Star Formation in Tadpole Galaxies
  Tadpole Galaxies look like a star forming head with a tail structure to the
side. They are also named cometaries. In a series of recent works we have
discovered a number of issues that lead us to consider them extremely
interesting targets. First, from images, they are disks with a lopsided
starburst. This result is firmly established with long slit spectroscopy in a
nearby representative sample. They rotate with the head following the rotation
pattern but displaced from the rotation center. Moreover, in a search for
extremely metal poor (XMP) galaxies, we identified tadpoles as the dominant
shapes in the sample- nearly 80% of the local XMP galaxies have a tadpole
morphology. In addition, the spatially resolved analysis of the metallicity
shows the remarkable result that there is a metallicity drop right at the
position of the head. This is contrary to what intuition would say and
difficult to explain if star formation has happened from gas processed in the
disk. The result could however be understood if the star formation is driven by
pristine gas falling into the galaxy disk. If confirmed, we could be unveiling,
for the first time, cool flows in action in our nearby world. The tadpole class
is relatively frequent at high redshift - 10% of resolvable galaxies in the
Hubble UDF but less than 1% in the local Universe. They are systems that could
track cool flows and test models of galaxy formation.
