ALMA-IMF

XVII. Census and lifetime of high-mass prestellar cores in 14 massive protoclusters

¹ Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France
² Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Morelia, Michoacán 58089, Mexico
³ INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁴ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
⁵ Departamento de Astronomía, Universidad de Concepción, Casilla 160-C, 4030000 Concepción, Chile
⁶ Laboratoire de Physique de l’École Normale Supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université de Paris, Paris, France
⁷ Observatoire de Paris, PSL University, Sorbonne Université, LERMA, 75014, Paris, France
⁸ Department of Astronomy, University of Florida, PO Box 112055, Gainesville, FL, USA
⁹ Departments of Astronomy and Chemistry, University of Virginia, Charlottesville, VA 22904, USA
¹⁰ SKA Observatory, Jodrell Bank, Lower Withington, Macclesfield SK11 9FT, UK
¹¹ Instituto Argentino de Radioastronomía (CCT-La Plata, CONICET; CICPBA), C.C. No. 5, 1894, Villa Elisa, Buenos Aires, Argentina
¹² Department of Astronomical Science, SOKENDAI (The Graduate University for Advanced Studies), 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
¹³ The Graduate University for Advanced Studies (SOKENDAI), 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan
¹⁴ Joint Alma Observatory (JAO), Alonso de Córdova 3107, Vitacura, Santiago, Chile
¹⁵ Max Planck Institute for Radio Astronomy, Auf dem Hügel 69, 53121 Bonn, Germany
¹⁶ Department of Astronomy, Universidad de Chile, Camino El Observatorio 1515, Santiago, Chile
¹⁷ Franco-Chilean Laboratory for Astronomy, IRL 3386, CNRS and Universidad de Chile, Santiago, Chile

^★ Corresponding author; maxime.valeille-manet@u-bordeaux.fr

Received: 28 June 2024
Accepted: 27 January 2025

Abstract

Context. High-mass prestellar cores are extremely rare. Until recently, the search for such objects has been hampered by small sample sizes, leading to large ambiguities in their lifetimes and hence the conditions in the cores in which high-mass stars (≳8 M_⊙) form.

Aims. Here we leverage the large sample (~580 cores) detected in the ALMA-IMF survey to identify both protostellar and prestellar cores to estimate their relative lifetimes.

Methods. We used CO and SiO outflows to identify protostellar cores. We present a new automated method based on aperture line emission and background subtraction to systematically detect outflows associated with each of the 141 most massive cores. Massive cores that are not driving an outflow in either tracer are identified as prestellar. After careful scrutiny of the sample, we derived statistical lifetime estimates for the prestellar phase.

Results. Our automated method allows the efficient detection of CO and SiO outflows and has a performance efficiency similar to that of more cumbersome classical techniques. We identified 30 likely prestellar cores with M≳ 8 M_⊙, of which 12 have core masses M≳ 16 M_⊙. The latter group contains the best candidates for high-mass star precursors. Moreover, most of these 12 high-mass prestellar cores are located inside the crowded central regions of the protoclusters, where most high-mass stars are expected to form. Using the relative ratios of prestellar to protostellar cores, and assuming a high-mass protostellar lifetime of 300 kyr, we derive a prestellar core lifetime of 120 kyr to 240 kyr for cores with masses 8 M_⊙ < M < 16 M_⊙. For 30 M_⊙ < M < 55 M_⊙, the lifetimes range from 50 kyr to 100 kyr. The spread in timescales reflects different assumptions for scenarios for the mass reservoir evolution. These timescales are remarkably long compared to the 4 kyr to 15 kyr free-fall time of the cores. Hence, we suggest that high-mass cores live ~10 to 30 free-fall times, with a tentative trend of a slight decrease with core mass. Such high ratios suggest that the collapse of massive cores is slowed down by non-thermal support of turbulent, magnetic or rotational origin at or below the observed scale.