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.

Abstract. We observed the (J, K) = (1, 1) and (J, K) = (2, 2) inversion transitions of the NH 3 molecule towards several regions with molecular or optical outflows: RNO 43, HH 83, HH 84, HH 86/87/88, L1641-N, L100, L483, L673, IRAS 20188+3928, L1228, L1048, HHL 73, L1251 (IRAS 22343 + 7501 and IRAS 22376+7455) and L1262, using the 37 m radio telescope of the Haystack Observatory. Additionally, we searched for the 6 16 −5 23 H 2 O maser line towards nine regions, detecting a weak H 2 O maser near IRAS 20188+3928. We detected and mapped NH 3 emission in 14 of the 15 regions observed, and we estimated physical parameters for the high density gas. We systematically found that the position of the best candidate for the outflow excitation in each region is very close to an NH 3 emission peak. From a statistical study of the data presented in this paper, together with previously published data, we conclude that the NH 3 line emission is more intense towards molecular outflow sources than towards sources with only optical outflows. Therefore, molecular outflows appear to be associated with larger amounts of high density gas. This result suggests a possible evolutive scheme in which young objects associated with molecular outflows lose progressively their neighboring high-density gas, weakening both the NH 3 emission and the molecular outflow in the process, and making optical jets more easily detectable as the total amount of gas decreases.

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Aims. The aim of this paper is to study with high angular resolution a dense core associated with a low-luminosity IRAS source, IRAS 00213+6530, in order to investigate whether low mass star formation is taking place in isolation. Methods. We carried out observations at 1.2 mm with the IRAM 30 m telescope, and VLA observations in the continuum mode at 6 cm, 3.6 cm, 1.3 cm and 7 mm, together with H 2 O maser and NH 3 lines toward IRAS 00213+6530. Additionally, we observed the CCS J N = 2 1 -1 0 transition, and H 2 O maser emission using the NASA 70 m antenna at Robledo de Chavela, Spain. We studied the nature of the centimeter and millimeter emission of the young stellar objects (YSOs) found in the region, and the physical properties of the dense gas and dust emission. Results. The centimeter and millimeter continuum emission, together with the near infrared data from 2MASS allowed us to identify three YSOs, IRS 1, VLA 8A, and VLA 8B, with different radio and infrared properties, and which seem to be in different evolutionary stages. IRS 1, detected only in the infrared, is in the more advanced stage. On the other hand, VLA 8A, bright at centimeter and millimeter wavelengths, coincides with a near infrared 2MASS source, whereas VLA 8B has no infrared emission associated with it and is in the earliest evolutionary stage. The overall structure of the NH 3 emission consists of three clouds. Two of these, MM1 and MM2, are associated with dust emission at millimeter wavelengths, while the southern cloud is only detected in NH 3 . The YSOs are embedded in MM1, where we found evidence of line broadening and temperature enhancements. On the other hand, the southern cloud and MM2 appear to be quiescent and starless. Concerning the 1.2 mm dust emission, we modeled the radial intensity profile of MM1. The model fits the data reasonably well, but it underestimates the intensity at small projected distances from the 1.2 mm peak, probably due to the presence of multiple YSOs embedded in the dusty envelope. There is a strong differentiation in the relative NH 3 abundance with low values of ∼2 × 10 −8 toward MM1, which harbors the YSOs, and high values, up to 10 −6 , toward the southern cloud and MM2, suggesting that these clouds could be in a young evolutionary stage. Conclusions. IRAS 00213+6530 harbors a multiple system of low-mass protostars, indicating that star formation in this cloud is taking place in groups or clusters, rather than in isolation. The low-mass YSOs found in IRAS 00213+6530 are in different evolutionary stages, suggesting that star formation takes place in different episodes.

We present the results of the observations of the (J, K) = (1, 1) and the (J, K) = (2, 2) inversion transitions of the NH 3 molecule toward a large sample of 40 regions with molecular or optical outflows, using the 37 m radio telescope of the Haystack Observatory. We detected NH 3 emission in 27 of the observed regions, which we mapped in 25 of them. Additionally, we searched for the 6 16 −5 23 H 2 O maser line toward six regions, detecting H 2 O maser emission in two of them, HH265 and AFGL 5173. We estimate the physical parameters of the regions mapped in NH 3 and analyze for each particular region the distribution of high density gas and its relationship with the presence of young stellar objects. In particular, we identify the deflecting high-density clump of the HH270/110 jet. We were able to separate the NH 3 emission from the L1641-S3 region into two overlapping clouds, one with signs of strong perturbation, probably associated with the driving source of the CO outflow, and a second, unperturbed clump, which is probably not associated with star formation. We systematically found that the position of the best candidate for the exciting source of the molecular outflow in each region is very close to an NH 3 emission peak. From the global analysis of our data we find that in general the highest values of the line width are obtained for the regions with the highest values of mass and kinetic temperature. We also found a correlation between the nonthermal line width and the bolometric luminosity of the sources, and between the mass of the core and the bolometric luminosity. We confirm with a larger sample of regions the conclusion of Anglada et al. (1997) that the NH 3 line emission is more intense toward molecular outflow sources than toward sources with optical outflow, suggesting a possible evolutionary scheme in which young stellar objects associated with molecular outflows progressively lose their neighboring high-density gas, weakening both the NH 3 emission and the molecular outflow in the process, and making optical jets more easily detectable as the total amount of gas decreases.