74 MHz Discrete HII Absorption Regions Towards The Inner Galaxy

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dc.creatorNord, Michael E.
dc.creatorHenning, P. A.
dc.creatorRand, R. J.
dc.creatorLazio, T. Joseph W.
dc.creatorKassim, Namir E.
dc.date2006-03-02
dc.date.accessioned2026-07-07T11:25:19Z
dc.date.available2026-07-07T11:25:19Z
dc.descriptionAt low radio frequencies (< 100 MHz), classical HII regions may become optically thick (optical depth > 1) and can be observed as discrete absorption regions against the Galactic nonthermal background emission created by Galactic cosmic ray electrons spiraling around magnetic fields. In this work we present 74 MHz observations in the region 26>l>-15, -5<b<5, and report the detection of 92 absorption features associated with known HII regions, and derive the brightness temperature of the Galactic cosmic ray electron synchrotron emission emanating from the column behind these regions. For the 42 HII regions with known distances, the average emissivity of the column behind the HII region is derived. 74 MHz emissivity values range between 0.3 and 1.0 Kelvin per parsec for a model assuming uniform distribution of emissivity. Methods for utilizing this type of data to model the 3-dimensional distribution of cosmic ray emissivity and the possibility of using this method to break the HII region kinematic distance degeneracy are discussed.
dc.descriptionAccepted, The Astronomical Journal
dc.identifierhttps://arxiv.org/abs/astro-ph/0603057
dc.identifierhttp://arxiv.org/abs/astro-ph/0603057
dc.identifierAstron.J.132:242-252,2006
dc.identifierdoi:10.1086/504407
dc.identifier.urihttp://salesiana.dossiersoluciones.com/handle/123456789/195471
dc.subjectAstrophysics
dc.title74 MHz Discrete HII Absorption Regions Towards The Inner Galaxy
dc.typetext

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