Observational Evidence of Evolving Dark Matter Profiles at $z\leq 1$

Abstract

We investigate the dark matter halos of 256 star-forming disc-like galaxies at $z\sim 1$ using the KMOS redshift one spectroscopic survey (KROSS). This sample covers the redshifts $0.6 \leq z \leq 1.04$, effective radii $0.69 \leq R_e [\mathrm{kpc}] \leq 7.76$, and total stellar masses $8.7 \leq log(M_{\mathrm{star}} \ [\mathrm{M_\odot}]) \leq 11.32$. We present a mass modelling approach to study the rotation curves of these galaxies, which allow us to dynamically calculate the physical properties associated with the baryons and the dark matter halo. For the former we assume a Freeman disc, while for the latter we employ the NFW and the Burkert halo profiles, separately. At the end, we compare the results of both cases with state-of-the-art cosmological galaxy simulations (EAGLE, TNG100 and TNG50). We find that the {\em cored} dark matter halo emerged as the dominant quantity from a radius 1-3 times the effective radius. Its fraction to the total mass is in good agreement with the outcome of hydrodynamical galaxy simulations. Remarkably, we found that the dark matter core of $z\sim 1$ star-forming galaxies are smaller and denser than their local counterparts. We conclude that dark matter halos have gradually expanded over the past 6.5 Gyrs. That is, observations are capable of capturing the dark matter response to the baryonic processes (e.g. feedbacks), and thus giving us the first empirical evidence of {\em gravitational potential fluctuations} in the inner region of galaxies, which can be verified with deep surveys and future missions.