Active Galactic Nucleus and Extended Starbursts in a Mid-stage Merger VV114

TL;DR

This study uses high-resolution ALMA observations to map dense gas in a mid-stage galaxy merger, revealing dense gas structures associated with both an active nucleus and star-forming regions, highlighting the power of dense gas tracers.

Contribution

First detailed ALMA mapping of dense gas in a mid-stage galaxy merger, distinguishing between AGN-related and star formation-related dense gas structures.

Findings

Detection of compact dense gas associated with the AGN

Extended filamentary dense gas aligned with star-forming regions

Moderately dense gas conditions inferred from radiative transfer models

Abstract

High resolution (0.4 arcsec) Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 0 observations of HCO+(4-3) and HCN(4-3) toward a mid-stage infrared bright merger VV114 have revealed compact nuclear (<200 pc) and extended (3 - 4 kpc) dense gas distribution across the eastern part of the galaxy pair. We find a significant enhancement of HCN(4-3) emission in an unresolved compact and broad (290km/s) component found in the eastern nucleus of VV114, and we suggest dense gas associated with the surrounding material around an Active Galactic Nucleus (AGN), with a mass upper limit of < 4 x 10^8 Msun. The extended dense gas is distributed along a filamentary structure with resolved dense gas concentrations (230pc; 10^6 Msun) separated by a mean projected distance of 600 pc, many of which are generally consistent with the location of star formation traced in Pa alpha emission. Radiative transfer calculations suggest moderately dense (10^5 - 10^6 cm^-3) gas averaged over the entire emission region. These new ALMA observations demonstrate the strength of the dense gas tracers in identifying both the AGN and star formation activity in a galaxy merger, even in the most dust enshrouded environments in the local universe.