HCN $J$=4-3, HNC $J$=1-0, ${\mathrm{H}}^{13}\mathrm{CN}$ $J$=1-0, and $\mathrm{H}{\mathrm{C}}_3\mathrm{N}$ $J$=10-9 Maps of Galactic Center Region I: Spatially-Resolved Measurements of Physical Conditions and Chemical Composition

Abstract

This {\it supplement} paper presents the maps of HCN $J$=4-3, HNC $J$=1-0, ${\mathrm{H}}^{13}\mathrm{CN}$ $J$=1-0, and HC${}_3$N $J$=10-9 for the Galactic central molecular zone (CMZ), which have been obtained using the Atacama Submillimeter Telescope Experiment and Nobeyama Radio Observatory 45-m telescope. Three-dimensional maps (2-D in space and 1-D in velocity) of the gas kinetic temperature ($T_{\mathrm{kin}}$), hydrogen volume density ($n_{{\mathrm{H}}_2}$), and fractional abundances of eight molecules (HCN, HNC, $\mathrm{H}{\mathrm{C}}_3\mathrm{N}$, HCO${}^{+}$, ${\mathrm{H}}_2\mathrm{CO}$, SiO, CS, and ${\mathrm{N}}_2{\mathrm{H}}^{+}$) have been constructed from our and archival data. We have developed a method with hierarchical Bayesian inference for this analysis, which has successfully suppressed the artificial correlations among the parameters created by systematic errors due to the deficiency in the simple one-zone excitation analysis and the calibration uncertainty. The typical values of $T_{\mathrm{kin}}$ and $n_{{\mathrm{H}}_2}$ are $10^{1.8}$K and $10^{4.2}{\mathrm{cm}}^{-3}$, respectively, and the presence of an additional cold/low-density component is also indicated. The distribution of high-temperature regions is poorly correlated with known active star-forming regions, while a few of them coincide with shocked clouds. Principal component analysis has identified two distinct groups in the eight analyzed molecules: one group with large PC1 and PC2 scores and the other with a large $T_{\mathrm{kin}}$ dependence, which could be explained using two regimes of shock chemistry with fast ($\gtrsim 20{\mathrm{km}\mathrm{s}}^{-1}$) and slow ($\lesssim 20{\mathrm{km}\mathrm{s}}^{-1}$) velocity shocks, respectively. This supports the idea that the mechanical sputtering of dust grains and the mechanical heating play primary roles in the chemical and thermal processes in CMZ clouds.

51 pages, 58 figures, Accepted for publication in Astrophysical Journal Supplement Series