A New Exact Method for Line Radiative Transfer

Abstract

We present a new method, the Coupled Escape Probability (CEP), for exact calculation of line emission from multi-level systems, solving only algebraic equations for the level populations. The CEP formulation of the classical two-level problem is a set of {\em linear equations}, and we uncover an exact analytic expression for the emission from two-level optically thick sources that holds as long as they are in the "effectively thin" regime. In comparative study of a number of standard problems, the CEP method outperformed the leading line transfer methods by substantial margins. The algebraic equations employed by our new method are already incorporated in numerous codes based on the escape probability approximation. All that is required for an exact solution with these existing codes is to augment the expression for the escape probability with simple zone-coupling terms. As an application, we find that standard escape probability calculations generally produce the correct cooling emission by the CII 158 mic line but not by the ${}^3$P lines of OI.

arXiv commentTo be published in MNRAS, 13 pages, 10 figures

References in corpus (2)

• Numerical methods for non-LTE line radiative transfer: Performance and convergence characteristics
• Escape probability methods versus "exact" transfer for modelling the X-ray spectrum of Active Galactic Nuclei and X-ray binaries

Cited by in corpus (33)

• A computer program for fast non-LTE analysis of interstellar line spectra
• Chemical Modelling of Young Stellar Objects, I. Method and Benchmarks
• An ALMA multi-line survey of the ISM in two quasar host-companion galaxy pairs at $z>6$
• Molecular line radiative transfer in protoplanetary disks: Monte Carlo simulations versus approximate methods
• Probing the role of polycyclic aromatic hydrocarbons in the photoelectric heating within photodissociation regions
• The Effect of 53 micron IR Radiation on 18 cm OH Megamaser Emission
• Detection of Class I Methanol (CH3OH) Maser Candidates in Supernova Remnants
• Far-infrared study of tracers of oxygen chemistry in diffuse clouds
• Probing the full CO spectral line energy distribution (SLED) in the nuclear region of a quasar-starburst system at $z=6.003$
• Synthetic observations of star formation and the interstellar medium
• Line profiles of water for the photon dominated region and embedded sources in the S140 region
• Unveiling the chemistry of interstellar CH: Spectroscopy of the 2 THz $N=2\leftarrow 1$ ground state line
• Class I Methanol (CH${}_3$OH) Maser Conditions near Supernova Remnants
• Radiative transfer and molecular data for astrochemistry (Review)
• Far-Infrared detection of neutral atomic oxygen toward the Horsehead Nebula
• ALMA Multiple-Transition Molecular Line Observations of the Ultraluminous Infrared Galaxy IRAS 20551-4250: Different HCN, HCO+, HNC Excitation and Implications for Infrared Radiative Pumping
• MOLPOP-CEP: An Exact, Fast Code for Multi-Level Systems
• NH${}_3$(3,3) and CH${}_3$OH near Supernova Remnants: GBT and VLA Observations
• The CH radical at radio wavelengths: Revisiting emission in the 3.3GHz ground state lines
• Rotating Disks and Non-Kinematic Double Peaks
• An efficient Monte Carlo model for the slowing down of photoelectrons. Application to H-$\alpha$ in exoplanet atmospheres
• Unveiling the warm dense ISM in $z>6$ quasar host galaxies via water vapor emission
• A New 3D Maser Code Applied to Flaring Events
• H${}_2$D${}^{+}$ line emission in Proto-Planetary Disks
• Study of Interstellar Molecular Clouds using Formaldehyde Absorption toward Extragalactic Radio Sources
• Polarized Maser Emission with In-Source Faraday Rotation
• Shocks in the warm neutral medium I -- Theoretical model
• Detection of 4765 MHz OH Emission in a Pre-Planetary Nebula -- CRL 618
• Revisiting rotationally excited CH at radio wavelengths: A case study towards W51
• An nl-model with radiative transfer for hydrogen recombination line masers
• Shocks in the warm neutral medium II -- Origin of neutral carbon at high pressure
• On Broyden's method for the solution of the multilevel non-LTE radiation transfer problem
• Recent Developments in Maser Theory