A multi-transition HCN and HCO+ study of 12 nearby active galaxies: Active galactic nucleus versus starburst environments

作者：Krips M^*; Neri R; Garcia Burillo S; Martin S; Combes F; Gracia Carpio J; Eckart A

来源：Astrophysical Journal, 2008, 677(1): 262-275.

DOI：10.1086/527367

• galaxies : active
• galaxies : individual (Arp 220, M82, Markarian 231
• NGC 1068, NGC 2140, NGC 3627, NGC 4569, NGC 4826, NGC 5194, NGC 6240, NGC 6946, NGC 6951)
• galaxies : ISM
• radio lines : galaxies

Recent studies have indicated that the HCN-to-CO(J = 1-0) and HCO+-to-HCN(J = 1-0) ratios are significantly different between galaxies with AGN ( active galactic nucleus) and SB ( starburst) signatures. In order to study the molecular gas properties in active galaxies and search for differences between AGN and SB environments, we observed the HCN(J = 1-0), (J = 2-1), (J = 3-2), HCO+(J = 1-0), and HCO+(J = 3-2) emission with the IRAM 30 m in the center of 12 nearby active galaxies which either exhibit nuclear SB and/or AGN signatures. Consistent with previous results, we find a significant difference of the HCN(J = 2-1)-to-HCN(J = 1-0), HCN(J = 3-2)-to-HCN(J = 1-0), HCO+(J = 3-2)-to-HCO+(J = 1-0), and HCO+-to-HCN intensity ratios between the sources dominated by an AGN and those with an additional or pure central SB: the HCN, HCO+, and HCO+-to-HCN intensity ratios tend to be higher in the galaxies of our sample with a central SB as opposed to the pure AGN cases, which show rather low intensity ratios. Based on an LVG analysis of these data, i.e., assuming purely collisional excitation, the ( average) molecular gas densities in the SB-dominated sources of our sample seem to be systematically higher than in the AGN sources. The LVG analysis seems to further support systematically higher HCN and/or lower HCO+ abundances as well as similar or higher gas temperatures in AGNs compared to the SB sources of our sample. In addition, we find that the HCN-to-CO ratios decrease with increasing rotational number J for the AGNs while they stay mostly constant for the SB sources.

• 出版日期2008-4-10