Reliable Tests of Faint-end UV Luminosity Function in Strong Lensing Fields, and Implications for Wave Dark Matter Models

Galactic luminosity functions (LFs) are one of the most
fundamental observables for testing different cosmological models, including, but not exclusive to, different dark matter models. The abundance of faint galaxies at high redshifts is particularly informative in comparing two mainstream cold dark matter (CDM) models: dark matter as a heavy particle and dark matter as ultralight particles with wave-like properties. To better detect faint galaxies at high redshifts, observations have increasingly turned to massive galaxy cluster fields, where the strong gravitational lensing power allows us to reach 4-5 magnitudes fainter than would otherwise be possible. Nonetheless, reliable faint-end LFs remain hard to obtain in strong lensing fields, with accurately determining galaxy redshifts being the most fundamental challenge. Recently, Shipley et al, 2018 (S18) reported an excess of z~4 galaxies in the Hubble Frontier Fields (HFF) clusters relative to their accompanying blank non-lensing fields, for which no clear explanation has been offered. In this talk, I will demonstrate that the observed excess is the result of strong contamination by the misidentified low-redshift galaxies sharing similar spectral energy distributions as their high-z counterparts, and provide a quantitative estimate of the contamination level. I will also comment on the prospect of individually mitigating the contaminants by combining deep HST+JWST data, and then perform a more reliable test on the faint-end of UV LFs in the HFF cluster fields. From the analysis, we found no evidence of faint-end turnovers in LFs, suggesting the mass of the wave dark matter particle is above 2.97E-22eV at 95% confidence level. This is in contradiction with the favored mass scale of wave dark matter from local observations, and I will discuss how to resolve this discrepancy in the framework where wave dark matter is
composed of multiple ultralight scalar species.