Aligned metal absorbers and the ultraviolet background at the end of reionization

Doughty, Caitlin; Finlator, Kristian; Oppenheimer, Benjamin D.; Davé, Romeel; Zackrisson, Erik

doi:10.1093/mnras/sty156

Cited by 19 publications

(18 citation statements)

References 47 publications

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“…Our results suggest a significant change to circumgalactic gas presumed to give rise to these absorption systems, with a combination of lower chemical abundances and a softer ionizing UV background at z ∼ 6 in comparison to z = 3, but cannot distinguish the relative contributions of these factors. Simulations suggest that improved observations of numerous low-and high-ionization species may yield sufficient discriminatory data (Finlator et al 2016;Doughty et al 2018). As more high-redshift quasars are observed and more high-SNR spectra are obtained (e.g., Bosman et al 2017), increased absorption pathlength and sensitivity will provide more detail on the nature of LIAs and the apparent disappearance of absorption from the high-ionization phase.…”

Section: Discussionmentioning

confidence: 99%

Heavy Element Absorption Systems at 5.0 < z < 6.8: Metal-poor Neutral Gas and a Diminishing Signature of Highly Ionized Circumgalactic Matter

Cooper

Simcoe

Cooksey

et al. 2019

ApJ

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Ratios of different ions of the same element encode ionization information independently from relative abundances in quasar absorption line systems, crucial for understanding the multiphase nature and origin of absorbing gas, particularly at z > 6 where H I cannot be observed. Observational considerations have limited such studies to a small number of sightlines, with most surveys at z > 6 focused upon the statistical properties of individual ions such as Mg II or C IV. Here we compare high-and low-ionization absorption within 69 intervening systems at z > 5, including 16 systems at z > 6, from Magellan/FIRE spectra of 47 quasars together with a Keck/HIRES spectrum of the 'ultraluminous' z = 6.3 quasar SDSSJ010013.02+280225.8. The highest redshift absorbers increasingly exhibit lowionization species alone, consistent with previous single-ion surveys that show the frequency of Mg II is unchanging with redshift while C IV absorption drops markedly toward z = 6. We detect no C IV or Si IV in half of all metal-line absorbers at z > 5.7, with stacks not revealing any slightly weaker C IV just below our detection threshold, and most of the other half have N CII > N CIV . In contrast, only 20% of absorbers at 5.0-5.7 lack high-ionization gas, and a search of 25 HIRES sightlines at z ∼ 3 yielded zero such examples. We infer these low-ionization high-redshift absorption systems may be analogous to metal-poor Damped Lyman-α systems (∼ 1% of the absorber population at z ∼ 3), based on incidence rates and absolute and relative column densities. Simple photoionization models suggest that circumgalactic matter at redshift six has systematically lower chemical abundances and experiences a softer ionizing background relative to redshift three.

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Section: Discussionmentioning

confidence: 99%

Heavy Element Absorption Systems at 5.0 < z < 6.8: Metal-poor Neutral Gas and a Diminishing Signature of Highly Ionized Circumgalactic Matter

Cooper

Simcoe

Cooksey

et al. 2019

ApJ

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“…5), which could produce significant effects on the observable ionization structure of the IGM. This is particularly interesting because high-ionization species such as C iv and Si iv have been observed in the IGM at high redshift (e.g., Ryan-Weber et al 2006D'Odorico et al 2013;Doughty et al 2018). The metals in the IGM are likely expelled from galaxies via large-scale outflows, which explains why they are detected in small and dense clumps that could indicate the locations of galaxies.…”

Section: Highly Ionized Absorbers In the Igmmentioning

confidence: 99%

Contribution from stars stripped in binaries to cosmic reionization of hydrogen and helium

Götberg

Mink

McQuinn

et al. 2020

A&A

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Massive stars are often found in binary systems and it has been argued that binary products boost the ionizing radiation of stellar populations. Accurate predictions for binary products are needed to understand and quantify their contribution to Cosmic Reionization. We investigate the contribution of stars stripped in binaries since (1) they are, arguably, the best-understood products of binary evolution, (2) we recently produced the first non-LTE radiative transfer calculations for the atmospheres of these stripped stars that predict their ionizing spectra, and (3) they are very promising sources since they boost the ionizing emission of stellar populations at late times. This allows stellar feedback to clear the surroundings such that a higher fraction of their photons can escape and ionize the intergalactic medium. Combining our detailed predictions for the ionizing spectra with a simple cosmic reionization model, we estimate that stripped stars contributed tens of percent of the photons that caused cosmic reionization of hydrogen, depending on the assumed escape fractions. More importantly, stripped stars harden the ionizing emission. We estimate that the spectral index for the ionizing part of the spectrum can increase to −1 compared to −2 for single stars. At high redshift, stripped stars and massive single stars combined dominate the He ii-ionizing emission, but we expect active galactic nuclei drive cosmic helium reionization. Further observational consequences we expect are (1) high ionization states for the intergalactic gas surrounding stellar systems, such as C iv and Si iv and (2) additional heating of the intergalactic medium of up to a few thousand Kelvin. Quantifying these warrants the inclusion of accurate models for stripped stars and other binary products in full cosmological simulations.

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“…The comparisons in Figures 4-5 reiterate that cosmological simulations confront grave difficulty in attempting to match simultaneously observations of the UVB, the galaxy stellar mass function, and the C IV and Si IV CDDs at high redshift. Although the C IV/Si IV abundance ratio is a tracer of the UVB's spectral hardness that could constrain the relative contributions of galaxies and AGN (Finlator et al 2016;Doughty et al 2018), these figures suggest that it could alternatively probe the details of how ionizing light escapes from galaxies. In reality, as pointed out by Zackrisson et al (2013), the IB and DB scenarios are opposite extremes and young stars will be separated from the CGM by sightlines spanning a distribution of column densities.…”

Section: A Model For Density-bounded Escapementioning

confidence: 99%

The Faint Host Galaxies of C IV Absorbers at z > 5

Finlator,

Doughty,

Cai

et al. 2020

Preprint

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We explore the expected galaxy environments of C IV absorbers at z > 5 using the Technicolor Dawn simulations. These simulations reproduce the observed history of reionization, the z ∼ 6 galaxy stellar mass function, the Lyα forest transmission at z > 5, and the Si IV column density distribution (CDD) at z ≈ 5.5. Nonetheless, the C IV CDD remains underproduced. Comparison with observed C II/Si II equivalent width ratios and the C II line incidence suggests that a low carbon yield accounts for some, but not all, of the C IV discrepancy. Alternatively, a density-bounded escape scenario could harden the metagalactic ionizing background more dramatically even than binary stellar evolution, boosting the C IV CDD into near-agreement with observations. In this case galaxies ionize more efficiently and fewer are required to host a given high-ionization absorber. Absorbers' environments therefore constrain ionizing escape. Regardless of the escape scenario, galaxies correlate with C IV absorbers out to 300 proper kpc (pkpc). The correlation strengthens independently with galaxy luminosity and C IV column density. Around strong systems (log(N C IV /cm −2 ) > 14)), the overdensity of galaxies with M UV < −18 or log(L Lyα /erg s −1 ) > 41.9 declines from 200-300 within 100 pkpc to 40-60 within 250 pkpc. The previously-suggested association between strong C IV absorbers and Lyα emitters at z > 5 is not expected. It may arise if both populations inhabit large-scale voids, but for different reasons. Although most neighboring galaxies are too faint for HST, JWST will, with a single pointing, identify ∼ 10 neighboring galaxies per strong C IV absorber at z > 5. Ground-based tests of these predictions are possible via deep surveys for Lyα emission using integral field units.

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Aligned metal absorbers and the ultraviolet background at the end of reionization

Cited by 19 publications

References 47 publications

Heavy Element Absorption Systems at 5.0 < z < 6.8: Metal-poor Neutral Gas and a Diminishing Signature of Highly Ionized Circumgalactic Matter

Heavy Element Absorption Systems at 5.0 < z < 6.8: Metal-poor Neutral Gas and a Diminishing Signature of Highly Ionized Circumgalactic Matter

Contribution from stars stripped in binaries to cosmic reionization of hydrogen and helium

The Faint Host Galaxies of C IV Absorbers at z > 5

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