2023A&A...673A.146S

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 × 10⁵M_⊙. 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.