The Impact of Line Misidentification on Cosmological Constraints from Euclid and Other Spectroscopic Galaxy Surveys
Abstract
We perform forecasts for how baryon acoustic oscillation (BAO) scale and redshiftspace distortion (RSD) measurements from future spectroscopic emission line galaxy surveys such as Euclid are degraded in the presence of spectral line misidentification. Using analytic calculations verified with mock galaxy catalogs from lognormal simulations, we find that constraints are degraded in two ways, even when the interloper power spectrum is modeled correctly in the likelihood. First, there is a loss of signaltonoise ratio for the power spectrum of the target galaxies, which propagates to all cosmological constraints and increases with contamination fraction, f _{ c }. Second, degeneracies can open up between f _{ c } and cosmological parameters. In our calculations, this typically increases BAO scale uncertainties at the 10%20% level when marginalizing over parameters determining the broadband power spectrum shape. External constraints on f _{ c } or parameters determining the shape of the power spectrum, for example, from cosmic microwave background measurements, can remove this effect. There is a nearperfect degeneracy between f _{ c } and the power spectrum amplitude for low f _{ c } values, where f _{ c } is not well determined from the contaminated sample alone. This has the potential to strongly degrade RSD constraints. The degeneracy can be broken with an external constraint on f _{ c }, for example, from crosscorrelation with a separate galaxy sample containing the misidentified line or deeper subsurveys.
 Publication:

The Astrophysical Journal
 Pub Date:
 July 2019
 DOI:
 10.3847/15384357/ab22a0
 arXiv:
 arXiv:1811.10668
 Bibcode:
 2019ApJ...879...15A
 Keywords:

 cosmology: observations;
 distance scale;
 largescale structure of universe;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 18 pages, 7 figures, updated to match version accepted by ApJ (extra paragraph added at the end of Section 4.3, minor text edits)