A Multi-Transition HCN and HCO+ Study of 12 Nearby Active Galaxies: Active Galactic Nucleus versus Starburst Environments

By M. Krips, R. Neri, S. García-Burillo, S. Martin, F. Combes, J. Graciá-Carpio, A. Eckart. 2007

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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.

Subfields: Astronomy and Astrophysics, Atmospheric Science

View Paper: https://www.semanticscholar.org/paper/e042b808e41422085ce9e840bf89752b33e6b331

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Citations in the corpus

THE MOLECULAR GAS IN LUMINOUS INFRARED GALAXIES. II. EXTREME PHYSICAL CONDITIONS AND THEIR EFFECTS ON THE Xco FACTOR (2012, methodology): “The n-Tkin solution degeneracies of the Large Velocity Gradient (LVG) radiative transfer models typically used in such studies translate to a wide range of XHCN factors, ranging from ∼10Xl and reaching up to ∼(50-90)Xl (Krips et al. 2008; Gracia-Carpio et al. 2008).”
Dusty Star Forming Galaxies at High Redshift (2014, background): “At least some evidence for this has been seen by Krips et al. (2008) and Graciá-Carpio et al. (2008) in nearby active systems.”
THE CO-TO-H2 CONVERSION FACTOR AND DUST-TO-GAS RATIO ON KILOPARSEC SCALES IN NEARBY GALAXIES (2012, background): “Enhanced AGN activity could affect molecular gas properties in the nuclei (e.g. Krips et al. 2008), but the relatively weak AGN present in the KINGFISH galaxies may not dominate on the kpc scales we study here.”
Spectral imaging of the Central Molecular Zone in multiple 3-mm molecular lines (2011, background): “Krips et al. (2008) also measure HCO+ and they deriveL′ HCO+ /L′HCN ratio in the 0.5 to 1.6 range.”
Molecular line emission in NGC 1068 imaged with ALMA: I. An AGN-driven outflow in the dense molecular gas (2014, methodology): “However, the H2 map only traces a small fraction of the total molecular gas reservoir of the CND, which is known to be much denser (n(H2) ' 105−6 cm−3; Sternberg et al. 1994; Usero et al. 2004; Krips et al. 2008, 2011; Pérez-Beaupuits et al. 2007, 2009).”
Star-formation laws in luminous infrared galaxies. New observational constraints on models (2011, methodology): “The current observational evidence contradicts the existence of these abnormally low HCN densities, at least in the galaxies for which reliable estimates of nHCN(H2) exist (e.g., Tacconi et al. 1994; Sternberg et al. 1994; Usero et al. 2004; Krips et al. 2008; Graciá-Carpio et al.”