Investigating the role of bars in quenching star formation using spatially resolved ultraviolet-optical colour maps

Abstract

Context. Bars are ubiquitously found in disc galaxies and they are known to drive galaxy evolution through secular processes. However, the specific contribution of the bars in the suppression of star formation is still a matter of debate.

Aims. Our aim is to investigate the role of bars in quenching star formation using spatially resolved UV-optical colour maps and radial colour profiles of a sample of 17 centrally quenched barred galaxies in the redshift range of 0.02–0.06.

Methods. We selected the sample of centrally quenched barred galaxies based on their location in the SFR-M⋆ plane. They are classified as passive based on the parameters from the Max Planck Institute for Astrophysics (MPA) and Johns Hopkins University (JHU) value-added catalogue (MPA – JHU VAC); however, they have also been classified as non-passive based on the parameters from the GALEX-SDSS-WISE Legacy (GSWLC) catalogue, indicating a passive inner region and recent star formation in their extended disc. We used the archival SDSS optical r-band and GALEX far- and near- ultraviolet (FUV and NUV) imaging data of these galaxies and created spatially resolved (FUV−NUV versus NUV−r) colour-colour maps to understand the nature of the UV emission from different regions of these galaxies. We also analysed their NUV−r colour radial profiles and use the NUV−r colour as a proxy for the stellar population age in the different regions of these galaxies. We also analysed a control sample of eight centrally quenched unbarred galaxies to disentangle the effect of bulge and bar in quenching star formation.

Results. The centrally quenched barred galaxies display redder colours (NUV−r > 4 – 4.5 mag) in the inner regions, up to the length of the bar, indicating the age of the stellar population in these regions is older than > 1 Gyr. Most barred galaxies in our sample host pseudo-bulges and do not host an active galactic nucleus (AGN), indicating that the most probable reason for the internal quenching of these galaxies is the action of stellar bar. In comparison to their unbarred counterparts, lying in a similar regime of stellar mass and redshifts, the barred galaxies show redder colours (NUV−r > 4 mag) to a larger spatial extent.

Conclusions. In their later stages of evolution, bars turn the inner regions of galaxies redder, leading to quenching, with the effect being most prominent up to the ends of the bar and creating a region dominated by older stellar population. This may occur because bars have already funneled gas to the galactic centre leaving behind no fuel for further star formation. Spatially resolved studies of a larger sample of barred galaxies at different redshifts will provide more insights to the role of bar in quenching star formation and the different evolutionary stages of quenching.