Measurements reveal different pattern speeds for bar and spiral arms in barred spiral galaxies, indicating varied formation mechanisms.
We measure independent pattern speeds for bar and spiral arms in 98 barred spiral galaxies with Mapping Nearby Galaxies at Apache Point Observatory data. Some galaxies exhibit statistically different pattern speeds (Ω bar ≠ Ω spiral ), while others have statistically equal pattern speeds. We find no trends of ΔΩ with stellar mass or galaxy color. Our results are consistent with a Universe which might have some bar-driven spirals (ΔΩ = 0), but some spirals in barred galaxies must be tidally driven or self-excited (ΔΩ ≠ 0). These results demonstrate the potential for ΔΩ measurements to constrain spiral arm formation mechanisms.
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Pearlstein et al. (2025) studied this question.
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