Lyman-alpha forest: Friend or Foe?

Shirley Ho

June 17, 2010

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Abstract: Lyman-alpha forest has undergone many ups and downs in popularity in the field of astrophysics. Is Lyman-alpha forest useful for us? Here, we will discuss two cosmological applications of Lyman Alpha Forest that has never been done before: As a BAO (baryon acoustic oscillations) probe and as a f_nl (primordial non-gaussianities) probe. We present the first simulation of signatures of Baryon Acoustic Oscillations and Primordial Non-gaussianities on Lyman-alpha forest data containing mock quasar sight-lines. We use large dark-matter only simulations onto which we paint the Lyman alpha field using the fluctuating Gunn-Peterson approximation. We argue that this approach should be sufficient for the mean signature on the scales of interest. Our results indicate that Lyman alpha flux provides a good tracer of the underlying dark matter field on large scales and that redshift space distortions are well described by a simple linear theory prescription. We also investigate the effect of a fluctuating photo-ionizing background using a simplified model and show that both the signature of BAO and fnl are not affected by the fluctuating UV background when the amplitude of fluctuation is small.