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

TL;DR

This study investigates the kinematics of galaxies in the core of the SPT2349-56 protocluster at redshift 4.3, revealing predominantly rotating, star-forming galaxies with disturbed morphologies in a dense environment.

Contribution

First detailed kinematic analysis of multiple galaxies in a high-redshift protocluster core using high-resolution [CII] data and 3D-Barolo, highlighting their rotation and disturbance characteristics.

Findings

Six out of seven galaxies are rotating discs.

Average rotation velocity is 357 km/s, with low velocity dispersion.

Galaxies are kinematically rotating but morphologically disturbed.

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-$\mu$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 $V_{\mathrm{rot}}/\sigma_{\mathrm{disp}} = 4.5 \pm 1.3$. The weighted mean rotation velocity ($V_{\mathrm{rot}}$) and velocity dispersion ($\sigma_{\mathrm{disp}}$) 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 $V/\sigma$ values, with the exception that they are morphologically disturbed, kinematically rotating and interacting galaxies in an extreme protocluster environment.