Near-infrared spectroscopy and a search for CO emission in three extremely luminous IRAS sources:: IRAS F09105+4108, IRAS F15307+3252, and PG 1634+706

Rest-frame 0.48-1.1 mu m emission-line strengths and molecular gas mass (H-2) upper limits for three luminous infrared sources-the hyperluminous infrared galaxies IRAS F09105 + 4108 (z = 0.4417), IRAS F15307 + 3252 (z = 0.926), and the optically selected QSO PG 1634 + 706 (z = 1.338)-are presented. Diagnostic emission-line ratios ([O III] lambda 5007/H beta, [S II] lambda lambda 6716, 6731/H alpha, [N II] lambda 6583/H alpha, and [S III] lambda lambda 9069, 9532/H alpha) indicate a Seyfert 2-like spectrum for both infrared galaxies, consistent with previously published work. The upper limits of molecular gas mass for all three sources are M(H-2) < (1-3) x 10(10) h(-2) M. (q(0) = 0.5, H-0 = 100 h km s(-1) Mpc(-1)), less than that of the most gas-rich infrared galaxies in the local universe. All three sources have L-ir/L-CO' similar to 1300-2000 and thus are the extragalactic sources with the most extreme Lir/LCO' values measured to date. Given the relatively warm far-infrared colors for all three objects, much of their infrared luminosity may emanate from a relatively modest amount of warm dust (e.g., M-d similar to 10(5)-10(7) h(-2) M., T-d = 200-100 K) near the AGN. For F09105 + 4108 and F15307 + 3252, the implied circumnuclear covering factor of this dust similar to 90%, while for PG 1634 + 706 the covering factor is only similar to 35%.