SYSTEMATIC CONTINUUM ERRORS IN THE Lyα FOREST AND THE MEASURED TEMPERATURE–DENSITY RELATION

Continuum fitting uncertainties are a major source of error in estimates of the temperature-density relation (usually parametrized as a power-law, T ^ - 1) of the inter-galactic medium (IGM) through the flux probability distribution function (PDF) of the Lyman- forest. Using a simple order-of-magnitude calculation, we show that few percent-level systematic errors in the placement of the quasar continuum due to e. g. a uniform low-absorption Gunn-Peterson component, could lead to errors in of order unity. This is quantified further using a simple semi-analytic model of the Lya forest flux PDF. We find that under- (over-) estimates in the continuum level can lead to a lower (higher) measured value of. Within current observational uncertainties, continuum biases double the error in from _ 0. 1 to _ 0. 2 within our model. We argue that steps need to be taken to directly estimate the level of continuum bias in order to make recent claims of an inverted \ more robust.