Context. Hatchell et al. (2005, A&A, 440, 151) (Paper I) published a submillimetre continuum map of the Perseus molecular cloud, detecting the starless and protostellar cores within it. Aims. To determine the evolutionary stage of each submm core in Perseus, and investigate the lifetimes of these phases. Methods. We compile spectral energy distributions (SEDs) from 2MASS (1-2 µm), Spitzer IRAC (3.6, 4.5, 5.8, 8.0 µm), Michelle (11 and 18 µm), IRAS (12, 25, 60, 100 µm), SCUBA (450 and 850 µm) and Bolocam (1100 µm) data. Sources are classified starless/protostellar on the basis of infrared and/or outflow detections and Class I/Class 0 on the basis of T bol , L bol /L smm and F 3.6 /F 850 . In order to investigate the dependence of these evolutionary indicators on mass, we construct radiative transfer models of Class 0 sources. Results. Of the submm cores, 56/103 (54%) are confirmed protostars on the basis of infrared emission or molecular outflows. Of these, 22 are classified Class 1 on the basis of three evolutionary indicators, 34 are Class 0, and the remaining 47 are assumed starless. Perseus contains a much greater fraction of Class 0 sources than either Taurus or Rho Oph. We derive estimates for the correlation between bolometric luminosity and envelope mass for Class I and Class 0 sources. Conclusions. Comparing the protostellar with the T Tauri population, the lifetime of the protostellar phase in Perseus is 0.25−0.67 Myr (95% confidence limits). The relative lifetime of the Class 0 and Class 1 phases are similar, confirming the results of Visser et al. (2002, AJ, 124, 2756 in isolated cores. We find that for the same source geometry but different masses, evolutionary indicators such as T bol vary their value. It is therefore not always appropriate to use a fixed threshold to separate Class 0 and Class I sources. More modelling is required to determine the observational characteristics of the Class 0/Class I boundary over a range of masses.

Abstract. We present a complete survey of current star formation in the Perseus molecular cloud, made at 850 and 450 µm with SCUBA at the JCMT. Covering 3 deg 2 , this submillimetre continuum survey for protostellar activity is second in size only to that of ρ Ophiuchus (Johnstone et al. 2004, ApJ, 611, L45). Complete above 0.4 M (5σ detection in a 14 beam), we detect a total of 91 protostars and prestellar cores. Of these, 80% lie in clusters, representative of star formation across the Galaxy. Two of the groups of cores are associated with the young stellar clusters IC 348 and NGC 1333, and are consistent with a steady or reduced star formation rate in the last 0.5 Myr, but not an increasing one. In Perseus, 40-60% of cores are in small clusters (<50 M ) and isolated objects, much more than the 10% suggested from infrared studies. Complementing the dust continuum, we present a C 18 O map of the whole cloud at 1 resolution. The gas and dust show filamentary structure of the dense gas on large and small scales, with the high column density filaments breaking up into clusters of cores. The filament mass per unit length is 5-11 M per 0.1 pc. Given these filament masses, there is no requirement for substantial large scale flows along or onto the filaments in order to gather sufficient material for star formation. We find that the probability of finding a submillimetre core is a strongly increasing function of column density, as measured by C 18 O integrated intensity, P(core) ∝ I 3.0 . This power law relation holds down to low column density, suggesting that there is no A v threshold for star formation in Perseus, unless all the low-A v submm cores can be demonstrated to be older protostars which have begun to lose their natal molecular cloud.

ABSTRACT. Hi-GAL, the Herschel infrared Galactic Plane Survey, is an Open Time Key Project of the Herschel Space Observatory. It will make an unbiased photometric survey of the inner Galactic plane by mapping a 2°wide strip in the longitude range |l| < 60°in five wavebands between 70 μm and 500 μm. The aim of Hi-GAL is to detect the earliest phases of the formation of molecular clouds and high-mass stars and to use the optimum combination of Herschel wavelength coverage, sensitivity, mapping strategy, and speed to deliver a homogeneous census of starforming regions and cold structures in the interstellar medium. The resulting representative samples will yield the variation of source temperature, luminosity, mass and age in a wide range of Galactic environments at all scales from massive YSOs in protoclusters to entire spiral arms, providing an evolutionary sequence for the formation of intermediate and high-mass stars. This information is essential to the formulation of a predictive global model of the role of environment and feedback in regulating the star-formation process. Such a model is vital to understanding star formation on galactic scales and in the early universe. Hi-GAL will also provide a science legacy for decades to come with incalculable potential for systematic and serendipitous science in a wide range of astronomical fields, enabling the optimum use of future major facilities such as JWST and ALMA.

We present a census of molecular outflows across four active regions of star formation in the Perseus molecular cloud (NGC 1333, IC348/HH211, L1448 and L1455), totalling an area of over 1000 arcmin 2 . This is one of the largest surveys of outflow evolution in a single molecular cloud published to date. We analyse large-scale, sensitive CO J = 3 → 2 data sets from the James Clerk Maxwell Telescope, including new data towards NGC 1333. Where possible we make use of our complementary 13 CO and C 18 O data to correct for the 12 CO optical depth and measure ambient cloud properties. Of the 65 submillimetre cores in our fields, we detect outflows towards 45. 24 of these are marginal detections where the outflow's shape is unclear or could be confused with the other outflows. We compare various parameters between the outflows from Class 0 and I protostars, including their mass, momentum, energy and momentum flux. Class 0 outflows are longer, faster, more massive and have more energy than Class I outflows. The dynamical time-scales we derive from these outflows are uncorrelated to the age of the outflow driving source, computed from the protostar's bolometric temperature. We confirm the results of Bontemps et al. that outflows decrease in force as they age. There is a decrease in momentum flux from the Class 0 to I stage: F CO = (0.8 ± 0.3) × 10 −4 compared to (1.1 ± 0.3) × 10 −5 M km s −1 yr −1 , suggesting a decline in the mass accretion rate assuming the same entrainment fraction for both classes of outflow. If F rad = L bol /c is the flux expected in radiation from the central source, then F CO (Class I) ∼ 100F rad and F CO (Class 0) ∼ 1000F rad . Furthermore, we confirm there are additional sources of mass loss from protostars. If a core's mass is only lost from outflows at the current rate, cores would endure a few million years, much longer than current estimates for the duration of the protostellar stage. Finally, we note that the total energy contained in outflows in NGC 1333, L1448 and L1455 is greater than the estimated turbulent energy in the respective regions, which may have implications for the regions' evolution.

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.