Baryon dominated ultra-diffuse galaxies

TL;DR

This study uses 21-cm observations and 3D kinematic modeling to analyze gas dynamics in ultra-diffuse galaxies, revealing they are baryon-dominated and outliers in the baryonic Tully-Fisher relation, with no missing baryons.

Contribution

It provides the first detailed gas kinematic analysis of HI-rich ultra-diffuse galaxies, showing they are baryon-dominated and challenge existing galaxy formation models.

Findings

UDGs are strong outliers from the BTFR, rotating too slowly for their baryonic mass.

These galaxies have baryon fractions consistent with the cosmological mean, with no missing baryons.

Their dynamics are dominated by baryons, indicating little dark matter within their discs.

Abstract

By means of interferometic 21-cm observations and a 3D kinematic modeling technique, we study the gas kinematics of six HI-rich ultra-diffuse galaxies (UDGs). We derive robust circular velocities and baryonic masses, that allow us to study the position of our UDGs with respect to the baryonic Tully-Fisher relation (BTFR). Somewhat surprisingly, we find that these galaxies are strong outliers from the BTFR, rotating too slowly for their baryonic mass. Moreover, their position in the circular velocity--baryonic mass plane implies that they have a baryon fraction inside their virial radii compatible with the cosmological mean, meaning that they have no "missing baryons". Unexpectedly, the dynamics of our galaxies are dominated by the baryons, leaving small room for dark matter inside their discs.