Structure and Kinematics of Molecular Disks in Fast-Rotator Early-Type Galaxies

TL;DR

This study uses interferometric observations to analyze the structure and kinematics of molecular disks in four fast-rotator early-type galaxies, revealing insights into their formation and gas origins.

Contribution

It provides high-resolution CO observations of four lenticular galaxies, comparing gas, stellar, and ionized gas kinematics to understand their formation histories and gas origins.

Findings

Molecular gas exists in kpc-scale disks with regular kinematics.

Disks are aligned with stellar axes and match circular velocities in luminous galaxies.

External gas origin confirmed in at least one galaxy, with some kinematic discrepancies observed.

Abstract

We present interferometric observations resolving the CO emission in the four gas-rich lenticular galaxies NGC 3032, NGC 4150, NGC 4459, and NGC 4526, and we compare the CO distribution and kinematics to those of the stars and ionized gas. Counterrotation documents an external origin for the gas in at least one case (NGC 3032), and the comparisons to stellar and ionized gas substructures in all four galaxies offer insights into their formation histories. The molecular gas is found in kpc-scale disks with mostly regular kinematics and average surface densities of 100 to 200 \msunsqpc. The disks are well aligned with the stellar photometric and kinematic axes. In the two more luminous Virgo Cluster members NGC 4459 and NGC 4526 the molecular gas shows excellent agreement with circular velocities derived independently from detailed modeling of stellar kinematic data. There are also two puzzling instances of disagreements between stellar kinematics and gas kinematics on sub-kpc scales. In the inner arcseconds of NGC 3032 the CO velocities are significantly lower than the inferred circular velocities, and the reasons may possibly be related to the external origin of the gas but are not well understood. In addition, the very young population of stars in the core of NGC 4150 appears to have the opposite sense of rotation from the molecular gas.