Kiloparsec-scale AGN outflows and feedback in merger-free galaxies

Smethurst, Rebecca J and Simmons, Brooke and Coil, A.L. and Lintott, Chris J and Keel, William and Masters, Karen L. and Glikman, Eilat and Leung, Gene and Shanahan, J. and Garland, Izzy (2021) Kiloparsec-scale AGN outflows and feedback in merger-free galaxies. Monthly Notices of the Royal Astronomical Society, 507 (3). pp. 3985-3997. ISSN 0035-8711

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Abstract

Recent observations and simulations have challenged the long-held paradigm that mergers are the dominant mechanism driving the growth of both galaxies and supermassive black holes (SMBH), in favour of non-merger (secular) processes. In this pilot study of merger-free SMBH and galaxy growth, we use Keck Cosmic Web Imager spectral observations to examine four low-redshift (0.043 < z < 0.073) disc-dominated ‘bulgeless’ galaxies hosting luminous active galactic nucleus (AGN), assumed to be merger-free. We detect blueshifted broadened [O III] emission from outflows in all four sources, which the [OIII]/Hβ ratios reveal are ionized by the AGN. We calculate outflow rates in the range 0.12−0.7 M⊙ yr−1⁠, with velocities of 675−1710 km s−1⁠, large radial extents of 0.6−2.4 kpc⁠, and SMBH accretion rates of 0.02−0.07 M⊙ yr−1⁠. We find that the outflow rates, kinematics, and energy injection rates are typical of the wider population of low-redshift AGN, and have velocities exceeding the galaxy escape velocity by a factor of ∼30, suggesting that these outflows will have a substantial impact through AGN feedback. Therefore, if both merger-driven and non-merger-driven SMBH growth lead to co-evolution, this suggests that co-evolution is regulated by feedback in both scenarios. Simulations find that bars and spiral arms can drive inflows to galactic centers at rates an order of magnitude larger than the combined SMBH accretion and outflow rates of our four targets. This work therefore provides further evidence that non-merger processes are sufficient to fuel SMBH growth and AGN outflows in disc galaxies.