Carbon radio recombination lines from gigahertz to megahertz frequencies towards Orion A

Abstract

Context. The combined use of carbon radio recombination lines (CRRLs) and the 158 $\mu$m-[CII] line is a powerful tool for the study of the energetics and physical conditions (e.g., temperature and density) of photodissociation regions (PDRs). However, there are few observational studies that exploit this synergy. Aims. Here we explore the relation between CRRLs and the 158 $\mu$m-[CII] line in light of new observations and models. Methods. We present new and existing observations of CRRLs in the frequency range 0.15--230 GHz with ALMA, VLA, the GBT, Effelsberg 100m, and LOFAR towards Orion~A (M42). We complement these observations with SOFIA observations of the 158 $\mu$m-[CII] line. We studied two PDRs: the foreground atomic gas, known as the Veil, and the dense PDR between the HII region and the background molecular cloud. Results. In the Veil we are able to determine the gas temperature and electron density, which we use to measure the ionization parameter and the photoelectric heating efficiency. In the dense PDR, we are able to identify a layered PDR structure at the surface of the molecular cloud to the south of the Trapezium cluster. There we find that the radio lines trace the colder portion of the ionized carbon layer, the C${}^{+}$/C/CO interface. By modeling the emission of the $158$~$\mu$m-[CII] line and CRRLs as arising from a PDR we derive a thermal pressure $>5\times 10^7$ K cm${}^{-3}$ and a radiation field $G_0\approx 10^5$ close to the Trapezium. Conclusions. This work provides additional observational support for the use of CRRLs and the 158 $\mu$m-[CII] line as complementary tools to study dense and diffuse PDRs, and highlights the usefulness of CRRLs as probes of the C${}^{+}$/C/CO interface.

18 pages, 16 figures, accepted for publication in A&A

References in corpus (20)

• The distance to the Orion Nebula
• Early Science with SOFIA, the Stratospheric Observatory for Infrared Astronomy
• GREAT: the SOFIA high-frequency heterodyne instrument
• Herschel-Planck dust optical-depth and column-density maps: I. Method description and results for Orion
• Compression and ablation of the photo-irradiated cloud the Orion Bar
• The On The Fly Imaging Technique
• The upGREAT 1.9 THz multi-pixel high resolution spectrometer for the SOFIA Observatory
• The ALMA View of the OMC1 Explosion in Orion
• The three dimensional dynamic structure of the inner Orion Nebula
• The Orion HII Region and the Orion Bar in the Mid-Infrared
• [CII] emission from L1630 in the Orion B molecular cloud
• IRAM-30m large scale survey of ${}^{12}$CO(2-1) and ${}^{13}$CO(2-1) emission in the Orion molecular cloud
• Carbon and hydrogen radio recombination lines from the cold clouds towards Cassiopeia A
• Low Frequency Carbon Radio Recombination Lines I: Calculations of Departure Coefficients
• Mapping young stellar populations towards Orion with Gaia DR1
• Discovery of Carbon Radio Recombination Lines in M82
• LOFAR observations of decameter carbon radio recombination lines towards Cassiopeia A
• Low Frequency Carbon Radio Recombination Lines II: The Diffuse Interstellar Medium
• High Spectral and Spatial Resolution Observations of the PDR Emission in the NGC2023 Reflection Nebula with SOFIA and APEX
• The Survey of Lines in M31 (SLIM): The Drivers of the [CII]/TIR Variation

Cited by in corpus (16)

• The LOFAR Two-metre Sky Survey -- V. Second data release
• Photodissociation and X-Ray Dominated Regions
• PDRs4All III: JWST's NIR spectroscopic view of the Orion Bar
• The initial gas-phase sulfur abundance in the Orion Molecular Cloud from sulfur radio recombination lines
• Molecular globules in the Veil bubble of Orion. IRAM 30m 12CO, 13CO, and C18O 2-1 expanded maps of Orion A
• Contribution of polycyclic aromatic hydrocarbon ionization to neutral gas heating in galaxies: model versus observations
• [CII] $158\mu \mathrm{m}$ line emission from Orion A. I. A template for extragalactic studies?
• PDRs4All VI: Probing the Photochemical Evolution of PAHs in the Orion Bar Using Machine Learning Techniques
• Observation and calibration strategies for large-scale multi-beam velocity-resolved mapping of the [CII] emission in the Orion molecular cloud
• Hunting for the elusive methylene radical
• The ionization fraction in OMC-2 and OMC-3
• First Detection of Radio Recombination Lines of Ions Heavier than Helium
• Multiline observations of hydrogen, helium, and carbon radio-recombination lines toward Orion A: A detailed dynamical study and direct determination of physical conditions
• Low-Frequency Radio Recombination Lines Away From the Inner Galactic Plane
• Structure of the W3A Low Density Foreground Region
• Imaging the jet of MWC 349A with resolved Radio Recombination Line emission from ALMA