Optical/Near-IR Polarization Survey of Sh 2-29: Magnetic Fields, Dense
  Cloud Fragmentations and Anomalous Dust Grain Sizes
  Sh 2-29 is a conspicuous star-forming region marked by the presence of
massive embedded stars as well as several notable interstellar structures. In
this research, our goals were to determine the role of magnetic fields and to
study the size distribution of interstellar dust particles within this
turbulent environment. We have used a set of optical and near-infrared
polarimetric data obtained at OPD/LNA (Brazil) and CTIO (Chile), correlated
with extinction maps, 2MASS data and images from DSS and Spitzer. The region's
most striking feature is a swept out interstellar cavity whose polarimetric
maps indicate that magnetic field lines were dragged outwards, pilling up along
its borders. This led to a higher magnetic strength value ($\approx400\,\mu$G)
and an abrupt increase in polarization degree, probably due to an enhancement
in alignment efficiency. Furthermore, dense cloud fragmentations with peak
$A_{V}$ between 20 and 37 mag were probably triggered by its expansion. The
presence of $24\,\mu$m point-like sources indicates possible newborn stars
inside this dense environment. A statistical analysis of the angular dispersion
function revealed areas where field lines are aligned in a well-ordered
pattern, seemingly due to compression effects from the HII region expansion.
Finally, Serkowski function fits were used to study the ratio of the
total-to-selective extinction, reveling a dual population of anomalous grain
particles sizes. This trend suggests that both effects of coagulation and
fragmentation of interstellar grains are present in the region.
