We introduce the BlueTides simulation and report initial results for the luminosity functions of the first galaxies and AGN, and their contribution to reionization. BlueTides was run on the BlueWaters cluster at NCSA from z = 99 to z = 8.0 and includes 2×70403 particles in a 400 h −1 Mpc per side box, making it the largest hydrodynamic simulation ever performed at high redshift. BlueTides includes a pressureentropy formulation of smoothed particle hydrodynamics, gas cooling, star formation (including molecular hydrogen), black hole growth and models for stellar and AGN feedback processes. The star formation rate density in the simulation is a good match to current observational data at z ∼ 8 − 10. We find good agreement between observations and the predicted galaxy luminosity function in the currently observable range −18 ≤ M UV ≤ −22.5 with some dust extinction required to match the abundance of brighter objects. BlueTides implements a patchy reionization model that produces a fluctuating UV background. BlueTides predicts number counts for galaxies fainter than current observational limits which are consistent with extrapolating the faint end slope of the luminosity function with a power law index α ∼ −1.8 at z ∼ 8 and redshift dependence of α ∼ (1 + z) −0.4 . The AGN population has a luminosity function well fit by a power law with a slope α ∼ −2.4 that compares favourably with the deepest CANDELS-Goods fields. We investigate how these luminosity functions affect the progress of reionization, and find that a high Lyman-α escape fraction (f esc ∼ 0.5) is required if galaxies dominate the ionising photon budget during reionization. Smaller galaxy escape fractions imply a large contribution from faint AGN (down to M UV = −12) which results in a rapid reionization, disfavoured by current observations.

SPHEREx, the Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer, is a proposed NASA MIDEX mission selected for Phase A study pointing to a downselect in early CY2019, leading to launch in CY2023. SPHEREx would carry out the first all-sky spectral survey at wavelengths between 0.75 and 2.42 µm [with spectral resolution R=41], 2.42 and 3.82 µm [with R=35], 3.82 and 4.42 µm [with R=110], and 4.42 and 5.00 µm [with R=130]. At the end of its two-year mission, SPHEREx would obtain 0.75-to-5µm spectra of every 6.2×6.2 arcsec pixel on the sky, with a 5-sigma sensitivity AB>19 per spectral/spatial resolution element. SPHEREx would obtain spectra of every sources in the 2MASS PSC (1.2µm, 1.6µm, 2.2µm) catalog to at least (40 σ, 60 σ, 150 σ) per spectral channel, and spectra with S/N ≥3 per frequency element of the faintest sources detected by WISE. More details concerning SPHEREx are available at http://spherex.caltech.edu. The SPHEREx team has proposed three specific science investigations to be carried out with this unique data set: cosmic inflation, interstellar and circumstellar ices, and the extra-galactic background light.Though these three scientific issues are undoubtedly compelling, they are far from exhausting the scientific output of SPHEREx. Indeed, as Table 1 shows, SPHEREx would create a unique all-sky spectral database including spectra of very large numbers of astronomical and solar system targets, including both extended and diffuse sources. These spectra would enable a wide variety of scientific investigations, and the SPHEREx team is dedicated to making the SPHEREx data available to the scientific community to facilitate these investigations, which we refer to as Legacy Science. To that end, we have sponsored two workshops for the general scientific community to identify the most interesting Legacy Science themes and to ensure that the SPHEREx data products are responsive to their needs. In February of 2016, some 50 scientists from all scientific fields met in Pasadena to develop these themes and to understand their implications for the SPHEREx mission. The results of this initial workshop are reported in Doré et al., 2016. Among other things, discussions at the 2016 workshop highlighted many synergies between SPHEREx Legacy Science and other contemporaneous astronomical missions, facilities, and databases. Consequently, in January 2018 we convened a second workshop at the Center for Astrophysics in Cambridge to focus specifically on these synergies. This white paper, which contains substantial contributions from the participants, presents some of the highlights of the 2018 SPHEREx workshop. 1

The Lyman Continuum photon production efficiency (ξ ion ) is a critical ingredient for inferring the number of photons available to reionise the intergalactic medium. To estimate the theoretical production efficiency in the high-redshift Universe we couple the BlueTides cosmological hydrodynamical simulation with a range of stellar population synthesis models. We find Lyman Continuum photon production efficiencies of log 10 (ξ ion /erg −1 Hz) ≈ 25.1 − 25.5 depending on the choice of stellar population synthesis model. These results are broadly consistent with recent observational constraints at high-redshift though favour a model incorporating the effects of binary evolution.

We use the large cosmological hydro-dynamic simulation BlueTides to predict the photometric properties of galaxies during the epoch of reionisation (z = 8 − 15). These properties include the rest-frame UV to near-IR broadband spectral energy distributions, the Lyman continuum photon production, the UV star formation rate calibration, and intrinsic UV continuum slope. In particular we focus on exploring the effect of various modelling assumptions, including the assumed choice of stellar population synthesis model, initial mass function, and the escape fraction of Lyman continuum photons, upon these quantities. We find that these modelling assumptions can have a dramatic effect on photometric properties leading to consequences for the accurate determination of physical properties from observations. For example, at z = 8 we predict that nebular emission can account for up-to 50% of the rest-frame R-band luminosity, while the choice of stellar population synthesis model can change the Lyman continuum production rate up to a factor of ×2.

In this paper, we study the filamentary structures and the galaxy alignment along filaments at redshift z = 0.06 in the MassiveBlack-II simulation, a state-of-the-art, high-resolution hydrodynamical cosmological simulation which includes stellar and AGN feedback in a volume of (100 Mpc/h) 3 . The filaments are constructed using the subspace constrained mean shift (SCMS; Ozertem & Erdogmus (2011) and Chen et al. (2015a)). First, we show that reconstructed filaments using galaxies and reconstructed filaments using dark matter particles are similar to each other; over 50% of the points on the galaxy filaments have a corresponding point on the dark matter filaments within distance 0.13 Mpc/h (and vice versa) and this distance is even smaller at high-density regions. Second, we observe the alignment of the major principal axis of a galaxy with respect to the orientation of its nearest filament and detect a 2.5 Mpc/h critical radius for filament's influence on the alignment when the subhalo mass of this galaxy is between 10 9 M /h and 10 12 M /h. Moreover, we find the alignment signal to increase significantly with the subhalo mass. Third, when a galaxy is close to filaments (less than 0.25 Mpc/h), the galaxy alignment toward the nearest galaxy group depends on the galaxy subhalo mass. Finally, we find that galaxies close to filaments or groups tend to be rounder than those away from filaments or groups.