We present a new investigation of the thermal history of the intergalactic medium (IGM) during and after reionization using the Lyman-α forest flux power spectrum at 4.0 z 5.2. Using a sample of 15 highresolution spectra, we measure the flux power down to the smallest scales ever probed at these redshifts (−1 log(k/km −1 s) −0.7). These scales are highly sensitive to both the instantaneous temperature of the IGM and the total energy injected per unit mass during and after reionization. We measure temperatures at the mean density of T 0 ∼ 7000-8000 K, consistent with no significant temperature evolution for redshifts 4.2 z 5.0. We also present the first observational constraints on the integrated IGM thermal history, finding that the total energy input per unit mass increases from u 0 ∼ 4.6 eV m −1 p to 7.3 eV m −1 p from z ∼ 6 to 4.2 assuming a Λ-CDM cosmology. We show how these results can be used simultaneously to obtain information on the timing and the sources of the reionization process. Our first proof of concept using simplistic models of instantaneous reionization produces results comparable to and consistent with the recent Planck constraints, favoring models with z rei ∼ 8.5 +1.1 −0.8 .

Previous studies have noted difficulties in modeling the highest opacities of the z > 5.5 Lyα forest, epitomized by the extreme Lyα trough observed towards quasar ULAS J0148+0600. One possibility is that the most opaque regions at these redshifts contain significant amounts of neutral hydrogen. This explanation, which abandons the common assumption that reionization ended before z = 6, also reconciles evidence from independent observations of a significantly neutral Universe at z = 7.5. Here we explore a model in which the neutral fraction is still ≈ 10% at z = 5.5. We confirm that this model can account for the observed scatter in Lyα forest opacities, as well as the observed Lyβ transmission in the J0148 trough. We contrast the model with a competing "earlier" reionization scenario characterized by a short mean free path and large fluctuations in the post-reionization ionizing background. We consider Lyα and Lyβ effective optical depths, their correlations, trough size distributions, dark pixel fractions, the IGM thermal history, and spatial distributions of Lyman-α emitters around forest sight lines. We find that the models are broadly similar in almost all of these statistics, suggesting that it may be difficult to distinguish between them definitively. We argue that improved constraints on the mean free path and the thermal history at z > 5 could go a long way towards diagnosing the origin of the z > 5.5 opacity fluctuations.

We use cosmological hydrodynamical simulations to assess the feasibility of constraining the thermal history of the intergalactic medium during reionisation with the Lyα forest at z ≃ 5 . The integrated thermal history has a measureable impact on the transmitted flux power spectrum that can be isolated from Doppler broadening at this redshift. We parameterise this using the cumulative energy per proton, u 0 , deposited into a gas parcel at the mean background density, a quantity that is tightly linked with the gas density power spectrum in the simulations. We construct mock observations of the line of sight Lyα forest power spectrum and use a Markov Chain Monte Carlo approach to recover u 0 at redshifts 5 < ∼ z < ∼ 12. A statistical uncertainty of ∼ 20 per cent is expected (at 68 per cent confidence) at z ≃ 5 using high resolution spectra with a total redshift path length of ∆z = 4 and a typical signal-to-noise ratio of S/N = 15 per pixel. Estimates for the expected systematic uncertainties are comparable, such that existing data should enable a measurement of u 0 to within ∼ 30 per cent. This translates to distinguishing between reionisation scenarios with similar instantaneous temperatures at z ≃ 5, but with an energy deposited per proton that differs by 2-3 eV over the redshift interval 5 < ∼ z < ∼ 12. For an initial temperature of T ∼ 10 4 K following reionisation, this corresponds to the difference between early (z re = 12) and late (z re = 7) reionisation in our models.

Arbuscular mycorrhizal fungi (AMF) establish symbiotic interaction with 80% of known land plants. It has a pronounced impact on plant growth, water absorption, mineral nutrition, and protection from abiotic stresses. Plants are very dynamic systems having great adaptability under continuously changing drying conditions. In this regard, the function of AMF as a biological tool for improving plant drought stress tolerance and phenotypic plasticity, in terms of establishing mutualistic associations, seems an innovative approach towards sustainable agriculture. However, a better understanding of these complex interconnected signaling pathways and AMF-mediated mechanisms that regulate the drought tolerance in plants will enhance its potential application as an innovative approach in environmentally friendly agriculture. This paper reviews the underlying mechanisms that are confidently linked with plant–AMF interaction in alleviating drought stress, constructing emphasis on phytohormones and signaling molecules and their interaction with biochemical, and physiological processes to maintain the homeostasis of nutrient and water cycling and plant growth performance. Likewise, the paper will analyze how the AMF symbiosis helps the plant to overcome the deleterious effects of stress is also evaluated. Finally, we review how interactions between various signaling mechanisms governed by AMF symbiosis modulate different physiological responses to improve drought tolerance. Understanding the AMF-mediated mechanisms that are important for regulating the establishment of the mycorrhizal association and the plant protective responses towards unfavorable conditions will open new approaches to exploit AMF as a bioprotective tool against drought.

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).

We study the effect of different feedback prescriptions on the properties of the low redshift (z ≤ 1.6) Lyα forest using a selection of hydrodynamical simulations drawn from the Sherwood simulation suite. The simulations incorporate stellar feedback, AGN feedback and a simplified scheme for efficiently modelling the low column density Lyα forest. We confirm a discrepancy remains between Cosmic Origins Spectrograph (COS) observations of the Lyα forest column density distribution function (CDDF) at z ≃ 0.1 for high column density systems (N HI > 10 14 cm −2 ), as well as Lyα velocity widths that are too narrow compared to the COS data. Stellar or AGN feedbackas currently implemented in our simulations -have only a small effect on the CDDF and velocity width distribution. We conclude that resolving the discrepancy between the COS data and simulations requires an increase in the temperature of overdense gas with ∆ = 4-40, either through additional He II photo-heating at z > 2 or fine-tuned feedback that ejects overdense gas into the IGM at just the right temperature for it to still contribute significantly to the Lyα forest. Alternatively a larger, currently unresolved turbulent component to the line width could resolve the discrepancy.

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We present a new, uniform analysis of the H i transmitted flux (F) and H i column density ($N_{\mathrm{H\,{\small I}}}$) distribution in the low-density IGM as a function of redshift z for 0 &lt; z &lt; 3.6 using 55 HST/COS FUV (Δz = 7.2 at z &lt; 0.5), five HST/STIS + COS NUV (Δz = 1.3 at z ∼ 1) and 24 VLT/UVES, and Keck/HIRES (Δz = 11.6 at 1.7 &lt; z &lt; 3.6) AGN spectra. We performed a consistent, uniform Voigt profile analysis to combine spectra taken with different instruments, to reduce systematics and to remove metal-line contamination. We confirm previously known conclusions on firmer quantitative grounds in particular by improving the measurements at z ∼ 1. Two flux statistics at 0 &lt; F &lt; 1, the mean H i flux and the flux probability distribution function (PDF), show that considerable evolution occurs from z = 3.6 to z = 1.5, after which it slows down to become effectively stable for z &lt; 0.5. However, there are large sightline variations. For the H i column density distribution function (CDDF, f ∝ $N_{\rm H\,{\small I}}^{-\beta }$) at $\log (N_{\mathrm{H\,{\small I}}}/1\, {\mathrm{cm}^{-2}})$ ∈ [13.5, 16.0], β increases as z decreases from β = 1.60 at z ∼ 3.4 to β = 1.82 at z ∼ 0.1. The CDDF shape at lower redshifts can be reproduced by a small amount of clockwise rotation of a higher-z CDDF with a slightly larger CDDF normalization. The absorption line number per z (dn/dz) shows a similar evolutionary break at z ∼ 1.5 as seen in the flux statistics. High-$N_{\mathrm{H\,{\small I}}}$ absorbers evolve more rapidly than low-$N_{\mathrm{H\,{\small I}}}$ absorbers to decrease in number or cross-section with time. The individual dn/dz shows a large scatter at a given z. The scatter increases towards lower z, possibly caused by a stronger clustering at lower z.