ALMAGAL

VIII. Early phases of triggered star formation in source AG286.0716–1.8229

¹ INAF-Istituto di Astrofisica e Planetologia Spaziale, Via Fosso del Cavaliere 100, 00133 Roma, Italy
² I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
³ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁴ INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁵ Max-Planck-Institute for Extraterrestrial Physics (MPE), Garching bei München, Germany
⁶ Laboratory for the study of the Universe and eXtreme phenomena (LUX), Observatoire de Paris, Meudon, France
⁷ Dipartimento di Fisica, Università di Roma Tor Vergata, Via della Ricerca Scientifica 1, 00133 Roma, Italy
⁸ Institut de Ciències de l’Espai (ICE), CSIC, Campus UAB, Carrer de Can Magrans s/n, 08193, Bellaterra (Barcelona), Spain
⁹ Institut d’Estudis Espacials de Catalunya (IEEC), 08860, Castelldefels (Barcelona), Spain
¹⁰ University of Connecticut, Department of Physics, 2152 Hillside Road, Unit 3046 Storrs, CT 06269, USA
¹¹ Institute of Astronomy and Astrophysics, Academia Sinica, 11F of ASMAB, AS/NTU No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan
¹² East Asian Observatory, 660 N. A’ohoku, Hilo, Hawaii, HI 96720, USA
¹³ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
¹⁴ Jodrell Bank Centre for Astrophysics, Oxford Road, The University of Manchester, Manchester M13 9PL, UK
¹⁵ Universität Heidelberg, Zentrum für Astronomie, Institut für Theoretische Astrophysik, Heidelberg, Germany
¹⁶ Universität Heidelberg, Interdisziplinäres Zentrum für Wissenschaftliches Rechnen, Heidelberg, Germany
¹⁷ Center for Astrophysics | Harvard & Smithsonian, 60 Garden St, Cambridge, MA 02138, USA
¹⁸ Elizabeth S. and Richard M. Cashin Fellow at the Radcliffe Institute for Advanced Studies at Harvard University, 10 Garden Street, Cambridge, MA 02138, USA
¹⁹ Center for Data and Simulation Science, University of Cologne, Germany
²⁰ ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, Dwingeloo, 7991 PD, The Netherlands
²¹ Dipartimento di Fisica e Astronomia, Università degli Studi di Firenze, Via G. Sansone 1, 50019 Sesto Fiorentino, Firenze, Italy
²² SKA Observatory, Jodrell Bank, Lower Withington, Macclesfield, SK11 9FT, UK
²³ UK ALMA Regional Centre Node M13 9PL, UK
²⁴ Universidad Nacional Autònoma de Mèxico, Instituto de Radioastronomìa y Astrofísica, Apartado Postal 3-72, 58089 Morelia Michoacàn, Mexico
²⁵ Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
²⁶ National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA
²⁷ Université Paris-Saclay, Université Paris-Cité, CEA, CNRS, AIM, 91191 Gif-sur-Yvette, France
²⁸ School of Engineering and Physical Sciences, Isaac Newton Building, University of Lincoln, Brayford Pool, Lincoln LN6 7TS, UK
²⁹ Korea Astronomy and Space Science Institute, 776 Daedeokdae-ro, Yuseong-gu, Daejeon 34055, Republic of Korea
³⁰ University of Science and Technology, Korea (UST), 217 Gajeongro, Yuseong-gu, Daejeon 34113, Republic of Korea
³¹ UK Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
³² Faculty of Physics, University of Duisburg-Essen, Lotharstraße 1, 47057 Duisburg, Germany
³³ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
³⁴ INAF-Istituto di Radioastronomia & Italian ALMA Regional Centre, Via P. Gobetti 101, 40129 Bologna, Italy
³⁵ Department of Astronomy, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan
³⁶ Department of Astrophysics, University of Vienna, Turkenschanzstrasse 17, 1180 Vienna, Austria
³⁷ Dipartimento di Fisica e Astronomia, Alma Mater Studiorum – Università di Bologna, Italy
³⁸ SRON Netherlands Institute for Space Research, Landleven 12, 9747 AD Groningen, The Netherlands
³⁹ Kapteyn Astronomical Institute, University of Groningen, The Netherlands
⁴⁰ Zhejiang Laboratory, Hangzhou 311100, PR China
⁴¹ Universidad Autonoma de Chile, Pedro de Valdivia 425, 9120000 Santiago de Chile, Chile

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Received: 24 December 2025
Accepted: 20 March 2026

Abstract

Context. Several theoretical and observational studies have shown that new waves of triggered star formation can be induced by the feedback from newly formed massive protostars, due to the expansion of H II regions.

Aims. We used the millimeter dust continuum data of the ALMAGAL survey and the Anderson et al. (2014) catalog of H II regions to search for signatures of possible triggered star formation at its onset, and selected one ALMAGAL source for ALMA follow-up observations.

Methods. For this study we selected the source AG286.0716–1.8229, in which six cores were detected at a resolution of ~7600 au, but only two at a higher resolution. The four cores not detected at higher resolution are prestellar core candidates. We used archival data from the SARAO Meerkat Galactic Plane Survey and Rapid Askap Continuum Survey to confirm whether a H II region is present in the field. We observed the source with ALMA in Band 4, covering the emission of DCO⁺(2–1), N₂D⁺(2–1), DCN (2–1), and CH₃CCH (9–8), to infer from the chemical composition and temperature estimates whether these cores are in an early phase of the star-formation process, which allows us to classify them as prestellar cores. The new Band 4 continuum image revealed additional three cores outside of the ALMAGAL field of view (FoV), making a total of nine cores in the region, eight of which are located along an arch that has a radius of ~0.75 pc. We also used the continuum and molecular emission to estimate the mass of these cores, to determine whether they are gravitationally bound or transient objects.

Results. We have derived a spectral index between −0.14 and −0.4, in the frequency range of 0.8–1.6 GHz for the candidateH II region, which is consistent with optically thin free-free emission. The H II region spatially coincides (as projected on the plane of the sky) with the position of one of the cores, which in the new ALMA Band 4 observations does not have a compact morphology. The N₂D⁺and DCO⁺emission peaks at the position of three out of four prestellar core candidates, and the overall emission in both the line and the continuum, which extends outside of the FoV of the ALMAGAL observations, reveals a clear arched shape centered on the H II region. We were able to estimate the gas temperature of only the most evolved core, using the CH₃CCH emission. The resulting value of 39 ± 5 K is also an upper limit for the other cores. Using plausible temperature ranges for each core, based on the information from chemical tracers and the dust continuum, we derived mass ranges for the cores (~2–16 M_⊙) as well as ranges for the virial parameter (~0.3–5). All the cores along the arch have virial parameters consistent with bound objects, with only one exception.

Conclusions. Comparing the typical separation and mass of the cores with those expected in the case of the collect and collapse scenario and with the thermal Jean length and mass, the best agreement is found with the characteristic scales in the case of triggered star formation. The same methodology can be applied to further ALMAGAL sources to identify optimal targets to study a larger sample of prestellar cores in an environment affected by the presence of a H II region.