We present the deepest study to date of the Lyα luminosity function in a blank field using blind integral field spectroscopy from MUSE. We constructed a sample of 604 Lyα emitters (LAEs) across the redshift range 2.91 < z < 6.64 using automatic detection software in the Hubble Ultra Deep Field. The deep data cubes allowed us to calculate accurate total Lyα fluxes capturing low surface-brightness extended Lyα emission now known to be a generic property of high-redshift star-forming galaxies. We simulated realistic extended LAEs to fully characterise the selection function of our samples, and performed flux-recovery experiments to test and correct for bias in our determination of total Lyα fluxes. We find that an accurate completeness correction accounting for extended emission reveals a very steep faint-end slope of the luminosity function, α, down to luminosities of log 10 L erg s −1 < 41.5, applying both the 1/V max and maximum likelihood estimators. Splitting the sample into three broad redshift bins, we see the faint-end slope increasing from −2.03 +1.42 −0.07 at z ≈ 3.44 to −2.86 +0.76 −∞ at z ≈ 5.48, however no strong evolution is seen between the 68% confidence regions in L *-α parameter space. Using the Lyα line flux as a proxy for star formation activity, and integrating the observed luminosity functions, we find that LAEs' contribution to the cosmic star formation rate density rises with redshift until it is comparable to that from continuum-selected samples by z ≈ 6. This implies that LAEs may contribute more to the star-formation activity of the early Universe than previously thought, as any additional inter-glactic medium (IGM) correction would act to further boost the Lyα luminosities. Finally, assuming fiducial values for the escape of Lyα and LyC radiation, and the clumpiness of the IGM, we integrated the maximum likelihood luminosity function at 5.00 < z < 6.64 and find we require only a small extrapolation beyond the data (< 1 dex in luminosity) for LAEs alone to maintain an ionised IGM at z ≈ 6.

We study the extent to which very bright (-< <-M 23.0 21.75 UV ) Lyman-break-selected galaxies at redshifts  z 7 display detectable Lyα emission. To explore this issue, we obtained follow-up optical spectroscopy of 9  z 7 galaxies from a parent sample of 24  z 7 galaxy candidates selected from the 1.65 deg 2 COSMOS-UltraVISTA and SXDS-UDS survey fields using the latest near-infrared public survey data, and new ultra-deep Subaru z′-band imaging (which we also present and describe in this paper). Our spectroscopy yielded only one possible detection of Lyα at z = 7.168 with a rest-frame equivalent width Å = -+ EW 3.7 0 1.1 1.7 . The relative weakness of this line, combined with our failure to detect Lyα emission from the other spectroscopic targets, allows us to place a new upper limit on the prevalence of strong Lyα emission at these redshifts. For conservative calculation and to facilitate comparison with previous studies at lower redshifts, we derive a 1σ upper limit on the fraction of UV-bright galaxies at  z 7 that display Å > EW 50 0 , which we estimate to be <0.23. This result may indicate a weak trend where the fraction of strong Lyα emitters ceases to rise, and possibly falls between z;6 and  z 7. Our results also leave open the possibility that strong Lyα may still be more prevalent in the brightest galaxies in the reionization era than their fainter counterparts. A larger spectroscopic sample of galaxies is required to derive a more reliable constraint on the neutral hydrogen fraction atz 7 based on the Lyα fraction in the bright galaxies.

We present results from Subaru Fiber Multi Object Spectrograph near-infrared spectroscopy of 118 star-forming galaxies at z ∼ 1.5 in the Subaru Deep Field. These galaxies are selected as [O ii]λ3727 emitters at z ≈ 1.47 and 1.62 from narrow-band imaging. We detect the Hα emission line in 115 galaxies, the [O iii]λ5007 emission line in 45 galaxies, and Hβ, [N ii]λ6584, and [S ii]λλ6716, 6731 in 13, 16, and 6 galaxies, respectively. Including the [O ii] emission line, we use the six strong nebular emission lines in the individual and composite rest-frame optical spectra to investigate the physical conditions of the interstellar medium in star-forming galaxies at z ∼ 1.5. We find a tight correlation between Hα and [O ii], which suggests that [O ii] can be a good star formation rate indicator for galaxies at z ∼ 1.5. The line ratios of Hα/[O ii] are consistent with those of local galaxies. We also find that [O ii] emitters have strong [O iii] emission lines. The [O iii]/[O ii] ratios are larger than normal star-forming galaxies in the local universe, suggesting a higher ionization parameter. Less massive galaxies have larger [O iii]/[O ii] ratios. With evidence that the electron density is consistent with local galaxies, the high ionization of galaxies at high redshifts may be attributed to a harder radiation field by a young stellar population and/or an increase in the number of ionizing photons from each massive star.

This study examines the optimal timing for the decommissioning and equipment replacement of nuclear power plants. We consider that the firm has two options of decommissioning and equipment replacement, and determines to exercise these options under electricity price uncertainty. This problem is formulated as two optimal stopping problems. The solution of this model provides the value of the nuclear power plant and the threshold values for decommissioning and replacement. The dependence of decommissioning and replacement strategies on uncertainty and each cost is shown. In order to investigate the probability of events for decommissioning and replacement, Monte Carlo calculations are performed. We also show the probability distribution and the conditional expected time for each event.

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