No abstract

We report on Submillimeter Array observations of the 870 µm continuum and CO (3-2), 13 CO (2-1) and C 18 O (2-1) line emission of a faint object, SMM2E, near the driving source of the HH 797 outflow in the IC 348 cluster. The continuum emission shows an unresolved source for which we estimate a mass of gas and dust of 30 M Jup , and the CO (3-2) line reveals a compact bipolar outflow centred on SMM2E, and barely seen also in 13 CO (2-1). In addition, C 18 O (2-1) emission reveals hints of a possible rotating envelope/disk perpendicular to the outflow, for which we infer a dynamical mass of ∼ 16 M Jup . In order to further constrain the accreted mass of the object, we gathered data from Spitzer, Herschel, and new and archive submillimetre observations, and built the Spectral Energy Distribution (SED). The SED can be fitted with one single modified black-body from 70 µm down to 2.1 cm, using a dust temperature of ∼ 24 K, a dust emissivity index of 0.8, and an envelope mass of ∼ 35 M Jup . The bolometric luminosity is 0.10 L ⊙ , and the bolometric temperature is 35 K. Thus, SMM2E is comparable to the known Class 0 objects in the stellar domain. An estimate of the final mass indicates that SMM2E will most likely remain substellar, and the SMM2E outflow force matches the trend with luminosity known for young stellar objects. Thus, SMM2E constitutes an excellent example of a Class 0 proto-brown dwarf candidate which forms as a scaled-down version of low-mass stars. Finally, SMM2E seems to be part of a wide (∼ 2400 AU) multiple system of Class 0 sources.

We aim at characterising dense cores in the clustered environments associated with intermediate/high-mass star-forming regions. For this, we present an uniform analysis of Very Large Array NH 3 (1,1) and (2,2) observations towards a sample of 15 intermediate/high-mass star-forming regions, where we identify a total of 73 cores, classify them as protostellar, quiescent starless, or perturbed starless, and derive some physical properties. The average sizes and ammonia column densities of the total sample are ∼ 0.06 pc and ∼ 10 15 cm −2 , respectively, with no significant differences between the starless and protostellar cores, while the linewidth and rotational temperature of quiescent starless cores are smaller, ∼ 1.0 km s −1 and 16 K, than linewidths and temperatures of protostellar (∼ 1.8 km s −1 and 21 K), and perturbed starless (∼ 1.4 km s −1 and 19 K) cores. Such linewidths and temperatures for these quiescent starless cores in the surroundings of intermediate/high-mass stars are still significantly larger than the typical linewidths and rotational temperatures measured in starless cores of low-mass star-forming regions, implying an important non-thermal component. We confirm at high angular resolutions (spatial scales ∼ 0.05 pc) the correlations previously found with single-dish telescopes (spatial scales 0.1 pc) between the linewidth and the rotational temperature of the cores, as well as between the rotational temperature and the linewidth with respect to the bolometric luminosity. In addition, we find a correlation between the temperature of each core and the incident flux from the most massive star in the cluster, suggesting that the large temperatures measured in the starless cores of our sample could be due to heating from the nearby massive star. A simple virial equilibrium analysis seems to suggest a scenario of a self-similar, self-graviting, turbulent, virialised hierarchy of structures from clumps (∼ 0.1-10 pc) to cores (∼ 0.05 pc). A closer inspection of the dynamical state taking into account external pressure effects, reveal that relatively strong magnetic field support may be needed to stabilise the cores, or that they are unstable and thus on the verge of collapse.

We present Submillimeter Array (SMA) observations at 345 GHz towards the intermediate/high-mass cluster-forming region NGC 6334 V. From the dust emission we spatially resolve three dense condensations, the brightest one presenting the typical chemistry of a hot core. The magnetic field (derived from the dust polarized emission) shows a bimodal converging pattern towards the hot core. The molecular emission traces two filamentary structures at two different velocities, separated by 2 km s −1 , converging to the hot core and following the magnetic field distribution. We compare the velocity field and the magnetic field derived from the SMA observations with MHD simulations of star-forming regions dominated by gravity. This comparison allows us to show how the gas falls in from the larger-scale extended dense core (∼ 0.1 pc) of NGC 6334 V towards the higher-density hot core region (∼ 0.02 pc) through two distinctive converging flows dragging the magnetic field, whose strength seems to have been overcome by gravity.