Bibcode
Elmegreen, D. M.; Muñoz-Tuñón, C.; Sánchez-Almeida, J.; Méndez-Abreu, J.; Elmegreen, B. G.
Bibliographical reference
The Astrophysical Journal, Volume 767, Issue 1, article id. 74, 15 id. (2013).
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4
2013
Journal
Citations
65
Refereed citations
60
Description
Tadpole galaxies, with a bright peripheral clump on a faint tail, are
morphological types unusual in the nearby universe but very common early
on. Low mass local tadpoles were identified and studied photometrically
in a previous work, which we complete here analyzing their chemical and
dynamical properties. We measure Hα velocity curves of seven local
tadpoles, representing 50% of the initial sample. Five of them show
evidence for rotation (~70%), and a sixth target hints at it. Often the
center of rotation is spatially offset with respect to the tadpole head
(three out of five cases). The size and velocity dispersion of the heads
are typical of giant H II regions, and three of them yield dynamical
masses in fair agreement with their stellar masses as inferred from
photometry. In four cases the velocity dispersion at the head is reduced
with respect to its immediate surroundings. The oxygen metallicity
estimated from [N II] λ6583/Hα often shows significant
spatial variations across the galaxies (~0.5 dex), being smallest at the
head and larger elsewhere. The resulting chemical abundance gradients
are opposite to the ones observed in local spirals, but agrees with disk
galaxies at high redshift. We interpret the metallicity variation as a
sign of external gas accretion (cold-flows) onto the head of the
tadpole. The galaxies are low-metallicity outliers of the
mass-metallicity relationship. In particular, two of the tadpole heads
are extremely metal poor, with a metallicity smaller than a tenth of the
solar value. These two targets are also very young (ages smaller than 5
Myr). All these results combined are consistent with the local tadpole
galaxies being disks in early stages of assembling, with their star
formation sustained by accretion of external metal-poor gas.
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Casiana
Muñoz Tuñón