J/ApJ/923/78ivo://CDS.VizieR/J/ApJ/923/78doi:10.26093/cds/vizier.19230078CDSSawant A.N.Pellegrini E.W.Oey M.S.Lopez-Hernandez J.Micheva G.2023-11-03T12:23:02Z2023-07-19T13:57:13ZCDS support team

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

cds-question@unistra.frgalaxiesvisible-astronomyh-ii-regionschemical-abundancesWe employ ionization-parameter mapping (IPM) to infer the optical depth of HII regions in the northern half of M33. We construct [OIII]{lambda}5007/[OII]{lambda}3727 and [OIII]{lambda}5007/[SII]{lambda}6724 ratio maps from narrowband images continuum-subtracted in this way, from which we classify the HII regions by optical depth to ionizing radiation, based on their ionization structure. This method works relatively well in the low-metallicity regime, 12+log(O/H)<=8.4, where [OIII]{lambda}{lambda}4959,5007 is strong. However, at higher metallicities, the method breaks down due to the strong dependence of the [OIII]{lambda}{lambda}4959,5007 emission lines on the nebular temperature. Thus, although O^++^ may be present in metal-rich HII regions, these commonly used emission lines do not serve as a useful indicator of its presence, and hence the O ionization state. In addition, IPM as a diagnostic of optical depth is limited by spatial resolution. We also report a region of highly excited [OIII] extending over an area ~1kpc across and [OIII]{lambda}5007 luminosity of 4.9+/-1.5x10^38^erg/s, which is several times higher than the ionizing budget of any potential sources in this portion of the galaxy. Finally, this work introduces a new method for continuum subtraction of narrowband images based on the dispersion of pixels around the mode of the diffuse-light flux distribution. In addition to M33, we demonstrate the method on CIII]{lambda}1909 imaging of Haro 11, ESO338-IG004, and Mrk 71.2021ApJ...923...78Shttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/923/78CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/A+A/426/11 : XMM-Newton survey of M33 (Pietsch+, 2004)J/A+A/462/535 : Low-metallicity HII regions and galaxies (Yin+, 2007)J/AJ/134/2474 : Ha emission-line stars in 7 dwarfs galaxies (Massey+, 2007)J/ApJ/733/123 : The Wolf-Rayet content of M33 (NGC 598) (Neugent+, 2011)J/ApJ/755/40 : HII reg. in Magellanic clouds from MCELS (Pellegrini+, 2012)J/A+A/559/A114 : Updated O3N2 and N2 abundance indicators (Marino+, 2013)J/ApJ/842/97 : Spectroscopic obs. of 413 HII regions in M33 (Lin+, 2017)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/923/78https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/923/78http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/923/78https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/923/78https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/923/78http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/923/78GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/ApJ/923/78/table2 (HII regions in northern M33)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/923/78/table2?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/923/78/table2?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/923/78/table2?GETtext/xml+votable180.050000true23.226583330.84111110.0055555555555555566/2155 2241https://cdsarc.cds.unistra.fr/viz-bin/moc/J/ApJ/923/78?format=asciiOpticaldefaultJ/ApJ/923/78/table2HII regions in northern M33recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintSimbadSimbad column added by the CDSmeta.ref.urlcharRAJ2000[1] Hour of Right Ascension (J2000)pos.eq.ra;meta.mainDEJ2000[30/31] Degree of Declination (J2000)pos.eq.dec;meta.main12+log(O/H)[8/8.7] Metallicity (12+log(O/H)) (1)phys.abund.Zfloate_12+log(O/H)[0.003/0.03] Lower error of 12+log(O/H) (1)stat.errorfloatE_12+log(O/H)[0.003/0.03] Upper error of 12+log(O/H) (1)stat.error;stat.maxfloatOpac[1/5] Opacity classification (2)src.classintLHa[4.6/4710] H-alpha luminosity of the object, 10+36erg/s1e+29Wphys.luminosity;em.line.Halphadoublee_LHa[0.01/63] Error in LHa1e+29Wstat.errorfloatLOII[2/1750] OII luminosity of the object, 10+36erg/s1e+29Wphys.luminositydoublee_LOII[0.01/61] Error in LOII1e+29Wstat.errorfloatLOIII[0.1/2030] OIII luminosity of the object, 10+36erg/s1e+29Wphys.luminositydoublee_LOIII[0.03/29] Error in LOIII1e+29Wstat.errorfloatLSII[0.9/802] SII luminosity of the object, 10+36erg/s1e+29Wphys.luminositydoublee_LSII[0.02/40] Error in LSII1e+29Wstat.errorfloatL17Display data from Lin+ 2017, J/ApJ/842/97 within 12"meta.ref.urlintnullableNameObject Identifiermeta.id;meta.mainchar