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Register a new userCompleting the Census of Ly-alpha Emitters at the Reionization Epoch
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We carried out extended spectroscopic confirmations of Ly-alpha 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 Ly-alpha luminosity, both photometrically and spectroscopically, to accurately determine the Ly-alpha and rest-UV luminosity functions (LFs). The substantially improved evaluation of the Ly-alpha 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 Ly-alpha 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 (EW_0) distribution at z=6.5 seems to be systematically smaller than z=5.7, and it shows an extended tail toward larger EW_0. The bright end of the rest-UV LF can be reproduced from the observed Ly-alpha LF and a reasonable EW_0-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 towards faint magnitudes. Low-luminosity LAEs could dominate the ionizing photon budget, though this inference depends strongly on the uncertain faint-end slope of the Ly-alpha LF.
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We present a novel method to investigate cosmic reionization, using joint spectral information on high redshift Lyman Alpha Emitters (LAE) and quasars (QSOs). Although LAEs have been proposed as reionization probes, their use is hampered by the fact their Ly{alpha} line is damped not only by intergalactic HI but also internally by dust. Our method allows to overcome such degeneracy. First, we carefully calibrate a reionization simulation with QSO absorption line experiments. Then we identify LAEs in two simulation boxes at z=5.7 and z=6.6 and we build synthetic images/spectra of a prototypical LAE. At redshift 5.7, we find that the Ly{alpha} transmissivity (T_LAE) ~ 0.25, almost independent of the halo mass. This constancy arises from the conspiracy of two effects: (i) the intrinsic Ly{alpha} line width and (ii) the infall peculiar velocity. At higher redshift, z=6.6, where the transmissivity is instead largely set by the local HI abundance and LAE transmissivity consequently increases with halo mass from 0.15 to 0.3. Although outflows are present, they are efficiently pressure-confined by infall in a small region around the LAE; hence they only marginally affect transmissivity. Finally, we cast LOS originating from background QSOs passing through foreground LAEs at different impact parameters, and compute the quasar transmissivity (T_QSO). At smaller impact parameters, d < 1 cMpc, a positive correlation between T_QSO and halo mass is found at z = 5.7, which tends to become less pronounced (i.e. flatter) at larger distances. By cross-correlating T_LAE and T_QSO, we can obtain a HI density estimate unaffected by dust. At z= 5.7, the cross-correlation is relatively weak,whereas at z = 6.6 we find a clear positive correlation. We conclude by briefly discussing the perspectives for the application of the method to existing and forthcoming data.
We calculate Lyman Alpha Emitter (LAE) angular correlation functions (ACFs) at $z simeq 6.6$ and the fraction of lifetime (for the 100 Myrs preceding $zsimeq6.6$) galaxies spend as Lyman Break Galaxies (LBGs) or as LBGs with Lyman Alpha (Ly$alpha$) emission using a model that combines SPH cosmological simulations (GADGET-2), dust attenuation and a radiative transfer code (pCRASH). The ACFs are a powerful tool that significantly narrows the 3D parameter space allowed by LAE Ly$alpha$ and UV luminosity functions (LFs) alone. With this work, we simultaneously constrain the escape fraction of ionizing photons $f_{esc}=0.05-0.5$, the mean fraction of neutral hydrogen in the intergalactic medium (IGM) $langle chi_{HI} rangle leq 0.01$ and the dust-dependent ratio of the escape fractions of Ly$alpha$ and UV continuum photons $f_{alpha}/f_c=0.6-1.2$. Our results show that reionization has the largest impact on the amplitude of the ACFs, and its imprints are clearly distinguishable from those of $f_{esc}$ and $f_alpha/f_c$. We also show that galaxies with a critical stellar mass of $M_* = 10^{8.5} (10^{9.5})M_{odot}$ produce enough luminosity to stay visible as LBGs (LAEs). Finally, the fraction of time during the past 100 Myrs prior to z=6.6 a galaxy spends as a LBG or as a LBG with Ly$alpha$ emission increases with the UV magnitude (and the stellar mass $M_*$): considering observed (dust and IGM attenuated) luminosities, the fraction of time a galaxy spends as a LBG (LAE) increases from 65% to 100% (0-100%) as $M_{UV}$ decreases from $M_{UV} = -18.0$ to $-23.5$ ($M_*$ increases from $10^8-10^{10.5} M_{odot}$). Thus in our model the brightest (most massive) LBGs most often show Ly$alpha$ emission.
We report an extensive search for Lyman-alpha emitters (LAEs) at z=6.5 in the Subaru Deep Field. Subsequent spectroscopy with Subaru and Keck identified eight more LAEs, giving a total of 17 spectroscopically confirmed LAEs at z=6.5. Based on this spectroscopic sample of 17, complemented by a photometric sample of 58 LAEs, we have derived a more accurate Lyman-alpha luminosity function of LAEs at z=6.5, which reveals an apparent deficit at the bright end of ~0.75 mag fainter L*, compared with that observed at z=5.7. The difference in the LAE luminosity functions between z=5.7 and 6.5 is significant at the 3-sigma level, which is reduced to 2-sigma when cosmic variance is taken into account. This result may imply that the reionization of the universe has not been completed at z=6.5. We found that the spatial distribution of LAEs at z=6.5 was homogeneous over the field. We discuss the implications of these results for the reionization of the universe.
We present results of a survey of Lyman $alpha$ emitters (LAEs) at $z=6.5$ which is thought to be the final epoch of the cosmic reionization. In a $approx530$ arcmin$^2$ deep image of the SSA22 field taken through a narrowband filter NB912 installed in the Subaru/Suprime-Cam, we have found only 14 LAE candidates with $L_{rm Lyalpha}ga3times10^{42}$ erg s$^{-1}$. Even applying the same colour selection criteria, the number density of the LAE candidates is a factor of 3 smaller than that found at the same redshift in the Subaru Deep field (SDF). Assuming the number density in the SDF is a cosmic average, the probability to have a number density equal to or smaller than that found in the SSA22 field is only 7% if we consider fluctuation by the large-scale structure (i.e. cosmic variance) and Poisson error. Therefore, the SSA22 field may be a rare void at $z=6.5$. On the other hand, we have found that the number density of $i$-drop galaxies with $25.5<z<26.0$ in the SSA22 field agrees well with that in the SDF. If we consider a scenario that a larger neutral fraction of intergalactic hydrogen, $x_{rm HI}$, in the SSA22 field obscures a part of Ly$alpha$ emission, $x_{rm HI}$ in the SSA22 field should be about 2 times larger than that in the SDF. This can be translated into $x_{rm HI}<0.9$ at $z=6.5$ in the SSA22 field. A much larger survey area than previous ones is required to overcome a large fluctuation reported here and to obtain a robust constraint on $x_{rm HI}$ at the end of the reionization from LAEs.
The Ly-alpha luminosity function (LF) of high-redshift Ly-alpha emitters (LAEs) is one of the few observables of the re-ionization epoch accessible to date with 8-10 m class telescopes. The evolution with redshift allows one to constrain the evolution of LAEs and their role in re-ionizing the Universe at the end of the Dark Ages. We have performed a narrow-band imaging program at 1.06 microns at the CFHT, targeting Ly-alpha emitters at redshift z ~ 7.7 in the CFHT-LS D1 field. From these observations we have derived a photometric sample of 7 LAE candidates at z ~ 7.7. We derive luminosity functions for the full sample of seven objects and for sub-samples of four objects. If the brightest objects in our sample are real, we infer a luminosity function which would be difficult to reconcile with previous work at lower redshift. More definitive conclusions will require spectroscopic confirmation.
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