Abstract
In recent years, the autocorrelation of the Lyman-\alpha forest has been
used to observe the baryon acoustic peak at redshift 2 < z < 3.5 using tens of
thousands of QSO spectra from the BOSS survey. However, the interstellar medium
of the Milky-Way introduces absorption lines into the spectrum of any
extragalactic source. These lines, while weak and undetectable in a single BOSS
spectrum, could potentially bias the cosmological signal. In order to examine
this, we generate absorption line maps by stacking over a million spectra of
galaxies and QSOs. We find that the systematics introduced are too small to
affect the current accuracy of the baryon acoustic peak, but are comparable to
the statistical noise level expected from future surveys such as the Dark
Energy Spectroscopic Instrument (DESI). We outline a method to account for this
with future datasets.
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