Ci](1–0) observations in M33 A study of CO dark H2gas in M33

Abstract

Based on [Ci] (1–0) observations and complementary Hi, 12/13 CO (1–0), 12 CO (2–1) and [Cii] data we estimated the column density and fraction of molecular hydrogen in GMCs along the major axis of the galaxy M33. We found that on average 75%± 14% of the hydrogen is in molecular form. Roughly 40–45% of the H 2 is both traced by [Cii] and CO, while ∼ 15% by the [Ci] lines. The found CO-dark H 2 gas fractions are within the predictions by Wolfire et al. (2010) for a half solar metallicity, Z = 0.5 Z ⊙ , as in M33.