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Register a new userThe Evolution of the Ultraluminous Ly-alpha Luminosity Function over z=5.7-6.6
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Ultraluminous Lyman alpha (Lya) emitting galaxies (ULLAEs) with log L (Lya)>43.5 erg/s near the epoch of reionization (z>5) make up the bright end of the LAE luminosity function (LF) and may provide insight into the process of reionization, including the formation of ionized bubbles around these extreme systems. We present a spectroscopic LF for ULLAEs at z=5.7. We used data from the HEROES ~45 sq. deg Subaru Hyper Suprime-Cam survey, which is centered on the North Ecliptic Pole and has both broadband (grizY) and narrowband (NB816 and NB921) imaging, to select candidate ULLAEs based on a NB816 excess and a strong broadband Lyman break. We spectroscopically observed 17 ULLAE candidates with DEIMOS on Keck II. We confirmed 12 as LAEs at z=5.7, 9 of which are ULLAEs. The remaining sources are an AGN at z=5.7, an [OIII]5007 emitter at z=0.63, a red star, and two spectroscopic non-detections. Using the 9 confirmed ULLAEs, we construct a ULLAE LF at z=5.7. After applying a comprehensive incompleteness correction, we compare our new z=5.7 LF with our recent z=6.6 LF and with other LFs from the literature to look for evolution at the ultraluminous end. We find the overall ratio of the z=5.7 to z=6.6 ULLAE comoving number densities to be 1.92 (+1.12, -0.71), which corresponds to a LF offset of 0.28 (+0.20, -0.20) dex.
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We present the luminosity function (LF) for ultraluminous Ly$alpha$ emitting galaxies (LAEs) at z = 6.6. We define ultraluminous LAEs (ULLAEs) as galaxies with logL(Ly$alpha$) > 43.5 erg s$^{-1}$. We select our main sample using the g, r, i, z, and NB921 observations of a wide-area (30 deg$^2$) Hyper Suprime-Cam survey of the North Ecliptic Pole (NEP) field. We select candidates with g, r, i > 26, NB921 $leq$ 23.5, and NB921 - z $leq$ 1.3. Using the DEIMOS spectrograph on Keck II, we confirm 9 of our 14 candidates as ULLAEs at z = 6.6 and the remaining 5 as an AGN at z = 6.6, two [OIII]$lambda$5007 emitting galaxies at z = 0.84 and z = 0.85, and two non-detections. This emphasizes the need for full spectroscopic follow-up to determine accurate LFs. In constructing the ULLAE LF at z = 6.6, we combine our 9 NEP ULLAEs with two previously discovered and confirmed ULLAEs in the COSMOS field: CR7 and COLA1. We apply rigorous corrections for incompleteness based on simulations. We compare our ULLAE LF at z = 6.6 with LFs at z = 5.7 and z = 6.6 from the literature. Our data reject some previous LF normalizations and power law indices, but they are broadly consistent with others. Indeed, a comparative analysis of the different literature LFs suggests that none is fully consistent with any of the others, making it critical to determine the evolution from z = 5.7 to z = 6.6 using LFs constructed in exactly the same way at both redshifts.
We present the Ly$alpha$ luminosity functions (LFs) at $z=$5.7 and 6.6 derived from a new large sample of 1,266 Ly$alpha$ emitters (LAEs) identified in total areas of 14 and 21 deg$^2$, respectively, based on the early narrowband data of the Subaru/Hyper Suprime-Cam (HSC) survey. Together with careful Monte-Carlo simulations that account for the incompleteness of the LAE selection and the flux estimate systematics in the narrowband imaging, we have determined the Ly$alpha$ LFs with the unprecedentedly small statistical and systematic uncertainties in a wide Ly$alpha$ luminosity range of $10^{42.8-43.8}$ erg s$^{-1}$. We obtain the best-fit Schechter parameters of $L^{*}_{{rm Lya}}=1.6^{+2.2}_{-0.6} (1.7^{+0.3}_{-0.7}) times10^{43}$ erg s$^{-1}$, $phi^{*}_{{rm Lya}}=0.85^{+1.87}_{-0.77} (0.47^{+1.44}_{-0.44})times10^{-4}$ Mpc$^{-3}$, and $alpha=-2.6^{+0.6}_{-0.4} (-2.5^{+0.5}_{-0.5})$ at $z=5.7$ ($6.6$). We confirm that our best-estimate Ly$alpha$ LFs are consistent with the majority of the previous studies, but find that our Ly$alpha$ LFs do not agree with the high number densities of LAEs recently claimed by Matthee/Santos et al.s studies that may overcorrect the incompleteness and the flux systematics. Our Ly$alpha$ LFs at $z=5.7$ and $6.6$ show an indication that the faint-end slope is very steep ($alpha simeq -2.5$), although it is also possible that the bright-end LF results are enhanced by systematic effects such as the contribution from AGNs, blended merging galaxies, and/or large ionized bubbles around bright LAEs. Comparing our Ly$alpha$ LF measurements with four independent reionization models, we estimate the neutral hydrogen fraction of the IGM to be $x_{rm HI}=0.3pm0.2$ at $z=$6.6 that is consistent with the small Thomson scattering optical depth obtained by Planck 2016.
We report results of a deep wide-field narrowband survey for redshift z~5.7 Ly alpha emitters carried out with SuprimeCam on Subaru 8.3-m telescope. Deep narrowband imaging of the SSA22 field through a 120 A bandpass filter centered at 8150 A was combined with deep multicolor RIz SuprimeCam broadband imaging, and BVRZ imaging taken with CFHTs CFH12K camera to select high-redshift galaxy candidates. Spectroscopic observations were made using the new wide-field multi-object DEIMOS spectrograph on Keck for 22 of the 26 candidate objects. Eighteen objects were identified as z~5.7 Lyman alpha emitters, and a further nineteenth candidate was identified based on an LRIS spectrum. At the 3.3 A resolution of the DEIMOS spectra the asymmetric profile for Ly alpha emission with its steep blue fall-off can be clearly seen. We use this to describe the distribution of equivalent widths and the continuum color break properties for z~5.7 Ly alpha galaxies compared with foreground objects. The large majority (>75%) of Ly alpha lines have rest frame equivalent widths less than 240 A and can be understood in terms of young star forming galaxies with a Salpeter initial mass function for the stars. With narrowband selection criteria of I-N > 0.7 and N<25.05 (AB mags) we find a surface density of Ly alpha emitters of 0.03 per square arcminute per (deltaz=0.1) to a limiting flux just under 2e-17 erg/cm2/s. The luminosity function of the Ly alpha emitters is similar to that at lower redshifts to the lowest measurable luminosity of 1e43 ergs/s as is the universal star formation rate based on their continuum properties. We note that the objects are highly structured in both spatial and spectral properties on the angular scale of the fields (~60 Mpc), and that multiple fields will have to be averaged to accurately measure their ensemble properties.
We present the photometric determination of the bright-end (L_Lya>10^43.5 erg/s) of the Lya luminosity function (LF) within four redshifts windows in the interval 2.2<z<3.3. Our work is based on the Javalambre Photometric Local Universe Survey (J-PLUS) first data-release, which provides multiple narrow-band measurements over ~1000 deg^2, with limiting magnitude r~22. The analysis of high-z Lya-emitting sources over such a wide area is unprecedented, and allows to select a total of ~14,500 hyper-bright (L_Lya>10^43.3 erg/s) Lya-emitting candidates. We test our selection with two spectroscopic follow-up programs at the GTC telescope, confirming ~89% of the targets as line-emitting sources, with ~64% being genuine z~2.2 QSOs. We extend the 2.2<z<3.3 Lya LF for the first time above L_Lya~10^44 erg/s and down to densities of ~10^-8 Mpc^-3. Our results unveil with high detail the Schechter exponential-decay of the brightest-end of the Lya LF, complementing the power-law component of previous LF determinations at 43.3<Log_10(L_Lya / [erg/s])<44. We measure Phi^*=(3.33+-0.19)x10^-6, Log(L^*)=44.65+-0.65 and alpha=-1.35+-0.84 as an average over the redshifts we probe. These values are significantly different than the typical Schechter parameters measured for the Lya LF of high-z star-forming LAEs. This suggests that z>2 AGN/QSOs (likely dominant in our samples) are described by a structurally different LF than z>2 star-forming LAEs, namely with L^*_QSOs ~ 100 L^*_LAEs and Phi^*_QSOs ~ 10^-3 Phi^*_LAEs. Finally, our method identifies very efficiently as high-z line-emitters sources without previous spectroscopic confirmation, currently classified as stars (~2000 objects in each redshift bin, on average). Assuming a large predominance of Lya-emitting AGN/QSOs in our samples, this supports the scenario by which these are the most abundant class of z>2 Lya emitters at L_Lya>10^43.3 erg/s.
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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