We present dust attenuation properties of spectroscopically confirmed star
forming galaxies on the main sequence at redshift ~4.4-5.8. Our analyses are
based on the far infrared continuum observations of 118 galaxies at rest-frame
158μm obtained with the ALMA large program ALPINE. We study the
connection between the UV spectral slope (β), stellar mass (M⋆),
and infrared excess (IRX=LIR/LUV). Twenty-three galaxies are
individually detected in the continuum at >3.5σ significance. We
perform a stacking analysis using both detections and non-detections to study
the average dust attenuation properties at z~4.4-5.8. The individual detections
and stacks show that the IRX-β relation at z~5 is consistent with a
steeper dust attenuation curve than typically found at lower redshifts (z<4).
The attenuation curve is similar to or even steeper than that of the extinction
curve of the Small Magellanic Cloud (SMC). This systematic change of the
IRX-β relation as a function of redshift suggests an evolution of dust
attenuation properties at z>4. Similarly, we find that our galaxies have
lower IRX values up to 1 dex on average at fixed mass compared to previously
studied IRX-M⋆ relations at z≲4, albeit with significant
scatter. This implies a lower obscured fraction of star-formation than at lower
redshifts. Our results suggest that dust properties of UV-selected star forming
galaxies at z≳4 are characterised by (i) a steeper attenuation curve
than at z≲4, and (ii) a rapidly decreasing dust obscured fraction of
star formation as a function of redshift. Nevertheless, even among this
UV-selected sample, massive galaxies (logM⋆/M⊙>10) at z~5-6
already exhibit an obscured fraction of star formation of ∼45%,
indicating a rapid build-up of dust during the epoch of reionization.STFC
ER