Following Bi & Davidsen ( 1997 ) , we perform one dimensional semi analytic simulations along the lines of sight to model the intergalactic medium ( IGM ) .
Since this procedure is computationally efficient in probing the parameter space – and reasonably accurate – we use it to recover the values of various parameters related to the IGM ( for a fixed background cosmology ) by comparing the model predictions with different observations .
For the currently favoured LCDM model ( \Omega _ { m } = 0.4 , \Omega _ { \Lambda } = 0.6 and h = 0.65 ) , we obtain , using statistics obtained from the transmitted flux , constraints on ( i ) the combination f = ( \Omega _ { B } h ^ { 2 } ) ^ { 2 } / J _ { -12 } , where \Omega _ { B } is the baryonic density parameter and J _ { -12 } is the total photoionisation rate in units of 10 ^ { -12 } s ^ { -1 } , ( ii ) temperature T _ { 0 } corresponding to the mean density and ( iii ) the slope \gamma of the effective equation of state of the IGM at a mean redshift z \simeq 2.5 .
We find that 0.8 < ( T _ { 0 } / 10 ^ { 4 } { K } ) < 2.5 and 1.3 < \gamma < 2.3 .
while the constraint obtained on f is 0.020 ^ { 2 } < f < 0.032 ^ { 2 } .
A reliable lower bound on J _ { -12 } can be used to put a lower bound on \Omega _ { B } h ^ { 2 } , which can be compared with similar constraints obtained from Big Bang Nucleosynthesis ( BBN ) and CMBR studies .
We find that if J _ { -12 } > 1.2 , the lower bound on \Omega _ { B } h ^ { 2 } is in violation of the BBN value .