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Stellar kinematics

Purpose

The stellarKinematics module measures the stellar kinematics of the observed spectra. nGIST is currently equipped with one routine that can readily be used by setting the configuration parameter KIN: METHOD to 'ppxf'. In particular, this routine employs the pPXF routine of Cappellari and Emsellem (2004). More precisely:

  • Initial guesses: The used initial guess for the stellar velocity is 0 (as all spectra have been shifted to rest-frame). The initial guess for the velocity dispersion is defined in the configuration parameter KIN: SIGMA. Alternatively, one can define initial guesses for all bins separately, i.e. by supplying the file *_kin-guess.fits in the output directory before the run. This file must contain a column V and SIGMA (as in the output file *_kin.fits), defining an initial guess for each spatial bin.

  • A spectral mask is applied, according to the masking file defined by KIN: SPEC_MASK. See Configuration for details.

  • The module calculates the stellar velocity, sigma, and higher-order velocity moments (depending on how many are specified, currently up to 6 have been tested). An iterative sigma-clipping process can be turned on to clean the spectra.

  • A set of SSP templates must be input. Currently, nGIST has been tested on the MILES stars and SSPs, eMILES, SMILES libraries, the IndoUS library, the X-shooter stellar library, and Walcher+2009 templates. Only the MILES SSPs are included in the default nGIST distribution, though any other library can be employed by writing a read-in module for it, following the example in your /ngist/ngistPipeline/prepareTemplates/miles.py directory.

Config file input

KIN :
  METHOD : 'ppxf' # Name of the routine in stellarKinematics/ (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).
  SPEC_MASK : 'specMask_KIN' # File to define wavelength ranges to be masked during the stellar kinematics fit. The specified path is relative to the configDir path in defaultDir.
  LMIN : 4750 # Rest-frame wavelength range used for the stellar kinematics analysis [in Angst.]
  LMAX : 7100
  SIGMA : 100 # Initial guess of the velocity dispersion of the system [in km/s]
  MOM : 4 # Number of kinematic moments to be extracted
  ADEG : 12 # Degree of the additive Legendre polynomial. Set '-1' to not include any additive polynomials
  MDEG : 0 # Degree of the multiplicative Legendre polynomial. Set '0' to not include any multiplicative polynomials
  REDDENING : null # Initial guess on the stellar reddening E(B-V), in order to measure the stellar reddening. Note: This cannot be used together with multiplicative polynomials.
  MC_PPXF : 0 # Number of Monte-Carlo simulations to extract errors on the stellar kinematics. Formal errors are saved in any case.
  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' # 
  LIBRARY : 'MILES/' # options are 'MILES/'
  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

  • _kin.fits: Results of the extraction of stellar kinematics and their errors

    • Columns: V SIGMA H3 H4 etc Stellar kinematics. The number of columns here will correspond to value of the MOM keyword. For example, MOM: 4 will return V SIGMA H3 H4, while MOM:6 will return V SIGMA H3 H4 H5 H6 | ERR_* Errors on the stellar kinematics from MC-simulations | FORM_ERR_* Formal errors on the stellar kinematics | REDDENING Extinction calculated by PPXF

    • Rows: One line per bin.

  • _kin-bestfit.fits, Extension 1:

    • The best fit to the spectrum

    • Columns: BESTFIT The best fit to the spectrum

    • Rows: One fit per bin.

  • _kin-bestfit.fits, Extension 2:

    • Columns: LOGLAM The corresponding wavelength array

  • _kin-bestfit.fits, Extension 3:

    • Columns: GOODPIX The spectral pixels included in the fit

  • _kin-optimalTemplates.fits: Extension 1

    • Optimal template for the fit on each bin.

    • Columns: OPTIMAL_TEMPLATES Optimal templates

    • Rows: One template per bin.

  • _kin-optimalTemplates.fits: Extension 2

    • Columns: LOGLAM_TEMPLATE The corresponding wavelength array

  • _kin-SpectralMask.fits, Extension 1:

    • Columns: SPECTRAL_MASK The spectral pixels masked out in the fit

    • Rows: One mask per bin

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.