Molecular abundances in the Magellanic Clouds I. A multiline study of five cloud cores?

Nine H ii regions of the LMC were mapped in 13CO(1–0) and three in 12CO(1–0) to study the physical properties of the interstellar medium in the Magellanic Clouds. For N113 the molecular core is found to have a peak position which differs from that of the associatedH ii regionby20′′. Toward this molecular core the 12CO and 13CO peak TMB line temperatures of 7.3K and 1.2K are the highest so far found in theMagellanic Clouds. The molecular concentrations associated with N113, N44BC, N159HW, and N214DE in the LMC and LIRS 36 in the SMC were investigated in a variety of molecular species to study the chemical properties of the interstellar medium. I(HCO+)/I(HCN) and I(HCN)/I(HNC) intensity ratios as well as lower limits to the I(13CO)/I(C18O) ratio were derived for the rotational 1–0 transitions. Generally, HCO+ is stronger than HCN, and HCN is stronger than HNC. The high relative HCO+ intensities are consistent with a high ionization flux from supernovae remnants and young stars, possibly coupled with a large extent of theHCO+ emission region. The bulk of theHCN arises fromrelatively compact dense cloud cores.Warmor shockedgas enhances HCN relative to HNC. From chemical model calculations it is predicted that I(HCN)/I(HNC) close to one should be obtained with higher angular resolution (<∼ 30′′) toward the cloud cores. Comparing virial masses with those obtained from the integrated CO intensity provides an H2 mass-to-CO luminosity conversion factor of 1.8× 1020 mol cm−2 (K km s−1)−1 for N113 and 2.4 × 1020 mol cm−2 (K km s−1)−1 for N44BC. This is consistent with values derived for the Galactic disk. Send offprint requests to: Y.-N. Chin ? Based on observations with the Swedish-ESO Submillimeter Telescope (SEST) at the European Southern Observatory (ESO), La Silla, Chile ?? Present address: Institute of Astronomy and Astrophysics, Academica Sinica, P.O. Box 1-87, Nankang, Taipei, Taiwan ??? Present address: Institut für Planetenerkundung, DLR, Rudower Chaussee 5, D-12489 Berlin, Germany