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Is GFM_StellarPhotometrics in stars/wind calculated in exact the same way as model A in Nelson+ (2018a)? I have tried the four SDSS filters, but I cannot reproduce GFM_StellarPhotometrics within 0.1 mag using python wrapper of FSPS. It seems like that there are lots of star particles with metallicity out of metallicity range of Padova isochrone, how do you extrapolate the table?

The Model A of Nelson+18 is made with FSPS, as described in that paper.

The GFM_StellarPhotometrics in the snapshot are from a different, older method, based on BC03. The following code snippet will produce the interpolation table used to make GFM_StellarPhotometrics, so if you do a simple interpolation using it you should be able to reproduce those snapshot values.

def makeStellarPhotometricsHDF5_BC03():
    """ Create stellar_photometrics.hdf5 file using BC03 models, as used for Illustris and IllustrisTNG runs.
    Bands: UBVK (Buser U,B3,V,IR K filter + Palomar200 IR detectors + atmosphere.57) in Vega, griz (sdss) in AB
    Requires: http://www.bruzual.org/bc03/Original_version_2003/bc03.models.padova_1994_chabrier_imf.tar.gz
    Produces: 87f665fe5cdac109b229973a2b48f848  stellar_photometrics.hdf5
    Original: f4bcd628b35036f346b4e47f4997d55e  stellar_photometrics.hdf5
      (all datasets between the two satisfy np.allclose(rtol=1e-8,atol=8e-4))
    """
    import numpy as np
    import h5py
    import glob

    filenames1 = sorted(glob.glob("bc2003_hr_m*_chab_ssp.1color")) # m22-m72
    filenames2 = sorted(glob.glob("bc2003_hr_m*_chab_ssp.1ABmag")) # m22-m72

    # linear metallicities (mass_metals/mass_total), not in solar!
    Zvals = [0.0001, 0.0004, 0.004, 0.008, 0.02, 0.05]
    bandNames = ['U','B','V','K','g','r','i','z']

    nAgeVals = 220
    assert len(Zvals) == len(filenames1) == len(filenames2)

    # allocate
    ages = np.zeros(nAgeVals)
    mags = {}
    for bandName in bandNames:
        mags[bandName] = np.zeros( [len(Zvals),nAgeVals] )

    # load BC03 model files
    for i in range(len(Zvals)):
        data1 = np.loadtxt(filenames1[i])
        data2 = np.loadtxt(filenames2[i])

        # verify expected number of rows/ages, and that we process the correct metallicity files
        assert data1.shape[0] == data2.shape[0] == nAgeVals
        with open(filenames1[i], 'r') as f:
            assert "Z=%g" % Zvals[i] in f.read()
        with open(filenames2[i], 'r') as f:
            assert "Z=%g" % Zvals[i] in f.read()

        ages = data1[:,0] - 9.0 # log yr -> log Gyr, same in all files
        mags['U'][i,:] = data1[:,2]
        mags['B'][i,:] = data1[:,3]
        mags['V'][i,:] = data1[:,4]
        mags['K'][i,:] = data1[:,5]

        mags['g'][i,:] = data2[:,2]
        mags['r'][i,:] = data2[:,2] - data2[:,4]
        mags['i'][i,:] = data2[:,2] - data2[:,5]
        mags['z'][i,:] = data2[:,2] - data2[:,6]

    # write output
    with h5py.File('stellar_photometrics.hdf5', 'w') as f:

        f["N_LogMetallicity"]    = np.array([len(Zvals)], dtype='int32')
        f["N_LogAgeInGyr"]       = np.array([nAgeVals], dtype='int32')
        f["LogMetallicity_bins"] = np.log10(np.array(Zvals, dtype='float64'))
        f["LogAgeInGyr_bins"]    = ages

        for bandName in bandNames:
            f["Magnitude_"+bandName] = mags[bandName]

Thank you!