Warm ionized gas outflows in Active Galactic Nuclei: What causes them?

Abstract

The driving force behind outflows, often invoked to understand the correlation between the supermassive black holes powering active galactic nuclei (AGN) and their host galaxy properties, remains uncertain. We provide new insights into the mechanisms that trigger warm ionized outflows in AGN, based on findings from the MaNGA survey. Our sample comprises 538 AGN with strong [O iii] λ5007 emission lines, of which 197 are detected in radio and 341 are radio-undetected. We analyzed the [O iii] λ5007 line in summed spectra, extracted over their central 500 × 500 pc2 region. The calculated Balmer 4000 Å break, Dn4000, is larger than 1.45 for ∼95% of the sources, indicating that the specific star formation rate in their central regions is less than 10−11.5 yr−1, which points to evidence of negative AGN feedback suppressing star formation. Considering the whole sample, radio-detected sources show a greater outflow detection rate (56% ± 7%) than radio-undetected sources (25% ± 3%). They also show higher velocity, mass outflow rate, outflow power, and outflow momentum rate. We noticed a strong correlation between outflow characteristics and bolometric luminosity in both samples, except that the correlation is steeper for the radio-detected sample. Our findings suggest that (a) warm ionized outflows are prevalent in all types of AGN, (b) radiation from AGN is the primary driver of these outflows, (c) radio jets are likely to play a secondary role in enhancing the gas kinematics over and above that caused by radiation, and (d) there is very little star formation in the central regions of the galaxies, possibly due to negative feedback from AGN activity.