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6.13 Spectral Line fitting with specfit

specfit is a powerful task to perform spectral line fits in data cubes. Three types of fitting functions are currently supported, polynomials, Gaussians, and Lorentians. specfit can fit these functions in two ways: over data that were averaged across a region (multifit=False) or on a pixel by pixel basis (multifit=True).

#  specfit :: Fit 1-dimensional gaussians and/or polynomial models to an image or image region  
imagename           =         ’’        #  Name of the input image  
box                 =         ’’        #  Rectangular box in direction coordinate  
                                        #   blc, trc. Default: entire image ("").  
region              =         ’’        #  Region of interest. See help par.region  
                                        #   for possible specifications. Default: Do  
                                        #   not use a region.  
chans               =         ’’        #  Channels to use. Channels must be  
                                        #   contiguous. Default: all channels ("").  
stokes              =         ’’        #  Stokes planes to use. Planes must be  
                                        #   contiguous. Default: all stokes ("").  
axis                =         -1        #  The profile axis. Default: use the  
                                        #   spectral axis if one exists, axis 0  
                                        #   otherwise (<0).  
mask                =         ’’        #  Mask to use. See help par.mask. Default is  
                                        #   none..  
poly                =         -1        #  Order of polynomial element.  Default: do  
                                        #   not fit a polynomial (<0).  
estimates           =         ’’        #  Name of file containing initial estimates.  
                                        #   Default: No initial estimates ("").  
     ngauss         =          1        #  Number of Gaussian elements.  Default: 1.  
     pampest        =         ’’        #  Initial estimate of PCF profile (gaussian  
                                        #   or lorentzian) amplitudes.  
     pcenterest     =         ’’        #  Initial estimate PCF profile centers, in  
                                        #   pixels.  
     pfwhmest       =         ’’        #  Initial estimate PCF profile FWHMs, in  
                                        #   pixels.  
     pfix           =         ’’        #  PCF profile parameters to fix during fit.  
     pfunc          =         ’’        #  PCF singlet functions to fit. "gaussian"  
                                        #   or "lorentzian" (minimal match  
                                        #   supported). Unspecified means all  
                                        #   gaussians.  
 
minpts              =          0        #  Minimum number of unmasked points  
                                        #   necessary to attempt fit.  
multifit            =       True        #  If true, fit a profile along the desired  
                                        #   axis at each pixel in the specified  
                                        #   region. If false, average the non-fit  
                                        #   axis pixels and do a single fit to that  
                                        #   average profile. Default False.  
     amp            =         ’’        #  Name of amplitude solution image. Default:  
                                        #   do not write the image ("").  
     amperr         =         ’’        #  Name of amplitude solution error image.  
                                        #   Default: do not write the image ("").  
     center         =         ’’        #  Name of center solution image. Default: do  
                                        #   not write the image ("").  
     centererr      =         ’’        #  Name of center solution error image.  
                                        #   Default: do not write the image ("").  
     fwhm           =         ’’        #  Name of fwhm solution image. Default: do  
                                        #   not write the image ("").  
     fwhmerr        =         ’’        #  Name of fwhm solution error image.  
                                        #   Default: do not write the image ("").  
     integral       =         ’’        #  Prefix of ame of integral solution image.  
                                        #   Name of image will have gaussian  
                                        #   component number appended.  Default: do  
                                        #   not write the image ("").  
     integralerr    =         ’’        #  Prefix of name of integral error solution  
                                        #   image. Name of image will have gaussian  
                                        #   component number appended.  Default: do  
                                        #   not write the image ("").  
 
model               =         ’’        #  Name of model image. Default: do not write  
                                        #   the model image ("").  
residual            =         ’’        #  Name of residual image. Default: do not  
                                        #   write the residual image ("").  
wantreturn          =       True        #  Should a record summarizing the results be  
                                        #   returned?  
logresults          =       True        #  Output results to logger?  
gmncomps            =          0        #  Number of components in each gaussian  
                                        #   multiplet to fit  
gmampcon            =         ’’        #  The amplitude ratio constraints for non-  
                                        #   reference components to reference  
                                        #   component in gaussian multiplets.  
gmcentercon         =         ’’        #  The center offset constraints (in pixels)  
                                        #   for non-reference components to reference  
                                        #   component in gaussian multiplets.  
gmfwhmcon           =         ’’        #  The FWHM  ratio constraints for non-  
                                        #   reference components to reference  
                                        #   component in gaussian multiplets.  
gmampest            =      [0.0]        #  Initial estimate of individual gaussian  
                                        #   amplitudes in gaussian multiplets.  
gmcenterest         =      [0.0]        #  Initial estimate of individual gaussian  
                                        #   centers in gaussian multiplets, in  
                                        #   pixels.  
gmfwhmest           =      [0.0]        #  Initial estimate of individual gaussian  
                                        #   FWHMss in gaussian multiplets, in pixels.  
gmfix               =         ’’        #  Parameters of individual gaussians in  
                                        #   gaussian multiplets to fix during fit.  
logfile             =         ’’        #  File in which to log results. Default is  
                                        #   not to write a logfile.  
goodamprange        =      [0.0]        #  Acceptable amplitude solution range. [0.0]  
                                        #   => all amplitude solutions are  
                                        #   acceptable.  
goodcenterrange     =      [0.0]        #  Acceptable center solution range in pixels  
                                        #   relative to region start. [0.0] => all  
                                        #   center solutions are acceptable.  
goodfwhmrange       =      [0.0]        #  Acceptable FWHM solution range in pixels.  
                                        #   [0.0] => all FWHM solutions are  
                                        #   acceptable.  
sigma               =         ’’        #  Standard deviation array or image name.  
async               =      False        #  If true the taskname must be started using  
                                        #   specfit(...)  
 

  6.13.1 Polynomial Fits
  6.13.2 Lorentzian and Gaussian Fits
   6.13.2.1 One or more single Gaussian/Lorentzian
   6.13.2.2 Gaussian Multiplets
  6.13.3 Pixel-by-pixel fits


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