Talks and presentations

Understanding the CMB: from inhomogeneities to that plot you know

August 28, 2021

Invited lecture, alpha-Cen 2021 Summer School, online conference, Beijing, China

The Cosmic Microwave Background (CMB), the frozen photons from when the Universe was approximately 350 thousand years olf, is a gold mine for cosmologists. We have used it to learn about how the Universe started, what are its components, and how it might end. In this talk, I will give a brief overview of where does the CMB comes from, what makes it special, and how to extract information from it.

Constraining the astrophysics of reionization with DESI

May 01, 2021

Contributed Talk, Guo Shoujing Meeting, Hangzhou, China

The impact of reionization on the Lyman-alpha forest power spectrum has recently been shown to be quite significant even at low redshifts (z~2). This memory of reionization survives cosmological time scales because of i) the patchy nature of reionization and ii) underdense regions (i.e. gas in minivoids) which reionize to high entropy and are later compressed (and heated to even larger temperatures) by shocks from denser regions. This effect opens a novel window into the astrophysics of reionization from the post-reionization Universe, which will become online as soon as DESI achieves the near milestone of the first measurement of the 3D Lyman-alpha power spectrum. Here, we forecast, for the first time, the ability of DESI to extract the astrophysics of reionization from the Lyman alpha forest power spectrum. In particular, we found that the 1-sigma errors are 12.2 and 6.91 for the ionization efficiency and threshold mass, respectively. These errors are competitive (but reasonably larger than) previously forecasted errors on the same parameters by using a mock 1000h observation with HERA and SKA. Furthermore, we demonstrate the previously unforeseen ability of DESI to infer the global reionization history, which is naturally worse compared to instruments designed to probe the Epoch of Reionization. Although the performance of DESI is inferior, the prospect for rich cross-correlations due to different systematics is exciting. Besides, DESI may measure the 3D Lyman-alpha power spectrum before the 21cm power spectrum is measured.

Searching the Cosmos: Ripples from Avant-Garde Cosmological Probes

December 07, 2020

Contributed Talk, alpha-Cen 2020 Annual Meeting, online conference, Beijing, China

I will give a brief overview of my research in the field of cosmology. In particular, I will talk very briefly about my research in Primordial Black Holes as dark matter candidates. Furthermore, I will talk about mu current research program on the thermal fossils from hydrogen reionization, and how their ripples from 12.8 billion years ago can help us learn more about how the Universe transitions from mainly neutral to highly ionized. In addition, I will mention the interesting open questions that require further investigation.

Lyman-alpha forest power spectrum as an emerging window into the epoch of reionization and cosmic dawn

November 01, 2020

Contributed Talk, Guo Shoujing Meeting, Zhuhai, Guangdong, China

During cosmic reionization, the IGM is heated by ultraviolet photons sourced primarily by the first stars and galaxies. This extreme heating leaves an imprint in the IGM via disrupting the neutral gas with the injection of thermal energy. The thermal relics, i.e. the disruption to the temperature-density evolution of the IGM due to this imprint, has been recently shown to survive to lower redshifts than previously thought (z~2). In this talk, I will demonstrate that these thermal relics depend on the astrophysics of reionization, thus they can, theoretically, be used to distinguish between different reionization histories. In the second part of the talk, I will show how these thermal relics in the Lyman-alpha forest power spectrum — currently a broadband systematic effect for the Lyman-alpha community —could potentially become a novel window into the epoch of reionization.

Lyman-alpha forest power spectrum as an emerging window into the epoch of reionization and cosmic dawn

July 06, 2020

Recorded Talk, Sazerac, online conference, Beijing, China

The memory of reionization in the Lya forest was recently shown to survive to lower redshifts than previously thought (z~2). This unconventional result originated from carefully tracking the small-scale structure to below jean mass prior to reionization with high-resolution simulations. As a result, one is able to track the HEMD (High-Entropy, Mean-Density) gas in mini-voids, which takes cosmological timescales to relax into the usual-temperature density relation of the IGM. Here, I will show how the memory of inhomogeneous reionization in the Lya forest power spectra — currently a broadband systematic effect for the Lya forest community- could potentially become a window into the Epoch of Reionization.