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\title{Fermi-LAT study of the ISM in Chamaeleon region using the Planck thermal dust optical depth
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\author{\speaker{Katsuhiro Hayashi}\\
        Nagoya University
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        E-mail: \email{khayashi@a.phys.nagoya-u.ac.jp
}}

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\abstract{
  Diffuse gamma-ray emission from local molecular clouds is a powerful probe of the local interstellar gas and cosmic rays. Most of previous LAT studies of the molecular cloud regions assumed that the gamma-ray emitting interstellar gas is decomposed into three components: atomic hydrogen, molecular hydrogen and some excess gas not traced by standard HI and CO surveys. In each phase, uniform gas and dust properties are assumed. In this study, we examine the Chamaeleon molecular cloud region with a different approach, using total gas column density (NH) models based on the dust optical depth at 353 GHz (τ353) obtained from the Planck dust emission model. The relation between NH and dust optical depth in local molecular clouds exhibits a deviation from a simple linear relation (e.g., Roy et al. 2013 and Planck Collaboration XXVIII, 2015), possibly due to evolution of dust grains in cores of clouds. In fitting gamma-ray data with several NH models, including both linear and non-linear relations with τ353, we found that a non-linear relation of τ353 proportional to the ~1.3-th power of NH gives the best fit, which may indicate dust evolution in the local molecular cloud complex.
}

\FullConference{7th Fermi Symposium 2017\\
		15-20 October 2017\\
		Garmisch-Partenkirchen, Germany}


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