We present the first statistical survey of the properties of the 12 CO(1-0) and 12 CO(3-2) line emission from the nuclei of a nearly complete subsample of 60 infrared (IR) luminous galaxies selected from SCUBA Local Universe Galaxy Survey (SLUGS). This subsample is flux limited at S 60µm ≥ 5.24 Jy with far-IR (FIR) luminosities mostly at L F IR > 10 10 L ⊙ . We compare the emission line strengths of 12 CO(1-0) and (3-2) transitions at a common resolution of 15 ′′ . The measured 12 CO(3-2) to (1-0) line intensity ratios r 31 vary from 0.22 to 1.72 with a mean value of 0.66 for the sources observed, indicating a large spread of the degree of excitation of CO in the sample. These CO data, together with a wide range of data at different wavelengths obtained from the literature, allow us to study the relationship between the CO excitation conditions and the physical properties of gas/dust and star formation in the central regions of galaxies. Our analysis shows that there is a non-linear relation between CO and FIR luminosities, such that their ratio L CO /L F IR decreases linearly with increasing L F IR . This behavior was found to be consistent with the Schmidt Law relating star formation rate to molecular gas content, with an index N = 1.4 ± 0.3. We also find a possible

For the Antennae interacting galaxy pair, we have obtained high quality, fully sampled 12 CO J=1-0 and 3-2 maps of the regions surrounding the nuclei and the area of overlap between the two galaxies. The maps possess an angular resolution of 15 ′′ or 1.5 kpc, so far the highest resolution maps available at both the J=1-0 and 3-2 transitions. In addition, 12 CO J=2-1 data have been obtained for the positions of the two nuclei as well as in part of the overlap region with 20 ′′ angular resolution. The 12 CO J=1-0, 2-1, 3-2 emission all peak in an off-nucleus region adjacent to where the two disks overlap. Use of the conventional X factor yields ∼ 4 × 10 9 M ⊙ molecular gas mass in the overlap region. It is difficult to understand how such a large amount of molecular gas can be accumulated in this region given the relatively short lifetime of molecular clouds and the limited period of time for this region to form.Line emission at 13 CO J=2-1 and 3-2 is detected at selected points in the two nuclei and the overlap region. Both the 12 CO/ 13 CO J=2-1 and 3-2 integrated intensity ratios are remarkably high in the overlap region. This is the first published case in which such high 12 CO/ 13 CO J=2-1 and 3-2 ratios are found outside a galactic nucleus. Detailed LVG modeling indicates that the 12 CO and 13 CO emission originate in different spatial components. The 12 CO emission may originate within a non-virialized low density gas component with a large velocity gradient. Assuming a CO-to-H 2 abundance ratio of 10 −4 , the X factor given by the LVG model is an order of magnitude lower than the conventional value for molecular clouds in the Milky Way, but it scales inversely as the assumed value for this ratio. Accordingly, we suggest the possibility that the strong CO emission in the overlap region of the Antennae galaxies is associated with increased radiative efficiency, possibly caused by a large velocity dispersion within the individual molecular clouds.A comparison of the CO J=3-2 emission with the SCUBA 850 µm continuum in the Antennae galaxies shows that the CO line emission contributes globally 46% of the 850 µm continuum flux and that the ratio of 12 CO J=3-2 to SCUBA 850 µm flux varies by a factor of two across the system. After correcting for the 12 CO J=3-2 contamination, the dust emission at 850 µm detected by SCUBA is consistent with the thermal emission from a single warm dust component with a mass of 1.7 ×10 7 M ⊙ .

No abstract

Abstract. The Taffy Galaxies system, UGC 12914/5, contains huge amounts of molecular gas in the bridge region between the receding spirals after a direct collision. 2−9 × 10 9 M of molecular gas is present between the galaxies, more than the CO emission from the entire Milky Way! Such dense gas can only be torn off by collisions between dense clouds, in this case with relative velocities of about 800 km s −1 , such that the remnant cloud acquires an intermediate velocity and is left in the bridge after separation of the colliding galaxies. We suggest that after ionization in the collision front, the gas cooled and recombined very quickly such that the density remained high and the gas left the colliding disks in molecular form.

ABSTRACT. New, low-noise receivers have allowed detection, in several giant H II regions, of RydbergRydberg transitions of hydrogen that cover a large range of *n-values in a single observing window. This, in turn, allows lines covering a large range in principal quantum number n to be detected simultaneously with the same antenna beam. We have employed a new frequency-switching technique which allows a very precise determination of the line widths. We have used this technique with the NRAO 140 foot telescope to observe lines in W51 and Orion A near 6 GHz, with *n-values that vary by a factor of D21 (*n \ 1ÈD21) and corresponding n-values that vary by a factor of 2.7 (n \ 102È274). By generating Voigt line proÐles using GriemÏs theory of impact broadening by electrons, inserting them into a telescope data Ðle, and processing them in a manner identical to that of the telescope data, we have been able to examine how the observing and reduction techniques a †ect both the line widths and line areas as n increases. For n ¹ 180, *n ¹ 6, our restored line widths and areas give densities of and 4000 cm~3 in W51 and Orion A, respectively. N e \ 2500 These densities are higher than reported previously with a 5@ beamwidth. For higher n-values we are unable to Ðt our data using GriemÏs theory. For n [ 180, *n [ 6, our telescope-measured line widths fall rapidly below predicted values, while the line areas simultaneously increase above predicted values. This behavior of the line area as the line widths decrease is inconsistent with GriemÏs theory or an instrumental e †ect. Observations of Orion A at 17.6 GHz, with a beamwidth, require a density in excess of cm~3 1@ .7 N e \ 20,000 to Ðt. Although the detected lines cover a range in n and *n from 71 to 177 and 1 to 17, respectively, there is no evidence for a line width decrease at the high *n-values. We conclude from this that the line narrowing seen at 6 GHz is related to the principal quantum number.