Dust, Gas, and the Evolutionary Status of the Radio Galaxy 8C 1435+635 atz= 4.25

We present the results of new rest-frame far-IR observations of the z = 4.25radio galaxy, 8C1435+635, which not only confirm that it contains an enormousquantity of dust (as first inferred from its mm-wave detection by Ivison 1995)but also allow the first meaningful constraints to be placed on the mass ofthis dust and associated gas. The new measurements consist of: (i) cleardetections of sub-mm continuum emission at 450 and 850um obtained with the newsub-mm bolometer array, SCUBA, on the JCMT, (ii) continuum upper limits at 350,750 and 175um obtained with SCUBA and the PHT far-IR camera aboard ISO, and(iii) a sensitive upper limit on the CO(4-3) line flux obtained with the IRAM30-m MRT. The resulting rest-frame 33- to 238-um continuum coverage allows usto deduce that 2E8 Msun of dust at a temperature of 40 +/- 5 K is responsiblefor the observed mm/sub-mm emission. Using our CO upper limit, which constrainsM(H2)/M(dust) to <950, we go on to calculate robust limits on the total gasreserves (H2 + HI) which are thereby constrained to between 4E10 and 1.2E12Msun. The sub-mm properties of 8C1435+635 are thus strikingly similar to thoseof the z = 3.80 radio galaxy, 4C41.17, the only other high-redshift galaxydetected to date at sub-mm wavelengths whose properties appear not to beexaggerated by gravitational lensing (Dunlop et al. 1994; Hughes, Dunlop &Rawlings 1997). The inferred gas masses of both objects are sufficiently largeto suggest that the formative starbursts of massive elliptical galaxies arestill in progress at around z = 4. Observations of complete samples of radiogalaxies spanning a range of redshifts and radio luminosities will be requiredto determine if the spectacular far-IR properties of 8C1435+635 and 4C41.17 areprimarily due to their extreme redshifts or their extreme radio luminosities.Comment: 7 pages, 3 figures, LaTeX, uses emulateapj.sty (included), accepted for Ap