How to Fit One Spectrum

The low-level functions in the DAP treat each spectrum independently. As such, it’s possible to use these low-level DAP functions to effectively fit any spectrum you like, with the caveat that you’ll need to vet the results. Here, we guide you through the example script $MANGADAP_DIR/examples/fit_one_spec.py. It is not sufficiently abstracted to be an executable (included in $MANGADAP_DIR/bin); however, we may eventually provide such an executable. For now, the script is meant to provide a worked example for generating your own script.

Overall Workflow

  1. Read in desired spectrum and associated galaxy redshift.

  2. Generate a mask (i.e., a “SpectralPixelMask”) of the 5577 Ang sky emission line and intrinsic galaxy emission lines.

  3. Read in the desired spectral template library (using mangadap.proc.templatelibrary.TemplateLibrary).

  4. Use pPXF to fit a linear combination of these templates to the spectrum.

  5. Calculate moments of the emission lines after subtracting the stellar continuum (using “EmissionLineMoments”). (??? is this what is actually happening???)

  6. Generate a new mask including only the 5577 Ang sky emission line.

  7. Perform a simultaneous fit of the stellar continuum and emission lines while holding the stellar kinematics determined from the initial pPXF run fixed. This is the model of the spectrum that is ultimately output by the DAP.

  8. Re-measure the emission line moments.

User-Supplied Inputs

  1. Plate-ifu (“plt” and “ifu”)

  2. Spaxel coordinates (“x” and “y”)

  3. Stellar continuum template keyword (e.g., “sc_tpl_key = ‘MILESHC’”)

    This keyword specifies the template library that should be used in the initial run of pPXF (step 4 in the Overall Workflow).

    The desired template set must have an associated configuration file (*.ini) in $MANGADAP_DIR/python/mangadap/config/spectral_templates in which this keyword is specified. The templates themselves must exist in a subdirectory of $MANGADAP_DIR/data/spectral_templates/.

    We strongly recommend using the MILESHC keyword here, as we have found other template libraries are very likely to yield unreliable stellar kinematics.

  4. Emission plus stellar continuum template keyword (e.g., “el_tpl_key = ‘MILESHC’”)

    This keyword specifies the template library that should be used in the second continuum+emission line fitting step (step 7 in the Overall Workflow). This need not be the same as the stellar continuum template keyword described above. However, as above, this library must have an associated *.ini configuration file, and must exist within the spectral_templates subdirectory.

  5. Emission line database to be used for calculating emission-line moments (e.g., elmom_key = 'ELBMILES')

    TBW

  6. Emission line database to be used for fitting emission lines (e.g., elfit_key = 'ELPMILES')

    TBW

  7. Desired spectral pixel scale of the templates relative to the data (“velscale_ratio”)

    TBW

  8. Emission line database to be used for emission-line masking. This is specified in the lines

    # Mask the 5577 sky line and the emission lines
sc_pixel_mask = SpectralPixelMask(artdb=ArtifactDB.from_key('BADSKY'),
                                  emldb=EmissionLineDB.from_key('ELPFULL'))

Examining the Results

TBW