Tidal pre-conditioning and ram-pressure stripping in NGC 1427A. Deep VLT/MUSE spectroscopy and FUV-to-radio observations trace a Fornax Cluster dwarf in transformation

TL;DR

This study uses multi-wavelength observations and spectroscopy to analyze how environmental factors like ram-pressure stripping and tidal interactions are transforming the gas-rich dwarf galaxy NGC 1427A in the Fornax cluster.

Contribution

It provides a detailed, spatially resolved multi-phase analysis of the transformation processes affecting a dwarf galaxy in a cluster environment.

Findings

Gas and stars show decoupled kinematics, with gas being blueshifted and rotated differently.

Evidence of stripping and gravitational perturbations, likely from a recent dwarf-dwarf fly-by.

NGC 1427A is at the early stage of environmental quenching, useful for understanding dwarf galaxy evolution.

Abstract

The early environmental transformation of low-mass cluster galaxies from gas-rich to gas-poor remains poorly constrained, partly because clear, phase-resolved observations are rare. NGC 1427A, a disturbed star-forming dwarf in the Fornax cluster, offers a favorable case for studying this process. We aim to build a spatially resolved, multi-phase picture of NGC 1427A to constrain the roles of ram-pressure stripping and tidal perturbations. We combine a deep, spatially contiguous VLT/MUSE mosaic with ancillary data from the FUV to the radio. Full-spectrum fitting of the MUSE cube yields maps of stellar kinematics, ages, metallicities, and continuum attenuation, while emission-line modeling provides ionized-gas kinematics, Balmer-decrement reddening, and star-formation-rate surface densities. Ancillary multi-wavelength data trace neutral and molecular gas, dust, and recent star formation, placing the MUSE-based results in a broader multi-phase context. We find a pronounced decoupling between stars and gas: the H I and ionized gas rotate about an axis tilted with respect to the stellar field and are globally blueshifted. Stellar and nebular attenuation, infrared dust tracers, and H I morphology indicate stripping with a strong line-of-sight component that has reached the ISM. At the same time, the asymmetric gas and dust distribution, together with structured and time-dependent star formation, points to an additional gravitational perturbation, with a recent mild fly-by by a nearby dwarf being the favored interpretation. We propose that dwarf-dwarf tidal effects have torqued and pre-conditioned the gas, while the Fornax intracluster medium is driving ram-pressure stripping that now reaches the ISM and coincides with a declining global star formation rate. This places NGC 1427A at the onset of environmental quenching, making it a useful benchmark for early cluster dwarf transformation.