Stellar kinematics in the nuclear regions of nearby LIRGs with VLT-SINFONI. Comparison with gas phases and implications for dynamical mass estimations

TL;DR

This study compares stellar and gas kinematics in nearby LIRGs using VLT-SINFONI data, revealing that gas can reliably estimate dynamical masses despite differences in stellar and gas orbital properties.

Contribution

It provides the first detailed comparison of stellar and gas kinematics in the nuclear regions of LIRGs, demonstrating the reliability of gas kinematics for mass estimates.

Findings

Gas and stellar kinematics are similar in different gas phases.

Stars rotate in thicker, warmer discs compared to gas.

Gas kinematics can be used to estimate dynamical mass accurately.

Abstract

In this work we use seeing-limited SINFONI H- and K-band spectroscopy to analyse the spatially resolved kinematics of the stellar component in the inner r<1-2 kpc of ten nearby (mean z=0.014) LIRGs. We compare the stellar kinematics with those for different gas phases, and analyse the relative effects of using different tracers when estimating dynamical masses. The stellar velocity and velocity dispersion maps are extracted in both near-IR bands by fitting the continuum emission using pPXF while we use the gas kinematics from previous works. We find that the different gas phases have similar kinematics, whereas the stellar component is rotating with slightly lower velocities (V$_*$~0.8V$_g$) but in significantly warmer orbits ($\sigma_*$~2$\sigma_g$) than the gas phases. These values indicate that stars are rotating in thick discs while the gas phases are confined in dynamically cooler rotating discs. However, these differences do not lead to significant discrepancies between the dynamical mass estimations based on the stellar and gas kinematics. This result suggests that the gas kinematics can be used to estimate M$_{dyn}$ also in z~2 SFGs, a galaxy population that shares many structural and kinematic properties with local LIRGs.