D ynam ics ofbarred galaxies:eects ofdisk height

A B ST R A C T W estudy dynam icsofbarsin m odelsofdisk galaxiesem beded in realisticdark m atter halos.W end that disk thickness plays an im portant,ifnot dom inant,role in the evolution and structureofthebars.W ealsom akeextensivenum ericaltestsofdierent N -body codesused to study bardynam ics.M odelswith thick diskstypically used in this type ofm odeling (height-to-length ratio hz=Rd = 0:2)produce slowly rotating, and very long,bars.In contrast,m ore realistic thin diskswith the sam e param eters asin ourGalaxy (hz=Rd � 0:1)produce barswith norm allength RbarRd,which rotate quickly with the ratio ofthe corotation radius to the bar radius R = 1:2 1:4 com patible with observations.Bars in these m odels do not show a tendency to slow down,and m ay lose aslittle as2-3 percentoftheirangularm om entum due to dynam icalfriction with the dark m atter over cosm ologicaltim e.W e attribute the dierencesbetween the m odelsto a com bined eectofhigh phase-space density and sm allerJeansm assi...