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arXiv · 2610.27201

Ionized Gas Kinematics and Star-forming Clumps in Extremely Metal-poor Galaxies

Jyoti Yadav·Casiana Muñoz Tuñón·Cecilia Farina·Alejandro Lumbreras-Calle·Jorge Sánchez Almeida·Bruce G. Elmegreen
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Abstract

Extremely Metal Poor (XMP) galaxies are the least chemically evolved objects in the local Universe and provide important constraints on galaxy formation in low-metallicity environments. This work investigates the ionised gas kinematics and star formation properties of XMP galaxies to identify disturbed or multi-component gas motions and explore their connection with star formation. We analyse long-slit spectroscopic observations of nine XMP galaxies obtained with the Intermediate Dispersion Spectrograph on the 2.5m Isaac Newton Telescope. The study uses the H$α$ emission line to trace ionised gas and emission-line ratios to derive gas-phase metallicities. The kinematic analysis reveals that some galaxies exhibit ordered rotation, with kinematic centres not always coincident with the luminous star-forming heads. Most systems show disturbed, asymmetric, or declining velocity profiles, while localized distortions near bright star-forming heads suggest that massive clumps influence the surrounding gas dynamics. We derive dynamical masses for the dominant clumps and investigate the mass--metallicity and size--metallicity relations. The clumps exhibit low metallicities consistent with the XMP regime and comparable to those observed in low-mass dwarf galaxies. Three galaxies show counter-rotating or kinematically decoupled ionised-gas components, indicating complex gas kinematics and possible external gas acquisition. Our sample is predominantly composed of isolated systems, with metal-poor star formation concentrated in compact head regions. These properties may reflect gas accretion through mergers, interactions, or the acquisition of metal-poor gas from the intergalactic medium and cosmic filaments. Internal processes such as outflows, gas mixing, recycling, and stochastic star formation may also contribute to the observed properties.

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Jyoti Yadav, Casiana Muñoz Tuñón, Cecilia Farina, Alejandro Lumbreras-Calle, Jorge Sánchez Almeida, Bruce G. Elmegreen. 2026-10-19. Ionized Gas Kinematics and Star-forming Clumps in Extremely Metal-poor Galaxies. https://arxiv.org/abs/2610.27201

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