Emission-line Moments

Analysis class: mangadap.proc.emissionlinemoments.EmissionLineMoments

Reference root: $MANGA_SPECTRO_ANALYSIS/$MANGADRP_VER/$MANGADAP_VER/[PLATE]/[IFUDESIGN]/ref

Reference file:

  • Before Gaussian emission-line modeling: manga-[PLATE]-[IFUDESIGN]-[DRPQA_KEY]-[BIN_KEY]-[CONTINUUM_KEY]-[ELMOM_KEY].fits.gz
  • After Gaussian emission-line modeling: manga-[PLATE]-[IFUDESIGN]-[DRPQA_KEY]-[BIN_KEY]-[CONTINUUM_KEY]-[ELFIT_KEY]-[ELMOM_KEY].fits.gz

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

Example config: emomm.ini

[default]
 key                = EMOMMPL9
 minimum_snr        = 0.0
 artifact_mask      = BADSKY
 emission_passbands = ELBMPL9
 redo_postmodeling  = True
 fit_vel_name       = Ha-6564
Important class dependencies:
  • mangadap.proc.bandpassfilter: Provides the core functions that perform the bandpass integrals.
  • mangadap.par.emissionmomentsdb.EmissionMomentsDB: Generalized class that provides the detailed parameters for a set of emission-line windows used to perform non-parametric moments.
  • mangadap.proc.spectralfitting.EmissionLineFit: Provides functions common to both the moment and Gaussian-fit calculations.
  • mangadap.util.pixelmask.SpectralPixelMask: Used to mask spectral regions.
Algorithm:

  • Read the artifact database to setup the mangadap.util.pixelmask.SpectralPixelMask object based on the artifact_mask config.

  • Set up the mangadap.par.emissionmomentsdb.EmissionMomentsDB using the emission_passbands config.

  • Determine the binned spectra above the S/N limit set by the minimum_snr config.

  • Use the mangadap.proc.stellarcontinuummodel.StellarContinuumModel object to construct the stellar continuum for each binned spectrum.

  • Subtract the continuum using mangadap.proc.spectralfitting.EmissionLineFit.subtract_continuum(). If a binned spectrum does not have a fitted stellar continuum, the moment analysis is performed on the binned spectrum without any continuum subtraction.

  • Measure the moments using mangadap.proc.emissionlinemoments.EmissionLineMoments.measure_moments().

    • Redshift the emission-line passbands based on the NSA redshift.
    • Determine the pseudo-continuum in the red and blue bands using mangadap.proc.bandpassfilter.pseudocontinuum().
    • Set the slope and intercept of a linear continuum beneath extrapolation between the two sidebands for all emission-lines.
    • For each emission line, measure the first 3 moments of the pseudo-continuum-subtracted spectra using mangadap.proc.emissionlinemoments.EmissionLineMoments.single_band_moments(): (0) integrated flux; (1) intensity weighted redshift (\(cz\)); and (2) intensity weighted \((cz)^2\).
    • Determine the instrumental dispersion at the 1st moment locations of each line using mangadap.proc.spectralfitting.EmissionLineFit.instrumental_dispersion().
    • Flag any measurement without a continuum spectrum as NOCORRECTION.
    • If any of the passbands (blue, red, main) are incomplete (or empty) due to masked pixels or straddle the jump between where there is and is not a viable continuum subtracted, or if that jump occurs between the blue and red passbands, flag the moments as FITFAILED in the MAPS file.
    • Mask any “dummy” bands. Dummy bands are used to ensure that the emission-line moment channels match the emission-line Gaussian-fit channels in the output MAPS file.

  • Using the 0th moment (integrated flux) and the binned spectra (‘’without’’ continuum subtraction), measure the emission-line equivalent widths using mangadap.proc.bandpassfilter.emission_line_equivalent_width().

  • Construct emission-line-moments 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 emission-line-moment bin ID of -1.