John Moustakas

Observational Cosmology

Although there were provocative hints throughout the second half of the twentieth century, it was not until the late 1990s that astronomers found definitive evidence that the expansion of the universe is accelerating, driven by an unknown phenomenon now called dark energy. Understanding the nature of dark energy remains one of the most important open problems in all of physics.

I have been a member of the Dark Energy Spectroscopic Instrument (DESI) collaboration since 2014. DESI is building the most precise three-dimensional map of the universe ever made by measuring spectroscopic redshifts for tens of millions of galaxies and quasars.

Highlights

Two broad wedges made of thousands of tiny dots in shades of blue on a black background. A magnified inset reveals a filamentary network of galaxies.
The map from five years of DESI observations; each dot is a galaxy or quasar. Credit: Claire Lamman/DESI collaboration.

The largest three-dimensional map of the universe

DESI measures the redshifts of tens of millions of galaxies and quasars, chosen from the DESI Legacy Imaging Surveys by a target-selection pipeline that I helped build (Myers et al. 2023). The imprint of baryon acoustic oscillations in this map measures the expansion history of the universe, and the first DESI results hint that dark energy may evolve with time.

Selected Papers

  1. The Target-selection Pipeline for the Dark Energy Spectroscopic Instrument
    A. Myers, J. Moustakas, S. Bailey et al. 2023, AJ, 165, 50 ADS arXiv DOI
  2. Target Selection and Validation of DESI Emission Line Galaxies
    A. Raichoor, J. Moustakas, J. Newman et al. 2023, AJ, 165, 126 ADS arXiv DOI

DESI Collaboration Papers

  1. DESI 2024 VI: cosmological constraints from the measurements of baryon acoustic oscillations
    A. Adame, J. Aguilar, (J. Moustakas, 118th coauthor) et al. 2025, JCAP, 2025, 021 ADS arXiv DOI
  2. DESI 2024 VII: cosmological constraints from the full-shape modeling of clustering measurements
    A. Adame, J. Aguilar, (J. Moustakas, 126th coauthor) et al. 2025, JCAP, 2025, 028 ADS arXiv DOI
  3. Validation of the Scientific Program for the Dark Energy Spectroscopic Instrument
    DESI Collaboration, A. Adame, (J. Moustakas, 172nd coauthor) et al. 2024, AJ, 167, 62 ADS arXiv DOI
  4. Overview of the Instrumentation for the Dark Energy Spectroscopic Instrument
    DESI Collaboration, B. Abareshi, (J. Moustakas, 168th coauthor) et al. 2022, AJ, 164, 207 ADS arXiv DOI
  5. The DESI Experiment Part I: Science,Targeting, and Survey Design
    DESI Collaboration, A. Aghamousa, (J. Moustakas, 185th coauthor) et al. 2016 (arXiv:1611.00036) ADS arXiv DOI
  6. The DESI Experiment Part II: Instrument Design
    DESI Collaboration, A. Aghamousa, (J. Moustakas, 185th coauthor) et al. 2016 (arXiv:1611.00037) ADS arXiv DOI