Arnab Chakraborty · Dunlap Fellow

The 21 cm line is the only practical probe that can map cosmic history in three dimensions from the present day back to z ∼ 30. It reaches into the “cosmic desert” that lies between the Cosmic Microwave Background at z ∼ 1100 and the optical galaxy surveys that stop near z ∼ 2, covering the Dark Ages, Cosmic Dawn, reionization, and the era when dark energy took over the expansion.

Getting there is hard for one reason above all others. Galactic and extragalactic foregrounds are four to five orders of magnitude brighter than the signal, and they are coupled to a chromatic instrument response through the primary beam, mutual coupling between elements, and time- and frequency-dependent gains. Most of my work is developing analysis tools that separates the two: calibration, RFI mitigation, beam characterisation, foreground filtering, and the validation framework that decides whether a detection is real rather than an artefact.

Some of the broad questions my research aims to address are:

Is dark energy a cosmological constant, or is it evolving? Can measurement of BAO using 21 cm line intensity mapping test this independently of optical surveys, and place competitive bounds on the sum of the neutrino masses?
How did first stars and galaxies formed? What is the reionization history and how did it progress? When reionization end? Can we use the 21 cm Forest as a complementary probe to EoR using upcoming SKA and pathfinder telescopes like uGMRT?
How do galaxies acquire and process the gas that fuels their star formation across cosmic time? How much cold neutral gas did galaxies hold at cosmic noon, and what regulated it? The 21 cm emission from neutral hydrogen is the direct tracer of star-formation inside a galaxy and also it's evolution. How we can probe this using current and upcoming telescopes?
How do you recover a signal buried far beneath the systematics that produce it, and how do you know when you have?

Background

Before Toronto I was a Trottier Chair Fellow in the Department of Physics and the Trottier Space Institute at McGill University (2021–2026), where I joined CHIME and led the auto-power spectrum detection. I completed my PhD at IIT Indore in 2021, where I built the wideband calibration, imaging and power-spectrum pipeline for the upgraded GMRT and used it to place the first post-upgrade constraints on the post-reionization 21 cm signal. I lead the Akashganga group within SKA-India and am a member of the SKAO Epoch of Reionization and Cosmology science working groups.

I am always glad to hear from students and potential collaborators. The best way to reach me is by email.