J/MNRAS/465/3977ivo://CDS.VizieR/J/MNRAS/465/3977doi:10.26093/cds/vizier.74653977CDSJames B.L.Koposov S.E.Stark D.P.Belokurov V.Pettini M.,Olszewski E.W.Mcquinn K.B.W.2024-08-16T20:20:17Z2019-06-05T11:58:46ZCDS support team

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

cds-question@unistra.frgalaxiesspectroscopyThe search for chemically unevolved galaxies remains prevalent in the nearby Universe, mostly because these systems provide excellent proxies for exploring in detail the physics of high-z systems. The most promising candidates are extremely metal-poor galaxies (XMPs), i.e. galaxies with <1/10 solar metallicity. However, due to the bright emission-line-based search criteria traditionally used to find XMPs, we may not be sampling the full XMP population. In 2014, we reoriented this search using only morphological properties and uncovered a population of ~150 'blue diffuse dwarf (BDD) galaxies', and published a sub-sample of 12 BDD spectra. Here, we present optical spectroscopic observations of a larger sample of 51 BDDs, along with their Sloan Digital Sky Survey (SDSS) photometric properties. With our improved statistics, we use direct-method abundances to confirm that BDDs are chemically unevolved (7.43<12+log(O/H)<8.01), with ~20 per cent of our sample classified as being XMP galaxies, and find that they are actively forming stars at rates of ~1-33x10^-2^M_{sun}_/yr in HII regions randomly embedded in a blue, low-surface-brightness continuum. Stellar masses are calculated from population synthesis models and estimated to be in the range log (M_*_/M_{sun}_)~=5-9. Unlike other low-metallicity star-forming galaxies, BDDs are in agreement with the mass-metallicity relation at low masses, suggesting that they are not accreting large amounts of pristine gas relative to their stellar mass. BDD galaxies appear to be a population of actively star-forming dwarf irregular (dIrr) galaxies which fall within the class of low-surface-brightness dIrr galaxies. Their ongoing star formation and irregular morphology make them excellent analogues for galaxies in the early Universe.2017MNRAS.465.3977Jhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/MNRAS/465/3977CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/MNRAS/448/2687 : Blue diffuse dwarf galaxies spectroscopic data (James+ 2015)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/MNRAS/465/3977https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/MNRAS/465/3977http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/MNRAS/465/3977https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/MNRAS/465/3977https://vizier.iucaa.in/viz-bin/votable?-source=J/MNRAS/465/3977http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/MNRAS/465/3977GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/MNRAS/465/3977/table14 (Blue diffuse dwarfs galaxies in the current observed (table 1) and photometric properties calculated from SDSS images (table 4))https://vizier.cds.unistra.fr/viz-bin/conesearch/J/MNRAS/465/3977/table14?https://vizier.iucaa.in/viz-bin/conesearch/J/MNRAS/465/3977/table14?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/MNRAS/465/3977/table14?GETtext/xml+votable180.050000true241.9759.117780.0055555555555555566/627 648 697 766 993 2148 4169 4906 5195 5472 5675 5706 5773 5847 5983 6085 6448 6598 7234 7282 7374 7606 7843 8717 10332 10435 10689 10775 11406 12310 17574 17697 17984 18286 18362 18975 19534 19565 19571 19851 20091 20416 21989 23279 27618 27826 28441 28458 28486 316313.588997330618193e-19 4.653515163505597e-19https://cdsarc.cds.unistra.fr/viz-bin/moc/J/MNRAS/465/3977?format=asciidefaultJ/MNRAS/465/3977/table14Blue diffuse dwarfs galaxies in the current observed (table 1) and photometric properties calculated from SDSS images (table 4)Dist? DistanceMpcpos.distanceintnullablerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintMassindicates stellar masses in table 5meta.ref.urlcharJKB[1/144] JKB identification numbermeta.id;meta.mainintprimarySDSSSDSS name, JHHMMSS.ss+DDMMSS.smeta.idcharAGC? AGC identification numbermeta.idintnullableRAJ2000Right ascension (J2000)pos.eq.ra;meta.mainDEJ2000Declination (J2000)pos.eq.dec;meta.mainz? Redshift (1)src.redshiftdoublenullablen_Dist[*)] Note on Dist (2)meta.notecharPASlit position angle of first exposure of the MMT observationsdegpos.posAng;obs.exposureintPA2? Slit position angle value of second exposure of the MMT observationsdegpos.posAng;obs.exposureintnullableTexpExposure time of first exposure of the MMT observationsstime.duration;obs.exposurecharTexp2? Exposure time of second exposure of the MMT observationsstime.duration;obs.exposurecharObs.DateUT date of the MMT observationstime.epoch;obscharn_JKB[*] Note on JKB (1)meta.notecharf_JKB[a] a for Known to be a single HII region within M 81meta.codechargmagSDSS g magnitudemagphot.mag;em.opt.Bfloatu-g? SDSS u-g colour indexmagphot.color;em.opt.U;em.opt.Bfloatnullableg-rSDSS g-r colour indexmagphot.color;em.opt.B;em.opt.Rfloatr-iSDSS r-i colour indexmagphot.color;em.opt.R;em.opt.Ifloati-zSDSS i-z colour indexmagphot.color;em.opt.I;em.opt.IfloatbMAG? Absolute B magnitude (2)magphys.magAbs;em.opt.BfloatnullableSuBrVSurface brightness in V bandmag.arcsec**-2phot.mag.sbfloatSimbadSimbad column added by the CDSmeta.ref.urlcharJ/MNRAS/465/3977/table2Ionic and elemental abundances for the BDD galaxies presented in this paper, derived from the emission-line measurements given in Table A1recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintJKBJKB identification numbermeta.id;meta.maincharNeElectron density, Ne([OII],[SII])cm**-3phys.density;phys.electronfloatE_NeError on Ne (upper value)cm**-3stat.error;stat.maxfloate_NeError on Ne (lower value)cm**-3stat.errorfloatl_Te[OIII]Limit flag on Te[OIII]meta.code.errorcharTe[OIII]Electron temperature from [OIII]Kphys.temperature.electron;phys.electroninte_Te[OIII]? rms uncertainty on Te[OIII]Kstat.errorintnullablel_Te[OII]Limit flag on Te[OII]meta.code.errorcharTe[OII]Electron temperature from [OII]Kphys.temperature.electron;phys.electroninte_Te[OII]? rms uncertainty on Te[OII]Kstat.errorfloatnullablel_O+/H+Limit flag on O+/H+meta.code.error;phys.abundcharO+/H+O+/H+ line ratiospect.line.intensity;arith.ratiofloate_O+/H+? rms uncertainty on O+/H+stat.error;phys.abundfloatnullablel_O2+/H+Limit flag on O2+/H+meta.code.error;phys.abundcharO2+/H+O2+/H+ line ratiospect.line.intensity;arith.ratiofloate_O2+/H+? rms uncertainty on O2+/H+stat.error;phys.abundfloatnullablel_12+log(O/H)Limit flag on 12+log(O/H)meta.code.errorchar12+log(O/H)Abundance 12+log(O/H)phys.abundfloate_12+log(O/H)? rms uncertainty on 12+log(O/H)stat.errorfloatnullablel_log(N/O)Limit flag on log(N/O)meta.code.errorcharlog(N/O)? Abundance log(N/O)phys.abundfloatnullablee_log(N/O)? rms uncertainty on log(N/O)stat.errorfloatnullablel_[O/H]Limit flag on [O/H]meta.code.error;phys.abundchar[O/H]Abundance [O/H]phys.abundfloate_[O/H]? rms uncertainty on [O/H]stat.error;phys.abundfloatnullableJ/MNRAS/465/3977/table3Physical properties of the new, extended sample of BDD galaxiesJKBJKB identification numbermeta.id;meta.maincharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintn_JKB[*] * for objects with uncertain distances, i.e. D<20Mpcmeta.notecharLHaH{alpha} luminosity for HII region1e+31Wphys.luminosity;em.line.Halphafloate_LHarms uncertainty on LHa1e+31Wstat.errorfloatSFRHaH{alpha} star formation rate for HII region0.01solMass.yr**-1phys.SFRfloate_SFRHarms uncertainty on SFRHa0.01solMass.yr**-1stat.errorfloatLHatot? Total H{alpha} luminosity (entire galaxy)1e+31Wphys.luminosity;em.line.Halphafloatnullablee_LHatot? rms uncertainty on LHatot1e+31Wstat.errorfloatnullableSFRHatot? Total H{alpha} star formation rate (entire galaxy)0.01solMass.yr**-1phys.SFRfloatnullablee_SFRHatot? rms uncertainty on SFRHatot0.01solMass.yr**-1stat.errorfloatnullablel_AgeLimit flag on Agemeta.code.error;time.agecharAgeAge, determined from EW(H{alpha}) and EW(H{beta})Myrtime.agefloate_Age? rms uncertainty on AgeMyrstat.error;time.agefloatnullableJ/MNRAS/465/3977/table5Stellar masses derived from stellar population synthesis and SDSS colours listed in Table 4recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintJKBJKB identification numbermeta.id;meta.mainintn_JKB[*] * for object with uncertain distances, i.e. D<20Mpcmeta.notecharf_JKB[a] a for Known to be a single HII region within M 81meta.codecharlogM*Stellar masslog(solMass)phys.massfloate_logM*rms uncertainty on logM*log(solMass)stat.errorfloatlogSSFRSpecific star formation rate derived from M* and total SFRs listed in Table 3log(yr**-1)meta.idfloate_logSSFRrms uncertainty on logSSFRlog(yr**-1)stat.errorfloatJ/MNRAS/465/3977/tablea1bH{beta} parameters for sources of table A1recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintJKBJKB identification numbermeta.id;meta.maincharFHbH{beta} line flux (in 10^-16^erg/s/cm^2^)1e-19W.m**-2phot.flux;em.line.Hbetafloate_FHbrms uncertainty on FHb1e-19W.m**-2stat.errorfloatIntHbH{beta} line intensity (in 10^-16^erg/s/cm^2^)1e-19W.m**-2spect.line.intensityfloate_IntHbrms uncertainty on IntHb1e-19W.m**-2stat.errorfloatE(B-V)Color excessmagphot.color.excessfloate_E(B-V)rms uncertainty on E(B-V)magstat.errorfloatJ/MNRAS/465/3977/tablea1Spectroscopic line fluxes and de-reddened line intensities as measured from the spectra shown in Fig. B1recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintJKBJKB identification numbermeta.id;meta.maincharElElementphys.atmol.elementcharl_FluxLimit flag on Fluxmeta.code.error;phot.fluxcharFlux? Line flux relative to H{beta}=100phot.flux;arith.ratiofloatnullablee_Flux? rms uncertainty on Fluxstat.error;phot.fluxfloatnullablel_IntLimit flag on Intmeta.code.errorcharInt? De-reddened line intensity relative to H{beta}=100spect.line.intensity;arith.ratiofloatnullablee_Int? rms uncertainty on Intstat.errorfloatnullable