# The Effect of Interstellar Absorption on Measurements of the Baryon Acoustic Peak in the Lyman-{\alpha} Forest

## TL;DR

This paper investigates how interstellar absorption lines in the Milky Way might bias measurements of the baryon acoustic peak in the Lyman-alpha forest, finding current effects negligible but potentially significant for future surveys like DESI.

## Contribution

It introduces a method to assess and mitigate interstellar absorption effects on baryon acoustic peak measurements in upcoming large-scale surveys.

## Key findings

- Current interstellar absorption effects are too small to impact existing measurements.
- Future surveys like DESI may need to account for these effects.
- A stacking method was used to generate absorption line maps from over a million spectra.

## Abstract

In recent years, the autocorrelation of the hydrogen 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 might be relevant to future surveys such as the Dark Energy Spectroscopic Instrument (DESI). We outline a method to account for this with future datasets.