The CO-to-H2 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-H₂ 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 a longitude-velocity diagram (LVD) at resolution ${\sim }{30^{\prime\prime}}\times 2$ 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) × 10²⁰ cm^-2 (K km s^-1)^-1, if we assume a normalization value of 0.59 × 10²⁰ cm^-2 (K km s^-1)^-1. The mean value is obtained as X_CO,iso = (0.48 ± 0.15) × 10²⁰ cm^-2 (K km s^-1)^-1 in the CMZ of our Galaxy.