Cosmic variance is the intrinsic scatter in the number density of galaxies due to fluctuations in the large-scale dark matter density field. In this work, we present a simple analytic model of cosmic variance in the high redshift Universe (z ∼ 5–15). We assume that galaxies grow according to the evolution of the halo mass function, which we allow to vary with large-scale environment. Our model produces a reasonable match to the observed ultraviolet luminosity functions in this era by regulating star formation through stellar feedback and assuming that the UV luminosity function is dominated by recent star formation. We find that cosmic variance in the UVLF is dominated by the variance in the underlying dark matter halo population, and not by differences in halo accretion or the specifics of our stellar feedback model. We also find that cosmic variance dominates over Poisson noise for future high-z surveys except for the brightest sources or at very high redshifts (z ≳ 12). We provide a linear approximation of cosmic variance for a variety of redshifts, magnitudes, and survey areas through the public Python package galcv. Finally, we introduce a new method for incorporating priors on cosmic variance into estimates of the galaxy luminosity function and demonstrate that it significantly improves constraints on that important observable.

We present the first results from the BAaDE (Bulge Asymmetries and Dynamic Evolution) survey. Though only a subset of the complete survey (∼2700 out of ∼20000 final sources), our data comprise the largest radio kinematic survey to date of stellar SiO masers observed toward the Galactic bulge and plane from −15 • < l < +12 • and −6 • < b < +6 • . Our sources include a substantial number of line-ofsight (LoS) velocities in high extinction regions within ±1 • of the Galactic plane. When matched with 2MASS a) photometry, our radio-detected sample lies significantly brighter than and red-ward of the first red giant branch tip, reaching extremes of (J − Ks) 0 > 8, colors consistent with Mira variables and mass losing AGB stars. We see a clean division into two kinematic populations: a kinematically cold (σ ∼ 50 km sec −1 ) population that we propose is in the foreground disk, consisting of giants with 2MASS Ks < 5.5, and a kinematically hot (σ ∼ 100 km sec −1 ) candidate bulge/bar population for most giants with Ks > 5.5. Only the kinematically hot giants with Ks > 5.5 include the reddest stars. Adopting 8.3 kpc to the Galactic Center, and correcting for foreground extinction, we find that most of the sources have M bol ∼ −5, consistent with their being luminous, and possibly intermediate age, AGB stars. We note some tension between the possibly intermediate age of the kinematically hot population, and its high velocity dispersion compared to the disk.

We present new subarcsecond-resolution Karl G. Jansky Very Large Array (VLA) imaging at 10 GHz of 155 ultraluminous (L bol ∼ 1011.7–1014.2 L ⊙) and heavily obscured quasars with redshifts z ∼ 0.4–3. The sample was selected to have extremely red mid-infrared–optical color ratios based on data from the Wide-Field Infrared Survey Explorer (WISE) along with a detection of bright, unresolved radio emission from the NRAO VLA Sky Survey (NVSS) or Faint Images of the Radio Sky at Twenty cm Survey. Our high-resolution VLA observations have revealed that the majority of the sources in our sample (93 out of 155) are compact on angular scales <0.″2 (≤1.7 kpc at z ∼ 2). The radio luminosities, linear extents, and lobe pressures of our sources are similar to young radio active galactic nuclei (e.g., gigahertz-peaked spectrum [GPS] and compact steep-spectrum [CSS] sources), but their space density is considerably lower. Application of a simple adiabatic lobe expansion model suggests relatively young dynamical ages (∼104–7 yr), relatively high ambient ISM densities (∼1–104 cm−3), and modest lobe expansion speeds (∼30–10,000 km s−1). Thus, we find our sources to be consistent with a population of newly triggered, young jets caught in a unique evolutionary stage in which they still reside within the dense gas reservoirs of their hosts. Based on their radio luminosity function and dynamical ages, we estimate that only ∼20% of classical large-scale FR I/II radio galaxies could have evolved directly from these objects. We speculate that the WISE-NVSS sources might first become GPS or CSS sources, of which some might ultimately evolve into larger radio galaxies.

The observed large-scale scatter in Lyα opacity of the intergalactic medium at z < 6 implies large fluctuations in the neutral hydrogen fraction that are unexpected long after reionization has ended. A number of models have emerged to explain these fluctuations that make testable predictions for the relationship between Lyα opacity and density. We present selections of z = 5.7 Lyα-emitting galaxies (LAEs) in the fields surrounding two highly opaque quasar sightlines with long Lyα troughs. The fields lie toward the z = 6.0 quasar ULAS J0148+0600, for which we reanalyze previously published results using improved photometric selection, and toward the z = 6.15 quasar SDSS J1250+3130, for which results are presented here for the first time. In both fields, we report a deficit of LAEs within 20 h −1 Mpc of the quasar. The association of highly opaque sightlines with galaxy underdensities in these two fields is consistent with models in which the scatter in Lyα opacity is driven by large-scale fluctuations in the ionizing UV background or by an ultra-late reionization that has not yet concluded at z = 5.7.

Cosmic variance from large-scale structure will be a major source of uncertainty for galaxy surveys at $z \gtrsim 6$, but that same structure will also provide an opportunity to identify and study dense environments in the early Universe. Using a robust model for galaxy clustering, we directly incorporate large-scale densities into an inference framework that simultaneously measures the high-z ($z \gtrsim 6$) UV luminosity function and the average matter density of each distinct volume in a survey. Through this framework, we forecast the performance of several major upcoming James Webb Space Telescope (JWST) galaxy surveys. We find that they can constrain field matter densities down to the theoretical limit imposed by Poisson noise and unambiguously identify over-dense (and under-dense) regions on transverse scales of tens of comoving Mpc. We also predict JWST will measure the luminosity function with a precision at z = 12 comparable to existing Hubble Space Telescope’s constraints at z = 8 (and even better for the faint-end slope). We also find that wide-field surveys are especially important in distinguishing luminosity function models.