A major goal of the Atacama Large Millimeter/submillimeter Array (ALMA) is to make accurate images with resolutions of tens of milliarcseconds, which at submillimeter (submm) wavelengths requires baselines up to ∼15 km. To develop and test this capability, a Long Baseline Campaign (LBC) was carried out from 2014 September to late November, culminating in end-to-end observations, calibrations, and imaging of selected Science Verification (SV) targets. This paper presents an overview of the campaign and its main results, including an investigation of the short-term coherence properties and systematic phase errors over the long baselines at the ALMA site, a summary of the SV targets and observations, and recommendations for science observing strategies at long baselines. Deep ALMA images of the quasar 3C 138 at 97 and 241 GHz are also compared to VLA 43 GHz results, demonstrating an agreement at a level of a few percent. As a result of the extensive program of LBC testing, the highly successful SV imaging at long baselines achieved angular resolutions as fine as 19 mas at ∼350 GHz. Observing with ALMA on baselines of up to 15 km is now possible, and opens up new parameter space for submm astronomy.

We have mapped the northern area (30 × 20 ) of a Local Group spiral galaxy M33 in 12 CO(J = 1-0) line with the 45 m telescope at the Nobeyama Radio Observatory. Along with Hα and Spitzer 24 μm data, we have investigated the relationship between the surface density of molecular gas mass and that of star formation rate (SFR) in an external galaxy (Kennicutt-Schmidt law) with the highest spatial resolution (∼80 pc) to date, which is comparable to scales of giant molecular clouds (GMCs). At positions where CO is significantly detected, the SFR surface density exhibits a wide range of over four orders of magnitude, from Σ SFR 10 −10 to ∼10 −6 M yr −1 pc −2 , whereas the Σ H 2 values are mostly within 10-40 M pc −2 . The surface density of gas and that of SFR correlate well at an ∼1 kpc resolution, but the correlation becomes looser with higher resolution and breaks down at GMC scales. The scatter of the Σ SFR -Σ H 2 relationship in the ∼80 pc resolution results from the variety of star-forming activity among GMCs, which is attributed to the various evolutionary stages of GMCs and to the drift of young clusters from their parent GMCs. This result shows that the Kennicutt-Schmidt law is valid only in scales larger than that of GMCs, when we average the spatial offset between GMCs and star-forming regions, and their various evolutionary stages.

We present a revised method for simultaneous determination of the pattern speed (Ω P ) and star formation timescale (t SF ) of spiral galaxies, which is originally proposed in our previous work. As this method utilizes offsets between molecular and young-stellar arms, we refer to it as the "Offset Method". Details of the method, its application, and results for CO and Hα images of 13 nearby spiral galaxies are described here. CO data are from our observations with the Nobeyama Millimeter Array for 2 galaxies, and from the BIMA SONG for the rest. Out of 13 galaxies, we were able to derive Ω P and t SF for 5 galaxies. We categorize them as "C" galaxies as their offsets are clear. Our findings from these galaxies are as follows. (1) The corotation radius calculated by the derived Ω P is close to the edge of the CO data, and is about half of the optical radius for 3 galaxies.(2) The derived t SF is roughly consistent with the free-fall time of typical molecular clouds, which indicates that the gravitational instability is the dominant mechanism triggering star formation in spiral arms. (3) The t SF is found to be almost independent of surface density of molecular gas, metallicity, or spiral arm strengths. The number of "C" galaxies and the quality of CO data, however, are not enough to confirm these relationships. We also find that 2 other galaxies show no offsets between CO and Hα, although their arms are clearly traced, and categorize them as "N" galaxies. The presence of a bar could account for this feature, since these 2 galaxies are both barred. With one galaxy excluded from our analysis due to its poor rotation curve, offsets of the remaining 5 galaxies are found to be ambiguous. Either their dependence on the rotational frequency cannot be explained by our picture, or the number or quality of data -2is not sufficient for the analysis. We categorize them as "A" galaxies. The possible reasons for this ambiguity are (1) the density wave is weaker, and/or (2) observational resolution and sensitivity are not enough to detect the spiral arms and their offsets clearly. The former is supported by our finding that the arm strengths of "A" galaxies are slightly weaker than that of "C" galaxies.