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Stellar populations

Purpose

The starFormationHistories module derives non-parametric star formation histories from the observed spectra. nGIST is currently equipped with one routine that can readily be used by setting the configuration parameter SFH: METHOD to 'ppxf'. In particular, this routine employs the pPXF routine of Cappellari & Emsellem (2004).

There are several options for the treatment of emission lines in this module:

  • To run the SFH module using the cleaned, emission-line subtracted spectra, you simply need to make sure that you ran the emission line module previously (i.e. set GAS: METHOD: 'ppxf')
  • To run the SFH module using the original (un-subtracted) spectrum, run the SFH module with the GAS module turned off (i.e. set GAS: METHOD: False).
  • To run the SFH module and mask all emission lines, use SFH: SPEC_MASK: 'specMask_KIN'
  • To run the SFH module and not mask any emission lines, use SFH: SPEC_MASK: 'specMask_SFH'.

Config file input

SFH :
  METHOD : 'ppxf' # Name of the routine in starFormationHistories/ (without .py) to perform the tasks. Set 'False' to turn off module. Set 'ppxf' to use the standard GIST implementation, exploiting the pPXF routine of Cappellari & Emsellem (2004).
  LMIN : 4750 # Rest-frame wavelength range used for the star formation histories analysis [in Angst.]
  LMAX : 5500
  SPEC_MASK : 'specMask_SFH' # File to define wavelength ranges to be masked during the star formation histories analysis. The specified path is relative to the configDir path in defaultDir.
  SPEC_EMICLEAN : False # Keyword (True/False) to enable/disable the use of emission line cleaned spectra from the Emission Line Fitting Module. 
  MOM : 4 # Number of kinematic moments to be extracted. If you use FIXED = True, this should be same number of moments used to extract the stellar kinematics before. Otherwise the parameter can be set independently.
  MDEG : 12 # Degree of the multiplicative Legendre polynomial. Set '0' to not include any multiplicative polynomials. Note that additive Legendre polynomials cannot be used for this module.
  REGUL_ERR : 1000000. # Regularisation error for the regularised run of pPXF. Note: Regularisation = 1 / REGUL_ERR
  NOISE : 1. # Set a wavelength independent noise vector to be passed to pPXF.
  FIXED : True # Fix the stellar kinematics to the results obtained with the stellar kinematics module [True / False]. If 'False', please provide an initial guess on the velocity dispersion of the systems [in km/s] by adding the parameter SIGMA.
  MC_PPXF : 0 # Added to add the option of running MC on the SFH module
  LSF_TEMP : 'lsf_MILES' # Path of the file specifying the line-spread-function of the spectral templates. The specified path is relative to the configDir path in defaultDir.
  TEMPLATE_SET : 'miles' # options are 'miles' or 'IndoUS (not recc.)'
  LIBRARY : 'MILES_SFH/' # options are 'MILES/', 'miles_ssp_ch/', or 'IndoUS/'
  NORM_TEMP : 'LIGHT' # Normalise the spectral template library to obtain light- or mass-weighted results [LIGHT / MASS]
  DOCLEAN : True # Keyword to turn on/off the sigma clipping. Set to 'False' for testing.

Output

Files

  • _sfh.fits:

    • Columns: AGE Age | METAL Metallicity | ALPHA Alpha enhancement | V SIGMA H3 H4 Stellar kinematics | FORM_ERR_* Formal errors on the stellar kinematics

    • Rows: One line per bin.

  • _sfh-weights.fits: The weights assigned to each template during the fit

    • Columns: WEIGHTS The weights

    • Rows: One line per bin.

  • _sfh-bestfit.fits, Extension 1:

    • The best fit to the spectrum

    • Columns: BESTFIT The best fit to the spectrum

    • Rows: One fit per bin.

  • _sfh-bestfit.fits, Extension 2:

    • Columns: LOGLAM The corresponding wavelength array

  • _sfh-bestfit.fits, Extension 3:

    • Columns: GOODPIX The spectral pixels included in the fit

Function returns

The module should end with return(None). If an uncaught exception occurs in the module, all following modules will be skipped for this galaxy. If you intend to manually skip all subsequent modules, simply raise an exception.