H. Cynthia Chiang

ALBATROS

Very little is known about the radio sky at frequencies below 30 MHz, and future observations may allow us to one day probe the cosmic "dark ages," an epoch that is unexplored to date. Measurements at these frequencies are extremely challenging because of RFI contamination and ionospheric effects. The state of the art among ground-based measurements dates from the 1960s, when Grote Reber caught brief glimpses of the 2 MHz sky at low resolution.

The Array of Long Baseline Antennas for Taking Radio Observations from the Sub-antarctic/Seventy-ninth parallel (ALBATROS) aims to map the low-frequency sky using arrays of autonomous antenna stations. Each antenna station will record baseband data for subsequent offline correlation. Our primary array is currently under construction at the McGill Arctic Research Station and will ultimately comprise roughly 8 antennas operating at 1.2-125 MHz with baselines up to 20 km. The first ALBATROS pathfinder was installed on Marion Island and operated between 2018 and 2023. We additionally have an ALBATROS test bed located at Uapishka Station, located in the Nitassinan of Pessamit in northern Quebec. Our work has been featured in several popular media outlets. (Left and center photo credits below: Anthony Zerafa)

PRI^ZM

At frequencies below 150 MHz, redshifted 21-cm emission can probe the era of cosmic dawn, when the first stars were born. The global 21-cm signal, averaged across the sky, captures the heating processes of these first stars and is expected to have an absorption trough around a redshift of 20. A first detection of this absorption feature was reported by the EDGES experiment in early 2018. Because measurements of the global 21-cm signal are dominated entirely by systematic effects rather than statistical noise, independent confirmation from multiple experiments is absolutely essential.

Probing Radio Intensity at high-Z from Marion (PRI^ZM) is an experiment that has been designed to study cosmic dawn in the universe using 50-150 MHz observations of globally averaged 21-cm emission. The experiment consists of two modified four-square antennas, operating at center frequencies of 70 and 100 MHz, and a dual-polarization spectrometer back end. PRI^ZM operated between 2017 and 2023 from Marion Island, an exceptionally isolated and radio-quiet location in the sub-Antarctic. Data analysis is currently in progress.

MIST

The Mapper of the IGM Spin Temperature (MIST) is a new experiment that will also search for the signature of cosmic dawn using observations of globally averaged 21-cm emission. MIST builds upon the instrumention and calibration lessons learned from EDGES, and the experiment is designed with several unique features to minimize instrumental systematics. MIST consists of a single blade dipole antenna that sits directly above soil, operating without a ground plane. The readout electronics and power systems are housed in an RF-tight enclosure located within the frame of the antnena, thus minimizing structural asymmetry and increasing portability. MIST has successfully observed from the McGill Arctic Research Station, in addition to shorter engineering runs at several other sites, and additional observing campaigns are planned for the future.

HIRAX

At late times (redshifts of 0.8 < z < 2.5), the distribution of galaxies on large scales contains remnant ripples imprinted by primordial sound waves in the early universe. These baryon acoustic oscillations (BAOs) are observed as an excess number of galaxies on scales of roughly 150 Mpc. By using the the characteristic size of these ripples as a "ruler," we can chart the expansion history of the universe and gain insight into the nature of dark energy, one of the greatest puzzles facing modern cosmology.

The Hydrogen Intensity and Real-time Analysis eXperiment (HIRAX) is an experiment that will map nearly all of the southern sky in radio continuum and neutral hydrogen line emission over a frequency range of 400 to 800 MHz. The primary goal of HIRAX is to study dark energy via 21-cm intensity mapping of BAOs. The instrument is also ideally suited for discovering new pulsars and transient radio sources, which can be followed up in more detail by the MeerKAT array. The HIRAX array will comprise 256 dishes, each six meters in diameter, placed in a compact, redundant, interferometer configuration. An eight-element prototype has already been constructed at the Hartebeesthoek Radio Astronomy Observatory, and the first pathfinder array will be constructed in the Karoo desert soon.

CHORD

The Canadian Hydrogen Observatory and Radio-transient Detector (CHORD) is an experiment that will also study BAOs via 21-cm intensity mapping, and the experiment will additionally be a powerful platform for studying fast radio bursts, 21-cm galaxies, pulsars, cosmic magnetism, and cross-correlation studies. The success of CHORD depends critically upon the level of redundancy achieved in the array, and my group focuses on developing precision hardware and software tools to ensure that CHORD can deliver its science.

Drones and ground-penetrating radar

One of the greatest challenges in precision low-frequency radio observations is characterizing the on-sky response of the instrument, or beam pattern. Many of our instruments are stationary and unable to actively scan celestial sources. To address the beam mapping challenge, my group is developing a custom-built drone that will fly a radio transmitter above our instruments. For some of our instruments (MIST, in particular), the on-sky beam response depends sensitively upon the electromagnetic properties of the underlying soil. My group is therefore also developing drone-based ground-penetrating radar hardware to rapidly characterize soil properites. This radar instrumentation will also be valuable for glaciology research that is co-located with our work in the high Arctic.

Former students/postdocs and their subsequent positions