Cyano radical emission at small spatial scales towards massive protostars

Abstract

Context. The cyano radical (CN), one of the first detected interstellar molecular species, is a key molecule in many astrochemical chains. In particular, it is detected towards molecular cores, the birth places of stars, and it is involved in the rich chemistry that takes place at these sites. Aims. At present, there are not many studies on the emission of this molecular species at small spatial scales towards massive young stellar objects. We therefore present a high-angular resolution CN study towards a sample of massive protostars, with the aim of unveiling the spatial distribution at the small scale of the emission of this radical in relation to star-forming processes. Methods. The interstellar CN has a strong emission line at the rest frequency 226 874.764 MHz, thus we searched for observing projects in the Atacama Large Millimeter Array (ALMA) database regarding high-mass star-forming regions observed at Band 6. The used data set was observed in ALMA Cycle 3 with angular and spectral resolutions of 0.′′7 and 1.13 MHz, respectively. A sample of ten high-mass star-forming regions located in the first Galactic quadrant were selected on the basis that they present a clear emission of CN at the mentioned frequency. Results. We found that the CN traces both molecular condensations and the diffuse and extended gas surrounding them. In general, the molecular condensations traced by the maximums of the CN emission do not spatially coincide with the peaks of the continuum emission at 1.3 mm, which trace the molecular cores where massive stars are born. Based on the presence or lack of near-IR emission associated with such cores, we suggest that our sample is composed of sources at different stages of evolution. The CN is present in all sources, suggesting that this radical may be ubiquitous along the different star formation stages, and hence it may be involved in different chemical reactions occurring during the period of star formation. Additionally, other molecules such as CH3OCHO and CH2CHCN were detected towards the continuum peaks of some of the analysed cores. We found that the missing flux coming from extended spatial scales that are filtered out by the interferometer is an important issue to take into account in the analysis of some spectral features and the spatial distribution of the emission.

Unveiling the substructure of the massive clump AGAL G035.1330−00.7450

“…On the other hand, Fig. 10 shows that the CN (2-1) line traces clumpy extended emission, in agreement with a recent work of Paron et al (2021), in which the cyano radical emission was analyzed with high-angular resolution ALMA data toward a sample of 10 massive clumps. In particular, toward AGAL35, it is worth noting that the CN peaks do not coincide spatially with the continuum dust cores.…”

“…Furthermore, it is clear that the CN (2-1) emission seems to surround the cores, which is particularly evident toward C1. This phenomenon was also observed in several other sources (see Paron et al 2021;Zapata et al 2008;Beuther et al 2004). Tassis et al (2012), based on nonequilibrium chemistry dynamical models, found that the CN molecule is depleted at densities above 10 5 cm −3 .…”

“…On the other hand, a complementary explanation is that the protostars are still deeply embedded in the cores and do not generate enough UV photons to produce CN emission (Beuther et al 2004). In addition, it is worth mentioning that the missing flux coming from more extended spatial scales that are filtered out by the interferometer could play an important role (Paron et al 2021).…”

Recent progress with observations and models to characterize the magnetic fields from star-forming cores to protostellar disks

“…On the contrary, CCH, CCS, and SO appear to deplete toward the core's center (Tafalla et al, 2006;Padovani et al, 2009b;Juárez et al, 2017;Seo et al, 2019). For massive cores, all these molecules but SO appear to be anticorrelated with the dust emission at scales of ≲ 0.05 pc (Dirienzo et al, 2015;Paron et al, 2021). The distribution of these molecules in the planet-forming disk is also complex, and combined with the expected magnetic field configuration, the interpretation of Zeeman observations is made difficult (Mazzei et al, 2020).…”

Gas-phase formation and spectroscopic characterization of the disubstituted cyclopropenylidenes c-C3(C2H)2, c-C3(CN)2, and c-C3(C2H)(CN)

“…Molecular structure of c-C 3 (C 2 H) 2 . Paron et al 2021) makes a c-C 3 H 2 nitrile derivative possible as well. While the search for c-C 3 HCN is still ongoing (Cernicharo et al 2021), its energetically viable formation mechanism most strongly resembles the formation mechanism of c-C 3 HC 2 H, both in reaction coordinate structures and in exothermicity (Flint & Fortenberry 2022).…”