Donghui Jeong

The HETDEX pilot survey - II. The evolution of the Lyα escape fraction from the ultraviolet slope and luminosity function of 1.9 < z < 3.8 LAEs

We study the escape of Lyα photons from Lyα emitting galaxies (LAEs) and the overall galaxy population using a sample of 99 LAEs at 1.9 (3-6) × 1042 erg s–1 (0.25-0.5 L*), have a mean E(B – V) = 0.13 ± 0.01, implying an attenuation of ~70% in the UV. They show a median UV uncorrected SFR = 11 M ☉ yr–1, dust-corrected SFR = 34 M ☉ yr–1, and Lyα equivalent widths (EWs) which are consistent with normal stellar populations. We measure a median Lyα escape fraction of 29%, with a large scatter and values ranging from a few percent to 100%. The Lyα escape fraction in LAEs correlates with E(B – V) in a way that is expected if Lyα photons suffer from similar amounts of dust extinction as UV continuum photons. This result implies that a strong enhancement of the Lyα EW with dust, due to a clumpy multi-phase interstellar medium (ISM), is not a common process in LAEs at these redshifts. It also suggests that while in other galaxies Lyα can be preferentially quenched by dust due to its scattering nature, this is not the case in LAEs. We find no evolution in the average dust content and Lyα escape fraction of LAEs from z ~ 4 to 2. We see hints of a drop in the number density of LAEs from z ~ 4 to 2 in the redshift distribution and the Lyα luminosity function, although larger samples are required to confirm this. The mean Lyα escape fraction of the overall galaxy population decreases significantly from z ~ 6 to z ~ 2, in agreement with recent results. Our results point toward a scenario in which star-forming galaxies build up significant amounts of dust in their ISM between z ~ 6 and 2, reducing their Lyα escape fraction, with LAE selection preferentially detecting galaxies which have the highest escape fractions given their dust content. The fact that a large escape of Lyα photons is reached by z ~ 6 implies that better constraints on this quantity at higher redshifts might detect re-ionization in a way that is uncoupled from the effects of dust.

Perturbation Theory Reloaded: Analytical Calculation of Nonlinearity in Baryonic Oscillations in the Real-Space Matter Power Spectrum

We compare the nonlinear matter power spectrum in real space calculated analytically from third-order perturbation theory with N-body simulations at 1 1, the shape of oscillations is distorted from the linear theory prediction. Nevertheless, our results suggest that one can correct the distortion caused by nonlinearity almost exactly. We also find that perturbation theory, which does not contain any free parameters, provides a significantly better fit to the simulations than the conventional approaches based on empirical fitting functions to simulations. Future work should include perturbation theory calculations of nonlinearity in redshift-space distortion and halo biasing in the weakly nonlinear regime. Subject headingg cosmology: theory — large-scale structure of universe Online material: color figures

THE HETDEX PILOT SURVEY. I. SURVEY DESIGN, PERFORMANCE, AND CATALOG OF EMISSION-LINE GALAXIES

We present a catalog of emission-line galaxies selected sol ly by their emission-line fluxes using a wide-field integral field spectrograph. This work is partially motivat ed as a pilot survey for the upcoming Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). We describe the observations, reductions, detections, redshift classifications, line fluxes, and counterpart information f r 397 emission-line galaxies detected over 169 ⊓⊔ with a 3500-5800̊A bandpass under 5̊ A full-width-half-maximum (FWHM) spectral resolution. Th e survey’s best sensitivity for unresolved objects under photometric conditions is between 4− 20× 10 erg s cm depending on the wavelength, and Ly α luminosities between3− 6× 10 erg s are detectable. This survey method complements narrowband and color-selection techni ques in the search for high redshift galaxies with its different selection properties and large volume probed. Th e four survey fields within the COSMOS, GOODS-N, MUNICS, and XMM-LSS areas are rich with existing, complemen tary data. We find 104 galaxies via their high redshift Lyα emission at1.9 < z < 3.8, and the majority of the remainder objects are low redshift [ OII]3727 emitters atz < 0.56. The classification between low and high redshift objects de pends on rest frame equivalent width, as well as other indicators, where available. Based o n matches to X-ray catalogs, the active galactic nuclei (AGN) fraction amongst the Ly α emitters (LAEs) is 6%. We also analyze the survey’s complete ness and contamination properties through simulations. We find fi ve high-z, highly-significant, resolved objects with full-width-half-maximum sizes> 44 ⊓⊔ which appear to be extended Ly α nebulae. We also find three high-z objects with rest frame Ly α equivalent widths above the level believed to be achievable with normal star formation, EW0 > 240Å. Future papers will investigate the physical properties o f this sample. Subject headings: galaxies: formation — galaxies: evolution —galaxies: high -redshift — cosmology: observations

Large-scale clustering of galaxies in general relativity

Several recent studies have shown how to properly calculate the observed clustering of galaxies in a relativistic context, and uncovered corrections to the Newtonian calculation that become significant on scales near the horizon. Here, we retrace these calculations and show that, on scales approaching the horizon, the observed galaxy power spectrum depends strongly on which gauge is assumed to relate the intrinsic fluctuations in galaxy density to matter perturbations through a linear bias relation. Starting from simple physical assumptions, we derive a gauge-invariant expression relating galaxy density perturbations to matter density perturbations on large scales, and show that it reduces to a linear bias relation in a synchronous-comoving gauge, corroborating an assumption made in several recent papers. We evaluate the resulting observed galaxy power spectrum, and show that it leads to corrections similar to an effective non-Gaussian bias corresponding to a local f_(NL,eff)≲0.5. This number can serve as a guideline as to which surveys need to take into account relativistic effects. We also discuss the scale-dependent bias induced by primordial non-Gaussianity in the relativistic context, which again is simplest in a synchronous-comoving gauge.

The Pesky Power Asymmetry

Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles St., Baltimore, MD 21218(Dated: March 27, 2013)Physical models for the hemispherical power asymmetry in the cosmic microwave background(CMB) reported by the Planck Collaboration must satisfy CMB constraints to the homogeneityof the Universe and quasar constraints to power asymmetries. We survey a variety of modelsfor the power asymmetry and show that consistent models include a modulated scale-dependentisocurvature contribution to the matter power spectrum or a modulation of the reionization opticaldepth, gravitational-wave amplitude, or scalar spectral index. We propose further tests to distinguishbetween the di erent scenarios.

Perturbation Theory Reloaded. II. Nonlinear Bias, Baryon Acoustic Oscillations, and Millennium Simulation in Real Space

We calculate the nonlinear galaxy power spectrum in real space, including nonlinear distortion of the baryon acoustic oscillations, using the standard third-order perturbation theory (PT). The calculation is based upon the assumption that the number density of galaxies is a local function of the underlying, nonlinear density field. The galaxy bias is allowed to be both nonlinear and stochastic. We show that the PT calculation agrees with the galaxy power spectrum estimated from the Millennium Simulation, in the weakly nonlinear regime (defined by the matter power spectrum) at high redshifts, 1 ≤ z ≤ 6. We also show that, once three free parameters characterizing galaxy bias are marginalized over, the PT power spectrum fit to the Millennium Simulation data yields unbiased estimates of the distance scale, D, to within the statistical error. This distance scale corresponds to the angular diameter distance, DA (z), and the expansion rate, H(z), in real galaxy surveys. Our results presented in this paper are still restricted to real space. The future work should include the effects of nonlinear redshift space distortion. Nevertheless, our results indicate that nonlinear galaxy bias in the weakly nonlinear regime at high redshifts is reasonably under control.

Testing Inflation with Large Scale Structure: Connecting Hopes with Reality

The statistics of primordial curvature fluctuations are our window into the period of inflation, where these fluctuations were generated. To date, the cosmic microwave background has been the dominant source of information about these perturbations. Large scale structure is however from where drastic improvements should originate. In this paper, we explain the theoretical motivations for pursuing such measurements and the challenges that lie ahead. In particular, we discuss and identify theoretical targets regarding the measurement of primordial non-Gaussianity. We argue that when quantified in terms of the local (equilateral) template amplitude

Teasing bits of information out of the CMB energy spectrum

f_{\rm NL}^{\rm loc}

Accurate predictions for the scale-dependent galaxy bias from primordial non-Gaussianity

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Peak-background split, renormalization, and galaxy clustering

f_{\rm NL}^{\rm eq}