Ade, P.A.R. and Aghanim, N. and Aniano, G. and Arnaud, M. and Ashdown, M. and Aumont, J. and Baccigalupi, C. and Banday, A.J. and Barreiro, R.B. and Bartolo, N. and Battaner, E. and Benabed, K. and Benoit-Lévy, A. and Bernard, J.-P. and Bersanelli, M. and Bielewicz, P. and Bonaldi, A. and Bonavera, L. and Bond, J.R. and Borrill, J. and Bouchet, F.R. and Boulanger, F. and Burigana, C. and Butler, R.C. and Calabrese, E. and Cardoso, J.-F. and Casandjian, J.M. and Catalano, A. and Chamballu, A. and Chiang, H.C. and Christensen, P.R. and Colombo, L.P.L. and Combet, C. and Couchot, F. and Crill, B.P. and Curto, A. and Cuttaia, F. and Danese, L. and Davies, R.D. and Davis, R.J. and De Bernardis, P. and de Rosa, A. and de Zotti, G. and Delabrouille, J. and Desert, F.-X. and Dickinson, C. and Diego, J.M. and Digel, S.W. and Dole, H. and Donzelli, S. and Dore, O. and Douspis, M. and Ducout, A. and Dupac, X. and Efstathiou, G. and Elsner, F. and Enßlin, T.A. and Eriksen, H.K. and Falgarone, E. and Finelli, F. and Forni, O. and Frailis, M. and Fraisse, A.A. and Franceschi, E. and Frejsel, A. and Fukui, Y. and Galeotta, S. and Galli, S. and Ganga, K. and Ghosh, T. and Giard, M. and Gjerløw, E. and Gonzalez-Nuevo, J. and Gorski, K.M. and Gregorio, A. and Grenier, I.A. and Gruppuso, A. and Hansen, F.K. and Hanson, D. and Harrison, D. and Henrot-Versille, S. and Hernandez-Monteagudo, C. and Herranz, D. and Hildebrandt, S.R. and Hivon, E. and Hobson, M. and Holmes, W.A. and Hovest, W. and Huffenberger, K.M. and Hurier, G. and Jaffe, A.H. and Jaffe, T.R. and Jones, W.C. and Juvela, M. and Keihanen, E. and Keskitalo, R. and Kisner, T.S. and Kneissl, R. and Knoche, J. and Kunz, M. and Kurki-Suonio, H. and Lagache, G. and Lamarre, J.-M. and Lasenby, A. and Lattanzi, M. and Lawrence, C.R. and Leonardi, R. and Levrier, F. and Liguori, M. and Lilje, P.B. and Linden-Vornle, M. and Lopez-Caniego, M. and Lubin, P.M. and Macias-Perez, J.F. and Maffei, B. and Maino, D. and Mandolesi, N. and Maris, M. and Marshall, D.J. and Martin, P.G. and Martinez-Gonzalez, E. and Masi, S. and Matarrese, S. and Mazzotta, P. and Melchiorri, A. and Mendes, L. and Mennella, A. and Migliaccio, M. 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 Natoli, P. and Norgaard-Nielsen, H.U. and Novikov, D. and Novikov, I. and Oxborrow, C.A. and Pagano, L. and Pajot, F. and Paladini, R. and Paoletti, D. and Pasian, F. and Perdereau, O. and Perotto, L. and Perrotta, F. and Pettorino, V. and Piacentini, F. and Piat, M. and Plaszczynski, S. and Pointecouteau, E. and Polenta, G. and Popa, L. and Pratt, G.W. and Prunet, S. and Puget, J.-L. and Rachen, J.P. and Reach, W.T. and Rebolo, R. and Reinecke, M. and Remazeilles, M. and Renault, C. and Ristorcelli, I. and Rocha, G. and Roudier, G. and Rusholme, B. and Sandri, M. and Santos, D. and Scott, D. and Spencer, L. and Stolyarov, V. and Strong, A.W. and Sudiwala, R. and Sunyaev, R. and Sutton, D. and Suur-Uski, A.-S. and Sygnet, J.-F. and Tauber, J.A. and Terenzi, L. and Tibaldo, L. and Toffolatti, L. and Tomasi, M. and Tristram, M. and Tucci, M. and Umana, G. and Valenziano, L. and Valiviita, J. and Van Tent, B. and Vielva, P. and Villa, F. and Wade, L.A. and Wandelt, B.D. and Wehus, I. and Yvon, D. and Zacchei, A. and Zonca, A. (2015) Planck intermediate results XXVIII. Interstellar gas and dust in the Chamaeleon clouds as seen by Fermi LAT and Planck. Astronomy & Astrophysics, 582 (A31). ISSN 0004-6361

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Abstract

The nearby Chamaeleon clouds have been observed in γ rays by the Fermi Large Area Telescope (LAT) and in thermal dust emission by Planck and IRAS. Cosmic rays and large dust grains, if smoothly mixed with gas, can jointly serve with the H I and 12CO radio data to (i) map the hydrogen column densities, NH, in the different gas phases, in particular at the dark neutral medium (DNM) transition between the H I-bright and CO-bright media; (ii) constrain the CO-to-H2 conversion factor, XCO; and (iii) probe the dust properties per gas nucleon in each phase and map their spatial variations across the clouds. We have separated clouds at local, intermediate, and Galactic velocities in H I and 12CO line emission to model in parallel the γ-ray intensity recorded between 0.4 and 100 GeV; the dust optical depth at 353 GHz, τ353; the thermal radiance of the large grains; and an estimate of the dust extinction, AVQ, empirically corrected for the starlight intensity. The dust and γ-ray models have been coupled to account for the DNM gas. The consistent γ-ray emissivity spectra recorded in the different phases confirm that the GeV–TeV cosmic rays probed by the LAT uniformly permeate all gas phases up to the 12CO cores. The dust and cosmic rays both reveal large amounts of DNM gas, with comparable spatial distributions and twice as much mass as in the CO-bright clouds. We give constraints on the H I-DNM-CO transitions for five separate clouds. CO-dark H2 dominates the molecular columns up to AV ≃ 0.9 and its mass often exceeds the one-third of the molecular mass expected by theory. The corrected AVQ extinction largely provides the best fit to the total gas traced by the γ rays. Nevertheless, we find evidence for a marked rise in AVQ/NH with increasing NH and molecular fraction, and with decreasing dust temperature. The rise in τ353/NH is even steeper. We observe variations of lesser amplitude and orderliness for the specific power of the grains, except for a coherent decline by half in the CO cores. This combined information suggests grain evolution. We provide average values for the dust properties per gas nucleon in the different phases. The γ rays and dust radiance yield consistent XCO estimates near 0.7 × 1020 cm-2 K-1 km-1 s. The AVQ and τ353 tracers yield biased values because of the large rise in grain opacity in the CO clouds. These results clarify a recurrent disparity in the γ-ray versus dust calibration of XCO, but they confirm the factor of 2 difference found between the XCO estimates in nearby clouds and in the neighbouring spiral arms.

Item Type:	Article
Keywords:	Planck Collaboration; Fermi Collaboration; ISM: structure; gamma rays: ISM; cosmic rays; dust, extinction; local insterstellar matter;
Academic Unit:	Faculty of Science and Engineering > Experimental Physics
Item ID:	14121
Identification Number:	https://doi.org/10.1051/0004-6361/201424955
Depositing User:	Dr. Anthony Murphy
Date Deposited:	02 Mar 2021 16:34
Journal or Publication Title:	Astronomy & Astrophysics
Publisher:	EDP Sciences
Refereed:	Yes
URI:	Publisher
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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