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

October 1998 • 1998ApJ...506..205E

Authors • Evans, A. S. • Sanders, D. B. • Cutri, R. M. • Radford, S. J. E. • Surace, J. A. • Solomon, P. M. • Downes, D. • Kramer, C.

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_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 ~ 10⁵-10⁷ 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 is ~90%, while for PG 1634+706 the covering factor is only ~35%.

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Roc Cutri

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