Through the Antlia Cluster: the environment shaping NGC 3281

Licentiatavhandling, 2026

Neutral atomic hydrogen (H I) provides the gas reservoir that fuels star formation and is highly sensitive to environmental mechanisms in galaxy clusters, making it a key tracer for understanding galaxy evolution. Environmental mechanisms in galaxy clusters alter the fate of this gas, thereby influencing galaxy evolution. These mechanisms range from gravitational interactions to hydrodynamical effects, which can ignite or enhance internal processes such as AGN activity, resulting in a complex interplay that shapes the observed properties of galaxies. In this licentiate thesis, we introduce the observational and theoretical framework required to study these processes, together with a detailed case study of a nearby galaxy undergoing these processes: We present an environmental study of the Seyfert 2 galaxy NGC 3281 in the Antlia cluster using deep MeerKAT H I and radio continuum observations, complemented by optical imaging. NGC 3281 hosts a truncated H I disk and is missing ∼81(+12/−29)% of its expected H I mass. We report the discovery of an isolated, large, starless H I cloud extending up to ∼200 kpc from NGC 3281 while carrying the kinematic signature of the galaxy’s rotation. Together with two smaller nearby H I clouds, this material accounts for ∼18(+25/−9)% of the inferred missing H I. The H I morphology and distribution indicate ram pressure stripping as the dominant mechanism shaping the gas, while the complete detachment of the cloud and faint stellar features suggest that a past weak gravitational interaction contributed to loosening the gas reservoir. We estimate that the main H I cloud was stripped from the galaxy ∼300–350 Myr ago. We detect strong redshifted H I absorption consistent with ongoing cold gas inflow, and the radio continuum emission reveals kpc-scale bipolar outflows emerging from the nucleus. NGC 3281 therefore represents one of the clearest nearby examples of a galaxy undergoing multiple simultaneous evolutionary processes.