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

TL;DR

This study measures dust in galactic halos using magnitude shifts in KiDS Data Release 4, confirming the presence of extended baryonic halos enriched with gas and dust, and demonstrating a novel methodology for such measurements.

Contribution

It introduces a new pipeline to measure halo dust using galaxy-galaxy lensing and magnitude shifts, validated with simulations and applied to KiDS data for the first time.

Findings

Halo and dust masses can be independently recovered.

Optical bands show measurable magnitude shifts due to dust.

Results align with previous studies, confirming extended baryonic halos.

Abstract

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 quantify this effect using multi-band magnitude shifts in the Kilo-Degree Survey (KiDS) Data Release 4, distinguishing it from achromatic magnification. Our pipeline is validated using MICE2 mock catalogues, and we explore 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 $\Delta z_{\mathrm B}\sim0.3$ 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 ($ZYJHK_{\rm s}$). In optical bands ($ugri$), joint analysis constrains halo mass and dust mass to $0.2$ dex and $0.3$ dex, respectively, yielding $M_{\rm dust}=7.24^{+0.52}_{-0.64} \times 10^7\,M_\odot$ and $\log(M_{\rm halo}^{\rm DM}/M_\odot)=12.33^{+0.08}_{-0.04}$. 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.