J/A+A/607/A118ivo://CDS.VizieR/J/A+A/607/A118doi:10.26093/cds/vizier.36070118CDSViti S.2017-11-28T09:16:17Z2017-11-23T07:47:57ZCDS support team

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

cds-question@unistra.frastronomical-modelsmolecular-cloudschemical-abundancesWe present a method to interpret molecular observations and molecular line ratios in nearby extragalactic regions. Ab initio grids of time dependent chemical models, varying in gas density, temperature, cosmic ray ionization rate, and radiation field, are used as input to RADEX calculations. Tables of abundances, column densities, theoretical line intensities, and line ratios for some of the most used dense gas tracers are provided. The degree of correlation as well as degeneracy inherent in molecular ratios is discussed. Comparisons of the theoretical intensities with example observations are also provided. We find that, within the parameters space explored, chemical abundances can be constrained by a well defined set of gas density-gas temperature-cosmic ray ionization rate for the species we investigate here. However, line intensities, as well as, more importantly, line ratios, from different chemical models can be very similar leading to a clear degeneracy. We also find that the gas subjected to a galactic cosmic ray ionization rate will not necessarily have reached steady state by 1 million years. The species most affected by time dependency effects are HCN and CS, both high density tracers. We use our ab initio method to fit an example set of data from two galaxies (M82 and, NGC 253). We find that (i) molecular line ratios can be easily matched even with erroneous individual line intensities; (ii) no set of species can be matched by a one-component ISM; (iii) a species may be a good tracer of an energetic process but only under specific density and temperature conditions. We provide tables of chemical abundances and line intensities ratios for some of the most commonly observed extragalactic tracers of dense gas for a grid of models. We show that by taking into consideration the chemistry behind each species and the individual line intensities, many degeneracies that arise by just using molecular line ratios can be avoided. Finally we show that using a species or a ratio as a tracer of an individual energetic process (e.g. cosmic rays, UV) ought to be done with caution.2017A&A...607A.118Vhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/607/A118CatalogResearchIsServedByTAP VizieR generic servicerelated-toJ/A+A/574/A127 : Photodissociation with mechanical heating (Kazandjian+, 2015)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/607/A118https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/607/A118http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/607/A118https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/607/A118https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/607/A118http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/607/A118GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapdefaultJ/A+A/607/A118/tablea2Grid of chemical models, molecular column densities and ratios of selected speciesrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintAllAll data for this modelmeta.ref.urlcharM[1/67] Model numbermeta.id;stat.fitintzeta[1-100000]? Cosmic ray ionization rate (1, 10, 500, 5000 or 100000) in standard galactic cosmic ray ionization field zeta0phot.count;em.X-rayintnullablechi[1-500] Radiation field (1, 10 or 500) in Draine unit (1 Draine = 1.69G_0_, G_0_=1 corresponds to 1.2uW/m^2^)stat.fit.paramintT[50-200]? Gas temperature (50, 100 or 200)Kphys.temperatureintnullablen_T[shock ] No temperature value at shockmeta.notecharnH[1e+4/1e+6] Gas densitycm**-3phys.columnDensityfloatAVInitial visual extinction before the passage of the shockmagphys.absorption;em.opt.VintN(CO)CO column densitycm**-2phys.columnDensitydoubleN(HCO+)HCO^+^ column densitycm**-2phys.columnDensitydoubleN(HCN)HCN column densitycm**-2phys.columnDensitydoubleN(CS)CS column densitycm**-2phys.columnDensitydoubleHCN/HCO+HCN/HCO^+^ line ratiospect.line.intensity;arith.ratiodoubleHCN/COHCN/CO line ratiospect.line.intensity;arith.ratiodoubleHCO+/COHCO^+^/CO line ratiospect.line.intensity;arith.ratiodoubleCS/COHS/CO line ratiospect.line.intensity;arith.ratiodoubleJ/A+A/607/A118/tablea5Column densities at 10^6^yrs for other selected speciesrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintAllAll data for this modelmeta.ref.urlcharM[1/67] Model numbermeta.id;stat.fitintN(CH3OH)CH_3_OH column densitycm**-2phys.columnDensitydoubleN(SiO)SiO column densitycm**-2phys.columnDensitydoubleN(HNC)HNC column densitycm**-2phys.columnDensitydoubleN(SO)SO column densitycm**-2phys.columnDensitydoubleN(HNCO)HNCO column densitycm**-2phys.columnDensitydoubleJ/A+A/607/A118/table1CH_3_OH and HNCO column densities at two different times 10^6^yrs for shock models onlyrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintAllAll data for this modelmeta.ref.urlcharM[1/67] Model numbermeta.id;stat.fitintTimeMTime when the temperature of the gas reaches its maximum (1)yrtime.ageintN(CH3HO)MCH_3_OH column density at TimeMcm**-2phys.columnDensitydoubleN(HNCO)MHNCO column density at TimeMcm**-2phys.columnDensitydoubleTime[1E+5] Second timeyrtime.agefloatN(CH3HO)CH_3_OH column density at Timecm**-2phys.columnDensitydoubleN(HNCO)HNCO column density at Timecm**-2phys.columnDensitydoubleJ/A+A/607/A118/table4Theoretical HCN/HCO^+^ ratiosrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintAllAll data for this modelmeta.ref.urlcharM[1/67] Model numbermeta.id;stat.fitintR10? HCN/HCO^+^ line ratio for transition (1, 0)spect.line.intensity;arith.ratiofloatnullableR21HCN/HCO^+^ line ratio for transition (2,1)spect.line.intensity;arith.ratiofloatR32? HCN/HCO^+^ line ratio for transition (3, 2)spect.line.intensity;arith.ratiofloatnullableR43? HCN/HCO^+^ line ratio for transition (4, 3)spect.line.intensity;arith.ratiofloatnullableR54? HCN/HCO^+^ line ratio for transition (5, 4)spect.line.intensity;arith.ratiofloatnullableR65HCN/HCO^+^ line ratio for transition (6, 5)spect.line.intensity;arith.ratiofloatR76HCN/HCO^+^ line ratio for transition (7, 6)spect.line.intensity;arith.ratiofloatR87HCN/HCO^+^ line ratio for transition (8, 7)spect.line.intensity;arith.ratiofloatR98HCN/HCO^+^ line ratio for transition (9, 8)spect.line.intensity;arith.ratiofloatR109HCN/HCO^+^ line ratio for transition (10, 9)spect.line.intensity;arith.ratiofloatJ/A+A/607/A118/table6*SiO theoretical integrated line intensities for chemical models at 10^6^yrsrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintAllAll data for this modelmeta.ref.urlcharM[1/67] Model numbermeta.id;stat.fitintJu1Upper levelphys.atmol.qnintJl1Lower levelphys.atmol.qnintI(SiO)1Theoretical SiO integrated line intensity for Ju1, Jl1 transitionK.km/sspect.line.intensitydoubleJu2Upper levelphys.atmol.qnintJl2Lower levelphys.atmol.qnintI(SiO)2Theoretical SiO integrated line intensity for Ju2, Jl2 transitionK.km/sspect.line.intensitydoubleJ/A+A/607/A118/tablea1Grid of chemical models and molecular abundances of selected speciesX(HCN)HCN abundancephys.abunddoublerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintAllAll data for this modelmeta.ref.urlcharM[1/67] Model numbermeta.id;stat.fitintzeta[1-100000] Cosmic ray ionization rate (1, 10, 500, 5000 or 100000) in standard galactic cosmic ray ionization field zeta0phot.count;em.X-rayintchi[1-500]? Radiation field (1, 10 or 500) in Draine unit (1 Draine = 1.69G_0_, G_0_=1 corresponds to 1.2uW/m^2^)stat.fit.paramintnullableT[50-200]? Gas temperature (50, 100 or 200)Kphys.temperatureintnullablen_T[shock ] No temperature value at shockmeta.notecharnH[1e+4/1e+6] Gas densitycm**-3phys.columnDensityfloatAVInitial visual extinction before the passage of the shockmagphys.absorption;em.opt.VintX(CO)CO abundancephys.abunddoubleX(HCO+)HCO^+^ abundancephys.abunddoubleX(CS)CS abundancephys.abunddoubleJ/A+A/607/A118/tablea4Column densities at 10^7^yrs for other selected speciesrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintAllAll data for this modelmeta.ref.urlcharM[1/67] Model numbermeta.id;stat.fitintN(SiO)SiO column densitycm**-2phys.columnDensitydoubleN(HNC)HNC column densitycm**-2phys.columnDensitydoubleN(SO)SO column densitycm**-2phys.columnDensitydoubleJ/A+A/607/A118/table7*Selected SO theoretical integrated line intensities for chemical models at 10^7^ yrsJl2Lower levelphys.atmol.qnJu2Upper levelphys.atmol.qnrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintAllAll data for this modelmeta.ref.urlcharM[1/67] Model numbermeta.id;stat.fitintJu1Upper levelphys.atmol.qnJl1Lower levelphys.atmol.qnI(SO)1? Theoretical SO integrated line intensity for Ju1, Jl1 transitionK.km/sphot.flux.density;em.radiodoublenullableI(SO)2? Theoretical SO integrated line intensity for Ju2, Jl2 transitionK.km/sphot.flux.density;em.radiodoublenullableJ/A+A/607/A118/table11*Selected HNCO theoretical integrated line intensities for chemical models at 10^6^yrsrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintAllAll data for this modelmeta.ref.urlcharM[1/67] Model numbermeta.id;stat.fitintJu1Upper levelphys.atmol.qnJl1Lower levelphys.atmol.qnI(HNCO)1? Theoretical HNCO integrated line intensity for Ju1, Jl1 transitionK.km/sphot.flux.density;em.radiodoublenullableJu2Upper levelphys.atmol.qnJl2Lower levelphys.atmol.qnI(HNCO)2? Theoretical HNCO integrated line intensity for Ju2, Jl2 transitionK.km/sphot.flux.density;em.radiodoublenullableJ/A+A/607/A118/tablea3Column densities at 10^6^yrs for Models showing changes between 1 and 10 million yearsrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintAllAll data for this modelmeta.ref.urlcharM[1/67] Model numbermeta.id;stat.fitintN(CO)CO column densitycm**-2phys.columnDensitydoubleN(HCO+)HCO^+^ column densitycm**-2phys.columnDensitydoubleN(HCN)HCN column densitycm**-2phys.columnDensitydoubleN(CS)CS column densitycm**-2phys.columnDensitydoubleJ/A+A/607/A118/table2*Theoretical integrated line intensities for final time step (10^7^yrs)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintAllAll data for this modelmeta.ref.urlcharM[1/67] Model numbermeta.id;stat.fitintJuUpper levelphys.atmol.qnintJlLower levelphys.atmol.qnintI(CO)CO theoretical integrated line intensity at (Ju, Jl) transitionK.km/sphot.flux.density;em.line.COdoubleI(HCO+)HCO^+^ theoretical integrated line intensity at (Ju, Jl) transitionK.km/sphot.flux.density;em.radiodoubleI(HCN)? HCN theoretical integrated line intensity at (Ju, Jl) transitionK.km/sphot.flux.density;em.radiodoublenullableI(CS)CS theoretical integrated line intensity at (Ju, Jl) transitionK.km/sphot.flux.density;em.radiodoubleJ/A+A/607/A118/table3*Theoretical integrated line intensities for chemical models at 10^6^ yrsJuUpper levelphys.atmol.qnintJlLower levelphys.atmol.qnintrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintAllAll data for this modelmeta.ref.urlcharM[1/67] Model numbermeta.id;stat.fitintI(CO)CO theoretical integrated line intensity at (Ju, Jl) transitionK.km/sphot.flux.density;em.line.COdoubleI(HCO+)HCO^+^ theoretical integrated line intensity at (Ju, Jl) transitionK.km/sphot.flux.density;em.radiodoubleI(HCN)? HCN theoretical integrated line intensity at (Ju, Jl) transitionK.km/sphot.flux.density;em.radiodoublenullableI(CS)CS theoretical integrated line intensity at (Ju, Jl) transitionK.km/sphot.flux.density;em.radiodoubleJ/A+A/607/A118/table8*Selected SO theoretical integrated line intensities, for chemical models at 10^6^yrsrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintAllAll data for this modelmeta.ref.urlcharM[1/67] Model numbermeta.id;stat.fitintJu1Upper levelphys.atmol.qnJl1Lower levelphys.atmol.qnI(SO)1? Theoretical SO integrated line intensity for Ju1, Jl1 transitionK.km/sphot.flux.density;em.radiodoublenullableJu2Upper levelphys.atmol.qnJl2Lower levelphys.atmol.qnI(SO)2? Theoretical SO integrated line intensity for Ju2, Jl2 transitionK.km/sphot.flux.density;em.radiodoublenullableJ/A+A/607/A118/table9*Selected HNC theoretical integrated line intensities for chemical models at 10^7^ yrsJl1Lower levelphys.atmol.qnintrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintAllAll data for this modelmeta.ref.urlcharM[1/67] Model numbermeta.id;stat.fitintJu1Upper levelphys.atmol.qnintI(HNC)1Theoretical HNC integrated line intensity for Ju1, Jl1 transitionK.km/sphot.flux.density;em.radiodoubleJu2Upper levelphys.atmol.qnintJl2Lower levelphys.atmol.qnintI(HNC)2Theoretical HNC integrated line intensity for Ju2, Jl2 transitionK.km/sphot.flux.density;em.radiodoubleJ/A+A/607/A118/table10*Selected HNC theoretical integrated line intensities, for chemical models at 10^6^yrsJl1Lower levelphys.atmol.qnintrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintAllAll data for this modelmeta.ref.urlcharM[1/67] Model numbermeta.id;stat.fitintJu1Upper levelphys.atmol.qnintI(HNC)1Theoretical HNC integrated line intensity for Ju1, Jl1 transitionK.km/sphot.flux.density;em.radiodoubleJu2Upper levelphys.atmol.qnintJl2Lower levelphys.atmol.qnintI(HNC)2Theoretical HNC integrated line intensity for Ju2, Jl2 transitionK.km/sphot.flux.density;em.radiodoubleJ/A+A/607/A118/table5*SiO theoretical integrated line intensities for chemical models at 10^7^ yrsrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintAllAll data for this modelmeta.ref.urlcharM[1/67] Model numbermeta.id;stat.fitintJu1Upper levelphys.atmol.qnintJl1Lower levelphys.atmol.qnintI(SiO)1Theoretical SiO integrated line intensity for Ju1, Jl1 transitionK.km/sspect.line.intensitydoubleJu2Upper levelphys.atmol.qnintJl2Lower levelphys.atmol.qnintI(SiO)2Theoretical SiO integrated line intensity for Ju2, Jl2 transitionK.km/sspect.line.intensitydouble