The role of bars in triggering active galactic nuclei galaxies

Abstract

Bars are considered an efficient mechanism for transporting gas toward the central regions of galaxies, potentially enhancing nuclear activity. However, the extent to which bars influence active galactic nuclei (AGNs), and whether their efficiency varies with environment, remain open questions. In this study, we aim to quantify the role of bars in triggering AGNs by comparing the AGN fraction in barred and non-barred galaxies across different environments. We constructed a sample from the Galaxy Zoo DECaLS catalog, ensuring a control selection where both samples share similar distributions in stellar mass, redshift, magnitude, concentration index, and local density parameter. AGNs were identified using spectroscopic data from the Sloan Digital Sky Survey, yielding 1330 barred AGNs and 1651 unbarred AGNs. We use the [OIII]5007 luminosity (Lum[OIII]) and the accretion rate parameter R as indicators of nuclear activity. Based on these, we applied criteria to distinguish powerful from weak AGNs, allowing a more precise assessment of the bar's impact on the supermassive black hole. Our analysis reveals that barred galaxies tend to host a higher fraction of powerful AGNs. From Lum[OIII], we find that more active nuclei reside in massive, blue galaxies with young stellar populations. We also observe a slight tendency for barred galaxies to host less massive black holes accreting more efficiently. The classification of strong and weak bars shows that more prominent bars correlate with higher nuclear activity. While this trend shows no significant differences in intermediate-density environments, it becomes evident in both low- and high-density regions, where galaxies with strong bars show enhanced AGN activity.