Dynamical Characterization of Galaxies at z~4-6 via Tilted Ring Fitting to ALMA [CII] Observations

TL;DR

This study demonstrates the feasibility of using tilted ring models to analyze the gas dynamics of high-redshift galaxies with ALMA [CII] data, enabling insights into their rotation curves and dark matter content.

Contribution

It introduces a method for dynamical characterization of early universe galaxies using ALMA data and tilted ring fitting, providing new tools for high-redshift galaxy analysis.

Findings

Rotation curves and dynamical masses derived for several z~4-6 galaxies.

Evidence for a dark matter halo of approximately 10^11 solar masses.

Assessment of observational effects on dynamical modeling results.

Abstract

Until recently, determining the rotational properties of galaxies in the early universe (z>4, Universe age <1.5Gyr) was impractical, with the exception of a few strongly lensed systems. Combining the high resolution and sensitivity of ALMA at (sub-) millimeter wavelengths with the typically high strength of the [CII] 158um emission line from galaxies and long-developed dynamical modeling tools raises the possibility of characterizing the gas dynamics in both extreme starburst galaxies and normal star forming disk galaxies at z~4-7. Using a procedure centered around GIPSY's ROTCUR task, we have fit tilted ring models to some of the best available ALMA [CII] data of a small set of galaxies: the MS galaxies HZ9 & HZ10, the Damped Lyman-alpha Absorber (DLA) host galaxy ALMA J0817+1351, the submm galaxies AzTEC/C159 and COSMOS J1000+0234, and the quasar host galaxy ULAS J1319+0950. This procedure directly derives rotation curves and dynamical masses as functions of radius for each object. In one case, we present evidence for a dark matter halo of O(10^11) solar masses. We present an analysis of the possible velocity dispersions of AzTEC/C159 and ULAS J1319+0950 based on matching simulated observations to the integrated [CII] line profiles. Finally, we test the effects of observation resolution and sensitivity on our results. While the conclusions remain limited at the resolution and signal-to-noise ratios of these observations, the results demonstrate the viability of the modeling tools at high redshift, and the exciting potential for detailed dynamical analysis of the earliest galaxies, as ALMA achieves full observational capabilities.