Star formation suppression and bar ages in nearby barred galaxies

Abstract

We present new spectroscopic data for 21 barred spiral galaxies, which we use to explore the effect of bars on disk star formation, and to place constraints on the characteristic lifetimes of bar episodes. The analysis centres on regions of heavily suppressed star formation activity, which we term 'star formation deserts'. Long-slit optical spectroscopy is used to determine Hβ absorption strengths in these desert regions, and comparisons with theoretical stellar population models are used to determine the time since the last significant star formation activity, and hence the ages of the bars. We find typical ages of ∼1 Gyr, but with a broad range, much larger than would be expected from measurement errors alone, extending from ∼0.25 Gyr to >4 Gyr. Low-level residual star formation, or mixing of stars from outside the 'desert' regions, could result in a doubling of these age estimates. The relatively young ages of the underlying populations coupled with the strong limits on the current star formation rule out a gradual exponential decline in activity, and hence support our assumption of an abrupt truncation event.

Redistribution of stars and gas in the star formation deserts of barred galaxies

“…If there were no radial migration of young stars from the disk to the SFD, then the age distribution of SFD stars would show a truncation within ∼ 1 Gyr after the time of bar formation. However, this is not the case, and the SFD age distributions show a gradual downturn instead of a truncation, which makes recovering the epoch of bar formation more complicated than James & Percival (2016, 2018 anticipated. The different shapes of age distributions for SFD and bar stars can provide an indication of when the bar formed, but the signal is weak and potentially hard to detect.…”

“…The method we propose to date bar formation in a galaxy relies on a very weak signal, which makes applying the SFD bar dating method more complex than previously suggested in James & Percival (2016, 2018. Indeed, the method we propose relies on the accurate recovery of SFH shapes for the bar and SFD.…”

“…These regions also display a deficit in surface stellar density (Gadotti & de Souza 2003;Gadotti 2008;Kim et al 2016). James & Percival (2016, 2018 assumed a truncated star formation model and found that SFD regions can be very old. If the truncation of star formation is caused by the bar, this feature can be used to determine the epoch of bar formation.…”

GASP XVIII: star formation quenching due to AGN feedback in the central region of a jellyfish galaxy

“…The likelihood for disk galaxies hosting stellar bar is found to be anti-correlated with specific star formation rate regardless of stellar mass and the prominence of the bulge (Cheung et al 2013). The presence of stellar bars can quench star formation in the central regions of galaxy by suppressing the star formation along the co-rotation radius of the bar (James & Percival 2018). The shock and shear generated within the galaxy due to the presence of a bar can create turbulence preventing the molecular gas from collapse thereby inhibiting star formation (Reynaud & Downes 1998).…”

Significance of bar quenching in the global quenching of star formation

“…Here we attempt to understand the significance of bar quenching in the global quenching of star formation of barred galaxies. The length of the stellar bar, a proxy for the strength of the bar (Elmegreen et al 2007;Guo et al 2019), is expected to enhance the impact of bar quenching in the galaxy (Spinoso et al 2017;James & Percival 2018). This is possible since star formation suppression happens over the region covered by the bar length.…”