Galaxy zoo DESI: large-scale bars as a secular mechanism for triggering AGN

Garland, Izzy L; Walmsley, Mike; Silcock, Maddie S; Potts, Leah M; Smith, Josh; Simmons, Brooke D; Lintott, Chris J; Smethurst, Rebecca J; Dawson, James M; Keel, William C; Kruk, Sandor; Mantha, Kameswara Bharadwaj; Masters, Karen L; O’Ryan, David; Popp, Jurgen and Thorne, Matthew R (2024). Galaxy zoo DESI: large-scale bars as a secular mechanism for triggering AGN. Monthly Notices of the Royal Astronomical Society, 532(2) pp. 2320–2330.

DOI: https://doi.org/10.1093/mnras/stae1620

Abstract

Despite the evidence that supermassive black holes (SMBHs) co-evolve with their host galaxy, and that most of the growth of these SMBHs occurs via merger-free processes, the underlying mechanisms which drive this secular co-evolution are poorly understood. We investigate the role that both strong and weak large-scale galactic bars play in mediating this relationship. Using 72,940 disc galaxies in a volume-limited sample from Galaxy Zoo DESI, we analyse the active galactic nucleus (AGN) fraction in strongly barred, weakly barred, and unbarred galaxies up to z = 0.1 over a range of stellar masses and colours. After controlling for stellar mass and colour, we find that the optically selected AGN fraction is 31.6 ± 0.9 per cent in strongly barred galaxies, 23.3 ± 0.8 per cent in weakly barred galaxies, and 14.2 ± 0.6 per cent in unbarred disc galaxies. These are highly statistically robust results, strengthening the tantalising results in earlier works. Strongly barred galaxies have a higher fraction of AGNs than weakly barred galaxies, which in turn have a higher fraction than unbarred galaxies. Thus, while bars are not required in order to grow a SMBH in a disc galaxy, large-scale galactic bars appear to facilitate AGN fuelling, and the presence of a strong bar makes a disc galaxy more than twice as likely to host an AGN than an unbarred galaxy at all galaxy stellar masses and colours.