PPMAP output files for M31

    Supplementary data for the article "Dust in the Eye of Andromeda"
    Marsh, K. A., Whitworth, A. P., Smith, M., Lomax, O., Eales, S. A.,
    Griffin, M. J. 2018

    Description of files:

    m31_diffcdens.fits    =	4D hypercube of differential column density, 
				with axes RA, Dec, dust temperature (T), dust 
				opacity index (beta). The sets of grid values 
				of T and beta are specified in the FITS header. 

    m31_sigdiffcdens.fits =	4D hypercube of 1-sigma uncertainty values of
				differential column density

    m31_cdens_05sig.fits  =	2D map of integrated line-of-sight column
				density in units of 10^20 H2 molecules / cm^2,
				truncated at the 5-sigma level.

    m31_beta_05sig.fits  =	2D map of mean line-of-sight dust opacity 
				index, truncated at the 5-sigma level.

    m31_temp_05sig.fits   =     2D map of mean line-of-sight dust temperature,
				truncated at the 5-sigma column density level.

    m31_tsig_05sig.fits   =     2D map of the standard deviation of dust
				temperature along the line of sight, truncated
				at the 5-sigma column density level.

    m31_tskew_05sig.fits   =    2D map of the skewness of the dust temperature
                                distribution along the line of sight, truncated
				at the 5-sigma column density level.

    m31_tkurt_05sig.fits   =    2D map of the kurtosis of the dust temperature
                                distribution along the line of sight, truncated
				at the 5-sigma column density level.

    NOTE REGARDING COORDINATES:
    The equinox of the coordinate system here is 2000. Since this is not set
    explicitly in the FITS headers, positional problems may be encountered
    depending on the default value in the WCS software being used. In such 
    cases the solution is to insert the keyword EQUINOX = 2000.0 into the 
    FITS headers.