Overview

One of the fundamental issues in astrophysical cosmology is to understand the formation and evolution of structures on various scales from the early Universe up to present time. EDGE will trace the cosmic history of the baryons, a key issue in the CV program (question 4.2), by measuring three tracers of cosmic structures:

Cosmic filaments

• Detect the largest reservoir of baryons from z~1 to the present time, predicted to reside in the Warm-Hot Intergalactic Medium (WHIM) by measuring densities down to 10-5 cm-3 (~30 times smaller than currently probed within clusters of galaxies)

• Place constraints on the interplay between diffuse baryons and star formation

Clusters of galaxies

• Trace the evolution and physics of clusters out to their formation epoch (z>1)

• Measure the thermodynamical and chemical proper¬ties of a fair sample out to the virial radius, a funda¬mental step to qualify clusters as cosmological probes and for constraining their evolution through the link with the WHIM

Gamma-Ray Bursts

• Study the evolution of massive star formation using Gamma-Ray Bursts (GRBs) to trace their explosions back to the early epochs of the Universe (z > 6)

• Measure the metals in the host galaxies of GRBs and the explosive enrichment in their close envi¬ron¬ment out to z>6

This is illustrated in the figure below where the unique capabili¬ties of EDGE are shown.

In addition EDGE, with its unprecedented observa¬tional capabilities, will provide key results for a number of Cosmic Vision related science issues (questions 4.1, 4.3, 3.3, 3.2, 2.1) including: the study of feedback mechanisms into the Interstellar Medium (Supernova Remnants, galaxy/Active Galactic Nuclei outflows), con¬straints on the Dark Matter and Dark Energy content of the Universe (through clusters and GRBs), equation of state of the densest matter (neutron stars), GRB physics, upper limits on light dark matter particles, accurate measurement of the geometry of space-time by measur¬ing X-ray afterglows of black hole mergers detected through gravitational waves, Active Galactic Nuclei and stellar population surveys, and Solar System physics.

Science methods and uniqueness

Several outstanding contributions to the study of the cosmic history of baryons are unique to X-ray astronomy. EDGE is specifically designed to exploit the X-ray band¬pass to investigate:

• Large scale, low density baryonic structures, including the WHIM and the outskirts of clusters of galaxies, which are visible only in X-rays. EDGE is uniquely posi-tioned to observe them by high resolution spectroscopy and imaging. It will use GRBs as bright backlight bea-cons.

• The early populations of massive stars that ignited in the Universe and cannot be observed individually by any planned facility. EDGE will observe their explo¬sive death and reconstruct the exact epoch of the first sig-nificant Fe enrichment, which is expected to sig¬nal the very first massive star explosions.