SAMUEL CABOT'S RESEARCH SITE

GALAXY SYSTEMS IN COSMOLOGICAL SIMULATIONS

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Surface brightness maps of selected galaxy clusters from the LAOZI cosmological simulations. The spatial extent is 100 kpc per side. From left-to-right, the columns plot emission from Lyman alpha, He II, and C IV, respectively. 

Ab initio cosmological simulations provide detailed views into the earliest stages of galaxy formation. They also provide insights into the distribution of matter and energy in the Universe that complement observational constraints and enable observational predictions.

In one case study, I investigated the power sources of Lyman Alpha Blobs (LABs) which are some of the brightest Lyman alpha sources of the early (z = 2 to 6) universe. These objects tend to be the progenitors of galaxy clusters. However, their power sources are unclear. In studies by Cantalupo et al. (2014) and Arrigoni Battaia et al. (2015), it is suggested that one LAB containing luminous quasar UM 287 is powered by photoionization of small, dense gas clumps. Such stringent conditions prompt consideration of alternative power sources. I analyzed LABs (Cabot, Cen & Zheng 2016) in the LAOZI simulations (Cen 2014) run under a Lambda CDM model of the Universe. I used radiative transfer (Cloudy, Ferland et al. 2013) to generate emission spectra of the LABs. I demonstrated that, like the Lyman alpha line, He II and C IV emission can be attributed mainly to shock-heated gas (collisional ionization and collisional excitation, respectively).

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Emission ratios for LABs, comparing LAOZI simulation model to observations (beta represents a dust attenuation parameter). The most stringent observational constraints are contained within the gray shaded region. The simulation model (shock-heated gas) is consistent with these constraints, as well as observations from other observed sources. 

In another case study, I analyzed galaxy clusters in LAOZI simulations in efforts to solve the "Missing Baryon Problem" (the fact that observations of galaxy clusters reveal a 16.4% deficit in the cosmic baryon fraction compared to CMB observations). In these systems, the baryon content attains the cosmic fraction just past the virial radius. These findings indicate that the missing baryons may comprise hot, diffuse plasma in the halos of such clusters.