Star Formation in Tadpole Galaxies

TL;DR

Tadpole galaxies, characterized by a starburst head and tail, are common in the early universe and may reveal insights into galaxy formation through cool gas inflows, with unique metallicity patterns suggesting pristine gas accretion.

Contribution

This study links tadpole galaxy morphology to metal-poor gas inflows, providing evidence for cool flows in nearby galaxies and their role in galaxy evolution.

Findings

Tadpole galaxies are prevalent among extremely metal-poor galaxies.

Metallicity drops at the starburst head suggest inflow of pristine gas.

Tadpoles are more common at high redshift, indicating evolutionary significance.

Abstract

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.