The CO-to-H_2 Conversion Factor in the Central Molecular Zone of the Milky Way using CO isotopologues

We performed correlation analyses between the ^12CO and ^13CO J=1-0 line intensities in order to derive the variability of the CO-to-H_2 conversion factor (X_ CO, iso) in the central molecular zone (CMZ) of our Galaxy. New high-resolution X_ CO, iso maps at a resolution of ∼ 30" and the longitude-velocity diagram (LVD) at resolution ∼ 30" × 2 km s^-1 are presented using the ^12CO and ^13CO archival survey data obtained by the Nobeyama 45 m telescope. We revealed the variation of X_ CO, iso in the CMZ within the range of X_ CO, iso∼ (0.2-1.3) × 10^20 cm^-2 (K km s^-1)^-1, if we assume the normalization value of 0.59 × 10^20 cm^-2 (K kms^-1)^-1. The mean value is obtained as X_ CO, iso = (0.48 ± 0.15) × 10^20 cm^-2 (K km s^-1)^-1 in the CMZ of our Galaxy.