ORion Alma New GEneration Survey (ORANGES) I. Dust continuum and free-free emission of OMC-2/3 filament protostars

Abstract

Context. The spectral energy distribution (SED) in the millimetre to centimetre range is an extremely useful tool for characterising the dust in protostellar envelopes as well as free-free emission from the protostar and outflow. Actually, the evolutionary status of solar-type protostars is often based on their SED in the near-infrared to millimetre range. In addition, the presence or absence of free-free emission can be considered an indicator of the source evolutionary stage (Class 0/I versus Class II/III). While many studies have been carried out towards low-and high-mass protostars, little exists so far about solar-type protostars in high-mass star-forming regions, which are likely to be representatives of the conditions where the Solar System was born. Aims. In this work we focus on the embedded solar-type protostars in the Orion Molecular Cloud (OMC) 2 and 3 filaments, which are bounded by nearby HII regions and which are, therefore, potentially affected by the high-UV illumination of the nearby OB stars. We use various dust parameters to understand whether the small-scale structure (≤ 1000 au) and the evolutionary status of these solar-type protostars are affected by the nearby HII regions, as is the case for the large-scale (≤ 10 4 au) gas chemical composition. Methods. We used the Atacama Large (sub-)Millimeter Array (ALMA) in the 1.3 mm band (246.2 GHz) to image the continuum of 16 young (Class 0/I) OMC-2/3 solar-type protostars, with an angular resolution of 0.25 (100 au). We completed our data with archival data from the ALMA and VLA VANDAM survey of Orion Protostars at 333 and 32.9 GHz, respectively, to construct the dust SED and extract the dust temperature, the dust emissivity spectral index, the envelope plus disk mass of the sources and to assess whether free-free emission is contaminating their dust SED in the centimetre range. Results. From the millimetre to centimetre range dust SED, we found low dust emissivity spectral indexes (β < 1) for the majority of our source sample and free-free emission towards only 5 of the 16 sample sources. We were also able to confirm or correct the evolutionary status of the source sample reported in the literature. Finally, we did not find any dependence of the source dust parameters on their location in the OMC-2/3 filament. Conclusions. Our results show that the small-scale dust properties of the embedded OMC-2/3 protostars are not affected by the high-UV illumination from the nearby HII regions and that the formation of protostars likely takes place simultaneously throughout the filament.

The role of magnetic fields in the formation of protostars, disks, and outflows

“…Interferometric observations have also found low spectral indices at millimeter wavelengths in the dusty ∼ 60 au disk surrounding L1527, a Class 0/I protostar and in the Class 0 protostar, L1157 (Nakatani et al 2020;Chiang et al 2012). In the Orion region, recent ALMA observations confirmed the low spectral indices of dust emission in 16 protostars at scales < 100 au (Bouvier et al 2021). Analyzing the dust properties of 12 nearby Class 0 protostars observed at 1.3 and 3.2 mm with the PdBI (CALYPSO survey), Galametz et al (2019) found that most Class 0 protostars, sampled from different star-forming regions, show significantly shallow dust emissivities at envelope radii ∼ 100 − 500 au, with β < 1 (see left panel of Figure 14).…”