Massive molecular gas companions uncovered by VLA CO(1-0) observations of the $z$ = 5.2 radio galaxy TN J0924$-$2201

Abstract

We present Karl G. Jansky Very Large Array (VLA) 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 CO-detected radio galaxies. With the angular resolution of $\sim 2^{\prime \prime }$, the CO(1-0) line emission is resolved into three clumps, within $\pm 500$ km\,s${}^{-1}$ relative to its redshift, where is determined by Ly$\alpha$. We find that they locate off-center and 12-33 kpc away from the center of the host galaxy, which has counterparts in $HST$ $i$-band, $Spitzer$/IRAC and ALMA Band-6 (230 GHz; 1.3 mm). With the ALMA detection, we estimate $L_{\mathrm{IR}}$ and SFR of the host galaxy to be $(9.3\pm 1.7)\times 10^{11}{L}_{\odot }$ and $110\pm 20$ $M_{\odot }\mathrm{y}{\mathrm{r}}^{-1}$, respectively. We also derive the $3\sigma$ upper limit of $M_{{\mathrm{H}}_2}<1.3\times 10^{10}$ $M_{\odot }$ at the host galaxy. The detected CO(1-0) line luminosities of three clumps, $L_{\mathrm{CO}(1-0)}^{\prime }$ = (3.2-4.7)$\times 10^{10}$ $\mathrm{K}\mathrm{km}{\mathrm{s}}^{-1}\mathrm{p}{\mathrm{c}}^2$, indicate the presence of three massive molecular gas reservoirs with $M_{{\mathrm{H}}_2}$ = (2.5-3.7)$\times 10^{10}$ $M_{\odot }$, by assuming the CO-to-H${}_2$ conversion factor ${\alpha }_{\mathrm{CO}}=0.8$ $M_{\odot }(\mathrm{K}\mathrm{km}{\mathrm{s}}^{-1}\mathrm{p}{\mathrm{c}}^2{)}^{-1}$, although the star formation rate (SFR) is not elevated because of the non-detection of ALMA 1.3 mm continuum (SFR $<$ 40 $M_{\odot }$ yr${}^{-1}$). From the host galaxy, the nearest molecular gas clump labeled as clump A, is apparently aligning with the radio jet axis, showing the radio-CO alignment. The possible origin of these three clumps around TN J0924$-$2201 can be interpreted as merger, jet-induced metal enrichment and outflow.

14 pages, 9 figures. Accepted for publication in ApJ

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• Gas-Poor Hosts and Gas-Rich Companions of $z\approx$3.5 Radio Active Galactic Nuclei: ALMA Insights into Jet Triggering and Feedback