Herschel and SCUBA-2 observations of dust emission in a sample of Planck cold clumps^★,★★

¹ Department of Physics, University of Helsinki, PO Box 64, 00014, Finland
e-mail: mika.juvela@helsinki.fi
² Yunnan Observatories, Chinese Academy of Sciences, 396 Yangfangwang, Guandu District, Kunming 650216, PR China
³ Chinese Academy of Sciences South America Center for Astronomy, China-Chile Joint Center for Astronomy, Camino El Observatorio 1515, Las Condes, Santiago, Chile
⁴ Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, 396 Yangfangwang, Guandu District, Kunming 650216, PR China
⁵ Center for Astronomical Mega-Science, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100012, PR China
⁶ Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE, UK
⁷ Korea Astronomy and Space Science Institute, 776 Daedeokdaero, Yuseong-gu, Daejeon 34055, Republic of Korea
⁸ East Asian Observatory, 660 N. A’ohōkū Place, Hilo, Hawaii 96720-2700, USA
⁹ UK ALMA Regional Centre Node, Jodrell Bank Centre for Astrophysics, The University of Manchester, Oxford Road, Manchester M13 9PL, UK
¹⁰ Astrophysics Research Institute, Liverpool John Moores University, Ic2, Liverpool Science Park, 146 Brownlow Hill, L3 5RF, Liverpool, UK
¹¹ Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, 1121 Budapest, Konkoly Thege Miklós út 15-17, Hungary
¹² Eövös Loránd University, Department of Astronomy, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary
¹³ Department of Physics and Astronomy, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
¹⁴ Institute of Astronomy and Astrophysics, Academia Sinica, 11F of Astronomy-Mathematics Building, AS/NTU No.1, Sec. 4, Roosevelt Rd, Taipei 10617, Taiwan
¹⁵ National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, PR China
¹⁶ Key Laboratory of Radio Astronomy, Chinese Academy of Science Nanjing, 210008, PR China
¹⁷ Institute of Physics I, University of Cologne, Germany
¹⁸ Laboratoire AIM, IRFU/Service d’Astrophysique - CEA/DSM - CNRS - Université Paris Diderot, Bât. 709, CEA-Saclay, 91191, Gif-sur-Yvette Cedex, France
¹⁹ Université de Toulouse, UPS-OMP, IRAP, 31028 Toulouse cedex 4, France
²⁰ CNRS, IRAP, 9 av. colonel Roche, BP 44346, 31028 Toulouse cedex 4, France
²¹ Graduate Institute of Astronomy, National Central University 300, Jhongli, Taoyuan 32001, Taiwan
²² Nobeyama Radio Observatory, National Astronomical Observatory of Japan, National Institutes of Natural Sciences, 462-2 Nobeyama, Minamimaki, Minamisaku, Nagano 384-1305, Japan
²³ Centre for Astrophysics Research, School of Physics Astronomy & Mathematics, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK
²⁴ IAPS - INAF, via Fosso del Cavaliere, 100, 00133 Roma, Italy
²⁵ European Southern Observatory, Karl-Schwarzschild-Str.2, 85748 Garching bei München, Germany
²⁶ Department of Astronomy, Peking University, 100871 Beijing, PR China
²⁷ School of Space Research, Kyung Hee University, 1732, Deogyeong-daero, Giheung-gu, Yongin-si, Gyeonggi-do, Republic of Korea
²⁸ Department of Astronomy and Space Science, Chungnam National University, 99 Daehak-ro, Yuseong-gu, Daejeon 34134, Korea

Received: 9 September 2017
Accepted: 2 December 2017

Abstract

Context. Analysis of all-sky Planck submillimetre observations and the IRAS 100 μm data has led to the detection of a population of Galactic cold clumps. The clumps can be used to study star formation and dust properties in a wide range of Galactic environments.

Aims. Our aim is to measure dust spectral energy distribution (SED) variations as a function of the spatial scale and the wavelength.

Methods. We examined the SEDs at large scales using IRAS, Planck, and Herschel data. At smaller scales, we compared JCMT/SCUBA-2 850 μm maps with Herschel data that were filtered using the SCUBA-2 pipeline. Clumps were extracted using the Fellwalker method, and their spectra were modelled as modified blackbody functions.

Results. According to IRAS and Planck data, most fields have dust colour temperatures T_C ~ 14–18 K and opacity spectral index values of β = 1.5–1.9. The clumps and cores identified in SCUBA-2 maps have T ~ 13 K and similar β values. There are some indications of the dust emission spectrum becoming flatter at wavelengths longer than 500 μm. In fits involving Planck data, the significance is limited by the uncertainty of the corrections for CO line contamination. The fits to the SPIRE data give a median β value that is slightly above 1.8. In the joint SPIRE and SCUBA-2 850 μm fits, the value decreases to β ~ 1.6. Most of the observed T-β anticorrelation can be explained by noise.

Conclusions. The typical submillimetre opacity spectral index β of cold clumps is found to be ~1.7. This is above the values of diffuse clouds, but lower than in some previous studies of dense clumps. There is only tentative evidence of a T-β anticorrelation and β decreasing at millimetre wavelengths.