The Herschel view of the dense core population in the Ophiuchus molecular cloud^★

¹ Laboratoire d’Astrophysique (AIM), CEA/DRF, CNRS, Université Paris-Saclay, Université Paris Diderot, Sorbonne Paris Cité, 91191 Gif-sur-Yvette, France
² Instituto de Radioastronomía Milimétrica, IRAM Avenida Divina Pastora 7, Local 20, 18012 Granada, Spain
e-mail: ladjelate@iram.es
³ Jeremiah Horrocks Institute, University of Central Lancashire, Preston, Lancashire, PR1 2HE, UK
⁴ Laboratoire de Physique de l’Ecole Normale Supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université de Paris, Paris, France
⁵ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, PT4150-762 Porto, Portugal
⁶ Department of Physics and Astronomy, Graduate School of Science and Engineering, Kagoshima University, 1-21-35 Korimoto, Kagoshima, Kagoshima 890-0065, Japan
⁷ National Astronomical Observatory of Japan, Osawa 2-21-1, Mitaka, Tokyo 181-8588, Japan
⁸ INAF – Istituto di Astrofisica e Planetologia Spaziali, Via Fosso del Cavaliere 100, 00133 Roma, Italy
⁹ National Research Council of Canada, Herzberg Astronomy & Astrophysics Research Centre, 5071 West Saanich Road Victoria, BC V9E 2E7, Canada
¹⁰ I. Physik. Institut, University of Cologne, 50937 Cologne, Germany
¹¹ Laboratoire d’Astrophysique de Bordeaux, CNRS/INSU, Université de Bordeaux, UMR 5804, France
¹² Dipartimento di Fisica, Università di Roma “Tor Vergata” Via della Ricerca Scientifica 1, 00133 Roma, Italy
¹³ INAF – Osservatorio Astronomico di Roma, Via di Frascati 33, 00078 Monte Porzio Catone, Italy
¹⁴ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
¹⁵ Université Grenoble Alpes, CNRS, Institut de Planétologie et d’Astrophysique de Grenoble, 38000 Grenoble, France

Received: 2 August 2019
Accepted: 20 January 2020

Abstract

Context. Herschel observations of nearby clouds in the Gould Belt support a paradigm for low-mass star formation, starting with the generation of molecular filaments, followed by filament fragmentation, and the concentration of mass into self-gravitating prestellar cores. In the case of the Ophiuchus molecular complex, a rich star formation activity has been documented for many years inside the clumps of L1688, the main and densest cloud of the complex, and in the more quiescent twin cloud L1689 thanks to extensive surveys at infrared and other wavelengths.

Aims. With the unique far-infrared and submillimeter continuum imaging capabilities of the Herschel Space observatory, the closeby (d = 139 pc) Ophiuchus cloud was extensively mapped at five wavelengths from 70 to 500 μm with the aim of providing a complete census of dense cores in this region, including unbound starless cores, bound prestellar cores, and protostellar cores.

Methods. Taking full advantage of the high dynamic range and multi-wavelength nature of the Herschel data, we used the multi-scale decomposition algorithms getsources and getfilaments to identify an essentially complete sample of dense cores and filaments in the cloud and study their properties.

Results. The densest clouds of the Ophiuchus complex, L1688 and L1689, which thus far are only indirectly described as filamentary regions owing to the spatial distribution of their young stellar objects, are now confirmed to be dominated by filamentary structures. The tight correlation observed between prestellar cores and filamentary structures in L1688 and L1689 supports the view that solar-type star formation occurs primarily in dense filaments. While the sub clouds of the complex show some disparities, L1689 being apparently less efficient than L1688 at forming stars when considering their total mass budgets, both sub clouds share almost the same prestellar core formation efficiency in dense molecular gas. We also find evidence in the Herschel data for a remarkable concentric geometrical configuration in L1688 which is dominated by up to three arc-like compression fronts and has presumably been created by shockwave events emanating from the Sco OB2 association, including the neighboring massive (O9V) star σ Sco.

Conclusions. Our Herschel study of the well-documented Ophiuchus region has allowed us to further analyze the influence of several early-type (OB) stars surrounding the complex, thus providing positive feedback and enhancing star formation activity in the dense central part of the region, L1688.