Revisiting the Group-dominant Elliptical NGC 5044 in the Radio Band: Continuum Emission and Detection of H <scp>i</scp> Absorption

Abstract We present new MeerKAT L -band (continuum and H i ) and upgraded Giant Metrewave Radio Telescope (300–850 MHz) observations of the archetypal cool-core group-dominant early-type galaxy NGC 5044. Our new continuum images reveal diffuse, steep spectrum ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>α</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0.99</mml:mn> <mml:mspace width="0.25em"/> <mml:mi mathvariant="normal">GHz</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>1.56</mml:mn> <mml:mspace width="0.25em"/> <mml:mi mathvariant="normal">GHz</mml:mi> </mml:mrow> </mml:msubsup> <mml:mo>=</mml:mo> <mml:mo>−</mml:mo> <mml:mn>1.53</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.6</mml:mn> </mml:math> ) radio emission extending about 25 kpc around the unresolved radio core. The observed radio emission overlaps the known X-ray cavities but is not confined to them. We also find the first direct evidence of neutral atomic gas in NGC 5044, in the form of a 3.8 σ significant two-component H i absorption line seen against the emission of the active nucleus. The peak velocities are well correlated with the previously reported CO(2–1) absorption, but the H i lines are moderately broader, spanning velocities from 265 to 305 km s −1 . We do not detect H i emission but place an upper limit of M H i &lt; 5.4 × 10 7 M ⊙ in the central 15″ (2.2 kpc) of the galaxy. This is significantly less than the estimated molecular gas content and implies a molecular-to-atomic mass ratio of &gt;∼1.7:1, consistent with these gas phases forming through cooling from the hot intra-group medium. We also constrain the spin temperature to T spin ≤ 950 K, indicating that the detected H i is in the cold neutral phase.