Near Infrared Spectroscopy and the Search for CO Emission in 3 Extremely Luminous IRAS Sources

Extract

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 ≥ 10¹³L_⊙ 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/Hβ, [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 × 10¹⁰h⁻²M_⊙ (q₀ = 0.5, H₀ = 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 extragalactic 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.