The Perseus ALMA Chemistry Survey (PEACHES). I. The Complex Organic Molecules in Perseus Embedded Protostars

Yao-Lun Yang,Satoshi Yamamoto,Ziwei E Zhang,Yoko Oya,Yichen Zhang,Nami Sakai,Yoshimasa Watanabe,Cecilia Ceccarelli,Nadia M Murillo,Tomoya Hirota,Ana López-Sepulcre,Aya E Higuchi,Bertrand Lefloch,Shaoshan Zeng,Muneaki Imai,Mathilde Bouvier,Takeshi Sakai

doi:10.3847/1538-4357/abdfd6

Abstract

Abstract To date, about two dozen low-mass embedded protostars exhibit rich spectra with lines of complex organic molecules (COMs). These protostars seem to possess a different enrichment in COMs. However, the statistics of COM abundance in low-mass protostars are limited by the scarcity of observations. This study introduces the Perseus ALMA Chemistry Survey (PEACHES), which aims at unbiasedly characterizing the chemistry of COMs toward the embedded (Class 0/I) protostars in the Perseus molecular cloud. Of the 50 embedded protostars surveyed, 58% of them have emission from COMs. 56%, 32%, and 40% of the protostars have CH3OH, CH3OCHO, and N-bearing COMs, respectively. The detectability of COMs depends neither on the averaged continuum brightness temperature, a proxy of the H2 column density, nor on the bolometric luminosity and the bolometric temperature. For the protostars with detected COMs, CH3OH has a tight correlation with CH3CN, spanning more than two orders of magnitude in column densities normalized by the continuum brightness temperature, suggesting a chemical relation between CH3OH and CH3CN and a large chemical diversity in the PEACHES samples at the same time. A similar trend with more scatter is also found between all identified COMs, which hints at a common chemistry for the sources with COMs. The correlation between COMs is insensitive to the protostellar properties, such as the bolometric luminosity and the bolometric temperature. The abundance of larger COMs (CH3OCHO and CH3OCH3) relative to that of smaller COMs (CH3OH and CH3CN) increases with the inferred gas column density, hinting at an efficient production of complex species in denser envelopes.

Highlights

Planet formation may start during the embedded phase of star formation (Tychoniec et al 2020)
In the scenario in which planets form from the embedded disks, resulting in substructures, the chemistry of embedded disks may play a significant role for the chemical composition of the forming planets
Given the compact size of complex organic molecules (COMs) emission ( 100 au) and the spatial resolution of ∼0 5 (∼150 au at 300 pc), we focused on the spectra toward the continuum sources to search for the COMs in the inner envelope

Summary

Introduction

Planet formation may start during the embedded phase of star formation (Tychoniec et al 2020). In the past two decades, observations show the emission of complex molecules toward the center of several protostellar cores. From the astronomical point of view, complex molecules are usually defined as a species that contains six or more atoms (Herbst & van Dishoeck 2009). It can be saturated (e.g., Cazaux et al 2003; Bottinelli et al 2007; Jørgensen et al 2016; Ceccarelli et al 2017; Lee et al 2017 and the ALMA PILS Survey) or unsaturated (e.g., carbon-chain molecules: Sakai & Yamamoto 2013; Sakai et al 2014; Law et al 2018). The saturated organic molecules, often called complex organic molecules (COMs) or interstellar

Results

Discussion

Conclusion