J/AJ/169/301ivo://CDS.VizieR/J/AJ/169/301CDSArcher H.N.Hunter D.A.Elmegreen B.G.Hunt L.K.O'Brien R.,Brinks E.Cigan P.Rubio M.Windhorst R.A.Jansen R.A.Mathews E.P.2026-04-02T06:28:33Z2026-03-03T08:52:21ZCDS support team

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

cds-question@unistra.frhst-photometrystar-forming-regionsstellar-massesstellar-agesco-line-emissiondwarf-galaxiesmolecular-cloudsWe investigate the stellar populations and molecular gas properties of a star- forming region within the dwarf irregular (dIrr) galaxy Wolf-Lundmark-Mellote (WLM). Low-metallicity dIrrs like WLM offer a valuable window into star formation in environments that are unlike those of larger, metal-rich galaxies such as the Milky Way. In these conditions, carbon monoxide (CO), typically used to trace molecular clouds, is more easily photodissociated by ultraviolet (UV) radiation, leading to a larger fraction of CO-dark molecular gas, where H2 exists without detectable CO emission, or CO-dark gas in the form of cold H i. Understanding the molecular gas content and the stellar populations in these star-forming regions provides important information about the role of CO-bright and CO-dark gas in forming stars. Using Hubble Space Telescope imaging across five Wide Field Camera 3 UVIS bands and CO observations from the Atacama Large Millimeter Array, we examine stellar populations within and outside CO cores and the photodissociation region. Our findings indicate similar physical characteristics such as age and mass across the different environments. Assuming 2% of molecular gas is converted to stars, we estimate the molecular gas content and determine that CO-dark gas constitutes a large fraction of the molecular reservoir in WLM. These results are consistent with molecular gas estimates using a previous dust-derived CO-to-H_2_ conversion factor ({alpha}_CO_) for WLM. These findings highlight the critical role of CO- dark gas in low-metallicity star formation.2025AJ....169..301Ahttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/AJ/169/301CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/AJ/136/2782 : Star formation efficiency in nearby galaxies (Leroy+, 2008)J/ApJ/703/517 : The Spitzer Local Volume Legacy: IR photometry (Dale+, 2009)J/AJ/144/134 : LITTLE THINGS survey of nearby dwarf galaxies (Hunter+, 2012)J/A+A/589/A28 : N66, N88 & N25+N26 emission line maps (Requena-Torres+, 2016)J/A+A/643/A141 : Tracing total molecular gas in galaxies (Madden+, 2020)J/ApJ/907/112 : The astrophysical dist. scale. III. The WLM gal. (Lee+, 2021)J/ApJS/260/41 : Dust extinction law in nearby galaxies. II. M33 (Wang+, 2022)J/A+A/672/A153 : CO(2-1) survey at 9pc resolution in SMC (Saldano+, 2023)http://archive.stsci.edu/doi/resolve/resolve.html?doi=10.17909/xyhn-3z68 : MASThttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/AJ/169/301https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/AJ/169/301http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/AJ/169/301https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/AJ/169/301https://vizier.iucaa.in/viz-bin/votable?-source=J/AJ/169/301http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/AJ/169/301GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/AJ/169/301/inPDR (Coordinates, magnitudes, mass, age, and observation parameters for sources inside the PDR and outside the CO cores (Tables 5, 12, 20))https://vizier.cds.unistra.fr/viz-bin/conesearch/J/AJ/169/301/inPDR?https://vizier.iucaa.in/viz-bin/conesearch/J/AJ/169/301/inPDR?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/AJ/169/301/inPDR?GETtext/xml+votable180.050000true0.5122-15.4680.005555555555555556Cone search capability for table J/AJ/169/301/outPDR (Coordinates, magnitudes, mass, age, and observation parameters for sources outside the PDR and outside the CO cores (Tables 7, 14, 22))https://vizier.cds.unistra.fr/viz-bin/conesearch/J/AJ/169/301/outPDR?https://vizier.iucaa.in/viz-bin/conesearch/J/AJ/169/301/outPDR?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/AJ/169/301/outPDR?GETtext/xml+votable180.050000true0.5151-15.4640.005555555555555556Cone search capability for table J/AJ/169/301/inPDRnoUV (Coordinates, magnitudes, mass, age, and observation parameters for sources inside the PDR and outside the CO cores not detected in the F275W filter (Tables 9, 16, 24))https://vizier.cds.unistra.fr/viz-bin/conesearch/J/AJ/169/301/inPDRnoUV?https://vizier.iucaa.in/viz-bin/conesearch/J/AJ/169/301/inPDRnoUV?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/AJ/169/301/inPDRnoUV?GETtext/xml+votable180.050000true0.5128-15.470.005555555555555556Cone search capability for table J/AJ/169/301/outPDRnoUV (Coordinates, magnitudes, mass, age, and observation parameters for sources outside the PDR and outside the CO cores not detected in the F275W filter (Tables 10, 17, 25))https://vizier.cds.unistra.fr/viz-bin/conesearch/J/AJ/169/301/outPDRnoUV?https://vizier.iucaa.in/viz-bin/conesearch/J/AJ/169/301/outPDRnoUV?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/AJ/169/301/outPDRnoUV?GETtext/xml+votable180.050000true0.5112-15.4730.0055555555555555566/171652.846559487404321e-19 7.884360181709501e-19https://cdsarc.cds.unistra.fr/viz-bin/moc/J/AJ/169/301?format=asciiRadiodefaultJ/AJ/169/301/inPDRCoordinates, magnitudes, mass, age, and observation parameters for sources inside the PDR and outside the CO cores (Tables 5, 12, 20)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRAJ2000Right ascension (J2000)degpos.eq.ra;meta.mainDEJ2000Declination (J2000)degpos.eq.dec;meta.mainF275WF275W apparent Vega magnitudemagphot.mag;em.UV.200-300nmfloate_F275WUncertainty in F275Wmagstat.error;phot.mag;em.UV.200-300nmfloatF336WF336W apparent Vega magnitudemagphot.mag;em.opt.Ufloate_F336WUncertainty in F336Wmagstat.error;phot.mag;em.opt.UfloatF438WF438W apparent Vega magnitudemagphot.mag;em.opt.Bfloate_F438WUncertainty in F438Wmagstat.error;phot.mag;em.opt.BfloatF555WF555W apparent Vega magnitudemagphot.mag;em.opt.Vfloate_F555WUncertainty in F555Wmagstat.error;phot.mag;em.opt.VfloatF625WF625W apparent Vega magnitudemagphot.mag;em.opt.Rfloate_F625WUncertainty in F625Wmagstat.error;phot.mag;em.opt.Rfloatlog(M)Log mass of starlog(solMass)phys.massfloate_log(M)Uncertainty in log(Mass)log(solMass)stat.error;phys.massfloatlog(Age)Log age of starlog(yr)time.agefloate_log(Age)Uncertainty in log(Age)log(yr)stat.error;time.agefloatAvA_V_ of starmagphys.absorptionfloate_AvUncertainty in Dust-Attenmagstat.error;phys.absorptionfloatshpF275WF275W sharpnessstat.fit.param;em.UV.200-300nmfloatchiF275WF275W chistat.fit.chi2;em.UV.200-300nmfloatshpF336WF336W sharpnessstat.fit.param;em.opt.UfloatchiF336WF336W chistat.fit.chi2;em.opt.UfloatshpF438WF438W sharpnessstat.fit.param;em.opt.BfloatchiF438WF438W chistat.fit.chi2;em.opt.BfloatshpF555WF555W sharpnessstat.fit.param;em.opt.VfloatchiF555WF555W chistat.fit.chi2;em.opt.VfloatshpF625WF625W sharpnessstat.fit.param;em.opt.RfloatchiF625WF625W chistat.fit.chi2;em.opt.RfloatJ/AJ/169/301/outPDRCoordinates, magnitudes, mass, age, and observation parameters for sources outside the PDR and outside the CO cores (Tables 7, 14, 22)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRAJ2000Right ascension (J2000)degpos.eq.ra;meta.mainDEJ2000Declination (J2000)degpos.eq.dec;meta.mainF275WF275W apparent Vega magnitudemagphot.mag;em.UV.200-300nmfloate_F275WUncertainty in F275Wmagstat.error;phot.mag;em.UV.200-300nmfloatF336WF336W apparent Vega magnitudemagphot.mag;em.opt.Ufloate_F336WUncertainty in F336Wmagstat.error;phot.mag;em.opt.UfloatF438WF438W apparent Vega magnitudemagphot.mag;em.opt.Bfloate_F438WUncertainty in F438Wmagstat.error;phot.mag;em.opt.BfloatF555WF555W apparent Vega magnitudemagphot.mag;em.opt.Vfloate_F555WUncertainty in F555Wmagstat.error;phot.mag;em.opt.VfloatF625WF625W apparent Vega magnitudemagphot.mag;em.opt.Rfloate_F625WUncertainty in F625Wmagstat.error;phot.mag;em.opt.Rfloatlog(M)Log mass of starlog(solMass)phys.massfloate_log(M)Uncertainty in log(Mass)log(solMass)stat.error;phys.massfloatlog(Age)Log age of starlog(yr)time.agefloate_log(Age)Uncertainty in log(Age)log(yr)stat.error;time.agefloatAvA_V_ of starmagphys.absorptionfloate_AvUncertainty in Dust-Attenmagstat.error;phys.absorptionfloatshpF275WF275W sharpnessstat.fit.param;em.UV.200-300nmfloatchiF275WF275W chistat.fit.chi2;em.UV.200-300nmfloatshpF336WF336W sharpnessstat.fit.param;em.opt.UfloatchiF336WF336W chistat.fit.chi2;em.opt.UfloatshpF438WF438W sharpnessstat.fit.param;em.opt.BfloatchiF438WF438W chistat.fit.chi2;em.opt.BfloatshpF555WF555W sharpnessstat.fit.param;em.opt.VfloatchiF555WF555W chistat.fit.chi2;em.opt.VfloatshpF625WF625W sharpnessstat.fit.param;em.opt.RfloatchiF625WF625W chistat.fit.chi2;em.opt.RfloatJ/AJ/169/301/inPDRnoUVCoordinates, magnitudes, mass, age, and observation parameters for sources inside the PDR and outside the CO cores not detected in the F275W filter (Tables 9, 16, 24)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRAJ2000Right ascension (J2000)degpos.eq.ra;meta.mainDEJ2000Declination (J2000)degpos.eq.dec;meta.mainF336WF336W apparent Vega magnitudemagphot.mag;em.opt.Ufloate_F336WUncertainty in F336Wmagstat.error;phot.mag;em.opt.UfloatF438WF438W apparent Vega magnitudemagphot.mag;em.opt.Bfloate_F438WUncertainty in F438Wmagstat.error;phot.mag;em.opt.BfloatF555WF555W apparent Vega magnitudemagphot.mag;em.opt.Vfloate_F555WUncertainty in F555Wmagstat.error;phot.mag;em.opt.VfloatF625WF625W apparent Vega magnitudemagphot.mag;em.opt.Rfloate_F625WUncertainty in F625Wmagstat.error;phot.mag;em.opt.Rfloatlog(M)Log mass of starlog(solMass)phys.massfloate_log(M)Uncertainty in log(Mass)log(solMass)stat.error;phys.massfloatlog(Age)Log age of starlog(yr)time.agefloate_log(Age)Uncertainty in log(Age)log(yr)stat.error;time.agefloatAvA_V_ of starmagphys.absorptionfloate_AvUncertainty in Dust-Attenmagstat.error;phys.absorptionfloatshpF336WF336W sharpnessstat.fit.param;em.opt.UfloatchiF336WF336W chistat.fit.chi2;em.opt.UfloatshpF438WF438W sharpnessstat.fit.param;em.opt.BfloatchiF438WF438W chistat.fit.chi2;em.opt.BfloatshpF555WF555W sharpnessstat.fit.param;em.opt.VfloatchiF555WF555W chistat.fit.chi2;em.opt.VfloatshpF625WF625W sharpnessstat.fit.param;em.opt.RfloatchiF625WF625W chistat.fit.chi2;em.opt.RfloatJ/AJ/169/301/outPDRnoUVCoordinates, magnitudes, mass, age, and observation parameters for sources outside the PDR and outside the CO cores not detected in the F275W filter (Tables 10, 17, 25)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRAJ2000Right ascension (J2000)degpos.eq.ra;meta.mainDEJ2000Declination (J2000)degpos.eq.dec;meta.mainF336WF336W apparent Vega magnitudemagphot.mag;em.opt.Ufloate_F336WUncertainty in F336Wmagstat.error;phot.mag;em.opt.UfloatF438WF438W apparent Vega magnitudemagphot.mag;em.opt.Bfloate_F438WUncertainty in F438Wmagstat.error;phot.mag;em.opt.BfloatF555WF555W apparent Vega magnitudemagphot.mag;em.opt.Vfloate_F555WUncertainty in F555Wmagstat.error;phot.mag;em.opt.VfloatF625WF625W apparent Vega magnitudemagphot.mag;em.opt.Rfloate_F625WUncertainty in F625Wmagstat.error;phot.mag;em.opt.Rfloatlog(M)Log mass of starlog(solMass)phys.massfloate_log(M)Uncertainty in log(Mass)log(solMass)stat.error;phys.massfloatlog(Age)Log age of starlog(yr)time.agefloate_log(Age)Uncertainty in log(Age)log(yr)stat.error;time.agefloatAvA_V_ of starmagphys.absorptionfloate_AvUncertainty in Dust-Attenmagstat.error;phys.absorptionfloatshpF336WF336W sharpnessstat.fit.param;em.opt.UfloatchiF336WF336W chistat.fit.chi2;em.opt.UfloatshpF438WF438W sharpnessstat.fit.param;em.opt.BfloatchiF438WF438W chistat.fit.chi2;em.opt.BfloatshpF555WF555W sharpnessstat.fit.param;em.opt.VfloatchiF555WF555W chistat.fit.chi2;em.opt.VfloatshpF625WF625W sharpnessstat.fit.param;em.opt.RfloatchiF625WF625W chistat.fit.chi2;em.opt.Rfloat