Issue |
A&A
Volume 699, July 2025
|
|
---|---|---|
Article Number | A34 | |
Number of page(s) | 26 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361/202452700 | |
Published online | 27 June 2025 |
ALMAGAL
IV. Morphological comparison of molecular and thermal dust emission using the histogram of oriented gradients method
1
INAF-Istituto di Astrofisica e Planetologia Spaziale,
Via Fosso del Cavaliere 100,
00133
Roma,
Italy
2
Institut de Ciències de l’Espai (ICE), CSIC, Campus UAB, Carrer de Can Magrans s/n,
08193
Bellaterra (Barcelona),
Spain
3
Institut d’Estudis Espacials de Catalunya (IEEC),
08860,
Castelldefels (Barcelona),
Spain
4
Dipartimento di Fisica, Sapienza Università di Roma,
Piazzale Aldo Moro 2,
00185
Rome,
Italy
5
Dipartimento di Fisica, Università di Roma Tor Vergata,
Via della Ricerca Scientifica 1,
00133
Roma,
Italy
6
I. Physikalisches Institut, Universität zu Köln,
Zülpicher Str. 77,
50937
Köln,
Germany
7
University of Connecticut, Department of Physics,
2152 Hillside Road, Unit 3046 Storrs,
CT
06269,
USA
8
Institute of Astronomy and Astrophysics, Academia Sinica,
11F of ASMAB, AS/NTU No. 1, Sec. 4, Roosevelt Road,
Taipei
10617,
Taiwan
9
East Asian Observatory,
660 N. A’ohoku, Hilo,
Hawaii,
HI
96720,
USA
10
INAF-Osservatorio Astrofisico di Arcetri,
Largo E. Fermi 5,
50125
Firenze,
Italy
11
Max Planck Institute for Astronomy,
Königstuhl 17,
69117
Heidelberg,
Germany
12
Jodrell Bank Centre for Astrophysics,
Oxford Road, The University of Manchester,
Manchester
M13 9PL,
UK
13
Universität Heidelberg, Zentrum für Astronomie, Institut für Theoretische Astrophysik,
Heidelberg,
Germany
14
Universität Heidelberg, Interdisziplinäres Zentrum für Wissenschaftliches Rechnen,
Heidelberg,
Germany
15
Center for Astrophysics | Harvard & Smithsonian,
60 Garden St,
Cambridge,
MA
02138,
USA
16
Elizabeth S. and Richard M. Cashin Fellow at the Radcliffe Institute for Advanced Studies at Harvard University,
10 Garden Street,
Cambridge,
MA
02138,
USA
17
Center for Data and Simulation Science, University of Cologne,
Germany
18
ASTRON, Netherlands Institute for Radio Astronomy,
Oude Hoogeveensedijk 4,
Dwingeloo,
7991
PD,
The Netherlands
19
Dipartimento di Fisica e Astronomia, Università degli Studi di Firenze,
Via G. Sansone 1,
50019
Sesto Fiorentino, Firenze,
Italy
20
SKA Observatory, Jodrell Bank, Lower Withington,
Macclesfield
SK11 9FT,
UK
21
UK ALMA Regional Centre Node,
M13 9PL,
UK
22
National Radio Astronomy Observatory,
520 Edgemont Road,
Charlottesville,
VA
22903,
USA
23
Max-Planck-Institute for Extraterrestrial Physics (MPE),
Garching bei München,
Germany
24
Laboratory for the study of the Universe and eXtreme phenomena (LUX), Observatoire de Paris,
Meudon,
France
25
Université Paris-Saclay, Université Paris-Cité, CEA, CNRS, AIM,
91191
Gif-sur-Yvette,
France
26
School of Engineering and Physical Sciences, Isaac Newton Building, University of Lincoln, Brayford Pool,
Lincoln
LN6 7TS,
UK
27
Faculty of Physics, University of Duisburg-Essen,
Lotharstraße 1,
47057
Duisburg,
Germany
28
Jet Propulsion Laboratory, California Institute of Technology,
4800 Oak Grove Drive,
Pasadena,
CA
91109,
USA
29
Shanghai Astronomical Observatory, Chinese Academy of Sciences,
Shanghai
200030,
PR
China
30
School of Physics and Astronomy, University of Leeds,
Leeds
LS2 9JT,
UK
31
INAF-Istituto di Radioastronomia & Italian ALMA Regional Centre,
Via P. Gobetti 101,
40129
Bologna,
Italy
32
Department of Astronomy, School of Science, The University of Tokyo,
7-3-1 Hongo, Bunkyo,
Tokyo
113-0033,
Japan
33
Department of Earth and Planetary Sciences, Institute of Science Tokyo, Meguro,
Tokyo
152-8551,
Japan
34
National Astronomical Observatory of Japan, National Institutes of Natural Sciences,
2-21-1 Osawa, Mitaka,
Tokyo
181-8588,
Japan
35
Dipartimento di Fisica e Astronomia, Alma Mater Studiorum – Università di Bologna,
Bologna,
Italy
36
SRON Netherlands Institute for Space Research,
Landleven 12,
9747
AD
Groningen,
The Netherlands
37
Kapteyn Astronomical Institute, University of Groningen,
The Netherlands
38
Departamento de Astronomía, Universidad de Chile,
Casilla 36-D,
Santiago,
Chile
39
Zhejiang Laboratory,
Hangzhou
311100,
PR
China
40
Universidad Autonoma de Chile,
Pedro de Valdivia 425,
9120000
Santiago de Chile,
Chile
★ Corresponding author: asanchez@ice.csic.es
Received:
22
October
2024
Accepted:
10
April
2025
Context. The study of molecular line emission is crucial to unveil the kinematics and the physical conditions of gas in star-forming regions. We use data from the ALMAGAL survey, which provides an unprecedentedly large statistical sample of high-mass star-forming clumps that helps us to remove bias and reduce noise (e.g., due to source peculiarities, selection, or environmental effects) to determine how well individual molecular species trace continuum emission.
Aims. Our aim is to quantify whether individual molecular transitions can be used reliably to derive the physical properties of the bulk of the H2 gas, by considering morphological correlations in their overall integrated molecular line emission with the cold dust. We selected transitions of H2CO, CH3OH, DCN, HC3N, CH3CN, CH3OCHO, SO, and SiO and compared them with the 1.38 mm dust continuum emission at different spatial scales in the ALMAGAL sample. We included two transitions of H2CO to understand whether the validity of the results depends on the excitation condition of the selected transition of a molecular species. The ALMAGAL project observed more than 1000 candidate high-mass star-forming clumps in ALMA band 6 at a spatial resolution down to 1000 au. We analyzed a total of 1013 targets that cover all evolutionary stages of the high-mass star formation process and different conditions of clump fragmentation.
Methods. For the first time, we used the method called histogram of oriented gradients (HOG) as implemented in the tool astroHOG on a large statistical sample to compare the morphology of integrated line emission with maps of the 1.38 mm dust continuum emission. For each clump, we defined two masks: the first mask covered the extended more diffuse continuum emission, and the second smaller mask that only contained the compact sources. We selected these two masks to study whether and how the correlation among the selected molecules changes with the spatial scale of the emission, from extended more diffuse gas in the clumps to denser gas in compact fragments (cores). Moreover, we calculated the Spearman correlation coefficient and compared it with our astroHOG results.
Results. Only H2CO, CH3OH, and SO of the molecular species we analyzed show emission on spatial scales that are comparable with the diffuse 1.38 mm dust continuum emission. However, according the HOG method, the median correlation of the emission of each of these species with the continuum is only ~24–29%. In comparison with the dusty dense fragments, these molecular species still have low correlation values that are below 45% on average. The weak morphological correlation suggests that these molecular lines likely trace the clump medium or outer layers around dense fragments on average (in some cases, this might be due to optical depth effects) or also trace the inner parts of outflows at this scale. On the other hand DCN, HC3N, CH3CN3 and CH3OCHO are well correlated with the dense dust fragments at above 60%. The lowest correlation is seen with SiO for the extended continuum emission and for compact sources. Moreover, unlike other outflow tracers, in a large fraction of the sources, SiO does not cover the area of the extended continuum emission well. This and the results of the astroHOG analysis reveal that SiO and SO do not trace the same gas, in contrast to what was previously thought. From the comparison of the results of the HOG method and the Spearman correlation coefficient, the HOG method gives much more reliable results than the intensity-based coefficient when the level of similarity of the emission morphology is estimated.
Key words: astrochemistry / molecular data / ISM: general / ISM: lines and bands / ISM: molecules
© 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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