J/A+A/621/A127ivo://CDS.VizieR/J/A+A/621/A127doi:10.26093/cds/vizier.36210127CDSPolderman I.M.Haverkorn M.Jaffe T.R.Alves M.I.R.2021-07-05T11:20:34Z2021-04-19T15:40:06ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frh-ii-regionsradio-continuum-emissioneffective-temperatureCosmic rays (CRs) and magnetic fields are dynamically important components in the Galaxy, and their energy densities are comparable to that of the turbulent interstellar gas. The interaction of CRs and Galactic magnetic fields (GMF) produces synchrotron radiation clearly visible in the radio regime. Detailed measurements of synchrotron radiation averaged over the line-of-sight (LOS), so-called synchrotron emissivities, can be used as a tracer of the CR density and GMF strength. Our aim is to model the synchrotron emissivity in the Milky Way using a three-dimensional dataset instead of LOS-integrated intensity maps on the sky. Using absorbed HII regions, we measured the synchrotron emissivity over a part of the LOS through the Galaxy, changing from a two-dimensional to a three-dimensional view. Performing these measurements on a large scale is one of the new applications of the window opened by current low-frequency arrays. Using various simple axisymmetric emissivity models and a number of GMF-based emissivity models, we were able to simulate the synchrotron emissivities and compare them to the observed values in the catalog. We present a catalog of low-frequency absorption measurements of HII regions, their distances and electron temperatures, compiled from literature. These data show that the axisymmetric emissivity models are not complex enough, but the GMF-based emissivity models deliver a reasonable fit. These models suggest that the fit can be improved by either an enhanced synchrotron emissivity in the outer reaches of the Milky Way or an emissivity drop near the Galactic center. Current GMF models plus a constant CR density model cannot explain low-frequency absorption measurements, but the fits improved with slight (ad hoc) adaptations. It is clear that more detailed models are needed, but the current results are very promising.2019A&A...621A.127Phttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/621/A127CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/AJ/132/242 : H II absorption regions at 74MHz (Nord+, 2006)J/other/PASA/33.20 : MWA Survey of Galactic HII regions (Hindson+, 2016)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/621/A127https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/621/A127http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/621/A127https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/621/A127https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/621/A127http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/621/A127GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/621/A127/tablea1 (Complete catalog of HII regions detected in absorption)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/621/A127/tablea1?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/621/A127/tablea1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/621/A127/tablea1?GETtext/xml+votable180.050000true161.21504-59.524730.0055555555555555566/1559 3307 3758 15363 15478 23639 23717 28808 28912-28913 28918 29101 29103 29114-29116 29118 29463 29505 29508-29510 29513 29515 29532 29535 30218-30219 38016 41759 41765 41767 41773 41776 41812-41813 41817 41820 41824 42159 42169 42172-42174 42190 42211-42213 42224 42227-42230 42376 42379 42382 42387 42390-42392 42398 42436 42438 42441 42449-42451 42456 42460 42462 42496-42497 42512 42516https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/621/A127?format=asciiRadiodefaultJ/A+A/621/A127/tablea1Complete catalog of HII regions detected in absorptionRefReference (2)meta.ref;pos.frameintrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintGLONGalactic longitudedegpos.galactic.lonGLATGalactic latitudedegpos.galactic.latDistDistance from the Sun to the HII regionkpcpos.distance;pos.heliocentricfloatn_Dist[ef] Note on Dist (1)meta.notechare_Distrms uncertainty on Distkpcstat.errorfloatTobsSky brightness temperature derived from the measured intensity at the observing frequency1000Kinstr.skyTempfloatn_Tobs[b] Note on Tobs (1)meta.notechare_Tobsrms uncertainty on Tobs1000Kstat.errorfloatn_e_Tobs[a] Note on e_Tobs (1)meta.notecharTFSynchrotron brightness temperature of the column1000Kphys.temperaturefloate_TFrms uncertainty on TF1000Kstat.errorfloatn_TF[*] TF in front of the HII region (if *), else behind the HII regionmeta.notecharTeElectron temperature of the HII region1000Kphys.temperature.electron;obs.field;phys.electronfloate_Terms uncertainty on Te1000Kstat.errorfloatn_Te[cd] Note on Te (1)meta.notecharepsFEmissivity of the columnK/pcphys.emissivityfloate_epsFrms uncertainty on epsFK/pcstat.errorfloatn_epsF[*] in front of the HII regions (if *), else behind the HII regionmeta.notechar_RA.icrsRight ascension (ICRS) (computed by VizieR, not part of the original data. The format may include more digits than the original data because of internal accuracy requirements in VizieR and across other CDS services)degpos.eq.ranullableindexed_DE.icrsDeclination (ICRS) (computed by VizieR, not part of the original data. The format may include more digits than the original data because of internal accuracy requirements in VizieR and across other CDS services)degpos.eq.decnullableindexed