Issue |
A&A
Volume 695, March 2025
|
|
---|---|---|
Article Number | A78 | |
Number of page(s) | 13 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361/202452191 | |
Published online | 10 March 2025 |
FAUST
XX. The chemical structure and temperature profile of the IRAS 4A2 hot corino at 20–50 au
1
DIFA, Dipartimento di Fisica e Astronomia, Università degli Studi di Bologna,
Via Gobetti 93/2,
40129
Bologna, Italy
2
ESO,
Karl Schwarzchild Str. 2,
85748
Garching bei München, Germany
3
Department of Astronomy, Stockholm University, AlbaNova University Centre,
106 91
Stockholm, Sweden
4
INAF, Osservatorio Astrofisico di Arcetri,
Largo E. Fermi 5,
50125
Firenze, Italy
5
National Radio Astronomy Observatory,
1011 Lopezville Rd,
Socorro,
NM
87801,
USA
6
Univ. Grenoble Alpes, CNRS, IPAG,
38000
Grenoble, France
7
Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México,
A.P. 3-72 (Xangari),
8701
Morelia, Mexico
8
Black Hole Initiative at Harvard University,
20 Garden Street,
Cambridge,
MA
02138,
USA
9
David Rockefeller Center for Latin American Studies, Harvard University,
1730 Cambridge Street,
Cambridge,
MA
02138,
USA
10
Institut de Radioastronomie Millimétrique (IRAM),
300 rue de la Piscine,
38406
Saint-Martin-d’Hères,
France
11
The Institute of Physical and Chemical Research (RIKEN),
2-1, Hirosawa,
Wako-shi, Saitama
351-0198,
Japan
12
Department of Astronomy, The University of Tokyo,
Bunkyo-ku, Tokyo
113-0033,
Japan
13
Leiden Observatory, Leiden University,
PO Box 9513,
23000
RA Leiden, The Netherlands
14
Center for Astrochemical Studies, Max-Planck-Institut für Extraterrestrische Physik,
Gießenbachstraße 1,
85748
Garching, Germany
15
Astrochemistry Laboratory, Code 691, NASA Goddard Space Flight Center,
8800 Greenbelt Road,
Greenbelt,
MD
20771,
USA
16
Centro de Astrobiología (CAB), INTA-CSIC,
Carretera de Ajalvir km 4,
Torrejón de Ardoz,
28850
Madrid,
Spain
17
NRC Herzberg Astronomy and Astrophysics,
5071 West Saanich Road,
Victoria,
BC
V9E 2E7,
Canada
18
Department of Physics and Astronomy, University of Victoria,
Victoria,
BC
V8P 5C2, Canada
19
Steward Observatory,
933 N Cherry Ave.,
Tucson,
AZ
85721, USA
20
The Graduate University for Advanced Studies (SOKENDAI),
Shonan Village,
Hayama, Kanagawa
240-0193, Japan
★ Corresponding author; jenny.frediani@astro.su.se; marta.desimone@eso.org
Received:
10
September
2024
Accepted:
24
January
2025
Context. Young low-mass protostars often possess hot corinos, which are compact, hot, and dense regions that are bright in interstellar complex organic molecules (iCOMs). In addition to their prebiotic role, iCOMs can be used as a powerful tool to characterize the chemical and physical properties of hot corinos.
Aims. Using ALMA/FAUST data, our aim was to explore the iCOM emission at <50 au scale around the Class 0 prototypical hot corino IRAS 4A2.
Methods. We imaged IRAS 4A2 in six abundant common iCOMs (CH3OH, HCOOCH3, CH3CHO, CH3CH2OH, CH2OHCHO, and NH2CHO), and derived their emitting sizes. The column density and gas temperature for each species were derived at 1σ from a multiline analysis by applying a non-LTE approach for CH3OH, and LTE population or rotational diagram analysis for the other iCOMs. Thanks to the unique estimates of the absorption from foreground millimeter dust toward IRAS 4A2, we derived for the first time unbiased gas temperatures and column densities.
Results. We resolved the IRAS 4A2 hot corino, and found evidence for a chemical spatial distribution in the inner 50 au, with the outer emitting radius increasing from ∼22–23 au for NH2CHO and CH2OHCHO, followed by CH3CH2OH (∼27 au), CH3CHO (∼28 au), HCOOCH3 (∼36 au), and out to ∼40 au for CH3OH. Combining our estimate of the gas temperature probed by each iCOM with their beam-deconvolved emission sizes, we inferred the gas temperature profile of the hot corino on scales of 20–50 au in radius, and found a power-law index q of approximately –1.
Conclusions. We observed, for the first time, a chemical segregation in iCOMs of the IRAS 4A2 hot corino, and derived the gas temperature profile of its inner envelope. The derived profile is steeper than when considering a simple spherical collapsing and optically thin envelope, hinting at a partially optically thick envelope or a gravitationally unstable disk-like structure.
Key words: astrochemistry / stars: formation / ISM: molecules / ISM: individual objects: IRAS 4A2
© The Authors 2025
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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