The Evolution of the Effective Equation of State of the IGM

Abstract

We develop a method to extract the "effective equation of state" of the intergalactic medium from the doppler b parameter distribution of the low-density Lyman-alpha forest. We test the method on numerical simulations and then apply it to published observations of the Lyman-alpha forest at redshifts z from 0 to 4. We find that the effective equation of state is close to isothermal at redshift z=3, indicating that a second reheating of the IGM took place at z=3. This reheating can plausibly be identified with the reionization of HeII observed to occur at z about 3.

Revised version accepted for publication in ApJ. Vol. 534 May 1, 2000 (in press); 32 pages, 13 figures, 7 tables

References in corpus (6)

• Cosmic Chemical Evolution
• Measuring the equation of state of the intergalactic medium
• The Metagalactic Ionizing Radiation Field at Low Redshift
• Compton Heating of the Intergalactic Medium by the Hard X-ray Background
• KECK HIRES Spectroscopy of APM 08279+5255
• The Lyman-alpha Forest and Heavy Element Systems of GB1759+7539

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