model fitting: ensure specutils has access to equivs & set targ solid angle

[gibsongreen]

This draft PR resolves:

1. UnitConversionError in Model Fitting plugin, specutils spec.with_flux_unit did not have access to pix2 custom unit equivalencies

To reproduce on main:

uri ='https://data.science.stsci.edu/redirect/JWST/jwst-data_analysis_tools/IFU_cube_continuum_fit/NGC4151_Hband.fits'

model = cubeviz.plugins['Model Fitting']
model.cube_fit = True
model.create_model_component()
model.calculate_fit()

2. TypeError: unsupported operand type(s) for *: 'CompositeUnit' and 'NoneType'. When toggling 'Cube Fit' in Model Fitting plugin, solid_angle_in_targ was not being set after targ_units was update to include a solid angle unit. Setting 'targ_units' triggered subsequent indirect conversion logic. By setting the solid_angle_in_targ we follow the same logic route and ensure we maintain output units in surface brightness.

To reproduce:

# example notebook cube
uri = "mast:JWST/product/jw02732-o004_t004_miri_ch1-shortmediumlong_s3d.fits"

uc = cubeviz.plugins['Unit Conversion']
uc.flux_unit = 'erg / (Angstrom s cm2)'

model = cubeviz.plugins['Model Fitting']
model.cube_fit = True
model.create_model_component()
model.calculate_fit()

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[codecov]

Codecov Report

Attention: Patch coverage is 85.71429% with 2 lines in your changes missing coverage. Please review.

Project coverage is 88.78%. Comparing base (6c946d3) to head (0a70c5f).
Report is 15 commits behind head on main.

Files with missing lines	Patch %	Lines
...igs/default/plugins/model_fitting/model_fitting.py	84.61%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3343      +/-   ##
==========================================
- Coverage   88.80%   88.78%   -0.03%     
==========================================
  Files         125      125              
  Lines       19137    19174      +37     
==========================================
+ Hits        16995    17023      +28     
- Misses       2142     2151       +9     

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[camipacifici]

Works for me, thank you!

[cshanahan1]

Good catch, I didn't clock this as a unit conversion when I was working on unit conversions for model fitting!

I do wonder if this will ever encounter one of the special cases where a spectral_density AND a pix2 equivalency are needed, and if with_flux_unit will handle that. Have you tested anything like that at all?

[gibsongreen]

I do wonder if this will ever encounter one of the special cases where a spectral_density AND a pix2 equivalency are needed, and if with_flux_unit will handle that. Have you tested anything like that at all?

The all_flux_unit_conversion_equivs calls _eqv_flux_to_sb_pixel which returns the PIX2 equivalency, and by passing pixar_sr if available and the spectral_axis to all_flux_unit_conversion_equivs in this call, should ensure that that special case is handled.

The manga cube in issue #3342 is in the 1e-17 (Erg / Angstrom s cm2) unit and this does get the PIX2 unit applied. I did make sure that cube was working so we could resolve the issue, but adding a test here for this specific edge base should be added here.

[gibsongreen]

Maybe in a small effort before flux_conversion and flux_conversion_general, these both right now return the converted values as an array or spectral_axis as a Quantity object. It'd be worth adding the ability to return the spec Spectrum1D object as well and then we can update this logic block.

@cshanahan1 if you test with this cube:
cubeviz.load_data(f"https://data.sdss.org/sas/dr17/manga/spectro/redux/v3_1_1/7443/stack/manga-7443-12703-LOGCUBE.fits.gz")

and convert the flux_unit to Jy, this no longer throughs a UnitConversionError for the case you brought up. Test coverage is there now too!

This PR is a blocker for a notebook we need merged once 4.1 is released next week, so I will create a ticket and start working on the Spectrum1D compatibility when converting flux.