Global dynamic scaling relations of HI-rich ultra-diffuse galaxies

TL;DR

This study analyzes the baryonic Tully-Fisher relation for 88 HI-rich ultra-diffuse galaxies, revealing a continuous distribution with some deviations likely influenced by high gas fractions and systemic biases.

Contribution

It provides the largest dynamical analysis of HI-rich UDGs, demonstrating their distribution in the BTFR and highlighting the role of gas content in deviations from standard relations.

Findings

HUDGs form a continuous BTFR distribution.

High-velocity HUDGs align with dwarf galaxies.

Low-velocity HUDGs deviate from BTFR.

Abstract

The baryonic Tully-Fisher relation (BTFR), which connects the baryonic mass of galaxies with their circular velocities, has been validated across a wide range of galaxies, from dwarf galaxies to massive galaxies. Recent studies have found that several ultra-diffuse galaxies (UDGs) deviate significantly from the BTFR, indicating a galaxy population with abnormal dynamical properties. However, such studies were still confined within a small sample size. In this study, we used the 100% complete Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA) to investigate the BTFR of 88 HI-rich UDGs (HUDGs), which is the largest UDG sample with dynamical information. We found that the HUDGs form a continuous distribution in the BTFR diagram, with high-velocity galaxies consistent with normal dwarf galaxies at 1 $\sigma$ level, and low-velocity galaxies deviating from the BTFR, in line with that reported in the literature. We point out that the observed deviation may be subject to various selection effects or systemic biases. Nevertheless, we found that the significance of the deviation of HUDGs from the BTFR and TFR are different, i.e., they either deviate from the BTFR or from the TFR. Our result indicates that a high-gas fraction may play an important role in explaining the deviation of HUDGs from BTFR.