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The star-forming activity in the H ii region RCW 42 is investigated using multiple wavebands, from near-infrared to radio wavelengths. Located at a distance of 5.8 kpc, this southern region has a bolometric luminosity of 1.8 × 106 L⊙. The ionized gas emission has been imaged at low radio frequencies of 610 and 1280 MHz using the Giant Metrewave Radio Telescope, India, and shows a large expanse of the H ii region, spanning 20 × 15 pc2. The average electron number density in the region is estimated to be ∼70 cm−3, which suggests an average ionization fraction of the cloud to be 11 % . An extended green object EGO G274.0649-01.1460 and several young stellar objects have been identified in the region using data from the 2MASS and Spitzer surveys. The dust emission from the associated molecular cloud is probed using Herschel Space Telescope, which reveals the presence of five clumps, C1-C5, in this region. Two millimetre emission cores of masses 380 and 390 M⊙ towards the radio emission peak have been identified towards C1 from the ALMA map at 1.4 mm. The clumps are investigated for their evolutionary stages based on association with various star-formation tracers, and we find that all the clumps are in active/evolved stage.

Abstract Annihilation studies have established that positrons bind to most molecules. They also provide measurements of the positron-molecule binding energies, which are found to vary widely and depend upon molecular size and composition. Trends of binding energy with global parameters such as molecular polarizability and dipole moment have been discussed previously. In this paper, the dependence of binding energy on molecular geometry is investigated by studying resonant positron annihilation on selected pairs of isomers. It is found that molecular geometry can play a significant role in determining the binding energies even for isomers with very similar polarizabilities and dipole moments. The possible origins of this dependence are discussed.

ABSTRACT Star-forming galaxies are rich reservoirs of dust, both warm and cold. But the cold dust emission is faint alongside the relatively bright and ubiquitous warm dust emission. Recently, evidence for a very cold dust (VCD) component has also been revealed via millimetre/submillimetre (mm/sub-mm) photometry of some galaxies. This component, despite being the most massive of the three dust components in star-forming galaxies, is by virtue of its very low temperature, faint and hard to detect together with the relatively bright emission from warmer dust. Here, we analyse the dust content of a carefully selected sample of four galaxies detected by IRAS, WISE, and South Pole Telescope (SPT), whose spectral energy distributions (SEDs) were modelled to constrain their potential cold dust content. Low-frequency radio observations using the Giant Metrewave Radio Telescope (GMRT) were carried out to segregate cold dust emission from non-thermal emission in mm/sub-mm wavebands. We also carried out AstroSat/Ultraviolet Imaging Telescope (UVIT) observations for some galaxies to constrain their SED at shorter wavelengths so as to enforce energy balance for the SED modelling. We constructed their SEDs across a vast wavelength range (extending from UV to radio frequencies) by assembling global photometry from GALEX FUV + NUV, UVIT,more »Johnson BRI, 2MASS, WISE, IRAC, IRAS, AKARI, ISO PHOT, Planck HFI, SPT, and GMRT. The SEDs were modelled with cigale to estimate their basic properties, in particular to constrain the masses of their total and VCD components. Although the galaxies’ dust masses are dominated by warmer dust, there are hints of VCD in two of the targets, NGC 7496 and NGC 7590.« less