LOCAL TADPOLE GALAXIES: DYNAMICS AND METALLICITY

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 H[alpha] 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. 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. The two targets are also very young. All the 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.