JOYS: MIRI/MRS spectroscopy of gas-phase molecules from the high-mass star-forming region IRAS 23385+6053
Artikel i vetenskaplig tidskrift, 2024

Context. Space-based mid-infrared (IR) spectroscopy is a powerful tool for the characterization of important star formation tracers of warm gas which are unobservable from the ground. The previous mid-IR spectra of bright high-mass protostars with the Infrared Space Observatory (ISO) in the hot-core phase typically show strong absorption features from molecules such as CO2, C2H2, and HCN. However, little is known about their fainter counterparts at earlier stages. Aims. We aim to characterize the gas-phase molecular features in James Webb Space Telescope Mid-Infrared Instrument Medium Resolution Spectrometer (MIRI/MRS) spectra of the young and clustered high-mass star-forming region IRAS 23385+6053. Methods. Spectra were extracted from several locations in the MIRI/MRS field of view, targeting two mid-IR sources tracing embedded massive protostars as well as three H2 bright outflow knots at distances of >8000 au from the multiple. Molecular features in the spectra were fit with local thermodynamic equilibrium (LTE) slab models, with their caveats discussed in detail. Results. Rich molecular spectra with emission from CO, H2, HD, H2O, C2H2, HCN, CO2, and OH are detected towards the two mid-IR sources. However, only CO and OH are seen towards the brightest H2 knot positions, suggesting that the majority of the observed species are associated with disks or hot core regions rather than outflows or shocks. The LTE model fits to 12CO2, C2H2, HCN emission suggest warm 120a-200 K emission arising from a disk surface around one or both protostars. The abundances of CO2 and C2H2 of ~10âà  à  7 are consistent with previous observations of high-mass protostars. Weak ~500 K H2O emission at ~6a-7 μm is detected towards one mid-IR source, whereas 250a-1050 K H2O absorption is found in the other. The H2O absorption may occur in the disk atmosphere due to strong accretion-heating of the midplane, or in a disk wind viewed at an ideal angle for absorption. CO emission may originate in the hot inner disk or outflow shocks, but NIRSpec data covering the 4.6 μm band head are required to determine the physical conditions of the CO gas, as the high temperatures seen in the MIRI data may be due to optical depth. OH emission is detected towards both mid-IR source positions and one of the shocks, and is likely excited by water photodissociation or chemical formation pumping in a highly non-LTE manner. Conclusions. The observed molecular spectra are consistent with disks having already formed around two protostars in the young IRAS 23385+6054 system. Molecular features mostly appear in emission from a variety of species, in contrast to the more evolved hot core phase protostars which typically show only absorption; however, further observations of young high-mass protostars are needed to disentangle geometry and viewing angle effects from evolution.

Stars: massive

Stars: formation

Stars: protostars

Stars: individual: IRAS 23385+6053

Astrochemistry

Författare

L. Francis

Universiteit Leiden

M. L. Van Gelder

Universiteit Leiden

E. F. van Dishoeck

Max-Planck-Gesellschaft

Universiteit Leiden

C. Gieser

Max-Planck-Gesellschaft

H. Beuther

Max-Planck-Gesellschaft

Łukasz Tychoniec

European Southern Observatory (ESO)

Universiteit Leiden

G. Perotti

Max-Planck-Gesellschaft

A. Caratti o. Garatti

Osservatorio Astronomico di Capodimonte

Patrick Kavanagh

Maynooth University

Tom Ray

Dublin Institute for Advanced Studies

Pamela Klaassen

Royal Observatory

Kay Justtanont

Chalmers, Rymd-, geo- och miljövetenskap, Astronomi och plasmafysik

H. Linnartz

Universiteit Leiden

W. R.M. Rocha

Universiteit Leiden

K. Slavicinska

Universiteit Leiden

M. Gudel

Eidgenössische Technische Hochschule Zürich (ETH)

Max-Planck-Gesellschaft

Universität Wien

T. Henning

Max-Planck-Gesellschaft

P. O. Lagage

Université Paris-Saclay

G. A Stlin

Oskar Klein Centre

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 683 A249

Ämneskategorier

Astronomi, astrofysik och kosmologi

Atom- och molekylfysik och optik

Annan fysik

DOI

10.1051/0004-6361/202348105

Mer information

Senast uppdaterat

2024-04-29