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 (XCO, iso) in the central molecular zone (CMZ) of our Galaxy. New high-resolution XCO, 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 XCO, iso in the CMZ within the range of XCO, iso ~ (0.2-1.3) × 10²⁰\ cm⁻²\ (K\ km\ s⁻¹)⁻¹, if we assume the normalization value of 0.59 × 10²⁰\ cm⁻²\ (K\ km\ s⁻¹)⁻¹. The mean value is obtained as XCO, iso = (0.48 ± 0.15) × 10²⁰\ cm⁻²\ (K\ km\ s⁻¹)⁻¹ in the CMZ of our Galaxy.