The CO-to-H2 conversion factor in the Central Molecular Zone of the Milky Way using CO isotopologues

Abstract

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 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 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 a 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.