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The structure and properties of the circumgalactic medium (CGM) between R ~30–100 kpc around nearby, massive spiral galaxies remain largely unknown. One hypothesis is that large quantities of gas are held in rotationally-supported disks of neutral hydrogen (HI) that extend out to ~100 kpc. While observations of individual galaxies have detected HI out to distances of 80 kpc, a larger sample is necessary to determine the frequency and characteristics of extended HI disks. Using the Green Bank Telescope (GBT) we conducted a comprehensive survey mapping HI along the major and minor axes of 20 mass-selected galaxies to distances of 100 kpc and a limiting column density of 2 x 1018 cm-2. We have determined the total extended HI mass and its distribution within each galaxy by fitting our data to HI distribution models. We have found rotationally-supported disks in ~50% of the sample that extend to distances between 40 and 100 kpc. 

ABSTRACT We present the results from an analysis of deep Herschel far-infrared (far-IR) observations of the edge-on disc galaxy NGC 3079. The point spread function-cleaned Photodetector Array Camera and Spectrometer (PACS) images at 100 and 160 µm display a 25 × 25 kpc2 X-shape structure centred on the nucleus that is similar in extent and orientation to that seen in H α, X-rays, and the far-ultraviolet. One of the dusty filaments making up this structure is detected in the Spectral and Photometric Imaging Receiver 250 µm map out to ∼25 kpc from the nucleus. The match between the far-IR filaments and those detected at other wavelengths suggests that the dusty material has been lifted out of the disc by the same large-scale galactic wind that has produced the other structures in this object. A closer look at the central 10 × 10 kpc2 region provides additional support for this scenario. The dust temperatures traced by the 100–160 µm flux ratios in this region are enhanced within a biconical region centred on the active galactic nucleus, aligned along the minor axis of the galaxy, and coincident with the well-known double-lobed cm-wave radio structure and H α–X-ray nuclear superbubbles. PACS imaging spectroscopy of the inner 6 kpc region reveals broad [C ii] 158 µm emission line profiles and OH 79 µm absorption features along the minor axis of the galaxy with widths well in excess of those expected from beam smearing of the disc rotational motion. This provides compelling evidence that the cool material traced by the [C ii] and OH features directly interacts with the nuclear ionized and relativistic outflows traced by the H α, X-ray, and radio emission.