J/A+A/679/A112ivo://CDS.VizieR/J/A+A/679/A112doi:10.26093/cds/vizier/bc-n7/lbbcCDSTafalla M.Usero A.Hacar A.2026-07-01T14:01:09Z2023-11-29T09:52:09ZCDS support team

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

cds-question@unistra.frmolecular-cloudschemical-abundancesradio-astronomyWe aim to characterize and compare the molecular-line emission of three clouds whose star-formation rates span one order of magnitude: California, Perseus, and Orion A. We used stratified random sampling to select positions representing the different column density regimes of each cloud and observed them with the IRAM 30 m telescope. We covered the 3 mm wavelength band and focused our analysis on CO, HCN, CS, HCO^+^, HNC, and N_2_H^+^. We find that the line intensities depend most strongly on the H_2_ column density, with which they are tightly correlated. A secondary effect, especially visible in Orion A, is a dependence of the line intensities on the gas temperature. We explored a method that corrects for temperature variations and show that, when it is applied, the emission from the three clouds behaves very similarly. CO intensities vary weakly with column density, while the intensity of traditional dense-gas tracers such as HCN, CS, and HCO^+^ varies almost linearly with column density. N_2_H^+^ differs from all other species in that it traces only cold dense gas. The intensity of the rare HCN and CS isotopologs reveals additional temperature-dependent abundance variations. Overall, the clouds have similar chemical compositions that, as the depth increases, are sequentially dominated by photodissociation, gas-phase reactions, molecular freeze-out, and stellar feedback in the densest parts of Orion A. Our observations also allowed us to calculate line luminosities for each cloud, and a comparison with literature values shows good agreement. We used our HCN(1-0) data to explore the behavior of the HCN conversion factor, finding that it is dominated by the emission from the outermost cloud layers. It also depends strongly on the gas kinetic temperature. Finally, we show that the HCN/CO ratio provides a gas volume density estimate, and that its correlation with the column density resembles that found in extragalactic observations.2023A&A...679A.112Thttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/679/A112CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/A+A/642/A76 : California molecular cloud CO datacubes (Zhang+, 2020)J/ApJ/921/23 : C^18^O dense cores identified in the CMC region (Guo+, 2021)J/ApJS/217/7 : Orion A dense cores based on 1.1mm and C^18^O (Shimajiri+, 2015J/ApJS/264/35 : C^18^O dense cores in Orion A molecular cloud (Takemura+, 2023https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/679/A112https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/679/A112http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/679/A112https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/679/A112https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/679/A112http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/679/A112GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/679/A112/tableb1 (California cloud data)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/679/A112/tableb1?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/679/A112/tableb1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/679/A112/tableb1?GETtext/xml+votable180.050000true64.8737.9955560.005555555555555556Cone search capability for table J/A+A/679/A112/tableb2 (Orion A data)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/679/A112/tableb2?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/679/A112/tableb2?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/679/A112/tableb2?GETtext/xml+votable180.050000true83.812083-6.6305560.0055555555555555565/316 401 5350 6/1231 1242-1243 1261-1263 1272 1274 1613 21382-21383 21389 21395 21404 21424-21425 21427-21428 21433-21434 21436-21438 22805https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/679/A112?format=asciiRadiodefaultJ/A+A/679/A112/tableb1California cloud datarecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintNameSource name (1)meta.id;meta.maincharDEJ2000Declination (J2000)pos.eq.dec;meta.mainRAJ2000Right ascension (J2000)pos.eq.ra;meta.mainNH2H_2_ column densitycm**-2phys.columnDensitydoublee_NH2H_2_ uncertainty column density uncertaintycm**-2stat.error;phys.columnDensityfloatInt1^12^CO(1-0) intensityK.km/sspect.line.intensitydoublee_Int1^12^CO(1-0) intensity uncertaintyK.km/sstat.errorfloatInt2^13^CO(1-0) intensityK.km/sspect.line.intensitydoublee_Int2^13^CO(1-0) intensity uncertaintyK.km/sstat.errorfloatInt3C^18^O(1-0) intensityK.km/sspect.line.intensitydoublee_Int3C^18^O(1-0) intensity uncertaintyK.km/sstat.errorfloatInt4HCN(1-0) intensity (1)K.km/sspect.line.intensitydoublee_Int4HCN(1-0) intensity uncertaintyK.km/sstat.errorfloatInt5CS(2-1) intensityK.km/sspect.line.intensitydoublee_Int5CS(2-1) intensity uncertaintyK.km/sstat.errorfloatInt6HNC(1-0) intensityK.km/sspect.line.intensitydoublee_Int6HNC(1-0) intensity uncertaintyK.km/sstat.errorfloatInt7HCO+(1-0) intensityK.km/sspect.line.intensitydoublee_Int7HCO+(1-0) intensity uncertaintyK.km/sstat.errorfloatInt8N_2_H+(1-0) intensity (2)K.km/sspect.line.intensitydoublee_Int8N_2_H++(1-0) intensity uncertaintyK.km/sstat.errorfloatInt9H^13^CN(1-0) intensityK.km/sspect.line.intensitydoublee_Int9H^13^CN(1-0) intensity uncertaintyK.km/sstat.errorfloatInt10C^34^S(2-1) intensityK.km/sspect.line.intensitydoublee_Int10C^34^S(2-1) intensity uncertaintyK.km/sstat.errorfloatInt11HN^13^C(1-0) intensityK.km/sspect.line.intensitydoublee_Int11HN^13^C(1-0) intensity uncertaintyK.km/sstat.errorfloatInt12H^13^CO+(1-0) intensityK.km/sspect.line.intensitydoublee_Int12H^13^CO+(1-0) intensity uncertaintyK.km/sstat.errorfloatJ/A+A/679/A112/tableb2Orion A datarecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintNameSource name (1)meta.id;meta.maincharRAJ2000Right ascension (J2000)pos.eq.ra;meta.mainDEJ2000Declination (J2000)pos.eq.dec;meta.mainNH2H_2_ column densitycm**-2phys.columnDensitydoublee_NH2H_2_ uncertainty column density uncertaintycm**-2stat.error;phys.columnDensityfloatInt1^12^CO(1-0) intensityK.km/sspect.line.intensitydoublee_Int1^12^CO(1-0) intensity uncertaintyK.km/sstat.errorfloatInt2^13^CO(1-0) intensityK.km/sspect.line.intensitydoublee_Int2^13^CO(1-0) intensity uncertaintyK.km/sstat.errorfloatInt3C^18^O(1-0) intensityK.km/sspect.line.intensitydoublee_Int3C^18^O(1-0) intensity uncertaintyK.km/sstat.errorfloatInt4HCN(1-0) intensity (1)K.km/sspect.line.intensitydoublee_Int4HCN(1-0) intensity uncertaintyK.km/sstat.errorfloatInt5CS(2-1) intensityK.km/sspect.line.intensitydoublee_Int5CS(2-1) intensity uncertaintyK.km/sstat.errorfloatInt6HNC(1-0) intensityK.km/sspect.line.intensitydoublee_Int6HNC(1-0) intensity uncertaintyK.km/sstat.errorfloatInt7HCO+(1-0) intensityK.km/sspect.line.intensitydoublee_Int7HCO+(1-0) intensity uncertaintyK.km/sstat.errorfloatInt8N_2_H+(1-0) intensity (2)K.km/sspect.line.intensitydoublee_Int8N_2_H++(1-0) intensity uncertaintyK.km/sstat.errorfloatInt9H^13^CN(1-0) intensityK.km/sspect.line.intensitydoublee_Int9H^13^CN(1-0) intensity uncertaintyK.km/sstat.errorfloatInt10C^34^S(2-1) intensityK.km/sspect.line.intensitydoublee_Int10C^34^S(2-1) intensity uncertaintyK.km/sstat.errorfloatInt11HN^13^C(1-0) intensityK.km/sspect.line.intensitydoublee_Int11HN^13^C(1-0) intensity uncertaintyK.km/sstat.errorfloatInt12H^13^CO+(1-0) intensityK.km/sspect.line.intensitydoublee_Int12H^13^CO+(1-0) intensity uncertaintyK.km/sstat.errorfloat