High-resolution HNC 3-2 SMA observations of Arp220

TL;DR

This study uses high-resolution SMA observations to analyze HNC 3-2 emission in Arp220, revealing luminous, possibly maser, emission in the western nucleus and contrasting conditions in the eastern nucleus, shedding light on starburst/AGN activity.

Contribution

First high-resolution SMA observations of HNC 3-2 in Arp220, identifying potential maser emission and differences between the two nuclei's environments.

Findings

Luminous HNC 3-2 emission in western nucleus

Possible weak maser amplification of HNC emission

Distinct physical conditions between the two nuclei

Abstract

We present high resolution (0."4) observations of HNC J=3-2 with the SubMillimeter Array (SMA). We find luminous HNC 3-2 line emission in the western part of Arp220, centered on the western nucleus, while the eastern side of the merger shows relatively faint emission. A bright (36 K), narrow (60 km/s) emission feature emerges from the western nucleus, superposed on a broader spectral component. A possible explanation is weak maser emission through line-of-sight amplification of the background continuum source. There is also a more extended HNC 3-2 emission feature north and south of the nucleus. This feature resembles the bipolar OH maser morphology around the western nucleus. Substantial HNC abundances are required to explain the bright line emission from this warm environment. We discuss this briefly in the context of an X-ray chemistry and radiative excitation. We conclude that the luminous and possibly amplified HNC emission of the western nucleus of the Arp220 merger reflects the unusual, and perhaps transient, environment of the starburst/AGN activity there. The faint HNC line emission towards Arp220-east reveals a real difference in physical conditions between the two merger nuclei.