An I-band calibration of the SBF method at blue colours(7)

An I-band calibration of the SBF method at blue colours

S.Mieskeetal.:SBFcalibrationatbluecolours

NameFCC222

1.036

FCC223

1.121

FCC241

0.900

FCC156

1.012

FCC196

0.898

FCC218

0.971

FCC140

0.881

FCC168

1.013

FCC214

1.016

FCC215

0.986

FCC192

0.860

LSB6-4

0.863

LSB10-8

20.01

28.72±0.37

5.5

0.29

0.04

0.64

31.76±0.45

31.24±0.39

30.73±0.37

19.87

28.26±0.37

8.1

0.17

0.02

0.86

31.31±0.45

30.79±0.39

30.27±0.37

19.40

28.74±0.45

4.2

0.41

0.01

0.68

31.21±0.52

30.98±0.47

30.75±0.45

19.07

28.75±0.37

7.5

0.27

0.03

0.62

31.09±0.45

30.93±0.39

30.76±0.37

18.88

28.69±0.37

9.9

0.24

0.04

0.66

31.05±0.45

30.88±0.39

30.70±0.37

18.54

29.11±0.37

4.5

0.39

0.02

0.67

32.07±0.45

31.60±0.39

31.12±0.37

18.17

29.07±0.27

7.6

0.21

0.02

0.73

31.61±0.37

31.34±0.30

31.08±0.27

17.67

29.17±0.27

5.3

0.24

0.07

0.79

32.04±0.37

31.61±0.30

31.18±0.27

17.24

29.24±0.31

7.1

0.41

0.42

1.20

31.61±0.41

31.43±0.34

31.25±0.31

16.40

29.31±0.20

9.4

0.22

0.03

0.65

32.18±0.33

31.75±0.24

31.32±0.20

15.86

29.56±0.20

11.0

0.23

0.02

0.71

31.44±0.33

31.44±0.33

31.44±0.33

15.65

mI

29.44±0.20

S/N4.1

BG0.05

GC0.07

seeing[′′]

0.65

(m M)A31.69±0.33

(m M)B31.57±0.24

(m M)C31.45±0.20

7(m M)D31.45±0.2031.44±0.3331.32±0.2031.25±0.3131.18±0.2731.08±0.2731.12±0.3731.05±0.4531.09±0.4531.21±0.5231.31±0.4530.73±0.37

Table1.ResultsofSBFmeasurementsforthe25FornaxdEswithS/N>3intheSBFmeasurement.Thegalaxiesareorderedbydecreasingbrightness.Inthe rstcolumn,the

reference

number

in

theFornaxClusterCatalogFCC(Ferguson&Sandage1989)isgiven.Thelastfourgalaxieshadbeentoofaintforthiscatalog.Theyarelabelledwitha eldnumberandrunningindexaccordingtoHilkeretal.(2003).AllcolumnshavemagnitudesasunitsexceptS/Nandseeing.(V I)0isthemeancolourofthephotometryfromHilkeretal.(2003)andthispaper.VisfromHilkeretal.(2003).Theotherparametersarederivedinthispaper.BGgivestheamountofbackground uctuationpresentintheoriginal uctuationimage,comprisingboth uctuationsfromundetectedbackgroundsourcesand uctuationsarisingfromfringing.(m M)Ato(m M)Dgivethefoursetsofdistancesobtainedwhenapplyingthefourdi erentcalibrationtestcases,seeSect.2.

ni cantcorrelationinthesensethatbadseeingdatahavestronger

mIisthata ttothesameseeingpowerspectrumyieldssys-tematicallyhigherP0whenexcludingmorelowkdatapoints(whichisthecaseforbadseeingdata).Wehavetestedthisforourstellarpowerspectra:fora xedassumedwidthofthepowerspectrum,the ttedP0dependsonlyverymarginally(toafewpercent)onthelimiting twavenumberk,evenwhenthe ttedpowerspectrumdatapointsareallbelow1/3ofP0.Wehavealsodouble-checkedwhetherforsomelargeseeingdatawemayerroneouslyhaveusedmarginallyresolvedobjectsforPSF tting.However,thiswasnotthecase.

Jensen,Tonry&Luppino(1998)arguethatpoorqualitySBFdatainIRSBFmeasurementsarepronetoarti cialincreasesofthe uctuationamplitudeduetoskybackground uctuations,imperfectgalaxymodellingorundetectedbackgroundsources.Forourdata,wecanmostlikelyexcludethee ectofsky uc-tuationsandundetectedbackgroundsources,seeSect.3.2.Thesky uctuationsareindependentofseeingandderiveddistance(seeabove),andtheglobularcluster uctuationsaresmall.We

concludethattheimperfectgalaxysubtraction(seee.g.rightpanelofFig.4)isthemajorcontributortotheincreaseof uc-tuationpoweratlargeseeing.ThisisbecausethePSFscaleapproachesthatexpectedforgalaxymodelresiduals(theSBFimagesfortheworstseeingdatahaveadiameterofonlyabout8PSFFHWM)suchthatthecommonlyappliedrejectionoflowwavenumbersinthepowerspectrum tcanapparentlynotremovealltheresidualpowerforthebadseeingdata.

FortheSBFcalibration,wethereforeexcludealldatawithsee-ingworsethan0.85′′FWHM.Doingthisremovesthedepen-denceofseeingon

mIvs.(V I)0.