Abstract
It has long been suspected that powerful radio sources may lower the efficiency with which stars form from the molecular gas in their host galaxy, however so far, alternative mechanisms, in particular related to the stellar mass distribution in the massive bulges of their host galaxies, have not been ruled out. We present new, arcsecond-resolution Atacama Large Millimeter Array (ALMA) CO(1−0) interferometry, which probes the spatially resolved, cold molecular gas in the nearby (z = 0.08), massive (Mstellar = 4 × 1011 M⊙), isolated, late-type spiral galaxy 2MASSX J23453269−044925, which is outstanding for having two pairs of powerful, giant radio jets, and a bright X-ray halo of hot circumgalactic gas. The molecular gas is in a massive (Mgas = 2.0 × 1010 M⊙), 24 kpc wide, rapidly rotating ring, which is associated with the inner stellar disk. Broad (FWHM = 70−180 km s−1) emission lines with complex profiles associated with the radio source are seen over large regions in the ring, indicating gas velocities that are high enough to keep the otherwise marginally Toomre-stable gas from fragmenting into gravitationally bound, star-forming clouds. About 1−2% of the jet kinetic energy is required to power these motions. Resolved star-formation rate surface densities derived from Galaxy Evolution Explorer and Wide-Field Infrared Survey Explorer fall by factors of 30−70 short of expectations from the standard Kennicutt–Schmidt law of star-forming galaxies, and near gas-rich early-type galaxies with signatures of star formation that are lowered by jet feedback. We argue that radio Active Galactic Nucleus (AGN) feedback is the only plausible mechanism to explain the low star-formation rates in this galaxy. Previous authors have already noted that the X-ray halo of J2345−0449 implies a baryon fraction that is close to the cosmic average, which is very high for a galaxy. We contrast this finding with other, equally massive, and equally baryon-rich spiral galaxies without prominent radio sources. Most of the baryons in these galaxies are in stars, not in the halos. We also discuss the implications of our results for our general understanding of AGN feedback in massive galaxies.
Highlights
It has long been suspected that powerful radio sources may lower the efficiency with which stars form from the molecular gas in their host galaxy, so far, alternative mechanisms, in particular related to the stellar mass distribution in the massive bulges of their host galaxies, have not been ruled out
Adopting instead αCO = 0.34 M [K km s−1 pc2]−1 as a lower limit, appropriate for optically thin gas at low excitation temperature (Bolatto et al 2013), we would find that Mgas, broad, opt thin = 1.2 × 109 M of molecular gas are perturbed by the radio source
We have presented an analysis of new Atacama Large Millimeter Array (ALMA) CO(1−0) interferometry of the massive spiral galaxy 2MASS J23454368−0449256 (J2345−0449) at z = 0.0755, which is exceptional for its multiple pairs of bright radio lobes reaching out to a maximum of 1.6 Mpc, and its bright X-ray halo (Bagchi et al 2014; Walker et al 2015)
Summary
The energy injection from active galactic nuclei (AGN) into the interstellar gas of their host galaxy is a widely accepted mechanism of galaxy evolution, which is mainly supported by the observation of fast outflows in galaxies associated with powerful AGN (e.g., Morganti et al 2005; Nesvadba et al 2006, 2008, 2017; Hardcastle et al 2012; Mahony et al 2013; Nyland et al 2013; Harrison et al 2014; Woo et al 2016; Karouzos et al 2016; Fiore et al 2017; Mukherjee et al 2018; Komossa et al 2018; Menci et al 2019; Zovaro et al 2019; Santoro et al 2020). A simple, straight forward way to break the degeneracy between radio AGN feedback and those other mechanisms would be to study the interstellar medium and star formation in a massive, gas-rich radio galaxy, which shows signatures of feedback, but which has neither bars, nor a rich environment, nor a bulge or unusually high stellar mass-surface densities. J2345−0449 is suited to investigate the impact of powerful radio activity onto the star formation in its host galaxy, because it shows no indication of several other, potentially rivaling quenching mechanisms: It has a small (
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