Revisiting the Dragonfly galaxy II. Young, radiatively efficient radio-loud AGN drives massive molecular outflow in a starburst merger at z = 1.92

Abstract

Radio-loud active galactic nuclei (RLAGNs) are a unique AGN population and were thought to be preferentially associated with supermassive black holes (SMBHs) at low accretion rates. They could impact the host galaxy evolution by expelling cold gas through the jet-mode feedback. In this work, we studied CO(6-5) line emission and continuum emission in a high-redshift radio galaxy, MRC 0152-209, at z = 1.92 using ALMA (Atacama Large Millimeter/submillimeter Array) up to a 0.024′′ resolution (corresponding to ∼200 pc at z = 1.92). This system is a starburst major merger comprising two galaxies: the north-west (NW) galaxy hosting the RLAGN with jet kinetic power Ljet ≥ 2×1046 erg s-1 and the other galaxy to the south-east (SE). Based on the spectral energy distribution fitting for the entire system (NW + SE galaxies), we find an AGN bolometric luminosity LAGN,bol ∼3 ×1046 erg s-1 with a lower limit of ∼0.9 ×1046 erg s-1 for the RLAGN. We estimate the black hole mass through MBH-M∗ scaling relations and find an Eddington ratio of λEdd ∼0.07-4 conserv ati vely by adopting the lower limit of LAGN,bol and considering the dispersion of the scaling relation. These results suggest that the RLAGN is radiatively efficient and the powerful jets could be launched from a super-Eddington accretion disc. ALMA Cycle 6 observations further reveal a massive ( MH2 = (1.1-2.3) ×109 M⊙), compact ( ∼500 pc), and monopolar molecular outflow perpendicular to the jet axis. The corresponding mass outflow rate (1200-300+300-2600 -600+600 M⊙yr-1 ) is comparable with the star formation rate of at least ∼2100 M⊙yr-1. Depending on the outflowing molecular gas mass, the outflow kinetic power/ L AGN, bol ratio of ∼0.008-0.02, and momentum boost factor of ∼3-24 agree with a radiative-mode AGN feedback scenario. On the other hand, the jets can also drive the molecular outflow within its lifetime of ∼2 ×105 yr without additional energy supply from AGN radiation. The jet-mode feedback is then capable of removing all cold gas from the host galaxy through the long-term, episodic launching of jets. Our study reveals a unique object where starburst acti vity, po werful jets, and rapid BH growth co-exist, which may represent a fundamental stage of AGN-host galaxy co-evolution.