J/ApJ/730/88ivo://CDS.VizieR/J/ApJ/730/88doi:10.26093/cds/vizier.17300088CDSEfremova B.V.Bianchi L.Thilker D.A.Neill J.D.Burgarella D.,Wyder T.K.Madore B.F.Rey S.-C.Barlow T.A.Conrow T.Forster K.,Friedman P.G.Martin D.C.Morrissey P.Neff S.G.Schiminovich D.,Seibert M.Small T.2017-06-29T08:56:16Z2013-06-05T13:57:00ZCDS support team

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

cds-question@unistra.frgalaxiesultraviolet-photometryvisible-astronomyh-alpha-photometryextinctionh-ii-regionsastronomical-object-identificationWe characterize the star formation in the low-metallicity galaxy NGC 6822 over the past few hundred million years, using GALEX far-UV (FUV, 1344-1786{AA}) and near-UV (NUV, 1771-2831{AA}) imaging, and ground-based H{alpha} imaging. From the GALEX FUV image, we define 77 star-forming (SF) regions with area >860pc^2^, and surface brightness <~26.8 mag (AB) arcsec^-2^, within 0.2{deg} (1.7kpc) of the center of the galaxy. We estimate the extinction by interstellar dust in each SF region from resolved photometry of the hot stars it contains: E(B-V) ranges from the minimum foreground value of 0.22mag up to 0.66+/-0.21mag. The integrated FUV and NUV photometry, compared with stellar population models, yields ages of the SF complexes up to a few hundred Myr, and masses from 2x10^2^M_{sun}_ to 1.5x10^6^M_{sun}_. The derived ages and masses strongly depend on the assumed type of interstellar selective extinction, which we find to vary across the galaxy. The total mass of the FUV-defined SF regions translates into an average star formation rate (SFR) of 1.4x10^-2^M_{sun}_/yr over the past 100Myr, and SFR=1.0x10^-2^M_{sun}_/yr in the most recent 10Myr. The latter is in agreement with the value that we derive from the H{alpha} luminosity, SFR=0.008M_{sun}_/yr. The SFR in the most recent epoch becomes higher if we add the SFR=0.02M_{sun}_/yr inferred from far-IR measurements, which trace star formation still embedded in dust (age <~ a few Myr).2011ApJ...730...88Ehttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/730/88CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toII/312 : GALEX-DR5 (GR5) sources from AIS and MIS (Bianchi+ 2011)VI/110 : Final Merged Log of IUE Observations (NASA-ESA, 2000)J/ApJS/192/6 : A GALEX UV imaging survey of nearby galaxies (Lee+, 2011)J/A+A/495/447 : PN and HII regions in NGC6822 (Hernandez-Martinez+, 2009)J/AJ/138/1203 : SF regions in nearby dwarf galaxies (Melena+, 2009)J/ApJ/706/599 : H{alpha} and UV SFR in the local volume (Lee+, 2009)J/ApJS/178/247 : H{alpha} and [NII] survey in local 11 Mpc (Kennicutt+, 2008)J/AJ/133/2393 : UBVRI phot. in 7 Local Group dwarfs galaxies (Massey+, 2007)J/AJ/134/2474 : Ha emission-line stars in 7 dwarfs galaxies (Massey+, 2007)J/AJ/132/378 : HST and UV photometry of NGC 6822 (Bianchi+, 2006)J/AJ/128/2170 : H{alpha} imaging of irregular galaxies (Hunter+, 2004)J/AJ/121/2020 : CTIO and WFPC2 photometry in NGC 6822 (Bianchi+, 2001)J/AJ/110/2715 : UBV photometry in NGC 6822, M31 and M33 (Massey+ 1995)J/A+AS/109/341 : UV properties of normal galaxies. II. (Rifatto+, 1995)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/730/88https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/730/88http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/730/88https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/730/88https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/730/88http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/730/88GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/ApJ/730/88/uv_sfr (Far-UV-selected star-forming region properties , ages and masses assuming different extinction curves)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/730/88/uv_sfr?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/730/88/uv_sfr?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/730/88/uv_sfr?GETtext/xml+votable180.050000true296.06025-14.77752780.005555555555555556Cone search capability for table J/ApJ/730/88/table2 (H{alpha} emission regions)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/730/88/table2?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/730/88/table2?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/730/88/table2?GETtext/xml+votable180.050000true296.1287083-14.78880560.0055555555555555566/29716 29718https://cdsarc.cds.unistra.fr/viz-bin/moc/J/ApJ/730/88?format=asciiUVOpticaldefaultJ/ApJ/730/88/uv_sfrFar-UV-selected star-forming region properties , ages and masses assuming different extinction curvesCommComment (6)meta.notecharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintID[1/77] FUV SF region identification number (<[EBT2011] EB-FUV NN> in Simbad) (1)meta.id;obs.fieldintn_ID[g] FUV source associated to H{alpha} emissionmeta.notecharRAJ2000[19] Hour of right ascension (J2000) (G1)pos.eq.ra;meta.mainDEJ2000[14] Degree of declination (J2000) (G1)pos.eq.dec;meta.mainArea1[150/5400] SF region area in arcsec^2^arcsec**2phys.angSizeintArea2Area in parsec^2^pc**2phys.areaintFUV[15.46/20.55] FUV (1344-1786{AA}) band AB magnitudemagphot.mag;em.UV.100-200nmfloate_FUV[0.01/0.06] FUV uncertainty (3)magstat.errorfloatNUVNUV (1771-2831{AA}) band AB magnitudemagphot.mag;em.UVfloate_NUVNUV uncertainty (3)magstat.errorfloatfFUV[0/1] Background fraction of FUV (4)phot.flux;arith.ratiofloatfNUV[0/1] Background fraction of NUV (4)phot.flux;arith.ratiofloatE(B-V)[0.22/0.66] Interstellar reddening (5)magphot.color.excessfloate_E(B-V)1{sigma} scatter in E(B-V) (5)magstat.errorfloatAge0[2/374] Age with Milky-Way type Rv=3.1 (2)Myrmeta.note;time.ageintE_Age0Positive error on Age0Myrstat.error;stat.maxinte_Age0Negative error on Age0Myrstat.errorintM0[0.2/1500] Mass with Milky-Way type Rv=3.1 (2)ksolMassmeta.note;phys.massfloatE_M0Positive error on M0ksolMassstat.error;stat.maxfloate_M0Negative error on M0ksolMassstat.errorfloatAge1? Age with LMC exinction (2)Myrtime.ageintnullableE_Age1? Positive error on Age1Myrstat.error;stat.maxintnullablee_Age1? Negative error on Age1Myrstat.errorintnullableM1? Mass with LMC exinction (2)ksolMassphys.massfloatnullableE_M1? Positive error on M1ksolMassstat.error;stat.maxfloatnullablee_M1? Negative error on M1ksolMassstat.errorfloatnullableAge2? Age with LMC2 extinction(2)Myrphys.absorptionintnullableE_Age2? Positive error on Age2Myrstat.error;stat.maxintnullablee_Age2? Negative error on Age2Myrstat.errorintnullableM2? Mass with LMC2 extinction (2)ksolMassphys.absorptionfloatnullableE_M2? Positive error on M2ksolMassstat.error;stat.maxfloatnullablee_M2? Negative error on M2ksolMassstat.errorfloatnullableECExtinction curve type adopted (2)meta.id;stat.fitcharJ/ApJ/730/88/table2H{alpha} emission regionsSimbadNameSimbad column added by the CDSmeta.idcharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintID[1/39] H{alpha} region identification number (<[EBT2011] EB-Ha NN> in Simbad)meta.id;obs.fieldintRAJ2000[19] Hour of right ascension (J2000) (G1)pos.eq.ra;meta.mainDEJ2000[14] Degree of declination (J2000) (G1)pos.eq.dec;meta.mainArea1[150/9500] Area in arcsec^2^arcsec**2phys.angSizeintArea2Area in pc^2^pc**2phys.areaintFHa[0.03/50.74] H{alpha} flux in units of 10^-13^erg/s/cm^2^1e-16W.m**-2phot.flux;em.line.Halphafloate_FHa[0.02/3.49] FHa uncertainty1e-16W.m**-2stat.errorfloatCommCross-identifications and comments (1)meta.id.crosschar