Spectral Stacking of deep MeerKAT data: search Neutral Hydrogen Clouds in the Inter-Galactic Medium of the Local Universe

The investigation of the large-scale distribution of neutral hydrogen (HI) within the cosmic web is fundamental in comprehending the intricate processes governing galaxy formation and evolution. Evidently, the star formation rate observed throughout cosmic history necessitates galaxies to continually replenish their gas reservoir. Theoretical simulations predict that this replenishment primarily occurs via accretion of pristine gas situated within the Inter Galactic Medium (IGM). Nonetheless, the detection and comprehensive characterization of these HI clouds have proven to be formidable endeavours, due to their faint luminosity, compact nature, and sparse distribution. I will present an innovative approach to search for neutral hydrogen clouds within the IGM. The methodology employs the spectral stacking technique applied to data from the MeerKAT Observations of Nearby Galactic Objects: Observing Southern Emitters (MHONGOOSE) survey, in conjunction with a one-dimensional source finder tool modelled after the established Source Finding Application (SoFiA-2). The outcome is the tentative detection of an excess of gas around some MHONGOOSE galaxies. In the talk I will focus on how to determine the robustness of these detections by systemically analysing the outcomes of spectral stacking on pure Gaussian noise, coupled with results of stacking state-of-art cosmological simulations. The proposed methodology opens a new avenue for investigating low surface brightness gaseous structures, that could be ultra-diffuse galaxies as well as pristine gas reservoirs.