Frederique Motte

We have carried out a submillimeter continuum and spectroscopic study of the W43 main complex, a massive star-forming region, which harbors a giant HII region. The maps reveal a filamentary structure containing ~50 fragments with masses of 40-4000 Msun and typical diameters of 0.25 pc. Their large sizes, large non-thermal velocities (Dv ~ 5 km/s), and high densities (n_H2 ~ 10^6 cm^-3) suggest that they are protoclusters and excellent sites to form massive stars. Follow-up observations are necessary, but we have already identified three protoclusters to be very good candidates for containing very young massive protostars. The starburst cluster, that excites the giant HII region has a large impact on the molecular complex. However, it remains unclear if this first episode of star formation is triggering the formation of new massive stars, through ionization shocks crossing the closeby molecular clouds. W43 is thus an ideal laboratory to investigate massive star formation from the protostellar phase to that of giant HII regions. Moreover, the very active star-forming complex W43 may be considered a Galactic mini-starburst region that could be used as a miniature model of starburst galaxies.

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 mean inner power law intensity index mi (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.Comment: 15 pages, 13 jpeg-figures. Astrophysical Journal, in pres

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 mean inner power law intensity index mi (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.

Astronomy & Astrophysics (A&A) is an international journal which publishes papers on all aspects of astronomy and astrophysics

We report the results of a submillimeter dust continuum survey of the protoclusters NGC 2068 and NGC 2071 in Orion B carried out at 850 microns and 450 microns with SCUBA on JCMT. The mapped region is ~ 32' x 18' in size (~ 4 pc x 2 pc) and consists of filamentary dense cores which break up into small-scale (~ 5000 AU) fragments, including 70 starless condensations and 5 circumstellar envelopes/disks. The starless condensations, seen on the same spatial scales as protostellar envelopes, are likely to be gravitationally bound and pre-stellar in nature. Their mass spectrum, ranging from ~ 0.3 Msun to ~ 5 Msun, is reminiscent of the stellar initial mass function (IMF). Their mass-size relation suggests that they originate from gravitationally-driven fragmentation. We thus argue that pre-collapse cloud fragmentation plays a major role in shaping the IMF.

We present a complete 1.3 mm continuum mapping survey of the embedded young stellar objects (YSOs) in the Taurus molecular cloud. We have also imaged several isolated Bok globules, as well as protostellar objects in the Perseus cluster. Our maps, taken with the IRAM 30 m telescope and the MPIfR bolometer arrays, are sensitive to the column density structure of the sources on spatial scales ranging from 1 500-5 000 AU to > 15 000-50 000 AU. For the protostellar envelopes mapped in Taurus, the results are roughly consistent with the predictions of the self-similar inside-out collapse model of Shu and collaborators. The envelopes observed in Bok globules are also qualitatively consistent with these predictions, providing the effects of magnetic pressure are included in the model. By contrast, the envelopes of Class 0 protostars in Perseus have finite radii ≾ 10 000 AU and are a factor of 3 to 12 denser than is predicted by the standard model. In cluster-forming regions, individual protostellar collapse thus appears to be induced in compact condensations resembling more finite-sized Bonnor-Ebert condensations than singular isothermal spheres. Accordingly, the beginning of protostellar evolution is suggested to be more violent, with larger accretion rates, in protoclusters compared to regions of distributed star formation like Taurus. Follow-up line observations of the envelopes' velocity fields are required to confirm this suggestion. We also find that roughly half of the Class I infrared sources of Taurus are either at the very end of the main accretion phase or already in the pre-main sequence phase. These sources are surrounded by only remnant, finite-sized envelopes (M env 4200 AU ≾ 0.01 M ⊙ and R out ≾ 1 500 AU). Lastly, our 1.3 mm continuum images reveal the presence of new candidate pre-stellar condensations and/or Class 0 protostars in the close environment of 8 Taurus Class I YSOs, 2 Bok globules, and 3 Perseus protostars.