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

摘要

Rest-frame 0.48-1.1 μm 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] λ5007/Hβ, [S Ⅱ] λλ6716, 6731/Hα, [N Ⅱ] λ6583/Hα, and [S Ⅲ] λλ9069, 9532/Hα) 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) solar mass (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) ～ 1300-2000 and thus are the extragalactic sources with the most extreme L_(ir)/L′_(CO) 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 ～ 10~5-10~7 h~(-2) solar mass, T_d = 200-100 K) near the AGN. For F09105+4108 and F15307+ 3252, the implied circumnuclear covering factor of this dust is ～90%, while for PG 1634 + 706 the covering factor is only ～35%.