Evolution of Dust-Obscured Star Formation and Gas to z=2.2 from HiZELS [GA]

http://arxiv.org/abs/1702.06182


We investigate the far-infrared properties of galaxies selected via deep, narrow-band imaging of the H$\alpha$ emission line in four redshift slices from $z=0.40$–$2.23$ over $\sim 1$deg$^2$ as part of the High-redshift Emission Line Survey (HiZELS). We use a stacking approach in the Herschel PACS/SPIRE bands, along with $850\,\mu$m imaging from SCUBA-2 to study the evolution of the dust properties of H$\alpha$-emitters selected above an evolving characteristic luminosity threshold, $0.2L^\star_{{\rm H}\alpha}(z)$. We investigate the relationship between the dust temperatures and the far-infrared luminosities of our stacked samples, finding that H$\alpha$-selection identifies cold, low-$L_{\rm IR}$ galaxies ($T_{\rm dust}\sim 14$k; $\log[L_{\rm IR}/{\rm L}_\odot]\sim 9.9$) at $z=0.40$, and more luminous, warmer systems ($T_{\rm dust}\sim 34$k; $\log[L_{\rm IR}/{\rm L}_\odot]\sim 11.5$) at $z=2.23$. Using a modified greybody model, we estimate “characteristic sizes” for the dust-emitting regions of HiZELS galaxies of $\sim 0.5$kpc, nearly an order of magnitude smaller than their stellar continuum sizes, which may provide indirect evidence of clumpy ISM structure. Lastly, we measure the dust masses from our far-IR SEDs along with metallicity-dependent gas-to-dust ratios ($\delta_{\rm GDR}$) to measure typical molecular gas masses of $\sim 10^{10}$M$_\odot$ for these bright H$\alpha$-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$\alpha$-selected galaxies, we find that typical star-forming galaxies brighter than $0.2L^{\star}_{{\rm H}\alpha}(z)$ host a significant fraction ($35\pm10$%) of the total gas content of the Universe, consistent with the predictions of the latest cosmological simulations.

Read this paper on arXiv…

A. Thomson, J. Simpson, I. Smail, et. al.
Wed, 22 Feb 17
2/37

Comments: 17 pages, 4 figures, accepted for publication in The Astrophysical Journal

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