Closing the Gap between Observed Low-Mass Galaxy HI Kinematics and CDM Predictions

TL;DR

This study uses deep HI observations and simulations to reconcile observed low-mass galaxy kinematics with $ ext{Lambda}$CDM predictions, improving the understanding of galaxy-halo connections at small scales.

Contribution

It demonstrates that deeper HI measurements align observed galaxy kinematics with $ ext{Lambda}$CDM predictions and refines the baryonic Tully-Fisher relation at low masses.

Findings

Deeper HI measurements approach the predicted kinematic relationship in $ ext{Lambda}$CDM.

Measurements of baryonic mass align with the low-mass end of the BTFR.

Data hints at the predicted rollover in the BTFR for low-mass galaxies.

Abstract

Testing the standard cosmological model ($\Lambda$CDM) at small scales is challenging. Galaxies that inhabit low-mass dark matter halos provide an ideal test bed for dark matter models by linking observational properties of galaxies at small scales (low mass, low velocity) to low-mass dark matter halos. However, the observed kinematics of these galaxies do not align with the kinematics of the dark matter halos predicted to host them, obscuring our understanding of the low-mass end of the galaxy-halo connection. We use deep HI observations of low-mass galaxies at high spectral resolution in combination with cosmological simulations of dwarf galaxies to better understand the connection between dwarf galaxy kinematics and low-mass halos. Specifically, we use HI line widths to directly compare to the maximum velocities in a dark matter halo, and find that each deeper measurement approaches the expected one-to-one relationship between the observed kinematics and the predicted kinematics in $\Lambda$CDM. We also measure baryonic masses and place these on the Baryonic Tully-Fisher relation (BTFR). Again, our deepest measurements approach the theoretical predictions for the low-mass end of this relation, a significant improvement on similar measurements based on line widths measured at 50\% and 20\% of the peak. Our data also hints at the rollover in the BTFR predicted by hydrodynamical simulations of $\Lambda$CDM for low-mass galaxies.