Rotation Curves in z ∼ 1–2 Star-forming Disks: Evidence for Cored Dark Matter Distributions

Abstract

We report high-quality, H α or CO rotation curves (RCs) to several R e for 41 large, massive, star-forming disk galaxies (SFGs) across the peak of cosmic galaxy evolution ( z ∼ 0.67–2.45), taken with the ESO-VLT, the LBT and IRAM-NOEMA. Most RC41 SFGs have reflection-symmetric RCs plausibly described by equilibrium dynamics. We fit the major axis position–velocity cuts using beam-convolved forward modeling generated in three dimensions, with models that include a bulge and turbulent disk component embedded in a dark matter (DM) halo. We include priors for stellar and molecular gas masses, optical light effective radii and inclinations, and DM masses from abundance-matching scaling relations. Two-thirds or more of the z  ≥ 1.2 SFGs are baryon dominated within a few R e of typically 5.5 kpc and have DM fractions less than maximal disks (median 〈 f DM ( R e ) 〉 = 0.12 ). At lower redshift ( z < 1.2), that fraction is less than one-third. DM fractions correlate inversely with the baryonic angular momentum parameter, baryonic surface density, and bulge mass. Inferred low DM fractions cannot apply to the entire disk and halo but more plausibly reflect a flattened, or cored, inner DM density distribution. The typical central “DM deficit” in these cores relative to Navarro–Frenk–White (NFW) distributions is ∼30% of the bulge mass. The observations are consistent with rapid radial transport of baryons in the first-generation massive gas-rich halos forming globally gravitationally unstable disks and leading to efficient build-up of massive bulges and central black holes. A combination of heating due to dynamical friction and AGN feedback may drive DM out of the initial cusps.