HI 21cm emission from the sub-damped Lyman-alpha absorber at z=0.0063
  towards PG1216+069
  We present HI 21cm emission observations of the z ~ 0.00632 sub-damped
Lyman-alpha absorber (sub-DLA) towards PG1216+069 made using the Arecibo
Telescope and the Very Large Array (VLA). The Arecibo 21cm spectrum corresponds
to an HI mass of ~ 3.2x10^7 solar masses, two orders of magnitude smaller than
that of a typical spiral galaxy. This is surprising since in the local Universe
the cross-section for absorption at high HI column densities is expected to be
dominated by spirals. The 21cm emission detected in the VLA spectral cube has a
low signal-to-noise ratio, and represents only half the total flux seen at
Arecibo. Emission from three other sources is detected in the VLA observations,
with only one of these sources having an optical counterpart. This group of HI
sources appears to be part of complex "W", believed to lie in the background of
the Virgo cluster. While several HI cloud complexes have been found in and
around the Virgo cluster, it is unclear whether the ram pressure and galaxy
harassment processes that are believed to be responsible for the creation of
such clouds in a cluster environment are relevant at the location of this cloud
complex. The extremely low metallicity of the gas, ~ 1/40 solar, also makes it
unlikely that the sub-DLA consists of material that has been stripped from a
galaxy. Thus, while our results have significantly improved our understanding
of the host of this sub-DLA, the origin of the gas cloud remains a mystery
