Significance of bar quenching in the global quenching of star formation

Abstract

The suppression of star formation in the inner kiloparsec regions of barred disk galaxies due to the action of bars is known as bar quenching. We investigate here the significance of bar quenching in the global quenching of star formation in the barred galaxies and their transformation to passive galaxies in the local Universe. We do this by measuring the offset of quenched barred galaxies from star-forming main sequence galaxies in the star formation rate-stellar mass plane and comparing it with the length of the bar, which is considered as a proxy of bar quenching. We constructed the star formation rate-stellar mass plane of 2885 local Universe face-on strong barred disk galaxies (z < 0.06) identified by Galaxy Zoo. The barred disk galaxies studied here fall on the star formation main sequence relation with a significant scatter for galaxies above stellar mass 10 10.2 M . We found that 34.97 % galaxies are within the intrinsic scatter (0.3 dex) of the main sequence relation, with a starburst population of 10.78 % (above the 0.3 dex) and a quenched population of 54.25 % (below the -0.3 dex) of the total barred disk galaxies in our sample. Significant neutral hydrogen (M HI >10 9 M with log M HI /M ∼ -1.0 to -0.5) is detected in the quenched barred galaxies with a similar gas content to that of the star-forming barred galaxies. We found that the offset of the quenched barred galaxies from the main sequence relation is not dependent on the length of the stellar bar. This implies that the bar quenching may not contribute significantly to the global quenching of star formation in barred galaxies. However, this observed result could also be due to other factors such as the dissolution of bars over time after star formation quenching, the effect of other quenching processes acting simultaneously, and/or the effects of environment.

More insights into bar quenching

“…Such regions are indeed observed in the form of cavities (or holes) in HI within the co-rotation radius of a few barred disc galaxies (Consolandi et al 2017;George et al 2019a;Newnham et al 2020). The region outside the co-rotation radius can have significant HI, so that even when the central regions are devoid of star formation, quenched barred galaxies can still be gas rich (George et al 2019b). This observed scenario is consistent with recent simulations in which the gas surface density is expected to be reduced along the bar region near the periphery of the co-rotation radius.…”

Bar quenching: Evidence from star-formation-rate indicators

“…The star-forming galaxies in the local Universe populate the main sequence within an intrinsic scatter of 0.3 dex, whereas the passive galaxies are offset from the relation in the SFR-M plane (Brinchmann et al 2004;Salim et al 2007;Noeske et al 2007;Elbaz et al 2007;Daddi et al 2007). We note that such a trend between the scaled bar length (bar length divided by the size of galaxy) and the offset distance from the main sequence was not observed for the barred galaxies in the local Universe (George et al 2019b, z ≤ 0.06), suggesting that the bar-quenching mechanism may not be contributing significantly to the global quenching of barred galaxies.…”

“…This suggests that any ongoing star formation outside the region covered by the SDSS 3" fibre is not fully accounted for when computing the total SFR of the galaxy. The SDSS 3" fibre does not cover the entire bar region of the sample galaxies (in the entire redshift range) studied by George et al (2019b). This implies that, in George et al (2019b), we were effectively probing the SFR and hence the quenching happening in the very central region of the barred galaxies and not the total SFR of the galaxy nor the SFR of the bar region.…”

“…The SDSS 3" fibre does not cover the entire bar region of the sample galaxies (in the entire redshift range) studied by George et al (2019b). This implies that, in George et al (2019b), we were effectively probing the SFR and hence the quenching happening in the very central region of the barred galaxies and not the total SFR of the galaxy nor the SFR of the bar region. This could explain the lack of correlation between the length of the bar and the offset distance of galaxies from the main sequence of the SFR-M relation for galaxies in the local Universe (George et al 2019b).…”

“…In George et al (2019b), we used the total SFR of the galaxies provided by the MPA/JHU SDSS DR7 catalogue 1 (Kauffmann et al 2003;Brinchmann et al 2004), which are derived from the Hα flux measured by the 3" SDSS fibre spectra for star-forming galaxies and using an empirical relation between specific SFR and the 4000 Å break strength (D4000 index) for active galactic nuclei (AGNs) or weak-emission-line galaxies. Aperture corrections are done on contribution to SFR outside the SDSS fibre from the spectral energy distribution (SED) fitting to SDSS ugriz photometry.…”