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

TL;DR

This study uses high-resolution CO (2-1) observations of NGC 3256 to analyze its molecular gas properties, revealing highly turbulent, hot, and mostly unbound gas on GMC scales, distinct from typical disc galaxies.

Contribution

It provides the highest resolution measurements of molecular gas in NGC 3256, showing the gas is highly turbulent, hot, and smoothly distributed down to 55 pc scales, unlike in disc galaxies.

Findings

Gas surface densities range from 8 to 5500 M$_{ ext{sun}}$ pc$^{-2}$.

Velocity dispersions range from 10 to 200 km s$^{-1}$.

Median virial parameters indicate most gas is unbound.

Abstract

We present the highest resolution CO (2-1) observations obtained to date (0.25") 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. Mass surface densities range from 8 to 5500 M$_{\odot}$ 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 to 19, although external pressure may bind some of the gas. High internal turbulent pressures of 10$^{5}$ to 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.