Hydrogen Masers. I: Theory and Prospects

Abstract

The discovery of the first naturally occurring high gain hydrogen recombination line (HRL) maser, in the millimeter and submillimeter spectrum of the emission line star MWC349, requires an expansion of current paradigms about HRLs. In this paper we re-examine in general the physics of non-LTE populations in recombining hydrogen and specify the conditions necessary for high-gain masing and lasing in HRLs. Saturation of masing recombination lines is a critical consideration. We draw attention to another non-LTE phenomenon active in hydrogen: the overcooling} of populations. Observationally the HRL overcooling might manifest itself as an anomalously weak emission recombination line, or as a ``dasar,'' that is, an anomalously strong absorption line. We briefly discuss the prospects of detecting hydrogen masers, lasers and dasars in several classes of galactic and extragalactic objects, including compact HII regions, Be or Wolf-Rayet stars, and AGNs.

20 pages (plain TeX), 20 encapsulated PostScript figures (tared and compressed) and one table (plain TeX); submitted to Ap.J.(Part 1)

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• A non-LTE radiative transfer model to study ionized outflows and disks. The case of MWC349A
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• A pilot search for mm-wavelength recombination lines from emerging ionized winds in pre-planetary nebulae candidates
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• Low Frequency Carbon Radio Recombination Lines II: The Diffuse Interstellar Medium
• The ionized warped disk and disk wind of the massive protostar Monoceros R2-IRS2 seen with ALMA
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• Herschel Planetary Nebula Survey (HerPlaNS): Hydrogen Recombination Laser Lines in Mz 3
• 3-cm Fine Structure Masers: A Unique Signature of Supermassive Black Hole Formation via Direct Collapse in the Early Universe
• The influence of continuum radiation fields on hydrogen radio recombination lines
• Inverted level populations of hydrogen atoms in ionized gas
• Evidence for the First Extragalactic Hydrogen Recombination Line Maser in NGC 253
• Expanded Very Large Array observations of the H66α and He66α recombination lines toward MWC 349A
• Photonic Astronomy and Quantum Optics
• High-n Hydrogen Recombination Lines from the First Galaxies
• Imaging the jet of MWC 349A with resolved Radio Recombination Line emission from ALMA
• Non-detection of Broad Hydrogen Radio Recombination Lines in Circinus Galaxy
• Non-Equilibrium Populations of Hydrogen in High-Redshift Galaxies