ALMA Maps of Dust and Warm Dense Gas Emission in the Starburst Galaxy IC 5179$^\star$

TL;DR

This study uses high-resolution ALMA observations to analyze the distribution and kinematics of warm dense gas and dust in the nuclear region of the starburst galaxy IC 5179, revealing complex structures and excitation differences.

Contribution

First high-resolution ALMA maps of CO(6-5) and dust emission in IC 5179's nucleus, showing detailed gas dynamics and spatial variations in excitation mechanisms.

Findings

CO(6-5) emission traces a circum-nuclear rotating gas disk.

Dust and CO emissions peak at different locations, indicating different excitation processes.

Detected fluxes account for a significant fraction of Herschel measurements.

Abstract

We present our high-resolution ($0^{\prime\prime}.15\times0^{\prime\prime}.13$, $\sim$34 pc) observations of the CO(6-5) line emission, which probes the warm and dense molecular gas, and the 434 $\mu$m dust continuum emission in the nuclear region of the starburst galaxy IC 5179, conducted with the Atacama Large Millimeter Array (ALMA). The CO(6-5) emission is spatially distributed in filamentary structures with many dense cores and shows a velocity field that is characteristic of a circum-nuclear rotating gas disk, with 90% of the rotation speed arising within a radius of $\lesssim150$ pc. At the scale of our spatial resolution, the CO(6-5) and dust emission peaks do not always coincide, with their surface brightness ratio varying by a factor of $\sim$10. This result suggests that their excitation mechanisms are likely different, as further evidenced by the Southwest to Northeast spatial gradient of both CO-to-dust continuum ratio and Pa-$\alpha$ equivalent width. Within the nuclear region (radius$\sim$300 pc) and with a resolution of $\sim$34 pc, the CO line flux (dust flux density) detected in our ALMA observations is $180\pm18$ Jy km/s ($71\pm7$ mJy), which account for 22% (2.4%) of the total value measured by Herschel.