Studying molecular gas in the central regions of the star burst
galaxies NGC 4945 and Circinus enables us to characterize the
physical conditions in these starbursts and compare them with
previous studies of local and high-z galaxies. Using the new
NANTEN2 4 m sub-millimeter telescope on Pampa La Bola, Chile, we
observed for the first time CO 4–3 and [CI] 1–0 at the centers of
both galaxies at linear scales of about 700 pc. We find that the
centers of NGC 4945 and Circinus are very [CI] bright objects,
exhibiting [CI] 1–0 luminosities of 91 and
67 K km s-1 kpc2, respectively. The [CI] 1–0/CO 4–3
integrated intensity rations show high values of about 1.2 in
NGC 4945 and 2.8 in Circinus. In both galaxies, the estimated
total [CI] cooling intensity of both fine structure transitions
is stronger by factors of ~1–3 compared to the total CO
cooling intensity. The CO/C abundance ratios are 0.2–2. Similarly low
values are found in Galactic translucent clouds
(Mookerjea et al. 2006).