Central molecular zones in galaxies: multitransition survey of dense gas tracers HCN, HNC, and HCO+
arXiv:2212.00814 · doi:10.1051/0004-6361/202244313
Abstract
New HCN, HNC, and HCO+ measurements of 46 normal galaxies in transitions up to J=4-3 are included in a multitransition database covering HCN and HCO+ (130 galaxies) and HNC (94 galaxies). The near-linear luminosity relations are dominated by distance effects and do not reflect galaxy physical properties. Individual galaxies show significant dispersion in both their luminosity and line ratio. Line ratios do not correlate well with either luminosities or other line ratios. Only the normalized J-transition ladders of HCN and HCO+ and the J=1-0 12CO/13CO isotopologue ratio are positively correlated with CO and far infrared (FIR) luminosity. The HCN and HCO+ molecules have very similar intensities and trace the same gas. In galaxies dominated by an active nucleus, HCO+ intensities are depressed relative to HCN intensities. Only a small fraction of the CO emission is directly associated with gas emitting in HCN and HCO, yet a significant fraction of even that gas appears to be translucent molecular gas. In the observed galaxy centers, the HCN/CO line intensity ratio is not a proxy for the dense gas fraction. Likewise, the FIR/HCN and FIR/CO ratios are not proxies for the star formation efficiency. The observed molecular line emission is fully consistent with UV-photon heating boosted by significant mechanical heating. The molecular gas sampled by HCN and HCO+ has low kinetic temperatures T(kin)=10-50 K, low densities n(H)=10^4-10^5 cm^(-3), and low optical depths in the ground-state lines. Most of the gas sampled by CO has densities lower by one to two orders of magnitude. For a mechanical heating fraction of 0.5, a modest energy input of only G=300 Go is required. A proper understanding of star formation requires a more appropriate determination of the gas mass than provided by the intensities of individual HCN or CO transitions.
19 pages, 11 figures, 8 tables, accepted by Astronomy & Astrophysics
References in corpus (34)
- The Critical Density and the Effective Excitation Density of Commonly Observed Molecular Dense Gas Tracers
- Diagnostics of irradiated dense gas in galaxy nuclei. II. A grid of XDR and PDR models
- A multi-transition HCN and HCO+ study of 12 nearby active galaxies: AGN versus SB environments
- The anatomy of the Orion B Giant Molecular Cloud: A local template for studies of nearby galaxies
- Evidence of enhanced star formation efficiency in luminous and ultraluminous infrared galaxies
- The evolution of CNO isotopes: a new window on cosmic star-formation history and the stellar IMF in the age of ALMA
- Dense gas in luminous infrared galaxies
- Is HCN a True Tracer of Dense Molecular Gas in LIRGs and ULIRGs?
- Dense Molecular Gas Tracers in the Outflow of the Starburst Galaxy NGC 253
- The HNC/HCN Ratio in Star-Forming Regions
- HCN/HNC intensity ratio: a new chemical thermometer for the molecular ISM
- HCN versus HCO+ as dense molecular gas mass tracer in Luminous Infrared Galaxies
- Millimeter Interferometric HCN(1-0) and HCO+(1-0) Observations of Luminous Infrared Galaxies
- Lambda = 3 mm line survey of nearby active galaxies
- Mechanical feedback in the molecular ISM of luminous IR galaxies
- New insights on the dense molecular gas in NGC253 as traced by HCN and HCO+
- A Hard X-ray Test of HCN Enhancements as a Tracer of Embedded Black Hole Growth
- Optical Depth Estimates and Effective Critical Densities of Dense Gas Tracers in the Inner Parts of Nearby Galaxy Discs
- ALMA HCN and HCO+ J=3-2 observations of optical Seyfert and luminous infrared galaxies -- Confirmation of elevated HCN-to-HCO+ flux ratios in AGNs --
- The Star Formation Rate - Dense Gas Relation in Galaxies as Measured by HCN (3-2) Emission
- ALMA Observations of Multiple-CO and C Lines Toward the Active Galactic Nucleus of NGC 7469: X-Ray-dominated Region Caught in the Act
- Diagnostics of the molecular component of PDRs with mechanical heating. II: line intensities and ratios
- Star Formation Occurs in Dense Gas, but What Does "Dense" Mean?
- ALMA Spatially-resolved Dense Molecular Gas Survey of Nearby Ultraluminous Infrared Galaxies
- A New Radio Molecular Line Survey of Planetary Nebulae: HNC/HCN as a Diagnostic of Ultraviolet Irradiation
- Molecular gas heating in Arp 299
- Origins of Scatter in the Relationship Between HCN 1-0 and Dense Gas Mass in the Galactic Center
- Understanding if molecular ratios can be used as diagnostics of AGN and starburst activity: The case of NGC 1068
- A chemical study of carbon fractionation in external galaxies
- Dense gas in local galaxies revealed by multiple tracers
- Sampling Molecular Gas in the Helix Planetary Nebula: Variation in HNC/HCN with UV Flux
- Dense Gas and Star Formation in Nearby Infrared Bright Galaxies: APEX survey of HCN and HCO+ J=2-1
- ALMA Sub-arcsec-resolution 183 GHz H2O and Dense Molecular Line Observations of Nearby Ultraluminous Infrared Galaxies
- Modelling Mechanical Heating in Star-Forming Galaxies: CO and 13CO Line Ratios as Sensitive Probes
Cited by in corpus (6)
- Dense Molecular Gas Properties of the Central Kpc of Nearby Ultraluminous Infrared Galaxies Constrained by ALMA Three Transition-line Observations
- CON-quest II. Spatially and spectrally resolved HCN/HCO+ line ratios in local luminous and ultraluminous infrared galaxies
- PRUSSIC II -- ALMA imaging of dense-gas tracers in SDP.81: Evidence for low mechanical heating and a sub-solar metallicity in a z=3.04 dusty galaxy
- A multi-scale investigation into the diagnostic potential of the HCN/HCO ratio for AGN and starburst activity in nearby galaxies
- PRUSSIC III -- ALMA and NOEMA survey of dense gas in high-redshift star-forming galaxies
- The MALATANG survey: Dense gas distribution on sub-kiloparsec scales across the disk of M82