Dense gas in nearby galaxies. XVI. The nuclear starburst environment in NGC 4945

摘要: A multi-line millimeter-wave study of the nearby starburst galaxy NGC4945 has been carried out using Swedish-ESO Submillimeter Telescope (SEST). The covers frequency range from 82 GHz to 354 and includes 80 transitions 19 molecules. 1.3 mm continuum data nuclear source are also presented. An analysis CO fluxes indicates that conversion factor between H-2 column density J = 1-0 integrated intensity is smaller than in galactic disk by factors 5-10. large number molecular species indicate presence a prominent high interstellar gas component characterized n(H2) similar 10(5) cm(-3). Some spectra show Gaussian profiles. Others exhibit two main velocity components, one at to450 km s(-1), other to710 s(-1). While former higher linewidth, latter arises more highly excited as indicated HCN, HCO+ CN spectra. Abundances calculated compared with abundances observed toward galaxies NGC 253 M sources. Apparent an "overabundance" HNC environment NGC4945. HNC/HCN line ratio to0.5, abundance to1. From comparison K-a 0 1 HNCO intensities, upper limit background radiation 30 K derived. HCN subthermally (T-ex 8 K), even less (Tex 3-4 indicating it dense its N 2-1 can be optically thin though emission moderately thick. Overall, fractional 4945 suggest reached stage evolution intermediate those 82. Carbon, nitrogen, oxygen sulfur isotope ratios determined. Within limits uncertainty, carbon appear same regions 253. High O-18/O-17, low O-16/O-18 N-14/N-15 perhaps S-32/S-34 (6.4 +/- 0.3, 195 45, 105 25 13.5 2.5 4945, respectively) characteristic properties which massive stars have had sufficient time affect isotopic composition surrounding medium.