Imaging the Molecular Outflows of the Prototypical ULIRG NGC 6240 with ALMA

TL;DR

This study uses high-resolution ALMA observations to image molecular outflows in NGC 6240, revealing broad CO emission features linked to nuclear outflows from the galaxy's double nuclei.

Contribution

First detailed high-resolution imaging of molecular outflows in NGC 6240, identifying broad CO components associated with nuclear outflows.

Findings

Detected strong CO concentration between nuclei

Identified broad CO velocity wings indicating outflows

Located large linewidth regions linked to nuclear activity

Abstract

We present 0".97 $\times$ 0".53 (470 pc $\times$ 250 pc) resolution CO ($J$ = 2-1) observations toward the nearby luminous merging galaxy NGC 6240 with the Atacama Large Millimeter/submillimeter Array. We confirmed a strong CO concentration within the central 700 pc, which peaks between the double nuclei, surrounded by extended CO features along the optical dust lanes ($\sim$11 kpc). We found that the CO emission around the central a few kpc has extremely broad velocity wings with full width at zero intensity $\sim$ 2000 km s$^{-1}$, suggesting a possible signature of molecular outflow(s). In order to extract and visualize the high-velocity components in NGC 6240, we performed a multiple Gaussian fit to the CO datacube. The distribution of the broad CO components show four extremely large linewidth regions ($\sim$1000 km s$^{-1}$) located 1-2 kpc away from both nuclei. Spatial coincidence of the large linewidth regions with H$\alpha$, near-IR H$_2$, and X-ray suggests that the broad CO (2-1) components are associated with nuclear outflows launched from the double nuclei.