A MEASUREMENT OF SMALL-SCALE STRUCTURE IN THE 2.2 ⩽<i>z</i>⩽ 4.2 Lyα FOREST

Lidz, Adam; Faucher-Giguère, Claude André; Dall'Aglio, Aldo; McQuinn, Matthew; Fechner, C.; Zaldarriaga, Matías; Hernquist, Lars; Dutta, Sourish

doi:10.1088/0004-637x/718/1/199

Cited by 160 publications

(322 citation statements)

References 77 publications

(240 reference statements)

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“…This provides constraints on the integral optical depth to the CMB last scattering surface, indicating that reionization must have been under way by z ∼ 11 (Planck Collaboration 2013; Bennett et al 2013); this assumes instantaneous reionization, which is unlikely to be a realistic scenario. Measurements from the thermal history of the IGM are consistent with this figure (Theuns et al 2002;Bolton et al 2010;Lidz et al 2010). …”

Section: Introductionsupporting

confidence: 79%

Distinguishing models of reionization using future radio observations of 21-cm 1-point statistics

Watkinson

Pritchard

2014

Monthly Notices of the Royal Astronomical Society

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We explore the impact of reionization topology on 21-cm statistics. Four reionization models are presented which emulate large ionized bubbles around over-dense regions (21CMFAST/ global-inside-out), small ionized bubbles in over-dense regions (local-inside-out), large ionized bubbles around under-dense regions (global-outside-in) and small ionized bubbles around under-dense regions (local-outside-in). We show that first generation instruments might struggle to distinguish global models using the shape of the power spectrum alone. All instruments considered are capable of breaking this degeneracy with the variance, which is higher in outside-in models. Global models can also be distinguished at small scales from a boost in the power spectrum from a positive correlation between the density and neutral-fraction fields in outside-in models. Negative skewness is found to be unique to inside-out models and we find that pre-SKA instruments could detect this feature in maps smoothed to reduce noise errors. The early, mid and late phases of reionization imprint signatures in the brightnesstemperature moments, we examine their model dependence and find pre-SKA instruments capable of exploiting these timing constraints in smoothed maps. The dimensional skewness is introduced and is shown to have stronger signatures of the early and mid-phase timing if the inside-out scenario is correct.

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Section: Introductionsupporting

confidence: 79%

Distinguishing models of reionization using future radio observations of 21-cm 1-point statistics

Watkinson

Pritchard

2014

Monthly Notices of the Royal Astronomical Society

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“…However, there is generally a lack of consistency between these measurements and those from other studies (Ricotti et al 2000;McDonald et al 2001;Zaldarriaga et al 2001;Lidz et al 2010). In particular Lidz et al (2010) found evidence for a much hotter IGM at z 3.5 than expected from current models (Puchwein et al 2015;Upton Sanderbeck et al 2016;Oñorbe et al 2016), in disagreement with Becker et al (2011).…”

mentioning

confidence: 68%

“…Irrespective of the nature of these sources, if they reionized intergalactic helium at z 4, these sources also likely contributed substantially to H I reionization (Madau & Haardt 2015). Unfortunately, it is not currently possible to probe the ionization state of He II via far-UV He II Lyα absorption at z 4, and constraints on He II reionization from the thermal state of the IGM do not all agree (Lidz et al 2010;Becker et al 2011;Upton Sanderbeck et al 2016). This paper introduces a new method to constrain the timing of He II reionization.…”

mentioning

confidence: 99%

The Thermal Proximity Effect: A New Probe of the He ii Reionization History and Quasar Lifetime

Khrykin

Hennawi

McQuinn

2017

ApJ

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Despite decades of effort, the timing and duration of He II reionization and the properties of the quasars believed to drive it, are still not well constrained. We present a new method to study both via the thermal proximity effect -the heating of the intergalactic medium (IGM) around quasars when their radiation doubly ionizes helium. We post-process hydrodynamical simulations with 1D radiative transfer and study how the thermal proximity effect depends on He II fraction, x HeII,0 , which prevailed in the IGM before the quasar turned on, and the quasar lifetime t Q . We find that the amplitude of the temperature boost in the quasar environment depends on x HeII,0 , with a characteristic value of ∆T ≃ 10 4 K for x HeII,0 = 1.0, whereas the size of the thermal proximity zone is sensitive to t Q ,with typical sizes of ≃ 100 cMpc for t Q = 10 8 yr. This temperature boost increases the thermal broadening of H I absorption lines near the quasar. We introduce a new Bayesian statistical method based on measuring the Lyα forest power spectrum as a function of distance from the quasar, and demonstrate that the thermal proximity effect should be easily detectable. For a mock dataset of 50 quasars at z ≃ 4, we predict that one can measure x HeII,0 to an (absolute) precision ≈ 0.04, and t Q to a precision of ≈ 0.1 dex. By applying our formalism to existing high-resolution Lyα forest spectra, one should be able to reconstruct the He II reionization history,providing a global census of hard photons in the high-z universe.

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“…This relation is established ∆z ∼ 1 − 2 after the end of cosmological reionization processes (Hui & Gnedin 1997;Trac et al 2008;Furlanetto & Oh 2009;McQuinn et al 2009). Motivated by this limiting behavior, a power-law parameterization for the thermal state is adopted in almost all analyses of the Lyα forest (e.g., McDonald et al 2005;Viel et al 2006;Lidz et al 2010). 1 Here we provide a simple explanation for the physics that sets the asymptotic relation as well as an understanding for how quickly this asymptote is reached.…”

Section: Introductionmentioning

confidence: 99%

On the intergalactic temperature–density relation

McQuinn

Sanderbeck

2015

Mon. Not. R. Astron. Soc.

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Cosmological simulations of the low-density intergalactic medium exhibit a strikingly tight power-law relation between temperature and density that holds over two decades in density. It is found that this relation should roughly apply ∆z ∼ 1 − 2 after a reionization event, and this limiting behavior has motivated the power-law parameterizations used in most analyses of the Lyα forest. This relation has been explained by using equations linearized in the baryonic overdensity (which does not address why a tight power-law relation holds over two decades in density) or by equating the photoheating rate with the cooling rate from cosmological expansion (which we show is incorrect). Previous explanations also did not address why recombination cooling and Compton cooling off of the cosmic microwave background, which are never negligible, do not alter the character of this relation. We provide an understanding for why a tight power-law relation arises for unshocked gas at all densities for which collisional cooling is unimportant. We also use our results to comment on (1) how quickly fluctuations in temperature redshift away after reionization processes, (2) how much shock heating occurs in the low-density intergalactic medium, and (3) how the temperatures of collapsing gas parcels evolve.

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A MEASUREMENT OF SMALL-SCALE STRUCTURE IN THE 2.2 ⩽z⩽ 4.2 Lyα FOREST

Cited by 160 publications

References 77 publications

Distinguishing models of reionization using future radio observations of 21-cm 1-point statistics

Distinguishing models of reionization using future radio observations of 21-cm 1-point statistics

The Thermal Proximity Effect: A New Probe of the He ii Reionization History and Quasar Lifetime

On the intergalactic temperature–density relation

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