J/AJ/157/241ivo://CDS.VizieR/J/AJ/157/241doi:10.26093/cds/vizier.51570241CDSHunter D.A.Elmegreen B.G.Berger C.L.2019-08-28T11:38:26Z2019-08-26T14:22:31ZCDS support team

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

cds-question@unistra.frgalaxiesmolecular-cloudsh-i-line-emissionWe identify 814 discrete H I clouds in 40 dwarf irregular galaxies from the LITTLE THINGS survey using an automated cloud-finding algorithm. The cloud masses range from ~10^3^ to 10^7^ M_{sun}_, have a surface density averaged over all of the clouds of ~9.65 M_{sun}_/pc^2^, and constitute 2%-53% of the total H I mass of the host galaxy. For individual clouds, the mass including He varies with cloud radius as logM_gas_=(2.11+/-0.04)xlogR_cl_+(0.78+/-0.08) and the internal velocity dispersion varies as logV_disp_=0.5xlogR_cl_-0.57+/-0.21. The H I clouds tend to be in the outer regions of the galaxies, with 72% of the galaxies having more than 70% of their clouds outside one disk scale length and 32% of the galaxies having more than 50% of their clouds outside the radius encircling the H II emission. Thirty-six percent of the clouds are essentially non-self-gravitating from H I alone, with a virial parameter that exceeds {alpha}_vir_~10, and 5% have {alpha}_vir_=<2. We estimate the missing molecular mass, based on the total star formation rate and a typical molecular consumption time of 2 Gyr, as observed in CO-rich galaxies. The resulting molecular fraction has a value averaged over the galaxies of 0.23 and correlates with both the surface density of star formation and the fraction of H I clouds in the outer regions. We conclude that a significant fraction of the inner parts of these dwarf galaxy disks is in the form of dark molecular gas, and that this fraction could be high enough to make the inner disks mildly gravitationally unstable as a precursor to star formation.2019AJ....157..241Hhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/AJ/157/241CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/AJ/128/2170 : H{alpha} imaging of irregular galaxies (Hunter+, 2004)J/ApJ/636/214 : HII regions in dwarf irregular galaxies (van Zee+, 2006)J/AJ/136/2563 : HI Nearby Galaxy Survey, THINGS (Walter+, 2008)J/AJ/136/2782 : Star formation efficiency in nearby galaxies (Leroy+, 2008)J/AJ/140/1194 : FUV/HI relations in nearby galaxies (Bigiel+, 2010)J/AJ/144/134 : LITTLE THINGS survey of nearby dwarf galaxies (Hunter+, 2012)J/AJ/146/104 : Dwarf galaxies surface brightness profiles. I.J/AJ/151/136 : LITTLE THINGS dwarf irregular galaxies FUV regionshttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/AJ/157/241https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/AJ/157/241http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/AJ/157/241https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/AJ/157/241https://vizier.iucaa.in/viz-bin/votable?-source=J/AJ/157/241http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/AJ/157/241GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/AJ/157/241/galaxies (galaxies (table 1) and galaxy cloud properties (table 3))https://vizier.cds.unistra.fr/viz-bin/conesearch/J/AJ/157/241/galaxies?https://vizier.iucaa.in/viz-bin/conesearch/J/AJ/157/241/galaxies?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/AJ/157/241/galaxies?GETtext/xml+votable180.050000true189.667083332.76638890.005555555555555556Cone search capability for table J/AJ/157/241/table2 (Cloud catalog)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/AJ/157/241/table2?https://vizier.iucaa.in/viz-bin/conesearch/J/AJ/157/241/table2?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/AJ/157/241/table2?GETtext/xml+votable180.050000true189.67041732.7688890.0055555555555555566/3042 3389 4522 4746 5287 5293 5607 5978 6399 6502 6560 7523 7769 7799 7876 7878 7956 7970 8028 8908 10762 10881 10970 11019 11041 11120 11143 11933 17165 18041 19833 19990 22495 26858 27351 27926 28149 28510 28610 28631 28636 29699 48942https://cdsarc.cds.unistra.fr/viz-bin/moc/J/AJ/157/241?format=asciiRadiodefaultJ/AJ/157/241/galaxiesgalaxies (table 1) and galaxy cloud properties (table 3)SimbadNameSimbad column added by the CDSmeta.idcharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintGalaxyGalaxy identifiermeta.id;meta.maincharDist[0.7/10.3] DistanceMpcpos.distance;pos.heliocentricfloatBeam[19/424] Beam size (1)pcphys.angSize;instr.beamintlogSFR[-3.88/-0.01]? Integrated star formation rate (2)log(solMass.yr**-1.kpc**-2)meta.idfloatnullablee_logSFR[0/0.06]? Uncertainty in logSFRlog(solMass.yr**-1.kpc**-2)stat.error;phys.SFRfloatnullablelogMHI[5.19/8.85] Total H I mass of the galaxy from Hunter et al. (2012, J/AJ/144/134)log(solMass)phys.massfloatRBr[0.13/2.8]? Radius at which the V-band surface brightness profile changes slope (Herrmann et al. 2013, J/AJ/146/104)kpcphys.size.radiusfloatnullablee_RBr[0/1.35]? Uncertainty in RBrkpcstat.errorfloatnullableRD[0.15/2.24] Disk scale length determined from the V-band (Herrmann et al. 2013, J/AJ/146/104)kpcsrc.morph.scLengthfloate_RD[0/0.25] Uncertainty in RDkpcstat.errorfloatRHa[0.3/5.58]? Extent of H{alpha} emission, R_H{alpha}_ (Hunter & Elmegreen 2004, J/AJ/128/2170)kpcphys.size.diameterfloatnullableRFUV[0.29/6.79]? Radius of the furthest out FUV knot identified on GALEX images (Hunter et al. 2016, J/AJ/151/136)kpcphys.size.radiusfloatnullablee_RFUV[0.01/0.1]? Uncertainty in RFUVkpcstat.errorfloatnullableNcl[1/161] Number of clouds identified in galaxymeta.numberintlogMcl[3.89/7.73] Log cloud masslog(solMass)phys.massfloatMcl/MHI[0.02/0.53] Ratio of cloud mass to total H I massphys.mass;arith.ratiofloatlogM3rd[3.24/6.59]? H I mass of third most massive cloud for galaxies with at least three cloudslog(solMass)phys.massfloatnullableFr-RBr[0/1]? Fraction of clouds beyond the break radius R_Br_statfloatnullableFr-RD[0/1] Fraction of clouds beyond one disk scale length R_D_statfloatFr-RHa[0/1]? Fraction of clouds beyond the extent of H{alpha} emission R_H{alpha}_statfloatnullableFr-RFUV[0/1]? Fraction of clouds beyond the furthest FUV knot R_FUV_statfloatnullable_RARight Ascension (J2000) from SIMBAD (not part of the original data)degpos.eq.ra;meta.main_DEDeclination (J2000) from SIMBAD (not part of the original data)degpos.eq.dec;meta.mainJ/AJ/157/241/table2Cloud catalogGalaxyGalaxy identifiermeta.id;meta.maincharCloud[1/161] Cloud identifiermeta.idintrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRAJ2000Hour of Right Ascension (J2000)pos.eq.ra;meta.mainDEJ2000Degree of Declination (J2000)pos.eq.dec;meta.mainVcen[-395.1/632] Central velocitykm/sphys.veloc;em.wl.centralfloatPA[-90.0/89.7] Position angledegpos.posAngfloatRcl[15/817] Cloud major axis radiuspcphys.sizeinte_Rcl[2/88] Uncertainty in Rclpcstat.errorintRatio[0.15/0.96] Minor-to-major axis ratiophys.size.axisRatiofloatS/N[4.3/61.2] Peak signal-to-noise ratiostat.snr;stat.maxfloatVdisp[0/12.8] Velocity dispersionkm/sphys.veloc.dispersionfloate_Vdisp[0/1.5] Uncertainty in Vdispkm/sstat.errorfloatlogMg[3.24/7.22] Log gas mass; H I + Helog(solMass)phys.massfloate_logMg[0.01/0.16] Uncertainty in logMglog(solMass)stat.errorfloatSgas[0.4/927.1] Gas surface density {Sigma}_gaz_solMass.pc**-2phot.flux.density.sbfloate_Sgas[0.1/168.8] Uncertainty in SgassolMass.pc**-2stat.errorfloatRgal[0.1/6.9] Radius from galaxy centerkpcphys.size.radiusfloatalpha[0.5/222.8]? Virial ratio {alpha}_vir_phys.mass;arith.ratiofloatnullablee_alpha[0/30.7]? Uncertainty in alphastat.error;pos.eq.rafloatnullable