Cold Gas and Star Formation in the Phoenix Cluster with JWST

We present integral field unit observations of the Phoenix Cluster with the JWST Mid-infrared Instrument’s Medium Resolution Spectrometer. We focus this study on the molecular gas, dust, and star formation in the brightest cluster galaxy (BCG). We use precise spectral modeling to produce maps of the silicate dust, molecular gas, and polycyclic aromatic hydrocarbons (PAHs) in the inner ∼50 kpc of the cluster. We measure the optical depth from silicates by comparing the observed H₂ line ratios to those predicted by excitation models. We provide updated measurements of the total molecular gas mass of 1 . 9 − 0.4 + 0.5 × 1 0 10 M_⊙, which agrees with CO-based estimates, providing an estimate of the CO-to-H₂ conversion factor of α CO = 0.8 ± 0.2 M ⊙ pc − 2 ( K km s − 1 ) − 1 ; an updated stellar mass of M_* = 2.6 ± 0.5 × 10¹⁰ M_⊙ ; and star formation rates (SFRs) averaged over 10 and 100 Myr of 〈SFR〉₁₀ = 1340 ± 100 M_⊙ yr⁻¹ and 〈SFR〉₁₀₀ = 740 ± 80 M_⊙ yr⁻¹, respectively. The H₂ emission seems to be powered predominantly by shocks and star formation within the central ∼20 kpc, induced by stellar feedback and radio jets from the active galactic nucleus. Additionally, we find nearly an order-of-magnitude drop in the SFRs estimated by PAH fluxes in cool core BCGs compared to field galaxies, suggesting that hot particles from the intracluster medium are destroying PAH grains even in the central-most tens of kiloparsecs.