accretion and outflows driven by stellar and active galactic nucleus (AGN) feedback are expected to influence the distribution and kinematics of gas in and around galaxies. Atomic hydrogen (H I) is an ideal tracer of these processes, and it is uniquely observable in nearby galaxies. Here we made use of wide-field (1° ×1°), spatially resolved (down to 22″), high-sensitivity (∼10¹⁸ cm⁻²) H I observations of five nearby spiral galaxies with stellar mass of ∼5 × 10¹⁰ M_⊙, taken with the MeerKAT radio telescope. Four of these were observed as part of the MHONGOOSE survey. We characterise the main H I properties in regions of a few hundred kiloparsecs around the discs of these galaxies, and compare them with synthetic H I data from a sample of 25 similarly massive star-forming galaxies from the TNG50 (20) and FIRE-2 (5) suites of cosmological hydrodynamical simulations. Overall, the simulated systems have H I and molecular hydrogen (H₂) masses in good agreement with the observations, but only when a pressure-based H₂ recipe is employed. The other recipes that we tested overestimate the H₂-to-H I mass fraction by up to an order of magnitude. On a local scale, we find two main discrepancies between the observed and simulated data. First, the simulated galaxies show a more irregular H I morphology than the observed galaxies, due to the presence of H I with column density < 10²⁰ cm⁻² up to ∼100 kpc from the galaxy centre, even though they inhabit more isolated environments than the observed targets. Second, the simulated galaxies and in particular those from the FIRE-2 suite, feature more complex and overall broader H I line profiles than the observed galaxies. We interpret this as being due to the combined effect of stellar feedback and gas accretion, which lead to a large-scale gas circulation that is more vigorous than in the observed galaxies. Our results indicate that, with respect to the simulations, gentler processes of gas inflows and outflows are at work in the nearby Universe, leading to more regular and less turbulent H I discs.