Emission-line Moments

Analysis class: EmissionLineMoments

Reference root: see method_path; $MANGA_SPECTRO_ANALYSIS/$MANGADRP_VER/$MANGADAP_VER/[METHOD]/[PLATE]/[IFUDESIGN]/ref for MaNGA

Reference file: see default_paths; for MaNGA the files are:

• Before Gaussian emission-line modeling:

  • manga-[PLATE]-[IFUDESIGN]-[RDXQA]-[BINNING]-[CONTINUUM]-[ELMOM].fits.gz

• After Gaussian emission-line modeling:

  • manga-[PLATE]-[IFUDESIGN]-[RDXQA]-[BINNING]-[CONTINUUM]-[ELFIT]-[ELMOM].fits.gz

Optional Parameters: see Analysis Plans. The table below lists the parameters defined by EmissionLineMomentsDef

Key	Type	Options	Default	Description
key	str		EMOMMPL11	Keyword used to distinguish between different emission-line moment databases.
minimum_snr	int, float		0.0	Minimum S/N of spectrum to analyze
pixelmask	SpectralPixelMask			Object used to mask spectral pixels
passbands	str		ELBMPL9	Either a string identifying the emission-line bandpass filter database to use, or the direct path to the parameter file defining the database
redo_postmodeling	bool		True	Redo the moment measurements after the emission-line modeling has been performed
fit_vel_name	str		Ha-6564	The name of the emission line used to set the redshift of each spaxel used to set the observed wavelength of the bandpasses.
overwrite	bool		False	If the output file already exists, redo all the calculations and overwrite it.

Important class dependencies:

• mangadap.proc.bandpassfilter: Provides the core functions that perform the bandpass integrals.

• EmissionMomentsDB: Generalized class that provides the detailed parameters for a set of emission-line windows used to perform non-parametric moments.

• EmissionLineFit: Provides functions common to both the moment and Gaussian-fit calculations.

• SpectralPixelMask: Used to mask spectral regions.

Algorithm:

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

• Set up the EmissionMomentsDB using the emission_passbands config.

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

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

• Subtract the continuum using subtract_continuum(). WARNING: 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 measure_moments().

  • Redshift the emission-line passbands based on the provided redshift.

  • Determine the pseudo-continuum in the red and blue bands using pseudocontinuum().

  • Set the slope and intercept of a linear continuum 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 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 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 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.