Bibcode
Olmo-García, A.; Sánchez Almeida, J.; Muñoz-Tuñón, C.; Filho, M. E.; Elmegreen, B. G.; Elmegreen, D. M.; Pérez-Montero, E.; Méndez-Abreu, J.
Bibliographical reference
The Astrophysical Journal, Volume 834, Issue 2, article id. 181, 22 pp. (2017).
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1
2017
Journal
Citations
25
Refereed citations
24
Description
The extremely metal-poor (XMP) galaxies analyzed in a previous paper
have large star-forming regions with a metallicity lower than the rest
of the galaxy. Such a chemical inhomogeneity reveals the external origin
of the metal-poor gas fueling star formation, possibly indicating
accretion from the cosmic web. This paper studies the kinematic
properties of the ionized gas in these galaxies. Most XMPs have a
rotation velocity around a few tens of km s‑1. The
star-forming regions appear to move coherently. The velocity is constant
within each region, and the velocity dispersion sometimes increases
within the star-forming clump toward the galaxy midpoint, suggesting
inspiral motion toward the galaxy center. Other regions present a local
maximum in velocity dispersion at their center, suggesting a moderate
global expansion. The Hα line wings show a number of faint
emission features with amplitudes around a few per cent of the main
Hα component, and wavelength shifts between 100 and 400 km
s‑1. The components are often paired, so that red and
blue emission features with similar amplitudes and shifts appear
simultaneously. Assuming the faint emission to be produced by expanding
shell-like structures, the inferred mass loading factor (mass loss rate
divided by star formation rate) exceeds 10. Since the expansion velocity
far exceeds the rotational and turbulent velocities, the gas may
eventually escape from the galaxy disk. The observed motions involve
energies consistent with the kinetic energy released by individual
core-collapse supernovae. Alternative explanations for the faint
emission have been considered and discarded.
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