The all-Galaxy CO survey of Dame, Hartmann, & Thaddeus (2001) is by far the most uniform, large-scale Galactic CO survey. Using a dendrogram-based decomposition of this survey, we present a catalog of 1064 massive molecular clouds throughout the Galactic plane. This catalog contains 2.5 × 10 8 solar masses, or 25 +10.7 −5.8 % of the Milky Way's estimated H 2 mass. We track clouds in some spiral arms through multiple quadrants. The power index of Larson's first law, the size-linewidth relation, is consistent with 0.5 in all regions -possibly due to an observational bias -but clouds in the inner Galaxy systematically have significantly (∼ 30%) higher linewidths at a given size, indicating that their linewidths are set in part by Galactic environment. The mass functions of clouds in the inner Galaxy versus the outer Galaxy are both qualitatively and quantitatively distinct. The inner Galaxy mass spectrum is best described by a truncated power-law with a power index of γ = −1.6 ± 0.1 and an upper truncation mass M 0 = (1.0 ± 0.2) × 10 7 M , while the outer Galaxy mass spectrum is better described by a non-truncating power law with γ = −2.2 ± 0.1 and an upper mass M 0 = (1.5 ± 0.5) × 10 6 M , indicating that the inner Galaxy is able to form and host substantially more massive GMCs than the outer Galaxy. Additionally, we have simulated how the Milky Way would appear in CO from extragalactic perspectives, for comparison with CO maps of other galaxies.

The very long and thin infrared dark cloud "Nessie" is even longer than had been previously claimed, and an analysis of its Galactic location suggests that it lies directly in the Milky Way's mid-plane, tracing out a highly elongated bonelike feature within the prominent Scutum-Centaurus spiral arm. Re-analysis of mid-infrared imagery from the Spitzer Space Telescope shows that this IRDC is at least 2, and possibly as many as 5 times longer than had originally been claimed by Nessie's discoverers, Jackson et al. (2010); its aspect ratio is therefore at least 300:1, and possibly as large as 800:1. A careful accounting for both the Sun's offset from the Galactic plane (∼ 25 pc) and the Galactic center's offset from the (l II , b II ) = (0, 0) position shows that the latitude of the true Galactic mid-plane at the 3.1 kpc distance to the Scutum-Centaurus Arm is not b = 0, but instead closer to b = −0.4, which is the latitude of Nessie to within a few pc.An analysis of the radial velocities of low-density (CO) and high-density (NH 3 ) gas associated with the Nessie dust feature suggests that Nessie runs along the Scutum-Centaurus Arm in position-position-velocity space, which means it likely forms a dense 'spine' of the arm in real space as well. The Scutum-Centaurus arm is the closest major spiral arm to the Sun toward the inner Galaxy, and, at the longitude of Nessie, it is almost perpendicular to our line of sight, making Nessie the easiest feature to see as a shadow elongated along the Galactic Plane from our location. Future high-resolution dust mapping and molecular line observations of the harder-to-find Galactic "bones" should allow us to exploit the Sun's position above the plane to gain a (very foreshortened) view "from above" of the Milky Way's structure.

The winds and radiation from massive stars clear out large cavities in the interstellar medium. These bubbles, as they have been called, impact their surrounding molecular clouds and may influence the formation of stars therein. Here we present James Clerk Maxwell Telescope observations of the J = 3-2 line of CO in 43 bubbles identified with Spitzer Space Telescope observations. These spectroscopic data reveal the three-dimensional structure of the bubbles. In particular, we show that the cold gas lies in a ring, not a sphere, around the bubbles indicating that the parent molecular clouds are flattened with a typical thickness of a few parsecs. We also mapped seven bubbles in the J = 4-3 line of HCO + and find that the column densities inferred from the CO and HCO + line intensities are below that necessary for "collect and collapse" models of induced star formation. We hypothesize that the flattened molecular clouds are not greatly compressed by expanding shock fronts, which may hinder the formation of new stars.

We present a study on the shells (and bubbles) in the Perseus molecular cloud using the COM-PLETE survey large-scale 12 CO(1-0) and 13 CO(1-0) maps. The twelve shells reported here are spread throughout most of the Perseus cloud and have circular or arc-like morphologies with a range in radius of about 0.1 to 3 pc. Most of them have not been detected before most likely as maps of the region lacked the coverage and resolution needed to distinguish them. The majority of the shells are coincident with infrared nebulosity of similar shape and have a candidate powering source near the center. We suggest they are formed by the interaction of spherical or very wide-angle winds powered by young stars inside or near the Perseus molecular cloud -a cloud that is commonly considered to be mostly forming low-mass stars. Two of the twelve shells are powered by high-mass stars close to the cloud, while the others appear to be powered by low or intermediate mass stars in the cloud. We argue that winds with a mass loss rate of about 10 −8 to 10 −6 M yr −1 are required to produce the observed shells. Our estimates indicate that the energy input rate from these stellar winds is similar to the turbulence dissipation rate. We conclude that in Perseus the total energy input from both collimated protostellar outflows and powerful spherical winds from young stars is sufficient to maintain the turbulence in the molecular cloud. Large scale molecular line and IR continuum maps of a sample of clouds will help determine the frequency of this phenomenon in other star forming regions.