A new analysis of high-resolution data from the Atacama Large Millimeter/submillimeter Array (ALMA) for 5 luminous or ultra-luminous infrared galaxies gives a slope for the Kennicutt-Schmidt (KS) relation equal to 1.74 +0.09 −0.07 for gas surface densities Σ mol > 10 3 M pc −2 and an assumed constant CO-to-H 2 conversion factor. The velocity dispersion of the CO line, σ v , scales approximately as the inverse square root of Σ mol , making the empirical gas scale height determined from H ∼ 0.5σ 2 /(πGΣ mol ) nearly constant, 150-190 pc, over 1.5 orders of magnitude in Σ mol . This constancy of H implies that the average midplane density, which is presumably dominated by CO-emitting gas for these extreme star-forming galaxies, scales linearly with the gas surface density, which, in turn, implies that the gas dynamical rate (the inverse of the free-fall time) varies with Σ 1/2 mol , thereby explaining most of the super-linear slope in the KS relation. Consistent with these relations, we also find that the mean efficiency of star formation per free-fall time is roughly constant, 5%-7%, and the gas depletion time decreases at high Σ mol , reaching only ∼ 16 Myr at Σ mol ∼ 10 4 M pc −2 . The variation of σ v with Σ mol and the constancy of H are in tension with some feedback-driven models, which predict σ v to be more constant and H to be more variable. However, these results are consistent with simulations in which large-scale gravity drives turbulence through a feedback process that maintains an approximately constant Toomre Q instability parameter.

Jets and outflows are an integral part of the star formation process. While there are many detailed studies of molecular outflows towards individual star-forming sites, few studies have surveyed an entire star-forming molecular cloud for this phenomenon. The 100-deg 2 Five College Radio Astronomy Observatory CO survey of the Taurus Molecular Cloud provides an excellent opportunity to undertake an unbiased survey of a large, nearby, molecular cloud complex for molecular outflow activity. Our study provides information on the extent, energetics and frequency of outflows in this region, which are then used to assess the impact of outflows on the parent molecular cloud. The search identified 20 outflows in the Taurus region, eight of which were previously unknown. Both 12 CO and 13 CO data cubes from the Taurus molecular map were used, and dynamical properties of the outflows are derived. Even for previously known outflows, our large-scale maps indicate that many of the outflows are much larger than previously suspected, with eight of the outflows (40 per cent) being more than a parsec long. The mass, momentum and kinetic energy from the 20 outflows are compared to the repository of turbulent energy in Taurus. Comparing the energy deposition rate from outflows to the dissipation rate of turbulence, we conclude that outflows by themselves cannot sustain the observed turbulence seen in the entire cloud. However, when the impact of outflows is studied in selected regions of Taurus, it is seen that locally outflows can provide a significant source of turbulence and feedback. The L1551 dark cloud which is just south of the main Taurus complex was not covered by this survey, but the outflows in L1551 have much higher energies compared to the outflows in the main Taurus cloud. In the L1551 cloud, outflows can not only account for the turbulent energy present, but are probably also disrupting their parent cloud. We conclude that for a molecular cloud like Taurus, an L1551-like episode occurring once every 10 5 years is sufficient to sustain the turbulence observed. Five of the eight newly discovered outflows have no known associated stellar source, indicating that they may be embedded Class 0 sources. In Taurus, 30 per cent of Class I sources and 12 per cent of flat-spectrum sources from the Spitzer young stellar object (YSO) catalogue have outflows, while 75 per cent of known Class 0 objects have outflows. Overall, the paucity of outflows in Taurus compared to the embedded population of Class I and flat-spectrum YSOs indicates that molecular outflows are a short-lived stage marking the youngest phase of protostellar life. The current generation of outflows in Taurus highlight an ongoing period of active star formation, while a large fraction of YSOs in Taurus have evolved well past the Class I stage.

We present J HCN 4 3 =  and J HCO 4 3 =  + maps of six nearby star-forming galaxies, NGC 253, NGC 1068, IC 342, M82, M83, and NGC 6946, obtained with the James Clerk Maxwell Telescope as part of the MALATANG survey. All galaxies were mapped in the central 2′×2′region at 14″ (FWHM) resolution (corresponding to linear scales of ∼0.2-1.0 kpc). The L IR -L′ dense relation, where the dense gas is traced by the J HCN 4 3 =  and the J HCO 4 3 =  + emission, measured in our sample of spatially resolved galaxies is found to follow the linear correlation established globally in galaxies within the scatter. We find that the luminosity ratio, L IR /L′ dense , shows systematic variations with L IR within individual spatially resolved galaxies, whereas the galaxy-integrated ratios vary little. A rising trend is also found between L IR /L′ dense ratio and the warm-dust temperature gauged by the 70 μm/100 μm flux ratio. We find that the luminosity ratios of IR/HCN (4-3) and IR/HCO + (4-3), which can be taken as a proxy for the star formation efficiency (SFE) in the dense molecular gas

We present ∼ 0.1" resolution (∼ 10 pc) ALMA observations of a molecular cloud identified in the merging Antennae galaxies with the potential to form a globular cluster, nicknamed the "Firecracker." Since star formation has not yet begun at an appreciable level in this region, this cloud provides an example of what the birth environment of a globular cluster may have looked like before stars form and disrupt the natal physical conditions. Using emission from 12 CO(2-1), 12 CO(3-2), 13 CO(2-1), HCN(4-3), and HCO + (4-3) molecular lines, we are able to resolve the cloud's structure and find that it has a characteristic radius of 22 pc and a mass of 1-9×10 6 M . We also put constraints on the abundance ratios of 12 CO/ 13 CO and H 2 / 12 CO. Based on the calculation of the mass, we determine that the commonly used CO-to-H 2 conversion factor in this region varies spatially, with average values in the range X CO = (0.12 − 1.1) × 10 20 cm −2 (K km s −1 ) −1 . We demonstrate that if the cloud is bound (as is circumstantially suggested by its bright, compact morphology), an external pressure in excess of P/k > 10 8 K cm −3 is required. This would be consistent with theoretical expectations that globular cluster formation requires high pressure environments, much higher than typical values found in the Milky Way. The position-velocity diagram of the cloud and its surrounding material suggests that this high pressure may be produced by ram pressure from the collision of filaments. The radial profile of the column density can be fit with both a Gaussian and a Bonnor-Ebert profile. If the Bonnor-Ebert fit is taken to be indicative of the cloud's physical structure, it would imply the cloud is gravitationally stable and pressure-confined. The relative line strengths of HCN and HCO + in this region also suggest that these molecular lines can be used as a tracer for the evolutionary stage of a cluster.

We study the relationship between dense gas and star formation in the Antennae galaxies by comparing ALMA observations of dense gas tracers (HCN, HCO + , and HNC J = 1 − 0) to the total infrared luminosity (L TIR ) calculated using data from the Herschel Space Observatory and the Spitzer Space Telescope. We compare the luminosities of our SFR and gas tracers using aperture photometry and employing two methods for defining apertures. We taper the ALMA dataset to match the resolution of our L TIR maps and present new detections of dense gas emission from complexes in the overlap and western arm regions. Using OVRO CO J = 1 − 0 data, we compare with the total molecular gas content, M(H 2 ) tot , and calculate star formation efficiencies and dense gas mass fractions for these different regions. We derive HCN, HCO + and HNC upper limits for apertures where emission was not significantly detected, as we expect emission from dense gas should be present in most star-forming regions. The Antennae extends the linear L TIR − L HCN relationship found in previous studies. The L TIR − L HCN ratio varies by up to a factor of ∼10 across different regions of the Antennae implying variations in the star formation efficiency of dense gas, with the nuclei, NGC 4038 and NGC 4039, showing the lowest SFE dense (0.44 and 0.70 ×10 −8 yr −1 ). The nuclei also exhibit the highest dense gas fractions (∼ 9.1% and ∼ 7.9%).