2MASS wide field extinction maps: V. Corona Australis
  We present a near-infrared extinction map of a large region ($\sim$870
deg$^2$) covering the isolated Corona Australis complex of molecular clouds. We
reach a 1-$\sigma$ error of 0.02 mag in the K-band extinction with a resolution
of 3 arcmin over the entire map. We find that the Corona Australis cloud is
about three times as large as revealed by previous CO and dust emission
surveys. The cloud consists of a 45 pc long complex of filamentary structure
from the well known star forming Western-end (the head, $N \geq10^{23}$
cm$^{-2}$) to the diffuse Eastern-end the tail, ($N \leq10^{21}$ cm$^{-2}$).
Remarkably, about two thirds of the complex both in size and mass lie beneath
A$_V\sim1$ mag. We find that the PDF of the cloud cannot be described by a
single log-normal function. Similar to prior studies, we found a significant
excess at high column densities, but a log-normal + power-law tail fit does not
work well at low column densities. We show that at low column densities near
the peak of the observed PDF, both the amplitude and shape of the PDF are
dominated by noise in the extinction measurements making it impractical to
derive the intrinsic cloud PDF below A$_K <$ 0.15 mag. Above A$_K \sim 0.15$
mag, essentially the molecular component of the cloud, the PDF appears to be
best described by a power-law with index $-3$, but could also described as the
tail of a broad and relatively low amplitude, log-normal PDF that peaks at very
low column densities.
