Predicting observables from simulations via dust radiative transfer

Much of my research focuses on predicting synthetic observations from 3-D hydrodynamical simulations of isolated disk galaxies and galaxy mergers. I do this in two steps: first, I calculate the dynamical evolution of the system using the Gadget-3 N-body/SPH code. In addition to the core gravitational and gas physics, the simulations include simple sub-resolution prescriptions for star formation, metal enrichment, black hole accretion, and stellar and active galactic nucleus (AGN) feedback. Please see Springel, Yoshida & White (2001), Springel & Hernquist (2003), Springel (2005), and Springel, Di Matteo, & Hernquist (2005) for details of the Gadget-3 code and the sub-resolution models used.

During the hydrodynamical simulations, I regularly save ‘snapshots' of the simulated galaxies, typically every 10 million years. Then, I use these snapshots as input for the Monte Carlo dust radiative transfer code Sunrise, for which I am the primary maintainer. It is the most widely used code for predicting spectra and images from galaxy simulations (see the paper list here). Sunrise first uses the metal density from the hydrodynamical simulations to determine the dust distribution in the galaxies, which it describes using an adaptive mesh. Then, spectral energy distributions (SEDs) are assigned to the star and black hole particles. After these steps are completed, the Monte Carlo radiative transfer is performed. This means that millions of 'photon packets' are propagated from the sources of radiation through the dusty ISM. The effects of dust absorption, scattering, and re-emission are calculated. The final output of the Sunrise calculation is UV-mm SEDs at every camera pixel for multiple viewing angles. To directly compare to observational data, we can use this output to produce monochromatic images in various filters, integrated SEDs and photometry, fiber or slit spectra, etc. For full technical details, see Jonsson (2006) and Jonsson, Groves, & Cox (2010).

The beautiful movie at the top of the page was made by Patrik Jonsson, Greg Novak, and Joel Primack for an NSF Visualization Challenge, and it nicely demonstrates the results of running Sunrise on a galaxy merger simulation.

One of the significant advantages of this technique is the ability to view a simulated galaxy from an arbitrary number of viewing angles. This is of course not possible for real galaxies. This gives us the possibility of being able to determine how the viewing angle affects observable quantities of interest, such as observed fluxes (e.g. Hayward et al. 2011) and AGN indicators (e.g. Snyder, Hayward et al. 2013). The below movie shows how the morphology of a galaxy merger changes with viewing angle. Three different times during the merger are shown.

It is also very useful to be able to see how the SED of a galaxy merger changes with time as physical quantities such as the star formation rate and dust mass change. An example from Lanz, Hayward et al. (2014) is shown in the movie below. Note how the SED becomes more luminous and hotter (i.e. the peak of the infrared emission shifts to shorter wavelengths) during the burst of star formation that occurs near merger coalescence.

With a variety of collaborators, I have applied Sunrise to a broad range of astrophysical phenomena. Below, I list the papers on which I am a co-author that directly rely on Sunrise results. Some of this work is described elsewhere on this site, but much is not, so please consult the papers listed below if you are interested in a work not discussed here.

Submillimeter galaxies: Hayward et al. (2011, 2012, 2013a); Narayanan, Hayward et al. (2010)Michalowski, Hayward et al. (2014)Michaowski et al. (2012)

Morphological and kinematic tracers of galaxy mergers: Hung, Hayward et al. (2016), in press

Validating and improving SED modeling techniques: Hayward & Smith (2015); Smith & Hayward (2015)Martínez-Galarza, Lanz, Smith, Hayward et al. (2014)

Understanding what shapes the far-IR SEDs of galaxies: Safarzadeh, Hayward, Ferguson, & Somerville (2015)

Illustris Galaxy Observatory: Torrey, Snyder, Vogelsberger, Hayward et al. (2015)

Testing SFR indicators: Hayward et al. (2014b)

Obscured AGN: Snyder, Hayward et al. (2013)

Post-starburst galaxies: Snyder, Cox, Hayward et al. (2011)Yesuf et al. (2014)

Compact quiescent galaxies: Wuyts, Cox, Hayward et al. (2010)

‘Dust-obscured galaxies’ (DOGs): Narayanan, Dey, Hayward et al. (2010)

Extended ultraviolet (XUV) disks: Bush, Cox, Hayward et al. (2010)

‘Warm’ ultraluminous infrared galaxies: Younger, Hayward et al. (2009)

Massive red galaxies: Wuyts et al. (2009)

© Christopher C. Hayward 2015-2016; all text may not be reproduced without permission. Images and animations can be used for non-commercial purposes with proper attribution. Last updated December 13, 2016.