Kinematic analysis of $\mathbf{z}=4.3$ galaxies in the SPT2349$-$56 protocluster core

Abstract

SPT2349$-$56 is a protocluster discovered in the 2500 deg${}^2$ South Pole Telescope (SPT) survey. In this paper, we study the kinematics of the galaxies found in the core of SPT2349$-$56 using high-resolution (1.55 kpc spatial resolution at $z=4.303$) redshifted [CII] 158-$\hat{I}¼$m data. Using the publicly available code 3D-Barolo, we analyze the seven far-infrared (FIR) brightest galaxies within the protocluster core. Based on conventional definitions for the detection of rotating discs, we classify six sources to be rotating discs in an actively star-forming protocluster environment, with weighted mean $V_{\mathrm{rot}}/\ddot{I}{ƒ}_{\mathrm{disp}}=4.5\pm 1.3$. The weighted mean rotation velocity ($V_{\mathrm{rot}}$) and velocity dispersion ($\ddot{I}{ƒ}_{\mathrm{disp}}$) for the sample are $357.1\pm 114.7$ km s${}^{-1}$ and $43.5\pm 23.5$ km s${}^{-1}$, respectively. We also assess the disc stability of the galaxies and find a mean Toomre parameter of $Q_{\mathrm{T}}=0.9\pm 0.3$. The galaxies show a mild positive correlation between disc stability and dynamical support. Using the position-velocity maps, we find that five sources further classify as disturbed discs, and one classifies as a strictly rotating disc. Our sample joins several observations at similar redshift with high $V/\ddot{I}ƒ$ values, with the exception that they are morphologically disturbed, kinematically rotating and interacting galaxies in an extreme protocluster environment.

28 pages (9 appendix pages), 14 figures (7 in appendix), 7 tables (3 in appendix). Accepted for publication in ApJ