Near Infrared Spectroscopy And The Search For Co Emission In 3 Extremely Luminous Iras Sources

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 (HyLIGs: L _ir ≥ 10¹³ L⨀ where L _ir ∼ L(8 – 1000μm) 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/Hß, [S II] λ6724/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. Upper limits on the molecular gas mass for all three sources are M(H₂) < 1 – 3 x 10¹⁰ h ^-2 M⨀ (q0 = 0.5, H ₀ = 100h km s^-1 Mpc^-1), less than the H₂ mass of the most gas-rich infrared galaxies in the local Universe. All three sources have L _ir/L′_CO ∼ 1300 – 2000, the most extreme values for extra-galactic sources measured to date. Given the relatively warm far-infrared colors for all three objects, much of their infrared luminosity may emanate from a relatively small quantity of hot dust near an AGN.