J/MNRAS/416/2ivo://CDS.VizieR/J/MNRAS/416/2doi:10.26093/cds/vizier.74160002CDSHeiner J.S.Allen R.J.Van Der Kruit P.C.2024-07-15T20:16:34Z2012-04-18T14:34:44ZCDS support team

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

cds-question@unistra.frgalaxiesmolecular-cloudsh-i-line-emissionultraviolet-astronomyWe derive total (atomic + molecular) hydrogen densities in giant molecular clouds (GMCs) in the nearby spiral galaxy M33 using a method that views the atomic hydrogen near regions of recent star formation as the product of photodissociation. Far-ultraviolet (FUV) photons emanating from a nearby OB association produce a layer of atomic hydrogen on the surfaces of nearby GMCs. Our approach provides an estimate of the total hydrogen density in these GMCs from observations of the excess FUV emission that reaches the GMC from the OB association and of the excess 21-cm radio HI emission produced after these FUV photons convert H2 into HI on the GMC surface. The method provides an alternative approach to the use of CO emission as a tracer of H2 in GMCs and is especially sensitive to a range of densities well below the critical density for CO(1-0) emission.2011MNRAS.416....2Hhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/MNRAS/416/2CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/MNRAS/416/2https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/MNRAS/416/2http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/MNRAS/416/2https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/MNRAS/416/2https://vizier.iucaa.in/viz-bin/votable?-source=J/MNRAS/416/2http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/MNRAS/416/2GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/MNRAS/416/2/table5 (Locations and FUV fluxes of candidate photodissociation regions (PDRs))https://vizier.cds.unistra.fr/viz-bin/conesearch/J/MNRAS/416/2/table5?https://vizier.iucaa.in/viz-bin/conesearch/J/MNRAS/416/2/table5?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/MNRAS/416/2/table5?GETtext/xml+votable180.050000true23.4640458330.647780560.0055555555555555566/2154-2155 2240-2241https://cdsarc.cds.unistra.fr/viz-bin/moc/J/MNRAS/416/2?format=asciiUVRadiodefaultJ/MNRAS/416/2/table5Locations and FUV fluxes of candidate photodissociation regions (PDRs)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintSeq[1/42] Source sequential numbermeta.recordintprimaryRAJ2000Right ascension (J2000)pos.eq.ra;meta.mainDEJ2000Declination (J2000)pos.eq.dec;meta.mainRadRadius (distance from M33 galaxy center)kpcpos.distancefloatFFUVFar-UV flux (in 10^-15^erg/cm2/s/{AA})1e-17W.m**-2.nm**-1phot.flux;em.UVfloatAp[36/180] Aperturearcsecphys.angSize;instr.fovintJ/MNRAS/416/2/table6Candidate photodissociation regions resultsrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintSeq[1/42] Source sequential numbermeta.recordintm_Seq[a-h] Multiplicity index on Seqmeta.code.multipcharrho(HI)Separation between the OB clusters and associated HI patchespcpos.distance;phys.sizeintNHIHI column density1e+21cm**-2phys.columnDensityfloatG0Incident flux G_0_phot.flux;em.UVfloatG/GbgSource contrastphot.flux;arith.ratiofloatnHTotal hydrogen volume densitycm**-3phys.densityinte_nH[0,1] Fractional error on nHstat.errorfloat