Search for high-mass protostars with ALMA revealed up to kilo-parsec scales (SPARKS)

Abstract

Context. Classical hot cores are rich in molecular emission, and they show a high abundance of complex organic molecules (COMs). The emergence of molecular complexity that is represented by COMs, in particular, is poorly constrained in the early evolution of hot cores. Aims. We put observational constraints on the physical location of COMs in a resolved high-mass protostellar envelope associated with the G328.2551−0.5321 clump. The protostar is single down to ~400 au scales and we resolved the envelope structure down to this scale. Methods. High angular resolution observations using the Atacama Large Millimeter Array allowed us to resolve the structure of the inner envelope and pin down the emission region of COMs. We use local thermodynamic equilibrium modelling of the available 7.5 GHz bandwidth around ~345 GHz to identify the COMs towards two accretion shocks and a selected position representing the bulk emission of the inner envelope. We quantitatively discuss the derived molecular column densities and abundances towards these positions, and use our line identification to qualitatively compare this to the emission of COMs seen towards the central position, corresponding to the protostar and its accretion disk. Results. We detect emission from 10 COMs, and identify a line of deuterated water (HDO). In addition to methanol (CH3OH), methyl formate (CH3OCHO) and formamide (HC(O)NH2) have the most extended emission. Together with HDO, these molecules are found to be associated with both the accretion shocks and the inner envelope, which has a moderate temperature of Tkin ~ 110 K. We find a significant difference in the distribution of COMs. O-bearing COMs, such as ethanol, acetone, and ethylene glycol are almost exclusively found and show a higher abundance towards the accretion shocks with Tkin ~ 180 K. Whereas N-bearing COMs with a CN group, such as vinyl and ethyl cyanide peak on the central position, thus the protostar and the accretion disk. The molecular composition is similar towards the two shock positions, while it is significantly different towards the inner envelope, suggesting an increase in abundance of O-bearing COMs towards the accretion shocks. Conclusions. We present the first observational evidence for a large column density of COMs seen towards accretion shocks at the centrifugal barrier at the inner envelope. The overall molecular emission shows increased molecular abundances of COMs towards the accretion shocks compared to the inner envelope. The bulk of the gas from the inner envelope is still at a moderate temperature of Tkin ~ 110 K, and we find that the radiatively heated inner region is very compact (<1000 au). Since the molecular composition is dominated by that of the accretion shocks and the radiatively heated hot inner region is very compact, we propose this source to be a precursor to a classical, radiatively heated hot core. By imaging the physical location of HDO, we find that it is consistent with an origin within the moderately heated inner envelope, suggesting that it originates from sublimation of ice from the grain surface and its destruction in the vicinity of the heating source has not been efficient yet.

Evolutionary study of complex organic molecules in high-mass star-forming regions

“…This has been found also by Fontani et al (2007) in hot cores, whereas other authors noticed differences between O-and N-bearing COMs in both the spatial distribution (e.g. Liu 2005;Csengeri et al 2019) and the radial velocities (Blake et al 1987). We also note that, given the increasing abundance trend, molecular destruction routes seem to be less efficient than formation/desorption mechanisms, especially at later evolutionary stages (i.e.…”

“…Moreover, interferometric observations (e.g. Sutton et al 1995;Blake et al 1996;Wyrowski et al 1999;Liu 2005) suggest that O-and N-bearing molecules trace different portions of a molecular star-forming clump (see also Csengeri et al 2019 and references therein). However, several details are still unclear.…”

ATOMS: ALMA Three-millimeter Observations of Massive Star-forming regions -- VIII. A search for hot cores by using C$_2$H$_5$CN, CH$_3$OCHO and CH$_3$OH lines

“…More recently, a large sample including 18 well-known high-mass star-forming regions was observed by the NOEMA with same spectral setup, suggesting that most molecules are destroyed in evolved cores having less emission lines (Gieser et al 2021). Of the detected hot cores, a few show chemical differentiation between nitrogen-and oxygen-bearing COMs (e.g., Wyrowski et al 1999;Qin et al 2010Qin et al , 2015Remijan et al 2004;Kalenskii & Johansson 2010;Suzuki et al 2018;Lee et al 2019;Csengeri et al 2019;Allen et al 2017;Jiménez-Serra et al 2012;Gieser et al 2019;Mills et al 2018). Chemical differentiation and heating mechanism are still longstanding problems due to a lack of large sample and systematic observations.…”

“…Due to small source sizes of hot cores, single dish observations suffer from beam dilution and sample the emission from both hot cores and surrounding cold envelopes. The millimeter/submillimeter interferometric arrays (e.g., SMA, NOEMA, and ALMA) offer larger bandwidth, higher spatial resolution and increased sensitivity, which have promoted the hot core observations greatly, but mainly focused on individual sources or small samples (Law et al 2021;van der Walt et al 2021;Beuther et al 2009;Qin et al 2008Qin et al , 2010Qin et al , 2015Rong et al 2016;Rivilla et al 2017;Bøgelund et al 2019;Guzmán et al 2018;Luo et al 2009;Csengeri et al 2019;Sakai et al 2013Sakai et al , 2018Zapata et al 2011;Mottram et al 2020;Fuente et al 2021;Belloche et al 2016Belloche et al , 2019Brogan et al 2016;Bonfand et al 2017;Xue et al 2019;wong & An 2018;Sánchez-Monge et al 2010Hernández-Hernández et al 2014;Peng et al 2019;Liu et al 2001Liu et al , 2002Remijan et al 2003Remijan et al , 2004Palau et al 2017;Wu et al 2014;Taniguchi et al 2020;Rathborne et al 2011;Orozco-Aguilera et al 2017;Ahmadi et al 2018;Mottram et al 2020;Pagani et al 2017;…”

Molecular Distributions of the Disk/Envelope System of L483: Principal Component Analysis for the Image Cube Data

“…In particular, Complex Organic Molecules (COMs), which consist of more than six atoms with one carbon atom at least, are found to be widely present in various environments of star formation: quiescent dense clouds, prestellar cores (e.g., Bacmann et al 2012;Cernicharo et al 2012;Ceccarelli et al 2017;Soma et al 2018;Scibelli & Shirley 2020), disk/envelope systems of protostellar cores (e.g., Cazaux et al 2003;Bottinelli et al 2004b;Kuan et al 2004;Pineda et al 2012;Jørgensen et al 2016;Oya et al 2016;Lee et al 2019;Imai et al 2019;Bianchi et al 2020), and outflow shock regions around protostars (e.g., Arce et al 2008;Sugimura et al 2011;Codella et al 2020;De Simone et al 2020). Many observations of COMs toward various sources reveal a chemical differentiation between nitrogen-bearing and oxygen-bearing COMs (e.g., Wyrowski et al 1999;Bottinelli et al 2004b;Kuan et al 2004;Beuther et al 2005;Fontani et al 2007;Calcutt et al 2018;Oya et al 2018;Csengeri et al 2019). These re-was evaluated to be between 75 • and 90 • (0 • for a pole-on configuration) with the ALMA observations of the CS and CCH line emission by Oya et al (2018), which confirms the nearly edge-on configuration of the disk/envelope system.…”