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Agnostic Stacking of Intergalactic Doublet Absorption: Measuring the NeVIII Population
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Agnostic Stacking of Intergalactic Doublet Absorption: Measuring the NeVIII Population
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Paper
Agnostic Stacking of Intergalactic Doublet Absorption: Measuring the NeVIII Population
2018
Overview
We present a blind search for doublet intergalactic metal absorption with a method dubbed `agnostic stacking'. Using a forward-modelling framework we combine this with direct detections in the literature to measure the overall metal population. We apply this novel approach to the search for NeVIII absorption in a set of 26 high-quality COS spectra. We probe to an unprecedented low limit of log N\\(>\\)12.3 at 0.47\\(\\leq z \\leq\\)1.34 over a pathlength \\(\\Delta\\)z = 7.36. This method selects apparent absorption without requiring knowledge of its source. Stacking this mixed population dilutes doublet features in composite spectra in a deterministic manner, allowing us to measure the proportion corresponding to NeVIII absorption. We stack potential NeVIII absorption in two regimes: absorption too weak to be significant in direct line studies (12.3 \\(<\\) log N \\(<\\) 13.7), and strong absorbers (log N \\(>\\) 13.7). We do not detect NeVIII absorption in either regime. Combining our measurements with direct detections, we find that the NeVIII population is reproduced with a power law column density distribution function with slope \\(\\beta = -1.86 \\substack{+0.18 \\\ -0.26}\\) and normalisation log \\(f_{13.7} = -13.99 \\substack{+0.20 \\\ -0.23}\\), leading to an incidence rate of strong NeVIII absorbers \\(dn/dz =1.38 \\substack{+0.97 \\\ -0.82}\\). We infer a cosmic mass density for NeVIII gas with 12.3 \\(<\\) log N \\(<\\) 15.0 of \\(\\Omega _{NeVIII} = 2.2 \\substack{+1.6 \\\ _-1.2} \\times 10^{-8}\\), a value significantly lower that than predicted by recent simulations. We translate this density into an estimate of the baryon density \\(\\Omega _{b} \\approx 1.8 \\times 10^{-3}\\), constituting 4\\% of the total baryonic mass.
Publisher
Cornell University Library, arXiv.org
Subject
