The kinematics of tadpole galaxies at intermediate redshift $z \sim 0.4 - 1.5$

Abstract: Galaxy morphology and kinematics encode complementary information about the assembly history of galaxies, but the extent to which they evolve in tandem remains unclear. Tadpole galaxies, characterized by their distinct head-tail morphology and pronounced asymmetry, provide an ideal laboratory for investigating whether strongly asymmetric galaxies can exhibit ordered galaxy-scale kinematics. In this work, we present a detailed analysis of the ionized-gas kinematics of 20 morphologically selected tadpole galaxies at redshifts $z=0.4 - 1.5$ in the Hubble Ultra Deep Field, using deep VLT/MUSE spectroscopy together with HST and JWST imaging. In 13 out of 20 galaxies, the 2D velocity maps derived from the MUSE [O\,{\sc ii}] $λ\lambda3726,3729$ emission show evidence for ordered motion, characterized by moderate velocity gradients along the kinematic major axis, while the remaining systems show no clear evidence for galaxy-scale ordered kinematics. In 16 galaxies, the [O\,{\sc ii}] and rest-frame optical emission, probed by HST/F775W, have spatially coincident centroids, with projected offsets of $&lt;2$~kpc. The morpho-kinematic position angles are also generally well aligned, with a median misalignment of $Δ{\rm PA}\sim12<sup>{\circ}$. Despite the strongly asymmetric tadpole morphologies, these results indicate that a substantial fraction of these systems retain coherent galaxy-scale gaseous kinematics, suggesting that morphological asymmetry need not imply a globally disordered dynamical state. Together, our analyses suggest that morphological and kinematic settlement does not occur simultaneously and these tadpole galaxies might represent a transient evolutionary phase towards the combined morpho-kinematic settlement process.