The MeerKAT Fornax Survey

I. Survey description and first evidence of ram pressure in the Fornax galaxy cluster

¹ INAF – Osservatorio Astronomico di Cagliari, Via della Scienza 5, 09047 Selargius (CA), Italy
e-mail: paolo.serra@inaf.it
² Netherlands Institute for Radio Astronomy (ASTRON), Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
³ Department of Physics and Electronics, Rhodes University, PO Box 94, Makhanda 6140, South Africa
⁴ Armagh Observatory and Planetarium, College Hill, Armagh BT61 9DG, UK
⁵ Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands
⁶ Department of Astronomy, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa
⁷ Department of Astronomy, Columbia University, New York, NY 10027, USA
⁸ Ruhr University Bochum, Faculty of Physics and Astronomy, Astronomical Institute, 44780 Bochum, Germany
⁹ South African Radio Astronomy Observatory, 2 Fir Street, Black River Park, Observatory, Cape Town 7925, South Africa
¹⁰ The Inter-University Institute for Data Intensive Astronomy, Department of Astronomy, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa
¹¹ INAF – Astronomical Observatory of Capodimonte, Salita Moiariello 16, 80131 Naples, Italy
¹² Argelander-Institut für Astronomie, Auf dem Hügel 71, 53121 Bonn, Germany
¹³ Centre for Space Research, North-West University, Potchefstroom 2520, South Africa
¹⁴ School of Physics and Astronomy, Cardiff University, Queens Buildings, The Parade, Cardiff CF24 3AA, UK

Received: 2 February 2023
Accepted: 23 February 2023

Abstract

The MeerKAT Fornax Survey maps the distribution and kinematics of atomic neutral hydrogen gas (H I) in the nearby Fornax galaxy cluster using the MeerKAT telescope. The 12 deg² survey footprint covers the central region of the cluster out to ∼R_vir and stretches south-west out to ∼2R_vir to include the NGC 1316 galaxy group. The H I column density sensitivity (3σ over 25 km s⁻¹) ranges from 5 × 10¹⁹ cm⁻² at a resolution of ∼10″ (∼1 kpc at the 20 Mpc distance of Fornax) down to ∼10¹⁸ cm⁻² at ∼1′ (∼6 kpc), and slightly below this level at the lowest resolution of ∼100″ (∼10 kpc). The H I mass sensitivity (3σ over 50 km s⁻¹) is 6 × 10⁵ M_⊙. The H I velocity resolution is 1.4 km s⁻¹. In this paper, we describe the survey design and H I data processing, and we present a sample of six galaxies with long, one-sided, starless H I tails (only one of which was previously known) radially oriented within the cluster and with measurable internal velocity gradients. We argue that the joint properties of the H I tails represent the first unambiguous evidence of ram pressure shaping the distribution of H I in the Fornax cluster. The disturbed optical morphology of all host galaxies supports the idea that the tails consist of H I that was initially pulled out of the galaxies’ stellar body by tidal forces. Ram pressure was then able to further displace the weakly bound H I and give the tails their current direction, length, and velocity gradient.