Green Bank Telescope observations of low column density HI around NGC 2997 and NGC 6946

Understand

Observations of ongoing HI accretion in nearby galaxies have only identified about 10% of the needed fuel to sustain star formation in these galaxies.

• Most of these observations have been conducted using interferometers and may have missed lower column density, diffuse, HI gas that may trace the missing 90% of gas.
• Such gas may represent the so-called "cold flows" predicted by current theories of galaxy formation to have never been heated above the virial temperature of the dark matter halo.
• As a first attempt to identify such cold flows around nearby galaxies and complete the census of HI down to N(HI)~10^18 cm^-2, I used the Robert C.