arXiv subjects

F. Motte

Publications and source records attributed to F. Motte.

148 records · Page 9Linked to original sources

arXiv2002

The Environment and Nature of the Class I Protostar Elias 29: Molecular Gas Observations and the Location of Ices

A (sub-)millimeter line and continuum study of the class I protostar Elias 29 in the Rho Ophiuchi molecular cloud is presented, whose goals are to understand the nature of this source, and to locate the ices that are abundantly present along this line of sight. Within 15-60" beams, several different components contribute to the line emission. Two different foreground clouds are detected, an envelope/disk system and a dense ridge of HCO+ rich material. The latter two components are spatially separated in millimeter interferometer maps. We analyze the envelope/disk system by using inside-out collapse and flared disk models. The disk is in a relatively face-on orientation (<60 degrees), which explains many of the remarkable observational features of Elias 29, such as its flat SED, its brightness in the near infrared, the extended components found in speckle interferometry observations, and its high velocity molecular outflow. It cannot account for the ices seen along the line of sight, however. A small fraction of the ices is present in a (remnant) envelope of mass 0.12-0.33 Msun, but most of the ices (~70%) are present in cool (T<40 K) quiescent foreground clouds. This explains the observed absence of thermally processed ices (crystallized H2O) toward Elias 29. Nevertheless, the temperatures could be sufficiently high to account for the low abundance of apolar (CO, N2, O2) ices. This work shows that it is crucial to obtain spectrally and spatially resolved information from single-dish and interferometric molecular gas observations in order to determine the nature of protostars and to interpret infrared ISO satellite observations of ices and silicates along a pencil beam.

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arXiv2001

High-Mass Proto-Stellar Candidates - II : Density structure from dust continuum and CS emission

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.

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arXiv2001

A SCUBA survey of the NGC 2068/2071 protoclusters

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.

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arXiv2000

Three high-redshift millimeter sources and their radio and near-infrared identifications

We present millimeter wavelength detections of three faint sources that are most likely high-redshift starburst galaxies. For one of the sources, which was previously discovered with SCUBA at 850 mu m, we present a detection with the IRAM interferometer at 240 GHz (1.25 mm) that shows the object unresolved at an angular resolution of 2.''5, and coincident within 1'' with a radio source and a galaxy detected in the near-infrared. The two other sources were discovered in a deep 250 GHz (1.2 mm) survey with the Max-Planck Millimeter Bolometer (MAMBO) array at the IRAM 30m telescope. Both have fluxes of ~4 mJy and radio counterparts with a 1.4 GHz flux density of ~75 muJy. Their radio-to-mm flux ratios suggest redshifts larger than 2. Both sources are faint in the optical and near-infrared, one showing a 20.5 mag K-band counterpart. From our data and that available in the literature, we estimate the redshift distribution of twenty-two faint mm and sub-mm sources and conclude that the majority of them are likely to be at z>2.

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