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arXiv · 1708.07842

Are high redshift Galaxies hot? - Temperature of z > 5 Galaxies and Implications on their Dust Properties

Andreas L. Faisst·Peter L. Capak·Lin Yan·Riccardo Pavesi·Dominik A. Riechers·Ivana Barisic·Kevin C. Cooke·Jeyhan S. Kartaltepe·Daniel C. Masters
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Abstract

Recent studies have found a significant evolution and scatter in the IRX-$β$ relation at z > 4, suggesting different dust properties of these galaxies. The total far-infrared (FIR) luminosity is key for this analysis but poorly constrained in normal (main-sequence) star-forming z > 5 galaxies where often only one single FIR point is available. To better inform estimates of the FIR luminosity, we construct a sample of local galaxies and three low-redshift analogs of z > 5 systems. The trends in this sample suggest that normal high-redshift galaxies have a warmer infrared (IR) SED compared to average z < 4 galaxies that are used as prior in these studies. The blue-shifted peak and mid-IR excess emission could be explained by a combination of a larger fraction of the metal-poor inter-stellar medium (ISM) being optically thin to ultra-violet (UV) light and a stronger UV radiation field due to high star formation densities. Assuming a maximally warm IR SED suggests 0.6 dex increased total FIR luminosities, which removes some tension between dust attenuation models and observations of the IRX-$β$ relation at z > 5. Despite this, some galaxies still fall below the minimum IRX-$β$ relation derived with standard dust cloud models. We propose that radiation pressure in these highly star-forming galaxies causes a spatial offset between dust clouds and young star-forming regions within the lifetime of O/B stars. These offsets change the radiation balance and create viewing-angle effects that can change UV colors at fixed IRX. We provide a modified model that can explain the location of these galaxies on the IRX-$β$ diagram.

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Andreas L. Faisst, Peter L. Capak, Lin Yan, Riccardo Pavesi, Dominik A. Riechers, Ivana Barisic, Kevin C. Cooke, Jeyhan S. Kartaltepe, Daniel C. Masters. 2017-08-25. Are high redshift Galaxies hot? - Temperature of z > 5 Galaxies and Implications on their Dust Properties. https://doi.org/10.3847/1538-4357%2Faa886c

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