2 O 02MNRAS.329. .481B 42 2 1 by Smith&Weedman(1970,1971).Suchbehaviourispuzzling, reviews havealreadydiscussedtheseproperties,suchasKennicutt regions. Theluminosityemittedthroughtherecombinationlinesof those ofvirializedsystems,suchasglobularclustersandelliptical hold: Locstars(BD+28°4211,BD33°2642andFeigellO; respective continuumfilters.So,toobtainphotometryofemission- per field.Nevertheless,aswehadexcellentphotometricconditions Table 4. measured outsidetheEarth’satmosphere.Theresultsarelistedin transmission curvesoftheusedfilters,scannedatORM,are Turnshek etal.1990)forwhichfluxiscalibratedandtabulated line regions,liketheGEHRs,someadhoccalibrationhastobe next stageisthefluxcalibrationofourphotometry.Narrow-band transmission ofthefilter),Xisnormalizedairmass(X=1at magnitude, Zisthezero-pointcorrectionforeachfilter(to T^calib ^obs3“Zà+AX,(2) introduction ofcolourcorrections.Thetransformationequations from observedtocalibratedmagnitudesdoesnotrequirethe Also, withinourownphotometricsystem,thetransformation limited numberofobservationspernight,asthereisonlyonestar The disadvantageofworkingwiththesefluxstandardstarsisthe 4.2 Atmosphericextinctioncorrection each filterwascalculatedasm=—2.5logF,sinceitwouldbe curve T(A),andF*(A)istheabsolutefluxofstar. where Aisthecentralwavelengthoffilterwithtransmission * “Jr(A)dA every 1or2A.Thishighresolutionallowsustocalculatetheir emission-line photometryisunusual.Therenosetofstandard zenith), andkistheextinctioninmagnitudesduetoairmassX. where misthestarcalibratedmagnitude,observed during thefirstfournightsofourrun,wecouldgatherdata available. Wecandefinetheabsolutefluxinafilteras absolute flux(ormagnitude)througheverysinglefilterofour adopted. Toachievethis,wehavechosenthreeHSTspectro- analogue totheUBVsystemusewithHa,H/3andtheir account forslightdifferencesbetweenthetabulatedandreal are writtenas available fromthesenightstoperformtheextinctioncorrection. system. Thiscanbeachievedbyintegratingnumerically,sincethe stars calibratedastoperformaroutinereductionprocess,andno A 0 calibobs The calibrationmagnitudeoftheobservedstandardstarsfor The magnitudesofthestandardstarswereobtainedperforming CCD photometryofgiantHuregions483 jF*(A)T(A)dA 10*13* 1415 10 1314*15* 10 13 10 15 14 10 13 13 H/3 11* 13*1415 11* 1314*15* 11 14 11 14 13 14 15 14 H/3< C (1) 2 O 02MNRAS.329. .481B reasonable approach.Thesetissolvednumericallybyleast- the followingnights,whensky conditionsareexpectedtobe DAOPHOT. WeconsideredadifferentvalueofZforeachfilter,but the region. with theoriginofcurve-of-growthmethodusedtofindtotalflux JKT focalplane.Thecoordinateszero-pointofthecoincides Figure 1.FindingchartforNGC588.Theaxesshowtheangularscale, 484 G.Boschetal. changes. ThevaluesofAZwere checked,inordertoseeif of Z,whichmightdifferfromthe previousoneduetoatmospheric calibration, wherethekparameter isknown,andfindthenewvalue within asmallrangeofwavelengths(4860-6650A),thisis estimated fromconvertingthepixeltoarcsecscaleforTeKCCDat assumed thesamevalueofkforallfilters.Asweareworking aperture photometryontheobservedstars,usingiraf’sversionof slightly different.Forthesenights wecanapplytheresultsof squares. TheresultsareshowninFig.12andlistedTable5. a A The setofdefinedextinction-corrected magnitudesisappliedto © Royal Astronomical Society •Provided bytheNASA Astrophysics DataSystem Figure 2.SameasFig.1forNGC592. --60 060 X (arcsec) X (arcsec) programme objects.Beforethis,images werealigned,cosmicray- throughout thewholefieldof the CCDandapplyittoour Having flat-fieldedtheframesanddefinedarelationbetween 4.3 Calibratingtheframes the lastnightofobservations.Thenumberstandardstars cleaned, andtheircontinuumcontribution subtractedfollowing can usetheflux-to-countsrelation established forthestandardstars observations werenotenoughtoquantifythisvariabilityand conditions alsochangedduringthenight,whichwascasefor standard procedures.Moredetails canbefoundinBosch(1999). absolute flux(ormagnitude)andthenumberofcountsdetected,we account forit,sowedecidednottousethedatafromlastnight. The fluxstandardstarshavealmost featurelesscontinua.Hence Figure 3.SameasFig.1forNGC595. Figure 4.SameasFig.1forNGC604. -■60 60 X (arcsec) © 2002RAS,MNRAS 329,481-496 s # x ür NGC595 NGC6Ö4 100 pc 2 O 02MNRAS.329. .481B exp -^— not havelargeradialvelocities,so thewavelengthsofemission velocities andobservedlinewidths. GalaxiesintheLocalGroupdo line for ourobjects.ThereforewecanconstructaGaussianemission use ofspectroscopyalreadypublishedintheliterature,fromwhich This isnotthecaseforlinefluxemittedbynebulae,as the fluxremainsalmostconstantthroughoutwholefilterrange. where Aandnebula luminosityfunction,as also agreeswellwithotherdeterminations suchasthetipofred GEHRS includedinthisstudyandlistedTable10.Thisindicator Cepheids, bytheHSTExtragalacticDistanceScaleKeyProject expressed incm.Distancesareusuallydistance 8.1 Luminosities 8 THELUMINOSITY-VELOCITY Section 8.4. (Freedman, Wilson&Madore1991;Kelsonetal.1996).Wehave © 2002RAS,MNRAS 329,481-496 In ordertocomparewithprevious determinations,wehave © Royal Astronomical Society •Provided bytheNASA Astrophysics DataSystem Figure 20.SameasFig.17forNGC6822III. Figure 19.SameasFig.17forNGC6822I. 2 regions. Melnick(1977)measuredlineprofilesanddetermined We haveincludedinTable11thecorrectiontologarithmic turbulent velocitiesforasetofGEHRsinnearbygalaxiesusing the estimationsintolarge-andsmall-scaleobservations.Wewill Velocity dispersionshavebeenindependentlyobtainedbyseveral The magnitudeofthesedisagreementsonthedistancescalesused in previousworks.Itcanbereadilyseenthatthedistanceto the differenceswithsamefactorsderivedfordistancesused luminosity calculatedwiththedistancesadoptedinthiswork,and use oftheavailabledistancesfromdifferentsourcesand MMTG. However,itmustbekeptinmindthateachstudyhasmade included resultsfromM79,Hippelein(1986,hereafterHH86)and Roy, Arsenault&Joneas(1986,hereafterRAJ86)obtainedanother HH86 obtainednewerFabry-Perotinterferometricdata,including the instrumentalprofile(7-andthermalcontributionto investigating therelationofvelocitydispersionwithlinear directly linkedtotheoverallluminositymeasuredforHu discuss inthissectionthelarge-scaleobservations,astheseare groups analysingthekinematicsofGEHRs.Theseeffortscanbe 8.2 Velocitydispersions of thecalculatedluminositiesalmostimpossible. galaxy isaconsiderablesourcefordisagreementinluminosities. discrepancies inthesedistancesintroducedifferentcorrections. observed widthoftheemissionline $now.offset().top) {
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