Dust Properties of [CII] Detected z $\sim$ 5.5 Galaxies: New HST/WFC3
  Near-IR Observations
  We examine the rest-frame ultra-violet (UV) properties of 10
[CII]$\lambda158\,{\rm \mu m}$$-$detected galaxies at $z\sim5.5$ in COSMOS
using new HST/WFC3 near-infrared imaging. Together with pre-existing $158\,{\rm
\mu m}-$continuum and [CII] line measurements by ALMA, we study their dust
attenuation properties on the IRX-$\beta$ diagram, which connects the total
dust emission ($\propto$ IRX=log($L_{FIR}/L_{1600}$)) to the line-of-sight dust
column ($\propto\beta$). We find systematically bluer UV continuum spectral
slopes ($\beta$) compared to previous low-resolution ground-based measurements,
which relieves some of the tension between models of dust attenuation and
observations at high redshifts. While most of the galaxies are consistent with
local starburst or Small Magellanic cloud like dust properties, we find
galaxies with low IRX values and a large range in $\beta$ that cannot be
explained by models of a uniform dust distribution well mixed with stars. A
stacking analysis of Keck/DEIMOS optical spectra indicates that these galaxies
are metal-poor with young stellar populations which could significantly alter
their spatial dust distribution.
