The ALMA-CRISTAL survey: Resolved kinematic studies of main sequence star-forming galaxies at 4<z<6

Abstract

We present a detailed kinematic study of a sample of 32 massive ($9.5\leqslant\log(M_*/{\rm M_{\odot}})\leqslant10.9$) main-sequence star-forming galaxies (MS SFGs) at $4<z<6$ from the ALMA-CRISTAL program. The data consist of deep (up to 15hr observing time per target), high-resolution ($\sim1$kpc) ALMA observations of the [CII]158$\mu$m line emission. This data set enables the first systematic kpc-scale characterisation of the kinematics nature of typical massive SFGs at these epochs. We find that $\sim50\%$ of the sample are disk-like, with a number of galaxies located in systems of multiple components. Kinematic modelling reveals these main sequence disks exhibit high-velocity dispersions ($\sigma_0$), with a median disk velocity dispersion of $\sim70{\rm kms^{-1}}$ and $V_{\rm rot}/\sigma_0\sim2$, and consistent with dominant gravity driving. The elevated disk dispersions are in line with the predicted evolution based on Toomre theory and the extrapolated trends from $z\sim0$-$2.5$ MS star-forming disks. The inferred dark matter (DM) mass fraction within the effective radius $f_{\rm DM}(<R_{\rm e})$ for the disk systems decreases with the central baryonic mass surface density, and is consistent with the trend reported by kinematic studies at $z\lesssim3$; roughly half the disks have $f_{\rm DM}(<R_{\rm e})\lesssim30\%$. The CRISTAL sample of massive MS SFGs provides a reference of the kinematics of a representative population and extends the view onto typical galaxies beyond previous kpc-scale studies at $z\lesssim3$.