J/ApJS/253/23ivo://CDS.VizieR/J/ApJS/253/23doi:10.26093/cds/vizier.22530023CDSArmentrout W.P.Anderson L.D.Wenger T.V.Balser D.S.Bania T.M.2023-08-16T14:19:32Z2021-05-06T16:14:08ZCDS support team

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

cds-question@unistra.frh-ii-regionsradio-continuum-emissioninfrared-sourcesThe Milky Way contains thousands of HII region candidates identified by their characteristic mid-infrared morphology, but lacking detections of ionized gas tracers such as radio continuum or radio recombination line emission. These targets thus remain unconfirmed as HII regions. With only ~2500 confirmed HII regions in the Milky Way, Galactic surveys are deficient by several thousand nebulae when compared to external galaxies with similar star formation rates. Using sensitive 9 GHz radio continuum observations with the Karl G. Jansky Very Large Array, we explore a sample of HII region candidates in order to set observational limits on the actual total population of Galactic HII regions. We target all infrared-identified "radio-quiet" sources from the Wide-field Infrared Survey Explorer Catalog of Galactic HII regions between 245{deg}>=l>=90{deg} with infrared diameters less than 80". We detect radio continuum emission from 50% of the targeted HII region candidates, providing strong evidence that most of the radio-quiet candidates are bona fide HII regions. We measure the peak and integrated radio flux densities and compare the inferred Lyman continuum fluxes using models of OB stars. We conclude that stars of approximately spectral type B2 and earlier are able to create HII regions with similar infrared and radio continuum morphologies as the more luminous HII regions created by O stars. From our 50% detection rate of "radio-quiet" sources, we set a lower limit of ~7000 for the HII region population of the Galaxy. Thus the vast majority of the Milky Way's HII regions remain to be discovered.2021ApJS..253...23Ahttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJS/253/23CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toVIII/58 : A Survey of Radio H II Regions in the Northern Sky (Lockman+ 1989)VIII/65 : 1.4GHz NRAO VLA Sky Survey (NVSS) (Condon+ 1998)J/A+A/171/261 : RRLs of Southern HII Regions (Caswell+ 1987)J/AJ/127/1632 : UBVR(UIT) photometry of O and OB stars in SMC (Oey+, 2004)J/ApJS/194/32 : The HII Region Discovery Survey (HRDS). II. (Anderson+, 2011)J/MNRAS/424/1925 : Spectrocopic Binarity of O and B type stars (Chini+, 2012)J/MNRAS/424/2442 : Catalog of bubbles from Milky Way Project (Simpson+, 2012)J/ApJS/212/1 : The WISE catalog of Galactic HII regions (Anderson+, 2014)J/ApJ/784/111 : Morphology of cand. intermediate-mass SFRs (Lundquist+, 2014)J/ApJS/221/26 : Radio obs. of Galactic WISE HII regions (Anderson+, 2015)J/ApJ/806/199 : RRL & continuum data of 21 Gal. H II regions (Balser+, 2015)J/ApJ/799/153 : Yellowballs in Milky Way project (Kerton+, 2015)J/A+A/588/A97 : Continuum sources from the THOR survey (Bihr+, 2016)J/ApJS/234/33 : A GBT survey of large Galactic HII regions (Anderson+, 2018)J/ApJ/870/32 : Kinematics in young star clusters & associations (Kuhn+, 2019)J/A+A/627/A175 : GLOSTAR. Radio Source Catalogue I (Medina+ 2019)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJS/253/23https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJS/253/23http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJS/253/23https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJS/253/23https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJS/253/23http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJS/253/23GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/ApJS/253/23/tablea1 (*VLA radio continuum parameters)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJS/253/23/tablea1?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJS/253/23/tablea1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJS/253/23/tablea1?GETtext/xml+votable180.050000true316.082666749.74836110.0055555555555555566/1307-1308 1329 1354 1433 1481 1791 1808 1848 1930 1962-1963 3031 3063 3157 3175 3302 3329 3342 3606 3609 3637-3639 3641 3644 3649 3728 3748 14263 14267 14270 14299 14306-14308 14316-14317 14321 14335 15390-15391 15409 15414 15434-15435 15438 15448-15449 15451 15456 15458 15460-15461 15469 15472 15474-15476 15621 15623-15624 15626 15629 15649 15676 15759 21457 21504 21510 21542 21671 22038 22045 22122 22208 22220 23637 23674 23765 23767 23773 23938 23968-23969 23982 24325 24426 24493 24507 24554 39804 39926 39935 40619https://cdsarc.cds.unistra.fr/viz-bin/moc/J/ApJS/253/23?format=asciiInfraredRadiodefaultJ/ApJS/253/23/tablea1*VLA radio continuum parametersrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintWISEWISE identifier (GLLL.lll+BB.bbb) from Anderson+, 2014, J/ApJS/212/1 (<[ABB2014] WISE GLLL.ll+BB.bbb> in Simbad)meta.id;meta.maincharRAJ2000Hour of Right Ascension (J2000)pos.eq.ra;meta.mainDEJ2000Degree of Declination (J2000)pos.eq.dec;meta.mainSint[0.12/164.1]? Integrated flux densitymJyphot.flux.density;em.radio.6-12GHzfloatnullablee_Sint[0.02/17.1]? Uncertainty in SintmJystat.errorfloatnullableSpeak[0.014/8]? peak flux densitymJy/beamphot.flux.density;em.radio.6-12GHz;stat.maxfloatnullablee_Speak[0.003/2.4] Uncertainty (map RMS) for Speak (1)mJy/beamstat.errorfloatArea[370/27270]? Region area (2)arcsec**2phys.area;obs.fieldintnullableExp[4/16] Integration timemintime.epochintFig4Figure sub-number on Figure 4 (column added by the author) (3)meta.bib.figintSimbadSimbad column added by the CDSmeta.ref.urlchar