Dark Matter Fraction in Disk-Like Galaxies Over the Past 10 Gyr

TL;DR

This study measures the dark matter fraction in star-forming disk galaxies from redshift 0.6 to 2.5, revealing its increase with radius, decrease with redshift, and dependence on galaxy mass, using advanced kinematic modeling techniques.

Contribution

It provides the first observational evidence of dark matter fraction evolution in disk galaxies over the past 10 Gyr, employing 3D forward modeling of integral field spectroscopic data.

Findings

Dark matter fraction increases with radius within galaxies.

Dark matter fraction decreases with increasing redshift.

Low-mass galaxies show more significant evolution in dark matter content.

Abstract

We present an observational study of the dark matter fraction in star-forming disk-like galaxies up to redshift $z \sim 2.5$, selected from publicly available integral field spectroscopic surveys: KMOS$^{\rm 3D}$, KGES, and KROSS. To model the $H\alpha$ kinematics of these galaxies, we employ 3D forward-modelling, which incorporates beam-smearing and inclination corrections, and yields rotation curves. Subsequently, these rotation curves are corrected for gas pressure gradients, resulting in circular velocity curves or `intrinsic' rotation curves. Our final sample comprises of 263 rotationally supported main sequence star-forming galaxies with redshifts ranging from $0.6 \leq z < 2.5$. We estimate the dark matter fraction of these galaxies by subtracting the baryonic mass from the total mass, where the total mass is derived from the intrinsic rotation curves. We provide novel observational evidence, suggesting that at a fixed redshift, the dark matter fraction gradually increases with radius such that the outskirts of galaxies are dark matter dominated, similarly to local star-forming disk galaxies. This observed dark matter fraction exhibits a decreasing trend with increasing redshift and, on average, the fraction within the effective radius (upto outskirts) remains above 50\%, similar to locals. We investigate the relationships between dark matter, baryon surface density, and circular velocity of galaxies. We observe that low stellar mass galaxies, with $\log(M_{\rm star}\ [\mathrm{M_\odot}]) \leq 10.0$, undergo a higher degree of evolution, which may be attributed to the hierarchical merging of galaxies. Most importantly, we discuss several sources of uncertainties and current limitations in the field, as well as their impact on the measurements of dark matter fraction and its trend across galactic scales and cosmic time.