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Register a new userA Faint Flux-Limited Lyman Alpha Emitter Sample at $zsim0.3$
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We present a flux-limited sample of $zsim0.3$ Ly$alpha$ emitters (LAEs) from Galaxy Evolution Explorer (GALEX) grism spectroscopic data. The published GALEX $zsim0.3$ LAE sample is pre-selected from continuum-bright objects and thus is biased against high equivalent width (EW) LAEs. We remove this continuum pre-selection and compute the EW distribution and the luminosity function of the Ly$alpha$ emission line directly from our sample. We examine the evolution of these quantities from $zsim0.3$ to $2.2$ and find that the EW distribution shows little evidence for evolution over this redshift range. As shown by previous studies, the Ly$alpha$ luminosity density from star-forming galaxies declines rapidly with declining redshift. However, we find that the decline in Ly$alpha$ luminosity density from $z=2.2$ to $z=0.3$ may simply mirror the decline seen in the H$alpha$ luminosity density from $z=2.2$ to $z=0.4$, implying little change in the volumetric Ly$alpha$ escape fraction. Finally, we show that the observed Ly$alpha$ luminosity density from AGNs is comparable to the observed Ly$alpha$ luminosity density from star-forming galaxies at $z=0.3$. We suggest that this significant contribution from AGNs to the total observed Ly$alpha$ luminosity density persists out to $zsim2.2$.
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We report the detection of the most luminous high-redshift Lyman Alpha Emitting galaxy (LAE) yet seen, with log L(Ly alpha) = 43.9 ergs/s. The galaxy -- COSMOS Lyman alpha 1, or COLA1 -- was detected in a search for ultra-luminous LAEs with Hyper Suprime-Cam on the Subaru telescope. It was confirmed to lie at z = 6.593 based on a Lyman alpha line detection obtained from followup spectroscopy with the DEIMOS spectrograph on Keck2. COLA1 is the first very high-redshift LAE to show a multi-component Lyman alpha line profile with a blue wing, which suggests that it could lie in a highly ionized region of the intergalactic medium and could have significant infall. If this interpretation is correct, then ultra-luminous LAEs like COLA1 offer a unique opportunity to determine the properties of the HII regions around these galaxies which will help in understanding the ionization of the z ~ 7 intergalactic medium.
We built a grid of photoionization models and compiled already available observational emission line intensities ($rm 1000 : < : lambda(AA) : < : 2000$) of confirmed star formation regions and Active Galactic Nucleus (AGNs) in order to classify five Ly$alpha$ emitter (LAE) objects at high redshift $(5.7 : < : z : < :7.2)$. We selected objects for which at least one metal emission-line was measured. The resulting sample is composed by the objects RXCJ2248.7-4431-ID3, HSCJ233408+004403, COSY, A1703-zd6, and CR7 (clump C). The photoionization models were built assuming a Power Law (associated with the presence of an AGN), a Direct Collapse Black Hole (DCBH), and Population II stars for the ionizing source. The resulting models were then compared with observational emission-line ratios in six diagnostic diagrams to produce a spectral classification of the sample. We found that CR7 (clump C), HSCJ233408+004403 and COSY probably have a non thermal ionizing source (AGN or DCBH) while the RXC J2248.7-4431-ID3 and A1703-zd6 seem to host a stellar cluster. Detailed photoionization models were constructed to reproduce observational emission line ratios of the sample of LAEs, and to derive chemical abundances and number of ionizing photons $Q(rm H)$ of these objects. From these models, we found metallicities in the range $(Z/Z_{odot})=0.1-0.5$ and $log Q(rm H) : > : 53$. Values for C/O abundance ratio derived for the LAEs seem to be consistent with those derived for local star forming objects with similar metallicities, while an overabundance of N/O was found for most of the LAEs.
(Abridged) We investigate the Lyman $alpha$ emitter luminosity function (LAE LF) within the redshift range $2.9 leq z leq 6$ from the first instalment of the blind integral field spectroscopic survey MUSE-Wide. This initial part of the survey probes a region of 22.2 arcmin$^2$ in the CANDELS/GOODS-S field. The dataset provided us with 237 LAEs from which we construct the LAE LF in the luminosity range $42.2 leq log L_mathrm{Lyalpha} [mathrm{erg,s}^{-1}]leq 43.5$ within a volume of $2.3times10^5$ Mpc$^3$. For the LF construction we utilise three different non-parametric estimators: The classical $1/V_mathrm{max}$ method, the $C^{-}$ method, and an improved binned estimator for the differential LF. All three methods deliver consistent results, with the cumulative LAE LF being $Phi(log L_mathrm{Lyalpha} [mathrm{erg,s}^{-1}] = 43.5) simeq 3times 10^{-6}$ Mpc$^{-3}$ and $Phi(log L_mathrm{Lyalpha} [mathrm{erg,s}^{-1}] = 42.2) simeq 2 times 10^{-3}$ Mpc$^{-3}$ towards the bright- and faint-end of our survey, respectively. By employing a non-parametric statistical test, as well as by comparing the full sample to sub-samples in redshift bins, we find no supporting evidence for an evolving LAE LF over the probed redshift and luminosity range. We determine the best-fitting Schechter function parameters $alpha = -1.84^{+0.42}_{-0.41}$ and $log L^* [mathrm{erg,s}^{-1}] = 42.2^{+0.22}_{-0.16}$ with the corresponding normalisation $log phi^* [mathrm{Mpc}^{-3}] = -2.71$. When correcting for completeness in the LAE LF determinations, we take into account that LAEs exhibit diffuse extended low surface-brightness haloes. We compare the resulting LF to one obtained where we apply a correction assuming compact point-like emission. We find that the standard correction underestimates the LAE LF at the faint end of our survey by a factor of 2.5.
We present measurements of the mean and scatter of the IGM Lyman-{alpha} opacity at 4.9 < z < 6.1 along the lines of sight of 62 quasars at z > 5.7, the largest sample assembled at these redshifts to date by a factor of two. The sample size enables us to sample cosmic variance at these redshifts more robustly than ever before. The spectra used here were obtained by the SDSS, DES-VHS and SHELLQs collaborations, drawn from the ESI and X-Shooter archives, reused from previous studies or observed specifically for this work. We measure the effective optical depth of Lyman-{alpha} in bins of 10, 30, 50 and 70 cMpc h-1, construct cumulative distribution functions under two treatments of upper limits on flux and explore an empirical analytic fit to residual Lyman-{alpha} transmission. We verify the consistency of our results with those of previous studies via bootstrap re-sampling and confirm the existence of tails towards high values in the opacity distributions, which may persist down to z = 5.2. Comparing our results with predictions from cosmological simulations, we find further strong evidence against models that include a spatially uniform ionizing background and temperature-density relation. We also compare to IGM models that include either a fluctuating UVB dominated by rare quasars or temperature fluctuations due to patchy reionization. Although both models produce better agreement with the observations, neither fully captures the observed scatter in IGM opacity. Our sample of 62 z > 5.7 quasar spectra opens many avenues for future study of the reionisation epoch.
We report the discovery of a new Einstein cross at redshift z_S = 2.701 based on Lyman-alpha emission in a cruciform configuration around an SDSS luminous red galaxy (z_L = 0.331). The system was targeted as a possible lens based on an anomalous emission line in the SDSS spectrum. Imaging and spectroscopy from the W. M. Keck Observatory confirm the lensing nature of this system. This is one of the widest-separation galaxy-scale lenses known, with an Einstein radius of ~1.84 arcsec. We present simple gravitational lens models for the system and compute the intrinsic properties of the lensed galaxy. The total mass of the lensing galaxy within the 8.8 +/- 0.1 kpc enclosed by the lensed images is (5.2 +/- 0.1) x 10^11 M_sun. The lensed galaxy is a low mass galaxy (0.2 L*) with a high equivalent-width Lyman-alpha line (EW_Lya_rest = 46 +/- 5 Angstroms). Follow-up studies of this lens system can probe the mass structure of the lensing galaxy, and can provide a unique view of an intrinsically faint, high-redshift, star-forming galaxy at high signal-to-noise ratio.
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