We present HI spectral-line imaging of the extremely metal-poor galaxy DDO 68. This system has a nebular oxygen abundance of only 3% Z$_{odot}$, making it one of the most metal-deficient galaxies known in the local volume. Surprisingly, DDO 68 is a r
elatively massive and luminous galaxy for its metal content, making it a significant outlier in the mass-metallicity and luminosity-metallicity relationships. The origin of such a low oxygen abundance in DDO 68 presents a challenge for models of the chemical evolution of galaxies. One possible solution to this problem is the infall of pristine neutral gas, potentially initiated during a gravitational interaction. Using archival HI spectral-line imaging obtained with the Karl G. Jansky Very Large Array, we have discovered a previously unknown companion of DDO 68. This low-mass (M$_{rm HI}$ $=$ 2.8$times$10$^{7}$ M$_{odot}$), recently star-forming (SFR$_{rm FUV}$ $=$ 1.4$times$10$^{-3}$ M$_{odot}$ yr$^{-1}$, SFR$_{rm Halpha}$ $<$ 7$times$10$^{-5}$ M$_{odot}$ yr$^{-1}$) companion has the same systemic velocity as DDO 68 (V$_{rm sys}$ $=$ 506 km s$^{-1}$; D $=$ 12.74$pm$0.27 Mpc) and is located at a projected distance of 42 kpc. New HI maps obtained with the 100m Robert C. Byrd Green Bank Telescope provide evidence that DDO 68 and this companion are gravitationally interacting at the present time. Low surface brightness HI gas forms a bridge between these objects.
This work presents an extended, neutral Hydrogen emission map around Magellanic-type dwarf irregular galaxy (dIm) NGC 1569. In the Spring of 2010, the Robert C. Byrd Green Bank Telescope (GBT) was used to map a 9 degree x 2 degree region in HI line e
mission that includes NGC 1569 and IC 342 as well as two other dwarf galaxies. The primary objective for these observations was to search for structures potentially connecting NGC 1569 with IC 342 group members in order to trace previous interactions and thus, provide an explanation for the starburst and peculiar kinematics prevalent in NGC 1569. A large, half-degree diameter HI cloud was detected that shares the same position and velocity as NGC 1569. Also, two long structures were discovered that are reminiscent of intergalactic filaments extending out in a v-shaped manner from NGC 1569 toward UGCA 92, a nearby dwarf galaxy. These filamentary structures extend for about 1.5 degrees, which is 77 kpc at NGC 1569. There is a continuous velocity succession with the 0.5 degree HI cloud, filaments, and main body of the galaxy. The 0.5 degree HI cloud and filamentary structures may be foreground Milky Way, but are suggestive as possible remnants of an interaction between NGC 1569 and UGCA 92. The data also show two tidal tails extending from UGCA 86 and IC 342, respectively. These structures may be part of a continuous HI bridge but more data are needed to determine if this is the case.
