Characterizing the line emission from molecular clouds. II. A comparative study of California, Perseus, and Orion A

Abstract

$Aims.$ We characterize the molecular-line emission of three clouds whose star-formation rates span one order of magnitude: California, Perseus, and Orion A. $Methods.$ We use stratified random sampling to select positions representing the different column density regimes of each cloud and observe them with the IRAM-30m telescope. We cover the 3 mm wavelength band and focus our analysis on CO, HCN, CS, HCO+, HNC, and N2H+. $Results.$ We find that the line intensities depend most strongly on the H2 column density. A secondary effect, especially visible in Orion A, is a dependence of the line intensities on the gas temperature. We explored a method that corrects for temperature variations and show that, when it is applied, the emission from the three clouds behaves very similarly. CO intensities vary weakly with column density, while the intensity of traditional dense-gas tracers such as HCN, CS, and HCO+ varies almost linearly with column density. N2H+ differs from all other species in that it traces only cold dense gas. The intensity of the rare HCN and CS isotopologs reveals additional temperature-dependent abundance variations. Overall, the clouds have similar chemical compositions that, as the depth increases, are sequentially dominated by photodissociation, gas-phase reactions, molecular freeze-out, and stellar feedback in the densest parts of Orion A. Our observations also allowed us to calculate line luminosities for each cloud, and a comparison with literature values shows good agreement. We used our HCN data to explore the behavior of the HCN conversion factor, finding that it is dominated by the emission from the outermost cloud layers. It also depends strongly on the gas kinetic temperature. Finally, we show that the HCN/CO ratio provides a gas volume density estimate, and that its correlation with the column density resembles that found in extragalactic observations.

arXiv comment36 pages, 19 figures, accepted for publication in A&A

References in corpus (77)

• Herschel Space Observatory - An ESA facility for far-infrared and submillimetre astronomy
• The CO-to-H2 Conversion Factor
• The Milky Way in Molecular Clouds: A New Complete CO Survey
• Cold Dark Clouds: The Initial Conditions for Star Formation
• On the Star Formation Rates in Molecular Clouds
• The chemical make-up of the Sun: A 2020 vision
• The Dark Molecular Gas
• Physical Conditions in Regions of Star Formation
• Systematic Molecular Differentiation in Starless Cores
• HCN Survey of Normal Spiral, IR-luminous and Ultraluminous Galaxies
• The Universality of Turbulence in Galactic Molecular Clouds
• Large-Scale Structure of the Molecular Gas in Taurus Revealed by High Linear Dynamic Range Spectral Line Mapping
• Tracing the Mass during Low-Mass Star Formation. II. Modelling the Submillimeter Emission from Pre-Protostellar Cores
• A Minimum Column Density of 1 g cm^-2 for Massive Star Formation
• CO Isotopologues in the Perseus Molecular Cloud Complex: the X-Factor and Regional Variations
• The COMPLETE Survey of Star-Forming Regions: Phase I Data
• Astrochemistry During the Formation of Stars
• A Large Catalog of Accurate Distances to Local Molecular Clouds: The Gaia DR2 Edition
• High-resolution wide-band Fast Fourier Transform spectrometers
• Star Formation Relations in Nearby Molecular Clouds
• Molecular Evolution in Collapsing Prestellar Cores
• Planck Early Results: Thermal dust in Nearby Molecular Clouds
• An ALMA study of the Orion Integral Filament: I. Evidence for narrow fibers in a massive cloud
• An Ammonia Spectral Atlas of Dense Cores in Perseus
• Herschel-Planck dust optical-depth and column-density maps: I. Method description and results for Orion
• The anatomy of the Orion B Giant Molecular Cloud: A local template for studies of nearby galaxies
• On the internal structure of starless cores. II. A molecular survey of L1498 and L1517B
• Evolution of Chemistry and Molecular Line Profile during Protostellar Collapse
• Star formation laws in Luminous Infrared Galaxies. New observational constraints on models
• Variations in the Star Formation Efficiency of the Dense Molecular Gas across the Disks of Star-Forming Galaxies
• The Green Bank Ammonia Survey (GAS): First Results of NH3 mapping the Gould Belt
• A molecular survey of outflow gas: velocity-dependent shock chemistry and the peculiar composition of the EHV gas
• A Uniform CO Survey of the Molecular Clouds in Orion and Monoceros
• The California Molecular Cloud
• EMPIRE: The IRAM 30-m Dense Gas Survey of Nearby Galaxies
• 3D shape of Orion A from Gaia DR2
• Molecular Line Emission as a Tool for Galaxy Observations (LEGO). I. HCN as a tracer of moderate gas densities in molecular clouds and galaxies
• The chemistry and spatial distribution of small hydrocarbons in UV-irradiated molecular clouds: the Orion Bar PDR
• Revealing the physical properties of molecular gas in Orion with a large scale survey in J=2-1 lines of 12CO, 13CO and C18O
• The structure and stability of molecular cloud cores in external radiation fields
• Molecular clouds have power-law probability distribution functions
• Fibers in the NGC1333 proto-cluster
• Testing the universality of the star formation efficiency in dense molecular gas
• Gravitational collapse of the OMC-1 region
• The HNC/HCN Ratio in Star-Forming Regions
• HCN/HNC intensity ratio: a new chemical thermometer for the molecular ISM
• Imaging chemical differentiation around the low-mass protostar L483-mm
• CO Abundance Variations in the Orion Molecular Cloud
• Millimeter-Wave Line Ratios and Sub-beam Volume Density Distributions
• The CARMA-NRO Orion Survey
• Herschel-Planck dust optical depth and column density maps - II. Perseus
• The CARMA-NRO Orion Survey: The filamentary structure as seen in C${}^{18}$O emission
• Parameterizing the interstellar dust temperature
• N2H+ and HC3N Observations of the Orion A Cloud
• Dissecting the molecular structure of the Orion B cloud: Insight from Principal Component Analysis
• LEGO II: A 3 mm molecular line study covering 100 pc of one of the most actively star-forming portions within the Milky Way Disc
• Characterizing the line emission from molecular clouds. Stratified random sampling of the Perseus cloud
• Do Spectroscopic Dense Gas Fractions Track Molecular Cloud Surface Densities?
• Star Formation Occurs in Dense Gas, but What Does "Dense" Mean?
• C18O, 13CO, and 12CO abundances and excitation temperatures in the Orion B molecular cloud: An analysis of the precision achievable when modeling spectral line within the Local Thermodynamic Equilibrium approximation
• HP2 survey: III The California Molecular Cloud--A Sleeping Giant Revisited
• Slow Star Formation in the Milky Way: Theory Meets Observations
• Molecular-Cloud-Scale Chemical Composition I: Mapping Spectral Line Survey toward W51 in the 3 mm Band
• Nobeyama 45-m mapping observations toward nearby molecular clouds, Orion A, Aquila Rift, and M17: Project overview
• Physical properties and chemical composition of the cores in the California molecular cloud
• 3D shape explains star formation mystery of California and Orion A
• Filament rotation in the California L1482 cloud
• Nobeyama 45 m Mapping Observations toward Orion A. II. Classification of cloud structures and variation of the ${}^{13}$CO/C${}^{18}$O abundance ratio due to far-UV Radiation
• A Complete HCN Survey of the Perseus Molecular Cloud
• TRAO Survey of Nearby Filamentary Molecular clouds, the Universal Nursery of Stars (TRAO FUNS) I. Dynamics and Chemistry of L1478 in the California Molecular Cloud
• A constant N${}_2$H${}^{+}$(1-0)-to-HCN(1-0) ratio on kiloparsec scales
• Probing the Cold Deep Depths of the California Molecular Cloud: The Icy Relationship between CO and Dust
• Tracers of Dense Gas in the Outer Galaxy
• HCN/HNC chemistry in shocks: a study of L1157-B1 with ASAI
• A wide-field CO survey towards the California Molecular Filament
• TIMES I: a Systematic Observation in Multiple Molecular Lines Toward the Orion A and Ophiuchus Clouds
• Do simulated molecular clouds look like real ones?

Cited by in corpus (13)

• Characterizing the line emission from molecular clouds. Stratified random sampling of the Perseus cloud
• Surveying the Whirlpool at Arcseconds with NOEMA (SWAN)- I. Mapping the HCN and N${}_2$H${}^{+}$ 3mm lines
• Parsec-scale cosmic-ray ionisation rate in Orion
• Emergence of high-mass stars in complex fiber networks (EMERGE). I. Early ALMA Survey: observations and massive data reduction
• 3D structure of the Milky Way out to 10 kpc from the Sun. Catalogue of large molecular clouds in the Galactic Plane
• Emergence of high-mass stars in complex fiber networks (EMERGE) III. Fiber networks in Orion
• Emergence of high-mass stars in complex fiber networks (EMERGE) IV. Environmental dependence of the fiber widths
• A 260 pc resolution ALMA map of HCN(1-0) in the galaxy NGC 4321
• Toward a robust physical and chemical characterization of heterogeneous lines of sight: The case of the Horsehead nebula
• Does the HCN/CO ratio trace the star-forming fraction of gas? II. Variations in CO and HCN Emissivity
• Surveying the Whirlpool at Arcseconds with NOEMA (SWAN) II: Survey design and observations
• Kinematics of young stellar objects in NGC 2024 based on infrared proper motions
• Estimating the dense gas mass of molecular clouds using spatially unresolved 3 mm line observations