Do Bars Drive Spiral Density Waves?

TL;DR

This study investigates whether strong bars in spiral galaxies drive spiral density waves by analyzing near-infrared observations, finding a weak correlation and suggesting bar-driven spirals may depend on bar growth and gas presence.

Contribution

The paper provides new observational evidence on the correlation between bar strength and spiral density waves, highlighting conditions under which bars may drive spirals.

Findings

Weak correlation between bar torque and spiral strength

Some galaxies have strong bars but weak or absent spirals

Bar-driven spirals may require gas and bar growth

Abstract

We present deep near-infrared K_s-band AAT IRIS2 observations of a selected sample of nearby barred spiral galaxies, including some with the strongest known bars. The sample covers a range of Hubble types from SB0- to SBc. The goal is to determine if the torque strengths of the spirals correlate with those of the bars, which might be expected if the bars actually drive the spirals as has been predicted by theoretical studies. This issue has implications for interpreting bar and spiral fractions at high redshift. Analysis of previous samples suggested that such a correlation exists in the near-infrared, where effects of extinction and star formation are less important. However, the earlier samples had only a few excessively strong bars. Our new sample largely confirms our previous studies, but still any correlation is relatively weak. We find two galaxies, NGC 7513 and UGC 10862, where there is a only a weak spiral in the presence of a very strong bar. We suggest that some spirals probably are driven by their bars at the same pattern speed, but that this may be only when the bar is growing or if there is abundant gas and dissipation.