J/AJ/151/136ivo://CDS.VizieR/J/AJ/151/136doi:10.26093/cds/vizier.51510136CDSHunter D.A.Elmegreen B.G.Gehret E.2018-05-16T07:02:13Z2018-03-21T08:13:23ZCDS support team

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

cds-question@unistra.frgalaxiesopen-star-clustersultraviolet-photometryvisible-astronomybroad-band-photometryWe examine FUV images of the LITTLE THINGS sample of nearby dwarf irregular (dIrr) and Blue Compact Dwarf galaxies to identify distinct young regions in their far outer disks. We use these data, obtained with the Galaxy Evolution Explorer satellite, to determine the furthest radius at which in situ star formation can currently be identified. The FUV knots are found at distances from the center of the galaxies of 1-8 disk scale lengths and have ages of =<20 Myr and masses of 20 M_{sun}_ to 1x10^5^ M_{sun}_. The presence of young clusters and OB associations in the outer disks of dwarf galaxies shows that dIrrs do have star formation taking place there in spite of the extreme nature of the environment. Most regions are found where the H I surface density is ~1 M_{sun}_/pc^2^, though both the H I and dispersed old stars go out much further. This limiting density suggests a cutoff in the ability to form distinct OB associations and perhaps even stars. We compare the star formation rates in the FUV regions to the average rates expected at their radii and beyond from the observed gas, using the conventional correlation for gas-rich regions. The localized rates are typically 10% of the expected average rates for the outer disks. Either star formation in dIrrs at surface densities <1 M_{sun}_/pc^2^ occurs without forming distinct associations, or the Kennicutt-Schmidt relation over-predicts the rate beyond this point. In the latter case, the stellar disks in the far-outer parts of dIrrs result from scattering of stars from the inner disk.2016AJ....151..136Hhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/AJ/151/136CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toII/312 : GALEX-DR5 (GR5) sources from AIS and MIS (Bianchi+ 2011)J/ApJS/162/49 : UBV imaging of irregular galaxies (Hunter+, 2006)J/AJ/136/2563 : HI Nearby Galaxy Survey, THINGS (Walter+, 2008)J/AJ/138/1203 : Star formation regions in nearby dwarf galaxies (Melena+, 2009)J/AJ/144/134 : LITTLE THINGS survey of nearby dwarf galaxies (Hunter+, 2012)J/AJ/146/104 : Dwarf galaxies surface brightness profiles. I.https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/AJ/151/136https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/AJ/151/136http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/AJ/151/136https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/AJ/151/136https://vizier.iucaa.in/viz-bin/votable?-source=J/AJ/151/136http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/AJ/151/136GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/AJ/151/136/table12 (Furthest FUV region (table 1) , photometry, ages and masses of FUV regions (table 2))https://vizier.cds.unistra.fr/viz-bin/conesearch/J/AJ/151/136/table12?https://vizier.iucaa.in/viz-bin/conesearch/J/AJ/151/136/table12?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/AJ/151/136/table12?GETtext/xml+votable180.050000true189.657532.7611110.0055555555555555566/3389 4522 4746 5293 5607 5978 6399 6502 6560 7523 7769 7799 7876 7956 7970 8028 8908 10762 10881 10970 11019 11041 11143 17165 18041 19833 19990 26858 27351 28149 28510 28610 28631 28636 29699 29718 489421.1848962891990175e-18 1.4134638842407062e-18https://cdsarc.cds.unistra.fr/viz-bin/moc/J/AJ/151/136?format=asciiUVOpticaldefaultJ/AJ/151/136/table12Furthest FUV region (table 1) , photometry, ages and masses of FUV regions (table 2)SimbadNameSimbad column added by the CDSmeta.idchare_RBr[0/1.35]? Uncertainty in RBrkpcstat.errorfloatnullablerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintIDGalaxy identifiermeta.id;meta.maincharDist[0.5/10.3] DistanceMpcpos.distancefloatRD[0.16/3.16] Disk scale length (1)kpcphys.angSize;srcfloate_RD[0/0.25] Uncertainty in RDkpcstat.errorfloatRBr[0.13/2.80]? Radius at which V-band surface brightness profile changes slope (1)kpcphys.size.radiusfloatnullableRAJ2000Hour of Right Ascension (J2000) (2)pos.eq.ra;meta.mainDEJ2000Degree of Declination (J2000) (2)pos.eq.dec;meta.mainRk[0.29/6.79] Radius of furthest FUV knot (3)kpcphys.size.radiusfloate_Rk[0/0.10] Uncertainty in Rkkpcstat.errorfloatRk/RD[0.6/7.7] Ratio of Rk to RDphys.size;arith.ratiofloate_Rk/RD[0/0.9] Uncertainty in Rk/RDstat.errorfloatRk/RBr[0.3/10.3]? Ratio of Rk to RBrphys.size;arith.ratiofloatnullablee_Rk/RBr[0.1/5.5]? Uncertainty in Rk/RBrstat.errorfloatnullableE(B-V)[0.050/0.558] The (B-V) color excessmagphot.color.excessfloatRad[4.2/120] Radius of photometry aperturearcsecphys.size.radiusfloatFUVmag[16.175/23.321] GALEX FUV band AB magnitudemagphot.mag;em.UVfloatFUVMag[-12.276/-0.905] GALEX FUV band absolute AB magnitude (1)magphys.magAbs;em.UV.100-200nmfloate_FUVMag[0.008/0.395] Uncertainty in FUVMagmagstat.error;phot.mag;em.UV.100-200nmfloat(F-N)[-1.178/0.176] GALEX (FUV-NUV) band color (1)magphot.color;em.UVfloate_(F-N)[0.009/0.611] Uncertainty in (F-N)magstat.errorfloatVMag[-13.063/-2.787]? Absolute V band magnitude (1)magphys.magAbs;em.opt.Vfloatnullablee_VMag[0.001/0.832]? Uncertainty in VMagmagstat.error;phot.mag;em.opt.Vfloatnullable(B-V)[-1.063/0.927]? The (B-V) color (1)magphot.color;em.opt.B;em.opt.Vfloatnullablee_(B-V)[0.002/0.885]? Uncertainty in (B-V)magstat.errorfloatnullable(U-B)[-1.730/0.725]? The (U-B) color (1)magphot.color;em.opt.U;em.opt.Bfloatnullablee_(U-B)[0.002/0.713]? Uncertainty in (U-B)magstat.errorfloatnullableNfit[0/3] Number of colors used in age determination (2)meta.numberintAge[2/20]? Cluster ageMyrtime.ageintnullablee_Age[1/12]? Uncertainty in Age (3)Myrstat.error;time.ageintnullableMass[16/130000]? Cluster masssolMassphys.massintnullablee_Mass[1/87000]? Uncertainty in MasssolMassstat.error;phys.massintnullable