J/ApJS/241/2ivo://CDS.VizieR/J/ApJS/241/2doi:10.26093/cds/vizier.22410002CDSLuisi M.Anderson L.D.Liu B.Roshi D.A.Churchwell Ed2019-08-21T06:52:30Z2019-08-12T10:38:44ZCDS support team

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

cds-question@unistra.frh-ii-regionsinterstellar-mediumradio-astronomyUsing Green Bank Telescope radio recombination line (RRL) data, we analyze the role of leaking radiation from HII regions in maintaining the ionization of the interstellar medium (ISM). We observed a sample of eight Galactic HII regions of various sizes, morphologies, and luminosities. For each region, the hydrogen RRL intensity decreases roughly as a power-law with the distance from the center of the region. This suggests that radiation leaking from the HII region is responsible for the majority of surrounding ionized gas producing RRL emission. Our results further indicate that the hydrogen RRL intensity appears to be fundamentally related to the HII region sizes traced by their photodissociation regions, such that physically smaller HII regions show a steeper decrease in intensity with an increasing distance from the region centers. As a result, giant HII regions may have a much larger effect in maintaining the ionization of the ISM. For six of the eight observed HII regions, we find a decrease in the ^4^He^+^/H^+^ abundance ratio with an increasing distance, indicating that He-ionizing photons are being absorbed within the ionization front of the HII region. There is enhanced carbon RRL emission toward directions with strong continuum background, suggesting that the carbon emission is amplified by stimulated emission.2019ApJS..241....2Lhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJS/241/2CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toIII/274 : Galactic O-Star Spectroscopic Survey (GOSSS) (Sota+, 2014)J/ApJ/653/1226 : Physical properties of galactic HII regions (Quireza+, 2006)J/ApJS/169/353 : Chandra sources in M17 (Broos+, 2007)J/ApJ/738/27 : Galactic HII regions RRL and continuum data (Balser+, 2011)J/MNRAS/411/705 : Spectrophotometric distances of HII regions (Moises+, 2011)J/ApJ/755/40 : HII reg. in Magellanic clouds from MCELS (Pellegrini+, 2012)J/ApJ/764/34 : HRDS IV. H, He & C radio recombination lines (Wenger+, 2013)J/ApJS/212/1 : The WISE catalog of Galactic HII regions (Anderson+, 2014)J/ApJ/810/42 : Hydrogen RRL parameters of H II regions (Anderson+, 2015)J/ApJS/240/14 : SIGGMA: inner galaxy data release (Liu+, 2019)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJS/241/2https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJS/241/2http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJS/241/2https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJS/241/2https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJS/241/2http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJS/241/2GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/ApJS/241/2/table1 (H II region properties)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJS/241/2/table1?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJS/241/2/table1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJS/241/2/table1?GETtext/xml+votable180.050000true275.18216-16.161530.005555555555555556Cone search capability for table J/ApJS/241/2/pointings (Observed positions (table 3) and radio continuum temperatures and source properties (table 5))https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJS/241/2/pointings?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJS/241/2/pointings?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJS/241/2/pointings?GETtext/xml+votable180.050000true60.81583351.3150.0055555555555555566/1781 1783 14641 21438 21439 29113 29116 29118 29119 29463 29469 29504 30256 30259 30262 30622 30644https://cdsarc.cds.unistra.fr/viz-bin/moc/J/ApJS/241/2?format=asciiRadiodefaultJ/ApJS/241/2/table1H II region propertiesSimbadNameSimbad column added by the CDSmeta.idcharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRegHII region identifiermeta.id;meta.maincharprimaryONameOther namemeta.idcharGLONGalactic longitudedegpos.galactic.lonGLATGalactic latitudedegpos.galactic.latRad[2.4/14.2] Radius of the HII region (see Section 3)pcphys.size.radius;obs.fieldfloatRgal[4.5/11.6] Galactocentric radiuskpcpos.distance;pos.galactocentricfloatDist[0.4/8.4] Distance to the Sun from Anderson+, 2014, J/ApJS/212/1kpcpos.distance;pos.heliocentricfloatSpTSpectral type of the ionizing source(s)src.spTypecharr_SpT[1/8] Reference (1)meta.ref;pos.frameintNpNumber of pointings in this region (link to Tables 3+5)meta.numberintnullable_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.decnullableindexedJ/ApJS/241/2/pointingsObserved positions (table 3) and radio continuum temperatures and source properties (table 5)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRegHII region identifiermeta.id.parentcharSourceSource name within HII region (1)meta.id;obs.fieldcharRAJ2000Hour of right ascension (J2000)pos.eq.ra;meta.mainDEJ2000Degree of declination (J2000)pos.eq.dec;meta.mainGLON[14.7/210] Galactic longitudedegpos.galactic.lonGLAT[-20.2/1.6] Galactic latitudedegpos.galactic.latfloatPDRPhotodissociation region (PDR) boundary (2)meta.codecharTc[0.01/215]? Continuum antenna temperature T_C_Kphot.antennaTemp;spect.continuumfloatnullablee_Tc[0.01/34]? 1{sigma} uncertainty in TcKstat.errorfloatnullableTe[1240/10780]? Local thermodynamic equilibrium (LTE) electron temperatureKphys.temperature.electron;pos.lg;phys.electronintnullablee_Te[680/2140]? 1{sigma} uncertainty in TeKstat.errorintnullableEM[270/2418330]? Emission measurepc.cm**-6phys.emissMeasureintnullablee_EM[360/492550]? 1{sigma} uncertainty in EMpc.cm**-6stat.errorintnullableJ/ApJS/241/2/table4H, He, and C RRL parameters for the 98 sourcesRegHII region identifiermeta.id.parentcharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintSourceSource name within HII regionmeta.id;obs.fieldcharTransLine transition; alpha, beta, or gammaphys.atmol.transProb;phys.atmol.transition;spect.linecharElElement; H, He, or Cphys.atmol.elementcharTL[1.2/14831]? Line intensitymKspect.line.intensityfloatnullablee_TL[0.1/22]? Mean 1{sigma} error on TLmKstat.errorfloatnullableFWHM[2.7/58.1]? FWHM line widthkm/sspect.line.widthfloatnullablee_FWHM[0/4]? Mean 1{sigma} error on FWHMkm/sstat.error;phys.angSizefloatnullableVLSR[-30/123.5]? LSR velocitykm/sphys.veloc;pos.lsrfloatnullablee_VLSR[0.1/2]? Mean 1{sigma} error on VLSRkm/sstat.error;phys.veloc;pos.lsrfloatnullablerms[0.5/25.6]? rms noisemKstat.stdev;instr.det.noisefloatnullabletintg[3/36] Total on-source integration timemintime.expoint