Nuclear Bar Catalyzed Star Formation: 13^CO, C18^O and Molecular Gas Properties in the Nucleus of Maffei 2

TL;DR

This study maps molecular gas and star-forming regions in Maffei 2's nucleus, revealing a nuclear bar's role in gas dynamics and starburst activity, with detailed isotopologue analysis and gas property modeling.

Contribution

It provides high-resolution molecular line maps and LVG modeling of the nuclear gas, highlighting the influence of a nuclear bar on star formation in Maffei 2.

Findings

Molecular gas is in low excitation, subthermal state.

The CO conversion factor is lower than the Galactic value.

Star formation is concentrated at nuclear bar orbit intersections.

Abstract

(Abridged) We present resolution maps of CO, its isotopologues, and HCN from in the center of Maffei 2. The J=1-0 rotational lines of 12^CO, 13^CO, C18^O and HCN, and the J=2-1 lines of 13^CO and C18^O were observed with the OVRO and BIMA arrays. The 2-1/1-0 line ratios of the isotopologues constrain the bulk of the molecular gas to originate in low excitation, subthermal gas. From LVG modeling, we infer that the central GMCs have n(H_2) ~10^2.75 cm^-3 and T_k ~ 30 K. Continuum emission at 3.4 mm, 2.7 mm and 1.4 mm was mapped to determine the distribution and amount of HII regions and dust. Column densities derived from C18^O and 1.4 mm dust continuum fluxes indicate the CO conversion factor in the center of Maffei 2 is lower than Galactic by factors of ~2-4. Gas morphology and the clear ``parallelogram'' in the Position-Velocity diagram shows that molecular gas orbits within the potential of a nuclear (~220 pc) bar. The nuclear bar is distinct from the bar that governs the large scale morphology of Maffei 2. Giant molecular clouds in the nucleus are nonspherical and have large linewidths. Dense gas and star formation are concentrated at the sites of the x_1-x_2 orbit intersections of the nuclear bar, suggesting that the starburst is dynamically triggered.