Probing Radio-Mode AGN Feedback in NGC 1316: ALMA CO Mapping at GMA Scales
Kana Morokuma (University of Tokyo)
Abstract:
Active galactic nuclei (AGN) feedback is essential for regulating the number density of massive galaxies. While radio-mode feedback is widely recognized for its large-scale impact, suppressing cooling flows in the intracluster and intergalactic media to prevent gas accretion onto central galaxies, recent simulations highlight a direct, small-scale effect. Relativistic jets and their associated ionizing bubbles can inject turbulence into molecular clouds, directly hindering star formation within galaxies. To investigate these effects, we conducted high-resolution (100 pc) CO(J=1-0) mapping of a nearby radio galaxy NGC 1316 (Fornax A) using ALMA, supplementing archival CO(J=2-1) and CO(J=3-2) data. Our analysis reveals: (1) a substantial contribution of single-dish data to the total CO(J=1-0) flux, (2) the identification of approximately 20 giant molecular cloud associations with high velocity dispersions relative to their sizes, suggesting gravitationally unbound structures, (3) globally typical CO line ratios of R21 = CO(J=2-1)/CO(J=1-0)~0.7 and R31 = CO(J=3-2)/CO(J=3-2)~0.3 (in Kelvin units), and (4) elevated R21 and R31 values approaching unity within the central CO spectral wind. These findings provide observational evidence supporting theoretical predictions of AGN feedback on small scales. Furthermore, the enhanced line ratios observed in the central region suggest that recent AGN activity is driving molecular gas outflow.
Caption:
Moment 0–2 and continuum maps of 12 CO(J=1–0) extracted from the data cube of NGC 1316 in the ICRS frame: (a) moment 0 (integrated intensity, Jy beam−1 km s−1), (b) moment 1 (velocity field, km s−1), (c) moment 2 (velocity dispersion, km s−1), and (d) continuum maps (mJy beam−1).
The white contours show moment 0 with contour levels of [1.0, 5.0, 10, 20] × 3σ mom0, 6ch , where σ mom0, 6ch is the rms noise of the moment-0 map when averaging six channels together (0.3 Jy beam−1 km s−1 ). The galaxy center is indicated with a white cross. The resultant ALMA beam is shown as a filled white ellipse in the bottom left corner of each panel.
Source: Morokuma-Matsui et al. (2019, PASJ, 71, 85)