The Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer (SPHEREx) will provide all-sky spectral survey data covering optical to mid-infrared wavelengths with a spatial resolution of 6.′′2, which can be widely used to study galaxy formation and evolution. We investigate the galaxy-galaxy blending in SPHEREx datasets using the mock galaxy catalogs generated from cosmological simulations and observational data. Only ∼0.7% of the galaxies will be blended with other galaxies in all-sky survey data with a limiting magnitude of 19 AB mag. However, the fraction of blended galaxies dramatically increases to ∼7–9% in the deep survey area around the ecliptic poles, where the depth reaches ∼22 AB mag. We examine the impact of the blending in the number count and luminosity function analyses using the SPHEREx data. We find that the number count can be overestimated by up to 10–20% in the deep regions due to the flux boosting, suggesting that the impact of galaxy-galaxy blending on the number count is moderate. However, galaxy-galaxy blending can marginally change the luminosity function by up to 50% over a wide range of redshifts. As we only employ the magnitude limit at Ks-band for the source detection, the blending fractions determined in this study should be regarded as lower limits.

Introduction
Data and Method
    Cosmological Simulation
    Deep Survey Data
    Comparison between Simulation and Survey Data
    Measurements of Blending Fraction
Result
    Blending in SPHEREx All-Sky Survey
    Blending in SPHEREx Deep Survey
Implication
    Number Count
    Luminosity Function
Summary and Overlook
Acknowledgments
References

• Yongjung Kim(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea)
• Bomee Lee(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea)
• Jeong Hwan Lee(Department of Astronomy and Atmospheric Sciences, Kyungpook National University, Daegu 41566, Republic of Korea, The Center for High Energy Physics, Kyungpook National University, Daegu 41566, Republic of Korea)
• Woong-Seob Jeong(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea)
• Yujin Yang(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea, University of Science and Technology, Daejeon 34113, Republic of Korea)
• Dohyeong Kim(Department of Earth Sciences, Pusan National University, Busan 46241, Republic of Korea)
• Hyunjin Shim(Department of Earth Science Education, Kyungpook National University, Daegu 41566, Republic of Korea)
• Minjin Kim(Department of Astronomy and Atmospheric Sciences, Kyungpook National University, Daegu 41566, Republic of Korea) Corresponding author
• Yigon Kim(Department of Astronomy and Atmospheric Sciences, Kyungpook National University, Daegu 41566, Republic of Korea)
• Hyunmi Song(Department of Astronomy and Space Science, Chungnam National University, Daejeon 34134, Republic of Korea) Corresponding author
• Kim Dachan(Department of Astronomy and Space Science, Chungnam National University, Daejeon 34134, Republic of Korea)