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Research Talk: Sandeep Kumar Kataria

Date: Mon. July 30th, 2018, 4:00 pm-5:00 pm
Location: Sears 552

The Impact of Bulges on Bar Formation and Bar Pattern Speed in Disk Galaxies

Sandeep Kumar Kataria (Indian Institute of Astrophysics, Bangalore)

We use N-body simulations of bar formation in an isolated galaxy to study the effect of bulge mass and bulge concentration on bar formation and bar pattern speed. Two sets of models are generated, one that has a dense bulge and high surface density disk and a second model that has a less concentrated bulge and a lighter disk. Our simulations of both the models show that there is an upper cut-off in bulge to disk mass ratio Mb/Md above which bars cannot form; the cut-off is smaller for denser bulges( Mb/Md = 0.2) compared to less denser ones (Mb/Md = 0.5). We define a new criterion for bar formation in terms of bulge to disk radial force ratio (Fb/Fd) at the disk scale length above which bars cannot form and show that if Fb/Fd > 0.35, a disk is stable against bar formation. This criterion agrees with the observations of barred galaxies from S4G catalogue. 

We have also studied the effect of bulge mass on bar pattern speed. We find that all bars initially rotate fast with R<1.4, where R is the ratio of corotation radii to bar semi-major axis. Further our study shows that bar pattern speed decreases with time and after 10 Gyr of evolution, most of the bars become slower (R>1.4). With these results we explain the perplexing nature of observations i.e. most of the bars are fast and independent of hubble type (Califa Survey) or  slowness and fastness of bars show weak correlation with hubble type (Rautiainen et al 2008).
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