Statistical Study of the Star Formation Efficiency in Bars: Is Star Formation Suppressed in Gas-Rich Bars? by Fumiya Maeda et al. on Tuesday 29 November

The dependence of star formation efficiency (SFE) on galactic structures,

especially whether the SFE in the bar region is lower than those in the other

regions, has recently been debated. We report the SFEs of 18 nearby gas-rich

massive star-forming barred galaxies with a large apparent bar major axis

($\geqq 75^{\prime\prime}$). We statistically measure the SFE by distinguishing

the center, bar-end, and bar regions for the first time. The molecular gas

surface density is derived from archival CO(1-0) and/or CO(2-1) data by

assuming a constant CO-to-H$_2$ conversion factor ($\alpha_{\rm CO}$), and the

star formation rate surface density is derived from a linear combination of

far-ultraviolet and mid-infrared intensities. The angular resolution is

$15^{\prime\prime}$, which corresponds to $0.3 - 1.8~\rm kpc$. We find that the

ratio of the SFE in the bar to that in the disk was systematically lower than

unity (typically $0.6-0.8$), which means that the star formation in the bar is

systematically suppressed. Our results are inconsistent with similar recent

statistical studies that reported that SFE tends to be independent of galactic

structures. This inconsistency can be attributed to the differences in the

definition of the bar region, spatial resolution, $\alpha_{\rm CO}$, and sample

galaxies. Furthermore, we find a negative correlation between SFE and velocity

width of the CO spectrum, which is consistent with the idea that the large

dynamical effects, such as strong shocks, large shear, and fast cloud-cloud

collisions caused by the noncircular motion of the bar, result in a low SFE.

arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.15681v1