RC100: Rotation Curves of 100 Massive Star-forming Galaxies at z = 0.6–2.5 Reveal Little Dark Matter on Galactic Scales

Abstract

We analyze Hα or CO rotation curves extending out to several galaxy effective radii for 100 massive, large, star-forming disk galaxies (SFGs) across the peak of cosmic galaxy star formation (z ∼ 0.6–2.5), more than doubling the previous sample presented by Genzel et al. and Price et al. The observations were taken with SINFONI and KMOS integral-field spectrographs at the ESO-Very Large Telescope, LUCI-LBT, NOEMA-IRAM, and Atacama Large Millimeter/submillimeter Array. We fit the major-axis kinematics with beam-convolved, forward models of turbulent rotating disks with bulges embedded in dark matter (DM) halos, including the effects of pressure support. The fraction of dark to total matter within the disk effective radius (R e ∼ 5 kpc), f DM(R e) = V 2 DM(R e)/V 2 circ(R e) decreases with redshift: at z ∼ 1 (z ∼ 2) the median DM fraction is 0.38 ± 0.23 (0.27 ± 0.18), and a third (half) of all galaxies are maximal disks with f DM(R e) < 0.28. DM fractions correlate inversely with the baryonic surface density, and the low DM fractions can be explained with a flattened, or cored, inner DM density distribution. At z ∼ 2, there is ≈40% less DM mass on average within R e compared to expected values based on cosmological stellar-mass–halo-mass relations. The DM deficit is more evident at high star formation rate surface densities (≳2.5 M ⊙ yr−1 kpc2) and galaxies with massive bulges (≥1010 M ⊙). A combination of stellar or active galactic nucleus feedback, and/or heating due to dynamical friction, may drive the DM from cuspy into cored mass distributions, pointing to an efficient buildup of massive bulges and central black holes at z ∼ 2 SFGs.