# Ionised gas kinematics and dynamical masses of $z\gtrsim6$ galaxies from JADES/NIRSpec high-resolution spectroscopy

**Authors:** Anna de Graaff, Hans-Walter Rix, Stefano Carniani, Katherine A. Suess, Stéphane Charlot, Emma Curtis-Lake, Santiago Arribas, William M. Baker, Kristan Boyett, Andrew J. Bunker, Alex J. Cameron, Jacopo Chevallard, Mirko Curti, Daniel J. Eisenstein, Marijn Franx, Kevin Hainline, Ryan Hausen, Zhiyuan Ji, Benjamin D. Johnson, Gareth C. Jones  
**arXiv:** [2308.09742](https://arxiv.org/abs/2308.09742)  
**Date:** 2023-08-18  
**Summary page:** https://www.summarizepaper.com/en/paper/2308.09742v1/

## Key points

- The study investigates the kinematic gas properties of six galaxies at redshifts between 5.5 and 7.4 in the JWST Advanced Deep Extragalactic Survey (JADES)
- High-resolution JWST/NIRSpec multi-object spectroscopy is used to analyze the rest-frame optical emission lines [OIII] and Hα
- The galaxies are small in size and have low stellar mass, with sizes of approximately 1 kiloparsec and stellar masses ranging from $10^7$ to $10^9$ solar masses
- The observed star formation rates suggest that these galaxies have cold gas masses approximately ten times larger than their stellar masses
- The ionized gas in these galaxies is spatially resolved by JWST, with indications of broadened lines and spatial velocity gradients
- A simple thin-disc model is employed to analyze the observations, along with a novel forward modeling software that considers complex geometry, point spread function, and pixellation of the NIRSpec instrument
- Both rotation-dominated structures and dispersion-dominated ones are detected, with velocity gradients up to 150 km/s indicating rotational motion and velocity dispersions up to 70 km/s comparable to those observed during cosmic noon periods in other studies
- Dynamical mass estimates range from $10^9$ to $10^{10}$ solar masses, which are up to forty times larger than the stellar masses and three times larger than the total baryonic mass (including gas and stars)
- Dark matter dominance or lower star formation efficiency may explain the large dynamical mass estimates compared to other studies conducted at lower redshifts

## Summary

In the study, the authors investigate the kinematic gas properties of six galaxies at redshifts between 5.5 and 7.4 in the JWST Advanced Deep Extragalactic Survey (JADES). They use high-resolution JWST/NIRSpec multi-object spectroscopy to analyze the rest-frame optical emission lines [OIII] and Hα. These galaxies are characterized by their small size and low stellar mass, with sizes of approximately 1 kiloparsec and stellar masses ranging from $10^7$ to $10^9$ solar masses. This makes them less massive than any previously studied galaxy kinematically at redshifts greater than 1. The observed star formation rates suggest that these galaxies have cold gas masses approximately ten times larger than their stellar masses. The authors find that the ionized gas in these galaxies is spatially resolved by JWST, with indications of broadened lines and spatial velocity gradients. To analyze these observations, they employ a simple thin-disc model and develop a novel forward modeling software that takes into account factors such as complex geometry, point spread function, and pixellation of the NIRSpec instrument. The analysis reveals that the sample includes both rotation- and dispersion-dominated structures. Velocity gradients of approximately 100-150 km/s are detected, indicating rotational motion, while velocity dispersions ranging from 30 to 70 km/s are comparable to those observed during cosmic noon. The dynamical masses derived from these models range from $10^9$ to $10^{10}$ solar masses, which are up to forty times larger than the stellar masses and three times larger than the total baryonic mass (including gas and stars). These findings hold even if the observed velocity gradients are attributed to ongoing mergers rather than rotating discs. Unless outflows dominate the observed emission line kinematics, this suggests that either dark matter dominates the centers of these galaxies or star formation is three times less efficient leading to higher inferred gas masses. The study provides valuable insights into the kinematic properties and dynamical masses of high-redshift galaxies, shedding light on their formation and evolution processes. By analyzing high resolution data obtained through JWST/NIRSpec multi-object spectroscopy combined with a novel forward modeling software developed for this purpose, it was possible to detect both rotation-dominated structures as well as dispersion dominated ones with velocity gradients up to 150 km/s indicating rotational motion while velocity dispersions up to 70 km/s were comparable to those observed during cosmic noon periods in other studies. The dynamical mass estimates were found up to 40 times larger than stellar mass estimates suggesting dark matter dominance or lower star formation efficiency in comparison with other studies conducted at lower redshifts.