Tzu‐Ching Chang
A5007163293- Radio Astronomy Observations and Technology
- Galaxies: Formation, Evolution, Phenomena
- Astrophysics and Cosmic Phenomena
- Astronomy and Astrophysical Research
- Gamma-ray bursts and supernovae
- Cosmology and Gravitation Theories
- Superconducting and THz Device Technology
- Stellar, planetary, and galactic studies
- Astrophysics and Star Formation Studies
- Astronomical Observations and Instrumentation
- Pulsars and Gravitational Waves Research
- Scientific Research and Discoveries
- Arctic and Antarctic ice dynamics
- Cryospheric studies and observations
- Spectroscopy and Laser Applications
- History and Developments in Astronomy
- Calibration and Measurement Techniques
- Antenna Design and Optimization
- Geophysics and Gravity Measurements
- Climate change and permafrost
- Soil Moisture and Remote Sensing
- Adaptive optics and wavefront sensing
- Planetary Science and Exploration
- Astrophysical Phenomena and Observations
- Advanced Vision and Imaging
China Medical University
2014-2025
Jet Propulsion Laboratory
2017-2024
National Health Research Institutes
2010-2024
California Institute of Technology
2018-2024
Feng Chia University
2024
National Taiwan Normal University
2019-2023
Institute of Astronomy and Astrophysics, Academia Sinica
2009-2022
Mike O'Callaghan Federal Medical Center
2020
National Sun Yat-sen University
2020
National Chiayi University
2017-2020
The expansion of the Universe appears to be accelerating, and mysterious antigravity agent this acceleration has been called "dark energy." To measure dynamics dark energy, baryon acoustic oscillations (BAO) can used. Previous discussions BAO energy test have focused on direct measurements redshifts as many 10(9) individual galaxies, by observing 21 cm line or detecting optical emission. Here we show how study oscillation in brightness accomplished economical three-dimensional intensity...
In this letter, 21 cm intensity maps acquired at the Green Bank Telescope are cross-correlated with large-scale structure traced by galaxies in WiggleZ Dark Energy Survey. The data span redshift range 0.6 < z 1 over two fields totaling ~41 deg. sq. and 190 hours of radio integration time. cross-correlation constrains Omega_HI b_HI r = [0.43 \pm 0.07 (stat.) 0.04(sys.)] x 10^-3, where is neutral hydrogen HI fraction, galaxy-hydrogen correlation coefficient, bias parameter. This most...
The GMRT Epoch of Reionization (EoR) experiment is an ongoing effort to measure the power spectrum from neutral hydrogen at high redshift. We have previously reported upper limit (70 mK)^2 wavenumbers k=0.65 h/Mpc using a basic piecewise-linear foreground subtraction. In this paper we explore use singular value decomposition remove foregrounds with fewer assumptions about structure. Using method also quantify, for first time, signal loss due filter and present new spectra adjusted loss,...
The Hydrogen Intensity and Real-time Analysis eXperiment (HIRAX) is a new 400-800MHz radio interferometer under development for deployment in South Africa. HIRAX will comprise 1024 six meter parabolic dishes on compact grid map most of the southern sky over course four years. has two primary science goals: to constrain Dark Energy measure structure at high redshift, study transients pulsars. observe unresolved sources neutral hydrogen via their redshifted 21-cm emission line (`hydrogen...
Abstract The large-scale distribution of neutral hydrogen in the Universe will be luminous through its 21 cm emission. Here, for first time, we use auto-power spectrum intensity fluctuations to constrain at z ∼ 0.8. Our data were acquired with Green Bank Telescope and span redshift range 0.6 &lt; 1 over two fields totalling ≈41 deg2 190 h radio integration time. dominant synchrotron foregrounds exceed signal by ∼103, but have fewer degrees freedom can removed efficiently. Even presence...
Following the first two annual intensity mapping workshops at Stanford in March 2016 and Johns Hopkins June 2017, we report on recent advances theory, instrumentation observation that were presented these meetings some of opportunities challenges identified looking forward. With preliminary detections CO, [CII], Lya low-redshift 21cm, a host experiments set to go online next few years, field is rapidly progressing all fronts, with great anticipation for flood new exciting results. This...
Abstract The microwave emission from a model snow field, consisting of randomly spaced ice spheres which scatter independently, is calculated. Mie scattering and radiative transfer theory are applied in manner similar to that used calculating optical properties clouds. extinction coefficient computed as function both wavelength ice-particle radius. Volume by the individual particles field significantly decreases for particle radii greater than few hundredths wavelength. Since mean annual...
We present a new upper limit to the 21cm power spectrum during Epoch of Reionization (EoR) which constrains reionization models with an unheated IGM. The GMRT-EoR experiment is ongoing effort make statistical detection neutral hydrogen emission at redshift z~9. Data from this constrain EoR, end Dark Ages arising formation first bright UV sources, probably stars or mini-quasars. results approximately 50 hours observations Giant Metrewave Radio Telescope in India December 2007. describe radio...
We report results from 21-cm intensity maps acquired the Parkes radio telescope and cross-correlated with galaxy 2dF survey. The data span redshift range $0.057<z<0.098$ cover approximately 1,300 square degrees over two long fields. Cross correlation is detected at a significance of $5.18\sigma$. amplitude cross-power spectrum low relative to expected dark matter power spectrum, assuming neutral hydrogen (HI) bias mass density equal measurements ALFALFA decrement pronounced statistically...
Concerted effort is currently ongoing to open up the Epoch of Reionization (z ∼15-6) for studies with IR and radio telescopes.Whereas detections have been made sources (Lyman-α emitters, quasars drop-outs) in this redshift regime relatively small fields view, no direct detection neutral hydrogen, via redshifted 21-cm line, has yet established.Such a expected coming years, surveys, could entire universe from z ∼6-200 astrophysical cosmological studies, opening not only Reionization, but also...
We estimate the 21 cm Radio Background from accretion onto first intermediate-mass Black Holes between $z\approx 30$ and 16$. Combining potentially optimistic, but plausible, scenarios for black hole formation growth with empirical correlations luminosity radio-emission observed in low-redshift active galactic nuclei, we find that a model of holes forming molecular cooling halos is able to produce background exceeds Cosmic Microwave (CMB) at $z \approx 17$ though models involving larger halo...
We present the joint analysis of Neutral Hydrogen (HI) Intensity Mapping observations with three galaxy samples: Luminous Red Galaxy (LRG) and Emission Line (ELG) samples from eBOSS survey, WiggleZ Dark Energy Survey sample. The HI intensity maps are Green Bank Telescope redshifted 21cm emission on 100deg2 covering redshift range $0.6<z<1.0$. process data by separating removing foregrounds FastICA, construct a transfer function to correct for effects foreground removal signal....
The Hydrogen Intensity and Real-time Analysis eXperiment (HIRAX) is a radio interferometer array currently in development, with an initial 256-element to be deployed at the South African Radio Astronomy Observatory (SARAO) Square Kilometer Array (SKA) site Africa. Each of 6m, $f/0.23$ dishes will instrumented dual-polarisation feeds operating over frequency range 400-800 MHz. Through intensity mapping 21 cm emission line neutral hydrogen, HIRAX provide cosmological survey distribution...
Abstract The dipole moment in the angular distribution of cosmic microwave background (CMB) is thought to originate from doppler effect and our motion relative CMB frame. Observations large-scale structure (LSS) should show a related “kinematic dipole” help test kinematic origin dipole. Intriguingly, many previous LSS studies suggest discrepancies with expectations CMB. Here, we reassess apparent inconsistency between measurements estimates NVSS catalog radio sources. We find that it...
We quantify the prospects for using emission lines from rotational transitions of CO molecule to perform an `intensity mapping' observation at high redshift during Epoch Reionization (EoR). The aim intensity mapping is observe combined many unresolved galaxies, measure spatial fluctuations in this emission, and use as a tracer large scale structure very early times history our Universe. This measurement would help determine properties molecular clouds -- sites star formation galaxies that...
This work describes a new instrument optimized for detection of the neutral hydrogen 21cm power spectrum between redshifts 0.5-1.5: Baryon Acoustic Oscillation Broadband and Broad-beam (BAOBAB) Array. BAOBAB will build on efforts first generation experiments which are targeting signal from Epoch Reionization at z ~ 10. At 1, emission in self-shielded overdense halos also presents an accessible signal, since dominant, synchrotron foreground is considerably fainter than redshift The principle...
TIME-Pilot is designed to make measurements from the Epoch of Reionization (EoR), when first stars and galaxies formed ionized intergalactic medium. This will be done via redshifted 157.7 um line singly carbon ([CII]). In particular, produce detection [CII] clustering fluctuations, a signal proportional integrated intensity, summed over all EoR galaxies. thus sensitive emission dwarf galaxies, thought responsible for balance ionizing UV photons, that difficult detect individually with JWST...
This white paper envisions a revolutionary post-DESI, post-LSST dark energy program based on intensity mapping of the redshifted 21cm emission line from neutral hydrogen at radio frequencies. The proposed survey has unique capability to quadruple volume Universe surveyed by optical programs, provide percent-level measurement expansion history $z \sim 6$, open window explore physics beyond concordance $Λ$CDM model, and significantly improve precision standard cosmological parameters. In...
Intensity mapping experiments survey the spectrum of diffuse line radiation rather than detect individual objects at high signal-to-noise ratio. Spectral maps unresolved atomic and molecular contain three-dimensional information about density environments emitting gas efficiently probe cosmological volumes out to redshift. also all other sources frequencies interest. Continuum foregrounds are typically ~102–103 times brighter signal. The instrumental response bright will produce new spectral...
We present the first application of a new foreground removal pipeline to current leading HI intensity mapping dataset, obtained by Green Bank Telescope (GBT). study 15hr and 1hr field data GBT observations previously presented in Masui et al (2013) Switzer (2013), covering about 41 square degrees at 0.6<z<1.0, for which cross-correlations may be measured with galaxy distribution WiggleZ Dark Energy Survey. In pipeline, we subtract Galactic continuum point source contamination using an...
Our current understanding of the Universe is established through pristine measurements structure in cosmic microwave background (CMB) and distribution shapes galaxies tracing large scale (LSS) Universe. One key ingredient that underlies cosmological observables field sources observed assumed to be initially Gaussian with high precision. Nevertheless, a minimal deviation from Gaussianityis perhaps most robust theoretical prediction models explain Universe; itis necessarily present even...
Our current understanding of the Universe is established through pristine measurements structure in cosmic microwave background (CMB) and distribution shapes galaxies tracing large scale (LSS) Universe. One key ingredient that underlies cosmological observables field sources observed assumed to be initially Gaussian with high precision. Nevertheless, a minimal deviation from Gaussianityis perhaps most robust theoretical prediction models explain Universe; itis necessarily present even...
Line intensity mapping (LIM) provides a unique and powerful means to probe cosmic structures by measuring the aggregate line emission from all galaxies across redshift. The method is complementary conventional galaxy redshift surveys that are object-based demand exquisite point-source sensitivity. Tomographic Ionized-carbon Mapping Experiment (TIME) will measure star formation rate (SFR) during reionization observing redshifted [CII] 158$\mu$m ($6 \lesssim z 9$) in LIM regime. TIME...