Cosmology with DESI Emission-Line Galaxies

The Growth of Structure Tension

The growth of structure, or $\sigma_8$, refers to how much matter clumps in a sphere of $8$ megaparsec at redshift $0$. This is an important cosmological parameter because its value signifies how the dark sector affects the large-scale structure. For example, the more dark energy density there is in the Universe, the lower is the value of $\sigma_8$ because matter will have less ability to clump or cluster together over time.

What’s interesting is that when we measure $\sigma_8$ using data from recent Universe and compare that value with the value derived from data based on early Universe, they persistently disagree with each other at $2 - 3 \sigma$ level. While this level of disagreement does not necessarily mean the discovery of ``new physics”, it is nevertheless puzzling as to what may be going on.

Combined with the more well-known Hubble tension, the $\sigma_8$ tension could potentially point to the existence of not-yet-understood galaxy physics, or perhaps more excitingly, a hint of “new fundamental physics”.

Dark Energy Spectroscopic Instrument

The Dark Energy Spectroscopic Instrument (DESI) is an ongoing spectroscopic galaxy survey that aims to observe $\sim 50$ million objects to generate the most precise $3$-D map of the Universe to-date. In this effort, DESI will be looking back as far as $~10$ billion years ago, or when the Universe was just $\sim 3$ billion years old.

Emission-Line Galaxies (ELGs)

Emission-Line Galaxies form the largest tracer class within DESI, approximately $\sim 20$ million ELGs will be observed over $5$ years. These star-forming galaxies are numerous in the redshift range $0.6 < z < 1.6$, making them ideal to study the early Universe.

Contributions so far

Paper 1: How do we select ELGs?

DESI Year 1 Cosmology Catalogue
Final ELG Target Selection
Target Selection Pipeline for DESI
Preliminary ELG Target Selection
Validation of ELG Target Selection Strategies

Paper 2: How does ELG imaging systematics affect cosmological inferece?

Imaging systematics biases ELG auto-power spectrum

Paper 3: DESI Imaging ELGs X Planck CMB Lensing

In collaboration-wide review. Coming out soon with exciting results!