Physical and chemical structure of high-mass star-forming regions

Unraveling chemical complexity with CORE: the NOEMA large program^★

¹ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: gieser@mpia.de
² Department of Chemistry, Ludwig Maximilian University, Butenandtstr. 5-13, 81377 Munich, Germany
³ Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
⁴ I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
⁵ INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁶ UK Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
⁷ Center for Astrophysics, Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
⁸ Centre for Astrophysics and Planetary Science, University of Kent, Canterbury, CT2 7NH, UK
⁹ Academia Sinica Institute of Astronomy and Astrophysics, No.1, Sec. 4, Roosevelt Rd, Taipei 10617, Taiwan, PR China
¹⁰ CAS Key Laboratory of FAST, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, PR China
¹¹ National Astronomical Observatory of Japan, National Institutes of Natural Sciences, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
¹² Instituto de Radioastronomía y Astrofísica (IRyA), UNAM, Apdo. Postal 72-3 (Xangari), Morelia, Michoacán 58089, Mexico
¹³ Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, 38406 Saint Martin d’Hères, France
¹⁴ Astrophysics Research Institute, Liverpool John Moores University, Liverpool, L3 5RF, UK
¹⁵ INAF, Osservatorio Astronomico di Cagliari, Via della Scienza 5, 09047 Selargius (CA), Italy
¹⁶ Institute of Astronomy and Astrophysics, University of Tübingen, Auf der Morgenstelle 10, 72076, Tübingen, Germany
¹⁷ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85748 Garching, Germany
¹⁸ Max Planck Institut for Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
¹⁹ Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France
²⁰ Physics Department, UMIST, PO Box 88, Manchester M60 1QD, UK
²¹ School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
²² European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
²³ LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, 75014 Paris, France
²⁴ Department of Physics and Astronomy, McMaster University, 1280 Main St. W, Hamilton, ON L8S 4M1, Canada

Received: 13 October 2020
Accepted: 22 February 2021

Abstract

Aims. Current star formation research centers the characterization of the physical and chemical properties of massive stars, which are in the process of formation, at the spatial resolution of individual high-mass cores.

Methods. We use sub-arcsecond resolution (~0.′′4) observations with the NOrthern Extended Millimeter Array at 1.37 mm to study the dust emission and molecular gas of 18 high-mass star-forming regions. With distances in the range of 0.7−5.5 kpc, this corresponds to spatial scales down to 300−2300 au that are resolved by our observations. We combined the derived physical and chemical properties of individual cores in these regions to estimate their ages. The temperature structures of these regions are determined by fitting the H₂CO and CH₃CN line emission. The density profiles are inferred from the 1.37 mm continuum visibilities. The column densities of 11 different species are determined by fitting the emission lines with XCLASS.

Results. Within the 18 observed regions, we identified 22 individual cores with associated 1.37 mm continuum emission and with a radially decreasing temperature profile. We find an average temperature power-law index of q = 0.4 ± 0.1 and an average density power-law index of p = 2.0 ± 0.2 on scales that are on the order of several 1000 au. Comparing these results with values of p derived from the literature presumes that the density profiles remain unchanged from clump to core scales. The column densities relative to N(C¹⁸O) between pairs of dense gas tracers show tight correlations. We applied the physical-chemical model MUlti Stage ChemicaL codE to the derived column densities of each core and find a mean chemical age of ~60 000 yr and an age spread of 20 000−100 000 yr. With this paper, we release all data products of the CORE project.

Conclusions. The CORE sample reveals well-constrained density and temperature power-law distributions. Furthermore, we characterized a large variety in molecular richness that can be explained by an age spread that is then confirmed by our physical-chemical modeling. The hot molecular cores show the greatest number of emission lines, but we also find evolved cores at an evolutionary stage in which most molecules are destroyed and, thus, the spectra appear line-poor once again.