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Galaxy SED catalogs

For select redshifts of \(z = \{6, 7, 8, 9, 10\}\) we produce galaxy spectral energy distribution (SED) catalogs for the flagship THESAN-1 simulation, directly mirroring the SUBFIND subhalo catalogs. The post-processing methodology for generating mock SEDs of THESAN galaxies from the star and dust distributions is outlined in Section 2.2 of Kannan et al. (2022).

Briefly, the intrinsic nebular emission is taken from Byler et al. (2017), which is based on photoionization calculations using CLOUDY. The underlying stellar radiation intensities and spectra are taken from the Flexible Stellar Population Synthesis (FSPS) model (Conroy, Gunn & White 2009). Dust attenuation is modeled using the Monte Carlo radiative transfer code SKIRT (Camps & Baes 2020), which accurately captures scattering and absorption by dust throughout the entire wavelength range considered 0.05 to 200 μm, discretized into 657 unequal bins. The radiative transfer calculations are performed on a Voronoi grid constructed from positions of the gas cells in the galaxy, mirroring the structure and geometry of the AREPO data as closely as possible. A redshift-dependent dust-to-metal ratio is used and dust emission is modeled assuming thermal equilibrium with the local radiation field. A Draine & Li (2007) dust mixture of amorphous silicate and graphitic grains, including varying amounts of polycyclic aromatic hydrocarbons (PAHs) particles, is assumed. Only sufficiently well-resolved, star-forming galaxies are considered, to ensure that the output SEDs from the SKIRT calculations are reasonably converged. We consider a galaxy well resolved if the stellar mass within twice the stellar half-mass radius is greater than 50 times the baryonic mass resolution of the simulation. We also require that at least one star particle be less than 5 Myr old, which ensures that there is recent on-going star formation within the halo. Given the resolution of the simulation, this roughly translates to haloes with a minimum star formation rate of just below \(0.1\,{\rm M}_{\odot} / {\rm yr}\).

There is a single HDF5 file for each snapshot named SED_[snapshot].hdf5 containing simulation attributes and subhalo datasets. A simple h5dump -A filename will outline the contents of the file. The main simulation attributes are provided in the HDF5 Header group, which lists the following quantities:
Header Attributes ▾
Attribute Dimensions Units Description
BoxSize 1 \({\rm ckpc} / h\) Spatial extent of the periodic box (in comoving units).
NumSubhalo 1 - Number of galaxies at this redshift that fall within the selection criteria.
NumberOfWavelengthBins 1 - Number of wavelength bins in which the flux is specified.
Time 1 - The scale factor \(a=1/(1+z)\) corresponding to the current output.
Flux_Unit 1 - The flux units are Jansky assuming an observed distance of 10 Mpc.
Wavelength_Unit 1 - The wavelength units are micron (μm).
Subhalo properties are saved as HDF5 datasets:
Datasets ▾
Attribute Dimensions Units Description
SED [N,W] \({\rm Jansky\ at\ 10\,Mpc}\) Dust-attenuated SED for each of the galaxies.
SED_Intrinsic [N,W] \({\rm Jansky\ at\ 10\,Mpc}\) Intrinsic SED for each of the galaxies.
SFR N \({\rm M}_{\odot} / {\rm yr}\) Sum of the instantaneous star-formation rates of gas cells within each halo.
StellarMass N \({\rm M}_{\odot}\) Total stellar mass of within each halo.
SubhaloNumber N - Subhalo ID in the SUBFIND subhalo catalog.
Wavelength W \({\rm micron}\) (μm) Wavelength values at which the flux is calculated.

Note: \(N\) and \(W\) denote the number of selected halos and wavelength bins, respectively.