Speaker
Description
Galaxies are embedded within larger halos of (predominantly) dark matter. Although gravitational lensing studies have provided a comprehensive understanding of the distribution of dark matter in these halos, their baryonic content remains less well understood.
One key baryonic component in galactic halos is dust, which can be transported from the interstellar medium to the circumgalactic medium through various mechanisms. In this work, we aim to investigate the amount and distribution of dust in galactic halos by measuring shifts in the observed magnitudes of background galaxies.
Dust particles preferentially absorb and scatter shorter-wavelength light, leading to a reddening of the spectra of background sources. In this study, we investigate this reddening effect by quantifying the dust-induced shift in the apparent magnitudes of galaxies, in multiple photometric bandpasses, with the Kilo-Degree Survey (KiDS) Data Release 4 (DR4). Magnification, which is an achromatic effect, is expected to produce consistent signals in the absence of dust extinction. Our analysis, following previous work, explores the measurement of extinction imprinted upon this otherwise achromatic signal. We explore potential systematic effects in magnification and reddening measurements when using galaxies used as background sources, in contrast to the use of quasars in previous work. We validate our measurement pipeline using mock galaxy catalogues from the MICE2 simulation suite, and subsequently perform an initial measurement of circumgalactic extinction using data from the KiDS DR4.
We validate our analysis pipeline on simulations, recovering input halo and dust masses using galaxy-galaxy lensing, magnification, and extinction, both independently and under joint analyses. We find that, by excluding red galaxies from the source sample, one can suppress systematic effects introduced by galaxy clustering. Additionally, applying specific brightness cuts is crucial to mitigate overlap between lens and source redshift distributions, caused by imprecise line-of-sight binning using photometric redshift estimates. Applying our pipeline to observational data from KiDS, we first validate the achromaticity of our magnification measurements in the absence of extinction, by computing the magnification signal in five near-infrared filters ($ZYJHK_{\rm s}$). In the infrared, our magnification measurements produce constraints of similar accuracy and precision as those measured using galaxy-galaxy lensing (GGL). In a joint analyses of GGL and magnification, now in four optical bands ($ugri$), we constrain the joint probability of halo mass and dust mass at $0.2$dex and $0.4$dex precision, respectively. We measure a dust mass of $6.03^{+0.73}{-0.78} \times 10^7,M\odot$ in the circumgalactic medium, and a mean halo mass of $\log\left(M_{\rm halo}^{\rm DM}/M_\odot\right)=12.39^{+0.04}_{-0.04}$. These measurements are consistent with results from previous studies. Our results represent the first successful measurement of magnification and halo extinction with KiDS data, and confirm previous measurements of using SDSS quasars. These observations provide further evidence that galaxies typically reside in extended baryonic halos, populated by gas and dust ejected by energetic feedback processes.
