Atomic carbon abundance at the centers of NGC 4945 and circinus

¹ KOSMA, I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany
² Argelander-Institut für Astronomie, Auf dem Hügel 71, 53121 Bonn, Germany

Abstract

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).