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At peak, long-duration gamma-ray bursts are the most luminous sources of electromagnetic radiation known. Since their progenitors are massive stars, they provide a tracer of star formation and star-forming galaxies over the whole of cosmic history. Their bright power-law afterglows provide ideal backlights for absorption studies of the interstellar and intergalactic medium back to the reionization era. The proposed THESEUS mission is designed to detect large samples of GRBs at $z>6$ in the 2030s, at a time when supporting observations with major next generation facilities will be possible, thus enabling a range of transformative science. THESEUS will allow us to explore the faint end of the luminosity function of galaxies and the star formation rate density to high redshifts; constrain the progress of re-ionisation beyond $z\gtrsim6$; study in detail early chemical enrichment from stellar explosions, including signatures of Population III stars; and potentially characterize the dark energy equation of state at the highest redshifts., Submitted to Experimental Astronomy

We report on the discovery of a peculiar Broad Absorption Line (BAL) quasar identified in our Gaia-assisted survey of red quasars. The systemic redshift of this quasar was difficult to establish due to the absence of conspicuous emission lines. Based on deep and broad BAL troughs (at least SiIV, CIV, and AlIII), a redshift of z=2.41 was established under the assumption that the systemic redshift can be inferred from the red edge of the BAL troughs. However, we observe a weak and spatially-extended emission line at 4450 AA most likely due to Lyman-alpha emission, which implies a systemic redshift of z=2.66 if correctly identified. There is also evidence for the onset of Lyman-alpha forest absorption bluewards of 4450 AA and evidence for H-alpha emission in the K-band consistent with a systemic redshift of z=2.66. If this redshift is correct, the quasar is an extreme example of a detached low-ionisation BAL quasar. The BAL lines must originate from material moving with very large velocities ranging from 22000 to 40000 km/s. To our knowledge, this is the first case of a systemic-redshift measurement based on extended Lyman-$\alpha$ emission for a BAL quasar, a method that should also be useful in cases of sufficiently distant BL Lac quasars without systemic-redshift information., Comment: 6 pages, 5 figures. Accepted for publication in A&A

We present deep spectroscopic follow-up observations of the Bremer Deep Field (BDF) where the two $z\sim$7 bright Ly$\alpha$ emitters (LAE) BDF521 and BDF3299 were previously discovered by Vanzella et al. (2011) and where a factor of $\sim$3-4 overdensity of faint LBGs has been found by Castellano et al. (2016). We confirm a new bright Ly$\alpha$ emitter, BDF2195, at the same redshift of BDF521, $z=7.008$, and at only $\sim$90 kpc physical distance from it, confirming that the BDF area is likely an overdense, reionized region. A quantitative assessment of the Ly$\alpha$ fraction shows that the number of detected bright emitters is much higher than the average found at z$\sim$7, suggesting a high Ly$\alpha$ transmission through the inter-galactic medium (IGM). However, the line visibility from fainter galaxies is at odds with this finding, since no Ly$\alpha$ emission is found in any of the observed candidates with $M_{UV}>$-20.25. This discrepancy can be understood either if some mechanism prevents Ly$\alpha$ emission from fainter galaxies within the ionized bubbles from reaching the observer, or if faint galaxies are located outside the reionized area and bright LAEs are solely responsible for the creation of their own HII regions. A thorough assessment of the nature of the BDF region and of its sources of re-ionizing radiation will be made possible by JWST spectroscopic capabilities., ERC STFC

Numerical simulations suggest that the first galaxies are formed in protogalactic halos with virial temperatures >= 10^4 K. It is likely that such halos are polluted with trace amounts of metals produced by the first generation of stars. The presence of dust can significantly change the chemistry and dynamics of early galaxies. In this article, we aim to assess the role of dust on the thermal and dynamical evolution of the first galaxies in the presence of a background UV flux, and its implications for the observability of Lyman alpha emitters and sub-mm sources. We have performed high resolution cosmological simulations using the adaptive mesh refinement code FLASH to accomplish this goal. We have developed a chemical network appropriate for these conditions and coupled it with the FLASH code. The main ingredients of our chemical model include the formation of molecules, a multi-level treatment of atomic hydrogen, line trapping of Lyman alpha photons and, photoionization and photodissociation processes in a UV background. We found that the formation of molecules (H_{2} and HD) is significantly enhanced in the presence of dust grains. The presence of a background UV flux strongly influences the formation of molecules by photodissociating them. We explore the evolution after a major merger, leading to the formation of a binary disk. These disks have gas masses of ~10^{7} M_sun at a redshift of 5.4. Each disk lies in a separate subhalo as a result of the merger event. The disks are supported by turbulent pressure due to the highly supersonic turbulence present in the halo. The presence of dust does not significantly reduce the Lyman alpha emission. The emission of Lyman alpha is extended and originates from the envelope of the halo due to line trapping effects. We also find that dust masses of 10^8 M_sun are required to observe the dust continuum emission from z 5 galaxies with ALMA., 12 pages, 10 figures, Accepted for publication in Astronomy and Astrophysics

High redshift quasars (HZQs) with redshifts of z >~ 6 are so rare that any photometrically-selected sample of sources with HZQ-like colours is likely to be dominated by Galactic stars and brown dwarfs scattered from the stellar locus. It is impractical to reobserve all such candidates, so an alternative approach was developed in which Bayesian model comparison techniques are used to calculate the probability that a candidate is a HZQ, P_q, by combining models of the quasar and star populations with the photometric measurements of the object. This method was motivated specifically by the large number of HZQ candidates identified by cross-matching the UKIRT Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS) to the Sloan Digital Sky Survey (SDSS): in the ~1900 deg^2 covered by the LAS in the UKIDSS Seventh Data Release (DR7) there are ~10^3 real astronomical point-sources with the measured colours of the target quasars, of which only ~10 are expected to be HZQs. Applying Bayesian model comparison to the sample reveals that most sources with HZQ-like colours have P_q = 0.1; these object were prioritized for reobservation by ranking according to P_q (and their likely redshift, which was also inferred from the photometric data). Most candidates were rejected after one or two (moderate depth) photometric measurements by recalculating P_q using the new data. That left seven confirmed HZQs, three of which were previously identified in the SDSS and four of which were new UKIDSS discoveries. The high efficiency of this Bayesian selection method suggests that it could usefully be extended to other HZQ surveys (e.g. searches by Pan-STARRS or VISTA) as well as to other searches for rare objects., Comment: submitted to MNRAS; 20 pages, 13 figures

The Lyα emission line is currently a leading tracer of star formation at cosmological distances. Since it becomes the strongest line in the optical-NIR window at redshift z ≥ 2.1. Lyα proves an invaluable tool by which to detect galaxy populations at highest redshifts and a versatile mean for galaxy evolution diagnostics. However, with respect to these promising Lyα-based cosmological studies, number of inconsistencies have first to be understood to ensure proper interpretations. This is the main goal of the present work. Since typical high-z galaxies are very faint and detailed observations are difficult, we present an alternative approach which relies on observations of their local analogs using the Hubble space telescope to investigate the Lyα escape mechanisms. Then, we perform Lyα radiative transfer simulations in local and distant galaxies to understand the link between the different galaxy populations. Finally, we present the first empirical estimate of the Lyα escape fraction in a large sample of Lyα emitters in order to calibrate different Lyα-based cosmological quantities., L'exploration de l'Univers lointain connait présentement un essor sans précédent, grâce notamment à une instrumentation de pointe en perpétuelle amélioration. Les galaxies primordiales sont devenues accessibles par une signature spectrale très intense : la raie de recombinaison de l'hydrogène Lyα. En procède une pléthore d'applications cosmologiques, qui demeurent cependant très fragiles et en proie à diverses incertitudes. En cause, la complexité du transfert radiatif de Lyα, qui est une raie résonante. La présente thèse a pour principal objectif la calibration et la consolidation des quantités, observations et interprétations astrophysiques basées sur l'émission Lyα, en particulier dans l'univers lointain. L'approche principale consiste à observer les analogues locaux des galaxies a flambée de formation d'étoiles distantes, permettant une étude détaillée de la physique Lyα à haute résolution grâce au télescope spatial Hubble. Une étude numérique présente ensuite la simulation du transfert radiatif de Lyα dans les galaxies locales et à un décalage spectral de 3, et le lien entre différentes populations de galaxies. Enfin, la dernière partie de ce travail présente une estimation empirique d'une quantité physique cruciale pour la calibration des observables Lyα, à savoir la fraction d'échappement fesc(Lyα), ainsi que les caractéristiques physiques des émetteurs Lyα détectés par GALEX.

We present strong-lensing analyses of three galaxy clusters, RX J2129.4 + 0009 (z = 0.235), MS 0451.6 - 0305 (z = 0.55), and MACS J2129.4 - 0741 (z = 0.589), using the powerful combination of Hubble Space Telescope (HSI) multiband observations, and Multi-Unit Spectroscopic Explorer (MUSE) spectroscopy. In RX J2129, we newly spectroscopically confirm 15 cluster members. Our resulting mass model uses 8 multiple image systems as we include a galaxy-galaxy lensing system north-east of the cluster, and is composed of 71 haloes including one dark matter cluster-scale halo and two galaxy-scale haloes optimized individually. For MS 0451, we report the spectroscopic identification of two new systems of multiple images in the northern region and 112 cluster members. Our mass model uses 16 multiple image systems and 146 haloes, including 2 large-scale haloes and 7 galaxy-scale haloes independently optimized. For MACS J2129, we report the spectroscopic identification of one new multiple image system at z = 4.41, and newly measure spectroscopic redshifts for four cluster members. Our mass model uses 14 multiple image systems, and is composed of 151 haloes, including 2 large-scale haloes and 4 galaxy-scale haloes independently optimized. Our best models have rms of 0.29, 0.6, 0.74 arcsec in the image plane for RX J2129, MS 0451, and MACS J2129, respectively. This analysis presents a detailed comparison with the existing literature showing excellent agreements, and discuss specific studies of lensed galaxies, e.g. a group of submillimetre galaxies at z = 2.9 in MS 0451, and a bright z = 2.1472 red singly imaged galaxy in MACS J2129.