Highly turbulent gas on GMC scales in NGC 3256, the nearest luminous infrared galaxy

We present the highest resolution CO (2-1) observations obtained to date (0.25 arcsec) of NGC 3256 and use them to determine the detailed properties of the molecular interstellar medium in the central 6 kpc of this merger. Distributions of physical quantities are reported from pixel-by-pixel measurements at 55 and 120 pc scales and compared to disc galaxies observed by PHANGS-ALMA (Physics at High Angular resolution in Nearby GalaxieS with Atacama Large Millimeter/Submillimeter Array). Mass surface densities range from 8 to 5500 M-circle dot pc(-2) and velocity dispersions from 10 to 200 km s(-1). Peak brightness temperatures as large as 37 K are measured, indicating the gas in NGC 3256 may be hotter than all regions in nearby disc galaxies measured by PHANGS-ALMA. Brightness temperatures even surpass those in the overlap region of NGC 4038/9 at the same scales. The majority of the gas appears unbound with median virial parameters of 7-19, although external pressure may bind some of the gas. High internal turbulent pressures of 10(5)-10(10) K cm(-3) are found. Given the lack of significant trends in surface density, brightness temperature, and velocity dispersion with physical scale we argue the molecular gas is made up of a smooth medium down to 55 pc scales, unlike the more structured medium found in the PHANGS-ALMA disc galaxies.

Automated summary

This study presents the highest resolution CO (2-1) observations obtained to date of NGC 3256, analyzing the detailed properties of the molecular interstellar medium in the central region of this merger. The gas in NGC 3256 may be hotter than in nearby disc galaxies, with majority of the gas appearing unbound and high internal turbulent pressures. Despite lack of significant trends with physical scale, the molecular gas is considered to be a smooth medium down to 55 pc scales, contrasting with the more structured medium found in PHANGS-ALMA disc galaxies.