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arXiv · 2601.21627

Galaxy-Galaxy Blending in SPHEREx Survey Data

Kim Dachan·Hyunmi Song·Yigon Kim·Minjin Kim·Hyunjin Shim·Dohyeong Kim·Yongjung Kim·Bomee Lee·Jeong Hwan Lee·Woong-Seob Jeong·Yujin Yang
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Abstract

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\farcs2, 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 $\sim0.7\%$ 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 $\sim7$--$9\%$ in the deep survey area around the ecliptic poles, where the depth reaches $\sim22$ 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 $K_s$-band for the source detection, the blending fractions determined in this study should be regarded as lower limits.

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Kim Dachan, Hyunmi Song, Yigon Kim, Minjin Kim, Hyunjin Shim, Dohyeong Kim, Yongjung Kim, Bomee Lee, Jeong Hwan Lee, Woong-Seob Jeong, Yujin Yang. 2026-01-29. Galaxy-Galaxy Blending in SPHEREx Survey Data. https://arxiv.org/abs/2601.21627

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