J/ApJ/846/71ivo://CDS.VizieR/J/ApJ/846/71doi:10.26093/cds/vizier.18460071CDSLeroy A.K.Schinnerer E.Hughes A.Kruijssen J.M.D.Meidt S.,Schruba A.Sun J.Bigiel F.Aniano G.Blanc G.A.Bolatto A.,Chevance M.Colombo D.Gallagher M.Garcia-Burillo S.Kramer C.,Querejeta M.Pety J.Thompson T.A.Usero A.2018-09-03T08:37:00Z2018-08-31T12:11:25ZCDS support team

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

cds-question@unistra.frgalaxiesco-line-emissioninterstellar-mediummolecular-physicsWe compare the structure of molecular gas at 40pc resolution to the ability of gas to form stars across the disk of the spiral galaxy M51. We break the PdBI Arcsecond Whirlpool Survey (PAWS; Schinnerer+ 2013ApJ...779...42S) into 370pc and 1.1kpc resolution elements, and within each we estimate the molecular gas depletion time ({tau}_Dep_^mol^), the star-formation efficiency per free-fall time ({epsilon}_ff_), and the mass-weighted cloud-scale (40pc) properties of the molecular gas: surface density, {Sigma}, line width, {sigma}, and b={Sigma}/{sigma}^2^{propto}{alpha}_vir_^-1^, a parameter that traces the boundedness of the gas. We show that the cloud-scale surface density appears to be a reasonable proxy for mean volume density. Applying this, we find a typical star-formation efficiency per free-fall time, {epsilon}_ff_(<{Sigma}_40pc_>)~0.3%-0.36%, lower than adopted in many models and found for local clouds. Furthermore, the efficiency per free-fall time anti-correlates with both {Sigma} and {sigma}, in some tension with turbulent star-formation models. The best predictor of the rate of star formation per unit gas mass in our analysis is b={Sigma}/{sigma}^2^, tracing the strength of self-gravity, with {tau}_Dep_^mol^{propto}b^-0.9^. The sense of the correlation is that gas with stronger self-gravity (higher b) forms stars at a higher rate (low {tau}_Dep_^mol^). The different regions of the galaxy mostly overlap in {tau}_Dep_^mol^ as a function of b, so that low b explains the surprisingly high {tau}_Dep_^mol^ found toward the inner spiral arms found by Meidt et al. (2013ApJ...779...45M).2017ApJ...846...71Lhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/846/71CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/A+A/291/943 : Protostellar cores (Ossenkopf+, 1994)J/ApJ/479/231 : PNe in M51, M96 & M101 (Feldmeier+ 1997)J/ApJ/577/31 : PNe in six galaxies (Ciardullo+, 2002)J/ApJ/633/871 : Positions and photometry of HII knots in M51 (Calzetti+, 2005)J/ApJ/671/333 : Aperture photometry in NGC 5194 (Kennicutt+, 2007)J/ApJ/686/948 : CO in extragalactic giant molecular clouds (Bolatto+, 2008)J/AJ/136/2782 : Star formation efficiency in nearby galaxies (Leroy+, 2008)J/AJ/136/2563 : HI Nearby Galaxy Survey, THINGS (Walter+, 2008)J/ApJ/704/842 : VIRUS-P spectroscopy of NGC 5194 (Blanc+, 2009)J/ApJ/699/1092 : Giant molecular clouds (SRBY) (Heyer+, 2009)J/ApJ/700/1299 : Gas-phase element depletions in the ISM (Jenkins, 2009)J/ApJS/184/1 : Molecular clouds in the LMC by NANTEN. II. (Kawamura+, 2009)J/ApJ/723/1019 : Galactic SFR and gas surface densities (Heiderman+, 2010)J/ApJ/784/3 : The PAWS catalogs of GMCs and islands in M51 (Colombo+, 2014)J/ApJ/789/81 : Multiwavelength survey of HII regions in NGC300 (Faesi+, 2014)J/ApJ/808/42 : CHemical Abundances of Spirals II. M51 (Croxall+, 2015)J/ApJ/833/229 : Star forming cloud-giant MC complexes (Lee+, 2016)J/A+A/593/A118 : HCN(1-0) cube for the nucleus of M51 (Querejeta+, 2016)J/ApJ/834/57 : MW molecular clouds from ^12^CO (Miville-Deschenes+, 2017)J/ApJ/835/278 : Molecular clouds in the dwarf galaxy NGC6822 (Schruba+, 2017)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/846/71https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/846/71http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/846/71https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/846/71https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/846/71http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/846/71GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/ApJ/846/71/table1 (Cloud-scale structure, IR, and CO in M51)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/846/71/table1?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/846/71/table1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/846/71/table1?GETtext/xml+votable180.050000true202.4696447.195170.0055555555555555566/11027https://cdsarc.cds.unistra.fr/viz-bin/moc/J/ApJ/846/71?format=asciiRadiodefaultJ/ApJ/846/71/table1Cloud-scale structure, IR, and CO in M51recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRAJ2000[202.4/202.6] Right Ascension (J2000)degpos.eq.ra;meta.mainDEJ2000[47.1/47.3] Declination (J2000)degpos.eq.dec;meta.mainBeam[10/30] Beam sizearcsecphys.angSize;instr.beamintRgal[0/5] Galactocentric radius (1)kpcpos.distance;pos.galactocentricfloatSigCO[5/518] CO molecular gas surface density ({Sigma}_mol_) (2)solMass.pc**-2phot.flux.density.sb;em.line.COfloatSigSFR[0.004/0.4] Star formation rate surface density ({Sigma}_SFR_) (3)solMass.yr**-1.kpc**-2phys.SFRfloatSigCO40pc[46.6/841.7] Cloud-scale CO molecular gas surface density (<{Sigma}_40pc_>) (2)solMass.pc**-2phot.flux.density.sb;em.line.COfloatrmsCO40pc[2.5/20.2] Cloud-scale RMS line width of CO (<{sigma}_40pc_>)km/sstat.stdev;spect.line.width;em.line.COfloatb40pc[1/7.7] Boundedness parameter (b={Sigma}/{sigma}^2^ {propto}{alpha}_vir_^-1^) (2)solMass.pc**-2.km**-2.s**-2stat.fit.paramfloatfarm[0/1] Beam fraction, CO flux, arm (4)phot.flux;arith.ratiofloatfia[0/1] Beam fraction, CO flux, interarm (4)phot.flux;arith.ratiofloatfctr[0/1] Beam fraction, CO flux, central region (4)phot.flux;arith.ratiofloat