A Computational Study on Additively Manufactured Welding Electrodes

Kirkman, Daniel; Pillay, Jeseelan; Padayachee, Jared

doi:10.17159/2309-8988/2019/v35a5

Cited by 5 publications

(5 citation statements)

References 7 publications

(8 reference statements)

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“…With the advent of the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST), it has become possible to obtain much improved measurements also at lower redshift (Savage et al 2014;Shull et al 2014;Danforth et al 2016;Werk et al 2016;Pachat et al 2016). The increased resolution and signal-to-noise (S/N) of the COS data enable the measurement of the column density of Ly-α absorbers to lower values and help resolve the thermal broadening for weaker absorbers, complementing earlier investigations of the low-redshift IGM (Weymann et al 1998;Janknecht et al 2006;Kirkman et al 2007).…”

Section: Introductionmentioning

confidence: 85%

Diagnosing galactic feedback with line broadening in the low-redshift Lyα forest

Viel

Haehnelt²,

Bolton

et al. 2017

Monthly Notices of the Royal Astronomical Society: Letters

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We compare the low redshift (z 0.1) Ly-α forest from hydrodynamical simulations with data from the Cosmic Origin Spectrograph (COS). We find tension between the observed number of lines with b-parameters in the range 25-45 km s −1 and the predictions from simulations that incorporate either vigorous feedback from active galactic nuclei or that exclude feedback altogether. The gas in these simulations is, respectively, either too hot to contribute to the Ly-α absorption or too cold to produce the required line widths. Matching the observed b−parameter distribution therefore requires feedback processes that thermally or turbulently broaden the absorption features without collisionally (over-)ionising hydrogen. This suggests the Ly-α forest b-parameter distribution is a valulable diagnostic of galactic feedback in the low redshift Universe. We furthermore confirm the low redshift Ly-α forest column density distribution is better reproduced by an ultraviolet background with an H I photo-ionisation rate a factor 1.5-3 higher than predicted by Haardt & Madau (2012).

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Section: Introductionmentioning

confidence: 85%

Diagnosing galactic feedback with line broadening in the low-redshift Lyα forest

Viel

Haehnelt²,

Bolton

et al. 2017

Monthly Notices of the Royal Astronomical Society: Letters

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“…To obtain realistic He ii transmission spectra, in particular in the absence of a foreground quasar, we have to rely on models for the corresponding UV backgrounds. Oñorbe et al (2017) obtained an empirical fit for the cosmic mean transmitted H i flux F HI to existing measurements (Fan et al 2006;Becker et al 2007;Kirkman et al 2007;Faucher-Giguère et al 2008;Becker & Bolton 2013) of the form…”

Section: H I and He Ii Uv Backgroundmentioning

confidence: 94%

Modeling the He ii Transverse Proximity Effect: Constraints on Quasar Lifetime and Obscuration

Schmidt

Worseck

Davies

et al. 2018

ApJ

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The He ii transverse proximity effect -enhanced He ii Lyα transmission in a background sightline caused by the ionizing radiation of a foreground quasar -offers a unique opportunity to probe the emission properties of quasars, in particular the emission geometry (obscuration, beaming) and the quasar lifetime. Building on the foreground quasar survey published in Schmidt et al. (2017), we present a detailed model of the He ii transverse proximity effect, specifically designed to include light travel time effects, finite quasar ages, and quasar obscuration. We post-process outputs from a cosmological hydrodynamical simulation with a fluctuating He ii UV background model, plus the added effect of the radiation from a single bright foreground quasar. We vary the age t age and obscured sky fractions Ω obsc of the foreground quasar, and explore the resulting effect on the He ii transverse proximity effect signal. Fluctuations in IGM density and the UV background, as well as the unknown orientation of the foreground quasar, result in a large variance of the He ii Lyα transmission along the background sightline. We develop a fully Bayesian statistical formalism to compare far UV He ii Lyα transmission spectra of the background quasars to our models, and extract joint constraints on t age and Ω obsc for the six Schmidt et al. (2017) foreground quasars with the highest implied He ii photoionization rates. Our analysis suggests a bimodal distribution of quasar emission properties, whereby one foreground quasar, associated with a strong He ii transmission spike, is relatively old (22 Myr) and unobscured Ω obsc < 35%, whereas three others are either younger than 10 Myr or highly obscured (Ω obsc > 70%).

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“…ForF we used both a flat prior (corresponding to performing a joint measurement ofF and the thermal state) and a Gaussian shaped prior. For the Gaussian prior we assumed a mean based on the fit by Oñorbe et al (2017a) to a compilation of recent measurements (Fan et al 2006;Kirkman et al 2007;Faucher-Giguère et al 2008b;Becker et al 2013) and a standard deviation based on the uncertainties for the most recent measurements at z Bosman et al 2018;Eilers et al 2018, for more recent mean flux measurements that are discrepant by a similar amount for 5.0 ≤ z ≤ 5.4).…”

Section: Parameters and Priorsmentioning

confidence: 99%

New Constraints on IGM Thermal Evolution from the Lyα Forest Power Spectrum

Walther

Oñorbe

Hennawi

et al. 2019

ApJ

171

194

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We determine the thermal evolution of the intergalactic medium (IGM) over 3 Gyr of cosmic time 1.8 < z < 5.4 by comparing measurements of the Lyα forest power spectrum to a suite of ∼ 70 hydrodynamical simulations. We conduct Bayesian inference of IGM thermal parameters using an end-to-end forward modeling framework whereby mock spectra generated from our simulation grid are used to build a custom emulator which interpolates the power spectrum between thermal grid points. The temperature at mean density T 0 rises steadily from T 0 ∼ 6000 K at z = 5.4, peaks at 14 000 K for z ∼ 3.4, and decreases at lower redshift reaching T 0 ∼ 7000 K by z ∼ 1.8. This evolution provides conclusive evidence for photoionization heating resulting from the reionization of He II, as well as the subsequent cooling of the IGM due to the expansion of the Universe after all reionization events are complete. Our results are broadly consistent with previous measurements of thermal evolution based on a variety of approaches, but the sensitivity of the power spectrum, the combination of high precision BOSS measurements of large-scale modes (k 0.02 s km −1 ) with our recent determination of the small-scale power, our large grid of models, and our careful statistical analysis allow us to break the well known degeneracy between the temperature at mean density T 0 and the slope of the temperature density relation γ that has plagued previous analyses. At the highest redshifts z ≥ 5 we infer lower temperatures than expected from the standard picture of IGM thermal evolution leaving little room for additional smoothing of the Lyα forest by free streaming of warm dark matter.

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A Computational Study on Additively Manufactured Welding Electrodes

Cited by 5 publications

References 7 publications

Diagnosing galactic feedback with line broadening in the low-redshift Lyα forest

Diagnosing galactic feedback with line broadening in the low-redshift Lyα forest

Modeling the He ii Transverse Proximity Effect: Constraints on Quasar Lifetime and Obscuration

New Constraints on IGM Thermal Evolution from the Lyα Forest Power Spectrum

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