The MAGPI Survey: co-evolution of baryons and dark matter in star-forming disk-like galaxies at $0.1\lesssim z\lesssim 0.85$

Abstract

We present a comprehensive analysis of the dark matter (DM) content and its structural dependence in star-forming disk-like galaxies at intermediate redshifts ($0.1\lesssim z\lesssim 0.85$), utilizing spatially resolved kinematic data from the MAGPI survey. We report the following: (1) Low stellar mass galaxies ($M_{\mathrm{star}}<10^{9.5}{M}_{\odot }$) are strongly DM dominated across all radii, with average $⟨f_{{}_{\mathrm{DM}}}⟩\sim 0.85$, while high-mass ($M_{\mathrm{star}}>10^{10.5}{M}_{\odot }$) systems exhibit relatively low DM fractions in their inner regions ($⟨f_{{}_{\mathrm{DM}}}⟩\sim 0.47$) which is equivalent to local massive disk galaxies (e.g., Milky Way and Andromeda). This suggests a mass-dependent structural dichotomy, most-likely governed by a combination of internal galactic processes and environmental influences. (2) A tight inverse correlation between $f_{{}_{\mathrm{DM}}}$ and baryon mass surface density ($\hat{I}{\pounds }_{\mathrm{bar}}$), with intrinsic scatter of $\sim 0.11$ dex. This is consistent with an inside-out baryon assembly scenario and suggests that the fundamental structural correlations of galaxies were already established by $z\sim 0.85$. (3) No significant evolution in $f_{{}_{\mathrm{DM}}}$ with redshift across the MAGPI window, and when combined with higher-redshift ($0.6\le z\le 1.5$) data from Sharma et al. 2025, we quantitatively show that the reported decline in $f_{{}_{\mathrm{DM}}}(z)$ is most-likely due to observational biases against low-mass systems at $z>1$. These results offer empirical evidence for a scenario in which disk-like galaxies evolve through a co-regulated build-up of baryonic and DM components, preserving internal structural regularities (such as the total mass distribution and rotation-curve shape) throughout cosmic time.

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