J/A+A/694/A26ivo://CDS.VizieR/J/A+A/694/A26doi:10.26093/cds/vizier.36940026CDSYang A.Y.Thompson M.A.Urquhart J.S.Brunthaler A.Menten K.M.,Gong Y.Tsai C.-W.Patel A.L.Li D.Cotton W.D.2025-03-03T20:02:00Z2025-01-30T12:17:47ZCDS support team

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

cds-question@unistra.frinterstellar-mediumh-ii-regionsradio-continuum-emissionTheoretical models of early accretion during the formation process of massive stars have predicted that HII regions exhibit radio variability on timescales of decades. However, large-scale searches for such temporal variations with sufficient sensitivity have not yet been carried out. We aim to identify HII regions with variable radio wavelength fluxes and to investigate the properties of the identified objects, especially those with the highest level of variability. We compared the peak flux densities of 86 ultracompact HII (UCHII) regions measured by the GLOSTAR and CORNISH surveys and identified variables that show flux variations higher than 30% over ~8yr timespan between these surveys. We found a sample of 38 variable UCHII regions, which is the largest sample identified to date. The overall occurrence of variability is 44+/-5%, suggesting that variation in UCHII regions is significantly more common than prediction. The variable UCHII regions are found to be younger than non-variable UCHII regions, with over 50% of them meeting the size criterion of hypercompact (HC) HII regions. We studied the 7 UCHII regions (the "Top7") that show the highest variability with variations >100%. The Top7 variable UCHII regions are optically thick at 4-8GHz and compact, suggesting they are in a very early evolutionary stage of HCHII or UCHII regions. There is a significant correlation between variability and the spectral index of the radio emission. No dependence is observed between the variations and the properties of the sources' natal clumps traced by submillimeter continuum emission from dust, although variable HII regions are found in clumps at an earlier evolutionary stage.2025A&A...694A..26Yhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/694/A26CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/A+A/627/A175 : GLOSTAR. Radio Source Catalogue I (Medina+ 2019)J/A+A/670/A9 : GLOSTAR. Radio Source Catalogue. II. (Dzib+, 2023)J/A+A/680/A92 : GLOSTAR. Radio Source Catalogue. III. (Yang+, 2023)J/ApJS/205/1 : CORNISH project II. Source catalog (Purcell+, 2013)J/A+A/615/A103 : A catalogue of northern ultra-compact H II regionsJ/MNRAS/473/1059 : Complete sample of Galactic clumps (Urquhart+, 2018)J/ApJS/235/3 : Massive outflows associated with ATLASGAL clumpshttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/694/A26https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/694/A26http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/694/A26https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/694/A26https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/694/A26http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/694/A26GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/694/A26/table1 (The 38 UCHII with radio flux variations)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/694/A26/table1?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/694/A26/table1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/694/A26/table1?GETtext/xml+votable180.050000true272.34705-20.135390.0055555555555555566/14343 29091 29097 29100 29115-29116 29504 29522 29532 29535 30218-30219 30244-30245 30256 30268-30269 30312 30417 30422https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/694/A26?format=asciiRadiodefaultJ/A+A/694/A26/table1The 38 UCHII with radio flux variationsn_thetadcon[*] Note on thetadcon (1)meta.notecharDiam[]? Linear diameter of the sourcepcpos.distancefloatnullableSpeakCPeak flux density CORNISH at 5GHzmJy/beamphot.flux.density;em.radio.3-6GHzfloate_SpeakCUncertainty in SpeakC at 5GHzmJy/beamstat.errorfloatthetaSAngular scale (geometric average)arcsecinstr.scalefloatthetadconDeconvolved angular scalearcsecinstr.scalefloatDist[]? Heliocentric distancepcpos.distancefloatnullablefvar? Flux variation fractionpcphot.flux;arith.ratiofloatnullablealpha? Spectral index fitted from the sub-images of GLOSTAR (2)spect.index;meta.modelledfloatnullablee_alpha? Uncertainty of the spectral index from the fitting process of the sub-images of GLOSTARstat.error;pos.eq.rafloatnullablerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintNameGalactic name (GLLL.llll+BB.bbbb)meta.id;meta.maincharGLONGalactic longitudedegpos.galactic.lonGLATGalactic latitudedegpos.galactic.latdoubleRAJ2000Right Ascension (J2000)degpos.eq.ra;meta.mainDEJ2000Declination (J2000)degpos.eq.dec;meta.mainSpeakGPeak flux density GLOSTAR at 5GHzmJy/beamphot.flux.density;em.radio.3-6GHzfloate_SpeakGUncertainty in SpeakG at 5GHzmJy/beamstat.errorfloat