H1821+643: The Most X-Ray and Infrared Luminous Active Galactic Nucleus (AGN) in the Swift/BAT Survey in the Process of Rapid Stellar and Supermassive Black Hole Mass Assembly

Abstract

H1821+643 is the most X-ray luminous nonbeamed active galactic nucleus (AGN) of L 14–150 keV = 5.2 × 10 45 erg s −1 in the Swift/Burst Alert Telescope (BAT) ultrahard X-ray survey, and it is also a hyperluminous infrared (IR) galaxy L IR = 10 13.2 L ⊙ residing in the center of a massive galaxy cluster, which is a unique environment achieving the rapid mass assembly of black holes (BH) and host galaxies in the local universe. We decompose the X-ray to IR spectral energy distribution (SED) into the AGN and starburst component using the SED-fitting tool CIGALE -2022.0 and show that H1821+643 consumes a large amount of cold gas ( M ̇ con ) with star formation rate of log ( SFR / M ⊙ yr − 1 ) = 3.01 ± 0.04 and BH accretion rate of log ( M ̇ BH / M ⊙ yr − 1 ) = 1.20 ± 0.05 . This high M ̇ con is larger than the cooling rate ( M ̇ cool ) of the intracluster medium, M ̇ con / M ̇ cool ≳ 1 , which is 1 to 2 orders of magnitude higher than the typical value of other systems, indicating that H1821+643 provides the unique and extreme environment of rapid gas consumption. We also show that H1821+643 has an efficient cooling path achieving from 10 7 to 10 2 K thanks to [O i ] 63 μ m, which is a main coolant in low temperature range (10 4 to 10 2 K) with a cooling rate of M ̇ cool = 3.2 × 10 5 M ⊙ yr − 1 , and the star-forming region extends over 40 kpc scale.