Validation of the DESI 2024 Lyman Alpha Forest BAL Masking Strategy
arxiv(2024)
摘要
Broad absorption line quasars (BALs) exhibit blueshifted absorption relative
to a number of their prominent broad emission features. These absorption
features can contribute to quasar redshift errors and add absorption to the
Lyman-alpha (LyA) forest that is unrelated to large-scale structure. We present
a detailed analysis of the impact of BALs on the Baryon Acoustic Oscillation
(BAO) results with the LyA forest from the first year of data from the Dark
Energy Spectroscopic Instrument (DESI). The baseline strategy for the first
year analysis is to mask all pixels associated with all BAL absorption features
that fall within the wavelength region used to measure the forest. We explore a
range of alternate masking strategies and demonstrate that these changes have
minimal impact on the BAO measurements with both DESI data and synthetic data.
This includes when we mask the BAL features associated with emission lines
outside of the forest region to minimize their contribution to redshift errors.
We identify differences in the properties of BALs in the synthetic datasets
relative to the observational data, as well as use the synthetic observations
to characterize the completeness of the BAL identification algorithm, and
demonstrate that incompleteness and differences in the BALs between real and
synthetic data also do not impact the BAO results for the LyA forest.
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