Correcting for the effects of the point spread function in intra-halo light measurements and application to deep Hyper Suprime-Cam data

Abstract

The intra-halo light (IHL) is the diffuse stellar component that surrounds galaxies, groups, and clusters. Its formation is intimately linked to the hierarchical assembly of the system, making it a key tracer of galaxy evolution. However, the low surface brightness (LSB) of the IHL makes it challenging to detect and also to distinguish from the point spread function (PSF) effect of the telescope. In this paper, we present two independent techniques that, when combined, provide a statistically robust estimation of the IHL component in galaxy groups and clusters. The first technique corrects for the PSF-scattering effect to obtain unbiased LSB measurements, while the second fits an exponential model to the IHL component using a Markov Chain Monte Carlo (MCMC) optimiser algorithm. To test our methodology, we build a set of 5440 Hyper Suprime-Cam Subaru Strategic Program Public Data Release 3 (HSC-SSP PDR3) mock observations of Galaxy And Mass Assembly (GAMA) groups, each containing an IHL component with a flux fraction ($\mathrm{f_{IHL}}$) ranging from 0.01 to 0.5. Our results demonstrate the importance of properly removing the PSF-scattered flux, especially at lower $\mathrm{f_{IHL}}$. Without the PSF correction, our IHL model overestimates the true flux by up to a factor of 100, and the effective radius by up to a factor of 10. Finally, we apply our methodology to real observations and estimate the $\mathrm{f_{IHL}}$ of the GAMA group G400138 using HSC-PDR3 UD data in the $\textit{g,r}$ and $\textit{i}$-bands, finding median IHL fractions of: $\mathrm{f_{g,IHL}}$ $\sim$ 0.19$^{+0.09}_{-0.01}$, $\mathrm{f_{r,IHL}}$ $\sim$ 0.08$^{+0.06}_{-0.02}$ and $\mathrm{f_{i,IHL}}$ $\sim$ 0.06$^{+0.04}_{-0.02}$.