The Fraction of [C <scp>ii</scp>] Emission Originating from Ionized Gas in Local Galaxies

Abstract This paper presents a statistical study of the division of the [C ii ] 158 μ m line into ionized and neutral components, using a new carbon-to-nitrogen abundance ratio, log(C/N) = 0.75, for a sample of 108 local galaxies. We investigate the correlation between the ionized-to-total [C ii ] ratio ([C ii ] ionized /[C ii ] total ) and the far-infrared color f 60/ f 100, finding a moderate negative correlation. Additionally, we explore the dependence of [C ii ] ionized /[C ii ] total on various physical properties. We find that [C ii ] ionized /[C ii ] total exhibits a weak negative correlation with the offset from the main sequence and a moderate negative correlation with the [O iii ]88 μ m/ [N ii ] 122 μ m. Furthermore, no significant correlation with molecular gas mass is found. It shows a positive correlation with metallicity. Our results suggest that [C ii ] ionized /[C ii ] total is influenced by the ionization parameter, star formation efficiency and metallicity.