Variation in XCO Factor in N55 Region

Abstract

The XCO factor is defined as XCO=N(H2)/W12CO. It is useful for estimating cloud mass. However, there is only limited research on how the XCO factor varies within a single cloud. Employing 12CO(J=1-0) and 13CO(J=1-0) spectral data, we computed an XCO factor of 3.6 ×1020cm−2 (K km s−1)−1 for luminous gas of the N55 region. Our analysis revealed a V-shaped correlation between the XCO factor and H2 column densities, while the relationship with excitation temperature exhibited obscurity. This suggests that the CO-to-H2 conversion is not consistent on small scale (∼1 pc). Additionally, we found that star formation activity has little influence on the variability in the XCO factor.