We present a detailed 1.2 mm continuum and CS spectral line study of a large sample of 69 massive star forming regions in very early stages of evolution, most of them prior to building up an ultracompact Hii region. The continuum data show a zoo of different morphologies and give detailed information on the spatial distributions, the masses, column densities and average densities of the whole sample.Fitting the radial intensity profiles shows that three parameters are needed to describe the spatial distribution of the sources: constant emission from the center out to a few arcsec radius followed by a first power law intensity distribution which steepens further outside into a second power law distribution. The inner flat region is possibly caused by fragmentation of the large scale cores into smaller sub-sources, whereas the steeper outer power law distributions indicate finite sizes of the cores.Separating the sources into sub-samples suggests that in the earliest stages prior to the onset of massive star formation the intensity radial distributions are rather flat resembling the structure of intensity peaks in more quiescent molecular clouds. Then in the subsequent collapse and accretion phase the intensity distributions become centrally peaked with steep power law indices. In this evolutionary stage the sources show also the broadest C 34 S linewidth. During the following phase, when ultracompact Hii regions evolve, the intensity power law radial distributions flatten out again. This is probably caused by the ignited massive stars in the center which disrupt the surrounding cores.The mean inner power law intensity index m i (I ∼ r −mi ) is 1.2 corresponding to density indices p (n ∼ r −p ) of 1.6. In total the density distribution of our massive star formations sites seem to be not too different from their low-mass counterparts, but we show that setting tight constrains on the density indices is very difficult and subject to many possible errors.The local densities we derive from CS calculations are higher (up to one order of magnitude) than the mean densities we find via the mm-continuum. Such inhomogeneous density distribution reflects most likely the ubiquitous phenomenon of clumping and fragmentation in molecular clouds. Linewidth-mass relations show a departure from virial equilibrium in the stages of strongly collapsing cores.

We describe a systematic program aimed at identifying and characterizing candidate high-mass protostellar objects (HMPOs). Our candidate sample consists of 69 objects selected by criteria based on those established by Ramesh & Sridharan (1997) using far-infrared, radio-continuum and molecular line data. Infrared-Astronomical-Satellite (IRAS) and Midcourse-Space-Experiment (MSX) data were used to study the larger scale environments of the candidate sources and to determine their total luminosities and dust temperatures.To derive the physical and chemical properties of our target regions, we observed continuum and spectral line radiation at millimeter and radio wavelengths. We imaged the free-free and dust continuum emission at wavelengths of 3.6 cm and 1.2 mm, respectively, searched for H 2 O and CH 3 OH maser emission and observed the CO J = 2 → 1 and several NH 3 lines toward all sources in our sample. Other molecular tracers were observed in a subsample.While dust continuum emission was detected in all sources, most of them show only weak or no emission at 3.6 cm. Where detected, the cm emission is frequently found to be offset from the mm emission, indicating that the free-free and dust emissions arise from different subsources possibly belonging to the same (proto)cluster. A comparison of the luminosities derived from the cm emission with bolometric luminosities calculated from the IRAS far-infrared fluxes shows that the cm emission very likely traces the most massive source, whereas the whole cluster contributes to the far-infrared luminosity. Estimates of the accretion luminosity indicate that a significant fraction of the bolometric luminosity is still due to accretion processes. The earliest stages of HMPO evolution we seek to identify are represented by dust cores without radio emission.Line wings due to outflow activity are nearly omnipresent in the CO observations, and the molecular line data indicate the presence of hot cores for several sources, where the abundances of various molecular species are elevated due to evaporation of icy grain mantles. Kinetic gas temperatures of 40 sources are derived from NH 3 (1,1) and (2,2) data, and we compare the results with the dust temperatures obtained from the IRAS data.Comparing the amount of dust, and hence the gas, associated with the HMPOs and with ultracompact Hii regions (UCHiis) we find that the two types of sources are clearly separated in mass-luminosity diagrams: for the same dust masses the UCHii regions have higher bolometric luminosities than HMPOs. We suggest that this is an evolutionary trend with the HMPOs being younger and reprocessing less (stellar) radiation in the IR than the more evolved UCHiis regions.These results indicate that a substantial fraction of our sample harbors HMPOs in a pre-UCHii region phase, the earliest known stage in the high-mass star formation process.

We present a study of molecular outflows toward a sample of 69 luminous IRAS point sources. The sample is associated with dense molecular gas and has far-infrared luminosities ranging from 10 2 to 10 5 L , indicating these objects as regions likely forming high-mass stars. Mapping in the CO J ¼ 2 1 line shows that molecular outflows are ubiquitous in these regions. Most of the outflows have masses of tens of M . The typical dynamical timescale of the flow, without correcting for inclination of the flow axis, is a few times 10 4 yr. The typical energy in the outflows is 10 46 ergs, comparable to the turbulent energy in the core. Nearly half of the outflows show spatially resolved bipolar lobes. This indicates that low-mass young stars that coexist in the region are not responsible for the bipolar outflows observed. It is the more massive stars that drive the outflow. The large detection rate of outflows in the region favors an accretion process in the formation of massive stars. The maximum mass-loss rate in the wind is about 10 À4 M yr À1 . If these outflows are driven via accretion, the accretion rate should be as high as a few times 10 À4 M yr À1

We present detailed submillimeter-through centimeter-wave observations of the extraordinary extragalactic transient AT2018cow. The apparent characteristicsthe high radio luminosity, the rise and long-lived emission plateau at millimeter bands, and the sub-relativistic velocity -have no precedent. A basic interpretation of the data suggests E k 4 × 10 48 erg coupled to a fast but sub-relativistic (v ≈ 0.13c) shock in a dense (n e ≈ 3 × 10 5 cm −3 ) medium. We find that the X-ray emission is not naturally explained by an extension of the radio-submm synchrotron spectrum, nor by inverse Compton scattering of the dominant blackbody UVOIR photons by energetic electrons within the forward shock. By ∆t ≈ 20 days, the X-ray emission shows spectral softening and erratic inter-day variability. Taken together, we are led to invoke an additional source of X-ray emission: the central engine of the event. Regardless of the nature of this central engine, this source heralds a new class of

Abstract. We present a comparison of Class  CH 3 OH (6.7 GHz) and H 2 O (22.2 GHz) masers at high spatial resolution in a sample of 29 massive star-forming regions. Absolute positions of both maser types are compared with mm dust continuum, cm continuum and mid-infrared sources. All maser features -regardless of the species -are associated with massive mm cores, but only 3 out of 18 CH 3 OH masers and 6 out of 22 H 2 O masers are associated with cm emission likely indicating the presence of a recently ignited massive star. These observations of a homogenous sample of massive, young star-forming regions confirm earlier results, obtained for each maser species separately, that both maser types are signposts of high-mass star formation in very early evolutionary stages. The data are consistent with models that explain CH 3 OH maser emission by radiative pumping in moderately hot cores, requiring the absence, or only weak, free-free cm continuum radiation due to recently ignited stars. Mid-infrared sources are associated with both maser types in approximately 60% of the observed fields. Thus, mid-infrared objects may power maser sites, but the detection of strong mid-infrared emission is not strictly necessary because it might be heavily extincted. A comparison of the spatial separations between the di fferent observed quantities and other properties of the star-forming regions does not reveal any correlation. Our data suggest that CH 3 OH and H 2 O masers need a similar environment (dense and warm molecular gas), but that, due to the different excitation processes (radiative pumping for CH 3 OH and collisional pumping for H 2 O), no spatial correlations exist. Spatial associations are probably coincidences due to insufficient angular resolution and projection effects. The kinematic structures we find in the different maser species show no recognizable pattern, and we cannot draw firm conclusions as to whether the features are produced in disks, outflows or expanding shock waves.