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[en] An experiment intended to measure the radiative lifetime of the 2P state of positronium, by monitoring the Lyman-α transition photon in coincidence with a signal indicating Ps formation, is described. (orig.)
[en] The experiment SOLLY consists of a hydrogen cell containing molecular hydrogen at low pressure and is sealed by magnesium fluoride windows. A hot filament dissociates the molecules into hydrogen atoms. By measuring the scattered Ly- α photons with a sideways mounted detector, the core region of the solar Ly- α line can be studied. Another detector is positioned along the optic axis at the rear of the instrument and measures the total intensity of the solar photons near 1216 A. First results of the rocket flight will be presented and discussed
[en] We carried out extended spectroscopic confirmations of Lyα emitters (LAEs) at z = 6.5 and 5.7 in the Subaru Deep Field. Now, the total number of spectroscopically confirmed LAEs is 45 and 54 at z = 6.5 and 5.7, respectively, and at least 81% (70%) of our photometric candidates at z = 6.5 (5.7) have been spectroscopically identified as real LAEs. We made careful measurements of the Lyα luminosity, both photometrically and spectroscopically, to accurately determine the Lyα and rest-UV luminosity functions (LFs). The substantially improved evaluation of the Lyα LF at z = 6.5 shows an apparent deficit from z = 5.7 at least at the bright end, and a possible decline even at the faint end, though small uncertainties remain. The rest-UV LFs at z = 6.5 and 5.7 are in good agreement, at least at the bright end, in clear contrast to the differences seen in the Lyα LF. These results imply an increase in the neutral fraction of the intergalactic medium from z = 5.7 to 6.5. The rest-frame equivalent width (EW0) distribution at z = 6.5 seems to be systematically smaller than z = 5.7, and it shows an extended tail toward larger EW0. The bright end of the rest-UV LF can be reproduced from the observed Lyα LF and a reasonable EW0-UV luminosity relation. Integrating this rest-UV LF provides the first measurement of the contribution of LAEs to the photon budget required for reionization. The derived UV LF suggests that the fractional contribution of LAEs to the photon budget among Lyman break galaxies significantly increases toward faint magnitudes. Low-luminosity LAEs could dominate the ionizing photon budget, though this inference depends strongly on the uncertain faint-end slope of the Lyα LF.
[en] We cross-correlate the positions of damped Lyman-α systems (DLAs) and their parent quasar catalog with a convergence map derived from the Planck cosmic microwave background (CMB) temperature data. We then make consistent measurements of the lensing signal of both samples in both Fourier and configuration space. By interpreting the excess signal present in the DLA catalog with respect to the parent quasar catalog as caused by the large scale structure traced by DLAs, we are able to infer the bias of these objects: bDLA=2.6±0.9. These results are consistent with previous measurements made in cross-correlation with the Lyman-α forest, although the current noise in the lensing data and the low number density of DLAs limits the constraining power of this measurement. We discuss the robustness of the analysis with respect to a number different systematic effects and forecast prospects of carrying out this measurement with data from future experiments.
[en] We report results of an unprecedentedly deep, blind search for Lyα emitters (LAEs) at z = 5.7 using the Inamori-Magellan Areal Camera and Spectrograph (IMACS), with the goal of identifying missing sources of reionization that could also be basic building blocks for today's L* galaxies. We describe how improvements in wide field imaging with the Baade telescope, upgrades to IMACS, and the accumulation of ∼20 hr of integration per field in excellent seeing led to the detection of single-emission-line sources as faint as F ∼ 2 x 10-18 erg s-1 cm-2, a sensitivity five times deeper than our first search. A reasonable correction for foreground interlopers implies a steep rise of approximately an order of magnitude in source density for a factor of four drop in flux, from F = 10-17.0 erg s-1 cm-2 to F = 10-17.6 (2.5 x 10-18) erg s-1 cm-2. At this flux the putative LAEs have reached a surface density of ∼1 arcmin-2-a comoving volume density of 4 x 10-3 Mpc-3, several times the density of L* galaxies today. Such a population of faint LAEs would account for a significant fraction of the critical flux density required to complete reionization at this epoch, and would be good candidates for building blocks of stellar mass ∼108-109 Msun for the young galaxies of this epoch.
[en] The important variations of the Hsub(α) line profile in the star T Tau were found on 14 spectra obtained at intervals of 6 or 7 min. This extraordinary fast changes shown for the first time are difficult to explain with the current theoretical models
[fr]On a trouve d'importantes variations du profil de la raie Hsub(α) de l'etoile T Tau, sur 14 spectres obtenus a des intervalles de temps de 6 a 7 mn. Ces variations extraordinairement rapides mises en evidence pour la premiere fois sont difficiles a expliquer avec les modeles theoriques actuellement existants