ALMAGAL

II. The ALMA evolutionary study of high-mass protocluster formation in the Galaxy: ALMA data processing and pipeline

¹ Institut de Ciències de l’Espai (ICE), CSIC, Campus UAB, Carrer de Can Magrans s/n, 08193 Bellaterra (Barcelona), Spain
² Institut d’Estudis Espacials de Catalunya (IEEC), 08860, Castelldefels (Barcelona), Spain
³ National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA
⁴ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁵ SKA Observatory, Jodrell Bank, Lower Withington, Macclesfield SK11 9FT, UK
⁶ Jodrell Bank Centre for Astrophysics, Oxford Road, The University of Manchester, Manchester M13 9PL, UK
⁷ UK ALMA Regional Centre Node M13 9PL, Manchester, UK
⁸ INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁹ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
¹⁰ INAF-Istituto di Astrofisica e Planetologia Spaziale, Via Fosso del Cavaliere 100, 00133 Roma, Italy
¹¹ Dipartimento di Fisica, Sapienza Università di Roma, Piazzale Aldo Moro 2, 00185 Rome, Italy
¹² I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
¹³ School of Engineering and Physical Sciences, Isaac Newton Building, University of Lincoln, Brayford Pool, Lincoln LN6 7TS, UK
¹⁴ Institute of Astronomy and Astrophysics, Academia Sinica, 11F of ASMAB, AS/NTU No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan
¹⁵ Center for Astrophysics | Harvard & Smithsonian, 60 Garden St, Cambridge, MA 02138, USA
¹⁶ University of Connecticut, Department of Physics, 2152 Hillside Road, Unit 3046 Storrs, CT 06269, USA
¹⁷ East Asian Observatory, 660 N. A’ohoku, Hilo, Hawaii, HI 96720, USA
¹⁸ UK Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
¹⁹ Universität Heidelberg, Zentrum für Astronomie, Institut für Theoretische Astrophysik, Heidelberg, Germany
²⁰ Universität Heidelberg, Interdisziplinäres Zentrum für Wissenschaftliches Rechnen, Heidelberg, Germany
²¹ Elizabeth S. and Richard M. Cashin Fellow at the Radcliffe Institute for Advanced Studies at Harvard University, 10 Garden Street, Cambridge, MA 02138, USA
²² Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
²³ Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030, PR China
²⁴ European Southern Observatory, Karl-Schwarzschild Str. 2, 85748 Garching bei München, Germany
²⁵ INAF-Istituto di Radioastronomia & Italian ALMA Regional Centre, Via P. Gobetti 101, 40129 Bologna, Italy
²⁶ Department of Earth and Planetary Sciences, Institute of Science Tokyo, Meguro, Tokyo 152-8551, Japan
²⁷ National Astronomical Observatory of Japan, National Institutes of Natural Sciences, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
²⁸ SRON Netherlands Institute for Space Research, Landleven 12, 9747 AD Groningen, The Netherlands
²⁹ Kapteyn Astronomical Institute, University of Groningen, Groningen, The Netherlands
³⁰ Center for Data and Simulation Science, University of Cologne, Cologne, Germany
³¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
³² Zhejiang Laboratory, Hangzhou 311100, PR China
³³ Dipartimento di Fisica e Astronomia, Università degli Studi di Firenze, Via G. Sansone 1, 50019 Sesto Fiorentino, Firenze, Italy
³⁴ Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
³⁵ Max-Planck-Institute for Extraterrestrial Physics (MPE), Garching bei München, Germany
³⁶ Laboratory for the study of the Universe and eXtreme phenomena (LUX), Observatoire de Paris, Meudon, France
³⁷ Faculty of Physics, University of Duisburg-Essen, Lotharstraße 1, 47057 Duisburg, Germany
³⁸ Centro de Astro-Ingeniería (AIUC), Pontificia Universidad Católica de Chile, Av. Vicuña Mackena 4860, Macul, Santiago, Chile
³⁹ Department of Astronomical Science, SOKENDAI (The Graduate University for Advanced Studies), 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁴⁰ Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
⁴¹ Dipartimento di Fisica, Università di Roma Tor Vergata, Via della Ricerca Scientifica 1, 00133 Roma, Italy
⁴² School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK

^★ Corresponding author; asanchez@ice.csic.es

Received: 22 October 2024
Accepted: 3 February 2025

Abstract

Context. Stars form preferentially in clusters embedded inside massive molecular clouds, many of which contain high-mass stars. Thus, a comprehensive understanding of star formation requires a robust and statistically well-constrained characterization of the formation and early evolution of these high-mass star clusters. To achieve this, we designed the ALMAGAL Large Program that observed 1017 high-mass star-forming regions distributed throughout the Galaxy, sampling different evolutionary stages and environmental conditions.

Aims. In this work, we present the acquisition and processing of the ALMAGAL data. The main goal is to set up a robust pipeline that generates science-ready products, that is, continuum and spectral cubes for each ALMAGAL field, with a good and uniform quality across the whole sample.

Methods. ALMAGAL observations were performed with the Atacama Large Millimeter/submillimeter Array (ALMA). Each field was observed in three different telescope arrays, being sensitive to spatial scales ranging from ≈1000 au up to ≈0.1 pc. The spectral setup allows sensitive (≈0.1 mJy beam⁻¹) imaging of the continuum emission at 219 GHz (or 1.38 mm), and it covers multiple molecular spectral lines observed in four different spectral windows that span about ≈4 GHz in frequency coverage. We have designed a Python-based processing workflow to calibrate and image these observational data. This ALMAGAL pipeline includes an improved continuum determination, suited for line-rich sources; an automatic self-calibration process that reduces phase-noise fluctuations and improves the dynamical range by up to a factor ≈5 in about 15% of the fields; and the combination of data from different telescope arrays to produce science-ready, fully combined images.

Results. The final products are a set of uniformly generated continuum images and spectral cubes for each ALMAGAL field, including individual-array and combined-array products. The fully combined products have spatial resolutions in the range 800–2000 au, and mass sensitivities in the range 0.02–0.07 M_⊙. We also present a first analysis of the spectral line information included in the ALMAGAL setup, and its potential for future scientific studies. As an example, specific spectral lines (e.g., SiO and CH₃CN) at ≈1000 au scales resolve the presence of multiple outflows in clusters and will help us to search for disk candidates around massive protostars. Moreover, the broad frequency bands provide information on the chemical richness of the different cluster members, which can be used to study the chemical evolution during the formation process of star clusters.