We compute the power spectrum of the Cosmic Microwave Background temperature anisotropies generated by the Intergalactic Medium .
To estimate the electron pressure along the line of sight and its contribution to the Sunyaev-Zeldovich component of the CMB anisotropies , we assume the non-linear baryonic density contrast is well described by a log-normal distribution .
For model parameters in agreement with observations and for an experiment operating in the Rayleigh-Jeans regime , the largest IGM contribution corresponds to scales l \approx 2000 .
The amplitude is rather uncertain and could be as large as 100 - 200 \mu K ^ { 2 } , comparable to the contribution of galaxy clusters .
The actual value is strongly dependent on the gas polytropic index \gamma , the amplitude of the matter power spectrum \sigma _ { 8 } , namely C _ { l } ^ { IGM } \sim ( \gamma ^ { 2 } \sigma _ { 8 } ) ^ { 12 } .
At all redshifts , the largest contribution comes from scales very close to the baryon Jeans length .
This scale is not resolved in numerical simulations that follow the evolution of gas on cosmological scales .
The anisotropy generated by the Intergalactic Medium could make compatible the excess of power measured by Cosmic Background Imager ( CBI ) on scales of l \geq 2000 with \sigma _ { 8 } = 0.9 .
Taking the CBI result as an upper limit , the polytropic index can be constraint to \gamma < 1.5 at 2 \sigma level at redshifts z \sim 0.1 - 0.4 .
With its large frequency coverage , the PLANCK satellite will be able to measure the secondary anisotropies coming from hot gas .
Cluster and Intergalactic Medium contributions could be separated by cross correlating galaxy/cluster catalogs with CMB maps .
This measurement will determine the state of the gas at low and intermediate redshifts .