AGN Fueling and Radio Jet Evolution in the Galaxy Group NGC 5044 Revealed by VLBA H <scp>I</scp> Absorption and Proper Motion Radio Observations

Abstract The role of cooling gas in triggering active galactic nucleus (AGN) feedback in the centers of galaxy groups and clusters remains a key open question. NGC 5044, the X-ray-brightest galaxy group, hosts the largest known reservoir of molecular gas among cool-core groups and exhibits multiple AGN outbursts, making it an ideal system in which to study AGN feeding. We present new multifrequency Very Long Baseline Array (VLBA) observations of NGC 5044 at 1.4 GHz, 4.9 GHz, and 8.4 GHz, combining continuum imaging with H I spectroscopy. At 1.4 GHz, we recovered the previously known symmetric northeast–southwest jets extending for ∼5.5 pc each, along with evidence for previously undetected, more extended faint emission aligned with the older, kiloparsec-scale outbursts. Comparison of 4.9 GHz and 8.4 GHz data from 2020 and 2024 reveals clear outward proper motion of jet components, yielding an average expansion speed of (0.10 ± 0.02) c and implying a dynamical age of ∼180 yr for the ejection of the parsec-scale jet components. The jet width profile suggests a transition from parabolic to conical collimation at a few ×10 4 Schwarzschild radii. We detect a narrow, redshifted H I absorption line at +264 km s −1 against the VLBA core, tracing a compact, cold atomic cloud within ∼10–20 pc of the AGN. The close correspondence in velocity with previously detected CO and H I absorption features in Atacama Large Millimeter/submillimeter Array and MeerKAT data, respectively, demonstrates that cold atomic and molecular gas coexists in infalling clouds at parsec scales. Overall, these results provide an unprecedented high-angular-resolution view of AGN cycling, jet growth, and feeding in a galaxy group environment.