We have observed the NGC 2403 group of galaxies using the Robert C. Byrd Green Bank Telescope ( GBT ) in a search for faint , extended neutral hydrogen clouds similar to the clouds found around the M81/M82 group , which is located approximately 250 kpc from the NGC 2403 group along the same filament of galaxies .
For an H i cloud with a size \leq 10 kpc within 50 kpc of a group galaxy , our 7 \sigma mass detection limit is 2.2 \times 10 ^ { 6 } M _ { \odot } for a cloud with a linewidth of 20 km s ^ { -1 } , over the velocity range from -890 to 1750 km s ^ { -1 } .
At this sensitivity level we detect 3 new H i clouds in the direction of the group , as well as the known galaxies .
The mean velocity of the new clouds differs from that of the group galaxies by more than 250 km s ^ { -1 } , but are in the range of Milky Way High Velocity Clouds ( HVCs ) in that direction .
It is most likely that the clouds are part of the Milky Way HVC population .
If H i clouds exist in the NGC 2403 group , their masses are less than 2.2 \times 10 ^ { 6 } M _ { \odot } .
We also compared our results to structures that are expected based on recent cosmological models , and found none of the predicted clouds .
If NGC 2403 is surrounded by a population of dark matter halos similar to those proposed for the Milky Way in recent models , our observations imply that their H i content is less than 1 % of their total mass .