J/AJ/169/18ivo://CDS.VizieR/J/AJ/169/18doi:10.26093/cds/vizier/be-59-jCDSden Brok J.Jimenez-Donaire M.J.Leroy A.Schinnerer E.Bigiel F.,Pety J.Petitpas G.Usero A.Teng Y.-H.Humire P.Koch E.W.,Rosolowsky E.Sandstrom K.Liu D.Zhang Q.Stuber S.Chevance M.,Dale D.A.Eibensteiner C.Galic I.Glover S.C.O.Pan H.-A.,Querejeta M.Smith R.J.Williams T.G.Wilner D.J.Zhang V.2026-07-02T11:45:29Z2025-10-22T14:48:31ZCDS support team

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

cds-question@unistra.frradio-astronomyinterferometryastronomical-modelsradio-galaxiesmolecular-cloudsco-line-emissionspectroscopyOver the past decade, several millimeter interferometer programs have mapped the nearby star-forming galaxy M51 at a spatial resolution of <=170 pc. This study combines observations from three major programs: the PdBI Arcsecond Whirlpool Survey, the SMA M51 large program, and the Surveying the Whirlpool at Arcseconds with NOEMA. The data set includes the (1-0) and (2-1) rotational transitions of 12CO, 13CO, and C18O isotopologues. The observations cover the r<3kpc region, including the center and part of the disk, thereby ensuring strong detections of the weaker 13CO and C18O lines. All observations are convolved in this analysis to an angular resolution of 4", corresponding to a physical scale of 170pc. We investigate empirical line ratio relations and quantitatively evaluate molecular gas conditions such as temperature, density, and the CO-to-H2 conversion factor ({alpha}CO). We employ two approaches to study the molecular gas conditions: (i) assuming local thermodynamic equilibrium (LTE) to analytically determine the CO column density and {alpha}CO, and (ii) using non-LTE modeling with RADEX to fit physical conditions to observed CO isotopologue intensities. We find that the {alpha}CO values in the center and along the inner spiral arm are ~0.5dex (LTE) and 0.1dex (non-LTE) below the Milky Way inner disk value. The average non-LTE {alpha}CO is 2.4+/-0.5M{sun}.pc^-2^.(K.km/s)^-1^. While both methods show dispersion due to underlying assumptions, the scatter is larger for LTE-derived values. This study underscores the necessity for robust CO line modeling to accurately constrain the molecular interstellar medium's physical and chemical conditions in nearby galaxies.2025AJ....169...18Dhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/AJ/169/18CatalogResearchIsServedByTAP VizieR generic servicerelated-toJ/A+A/432/369 : Leiden Atomic and Molecular Database (LAMDA) (Schoeier+, 2005)J/AJ/136/2782 : Star formation efficiency in nearby galaxies (Leroy+, 2008)J/A+A/549/A39 : A 3mm molecular line survey of NGC1068 (Aladro+, 2013)J/AJ/146/150 : Velocity dispersions of 12 nearby galaxies (Caldu-Primo+, 2013)J/ApJ/808/42 : CHemical Abundances of Spirals (CHAOS) II. M51 (Croxall+, 2015)J/ApJ/846/71 : M51 ISM structures from the CO maps of PAWS (Leroy+, 2017)J/ApJ/835/217 : Density distributions for mm-wave line ratios (Leroy+, 2017)J/ApJS/234/24 : VLA 33GHz obs. of star-forming regions (Murphy+, 2018)J/ApJ/880/127 : EMPIRE: IRAM 30m dense gas survey (Jimenez-Donaire+, 2019)J/A+A/625/A19 : 33 GHz continuum map of M51 (Querejeta+, 2019)J/ApJ/893/96 : CHAOS IV: NGC3184 LBT obs. & 3 other gal. abund. (Berg+, 2020)J/A+A/635/A131 : 12CO/13CO ratio in 126 nearby galaxy centers (Israel, 2020)J/ApJS/248/25 : SFRS: 3-33GHz VLA obs. of star-forming regions (Linden+, 2020)J/ApJS/257/21 : VERTICO: Virgo EnviRonment Traced In CO survey (Brown+, 2021)J/ApJ/927/149 : Low-J CO line ratios for 152 CO map pairs (Leroy+, 2022)J/A+A/679/A112 : California and Orion A clouds emission lines (Tafalla+, 2023)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/AJ/169/18https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/AJ/169/18http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/AJ/169/18https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/AJ/169/18https://vizier.iucaa.in/viz-bin/votable?-source=J/AJ/169/18http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/AJ/169/18GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapRadiodefaultJ/AJ/169/18/table7RADEX single-zone modeled line intensitiesrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintTkin[4/100] Kinetic temperatureKphys.temperaturefloatn(H2)[100/1e5] H2 volume densitycm**-3phys.densitydoubleN(CO)/dv[5e14/5e18] CO column density per line width dv (1)cm**-2.km**-1.sphys.columnDensitydouble[12CO/13CO][20/80] CO isotopologue abundance ratiophys.abundintbff[0.01/1] Beam filling factor, {phi}stat.fit.paramfloattau12CO[-0.09/3875] Optical depth, 12CO (1-0)phys.absorption.opticalDepthdoubletau13CO[-0.1/186.5] Optical depth, 13CO (1-0)phys.absorption.opticalDepthdoubleI-12CO(1-0)[-1.5e-13/1535] Simulated RADEX intensity for the (1-0) rotational transition of 12COK.km/sphot.flux.densitydoubleI-12CO(2-1)[0/1506] Simulated RADEX intensity for the (2-1) rotational transition of 12COK.km/sphot.flux.densitydoubleI-13CO(1-0)[-28/937] Simulated RADEX intensity for the (1-0) rotational transition of 13COK.km/sphot.flux.densitydoubleI-13CO(2-1)[4.8e-6/1362] Simulated RADEX intensity for the (2-1) rotational transition of 13COK.km/sphot.flux.densitydouble