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tokens: previous snapshot. The second criterion ensures that we exclude galaxies that experienced a merger within the past 150 Myr. 4. Synthetic Observations of the Simulations: Images and Spectra To generate synthetic observations, each simulation snapshot is post-processed with the dust radiative transfer software SUNRISE (Jonsson 2006 ; Jonsson Primack 2010 ; Jonsson et al. 2010 ). Synthetic images and spectra are created from the SUNRISE output. The synthetic Hubble Space Telescope ( HST ) images used in this paper are available as a high-level science product from MAST 12 12 https://archive.stsci.edu/prepds/vela : https://doi.org/10.17909/t9-ge0b-jm58 . 4.1. Dust Radiative Transfer with <monospace>SUNRISE</monospace> SUNRISE contains two primary steps. It first generates a spectral energy distribution (SED) for each source of radiation in the simulation. It then propagates the associated polychromatic rays through the 3D gas grid of the simulation, taking into account dust absorption and scattering, toward a user-defined camera(s). For each snapshot, the ART output is first loaded into the YT analysis software (Turk et al. 2011 ) and converted into the appropriate SUNRISE format. This is carried out using an updated version of the pipeline used in Moody et al. ( 2014 ). An SED is assigned to each star particle based on its age, mass, and metallicity using STARBURST99 (Leitherer et al. 1999 ) assuming a Kroupa ( 2001 ) initial mass function. Emission lines are generated from young star particles, less than 10 Myr old, using a starburst model from the photoionization and shock modeling code MAPPINGS III (Dopita et al. 2005 ; Groves et al. 2008 ). This model includes a central massive young stellar cluster whose SED is set with STARBURST99 , a surrounding H ii region, and a photodissociation region with a covering fraction of 0.2 (Groves et al. 2008 ). To account for 10 4 K thermal broadening, we convolve the original MAPPINGS III H α emission line with a 10 km s −1 1D Gaussian kernel. The dust density is assumed proportional to the gas metal mass using a dust-to-metals mass ratio of 0.4 (Dwek 1998 ). Consequently, the dust geometry is resolved to a typical gas cell size of 17–35 pc. We adopt the dust grain size distribution from Weingartner Draine ( 2001 ) and Draine Li ( 2007 ) and set the slope of the dust extinction law, R v , to the Milky Way value of 3.1 (e.g., Gordon et al. 2003 ). SUNRISE cameras are placed at 19 positions around the galaxy. The camera parameters are user-selected and not defaulted to SUNRISE. Of the cameras, six are random but remain fixed in comoving space over time, eight are random but change from timestep to timestep, and the remaining five are fixed with respect to the net angular momentum of the galaxy and, as such, change from timestep to timestep. Those fixed to the galaxy include one that is face-on, i.e., along the gas angular momentum axis; one that is reverse face-on; two that are edge-on; and one that is