Monday

Recent ALMA detections of the far-infrared [CII] 158 μm and [OIII] 88 μm emission lines have opened a new observational window for studying galaxies at high redshift, supplementing existing observations of the rest-frame UV. In this talk, I will present new [OIII] 88 μm observations of four galaxies at z ~ 7 recently detected by ALMA in [CII]. These bright Lyman-break galaxies were spectroscopically confirmed by blindly scanning for the [CII] line, unlike recent ALMA detections of [OIII] that were first spectroscopically confirmed through the detection of the Lyα line.

The [OIII] emission, corresponding to diffuse, highly ionized gas, and [CII] emission, tracing neutral gas and photon dissociation regions, allow some of the first explorations of the interstellar medium in the Epoch of Reionization (EoR). I will present a multi-wavelength comparison with new deep HST images of the rest-frame UV, whose compact morphology aligns well with [OIII] as opposed to the more spatially extended [CII] emission. This suggests we are witnessing intense star formation which locally shows extreme [OIII]/[CII] luminosity ratios that are indicative of 'leaking' ionizing radiation and hence may be of great importance to Reionization. Other regions in these galaxies, however, might be more metal-enriched and obscured by dust, as indicated by ALMA measurements of the dust continuum. I will present an analysis of spatially resolved maps of the [OIII]/[CII] ratio which can be used to infer physical parameters such as the ionization parameter. Probing the dust continuum at two wavelengths furthermore allows us to constrain key dust properties such as its temperature and dust yield, both currently largely unknown for galaxies in the EoR. Surprisingly, one source requires a modestly cool dust temperature and a large dust to stellar mass ratio. If confirmed, this would have important implications for build-up mechanisms of dust in the early Universe.