Evolution of Dust-obscured Star Formation and Gas to z = 2.2 from HiZELS

<jats:title>Abstract</jats:title>
<jats:p>We investigate the far-infrared (far-IR) properties of galaxies selected via deep, narrow-band imaging of the H<jats:italic>α</jats:italic> emission line in four redshift slices from <jats:inline-formula>
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<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaa61a6ieqn1.gif" xlink:type="simple"/>
</jats:inline-formula> over ∼1 deg<jats:sup>2</jats:sup> as part of the High-redshift Emission Line Survey (HiZELS). We use a stacking approach in the <jats:italic>Herschel</jats:italic> PACS/SPIRE far-IR bands, along with <jats:inline-formula>
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</jats:inline-formula> imaging from SCUBA-2 and Very Large Array 1.4 GHz imaging, to study the evolution of the dust properties of H<jats:italic>α</jats:italic>-emitters selected above an evolving characteristic luminosity threshold, <jats:inline-formula>
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<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaa61a6ieqn3.gif" xlink:type="simple"/>
</jats:inline-formula>. We investigate the relationship between the dust temperatures, <jats:italic>T</jats:italic>
<jats:sub>dust</jats:sub>, and the far-infrared luminosities, <jats:italic>L</jats:italic>
<jats:sub>IR</jats:sub>, of our stacked samples, finding that our H<jats:italic>α</jats:italic>-selection identifies cold, low-<jats:italic>L</jats:italic>
<jats:sub>IR</jats:sub> galaxies (<jats:inline-formula>
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</jats:inline-formula> K; <jats:inline-formula>
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<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaa61a6ieqn5.gif" xlink:type="simple"/>
</jats:inline-formula>) at <jats:italic>z</jats:italic> = 0.40, and more luminous, warmer systems (<jats:inline-formula>
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<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaa61a6ieqn6.gif" xlink:type="simple"/>
</jats:inline-formula> K; <jats:inline-formula>
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<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaa61a6ieqn7.gif" xlink:type="simple"/>
</jats:inline-formula>) at <jats:italic>z</jats:italic> = 2.23. Using a modified graybody model, we estimate “characteristic sizes” for the dust-emitting regions of H<jats:italic>α</jats:italic>-selected galaxies of ∼0.5 kpc, nearly an order of magnitude smaller than their stellar continuum sizes, which may provide indirect evidence of clumpy interstellar medium structure. Lastly, we use measurements of the dust masses from our far-IR stacking along with metallicity-dependent gas-to-dust ratios (<jats:inline-formula>
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<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaa61a6ieqn8.gif" xlink:type="simple"/>
</jats:inline-formula>) to measure typical molecular gas masses of <jats:inline-formula>
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<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaa61a6ieqn9.gif" xlink:type="simple"/>
</jats:inline-formula> for these bright H<jats:italic>α</jats:italic>-emitters. The gas depletion timescales are shorter than the Hubble time at each redshift, suggesting probable replenishment of their gas reservoirs from the intergalactic medium. Based on the number density of H<jats:italic>α</jats:italic>-selected galaxies, we find that typical star-forming galaxies brighter than <jats:inline-formula>
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<jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaa61a6ieqn10.gif" xlink:type="simple"/>
</jats:inline-formula> comprise a significant fraction (35 ± 10%) of the total gas content of the universe, consistent with the predictions of the latest state-of-the-art cosmological simulations.</jats:p>