Tag Archives: Dark Energy Survey Year 1 Results: Cosmological Constraints from Cosmic Shear

Dark Energy Survey Reports

The Universe we live in has a lot of matter and energy in it. We can see and measure matter and energy, but it is now clear that we can see only about 2% of what is there. We can tell that there is a lot of matter and energy out there that we simply cannot measure, it is called Dark Matter and Dark Energy. The universe is about 26% Dark Matter, and about 70% Dark Energy. What is all this Dark stuff? No one knows, but we sure need to find out, right?

Since 2013, a global collaboration of astronomers has been systematically surveying the sky to confirm the existence and assess the amount of Dark Energy. The Dark Energy Survey  is a heroic project, using a large telescope facility in the high desert of the Andes to spot and measure supernova. A massive amount of data is collected each night and stored in digital images.

The data is transferred through an optic fiber channel that runs up the spine of the America’s to Illinois, right down the street from where I sit. The data is organized into the archive, which is analyzed by science teams around the globe. It takes hours to transfer each night’s (irreplaceable) data to the data center, every day.

This summer, the DES is releasing a burst of ten papers to report the first year’s results [1]. (It has taken several years to analyze the first year’s data.  Unlike Hollywood movies, real life data analysis is hard work and takes time.)

The details of these analyses are largely beyond my own understanding, though I understand very well the scale of the computation and the system engineering this has required: this project is trying to measure the whole sky, and is looking for brief events that must be zoomed into. “Challenging” doesn’t begin to describe it.

Glancing through the papers, it is clear that this massive effort is yielding pretty solid results. To pick one paper arbitrarily, “Dark Energy Survey Year 1 Results: Cosmological Constraints from Cosmic Sheardiscusses one important thrust of the research, attempting to document the actual expansion of the Universe, and to improve estimates for the infamous cosmological constant that represents the “anti gravity” effects of Dark Matter and Energy.

The report itself is attributed to 135 authors from 51 institutions, and is based on observations of 36 million galaxies. The bulk of the paper describes the (complex) methods used to assemble and interpret the observational data. The results are close to earlier estimates of cosmological parameters from much smaller datasets. Results from other studies in this batch combine with these to tighten the estimated bounds on these values.

It’s all overwhelming, but as the authors dryly note, we really have no understanding of these fundamental facts yet. These are deep and fundamental mysteries, and we really need to know. The DES is an important step in understanding our universe.

Despite the overall success of modern cosmological study, however, there remain several fundamental mysteries that enter the model as purely phenomenological parameters. These include our lack of understanding of the value of the cosmological constant or of any motivation for a different driver of cosmic acceleration.” (p.2)

  1. The Dark Energy Survey. DES Year 1 Cosmology Results: Papers. 2017, https://www.darkenergysurvey.org/des-year-1-cosmology-results-papers/.
  2. The Dark Energy Survey. Home – The Dark Energy Survey. 2017, https://www.darkenergysurvey.org/.
  3. M. A. Troxel, N. MacCrann, J. Zuntz, T. F. Eifler, E. Krause, S. Dodelson, D. Gruen, J. Blazek, O. Friedrich, S. Samuroff, J. Prat, L. F. Secco, C. Davis, A. Ferté, J. DeRose, A. Alarcon, A. Amara, E. Baxter, M. R. Becker, G. M. Bernstein, S. L. Bridle, R. Cawthon, C. Chang, A. Choi, J. De Vicente, A. Drlica-Wagner, J. Elvin-Poole, J. Frieman, M. Gatti, W. G. Hartley, K. Honscheid, B. Hoyle, E. M. Huff, D. Huterer, B. Jain, M. Jarvis, T. Kacprzak, D. Kirk, N. Kokron, C. Krawiec, O. Lahav, A. R. Liddle, J. Peacock, M. M. Rau, A. Refregier, R. P. Rollins, E. Rozo, E. S. Rykoff, C. Sánchez, I. Sevilla-Noarbe, E. Sheldon, A. Stebbins, T. N. Varga, P. Vielzeuf, M. Wang, R. H. Wechsler, B. Yanny, T. M. C. Abbott, F. B. Abdalla, S. Allam, J. Annis, K. Bechtol, A. Benoit-Lévy, E. Bertin, D. Brooks, E. Buckley-Geer, D. L. Burke, A. Carnero Rosell, M. Carrasco Kind, J. Carretero, F. J. Castander, M. Crocce, C. E. Cunha, C. B. D’Andrea, L. N. da Costa, D. L. DePoy, S. Desai, H. T. Diehl, J. P. Dietrich, P. Doel, E. Fernandez, B. Flaugher, P. Fosalba, J. García-Bellido, E. Gaztanaga, D. W. Gerdes, T. Giannantonio, D. A. Goldstein, R. A. Gruendl, J. Gschwend, G. Gutierrez, D. J. James, T. Jeltema, M. W. G. Johnson, M. D. Johnson, S. Kent, K. Kuehn, S. Kuhlmann, N. Kuropatkin, T. S. Li, M. Lima, H. Lin, M. A. G. Maia, M. March, J. L. Marshall, P. Martini, P. Melchior, F. Menanteau, R. Miquel, J. J. Mohr, E. Neilsen, R. C. Nichol, B. Nord, D. Petravick, A. A. Plazas, A. K. Romer, A. Roodman, M. Sako, E. Sanchez, V. Scarpine, R. Schindler, M. Schubnell, M. Smith, R. C. Smith, M. Soares-Santos, F. Sobreira, E. Suchyta, M. E. C. Swanson, G. Tarle, D. Thomas, D. L. Tucker, V. Vikram, A. R. Walker, J. Weller, Y. Zhang and (DES Collaboration), Dark Energy Survey Year 1 Results: Cosmological Constraints from Cosmic Shear. The Dark Eneergy Survey, 2017. http://www.darkenergysurvey.org/wp-content/uploads/2017/08/y1a1_cosmic_shear-1.pdf