Massive Molecular Gas Companions Uncovered by Very Large Array CO(1-0) Observations of the z = 5.2 Radio Galaxy TN J0924-2201

Abstract

We present Karl G. Jansky Very Large Array K-band (19 GHz) observations of the redshifted CO(1-0) line emission toward the radio galaxy TN J0924-2201 at z = 5.2, which is one of the most distant radio galaxies with CO detected. With an angular resolution of ~2″, the CO(1-0) line emission is resolved into three clumps, within ±500 km s^-1 relative to its redshift, which is determined by Lyα. We find that the clumps are located off-center and 12-33 kpc away from the center of the host galaxy, which has counterparts in the Hubble Space Telescope i band, Spitzer/IRAC, and the Atacama Large Millimeter/submillimeter Array (ALMA) band 6 (230 GHz; 1.3 mm). With the ALMA detection, we estimate the infrared luminosity L _IR and the star formation rate (SFR) of the host galaxy to be (9.3 ± 1.7) × 10¹¹ L _⊙ and 110 ± 20 M _⊙ yr^-1, respectively. We also derive the 3σ upper limit of ${M}_{{{\rm{H}}}_{2}}\lt 1.3\times {10}^{10}$ M _⊙ at the host galaxy. The detected CO(1-0) line luminosities of the three clumps, $L{{\prime} }_{\mathrm{CO}(1-0)}$ = (3.2-4.7) × 10¹⁰ K km s^-1 pc², indicate the presence of three massive molecular gas reservoirs, with ${M}_{{{\rm{H}}}_{2}}$ = (2.5-3.7) × 10¹⁰ M _⊙, assuming a CO-to-H₂ conversion factor of α _CO = 0.8 ${M}_{\odot }{({\rm{K}}\,\mathrm{km}\,{{\rm{s}}}^{-1}\,{\mathrm{pc}}^{2})}^{-1}$ , although the SFR is not elevated due to the nondetection of the ALMA 1.3 mm continuum (SFR < 40 M _⊙ yr^-1). From the host galaxy, the nearest molecular gas clump, labeled "clump A," is apparently in alignment with the radio jet axis, showing radio-CO alignment. The origins of these three clumps around TN J0924-2201 can possibly be interpreted as outflows, mergers, or jet-induced metal enrichment.