J/ApJ/919/27ivo://CDS.VizieR/J/ApJ/919/27doi:10.26093/cds/vizier.19190027CDSKaplan K.F.Dinerstein H.L.Kim H.Jaffe D.T.2023-11-21T14:41:54Z2023-02-27T15:03:29ZCDS support team

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

cds-question@unistra.frmolecular-cloudsh-ii-regionsinterstellar-mediuminfrared-astronomyspectroscopymolecular-physicsWe present a comparative study of the near-infrared (NIR) H_2_ line emission from five regions near hot young stars: Sharpless 140, NGC2023, IC63, the Horsehead Nebula, and the Orion Bar. This emission originates in photodissociation or photon-dominated regions (PDRs), interfaces between photoionized and molecular gas near hot (O) stars or reflection nebulae illuminated by somewhat cooler (B) stars. In these environments, the dominant excitation mechanism for NIR emission lines originating from excited rotational-vibrational (rovibrational) levels of the ground electronic state is radiative or UV excitation (fluorescence), wherein absorption of far-UV photons pumps H2 molecules into excited electronic states from which they decay into the upper levels of the NIR lines. Our sources span a range of UV radiation fields (G_0_=10^2^-10^5^) and gas densities (n_H_=10^4^-10^6^cm^-3^), enabling examination of how these properties affect the emergent spectrum. We obtained high-resolution (R~45000) spectra spanning 1.45-2.45{mu}m on the 2.7m Harlan J. Smith Telescope at McDonald Observatory with the Immersion Grating INfrared Spectrometer (IGRINS), detecting up to over 170 transitions per source from excited vibrational states (v=1-14). The populations of individual rovibrational levels derived from these data clearly confirm UV excitation. Among the five PDRs in our survey, the Orion Bar shows the greatest deviation of the populations and spectrum from pure UV excitation, while Sharpless 140 shows the least deviation. However, we find that all five PDRs exhibit at least some modification of the level populations relative to their values under pure UV excitation, a result we attribute to collisional effects.2021ApJ...919...27Khttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/919/27CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toII/36 : UBV and uvby-beta obs. of Orion OB1 Association (Warren+ 1977)I/345 : Gaia DR2 (Gaia Collaboration, 2018)J/ApJ/786/29 : Catalog of distances to molecular clouds (Schlafly+, 2014)J/ApJ/838/152 : Deep NIR spectrum of the Orion Bar PDR (Kaplan+, 2017)J/A+A/630/A58 : Full infrared spectrum of molecular hydrogen (Roueff+, 2019)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/919/27https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/919/27http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/919/27https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/919/27https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/919/27http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/919/27GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/ApJ/919/27/table1 (Photon-dominated region (PDR) properties and observations)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/919/27/table1?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/919/27/table1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/919/27/table1?GETtext/xml+votable180.050000true334.805833363.29830560.0055555555555555566/3031 15667 21439 22854https://cdsarc.cds.unistra.fr/viz-bin/moc/J/ApJ/919/27?format=asciiInfrareddefaultJ/ApJ/919/27/table1Photon-dominated region (PDR) properties and observationsSimbadNameSimbad column added by the CDSmeta.idcharnullableIStarIlluminating starmeta.idcharStdStarStandard starmeta.idcharNamePDR namemeta.id;meta.maincharprimaryrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintTypePDR typesrc.classcharDist[188/764] Distancepcpos.distance;pos.heliocentricinte_Dist[9/50] Dist uncertaintypcstat.errorintr_DistReference on Dist (1)meta.ref;pos.framecharSpTSpectral typesrc.spTypecharr_SpTReference on SpT (1)meta.ref;pos.framecharTeff[23700/39000] Effective temperatureKphys.temperature.effectiveintr_TeffReference on Teff (1)meta.ref;pos.framecharG0[100/30000] UV intensity, G_0_ (2)phot.count;em.UVdoubler_G0Reference on G0 (1)meta.ref;pos.framecharnH[10000/1e+06] Gas density, n_H_cm**-3phys.densitydoubler_nHReference on nH (1)meta.ref;pos.framecharG0/nH[0.005/0.09] G0 to nH ratiocm**3stat.fit.omcdoubleRAJ2000Hour of right ascension (J2000)pos.eq.ra;meta.mainDEJ2000Degree of declination (J2000)pos.eq.dec;meta.mainDateDate of observation (UT)time.epochnullableExp[30/100] Exposure timemintime.duration;obs.exposureintPA[15/135] Position angledegpos.posAngintAk[0.3/0.72] K-band dust extinction (3)magphys.absorptionfloatO/P[1.3/3] ortho-to-para ratio (4)phys.abundfloate_O/P[0.1/0.4] O/P uncertaintystat.errorfloat1-0S/2-1S[2.4/5.4] Flux ratio of the H_2_ 1-0S(1) to 2-1S(1) lines in each PDR (5)phot.flux;arith.ratiofloate_1-0S/2-1S[0.3/0.7] 1-0S/2-1S uncertaintystat.errorfloatANameAbbreviated name used in other tables; column added by CDSmeta.idcharFH2Display the H2 line fluxes for this PDR (link to Table 2)meta.ref.urlcharLH2Display the H2 rovibrational level column densities for this PDR (link to Table 4)meta.ref.urlcharJ/ApJ/919/27/table2H_2_ line fluxes for our photon-dominated regions (normalized to the 4-2 O(3) line)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintlambda[1.45/2.5] H_2_ line vacuum wavelengthumem.wl;spect.linedoublevu[1/14] Transition upper vibrational statephys.mol;phys.atmol.transitionintJu[0/19] Transition upper rotational statephys.atmol.transitionintFs140[0.013/4.4]? Line flux for S 140 (1)phot.fluxfloatnullablee_Fs140[0.003/0.5]? One-sigma uncertainty in Fs140stat.errorfloatnullableFngc2023[0.01/8]? Line flux for NGC 2023 (1)phot.fluxfloatnullablee_Fngc2023[0.001/0.9]? One-sigma uncertainty in Fngc2023stat.errorfloatnullableFic63[0.02/5.3]? Line flux for IC 63 (1)phot.fluxfloatnullablee_Fic63[0.004/0.7]? One-sigma uncertainty in Fic63stat.errorfloatnullableFhorse[0.08/5.3]? Line flux for the Horsehead Nebula (1)phot.fluxfloatnullablee_Fhorse[0.01/0.5]? One-sigma uncertainty in Fhorsestat.errorfloatnullableForibar[0.02/23.4]? Line flux for the Orion Bar (1)phot.fluxfloatnullablee_Foribar[0.003/2.1]? One-sigma uncertainty in Foribarstat.errorfloatnullableIDH_2_ line rovibrational identifiermeta.id;meta.maincharJ/ApJ/919/27/table3Physical Constants for H_2_ LinesrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintIDH_2_ line rovibrational identifiermeta.id;meta.maincharlambda[1.45/2.5] H_2_ line vacuum wavelength (1)umem.wl;spect.linedoublevu[1/14] Transition upper vibrational statephys.mol;phys.atmol.transitionintJu[0/19] Transition upper rotational statephys.atmol.transitionintEu/k[6148/51782] Energy of the upper state (1)Kphys.energyintlogAul[-8/-5.5] Log rovibrational radiative transition probability (1)log(s**-1)phys.atmol.transProbfloatJ/ApJ/919/27/table4H_2_ rovibrational level column densities for our PDRs and comparison to pure UV-excited Cloudy modelrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintlambda[1.45/2.5] H_2_ line vacuum wavelengthumem.wl;spect.linedoublevu[1/14] Transition upper vibrational statephys.mol;phys.atmol.transitionintJu[0/19] Transition upper rotational statephys.atmol.transitionintlnRs140[-5.5/2.52]? Natural log of S 140 ratio (1)stat.fit.omcfloatnullableE_lnRs140[0.03/0.2]? Upper uncertainty in lnRs140stat.error;stat.maxfloatnullablee_lnRs140[0.03/0.3]? Lower uncertainty in lnRs140stat.errorfloatnullable(Nu/Nm)s140[0.2/11.26]? S 140 ratio (2)stat.fit.omcfloatnullablelnRngc2023[-7/3.2]? Natural log of NGC 2023 ratio (1)stat.fit.omcfloatnullableE_lnRngc2023[0.049/0.2]? Upper uncertainty in lnRngc2023stat.error;stat.maxfloatnullablee_lnRngc2023[0.05/0.3]? Lower uncertainty in lnRngc2023stat.errorfloatnullable(Nu/Nm)ngc2023[0.2/23]? NGC 2024 Nu/Nm ratio (2)stat.fit.omcfloatnullablelnRic63[-5.1/2.8]? Natural log IC 63 ratio (1)stat.fit.omcfloatnullableE_lnRic63[0.05/0.3]? Upper uncertainty in lnRic63stat.error;stat.maxfloatnullablee_lnRic63[0.05/0.3]? Lower uncertainty in lnRic63stat.errorfloatnullable(Nu/Nm)ic63[0.2/11.2]? IC 63 Nu/Nm ratio (2)stat.fit.omcfloatnullablelnRhorse[-3.2/2.8]? Natural log of Horsehead Nebula ratio (1)stat.fit.omcfloatnullableE_lnRhorse[0.02/0.2]? Upper uncertainty in lnRhorsestat.error;stat.maxfloatnullablee_lnRhorse[0.02/0.2]? Lower uncertainty in lnRhorsestat.errorfloatnullable(Nu/Nm)horse[0.36/7.1]? Horsehead Nebula ratio (2)stat.fit.omcfloatnullablelnRoribar[-5.4/4.2]? Natural log of Orion Bar ratio (1)stat.fit.omcfloatnullableE_lnRoribar[0.04/0.2]? Upper uncertainty in lnRoribarstat.error;stat.maxfloatnullablee_lnRoribar[0.04/0.2]? Lower uncertainty in lnRoribarstat.errorfloatnullable(Nu/Nm)oribar[0.3/16.5]? Orion Bar Nu/Nm ratio (2)stat.fit.omcfloatnullableIDH_2_ line rovibrational identifiermeta.id;meta.mainchar