In this paper, we review the extended halo material and the circumgalactic medium (CGM), including both dust and gas, and discuss promising science cases that could be realized using the KASI Deep Rolling Imaging Fast Telescope (K-DRIFT). Scattered starlight from cirrus clouds in our Galaxy poses one of the major challenges to studying the low surface brightness features of extragalactic sources. Therefore, it is essential to investigate how to discriminate extragalactic sources from cirrus cloud features. At the same time, interstellar dust clouds themselves are fundamental to understanding dust properties and the interstellar radiation field, both of which are essential for studies of chemical evolution and star formation in our Galaxy. Measuring the reddening of background sources, such as quasars, with K-DRIFT, which benefits from its broad field of view and accurate background subtraction, allows for the effective detection of extended dust in galactic halos, the CGM, and intracluster space. Observations of the Hα emission lines can be used to identify signatures of star formation activity within galaxies, as well as the environmental effects acting on them. Galactic winds driven by active galactic nuclei and starbursts can be traced through Hα emission. Strong ram pressure stripping effectively removes the interstellar medium (ISM) from galaxies. The stripped ISM becomes ionized or dissociated through mixing with the hot intracluster medium (ICM), forming Hα tails. The surface brightness of these Hα tails correlates not only with the presence of star formation in the tails but also the mixing stage of the stripped ISM and ICM. The Hα survey with K-DRIFT will enable the investigation of the evolutionary stages of ram pressure stripped galaxies in cluster environments, as well as the multiphase gas reservoir around galaxies and in the CGM.

Reverberation mapping (RM) is an ecient method to investigate the physical sizes of the broad line region (BLR) and dusty torus in an active galactic nucleus (AGN). The Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer (SPHEREx) mission will provide multi-epoch spectroscopic data at optical and near-infrared wavelengths. These data can be used for RM experiments with bright AGNs. We present results of a feasibility test using SPHEREx data in the SPHEREx deep regions for torus RM measurements. We investigate the physical properties of bright AGNs in the SPHEREx deep eld. Based on this information, we compute the eciency of detecting torus time lags in simulated light curves. We demonstrate that, in combination with complementary optical data with a depth of  20 mag in B􀀀band, lags of  750 days for tori can be measured for more than  200 bright AGNs. If high signal-to-noise ratio photometric data with a depth of  21{22 mag are available, RM measurements are possible for up to  900 objects. When complemented by well-designed early optical observations, SPHEREx can provide a unique dataset for studies of the physical properties of dusty tori in bright AGNs.