Onceweknowthesurfacebrightnessprofileofagalaxy,we.ppt

Onceweknowthesurfacebrightnessprofileofagalaxy,wecanintegrateitfrom0totothetotalintegratedapparentmagnitudeofagalaxyinagivenband:(foracirculargalaxy)Inpracticethesurfacebrightnessprofilesdonotextendtoinfinity,,whichrepresentsalwaysthesamephysicalradiusofagalaxy,(R25)=25mag/arcsec2Integratedabsolutemagnitudes:ponent(centralbulge,disk,bar,spiralarms,rings…),butalsobecausediskgalaxiescontainlargeamountsofdust,andhencetheyarenottransparent:Besidesthecontributionfromstars,theirappearancewilldependonthedistributionofgasanddust,-on,lighthastotopassthroughlongercolumnsofthegalaxy’(thereisnostellarformationgoingone).,however,therearelargeamountsofgasanddust,andthatwouldeventuallyaffecttheapparentmagnitudesofthistypeofgalaxies,dependingontheanglefromwhichthegalaxyisviewed:EdgeonFaceonSelf-ingfromthenearsideofthebulge(alongthemajoraxis)isabsorbedbythedustinthedisk,ingredderthanthatonthefarside(onthediskmajoraxis).,sincelightfromthenearsideismorescatteredthanthatonthefarside,:atsmallinclinations(nearlyfaceon)absorptiondominates,,,:TheinclinationismeasuredbythetiltofthediskwithrespecttotheplaneoftheskyShapesofdiskgalaxies:Thefollowingfiguresshowthedistributionofapparentaxisratioofasampleof~5000S0galaxies(left)and~13000spiralgalaxies(right)InS0galaxiesthedistrib