A5070588335- Galaxies: Formation, Evolution, Phenomena
- Radio Astronomy Observations and Technology
- Astrophysics and Cosmic Phenomena
- Astronomy and Astrophysical Research
- Stellar, planetary, and galactic studies
- Astrophysics and Star Formation Studies
- Gamma-ray bursts and supernovae
- Cosmology and Gravitation Theories
- History and Developments in Astronomy
- Superconducting and THz Device Technology
- Astrophysical Phenomena and Observations
- Antenna Design and Optimization
- Radio Wave Propagation Studies
- Astronomical Observations and Instrumentation
- Adaptive optics and wavefront sensing
- Dark Matter and Cosmic Phenomena
- Scientific Research and Discoveries
- CCD and CMOS Imaging Sensors
- Millimeter-Wave Propagation and Modeling
- Solar and Space Plasma Dynamics
- Particle Accelerators and Free-Electron Lasers
- Calibration and Measurement Techniques
- Electromagnetic Compatibility and Measurements
- Soil Moisture and Remote Sensing
- Gyrotron and Vacuum Electronics Research
University of California, Los Angeles
2016-2025
Massachusetts Institute of Technology
2024
UCLA Health
2009-2021
University of Washington
2016
Astronomy and Space
2004-2013
Solar System Exploration Research Virtual Institute
2010-2011
Ames Research Center
2010-2011
Yale University
2006-2008
Yale Cancer Center
2006-2008
Whitney Museum of American Art
2006-2007
We discuss new constraints on the epoch of cosmic reionization and test assumption that most ionizing photons responsible arose from high redshift star-forming galaxies. Good progress has been made in charting end through spectroscopic studies z~6-8 QSOs, gamma-ray bursts galaxies expected to host Lyman-alpha emission. However, stringent its duration have come integrated optical depth, tau, Thomson scattering microwave background. Using latest data abundance luminosity distribution distant...
We introduce a powerful semi-numeric modeling tool, 21cmFAST, designed to efficiently simulate the cosmological 21-cm signal. Our code generates 3D realizations of evolved density, ionization, peculiar velocity, and spin temperature fields, which it then combines compute brightness temperature. Although physical processes are treated with approximate methods, we compare our results state-of-the-art large-scale hydrodynamic simulation, find good agreement on scales pertinent upcoming...
Recently, there has been a great deal of interest in understanding the reionization hydrogen intergalactic medium (IGM). One major outstanding questions is how this event proceeds on large scales. Motivated by numerical simulations, we develop model for growth HII regions during era. We associate ionized with large-scale density fluctuations and use excursion set formalism to resulting size distribution. then consider ways which characterize morphology regions. show construct power spectrum...
Understanding cosmic reionization requires the identification and characterization of early sources hydrogen-ionizing photons. The 2012 Hubble Ultra Deep Field (UDF12) campaign has acquired deepest infrared images with Wide Camera 3 aboard Space Telescope and, for first time, systematically explored galaxy population deep into era when microwave background (CMB) data indicates was underway. UDF12 thus provides best constraints to date on abundance, luminosity distribution, spectral...
We present the results of deepest search to date for star-forming galaxies beyond a redshift z~8.5 utilizing new sequence near-infrared Wide Field Camera 3 images Hubble Ultra Deep Field. This `UDF12' campaign completed in September 2012 doubles earlier exposures with WFC3/IR this field and quadruples exposure key F105W filter used locate such distant galaxies. Combined additional imaging F140W filter, fidelity high candidates is greatly improved. Using spectral energy distribution fitting...
The relatively large Thomson optical depth, τes, inferred recently from the WMAP observations suggests that universe was reionized in a more complex manner than previously believed. However, value of τes provides only an integral constraint on history reionization and, by itself, cannot be used to determine nature sources responsible for this transition. Here we show evolution ionization state intergalactic medium (IGM) at high redshifts can measured statistically using fluctuations 21 cm...
Detailed theoretical studies of the high-redshift universe, and especially reionization, are generally forced to rely on time-consuming N-body codes and/or radiative transfer algorithms. We present a method construct seminumerical "simulations," which can efficiently generate realizations halo distributions ionization maps at high redshifts. Our procedure combines an excursion-set approach with first-order Lagrangian perturbation theory operates directly linear density velocity fields. As...
We present a new determination of the ultraviolet (UV) galaxy luminosity function (LF) at redshift z ≃ 7 and 8, first estimate 9. An accurate form evolution LF during this era is key importance for improving our knowledge earliest phases process cosmic reionization. Our analysis exploits to full new, deepest Wide Field Camera 3/infrared imaging from Hubble Space Telescope (HST) Ultra-Deep 2012 (UDF12) campaign, with dynamic range provided by including consistent all appropriate,...
A number of radio interferometers are currently being planned or constructed to observe 21 cm emission from reionization. Not only will such measurements provide a detailed view that epoch, but, since the also traces distribution matter in Universe, this signal can be used constrain cosmological parameters at 6 < z 20. The sensitivity an interferometer information may depend on how precisely angular dependence 3-D power spectrum measured. Utilizing analytic model for reionization, we...
The Wide Field Infrared Survey Telescope (WFIRST) is a 2.4m space telescope with 0.281 deg^2 field of view for near-IR imaging and slitless spectroscopy coronagraph designed > 10^8 starlight suppresion. As background information Astro2020 white papers, this article summarizes the current design anticipated performance WFIRST. While WFIRST does not have UV imaging/spectroscopic capabilities Hubble Space Telescope, wide surveys hundreds times more efficient. Some most ambitious multi-cycle...
The Experiment to Detect the Global Epoch of Reionization Signature (EDGES) recently reported a strong 21-cm absorption signal relative cosmic microwave background at z ∼ 18. While its anomalous amplitude may indicate new physics, in this work we focus on timing signal, as it alone provides an important constraint galaxy formation models. Although rest-frame ultraviolet luminosity functions (UVLFs) over broad range redshifts are well fit by simple models which star histories track assembly...
Abstract We report upper limits on the Epoch of Reionization 21 cm power spectrum at redshifts 7.9 and 10.4 with 18 nights data (∼36 hr integration) from Phase I Hydrogen Array (HERA). The show evidence for systematics that can be largely suppressed systematic models down to a dynamic range ∼10 9 respect peak foreground power. This yields 95% confidence limit <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi...
Abstract Recently, the Hydrogen Epoch of Reionization Array (HERA) has produced experiment’s first upper limits on power spectrum 21 cm fluctuations at z ∼ 8 and 10. Here, we use several independent theoretical models to infer constraints intergalactic medium (IGM) galaxies during epoch reionization from these limits. We find that IGM must have been heated above adiabatic-cooling threshold by 8, uncertainties about ionization radio background. Combining HERA with complementary observations...
Abstract We report the most sensitive upper limits to date on 21 cm epoch of reionization power spectrum using 94 nights observing with Phase I Hydrogen Epoch Reionization Array (HERA). Using similar analysis techniques as in previously reported limits, we find at 95% confidence that Δ 2 ( k = 0.34 h Mpc −1 ) ≤ 457 mK z 7.9 and 0.36 3496 10.4, an improvement by a factor 2.1 2.6, respectively. These are mostly consistent thermal noise over wide range after our data quality cuts, despite...
Abstract New James Webb Space Telescope (JWST) observations are revealing the first galaxies to be prolific producers of ionizing photons, which we argue gives rise a tension between different probes reionization. Over last two decades consensus has emerged where star-forming able generate enough photons drive reionization, given reasonable values for their number densities, efficiencies ξion (per unit UV luminosity), and escape fractions fesc. However, some new JWST infer high during...
Abstract We present results on the emission-line properties of z = 1.4–7.5 star-forming galaxies in Assembly Ultradeep Rest-optical Observations Revealing Astrophysics (AURORA) Cycle 1 JWST/NIRSpec program. Based its depth, continuous wavelength coverage from to 5 μ m, and medium spectral resolution ( R ∼ 1000), AURORA includes detections a large suite nebular emission lines spanning broad range rest-frame wavelength. investigate locations multiple different diagrams, including traditional...
We present results from a large volume simulation of hydrogen reionization. combine 3D radiative transfer calculations and an N-body simulation, describing structure formation in the intergalactic medium, to detail growth H II regions around high-redshift galaxies. Our tracks 10243 dark matter particles, box comoving side length 65.6 Mpc h-1. This allows us accurately characterize size distribution throughout most reionization process. At same time, our resolves many small galaxies likely...
We consider the evolution of sky-averaged 21-cm background during early phases structure formation. Using simple analytic models, we calculate thermal and ionization histories, assuming that stellar photons dominate radiation background. The resulting spectra can constrain properties first generations stars quasars. If Population II dominate, Lyα coupling renders intergalactic medium (IGM) visible before it is heated by X-rays long reionization. Thus has a strong absorption epoch followed...
Many models of early structure formation predict a period heating immediately preceding reionization, when X-rays raise the gas temperature above that cosmic microwave background.These are often assumed to heat intergalactic medium (IGM) uniformly, but in reality will more strongly closer sources.We develop framework for calculating fluctuations 21-cm brightness originate from this spatial variation rate.High-redshift sources highly clustered, leading significant (with fractional variations...
Outflows from quasars inevitably pollute the intergalactic medium (IGM) with magnetic fields. The short-lived activity of a quasar leaves behind an expanding magnetized bubble in IGM. We model expansion remnant bubbles and calculate their distribution as function size field strength at different redshifts. generically find that by redshift z ~ 3, about 5%-20% IGM volume is filled fields energy density ≳10% mean thermal photoionized (at ~104 K). As massive galaxies X-ray clusters condense out...
Reionization is inhomogeneous for two reasons: the clumpiness of intergalactic medium (IGM) and clustering discrete ionizing sources. While numerical simulations can in principle take both into account, they are at present limited by small box sizes. On other hand, analytic models have only examined limiting cases a clumpy IGM (with uniform emissivity) clustered sources (embedded IGM). Here, we an model evolving topology reionization that includes factors. At first, recombinations be ignored...
We consider the degree to which 21 cm tomography of high-redshift universe can distinguish different ionization histories. Using a new analytic model for size distribution H II regions that associates these ionized bubbles with large-scale galaxy overdensities, we compute angular power spectrum and other statistical properties brightness temperature during reionization. show imprint features on allow us separate histories discrete from those partial uniform (by, example, X-rays). also...
We present a catalog of high-redshift star-forming galaxies selected to lie within the redshift range z ≃ 7–8 using Ultra Deep Field 2012 (UDF12), deepest near-infrared (near-IR) exposures yet taken with Hubble Space Telescope (HST). As result increased near-IR exposure time compared previous HST imaging in this field, we probe ∼0.65 (0.25) mag fainter absolute UV magnitude, at ∼ 7 (8), which increases confidence measurement faint end slope galaxy luminosity function. Through 0.7 deeper...