J/ApJ/835/278ivo://CDS.VizieR/J/ApJ/835/278doi:10.26093/cds/vizier.18350278CDSSchruba A.Leroy A.K.Kruijssen J.M.D.Bigiel F.Bolatto A.D.,de Blok W.J.G.Tacconi L.van Dishoeck E.F.Walter F.2020-01-29T14:07:00Z2017-10-04T08:17:33ZCDS support team

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

cds-question@unistra.frmolecular-cloudsmillimeter-astronomysubmillimeter-astronomygalaxiesco-line-emissionWe present the Atacama Large Millimeter/submillimeter Array survey of CO(2-1) emission from the 1/5 solar metallicity, Local Group dwarf galaxy NGC 6822. We achieve high (0.9"~2pc) spatial resolution while covering a large area: four 250pcx250pc regions that encompass ~2/3 of NGC 6822's star formation. In these regions, we resolve ~150 compact CO clumps that have small radii (~2-3pc), narrow line width (~1km/s), and low filling factor across the galaxy. This is consistent with other recent studies of low-metallicity galaxies, but here shown with a 15x larger sample. At parsec scales, CO emission correlates with 8{mu}m emission better than with 24{mu}m emission and anticorrelates with H{alpha}, so that polycyclic aromatic hydrocarbon emission may be an effective tracer of molecular gas at low metallicity. The properties of the CO clumps resemble those of similar-size structures in Galactic clouds except of slightly lower surface brightness and with CO-to-H_2_ ratio ~1-2x the Galactic value. The clumps exist inside larger atomic-molecular complexes with masses typical for giant molecular clouds. Using dust to trace H_2_ for the entire complex, we find the CO-to-H_2_ ratio to be ~20-25x the Galactic value, but with strong dependence on spatial scale and variations between complexes that may track their evolutionary state. The H_2_-to-HI ratio is low globally and only mildly above unity within the complexes. The ratio of star formation rate to H_2_ is ~3-5x higher in the complexes than in massive disk galaxies, but after accounting for the bias from targeting star-forming regions, we conclude that the global molecular gas depletion time may be as long as in massive disk galaxies.2017ApJ...835..278Shttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/835/278CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/AJ/121/2020 : CTIO and WFPC2 photometry in NGC 6822 (Bianchi+, 2001)J/ApJ/551/852 : FCRAO CO survey of the outer Galaxy (Heyer+, 2001)J/ApJS/144/47 : Outer galaxy molecular cloud catalog (Brunt+, 2003)J/AJ/128/16 : HIPASS Bright Galaxy Catalog (Koribalski+, 2004)J/AJ/132/378 : HST and UV photometry of NGC 6822 (Bianchi+, 2006)J/A+A/462/L17 : Dense cores in interstellar molecular clouds (Alves+, 2007)J/ApJS/178/56 : CO observations of LMC Giant Molecular clouds (Fukui+, 2008)J/ApJ/699/742 : Properties of cores in the Pipe Nebula (Rathborne+, 2009)J/AJ/140/1194 : FUV/HI relations in nearby galaxies (Bigiel+, 2010)J/AJ/141/23 : HI holes in THINGS galaxies (Bagetakos+, 2011)J/ApJS/196/18 : CO survey of galactic molecular clouds. II. (Bieging+, 2011)J/ApJ/730/88 : Star-forming regions in NGC 6822 from UV (Efremova+, 2011)J/ApJS/197/16 : CO observations of LMC molecular clouds (MAGMA). (Wong+, 2011)J/AJ/143/74 : HST photometry in 6 dwarf galaxies (Bianchi+, 2012)J/AJ/143/133 : Dwarf galaxies from the ALFALFA survey (Huang+, 2012)J/AJ/144/134 : LITTLE THINGS survey of nearby dwarf galaxies (Hunter+, 2012)J/ApJ/774/73 : ALMA CO observations of 30 Dor (Indebetouw+, 2013)J/ApJ/794/107 : Distance to NGC6822 with Spitzer/FourStar data (Rich+, 2014)J/A+A/580/A112 : THOR. The HI, OH, Recombination Line Survey (Bihr+, 2015)J/ApJ/813/42 : O and B type stars in W3: first results (Kiminki+, 2015)J/A+A/582/A121 : Dust properties in galaxies (Remy-Ruyer+, 2015)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/835/278https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/835/278http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/835/278https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/835/278https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/835/278http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/835/278GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/ApJ/835/278/table6 (Molecular cloud catalog)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/835/278/table6?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/835/278/table6?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/835/278/table6?GETtext/xml+votable180.050000true296.265833-14.7266670.0055555555555555566/29718https://cdsarc.cds.unistra.fr/viz-bin/moc/J/ApJ/835/278?format=asciiMillimeterRadiodefaultJ/ApJ/835/278/table6Molecular cloud cataloge_alpha[0.2/38]? Uncertainty in alphastat.error;pos.eq.rafloatnullablerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintSeqGMC running sequence numbermeta.id;meta.mainintRAJ2000[19] Hour of Right Ascension (J2000)pos.eq.ra;meta.mainDEJ2000[14] Degree of Declination (J2000)pos.eq.dec;meta.mainVLSR[-73/-26] Local Standard of Rest velocitykm/sphys.veloc;pos.lsrfloatTpk[0.7/15] Peak brightness temperatureKphys.temperature;stat.maxfloatS/N[2/33] Peak signal-to-noise ratiostat.snr;stat.maxfloatRmaj[0.9/12]? Major Axis Radiuspcphys.sizefloatnullableRmin[0.2/5]? Minor Axis Radiuspcphys.angSize;srcfloatnullablePA? Position Angle (1)degpos.posAngintnullableRad[0.1/8]? Radiuspcphys.size.radiusfloatnullablee_Rad[0.1/3]? Uncertainty in Radpcstat.errorfloatnullablesigV[0.1/3]? Velocity dispersionkm/sphys.veloc.dispersionfloatnullablee_sigV[0/2]? Uncertainty in sigVkm/sstat.errorfloatnullableLCO[0/9] CO luminosity100K.km.s**-1.pc**2phys.luminosity;em.radiofloate_LCO[0/7] Uncertainty in LCO100K.km.s**-1.pc**2stat.errorfloatMvir[0.2/531]? Mass from virial theorem100solMassphys.massfloatnullablee_Mvir[0/229]? Uncertainty in Mvir100solMassstat.errorfloatnullablealpha[0.5/84]? Virial parameter (ratio of virial to luminous mass)phys.mass;arith.ratiofloatnullableSimbadSimbad column added by the CDSmeta.ref.urlchar