4.9. Bars in early- and late-types

Observations reveal that bars have different properties along the Hubble sequence (Elmegreen & Elmegreen 1985, 1989). In early-type galaxies, bars have flat profiles, while in late-types, they have exponential profiles. Also bars extend farther with respect to the disk exponential scale in late-types. Numerical simulations allow to interpret these features. Due to their relatively massive bulge, and large mass concentration, early-types have large precessing frequencies - / 2 and tend to have large _b (Combes & Elmegreen 1993). There exist then 2 ILRs, and bars end near their corotation. On the contrary, late-types have low - / 2, and low _b. Corotation is then far away in the disk, and lets the disk scale-length determine the bar length (see fig 13). The profile along the bar is therefore exponential, very similar to the disk profile. Early-types bars continuously grow in time, since angular momentum is transferred in outer regions. But late-types cannot, since there are not enough stars to accept angular momentum, and they stop to grow before. Since the existence of ILRs favors the radial gas inflows, the fueling appears more efficient in early-type galaxies.

Figure 13. Rotation curves for late and early-type galaxy models, compared with the bar pattern speed. The initial values are full lines, while the final values are dashed lines. Left: late-type model; Right: early-type (from Combes & Elmegreen 1993).