ALMA-IMF

XIII. N₂H⁺ kinematic analysis of the intermediate protocluster G353.41

¹ Departamento de Astronomía, Universidad de Concepción, Casilla 160-C, Concepción, Chile
e-mail: rodralvarezz@gmail.com
² Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
³ Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Morelia, Michoacán 58089, Mexico
⁴ SKA Observatory, Jodrell Bank, Lower Withington, Macclesfield SK11 9FT, UK
⁵ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁶ Astronomical Science Program, The Graduate University for Advanced Studies, SOKENDAI, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁷ Departments of Astronomy, University of Virginia, Charlottesville, VA 22904, USA
⁸ Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France
⁹ Laboratoire de Physique de l’École Normale Supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université Paris Cité, 75005 Paris, France
¹⁰ Observatoire de Paris, PSL University, Sorbonne Université, LERMA, 75014, Paris, France
¹¹ Department of Astronomy, University of Florida, P.O. Box 112055, Gainesville, FL 32611, USA
¹² Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
¹³ S. N. Bose National Centre for Basic Sciences, Sector-III, Salt Lake, Kolkata 700106, India
¹⁴ Astronomy Department, Universidad de Chile, Camino El Observatorio 1515, Las Condes, Santiago, Chile
¹⁵ Departament de Física Quàntica i Astrofísica (FQA), Universitat de Barcelona (UB), Martí i Franquès 1, 08028 Barcelona, Catalonia, Spain
¹⁶ Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona, Martí i Franquès, 1, 08028, Barcelona, Catalonia, Spain
¹⁷ Institut d’Estudis Espacials de Catalunya (IEEC), Gran Capità, 2–4, 08034 Barcelona, Catalonia, Spain
¹⁸ Instituto Argentino de Radioastronomía (CCT-La Plata, CONICET; CICPBA), C.C. No. 5, 1894, Villa Elisa, Buenos Aires, Argentina
¹⁹ Joint Alma Observatory (JAO), Alonso de Córdova 3107, Vitacura, Santiago, Chile
²⁰ School of Physics and Astronomy, Yunnan University, Kunming, 650091, PR China
²¹ Institute of Astronomy and Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan
²² Max-Planck-Institut für Radioastronomie, Auf dem Hü gel 69, 53121 Bonn, Germany

Received: 10 April 2024
Accepted: 12 June 2024

Abstract

The ALMA-IMF Large Program provides multi-tracer observations of 15 Galactic massive protoclusters at a matched sensitivity and spatial resolution. We focus on the dense gas kinematics of the G353.41 protocluster traced by N₂H⁺ (1−0), with a spatial resolution of ~0.02 pc. G353.41, at a distance of ~2kpc, is embedded in a larger-scale (~8 pc) filament and has a mass of ~2.5 × 10³ M_⊙ within 1.3 × 1.3 pc². We extracted the N₂H⁺ (1−0) isolated line component and decomposed it by fitting up to three Gaussian velocity components. This allows us to identify velocity structures that are either muddled or impossible to identify in the traditional position-velocity diagram. We identify multiple velocity gradients on large (~1 pc) and small scales (~0.2pc). We find good agreement between the N₂H⁺ velocities and the previously reported DCN core velocities, suggesting that cores are kinematically coupled with the dense gas in which they form. We have measured nine converging “V-shaped” velocity gradients (VGs) (~20 km s⁻¹ pc⁻¹) that are well resolved (sizes ~0.1 pc), mostly located in filaments, which are sometimes associated with cores near their point of convergence. We interpret these V-shapes as inflowing gas feeding the regions near cores (the immediate sites of star formation). We estimated the timescales associated with V-shapes as VG⁻¹, and we interpret them as inflow timescales. The average inflow timescale is ~67 kyr, or about twice the free-fall time of cores in the same area (~33 kyr) but substantially shorter than protostar lifetime estimates (~0.5 Myr). We derived mass accretion rates in the range of (0.35–8.77) × 10⁻⁴ M_⊙ yr⁻¹. This feeding might lead to further filament collapse and the formation of new cores. We suggest that the protocluster is collapsing on large scales, but the velocity signature of collapse is slow compared to pure free-fall. Thus, these data are consistent with a comparatively slow global protocluster contraction under gravity, and faster core formation within, suggesting the formation of multiple generations of stars over the protocluster’s lifetime.