DUST, GAS, AND THE EVOLUTIONARY STATUS OF THE RADIO GALAXY 8C 1435+635 AT Z=4.25

We present the results of new rest-frame far-IR observations of the z = 4.25 radio galaxy 8C 1435 + 635, which not only confirm that it cont ains an enormous quantity of dust (as first inferred from its millimet er-wave detection by Ivison in 1995), but also allow the first meaning ful constraints to be placed on the mass of this dust and associated g as. The new measurements consist of (1) clear detections of submillime ter continuum emission at lambda(obs) = 450 and 850 mu m obtained with the new submillimeter bolometer array, SCUBA, on the James Clerk Maxw ell Telescope, (2) continuum upper limits at lambda(obs) = 350, 750, a nd 175 mu m obtained with SCUBA and the PHT far-IR camera aboard the I nfrared Space Observatory, and (3) a sensitive upper limit on the CO ( 4-3) line flux obtained with the IRAM 30 m Millimeter Radio Telescope. The resulting rest-frame 33-238 mu m continuum coverage allows us to deduce that 2 x 10(8) M-circle dot of dust at a temperature of 40 +/- 5 K is responsible for the observed millimeter/ submillimeter emission . Using our CO upper limit, which constrains M-H2/M-d to less than 950 , we go on to calculate robust limits on the total gas reserves (H-2 H I), which are thereby constrained to between 4 x 10(10) and 1.2 x 1 0(12) M-circle dot. The submillimeter properties of 8C 1435 + 635 are thus strikingly similar to those of the z = 3.80 radio galaxy 4C 41.17 , the only other high-redshift galaxy detected to date at submillimete r wavelengths whose properties appear not to be exaggerated by gravita tional lensing. The inferred gas masses of both objects are sufficient ly large to suggest that the formative starbursts of massive elliptica l galaxies are still in progress at z similar or equal to 4. Observati ons of complete samples of radio galaxies spanning a range of redshift s and radio luminosities will be required to determine whether the spe ctacular far-IR properties of 8C 1435 + 635 and 4C 41.17 are primarily due to their extreme redshifts or to their extreme radio luminosities .