Properties of the dense core population in Orion B as seen by the Herschel Gould Belt survey^★,★★

¹ Laboratoire d’Astrophysique (AIM), CEA/DRF, CNRS, Université Paris-Saclay, Université Paris Diderot, Sorbonne Paris Cité, 91191 Gif-sur-Yvette, France
e-mail: pandre@cea.fr
² Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE, UK
e-mail: vkonyves@uclan.ac.uk
³ Department of Physics, Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan
⁴ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, PT4150-762 Porto, Portugal
⁵ I. Physik. Institut, University of Cologne, Cologne, Germany
⁶ Laboratoire d’Astrophysique de Bordeaux – UMR 5804, CNRS – Université Bordeaux 1, BP 89, 33270 Floirac, France
⁷ Instituto de Radioastronomía Milimétrica (IRAM), Av. Divina Pastora 7, Núcleo Central, 18012 Granada, Spain
⁸ Istituto di Astrofisica e Planetologia Spaziali-INAF, Via Fosso del Cavaliere 100, 00133 Roma, Italy
⁹ Laboratoire de Physique de l’École Normale Supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université de Paris, Paris, France
¹⁰ Department of Physics and Astronomy, University of Victoria, PO Box 355, STN CSC, Victoria, BC, V8W 3P6, Canada
¹¹ National Research Council Canada, 5071 West Saanich Road, Victoria, BC, V9E 2E7, Canada
¹² Department of Physics and Astronomy, University of Sheffield, Hounsfield Road, Sheffield S3 7RH, UK
¹³ INAF–Istituto di Radioastronomia, and Italian ALMA Regional Centre, Via Gobetti 101, 40129 Bologna, Italy
¹⁴ Department of Physics and Astronomy, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
¹⁵ RAL Space, STFC Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire, OX11 0QX, UK

Received: 30 November 2018
Accepted: 29 September 2019

Abstract

We present a detailed study of the Orion B molecular cloud complex (d ~ 400 pc), which was imaged with the PACS and SPIRE photometric cameras at wavelengths from 70 to 500 μm as part of the Herschel Gould Belt survey (HGBS). We release new high-resolution maps of column density and dust temperature for the whole complex, derived in the same consistent manner as for other HGBS regions. In the filamentary subregions NGC 2023 and 2024, NGC 2068 and 2071, and L1622, a total of 1768 starless dense cores were identified based on Herschel data, 490–804 (~28−45%) of which are self-gravitating prestellar cores that will likely form stars in the future. A total of 76 protostellar dense cores were also found. The typical lifetime of the prestellar cores was estimated to be t_pre^OrionB = 1.7_−0.6^+0.8Myr. The prestellar core mass function (CMF) derived for the whole sample of prestellar cores peaks at ~0.5 M_⊙ (in dN/dlogM format) and is consistent with a power-law with logarithmic slope −1.27 ± 0.24 at the high-mass end, compared to the Salpeter slope of − 1.35. In the Orion B region, we confirm the existence of a transition in prestellar core formation efficiency (CFE) around a fiducial value A_V^bg ~ 7 mag in background visual extinction, which is similar to the trend observed with Herschel in other regions, such as the Aquila cloud. This is not a sharp threshold, however, but a smooth transition between a regime with very low prestellar CFE at A_V^bg < 5 and a regime with higher, roughly constant CFE at A_V^bg ≳ 10. The total mass in the form of prestellar cores represents only a modest fraction (~20%) of the dense molecular cloud gas above A_V^bg ≳ 7 mag. About 60–80% of the prestellar cores are closely associated with filaments, and this fraction increases up to >90% when a more complete sample of filamentary structures is considered. Interestingly, the median separation observed between nearest core neighbors corresponds to the typical inner filament width of ~0.1 pc, which is commonly observed in nearby molecular clouds, including Orion B. Analysis of the CMF observed as a function of background cloud column density shows that the most massive prestellar cores are spatially segregated in the highest column density areas, and suggests that both higher- and lower-mass prestellar cores may form in denser filaments.