The CARMA 3mm Survey of the Inner $0.7^\circ\times0.4^\circ$ of the Central Molecular Zone

TL;DR

This study maps the inner Central Molecular Zone of the Galactic Center at 3mm wavelength with high resolution, providing detailed spectral line data and revealing interactions between cosmic rays and molecular gas.

Contribution

First high-resolution 3mm survey of the CMZ combining interferometric and single-dish data, with a catalog of sources and spectral line images covering key molecules.

Findings

Anti-correlation between I(HCN)/I(HCO$^{+}$) ratio and Fe K$\alpha$ emission.

Correlation between gas velocity dispersion and Fe K$\alpha$ intensity.

Evidence of cosmic ray interactions affecting molecular gas properties.

Abstract

The Central Molecular Zone (CMZ) of the Galactic Center has to date only been fully mapped at mm wavelengths with singledish telescopes, with resolution about 30$^{\prime\prime}$ (1.2 pc). Using CARMA, we mapped the innermost 0.25 square degrees of the CMZ over the region between -0$.\kern-.25em ^{^\circ}$2$ \leq l \leq $0$.\kern-.25em ^{^\circ}$5 and -0$.\kern-.25em ^{^\circ}$2$ \leq b \leq $0$.\kern-.25em ^{^\circ}$2 (90$\times$50 pc) with spatial and spectral resolution of $\sim$10$^{\prime\prime}$ (0.4 pc) and $\sim$2.5 km/s, respectively. We provide a catalog of 3mm continuum sources as well as spectral line images of SiO(J=2-1), HCO$^{+}$(J=1-0), HCN(J=1-0), N$_{2}$H$^{+}$(J=1-0), and CS(J=2-1), with velocity coverage VLSR= -200 to 200 km/s. To recover the large scale structure resolved out by the interferometer, the continuum-subtracted spectral line images were combined with data from the Mopra 22-m telescope survey, thus providing maps containing all spatial frequencies down to the resolution limit. We find that integrated intensity ratio of I(HCN)/I(HCO$^{+}$) is anti-correlated with the intensity of the 6.4 keV Fe K$\alpha$, which is excited either by high energy photons or low energy cosmic rays, and the gas velocity dispersion as traced by HCO$^{+}$ is correlated with Fe K$\alpha$ intensity. The intensity ratio and velocity dispersion patterns are consistent with variation expected from the interaction of low energy cosmic rays with molecular gas.