Measurement of circumgalactic extinction in the Kilo-Degree Survey's Data Release 4

Galaxies reside in extended dark matter halos, but their baryonic content, especially dust, remains less well understood. We aim to investigate the amount and distribution of dust in galactic halos by measuring shifts in the observed magnitudes of background galaxies. Dust absorbs and scatters shorter-wavelength light, reddening background sources. We quantified this effect using multi-band magnitude shifts in the Kilo-Degree Survey (KiDS) Data Release 4, distinguishing it from achromatic magnification. Our pipeline was validated using MICE2 mock catalogues, and we explored potential systematics arising from galaxy selection, in contrast to previous quasar-based studies. Simulations show that input halo and dust masses can be recovered independently and jointly using galaxy-galaxy lensing (GGL) and magnitude shifts. A minimum redshift separation of Δ z_ B and brightness cuts are required to minimise overlap effects and the effects of photometric noise, respectively. Applying our pipeline to KiDS data, we first confirm the achromaticity of magnitude shifts in five near-infrared filters (ZYJHK_̊m s). Joint analysis of GGL and multi-band magnitude shift (ugriZYJHK_̊m s) constrains halo mass and dust mass to 0.2 dex and 0.3 dex, respectively, yielding M_ ̊m dust =7.24^ +0.52 _ -0.64 10^7,M_⊙ and łog(M_ ̊m halo ^ ̊m DM /M_⊙)=12.33^ +0.08 _ -0.04 . These results agree with previous studies and represent the first successful measurement of magnitude shifts and halo extinction with KiDS, confirming that galaxies reside in extended baryonic halos enriched by gas and dust from feedback processes.