Dust Properties of [CII] Detected z $\sim$ 5.5 Galaxies: New HST/WFC3 Near-IR Observations

TL;DR

This study investigates dust properties of high-redshift galaxies at z~5.5 using HST and ALMA data, revealing bluer UV slopes and diverse dust distributions, challenging existing models of dust attenuation.

Contribution

It provides new near-infrared observations of z~5.5 galaxies and analyzes their dust attenuation properties, highlighting deviations from standard models due to diverse dust distributions.

Findings

Galaxies show bluer UV slopes than previous measurements.

Most galaxies have dust properties similar to local starbursts or SMC.

Some galaxies exhibit low IRX and diverse β, indicating complex dust distributions.

Abstract

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.