J/A+A/636/A2ivo://CDS.VizieR/J/A+A/636/A2doi:10.26093/cds/vizier.36360002CDSPolderman I.M.Haverkorn M.Jaffe T.R.2021-07-05T11:53:59Z2021-05-05T07:39:49ZCDS support team

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

cds-question@unistra.frh-ii-regionsmagnetic-fieldsCosmic rays (CRs) and the Galactic magnetic field (GMF) are fundamental actors in many processes in the Milky Way. The observed interaction product of these actors is Galactic synchrotron emission integrated over the line of sight (LOS). A comparison to simulations can be made with this tracer using existing GMF models and CR density models. This probes the GMF strength and morphology and the CR density. Our aim is to provide insight into the Galactic CR density and the distribution and morphology of the GMF strength by exploring and explaining the differences between the simulations and observations of synchrotron intensity. At low radio frequencies HII regions become opaque due to free-free absorption. Using these HII regions we can measure the synchrotron intensity over a part of the LOS through the Galaxy. The measured intensity per unit path length, that is, the emissivity, for HII regions at different distances, allows us to probe the variation in synchrotron emission not only across the sky but also in the third dimension of distance. Performing these measurements on a large scale is one of the new applications of the window opened by current low-frequency arrays. Using a number of existing GMF models in conjunction with the Galactic CR modeling code GALPROP, we can simulate these synchrotron emissivities. We present an updated catalog, compiled from the literature, of low-frequency absorption measurements of HII regions, their distances, and electron temperatures. We report a simulated emissivity that shows a compatible trend for HII regions that are near the observer. However, we observe a systematically increasing synchrotron emissivity for HII regions that are far from the observer, which is not compatible with the values simulated by the GMF models and GALPROP. Current GMF models plus a GALPROP generated CR density model cannot explain low-frequency absorption measurements. One possibility is that distances to all HII regions catalogued at the kinematic "far" distance are erroneously determined, although this is unlikely since it ignores all evidence for far distances in the literature. However, a detection bias due to the nature of this tracer requires us to keep in mind that certain sources may be missed in an observation. The other possibilities are an enhanced emissivity in the outer Galaxy or a diminished emissivity in the inner Galaxy.2020A&A...636A...2Phttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/636/A2CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/AJ/132/242 : H II absorption regions at 74MHz (Nord+, 2006)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/636/A2https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/636/A2http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/636/A2https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/636/A2https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/636/A2http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/636/A2GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/636/A2/tablea1 (Complete and updated catalog of HII regions detected in absorption)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/636/A2/tablea1?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/636/A2/tablea1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/636/A2/tablea1?GETtext/xml+votable180.050000true161.21504-59.524730.0055555555555555566/1559 3307 3758 15363 15478 23639 23717 28824 28828 28890-28891 28897-28898 28912-28913 28918 29101 29113-29116 29118 29463 29505 29508-29510 29512-29513 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/636/A2?format=asciidefaultJ/A+A/636/A2/tablea1Complete and updated catalog of HII regions detected in absorptionrecnoRecord 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.distancefloatn_Dist[5] Note on Dist (1)meta.notechare_Distrms uncertainty on Distancekpcstat.errorfloatTobsBrightness temperature derived from the measured intensity at the observing frequency1000Kphys.temperaturefloatn_Tobs[2] Note on Tobs (1)meta.notechare_Tobsrms uncertainty on Tobs1000Kstat.errorfloatTSynchrotron brightness temperature of the column in front (n_T=F) or behind (n_T=B) the HII region1000Kphys.temperaturefloatf_T[a] Flag on T (1)meta.codechare_Trms uncertainty on T1000Kstat.errorfloatn_T[FB] front or behind for synchrotron brightness temperaturemeta.notecharTeElectron temperature of the HII region1000Kphys.temperature.electron;phys.electron;obs.fieldfloate_Terms uncertainty on Te1000Kstat.errorfloatn_Te[1,3] Note on e_Te (1)meta.notecharepsEmissivity of the column in front (n_eps=F) or behind (n_eps=B) the HII regionK/pcphys.emissivityfloate_epsrms uncertainty on epsK/pcstat.errorfloatn_eps[FB] front or behind for emissivitymeta.notecharSourceOrigin paper of the data (2)meta.bibint_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