Constraining the thermal history of the warm-hot intergalactic medium

¹ Dipartimento di Astronomia e Scienza dello Spazio, Largo E. Fermi 2, 50125 Firenze, Italy e-mail: zappacos@nabhas.ps.uci.edu
² Osservatorio Astrofisico di Arcetri Largo E. Fermi 5, 50125 Firenze, Italy
³ Max-Planck-Institut für extraterrestrische Physik, Giessenbachstraße, 85748 Garching, Germany
⁴ Istituto di Radioastronomia, Sezione di Firenze – CNR Largo E. Fermi 5, 50125 Firenze, Italy
⁵ SISSA/International School for Advanced Studies via Beirut, 4 34014 Trieste, Italy

Received: 2 March 2004
Accepted: 22 December 2004

Abstract

We have identified a large-scale structure traced by galaxies at , within the Lockman Hole, by means of multi-object spectroscopic observations. By using deep XMM images we have investigated the soft X-ray emission from the Warm-Hot Intergalactic Medium (WHIM) expected to be associated with this large-scale structure and we set a tight upper limit to its flux in the very soft 0.2–0.4 keV band. The non-detection requires the WHIM at these redshifts to be cooler than 0.1 keV. Combined with the WHIM emission detections at lower redshift, our result indicates that the WHIM temperature rapidly decreases with redshift, as expected in popular cosmological models.