Planck Early Results XXIV: Dust in the diffuse interstellar medium and
  the Galactic halo
  This paper presents the first results of comparison of Planck along with IRAS
data with Green Bank Telescope 21-cm observations in 14 fields covering more
than 800 square degrees at high Galactic latitude. Galactic dust emission for
fields with average HI column density lower than 2 x 10^20 cm^-2 is well
correlated with 21-cm emission. The residual emission in these fields, once the
HI-correlated emission is removed, is consistent with the expected statistical
properties of the cosmic infrared background fluctuations. Fields with larger
column densities show significant excess dust emission compared to the HI
column density. Regions of excess lie in organized structures that suggest the
presence of hydrogen in molecular form, though they are not always correlated
with CO emission. Dust emission from intermediate-velocity clouds is detected
with high significance. Its spectral properties are consistent with, compared
to the local ISM values, significantly hotter dust (T~20 K), lower
sub-millimeter dust opacity, and a relative abundance of very small grains to
large grains about four times higher. These results are compatible with
expectations for clouds that are part of the Galactic fountain in which there
is dust shattering and fragmentation. Correlated dust emission in HVCs is not
detected; the average of the 99.9% confidence upper limits to the emissivity is
0.15 times the local ISM value at 857 and 3000 GHz, in accordance with gas
phase evidence for lower metallicity and depletion in these clouds. Unexpected
anti-correlated variations of the dust temperature and emission cross-section
per H atom are identified in the local ISM and IVCs, a trend that continues
into molecular environments. This suggests that dust growth through
aggregation, seen in molecular clouds, is active much earlier in the cloud
condensation and star formation processes.
