Scientific Goals

Cosmic filaments

Thanks to its unique observational capabilities, EDGE will be able to study the role of the baryons in of the Universe from the early epochs, through Gamma-Ray Burst (GRB) explosions, via the period of cluster formation, down to very low redshifts.

High resolution spectroscopy of bright, distant continuum sources in the soft X-ray band will reveal the metals in the WHIM. We will use bright Gamma-ray Burst afterglows as our ‘backlight’ sources, or beacons, since they are an unlim­ited ‘renewable resource’, and occur out to very high redshifts (z > 7).

Complementary to the absorption spectroscopy, we will image the WHIM and the outskirts of clusters in the emission lines of H- and He-like C, O, and Ne, and the L shell lines of Fe.

Emission spectrum of a 4 arcmin2 area (top) and ab­sorption (bottom) spectrum of the same region of the sky as measured by EDGE. In the top panel the emission of two redshifted components is shown in black, whereas the emission of the Galactic foreground is shown in purple. In the bottom panel the spectrum of the same systems is shown but now in absorp­tion using a bright GRB as a beacon.		Sky distribution of O VII emission relative to that of the gas, showing the simulated gas particles (black) and 5 s detections of gas with overdensity d > 1000 (red), and with d < 1000 (purple). Area shown is 2.1 x 2.1 deg2 centered on z=0.2 and for a 1 Ms observation.

Clusters of galaxies

Clusters of galaxies are the largest structures to have decoupled from the Hubble flow. While still carrying the imprints of primordial cosmological fluctuations they are undergoing processes where prodigious amounts of energy, second only to those associated to the Big Bang, are being converted from one form to another.

We will measure the surface brightness, tem­pera­ture and metal abundance out to the virial radius for an adequate sample of clusters, with medium spectral resolution imaging, providing temperature measurements from the thermal continuum and iron abundance meas­urements from the Fe L-shell blend. With a high spectral resolution, lower angular resolution imager, we can measure detailed emission line spectra out to almost as far, thus providing constraints on bulk motion and turbulence, and accurate abun­dances for the low-Z elements, mostly O, as well as for Fe.

The vast improvement between XMM-Newton (left) and EDGE (right), mainly due to the better background and long observation times. The cir­cle gives R200.		Typical ICM temperature profiles for current mis­sions and expected EDGE measurements. The model (solid line) is from a hydrodynamical calculation of a massive system (Mvirial= 2.1 1015 M8, Roncarelli et al., 2006). For this model R500~0.65 R200.
Cumulative redshift distribution of EDGE surveys compared with the predictions for eROSITA. These predictions are based on the halo mass func­tion computed for the best-fit WMAP-3yr cosmology and by extrapolating the evolu­tion of the relation between mass and observed X-ray luminosity at z <0.6 (e.g. Vikhlinin et al. 2003; Lumb et al. 2004).		Cumulative redshift distribution for EDGE surveys where the X-ray temperature is measured with at the most 30 percent error at a 90 percent confidence level.

Gamma-Ray Bursts

It is well established that most long-duration gamma-ray bursts (GRBs) are caused by the explosive deaths of massive stars and, due to their enormous brightness and distances they can be seen throughout the observable Universe. Being characterized by copious amounts of penetrating high energy photons, they can probe the regions of the Universe beyond z>6, which are not accessible in the optical band.

The goal is to gather a sample of about 150 GRB afterglows (in 3 years) with 0.3-10 keV fluences >10^–6 erg cm^-2. This requires to localize and follow up about 250 GRBs. For this sample we will measure the redshift, charac­terize the star formation, and study the history of metals in both the close GRB environment and its host galaxy up to high-z by X-ray spectroscopy. Fast dissemination of the GRB coordinates, and particularly the early determination of the X-ray redshift measured by EDGE, will allow the community to carry out optical and IR follow up spectroscopy of the most interesting (i.e. high z) events.

Spectrum of a z=7 GRB afterglow with a fluence of      4  10-6 erg cm-2 (0.3-10 keV), a column density of     NH of 5 1022 cm2 and an abundance of 1/3 solar. Edges produced by Si, S, and Fe are clearly detected. Based on these edges the redshift and column densities can be accurately determined (Dz≈0.02).		Spectrum of a GRB at z=1, NH (host galaxy) of              3 1021 cm-2, T=2 104K, 0.3-10 keV fluence 4 10-6 erg cm-2, integration time 50 ks.