J/AJ/104/92ivo://CDS.VizieR/J/AJ/104/92doi:10.26093/cds/vizier.51040092CDSScowen P.A.Dufour R.J.Hester J.J.2023-04-06T16:49:25Z1997-12-09T19:59:48ZCDS support team

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

cds-question@unistra.frgalaxiesvisible-astronomyinterstellar-mediumh-ii-regionschemical-abundancesSpectrophotometrically calibrated CCD imagery of two overlapping 16 arc min fields in the SAB(rs)cdI galaxy M101 in the emission of H alpha, [O III] lambda 5007, H beta, and [S II] lambda 6723 are used to study various physical properties of the H II region population. Individual H II regions are identified and mapped using an automated algorithm, thus eliminating personal bias in the measurements. Characteristics of the population studied include the H II region luminosity function and radial variations in extinction, [O III]/H beta, O/H, [S II]/H alpha, ionization parameter, and numbers of ionizing photons. In addition, radial and azimuthal variations in the H II surface density are studied in comparison to that of H I and H_2 inferred from radio 21 cm and CO observations. It is demonstrated that the magnitude of trends and ``gradients'' found from such analyses depend on the surface brightness threshold set in defining the H II region boundaries; so results are presented for both low (log S(H alpha) = -15.7 ergs/s/cm^2/arcsec^2; 625 H II regions) and high (-15.0; 248 H II regions) thresholds. Radial gradients in both extinction, C(H beta), and O/H are seen in the H II region population -- with a distinct flattening in the O/H gradient seen in the outer disk beginning at about 10 kpc. The luminosity function of the H II region population found is similar to previous studies, though both the high and low ends are sensitive to the threshold levels set. Other parameters, such as the ionization parameters, luminosities, and size distribution, show no evidence for systematic variations with galactocentric distance. Current star formation processes active in the disk of M101 are analyzed two-dimensionally by comparison of the distribution of ionized and neutral hydrogen. The star formation efficiency shows considerable variation across the disk, suggesting significant spatial variation in the critical density for cloud collapse across the disk of M101 and thus departures from the simple Toomre model.1992AJ....104...92Shttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/AJ/104/92CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/AJ/104/92https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/AJ/104/92http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/AJ/104/92https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/AJ/104/92https://vizier.iucaa.in/viz-bin/votable?-source=J/AJ/104/92http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/AJ/104/92GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/AJ/104/92/table0 (Table of observed properties of HII regions used in paper. Not explicitly presented in paper - see last paragraph of Summary section in paper. [Rnum,RAh,RAm,RAs,DEd,DEm,DEs,A, Ha,Hb,O3,S2,Rad])https://vizier.cds.unistra.fr/viz-bin/conesearch/J/AJ/104/92/table0?https://vizier.iucaa.in/viz-bin/conesearch/J/AJ/104/92/table0?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/AJ/104/92/table0?GETtext/xml+votable180.050000true210.61601654.2278510.0055555555555555566/11434https://cdsarc.cds.unistra.fr/viz-bin/moc/J/AJ/104/92?format=asciiOpticaldefaultJ/AJ/104/92/fig34567Table of derived properties of HII regions used in Figures 3,4,5,6 and 7. Higher threshold used. [Rnum,CHb,O3Hb,S2Ha,OH,U,Q]recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRnum[2/323]+ HII Region Reference Numbermeta.id;meta.mainintprimaryindexedCHbBalmer Decrement as C(H beta)phot.flux;arith.ratiofloatO3HbRatio of [O III] to H betaphot.flux;arith.ratiofloatS2HaRatio of [S II] to H alphaphot.flux;arith.ratiofloatOHOxygen Abundance as 12+log(O/H)phys.abundfloatUIonization Parameterphys.ionizParam.raddoubleQNumber of Ionizing photons /s1e+45count.s**-1phys.luminositydoubleJ/AJ/104/92/table0Table of observed properties of HII regions used in paper. Not explicitly presented in paper - see last paragraph of Summary section in paper. [Rnum,RAh,RAm,RAs,DEd,DEm,DEs,A, Ha,Hb,O3,S2,Rad]recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRnum[2/323]+ HII Region Reference Numbermeta.id;meta.mainintprimaryindexedRA1950Region RA Hour (1950.0)pos.eq.ra;meta.mainDE1950[+] Sign of declinationpos.eq.dec;meta.mainnullableARegion Area, 1 pix = 1.2 arcsecpixel**2phys.area;instrintHaH alpha surf.brightness, 1pix=1.2"mW.m**-2.pixel**-1phot.flux.sbdoubleHbH beta surf.brightness, 1pix=1.2"mW.m**-2.pixel**-1phot.flux.sbdoubleO3surf.brightness, [OIII], 1pix=1.2"mW.m**-2.pixel**-1phot.flux.sbdoubleS2surf.brightness, [S II], 1pix=1.2"mW.m**-2.pixel**-1phot.flux.sbdoubleRadRadial distance of region in galaxypcpos.distanceint