Near‐Infrared Spectroscopy and a Search for CO Emission in Three Extremely LuminousIRASSources: IRAS F09105+4108, IRAS F15307+3252, and PG 1634+706

Abstract

Rest-frame 0.48-1.1 μm emission-line strengths and molecular gas mass (H2) 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(H2) < (1-3) × 1010 h-2 M☉ (q0 = 0.5, H0 = 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/L~1300-2000 and thus are the extragalactic sources with the most extreme L/L 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., Md ~ 105-107 h-2 M☉, Td = 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%.