The ^ { 12 } CO J = 4 \rightarrow 3 to J = 13 \rightarrow 12 lines of the interstellar medium from nearby galaxies , newly observable with the Herschel SPIRE Fourier Transform Spectrometer ( FTS ) , offer an opportunity to study warmer , more luminous molecular gas than that traced by ^ { 12 } CO J = 1 \rightarrow 0 .
Here we present a survey of 17 nearby infrared-luminous galaxy systems ( 21 pointings ) .
In addition to photometric modeling of dust , we modeled full ^ { 12 } CO spectral line energy distributions from J = 1 \rightarrow 0 to J = 13 \rightarrow 12 with two components of warm and cool CO gas , and included LTE analysis of [ C I ] , [ C II ] , [ N II ] , and H _ { 2 } lines .
CO is emitted from a low-pressure/high-mass component traced by the low-J lines and a high-pressure/low-mass component which dominates the luminosity .
We found that , on average , the ratios of the warm/cool pressure , mass , and ^ { 12 } CO luminosity are 60 \pm 30 , 0.11 \pm 0.02 , and 15.6 \pm 2.7 .
The gas-to-dust-mass ratios are < 120 throughout the sample .
The ^ { 12 } CO luminosity is dominated by the high-J lines and is 4 \times 10 ^ { -4 } L _ { FIR } on average .
We discuss systematic effects of single-component and multi-component CO modeling ( e.g. , single-component J \leq 3 models overestimate gas pressure by \sim 0.5 dex ) , as well as compare to Galactic star-forming regions .
With this comparison , we show the molecular interstellar medium of starburst galaxies is not simply an ensemble of Galactic-type GMCs .
The warm gas emission is likely dominated by regions resembling the warm extended cloud of Sgr B2 .