Spatially Resolved Chemistry in Nearby Galaxies II. The Nuclear Bar in Maffei 2

TL;DR

This study uses high-resolution imaging to analyze the spatial distribution of molecular species in Maffei 2's nuclear bar, revealing chemical groups linked to star formation and shocks, and identifying a molecular outflow.

Contribution

It provides the first detailed spatially resolved chemical analysis of Maffei 2's nuclear bar, highlighting correlations with star formation and shock chemistry, and introduces C2H as a dense PDR probe.

Findings

Molecular species show dramatic spatial variations across the nuclear bar.

Two main chemical groups are identified: grain chemistry molecules and star formation tracers.

C2H is associated with a molecular outflow with an age of 6-7 Myrs.

Abstract

We present 2" - 10" imaging of eleven transitions from nine molecular species across the nuclear bar in Maffei 2. The data were obtained with the BIMA and OVRO interferometers. The ten detected transitions are compared with existing CO isotopologues, HCN, CS and millimeter continuum data. Dramatic spatial variations among the mapped species are observed across the nuclear bar. A principle component analysis is performed to characterize correlations between the transitions, star formation and molecular column density. The analysis reveals that HCN, HNC, HCO+ and 3 mm continuum are tightly correlated, indicating a direct connection to massive star formation. We find two main morphologically distinct chemical groups, CH3OH, SiO and HNCO comprising the grain chemistry molecules, versus HCN, HNC, HCO+ and C2H, molecules strong in the presence of star formation. The grain chemistry molecules, HNCO, CH3OH and SiO, trace hydrodynamical bar shocks. The near constancy of the HNCO/CH3OH, SiO/CH3OH and SiO/HNCO ratios argue that shock properties are uniform across the nucleus. HCN/HCO+, HCN/HNC, HCN/CS and HCN/CO ratios are explained primarily by variations in density. High HCO+/N2H+ ratios are correlated with the C2H line, suggesting that this ratio may be a powerful new dense photon-dominated region (PDR) probe in external galaxies. C2H reveals a molecular outflow along the minor axis. The morphology and kinematics of the outflow are consistent with an outflow age of 6-7 Myrs.