Searching for HI around MHONGOOSE galaxies via spectral stacking

¹ Netherlands Institute for Radio Astronomy (ASTRON), Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
² Kapteyn Astronomical Institute, University of Groningen, PO Box 800 9700 AV Groningen, The Netherlands
³ Department of Astronomy, University of Cape Town, Private Bag X3, 7701 Rondebosch, South Africa
⁴ INAF – Osservatorio Astronomico di Cagliari, Via della Scienza 5 09047, Selargius, CA, Italy
⁵ INAF – Padova Astronomical Observatory, Vicolo dell’Osservatorio 5, I-35122 Padova, Italy
⁶ Ruhr University Bochum, Faculty of Physics and Astronomy, Astronomical Institute (AIRUB), 44780 Bochum, Germany
⁷ Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL10 9AB, United Kingdom
⁸ Department of Physics and Astronomy, University of Louisville, Natural Science Building 102, Louisville, KY 40292, USA
⁹ Universidad Andrés Bello, Facultad de Ciencias Exactas, Departamento de Ciencias Físicas – Instituto de Astrofísica, Fernández Concha 700, Las Condes, Santiago, Chile
¹⁰ Instituto de Astrofısica de Andalucıa (IAA-CSIC), Glorieta de la Astronomña s/n, E-18008 Granada, Spain
¹¹ Department of Physics, Engineering Physics and Astronomy, Queen’s University, Kingston, ON K7L 3N6, Canada
¹² Observatoire de Paris, LERMA, Collège de France, CNRS, PSL University, Sorbonne University, 75014 Paris, France
¹³ Max Planck Institute für Astronomie, Heidelberg, Germany
¹⁴ Aix-Marseille Univ., CNRS, CNES, LAM, 38 rue Frédéric Joliot Curie, 13338 Marseille, France
¹⁵ Argelander-Institut für Astronomie, Auf dem Hügel 71, 53121 Bonn, Germany
¹⁶ Australia Telescope National Facility, CSIRO, Space and Astronomy, PO Box 1130 Bentley, WA 6102, Australia
¹⁷ International Centre for Radio Astronomy Research, The University of Western Australia, Crawley WA 6009, Australia

^⋆ Corresponding author; veronese@astron.nl

Received: 2 September 2024
Accepted: 15 November 2024

Abstract

The observed star formation rates of galaxies in the Local Universe suggests that they are replenishing their gas reservoir across cosmic time. Cosmological simulations predict that this accretion of fresh gas can occur in a hot or a cold mode, yet the existence of low column density (∼10¹⁷ cm⁻²) neutral atomic hydrogen (HI) tracing the cold mode has not been unambiguously confirmed by observations. We present the application of unconstrained spectral stacking to attempt to detect the emission from this HI in the circumgalactic medium (CGM) and intergalactic medium (IGM) of six nearby star-forming galaxies from the MHONGOOSE sample for which full-depth observations are available. Our stacking procedure consists of a standard spectral stacking algorithm coupled with a one-dimensional spectral line finder designed to extract a reliable signal close to the noise level. In agreement with previous studies, we find that the amount of signal detected outside the HI disk is much smaller than implied by simulations. Furthermore, the column density limit that we achieve via stacking (∼10¹⁷ cm⁻²) suggests that direct detection of the neutral CGM and IGM component might be challenging in the future, even with the next generation of radio telescopes.