Below, I describe the primary collaborations in which I am currently involved.
Feedback in Realistic Environments (FIRE) project
The goal of the FIRE project (Hopkins et al. 2014) is to perform cosmological simulations of galaxies in which the detailed multiphase structure of the interstellar medium is resolved and all potentially important stellar feedback channels (supernovae, stellar winds, radiation pressure and photoheating) are implemented explicitly rather than via tuned ‘sub-grid’ models. (We are currently working to implement black hole growth and AGN feedback.) For this reason, the FIRE simulations represent the state of the art in terms of physical fidelity. I was involved in some of the pre-FIRE works in which an early version of the FIRE feedback model was applied to idealized simulations of galaxy mergers (Hopkins et al. 2013a,b).
Since coming to Caltech in September 2014, I have played an active role in various FIRE projects. I have studied the physical origin of the burstiness of the FIRE galaxies’ star formation histories and compared them with observational constraints (Sparre, Hayward et al. 2015b). I am currently mentoring multiple students on FIRE-related projects: Caltech undergrad Clark Esmerian is running Sunrise on the FIRE simulations to predict images and spatially resolved spectra. Caltech graduate student Kung-Yi Su is studying the effects of magnetic fields, turbulent diffusion, viscosity, and conduction, and Matt Orr, another Caltech grad student, is analyzing the spatially resolved Kennicutt-Schmidt relation in the FIRE simulations. Dalhousie University graduate student Tim Miller, who is spending a year at Caltech as a Visiting Student Researcher under my supervision, is studying dust obscuration in the FIRE simulations with the goal of determining how the star formation history of the Universe inferred from unresolved infrared sources is related to the true star formation history.
Illustris project
Because the current FIRE simulations are all ‘zoom’ simulations, in which a single z = 0 halo is simulated at very high resolution, only a handful of halos have been simulated. To simulate statistically representative populations of galaxies, lower-resolution, large-volume cosmological simulations must be used. For this reason, I am also involved in the Illustris project. I was involved in the creation of the Illustris Galaxy Observatory (Torrey, Snyder, Vogelsberger, Hayward et al. 2015) and mentored Martin Sparre (who was then a student at the DARK Cosmology Centre in Copenhagen) on a project in which we studied the ‘star formation main sequence’ and starburst galaxies in Illustris (Sparre, Hayward et al. 2015a). Other projects, including a study of submillimeter galaxies in Illustris, are underway.
Spitzer Interacting Galaxies Survey
I am the sole theorist involved in the Spitzer Interacting Galaxies Survey (SIGS; Lanz et al. 2013, Brassington et al. 2015). SIGS consistst of a sample of local galaxies that were selected to represent all stages of galaxy interactions (e.g. close pairs, final coalescence). For these galaxies, we have a variety of multi-wavelength (UV-infrared) data, including images and spectra. A key focus of the SIGS collaboration is to directly compare observed interacting galaxies with simulations and, more generally, to take advantage of the synergies yielded by theorists and observers working together. A few of our projects have been published or submitted (Hayward et al. 2014b; Lanz, Hayward et al. 2014; Martínez-Galarza, Lanz, Smith, Hayward et al. 2014; Hung, Hayward et al. 2016, in press), and various others are in preparation.
Other ongoing observational collaborations
Over the past few years, I have collaborated with a group of observers who study infrared-selected galaxies and AGN. The collaboration includes Profs. Anna Sajina (Tufts) and Alex Pope (UMass Amherst), Dr. Lin Yan (Caltech), and junior members of their groups. The focus of our collaboration is to compare the large sample of z ~ 0.3-3 infrared-selected galaxies for which they have panchromatic spectral energy distributions (SEDs) and mid-infrared spectra with my galaxy simulations, from which I predict panchromatic SEDs and spectra using the Sunrise dust radiative transfer code. The first two papers, which will form the bulk of Tufts student Eric Roebuck’s thesis, will be submitted soon. In Roebuck, Sajina, Hayward et al. (2015a, in prep.), we investigate how well the contribution of AGN to infrared emission can be inferred. This work has important implications for understanding feedack and black hole growth. In the second work (Roebuck, Sajina, Hayward et al. 2015b, in prep.), we fit the observed SEDs using my suite of simulated SEDs. For the vast majority of the observed SEDs, we are able to obtain good fits with one or more simulated SEDs, which is an impressive feat because the SEDs are ‘forward-modeled’ from simulations. This task is thus considerably more challenging than traditional SED modeling, in which many parameters are varied independently rather than predicted from simulations.
I also have an ongoing collaboration with Dr. Dan Smith (U. Hertfordshire), who I’ve had the pleasure of being friends with since our days as CERN summer students in 2003. Broadly speaking, we are interested in leveraging the synergy enabled by combining my expertise in galaxy formation simulations and his extensive experience observing galaxies. To date, we have focused on testing and improving SED modeling techniques. Our published work is described in detail here. We have multiple other projects underway and planned, including an investigation of spatially resolved (i.e. pixel-by-pixel) SED modeling. Our collaboration is supported by the Santander Universities partnership scheme.
Finally, I have recently joined both the South Pole Telescope Submillimeter Galaxies and Cosmological Evolution Survey (COSMOS) collaborations.