Emission-line Modeling
Analysis class: EmissionLineModel
Reference root: see method_path
;
$MANGA_SPECTRO_ANALYSIS/$MANGADRP_VER/$MANGADAP_VER/[METHOD]/[PLATE]/[IFUDESIGN]/ref
for MaNGA
Reference file: see default_paths
;
manga-[PLATE]-[IFUDESIGN]-[RDXQA]-[BINNING]-[CONTINUUM]-[ELFIT].fits.gz
for MaNGA
Optional Parameters: see Analysis Plans. The table below lists the parameters
defined by EmissionLineModelDef
Key |
Type |
Options |
Default |
Description |
---|---|---|---|---|
|
str |
|
Keyword used to distinguish between different emission-line moment databases. |
|
|
int, float |
0.0 |
Minimum S/N of spectrum to fit |
|
|
str |
|
Name of the emission-line moments band used to set the initial velocity guess for each spaxel. |
|
|
str |
Name of the emission-line moments band used to set the initial velocity dispersion guess for each spaxel. |
||
|
ParSet, dict |
Fitting function parameters |
||
|
Undefined |
Class used to perform the fit. |
||
|
Undefined |
Function or method that performs the fit; must be callable. |
||
|
bool |
False |
If the output file already exists, redo all the calculations and overwrite it. |
Important class dependencies:
SpectralPixelMask
: Used to mask spectral regions.
EmissionLineDB
: Generalized class that provides the detailed parameters for a set of emission lines to fit
lineprofiles
: Generalized class that provides the detailed profile shapes for each line.
EmissionLineTemplates
: Used to construct the emission-line templates to use with pPXF.
EmissionLineFit
: Provides functions common to both the moment and Gaussian-fit calculations.
Sasuke
: The equivalent ofPPXFFit
for the emission-line fits that is primarily a wrapper for pPXF. Critically, this uses the emission-line fitter contributed by Xihan Ji and Michele Cappellari,emline_fitter_with_ppxf()
.
TemplateLibrary
: If usingSasuke
to perform the fit, this generalized interface provides the spectral-template library for use in modeling the stellar continuum.
Elric
: Provides the main fitting functions when just fitting Gaussians to continuum-subtracted spectra. BEWARE: This class has not been used or tested regularly since MPL-5.
Algorithm:
Setup the fitting method:
Instantiate the
SpectralPixelMask
using theartifact_mask
andwaverange
from config.
The
BADSKY
artifact mask is read and used to build anArtifactDB
instance that masks the typical residuals around the strong sky line at 5577 angstroms.The
waverange
config parameter can be used to limit the fitted spectral range; will fit as much as possible if no range is provided.If
fit_method = elric
,baseline_order
sets the Legendre function used to set the baseline in each fitting window andwindow_buffer
sets the +/- window in angstroms around each line to use during the fit.If
fit_method = sasuke
:
etpl_line_sigma_mode
andetpl_line_sigma_min
determines the method used to set the emission-line template instrumental dispersion; the available options are set byetpl_line_sigma_options()
.
reject_boxcar
sets the size of the boxcar (pixels) to use for the rejection iterations.The templates used to fit the stellar continuum during the emission-line modeling can be different than those used during the stellar kinematics fit. Use
continuum_templates
andvelscale_ratio
to select the new templates and set their sampling. Ifcontinuum_templates
is not givenvelscale_ratio
is ignored and the templates are identical between the two modules. If the templates are switched, a newTemplateLibrary
object is instantiated. When switching template libraries, the templates must have their resolution matched to the MaNGA data so that the corrected stellar kinematics from the existingStellarContinuumModel
instance can be held fixed during the fitting.
bias
,degree
,mdegree
are passed directly to pPXF (at the momentmoments
is ignored and always 2!)
internal_reddening = True
forces use of the Calzetti (2000) attenuation law; will override any non-zeromdegree
.If
deconstruct_bins = True
, method will fit the emission lines on an individual spaxel basis instead of the binned spectra; currently this can only be used iffit_method = sasuke
.If
mom_vel_name
ormom_disp_name
is defined, the DAP will use the corresponding moment measurements from theEmissionLineMoments
object to set the initial guess for the velocity (default is the datacube metadata redshift) and/or velocity dispersion (default is 100 km/s) for the fit.If requested, call the “Elric” fitter:
WARNING: The Elric fitter has not been used in the DAP for some time. It should generally not be selected; if it is, one may need to spend some time debugging… For this reason, the method is not well documented here. Its main DAP wrapper fitting function is
fit_SpatiallyBinnedSpectra()
and its generalized fitting function isfit()
.Or, call “Sasuke” fitter:
The main DAP wrapper function is
fit_SpatiallyBinnedSpectra()
and does the following:
Get the binned spectra from the
SpatiallyBinnedSpectra
objectEither get the stellar templates from the
TemplateLibrary
object pointed to by theStellarContinuumModel
object or, if new templates were selected, build the newTemplateLibrary
instance (which must have its resolution matched to the MaNGA data).Get the fitted stellar kinematics from the
StellarContinuumModel
object usingmatched_kinematics()
.Determine which binned spectra have the
minimum_snr
from config, and have a good continuum model (cannot be flagged asNOVALUE
orFITFAILED
).If deconstructing bins:
Get the individual spaxel spectra from the
DataCube
objectApply the reddening defined in the
SpatiallyBinnedSpectra
objectGet the individual on-sky spaxel coordinates from the
ReductionAssessment
object and the unweighted on-sky binned-spectra coordinates from theSpatiallyBinnedSpectra
object.Run the generalized fitting function (see description below), providing the spectra to which the stellar-continuum results are “remapped” to for fitting the emission lines.
Measure the equivalent widths for the individual spaxels using
measure_equivalent_width()
.Otherwise:
Run the generalized fitting function (see description below), only providing the binned spectra.
Measure the equivalent widths for the binned spectra using
measure_equivalent_width()
.Construct the “emission-line baseline” as the difference between continuum+emission-line optimized fit from Sasuke and the stellar continuum fit for the stellar kinematics (from the
StellarContinuumModel
object)The generalized fitter is
mangadap.proc.sasuke.Sasuke.fit()
and initially proceeds very similarly tomangadap.proc.ppxffit.PPXFFit.fit()
:
Check the input spectra to fit, guess kinematics, and remapping coordinates if provided
Check and set stellar templates and stellar kinematics if provided
Determine the spectral resolution to use for the emission-line templates; available options are set by
etpl_line_sigma_options()
.Construct and add emission-line templates using
EmissionLineTemplates
.
Parse the
EmissionLineDB
object: Determine which lines to fit and how to group lines into the same template (flux ratio fixed and same kinematics) kinematic components (same velocity and velocity dispersion), velocity groups, and sigma groups using_parse_emission_line_database()
.Sample the desired spectral resolution at each input line center.
Convert the profile parameters into pixel coordinates.
Construct each template with the specified line profile using classes/methods in
mangadap.util.lineprofiles
. Lines with a fixed flux ratio are placed in the same template (this means they’ll also have tied velocities and velocity dispersions).Parse the velocity and sigma groups into tied parameters to provide to pPXF.
Given the template and object spectral range, determine the maximum viable fitting range for pPXF using
fitting_mask()
.Run fit iterations using
emline_fitter_with_ppxf()
.
If deconstructing the bins (for the Hybrid (HYB) binning scheme):
(a.) First fit the binned spectra (with a 3-sigma rejection iteration) forcing all the gas components into a single kinematic component (all velocities and velocity dispersions are tied).
(b.) Deconstruct the binned spectrum into its individual spaxels.
(c.) Use the result of the first fit to create a single, optimal stellar template and to set the starting kinematics for first fit to each spaxel.
(d.) Fit each spaxel (with a 3-sigma rejection iteration) with the optimized template and all gas components in a single kinematic component
(e.) Reset the starting guesses and refit each spaxel (without a rejection iteration) with the gas components in the appropriate velocity and sigma groups.
Otherwise:
Perform steps a, c, and e above, but just using the provided spectra (whether or not they’re bins or individual spaxels).
Parse the results of the fit iterations into the output using
_save_results()
.