Key points are not available for this paper at this time.
CO (1 -> 0) emission profiles are presented for 60 infrared luminous, L-ir_ (8-1000 microns) = 5 x 10¹0^-3 x 10¹2^ Lₛun_, H₀_ = 75 km s^-1^ Mpc^-1^, bright (F₆0 micron_ > 5. 24 Jy), IRAS galaxies at redshifts 1500-25, 000 km s^-1^ Most of these galaxies are sufficiently distant that a single 55" beam measures the total CO luminosity and hence the total molecular gas content. The data for these galaxies are analyzed together with that for a sample of 29 closer IRAS bright galaxies with Lᵢr_ down to 2 x 10¹0^ Lₛun_ mapped by Tinney et al. (1990). All of the IRAS bright galaxies are extremely rich in molecular gas with M (H₂_) = 1 x 10⁹^-6 x 10¹0^ Mₛun_, corresponding to 0. 5-30 times the mass of H₂_ gas in the Milky Way. The dust masses are evaluated from the IRAS data and the mean ratio of H₂_ gas to "warm dust" is 540 +/- 290. Including the mass of heavy elements and the contribution from H I implies a mean gas-to-dust ratio in the range 900-1100. The discrepancy between this value and the standard Galactic gas-to-dust ratio of ~ 150 could be due to the presence of large quantities of cold dust to which IRAS is insensitive, and/or errors in the assumed dust mass absorption coefficient. The infrared luminosity-to-H₂_ mass ratios, Lᵢr_/M (H₂_), range from 2-220 Lₛun_ M^-1^ₛun_, up to a factor of 55 times the mean ratio for molecular clouds in the Galaxy. The ratio Lᵢr_/M (H₂_) increases with increasing Lᵢr_, but shows no systematic dependence on M (H₂_). The higher values of Lᵢr_/M (H₂_) obtained in the most luminous galaxies suggests either an increased star formation efficiency and/or an additional source of luminosity. The kinetic energy of colliding galaxies is ruled out as a significant source of the luminosity in view of the independence of the Lᵢr_/M (H₂_) ratios on the galactic velocity dispersions and the merging time scales which are too long. If the excess luminosity is supplied by star formation, the implied lifetime of the interstellar medium is <= 3 x 10⁸^ yr. However, a significant number of the galaxies with the highest Lᵢr_/M (H₂_) ratios exhibit non-thermal optical emission lines characteristic of an active galactic nucleus (AGN), and an AGN appears to be an important energy source for these galaxies.
Sanders et al. (Fri,) studied this question.