The molecular gas in Luminous Infrared Galaxies I: CO lines, extreme physical conditions, and their drivers

摘要: We report results from a large molecular line survey of luminous infrared galaxies (L-IR greater than or similar to 10(11) L-circle dot) in the local Universe (z less 0.1), conducted during last decade with James Clerk Maxwell Telescope and IRAM 30-m telescope. This work presents CO 13CO data for 36 galaxies, further augmented by multi-J total luminosities available other (IR) bright literature. yields combined sample N = 70 star formation (SF) powered fraction their IR spanning L-IR((+))similar to(10(10)-2 x10(12))L-circle dot wide range morphologies. Simple comparisons spectral energy distributions (SLEDs) ones, as well radiative transfer models, discern surprisingly average interstellar medium (ISM) conditions, most surprises found high-excitation regime. These take form global SLEDs dominated very warm (T-kin 100 K) dense (n >= 10(4) cm(-3)) gas phase, involving galaxy-sized (similar to(few) x 10(9) M-circle mass reservoirs under conditions that are typically only to(13) per cent typical SF cloud Galaxy. Furthermore, some highest excitation ultraluminous (ULIRGs; L-IR 10(12)L(circle dot)) surpass even those solely compact SF-powered hot spots Galactic clouds. Strong supersonic turbulence high cosmic ray densities rather far-ultraviolet/optical photons supernova remnant induced shocks individual sites can globally amounts these merger-driven starbursts easily power extraordinary excitation. exciting possibility now be systematically investigated Herschel Atacama Large Milimeter Array (ALMA). As expected an IR-selected (and thus rate selected) galaxy sample, few cold found, fewer still low/moderate-density gravitationally bound state (i.e. type) emerges likely one. The rest remain compatible unbound low-density phase often ULIRGs. Such degeneracies, prominent when low-J SLED segment (J 10, 21 32) is available, advise against using its ratios so-called X-co M(H-2)/L-co(10) factor mode indicators, practice may have led misclassification ISM environments gas-rich discs distant Universe. Finally, we expect among LIRGs will strongly impact factor, issue examine detail Paper II.