David Cole
University of Leicester
9 December 2010
Overview
 Background and motivation
 Results
 Basis for further work
Bars are common in disc galaxies
Nair and Abraham 2010
How are bars formed
 Transfer of angular momentum
 Relative strength depends on the ability of the bar to
grow
 Bar instability
 Massive halo suppresses bar instability (self gravity) but
allows bar to grow.
 As bar increase in strength the pattern speed slows
Can a CMC destroy a bar?
 Shen & Sellwood (2004)
 Hozumi & Herquist( 2005)
 Athanassoula and Dehnen (2005)
 Bar can be destroyed but the CMC needs to be unfeasibly
massive ~ 5 to 10% of disk mass
 In the Milky Way this would be 2 to 4 x 109 M
My work
My work
No CMC
 Bar forms easily
 Can see transport of angular momentum from centre
 MD model forms very quickly due to the bar instability
 MH model forms more slowly due to suppression of self
gravity – spheroid imposed on m=2 Fourier component
of bar
 MH grows stronger – develops peanut
 As bar stengthens the pattern speed slows
Massive Disc
Massive Disc
Massive Halo
Massive Halo
Introduce CMC before bar formed
Introduce CMC before bar formed
Add CMC when bar formed
Add CMC when bar formed
Mechanisms
 Different mechanisms
 In MD suppression by suppressing the swing
amplification – wave transmission through the centre
 CMC blocks the transmission of the density wave
through the centre
 On introduction –destructing by suppression the box
orbits which come arbitrarily close to the centre
Orbits
From Contopoulos & Payannopoulos (1980)
Conclusions
 Mechanisms for suppression of a bar different to




destruction
Just feasible BH can suppress a bar.
Significant effect for MW mass disc at 8 x 108 M
The timing and creation of bars/CMC have an effect on
galaxy morphology
Future –
 convergence tests
 changes in central softening
 Implications for gas transport