2006ApJ...652L..21E

We present the Spitzer/IRS mid-infrared spectrum of the infrared-luminous (L_IR=4x10¹¹ L_☉) brightest cluster galaxy (BCG) in the X-ray-luminous cluster Zwicky 3146 (Z3146; z=0.29). The spectrum shows strong aromatic emission features, indicating that the dominant source of the infrared luminosity is star formation. The most striking feature of the spectrum, however, is the exceptionally strong molecular hydrogen (H₂) emission lines, which seem to be shock-excited. The line luminosities and inferred warm H₂gas mass (∼10¹⁰ M_☉) are 6 times larger than those of NGC 6240, the most H₂-luminous galaxy at z≲0.05. Together with the large amount of cold H₂detected previously (∼10¹¹ M_☉), this indicates that the Z3146 BCG contains disproportionately large amounts of both warm and cold H₂gas for its infrared luminosity, which may be related to the intracluster gas cooling process in the cluster core.