Knowledge Bank

Work done by Das 2020 (D20 \cite{Das2020b}) shows, along the minor axis, the velocity is consistent with an inflow/fountain in NGC 891 and an inflow/outflow in NGC 4565. Previous work done by Das 2024 (D24\cite{DasandRickel2024}) along the major axis shows the diffuse \hi is a co-rotating CGM or the outer part of an extended HI disk. From D20 and D24, the star formation of NGC 4565 can be sufficiently explained including the circumgalactic \hi, the depletion time, and the accretion rate. However, most accreting material in NGC 891 is missing. To obtain a 360\deg view, we probe the diffuse neutral circumgalactic medium (CGM) along the off axes of NGC 891 and NGC 4565 out to ~30 kpc using the Green Bank Telescope (GBT). We detect HI with varying spectral shapes, velocity widths, and column densities with a sensitivity of 10$\mathrm{<mrow\; data-mjx-texclass="ORD">16</mrow>}$ cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-2</mrow>}$ % 1 sigma. We compare our single-dish detections to the interferometric maps from the Westerbork Synthesis Radio Telescope (WSRT) obtained as part of the HALOGAS survey. We find that all of the emission detected by the GBT cannot be explained by the emission seen in WSRT maps.