Protostellar Interferometric Line Survey of the Cygnus X region (PILS-Cygnus)

Abstract

Context. Complex organic molecules (COMs) are commonly detected in and near star-forming regions. However, the dominant process in the release of these COMs from the icy grains – where they predominately form – to the gas phase is still an open question. Aims. We investigate the origin of COM emission in a high-mass protostellar source, CygX-N30 MM1, through high-angular-resolution interferometric observations over a continuous broad frequency range. Methods. We used 32 GHz Submillimeter Array observations with continuous frequency coverage from 329 to 361 GHz at an angular resolution of ~1″ to do a line survey and obtain a chemical inventory of the source. The line emission in the frequency range was used to determine column densities and excitation temperatures for the COMs. We also mapped out the intensity distribution of the different species. Results. We identified approximately 400 lines that can be attributed to 29 different molecular species and their isotopologues. We find that the molecular peak emission is along a linear gradient, and coincides with the axis of red- and blueshifted H2CO and CS emission. Chemical differentiation is detected along this gradient, with the O-bearing molecular species peaking towards one component of the system and the N- and S-bearing species peaking towards the other. The chemical gradient is offset from but parallel to the axis through the two continuum sources. The inferred column densities and excitation temperatures are compared to other sources where COMs are abundant. Only one deuterated molecule is detected, HDO, while an upper limit for CH2DOH is derived, leading to a D/H ratio of <0.1%. Conclusions. We conclude that the origin of the observed COM emission is probably a combination of the young stellar sources along with accretion of infalling material onto a disc-like structure surrounding a young protostar and located close to one of the continuum sources. This disc and protostar are associated with the O-bearing molecular species, while the S- and N-bearing species on the other hand are associated with the other continuum core, which is probably a protostar that is slightly more evolved than the other component of the system. The low D/H ratio likely reflects a pre-stellar phase where the COMs formed on the ices at warm temperatures (~30 K), where the deuterium fractionation would have been inefficient. The observations and results presented here demonstrate the importance of good frequency coverage and high angular resolution when disentangling the origin of COM emission.

Unlocking the sulphur chemistry in intermediate-mass protostars of Cygnus X

“…Despite the emission peak shifts for N30, a specific and different spatial distribution of all S-species was seen in the families. The organo-sulphurs show an extended pattern around the two binary components (MM1a and MM1b), their spatial distribution is more extended and not concentrated on a specific source, in contrast to the O-S family, which is concentrated around MM1a, as also pointed out by van der Walt et al (2021). It might be suggested that C-S is associated with both sources (i.e., MM1a and MM1b), while the O-S family is primarily associated with MM1a.…”

“…These observations of protostars allow us to target the S-chemistry in the hot core of intermediate-mass protostars. It was pointed out by van der Walt et al (2021) that the observed hot core toward Cyg X-N30 is not a traditional hot core, that is, a core in which the gas near the protostar is heated by the accretion luminosity, leading to a jump in the abundance of molecules when the icy mantles sublimate. However, we use the term hot core in this paper to mean the warm gas toward both sources, regardless of their actual physical origin.…”

“…Along with frequency coverage, we obtained continuum emission at 0.8 mm wavelengths for both sources. For full details of the observing strategy, data reduction, and cleaning, see van der Walt et al (2021). The data were reduced and imaged with CASA 5 (Common Astronomy Software Applications, McMullin et al 2007), while line analysis was done with the CASSIS 6 software (Centre d'Analyse Scientifique de Spectres Instrumentaux et Synthétiques, Vastel et al 2015).…”

Resolving desorption of complex organic molecules in a hot core

“…Deviations from this classification have been observed, for example, in IRAS 16293-2422A (Manigand et al 2020), where CH 3 OH and CH 3 OCHO, although being hot species, trace a more extended region. Moreover, most recent observations towards CygX-N30 do not reveal a significant difference in temperature between various COMs in general (van der Walt et al 2021). Such a classification that depends on binding energies is not straightforward as their values are uncertain and vary depending on the dust composition.…”

The Cygnus Allscale Survey of Chemistry and Dynamical Environments: CASCADE: Overview and first results toward DR20 from the Max Planck IRAM Observatory program (MIOP)

“…This and the presence of several OB associations, the results of many million years of recent star formation, and a super-bubble driven by stellar winds of the O stars and the famous Cygnus loop supernova remnant (also known as the Diamond ring) give testament to intense and widespread star formation that occurred over (at least) the past few million years. More recently, mm and centimeter (cm) wavelength observations have resulted in a wealth of data on the dust, ionized, and molecular gas emission in this region (e.g., Taylor et al 2003;Motte et al 2007Motte et al , 2010Molinari et al 2010;Cao et al 2019Cao et al , 2021Cao et al , 2022Li et al 2021;van der Walt et al 2021). Taken together, these substantial complementary data form a rich background that now allows placing all spatial scales into context and following the gas flow from the large molecular clouds to the small cores.…”