Ade, P.A.R. and Aghanim, N. and Arnaud, M. and Ashdown, M. and Aumont, J. and Baccigalupi, C. and Balbi, A. and Banday, A.J. and Barreiro, R.B. and Bartlett, J.G. and Battaner, E. and Benabed, K. and Benoit, A. and Bernard, J.-P. and Bersanelli, M. and Bhatia, R. and Bock, J.J. and Bonaldi, A. and Bond, J.R. and Borrill, J. and Bot, C. and Bouchet, F.R. and Boulanger, F. and Bucher, M. and Burigana, C. and Cabella, P. and Cardoso, J.-F. and Catalano, A. and Cayon, L. and Challinor, A. and Chamballu, A. and Chiang, L.-Y. and Chiang, C. and Christensen, P.R. and Clements, D.L. and Colombi, S. and Couchot, F. and Coulais, A. and Crill, B.P. and Cuttaia, F. and Danese, L. and Davies, R.D. and Davis, R.J. and De Bernardis, P. and de Gasperis, G. and de Rosa, A. and de Zotti, G. and Delabrouille, J. and Delouis, J.-M. and Desert, F.-X. and Dickinson, C. and Dobashi, K. and Donzelli, S. and Dore, O. and Dorl, U. and Douspis, M. and Dupac, X. and Efstathiou, G. and Enßlin, T.A. and Finelli, F. and Forni, O. and Frailis, M. and Franceschi, E. and Fukui, Y. and Galeotta, S. and Ganga, K. and Giard, M. and Giardino, G. and Giraud-Héraud, Y. and Gonzalez-Nuevo, J. and Gorski, K.M. and Gratton, S. and Gregorio, A. and Grupposo, A. and Harrison, D. and Helou, G. and Henrot-Versille, S. and Herranz, D. and Hildebrandt, S.R. and Hivon, E. and Hobson, M. and Holmes, W.A. and Hovest, W. and Hoyland, R.J. and Huffenberger, K.M. and Jaffe, A.H. and Jones, W.C. and Juvela, M. and Kawamura, A. and Keihanen, E. and Keskitalo, R. and Kisner, T.S. and Kneissl, R. and Knox, L. and Kurki-Suonio, H. and Lagache, G. and Lahteenmaki, A. and Lamarre, J.-M. and Lasenby, A. and Laureijs, R.J. and Lawrence, C.R. and Leach, S. and Leonardi, R. and Leroy, C. and Linden-Vornle, M. and Lopez-Caniego, M. and Lubin, P.M. and Macias-Perez, J.F. and MacTavish, C.J. and Madden, S. and Maffei, B. and Mandolesi, N. and Mann, R. and Maris, M. and Martinez-Gonzalez, E. and Masi, S. and Matarrese, S. and Matthai, F. and Mazzotta, P. and Meinhold, P.R. and Melchiorri, A. and Mendes, L. and Mennella, A. and Miville-Deschenes, M.-A. and Moneti, A. and Montier, L. and Morgante, G. and Mortlock, D. and Munshi, D. and Murphy, J.Anthony and Naselsky, P. and Nati, F. and Natoli, P. and Netterfield, C.B. and Norgaard-Nielsen, H.U. and Noviello, F. and Novikov, D. and Noviello, F. and Onishi, T. and Osborne, S. and Pajot, F. and Paladini, R. and Paradis, D. and Pasian, F. and Patanchon, G. and Perdereau, O. and Perotto, L. and Perrotta, F. and Piacentini, F. and Piat, M. and Plaszczynski, S. and Pointecouteau, E. and Polenta, G. and Ponthieu, N. and Poutanen, T. and Prezeau, G. and Prunet, S. and Puget, J.-L. and Reach, W.T. and Rebolo, R. and Reinecke, M. and Renault, C. and Ricciardi, S. and Riller, T. and Ristorcelli, I. and Rocha, G. and Rosset, C. and Rowan-Robinson, M. and Rubino-Martin, J.A. and Rusholme, B. and Sandri, M. and Savini, G. and Scott, D. and Seiffert, M.D. and Smoot, G.F. and Starck, J.-L. and Stivoli, F. and Stolyarov, V. and Sudiwala, R. and Sygnet, J.-F. and Tauber, J.A. and Terenzi, L. and Toffolatti, L. and Tomasi, M. and Torre, J.-P. and Tristram, M. and Tuovinen, J. and Umana, G. and Valenziano, L. and Varis, J. and Vielva, P. and Villa, F. and Vittorio, N. and Wade, L.A. and Wandelt, B.D. and Wilkinson, A. and Ysard, N. and Yvon, D. and Zacchei, A. and Zonca, A. (2011) Planck early results. XVII. Origin of the submillimetre excess dust emission in the Magellanic Clouds. Astronomy & Astrophysics, 536 (A17). pp. 1-17. ISSN 0004-6361

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Abstract

The integrated spectral energy distributions (SED) of the Large Magellanic Cloud (LMC) and SmallMagellanic Cloud (SMC) appear significantly flatter than expected from dust models based on their far-infrared and radio emission. The still unexplained origin of this millimetre excess is investigated here using the Planck data. The integrated SED of the two galaxies before subtraction of the foreground (Milky Way) and background (CMB fluctuations) emission are in good agreement with previous determinations, confirming the presence of the millimetre excess. In the context of this preliminary analysis we do not propose a full multi-component fitting of the data, but instead subtract contributions unrelated to the galaxies and to dust emission. The background CMB contribution is subtracted using an internal linear combination (ILC) method performed locally around the galaxies. The foreground emission from the Milky Way is subtracted as a Galactic Hi template, and the dust emissivity is derived in a region surrounding the two galaxies and dominated by Milky Way emission. After subtraction, the remaining emission of both galaxies correlates closely with the atomic and molecular gas emission of the LMC and SMC. The millimetre excess in the LMC can be explained by CMB fluctuations, but a significant excess is still present in the SMC SED. The Planck and IRAS–IRIS data at 100 μm are combined to produce thermal dust temperature and optical depth maps of the two galaxies. The LMC temperature map shows the presence of a warm inner arm already found with the Spitzer data, but which also shows the existence of a previously unidentified cold outer arm. Several cold regions are found along this arm, some of which are associated with known molecular clouds. The dust optical depth maps are used to constrain the thermal dust emissivity power-law index (β). The average spectral index is found to be consistent with β =1.5 and β =1.2 below 500 μm for the LMC and SMC respectively, significantly flatter than the values observed in the Milky Way. Also, there is evidence in the SMC of a further flattening of the SED in the sub-mm, unlike for the LMC where the SED remains consistent with β =1.5. The spatial distribution of the millimetre dust excess in the SMC follows the gas and thermal dust distribution. Different models are explored in order to fit the dust emission in the SMC. It is concluded that the millimetre excess is unlikely to be caused by very cold dust emission and that it could be due to a combination of spinning dust emission and thermal dust emission by more amorphous dust grains than those present in our Galaxy.

Item Type:	Article
Additional Information:	© ESO 2011 The original publication is available at DOI: 10.1051/0004-6361/201116473
Keywords:	Magellanic Clouds; dust; extinction; ISM; structure; galaxies; infrared; submillimeter; Planck Collaboration;
Academic Unit:	Faculty of Science and Engineering > Experimental Physics
Item ID:	4041
Depositing User:	Dr. Anthony Murphy
Date Deposited:	18 Dec 2012 15:41
Journal or Publication Title:	Astronomy & Astrophysics
Publisher:	EDP Sciences
Refereed:	Yes
URI:	http://www.aanda.org/ http://publications.edpsciences.org/
Use Licence:	This item is available under a Creative Commons Attribution Non Commercial Share Alike Licence (CC BY-NC-SA). Details of this licence are available here

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