ULTRALUMINOUS STAR-FORMING GALAXIES AND EXTREMELY LUMINOUS WARM MOLECULAR HYDROGEN EMISSION AT z=2.16 IN THE PKS 1138-26 RADIO GALAXY PROTOCLUSTER

A deep Spitzer Infrared Spectrograph map of the PKS 1138-26 galaxy protocluster reveals ultraluminous polycyclic aromatic hydrocarbon (PAH) emission from obscured star formation in three protocluster galaxies, including H alpha-emitter (HAE) 229, HAE 131, and the central Spiderweb Galaxy. Star formation rates of similar to 500-1100 M-circle dot yr(-1) are estimated from the 7.7 mu m PAH feature. At such prodigious formation rates, the galaxy stellar masses will double in 0.6-1.1 Gyr. We are viewing the peak epoch of star formation for these protocluster galaxies. However, it appears that extinction of H alpha is much greater (up to a factor of 40) in the two ULIRG HAEs compared to the Spiderweb. This may be attributed to different spatial distributions of star formation-nuclear star formation in the HAEs versus extended star formation in accreting satellite galaxies in the Spiderweb. We find extremely luminous mid-IR rotational line emission from warm molecular hydrogen in the Spiderweb Galaxy, with L(H-2 0-0 S(3)) = 1.4 x 10(44) erg s(-1) (3.7 x 10(10) L-circle dot), similar to 20 times more luminous than any previously known H2 emission galaxy (MOHEG). Depending on the temperature, this corresponds to a very large mass of > 9 x 10(6)-2 x 10(9) M-circle dot of T > 300K molecular gas, which may be heated by the PKS 1138-26 radio jet, acting to quench nuclear star formation. There is > 8 times more warm H2 at these temperatures in the Spiderweb than what has been seen in low-redshift (z < 0.2) radio galaxies, indicating that the Spiderweb may have a larger reservoir of molecular gas than more evolved radio galaxies. This is the highest redshift galaxy yet in which warm molecular hydrogen has been directly detected.