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 Ly α . 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) × 10 ^11 L _⊙ and 110 ± 20 M _⊙ yr ^−1 , respectively. We also derive the 3 σ 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) × 10 ^10 K km s ^−1 pc ^2 , indicate the presence of three massive molecular gas reservoirs, with ${M}_{{{\rm{H}}}_{2}}$ = (2.5–3.7) × 10 ^10 M _⊙ , assuming a CO-to-H _2 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.

Keywords

• High-redshift galaxies
• Radio galaxies
• Radio active galactic nuclei
• AGN host galaxies