ALMA-IMF

I. Investigating the origin of stellar masses: Introduction to the Large Program and first results

¹ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
e-mail: frederique.motte@univ-grenoble-alpes.fr
² Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France
³ AIM, CEA, CNRS, Université Paris-Saclay, Université de Paris, 91191 Gif-sur-Yvette, France
⁴ Universidad de Chile, Camino el Observatorio 1515, Las Condes, Santiago de Chile, Chile
⁵ Departamento de Astronomía, Universidad de Concepción, Casilla 160-C, 4030000 Concepción, Chile
⁶ Max-Planck-Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁷ Institut de RadioAstronomie Millimétrique (IRAM), Grenoble, France
⁸ Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Morelia, Michoacán 58089, Mexico
⁹ Department of Astronomy, University of Florida, PO Box 112055, USA
¹⁰ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
¹¹ National Astronomical Observatory of Japan, National Institutes of Natural Sciences, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
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 Laboratoire de Physique de l’École Normale Supérieure, ENS, Uni-versité PSL, CNRS, Sorbonne Université, Université de Paris, Paris, France
¹⁵ Observatoire de Paris, PSL University, Sorbonne Université, LERMA, 75014 Paris, France
¹⁶ S. N. Bose National Centre for Basic Sciences, Block JD, Sector III, Salt Lake, Kolkata 700106, India
¹⁷ Institut de Ciències de l’Espai (ICE, CSIC), Can Magrans, s/n, 08193 Cerdanyola del Vallès, Catalonia, Spain
¹⁸ Institut d’Estudis Espacials de Catalunya (IEEC), 08340 Barcelona, Catalonia, Spain
¹⁹ Instituto Argentino de Radioastronomía (CCT-La Plata, CONICET; CICPBA), C.C. No. 5, 1894, Villa Elisa, Buenos Aires, Argentina
²⁰ Department of Astronomy, Yunnan University, Kunming 650091, PR China
²¹ Institute of Astronomy, National Tsing Hua University, Hsinchu 30013, Taiwan
²² Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, Colorado 80389, USA
²³ University of Connecticut, Department of Physics, 196A Auditorium Road, Unit 3046, Storrs, CT 06269, USA
²⁴ Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
²⁵ Herzberg Astronomy and Astrophysics Research Centre, National Research Council of Canada, 5071 West Saanich Road, Victoria, Canada
²⁶ College of Science, Ibaraki University, 2-1-1 Bunkyo, Mito, Ibaraki 310-8512, Japan
²⁷ Institute of Astronomy and Astrophysics, Academia Sinica, No. 1, Section 4, Roosevelt Road, Taipei 10617, Taiwan
²⁸ Department of Earth Sciences, National Taiwan Normal University, Taipei 116, Taiwan
²⁹ Max Planck Institute for Radio Astronomy, Auf dem Hügel 69, 53121 Bonn, Germany
³⁰ Department of Astronomy, University of Maryland, College Park, MD 20742, USA
³¹ CSMES, The American University of Paris, 2bis passage Landrieu 75007 Paris, France
³² Departamento de Ingeniería Eléctrica, Universidad de Chile, Santiago, Chile
³³ 4-183 CCIS, University of Alberta, Edmonton, Alberta, Canada
³⁴ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
³⁵ National Radio Astronomy Observatory, PO Box O, Socorro, NM 87801, USA
³⁶ University of Connecticut, Department of Physics, 196A Auditorium Road, Unit 3046, Storrs, CT 06269, USA
³⁷ NVIDIA Research, 2788 San Tomas Expy, Santa Clara, CA 95051, USA
³⁸ School of Physics and Astronomy, Cardiff University, Cardiff, UK

Received: 30 June 2021
Accepted: 7 December 2021

Abstract

Aims. Thanks to the high angular resolution, sensitivity, image fidelity, and frequency coverage of ALMA, we aim to improve our understanding of star formation. One of the breakthroughs expected from ALMA, which is the basis of our Cycle 5 ALMA-IMF Large Program, is the question of the origin of the initial mass function (IMF) of stars. Here we present the ALMA-IMF protocluster selection, first results, and scientific prospects.

Methods. ALMA-IMF imaged a total noncontiguous area of ~53 pc², covering extreme, nearby protoclusters of the Milky Way. We observed 15 massive (2.5 −33 × 10³ M_⊙), nearby (2−5.5 kpc) protoclusters that were selected to span relevant early protocluster evolutionary stages. Our 1.3 and 3 mm observations provide continuum images that are homogeneously sensitive to point-like cores with masses of ~0.2 M_⊙ and ~0.6 M_⊙, respectively, with a matched spatial resolution of ~2000 au across the sample at both wavelengths. Moreover, with the broad spectral coverage provided by ALMA, we detect lines that probe the ionized and molecular gas, as well as complex molecules. Taken together, these data probe the protocluster structure, kinematics, chemistry, and feedback over scales from clouds to filaments to cores.

Results. We classify ALMA-IMF protoclusters as Young (six protoclusters), Intermediate (five protoclusters), or Evolved (four proto-clusters) based on the amount of dense gas in the cloud that has potentially been impacted by H II region(s). The ALMA-IMF catalog contains ~700 cores that span a mass range of ~0.15 M_⊙ to ~250 M_⊙ at a typical size of ~2100 au. We show that this core sample has no significant distance bias and can be used to build core mass functions (CMFs) at similar physical scales. Significant gas motions, which we highlight here in the G353.41 region, are traced down to core scales and can be used to look for inflowing gas streamers and to quantify the impact of the possible associated core mass growth on the shape of the CMF with time. Our first analysis does not reveal any significant evolution of the matter concentration from clouds to cores (i.e., from 1 pc to 0.01 pc scales) or from the youngest to more evolved protoclusters, indicating that cloud dynamical evolution and stellar feedback have for the moment only had a slight effect on the structure of high-density gas in our sample. Furthermore, the first-look analysis of the line richness toward bright cores indicates that the survey encompasses several tens of hot cores, of which we highlight the most massive in the G351.77 cloud. Their homogeneous characterization can be used to constrain the emerging molecular complexity in protostars of high to intermediate masses.

Conclusions. The ALMA-IMF Large Program is uniquely designed to transform our understanding of the IMF origin, taking the effects of cloud characteristics and evolution into account. It will provide the community with an unprecedented database with a high legacy value for protocluster clouds, filaments, cores, hot cores, outflows, inflows, and stellar clusters studies.