Unbiased Cosmological Parameter Estimation from Emission Line Surveys
  with Interlopers
  The galaxy catalogs generated from low-resolution emission line surveys often
contain both foreground and background interlopers due to line
misidentification, which can bias the cosmological parameter estimation. In
this paper, we present a method for correcting the interloper bias by using the
joint-analysis of auto- and cross-power spectra of the main and the interloper
samples. In particular, we can measure the interloper fractions from the
cross-correlation between the interlopers and survey galaxies, because the true
cross-correlation must be negligibly small. The estimated interloper fractions,
in turn, remove the interloper bias in the cosmological parameter estimation.
For example, in the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX)
low-redshift ($z<0.5$) [O II] $\lambda3727${\AA} emitters contaminate
high-redshift ($1.9<z<3.5$) Lyman-$\alpha$ line emitters. We demonstrate that
the joint-analysis method yields a high signal-to-noise ratio measurement of
the interloper fractions while only marginally increasing the uncertainties in
the cosmological parameters relative to the case without interlopers. We also
show the same is true for the high-latitude spectroscopic survey of Wide-Field
Infrared Survey Telescope (WFIRST) mission where contamination occurs between
the Balmer-$\alpha$ line emitters at lower redshifts ($1.1<z<1.9$) and Oxygen
([O III] $\lambda5007${\AA}) line emitters at higher redshifts ($1.7<z<2.8$).
