We present new measurements of the free-streaming of warm dark matter (WDM) from Lyman-$\alpha$ flux-power spectra. We use data from the medium resolution, intermediate redshift XQ-100 sample observed with the X-shooter spectrograph ($z=3–4.2$) and the high-resolution, high-redshift sample used in Viel et al. (2013) obtained with the HIRES/MIKE spectrographs ($z=4.2–5.4$). Based on further improved modelling of the dependence of the Lyman-$\alpha$ flux-power spectrum on the free-streaming of dark matter, cosmological parameters, as well as the thermal history of the intergalactic medium (IGM) with hydrodynamical simulations, we obtain the following limits, expressed as the equivalent mass of thermal relic WDM particles. The XQ-100 flux power spectrum alone gives a lower limit of 1.4 keV, the re-analysis of the HIRES/MIKE sample gives 4.1 keV while the combined analysis gives our best and significantly strengthened lower limit of 5.3 keV (all $2\sigma$ C.L.). The further improvement in the joint analysis is partly due to the fact that the two data sets have different degeneracies between astrophysical and cosmological parameters that are broken when the data sets are combined, and more importantly on chosen priors on the thermal evolution. These results all assume that the temperature evolution of the IGM can be modeled as a power law in redshift. Allowing for a nonsmooth evolution of the temperature of the IGM with sudden temperature changes of up to 5000 K reduces the lower limit for the combined analysis to 3.5 keV. A WDM with smaller thermal relic masses would require, however, a sudden temperature jump of 5000 K or more in the narrow redshift interval $z=4.6–4.8$, in disagreement with observations of the thermal history based on high-resolution resolution Lyman-$\alpha$ forest data and expectations for photo-heating and cooling in the low density IGM at these redshifts.

We present new upper limits on the volume-weighted neutral hydrogen fraction, $$\bar{x}_{\rm H\,\small {i}}$$, at z ∼ 5–6 derived from spectroscopy of bright quasars. The fraction of the Lyα and Lyβ forests that is ‘dark’ (with zero flux) provides the only model-independent upper limit on $$\bar{x}_{\rm H\,\small {i}}$$, requiring no assumptions about the physical conditions in the intergalactic medium or the quasar's unabsorbed UV continuum. In this work, we update our previous results using a larger sample (22 objects) of medium-depth (∼ few hours) spectra of high-redshift quasars obtained with the Magellan, MMT, and VLT. This significantly improves the upper bound on $$\bar{x}_{\rm H\,\small {i}}$$ derived from dark pixel analysis to $$\bar{x}_{\rm H\,\small {i}}\le 0.06{+0.05 (1\sigma )}$$ at z = 5.9 and $$\bar{x}_{\rm H\,\small {i}}\le 0.04{+0.05 (1\sigma )}$$ at z = 5.6. These results provide robust constraints for theoretical models of reionization, and provide the strongest available evidence that reionization has completed (or is very nearly complete) by z ≈ 6.

The redshifts of all cosmologically distant sources are expected to experience a small, systematic drift as a function of time due to the evolution o

The acronym ESPRESSO stems for Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations; this instrument will be the next VLT high resolution spectrograph. The spectrograph will be installed at the Combined‐Coudé Laboratory of the VLT and linked to the four 8.2 m Unit Telescopes (UT) through four optical Coudé trains. ESPRESSO will combine efficiency and extreme spectroscopic precision. ESPRESSO is foreseen to achieve a gain of two magnitudes with respect to its predecessor HARPS, and to improve the instrumental radial‐velocity precision to reach the 10 cm s^–1 level. It can be operated either with a single UT or with up to four UTs, enabling an additional gain in the latter mode. The incoherent combination of four telescopes and the extreme precision requirements called for many innovative design solutions while ensuring the technical heritage of the successful HARPS experience. ESPRESSO will allow to explore new frontiers in most domains of astro‐physics that require precision and sensitivity. The main scientific drivers are the search and characterization of rocky exoplanets in the habitable zone of quiet, nearby G to M‐dwarfs and the analysis of the variability of fundamental physical constants. The project passed the final design review in May 2013 and entered the manufacturing phase. ESPRESSO will be installed at the Paranal Observatory in 2016 and its operation is planned to start by the end of the same year.

ESPRESSO, the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations, will combine the efficiency of modern echelle spectrograph design with extreme radial-velocity precision. It will be installed on ESO's VLT in order to achieve a gain of two magnitudes with respect to its predecessor HARPS, and the instrumental radialvelocity precision will be improved to reach cm/s level. Thanks to its characteristics and the ability of combining incoherently the light of 4 large telescopes, ESPRESSO will offer new possibilities in various fields of astronomy. The main scientific objectives will be the search and characterization of rocky exoplanets in the habitable zone of quiet, nearby G to M-dwarfs, and the analysis of the variability of fundamental physical constants. We will present the ambitious scientific objectives, the capabilities of ESPRESSO, and the technical solutions of this challenging project.

We study cosmic metal enrichment via adaptive mesh refinement hydrodynamical simulations in a (10 Mpc h⁻¹)³ volume following the Population III (PopIII)–PopII transition and for different PopIII initial mass function (IMFs). We have analysed the joint evolution of metal enrichment on galactic and intergalactic scales at $ $z$ $ = 6 and $ $z$ $ = 4. Galaxies account for ≲9舁per舁cent of the baryonic mass; the remaining gas resides in the diffuse phases: (a) voids, i.e. regions with extremely low density (Δ ≤ 1), (b) the true intergalactic medium (IGM, 1 < Δ ≤ 10) and (c) the circumgalactic medium (CGM, 10 < Δ ≤ 10^2.5), the interface between the IGM and galaxies. At $ $z$ $ = 6, a galactic mass–metallicity relation is established. At $ $z$ $ = 4, galaxies with a stellar mass M_* ≃ 10^8.5舁M_⊙ show $ $\log ({\rm O}/H)+12=8.19$ $, consistent with observations. The total amount of heavy elements rises from $ $\Omega ^{\rm SFH}_{Z}=1.52\times 10^{-6}$ $ at $ $z$ $ = 6 to 8.05 × 10⁻⁶ at $ $z$ $ = 4. Metals in galaxies make up to ≃0.89 of such budget at $ $z$ $ = 6; this fraction increases to ≃0.95 at $ $z$ $ = 4. At $ $z$ $ = 6 ($ $z$ $ = 4), the remaining metals are distributed in CGM/IGM/voids with the following mass fractions: 0.06/0.04/0.01 (0.03/0.02/0.01). Analogously to galaxies, at $ $z$ $ = 4 a density–metallicity ($ $\Delta {\rm -}Z$ $) relation is in place for the diffuse phases: the IGM/voids have a spatially uniform metallicity, Z ∼ 10^−3.5舁Z_⊙; in the CGM, Z steeply rises with density up to ≃10⁻²舁Z_⊙. In all diffuse phases, a considerable fraction of metals is in a warm/hot ($ $T\, \mu ^{-1}>10^{4.5}\,{\rm K}$ $) state. Due to these physical conditions, $ ${{\rm C}\,{\small {iv}}}$ $ absorption line experiments can probe only ≃2舁per舁cent of the total carbon present in the IGM/CGM; however, metal absorption line spectra are very effective tools to study reionization. Finally, the PopIII star formation history is almost insensitive to the chosen PopIII IMF. PopIII stars are preferentially formed in truly pristine (Z = 0) gas pockets, well outside polluted regions created by previous star formation episodes.