Abstract.A statistical study of the properties of molecular outflows is performed based on an up-to-date sample. 391 outflows were identified in published articles or preprints before February 28, 2003. The parameters of position, morphology, mass, energy, outflow dynamics and central source luminosity are presented for each outflow source. Outflow lobe polarity is known for all the sources, and 84% are found to be bipolar. The sources are divided into low mass and high mass groups according to either the available bolometric luminosity of the central source or the outflow mass. The pace of discovery of outflows over the past seven years has increased much more rapidly than in previous periods. Surveys for outflows are still continuing. The number of high-mass outflows detected (139) has considerably increased, showing that they are commonly associated with massive as well as low mass stars. Energetic mass ejection may be a common aspect of the formation of high mass as well as low mass stars. Outflow masses are correlated strongly with bolometric luminosity of the center sources, which was obtained for the first time. There are also correlations between the central source luminosity and the parameters of mechanical luminosity and the thrust or force necessary to drive the outflow. The results show that flow mass, momentum and energy depend on the nature of the central source. Despite their similarity, there are differences between the high mass and low mass outflows. Low mass outflows are more collimated than high mass outflows. On average, the mass of high mass sources can be more than two orders of magnitude larger than those of low mass outflows. The relation between flow mass and dynamical time appears to differ for the two types of outflows. Low mass sources make up 90% of outflows associated with HH objects while high mass outflows make up 61% of the sources associated with H 2 O masers. Sources with characteristics of collapse or infall comprise 12% of the entire outflow sample. The spatial distribution of the outflow sources in the Galaxy is presented and the local occurrence rate is compared with the stellar birth rate.

We present Submillimeter Array (SMA) λ = 0.88 mm observations of an infrared dark cloud G28.34+0.06. Located in the quiescent southern part of the G28.34 cloud, the region of interest is a massive (>10 3 M ) molecular clump P1 with a luminosity of ∼10 3 L , where our previous SMA observations at 1.3 mm have revealed a string of five dust cores of 22-64 M along the 1 pc IR-dark filament. The cores are well aligned at a position angle (P.A.) of 48• and regularly spaced at an average projected separation of 0.16 pc. The new high-resolution, high-sensitivity 0.88 mm image further resolves the five cores into 10 compact condensations of 1.4-10.6 M , with sizes of a few thousand AU. The spatial structure at clump (∼1 pc) and core (∼0.1 pc) scales indicates a hierarchical fragmentation. While the clump fragmentation is consistent with a cylindrical collapse, the observed fragment masses are much larger than the expected thermal Jeans masses. All the cores are driving CO (3-2) outflows up to 38 km s −1 , the majority of which are bipolar, jet-like outflows. The moderate luminosity of the P1 clump sets a limit on the mass of protostars of 3-7 M . Because of the large reservoir of dense molecular gas in the immediate medium and ongoing accretion as evident by the jet-like outflows, we speculate that P1 will grow and eventually form a massive star cluster. This study provides a first glimpse of massive, clustered star formation that currently undergoes through an intermediate-mass stage.

We have identified outflows and bubbles in the Taurus molecular cloud based on the ∼ 100 deg 2 Five College Radio Astronomy Observatory 12 CO(1-0) and 13 CO(1-0) maps and the Spitzer young stellar object catalogs. In the main 44 deg 2 area of Taurus we found 55 outflows, of which 31 were previously unknown. We also found 37 bubbles in the entire 100 deg 2 area of Taurus, all of which had not been found before. The total kinetic energy of the identified outflows is estimated to be ∼ 3.9 × 10 45 erg, which is 1% of the cloud turbulent energy. The total kinetic energy of the detected bubbles is estimated to be ∼ 9.2 × 10 46 erg, which is 29% of the turbulent energy of Taurus. The energy injection rate from outflows is ∼ 1.3 × 10 33 erg s −1 , 0.4 -2 times the dissipation rate of the cloud turbulence. The energy injection rate from bubbles is ∼ 6.4 × 10 33 erg s −1 , 2 -10 times the turbulent dissipation rate of the cloud. The gravitational binding energy of the cloud is ∼ 1.5 × 10 48 erg, 385 and 16 times the energy of outflows and bubbles, respectively. We conclude that neither outflows nor bubbles can provide enough energy to balance the overall gravitational binding energy and the turbulent energy of Taurus. However, in the current epoch, stellar feedback is sufficient to maintain the observed turbulence in Taurus.

We present observations of the (J, K) p (1, 1) and (2, 2) inversion transitions toward the infrared dark NH 3 cloud G28.34ϩ0.06, using the Very Large Array. Strong emission is found to coincide well with the infrared NH 3 absorption feature in this cloud. The northern region of G28.34ϩ0.06 is dominated by a compact clump (P2) with a high rotation temperature (29 K) and large line width (4.3 km s ), and is associated with a strong water Ϫ1 maser (240 Jy) and a 24 mm point source with far-IR luminosity of L . We infer that P2 has embedded 3 10 , massive protostars although it lies in the 8 mm absorption region. The southern region has filamentary structures. The rotation temperature in the southern region decreases with the increase of the integrated intensity, which NH 3 indicates an absence of strong internal heating in these clumps. In addition, the compact core P1 in the south has small line width (1.2 km s ) surrounded by extended emission with larger line width (1.8 km s ), which Ϫ1 Ϫ1suggests a dissipation of turbulence in the dense part of the cloud. Thus, we suggest that P1 is at a much earlier evolutionary stage than P2, possibly at a stage that begins to form a cluster with massive stars.

A survey toward 674 Planck cold clumps of the Early Cold Core Catalogue (ECC) in the J=1-0 transitions of 12 CO, 13 CO and C 18 O has been carried out using the PMO 13.7 m telescope. 673 clumps were detected with the 12 CO and 13 CO, and 68% of the samples have C 18 O emission. Additional velocity components were also identified. A close consistency of the three line peak velocities was revealed for the first time. Kinematic distances are given out for all the velocity components and half of the clumps are located within 0.5 and 1.5 kpc. Excitation temperatures range from 4 to 27 K, slightly larger than those of T d . Line width analysis shows that the majority of ECC clumps are low mass clumps. Column densities N H 2 span from 10 20 to 4.5×10 22 cm −2 with an average value of (4.4±3.6)×10 21 cm −2 . N H 2 cumulative fraction distribution deviates from the lognormal distribution, which is attributed to optical depth. The average abundance ratio of the 13 CO to C 18 O in these clumps is 7.0±3.8, higher than the terrestrial value. Dust and gas are well coupled in 95% of the clumps. Blue profile, red profile and line asymmetry in total was found in less than 10% of the clumps, generally indicating star formation is not developed yet. Ten clumps were mapped. Twelve velocity components and 22 cores were obtained. Their morphologies include extended diffuse, dense isolated, cometary and filament, of which the last is the majority. 20 cores are starless. Only 7 cores seem to be in gravitationally bound state. Planck cold clumps are the most quiescent among the samples of weak-red IRAS, infrared dark clouds, UC Hii region candidates, EGOs and methanol maser sources, suggesting that Planck cold clumps have expanded the horizon of cold Astronomy.

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We observed thirteen Planck cold clumps with the James Clerk Maxwell Telescope/SCUBA-2 and with the Nobeyama 45 m radio telescope. The N 2 H + distribution obtained with the Nobeyama telescope is quite similar to SCUBA-2 dust distribution. The 82 GHz HC 3 N, 82 GHz CCS, and 94 GHz CCS emission are often distributed differently with respect to the N 2 H + emission. The CCS emission, which is known to be abundant in starless molecular cloud cores, is often very clumpy in the observed targets. We made deep single-pointing observations in DNC, HN 13 C, N 2 D + , cyclic-C 3 H 2 toward nine clumps. The detection rate of N 2 D + is 50%. Furthermore, we observed the NH 3 emission toward 15 Planck cold clumps to estimate the kinetic temperature, and confirmed that most of targets are cold ( 20 K). In two of the starless clumps observe, the CCS emission is distributed as it surrounds the N 2 H + core (chemically evolved gas), which resembles the case of L1544, a prestellar core showing