Stellar Kinematics

Analysis class: mangadap.proc.stellarcontinuummodel.StellarContinuumModel

Reference root: $MANGA_SPECTRO_ANALYSIS/$MANGADRP_VER/$MANGADAP_VER/common

Reference file: manga-[PLATE]-[IFUDESIGN]-[DRPQA_KEY]-[BIN_KEY]-[CONTINUUM_KEY].fits.gz

Config files: $MANGADAP_DIR/python/mangadap/config/stellar_continuum_modeling

Example config: gau_mileshc.ini

[default]
 key                    = MILESHCMPL9
 fit_type               = stellar_kinematics
 fit_method             = ppxf
 fit_iter               = nonzero_templates
 reject_boxcar          = 100
 filter_boxcar
 filter_op
 filter_iter
 filter_degree
 filter_mdegree
 minimum_snr            = 1.0
 waverange
 artifact_mask          = BADSKY
 emission_line_mask     = ELPMPL8
 template_library       = MILESHC
 match_resolution       = False
 velscale_ratio         = 4
 moments                = 2
 degree                 = 8
 mdegree                = -1
 bias
Important class dependencies:
  • mangadap.proc.spectralfitting.StellarKinematicsFit`: Provides the abstracted base classes for stellar kinematics fits.
  • mangadap.util.pixelmask.SpectralPixelMask: Used to mask the fitting regions for the fit.
  • mangadap.proc.templatelibrary.TemplateLibrary: Generalized interface that provides the spectral-template library for use in spectral fitting.
  • mangadap.proc.ppxffit.PPXFFit: Provides the core pPXF wrapper.
Algorithm:

  • Establish the fitting method, which includes setting up the mangadap.util.pixelmask.SpectralPixelMask using the artifact_mask, emission_line_mask, and waverange from config.

    • The BADSKY artifact mask is read and used to build an mangadap.par.artifactdb.ArtifactDB instance that masks the typical residuals around the strong sky line at 5577 angstroms.
    • The ELPFULL emission-line mask is read and used to build an mangadap.par.emissionlinedb.EmissionLineDB instance that is used to mask the emission lines in the associated parameter file. Each mask is 1500 km/s centered on the line at the input guess redshift.
    • The waverange config parameter can be used to limit the fitted spectral range; will fit as much as possible if no range is provided.

  • Using the mangadap.proc.spatiallybinnedspectra.SpatiallyBinnedSpectra object, select all binned spectra with S/N greater than minimum_snr in config.

  • The DAP nominally provides the stellar-continuum fit with the velocity and velocity dispersion from The DAP ObsInputPar as its initial guess redshift and velocity dispersion.

  • Instantiate the mangadap.proc.templatelibrary.TemplateLibrary objects as selected by the template_library config parameter.

    • If matching the spectral resolution to the galaxy data (match_resolution in config), the resolution is matched at the redshifted wavelengths of the galaxy data, adopting the input guess velocity as the redshift.
    • The template wavelength channel width is set to a fraction 1/velscale_ratio of the galaxy data.

  • Execute the fit_method selected in config. Currently, this can only be ppxf.

  • In mangadap.proc.ppxffit.PPXFFit.fit_SpatiallyBinnedSpectra():

    • Mask binned spectra, ignoring pixels masked as DONOTUSE, IGNORED, FLUXINVALID, or FORESTAR in DAP LOGCUBE file.

    • Call mangadap.proc.ppxffit.PPXFFit.fit() with the data from the mangadap.proc.templatelibrary.TemplateLibrary and mangadap.proc.spatiallybinnedspectra.SpatiallyBinnedSpectra objects.

      • If rejecting, the size of the boxcar (pixels) is set by reject_boxcar.
      • All filter_* config options are only used with fit_iter=fit_reject_filter.
      • moments, degree, mdegree, and bias are passed directly to pPXF.

    • Given the template and object spectral range, determine the maximum viable fitting range for pPXF using mangadap.proc.ppxffit.PPXFFit.fitting_mask().

    • Run through the specified iteration procedure, as selected by fit_iter in config; available options are set by mangadap.proc.ppxffit.PPXFFit.iteration_modes().

    • Parse the pPXF results into the data table saved to the reference file.

      • Spectra without a fit are flagged as either NOFIT or FITFAILED.
      • Check if returned kinematics are near the imposed boundaries: \(v \pm 2000\) km/s from the input redshift and \({\rm d}v/100 < \sigma < 1000\) km/s, where \({\rm d}v\) is the size of the pixel (\(\sim 70\) km/s). Leads to The NEARBOUND flag in the MAPS file.
      • Flag pixels rejected by the sigma-clipping iteration.

    • Calculate the dispersion corrections:

      • First construct three spectra: (1) the optimized template; (2) the optimized template redshifted to the best-fitting velocity and with a velocity dispersion of 100 km/s; (3) the same as spectrum 2 but also convolved to the nominal object spectrum resolution.
      • Use pPXF to fit spectra 2 and 3 with spectrum 1.
      • The quadrature difference of the fitted dispersion returned for the fit to spectrum 3 and spectrum 2 is provided as the correction (STELLAR_SIGMACORR in the MAPS file)

    • Convert the pPXF velocities and velocity errors to \(cz\) velocities in km/s using mangadap.proc.ppxffit.PPXFFit.convert_velocity().

  • Construct stellar-continuum BINID map. Bin IDs are the same as for the binned spectra except that any bin that does not meet the S/N limit are given a stellar-continuum bin ID of -1.