The DES project

Ramon Miquel

Since 2005, a group at IFAE, together with a group at ICE (Institut de Ciències de l’Espai), and another at CIEMAT (Centro de Investigaciones Energéticas, Medio Ambientales y Tecnológicas) and Universidad Autónoma de Madrid (UAM), collaborates in the DES (Dark Energy Survey) international project, led by Fermilab (USA). In late 2016 the group joined the Large Survey Synoptic Telescope (LSST), led by SLAC (USA).

INTRODUCTION

The Dark Energy Survey started in 2013 and is the largest photometric galaxy survey ever, having, in six years, imaged 5000 sq. deg. (a full octant of the sky) in five optical and near-infrared bands (grizY) to unprecedented depth (i_AB ~ 24), and measuring the position on the sky, distance and shape of more than 200 million galaxies up to redshift z ~ 1.4. IFAE is a founding member of the collaboration, and designed and produced a large fraction of the readout electronics of the DES camera, DECam. The survey has as its main goal to unveil the nature of the mysterious dark-energy component of the universe that powers its current accelerated expansion.

2023 ACTIVITIES

In 2021, DES presented the cosmological results from the data taken in the first three years of observations (DES-Y3), including more than 100 million distant galaxies, whose location on the sky, redshift, and shape and orientation were carefully measured and calibrated. The next major step will be the publication of the results of the cosmological analyses of the whole six years of observations (DES-Y6), now expected in fall 2024. During 2023, the analysis of the full data set proceeded at an increased pace. IFAE researchers co-lead two of the main DES science working groups: the large-scale structure (LSS) group and the redshifts group. Within the LSS group, the final results containing the Baryon Acoustic Oscillations (BAO) measurements with the full DES data sample are expected for early 2024.

In 2023, a UAB/IFAE researcher led a paper introducing a DES-Y3 high-redshift galaxy sample, and presenting its selection, characterization and clustering properties [C. Sánchez et al. (DES Collaboration) 2023, MNRAS 525, 3896]. The sample includes about 9 million galaxies extending up to redshift 2.5, and the measurement of its clustering in three redshift bins provides cosmological constraints that are complementary, consistent and competitive with those from the fiducial DES-Y3 cosmological analyses. Figure 1 shows the comparison between the determinations of the mean matter density in the universe using two DES-Y3 low-redshift samples and this high-redshift sample, as well as the corresponding redshift bins used, highlighting their agreement and complementarity.

Figure 1: Comparison of the constraints on the parameter combination Omega_m h from galaxy clustering analyses using three different galaxy samples in DES-Y3. The constraints from the high-redshift (high-z) sample are shown in red, while the constraint from the measurement of the Cosmic Microwave Background (Planck 2018) is shown in black. The inset panel on the right depicts the different redshift ranges probed by the three DES-Y3 galaxy samples.