Pushing HST to the limit. Detection completeness and morphology robustness of faint galaxies in the Extended Groth Strip field

Abstract

Reliable catalogs at the faint limit are essential for statistical studies of galaxy evolution. However, detection and structural measurements of faint galaxies remain challenging. We evaluate detection completeness and structural parameter uncertainties of faint galaxies in the CANDELS/EGS field using mock images and observations from the Space Telescope (HST) and Space Telescope (JWST). The framework is also applicable to large high-redshift surveys, including , the upcoming Chinese Space Station Survey Telescope (CSST), and the Space Telescope. Hubble James Webb Euclid Nancy Grace Roman We detected sources in the EGS F160W mosaic using a 1.5σ threshold and quantified detection completeness and false-detection rates with realistic mock images. Mock galaxy-pair tests assessed blending effects on both source detection and structural measurements in fitting. In addition, the overlap with CEERS observations was used to derive an empirical criterion for separating true faint galaxies from fake detections using HST photometry. We identify 72,467 sources in the CANDELS/EGS field, including 57,444 fainter than 25 mag in F160W. Detection completeness exceeds 95% for objects brighter than 25 mag but declines to $<50%$ beyond 27 mag (with a false detection rate gtrsim50%). Structure parameters from single modeling are reliable down to m_ =25 mag. For galaxies at 25<m_ <27 mag, systematic biases in the H H index reach Δ n ) introduce measurable biases in recovered while Δ q decreases from approximately -0.03 to -0.27. Close companions (∼ 0.3 arcsec magnitudes and shapes, while the impact becomes negligible at larger separations. An empirical criterion based on m_ F814W-F160W color, R_50, and z_ separates true faint galaxies from false detections, reaching 72% completeness and 84% purity. It yields a final catalog of 59,646 objects, which is consistent with previous CANDELS measurements at bright magnitudes while reaching fainter limits.