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Stellar Populations of Lyman Alpha Emitters at z = 3 - 4 Based on Deep Large Area Surveys in the Subaru-SXDS/UKIDSS-UDS Field  [PDF]
Yoshiaki Ono,Masami Ouchi,Kazuhiro Shimasaku,Masayuki Akiyama,James Dunlop,Duncan Farrah,Janice C. Lee,Ross McLure,Sadanori Okamura,Makiko Yoshida
Physics , 2009, DOI: 10.1111/j.1365-2966.2009.16034.x
Abstract: We investigate the stellar populations of Lyman alpha emitters (LAEs) at z=3.1 and 3.7 in 0.65 deg^2 of the Subaru/XMM-Newton Deep Field, based on rest-frame UV-to-optical photometry obtained from the Subaru/XMM-Newton Deep Survey, the UKIDSS/Ultra Deep Survey, and the Spitzer legacy survey of the UKIDSS/UDS. Among a total of 302 LAEs (224 for z=3.1 and 78 for z=3.7), only 11 are detected in the K band, i.e., brighter than K(3sigma)=24.1 mag. Eight of the 11 K-detected LAEs are spectroscopically confirmed. We find that the K-undetected objects, which should closely represent the LAE population as a whole, have low stellar masses of ~ 10^8 - 10^8.5 Msun, modest SFRs of 1 - 100 Msun yr^-1, and modest dust extinction of E(B-V) < 0.2. The K-detected objects are massive, Mstar ~ 10^9 - 10^10.5 Msun, and have significant dust extinction with a median of E(B-V) ~= 0.3. Four K-detected objects with the reddest spectral energy distributions, two of which are spectroscopically confirmed, are heavily obscured with E(B-V) ~ 0.65, and their continua resemble those of some local ULIRGs. Interestingly, they have large Lyman alpha equivalent widths ~= 70 - 250 A. If these four are excluded, our sample has a weak anti-correlation between EW(Lya) and Mstar. We compare the stellar masses and the specific star formation rates (sSFR) of LAEs with those of Lyman-break galaxies, distant red galaxies, submillimetre galaxies, and I- or K-selected galaxies with z_phot ~ 3. We find that the LAE population is the least massive among all the galaxy populations in question, but with relatively high sSFRs, while NIR-detected LAEs have Mstar and sSFR similar to LBGs. Our reddest four LAEs have very high sSFRs in spite of large Mstar, thus occupying a unique region in the Mstar versus sSFR space. (abridged)
The properties of the brightest Lyman alpha emitters at z~5.7  [PDF]
C. Lidman,M. Hayes,D. H. Jones,D. Schaerer,E. Westra,C. Tapken,K. Meisenheimer,A. Verhamme
Physics , 2011, DOI: 10.1111/j.1365-2966.2011.19994.x
Abstract: (Abridged) We use deep VLT optical and near-IR spectroscopy and deep Spitzer/IRAC imaging to examine the properties of two of the most luminous Lyman alpha emitters at z=5.7. The continuum red-ward of the Lyman alpha line is clearly detected in both objects, thus facilitating a relatively accurate measurement (10--20% uncertainties) of the observed rest-frame equivalent widths, which are around 160 Angstroms for both objects. Through detailed modelling of the profile of the Lyman alpha line with a 3-D Monte-Carlo radiative transfer code, we estimate the intrinsic rest-frame equivalent width of Lyman alpha and find values that are around 300 Angstroms, which is at the upper end of the range allowed for very young, moderately metal-poor star-forming galaxies. However, the uncertainties are large and values as high as 700 Angstroms are permitted by the data. Both Lyman alpha emitters are detected at 3.6 micron in deep images taken with the Spitzer Space Telescope. We use these measurements, the measurement of the continuum red-ward of Lyman alpha and other photometry to constrain the spectral energy distributions of these very luminous Lyman alpha emitters and to compare them to three similar Lyman alpha emitters from the literature. The contribution from nebular emission is included in our models: excluding it results in significantly higher masses. Evidence for dust is found in all objects, and emission from nebular lines often make a dominant contribution to the rest frame 3.6 micron flux. Rich in emission lines, these objects are prime targets for the next generation of extremely large telescopes, JWST and ALMA.
Understanding Lyman-alpha emitters  [PDF]
Kim K. Nilsson,Klaus Meisenheimer,Nicholas Bond,Eric Gawiser,Harold Francke,Daniel Kunth,Toru Yamada,Goran Ostlin
Physics , 2009, DOI: 10.1016/j.newar.2009.04.001
Abstract: This publication contains the conference summary of the Understanding Lyman-alpha Emitters conference held at the Max Planck Institute for Astronomy in Heidelberg October 6 - 10, 2008. The scope of the conference was to bring together most of the scientists working in the field of Lyman-alpha emitters, whether at low or high redshift, or on observational or theoretical aspects, and to summarise how far the field of study of galaxies with Lyman-alpha emission has come. An outlook towards the future of the field was also desired. As part of the conference, two days were dedicated to in total six discussion sessions. The topics were i) new methods and selection methods, ii) morphology, iii) what can the local Universe observations tell us about the high redshift Universe?, iv) clustering, v) SED fitting and vi) Ly-alpha blobs. The chairs of those sessions were asked to summarise the discussions, as presented in these proceedings.
The cool side of Lyman Alpha Emitters  [PDF]
Pratika Dayal,Andrea Ferrara,Alexandro Saro
Physics , 2009, DOI: 10.1111/j.1365-2966.2009.15995.x
Abstract: We extend a previous study of Lyman Alpha Emitters (LAEs) based on hydrodynamical cosmological simulations, by including two physical processes important for LAEs: (a) Lyman Alpha and continuum luminosities produced by cooling of collisionally excited HI in the galaxy, (b) dust formation and evolution; we follow these processes on a galaxy-by-galaxy basis. HI cooling on average contributes 16-18% of the Lyman Alpha radiation produced by stars, but this value can be much higher in low mass LAEs and further increased if the HI is clumpy. The continuum luminosity is instead almost completely dominated by stellar sources. The dust content of galaxies scales with their stellar mass, M_{dust} is proportional to M_*^0.7 and stellar metallicity, Z_*, such that M_{dust} is proportional to Z_*^1.7. As a result, the massive galaxies have Lyman Alpha escape fraction as low as f_alpha=0.1, with a LAE-averaged value decreasing with redshift such that it is (0.33,0.23) at z =(5.7,6.6). The UV continuum escape fraction shows the opposite trend with redshift, possibly resulting from clumpiness evolution. The model successfully reproduces the observed Lyman Alpha and UV luminosity functions at different redshifts and the Lyman Alpha equivalent width scatter to a large degree, although the observed distribution appears to be more more extended than the predicted one. We discuss possible reasons for such tension.
The abundance of Lyman-(α) emitters in hierarchical models  [PDF]
Morgan Le Delliou,Cedric Lacey,Carlton M. Baugh,Bruno Guiderdoni,Roland Bacon,Helene Courtois,Thierry Sousbie,Simon L. Morris
Physics , 2004, DOI: 10.1111/j.1745-3933.2005.00007.x
Abstract: We present predictions for the abundance of Ly-$\alpha$ emitters in hierarchical structure formation models. We use the {\tt GALFORM} semi-analytical model to explore the impact on the predicted counts of varying assumptions about the escape fraction of Ly-$\alpha$ photons, the redshift at which the universe reionised and the cosmological density parameter. A model with a fixed escape fraction gives a remarkably good match to the observed counts over a wide redshift interval. We present predictions for the expected counts in a typical observation with the Multi Unit Spectroscopic Explorer instrument proposed for the Very Large Telescope.
Molecular hydrogen in Lyman Alpha Emitters  [PDF]
Livia Vallini,Pratika Dayal,Andrea Ferrara
Physics , 2012, DOI: 10.1111/j.1365-2966.2012.20551.x
Abstract: We present a physically motivated model to estimate the molecular hydrogen (H2) content of high-redshift (z~5.7,6.6) Lyman Alpha Emitters (LAEs) extracted from a suite of cosmological simulations. We find that the H2 mass fraction, (f_H2), depends on three main LAE physical properties: (a) star formation rate, (b) dust mass, and (c) cold neutral gas mass. At z~5.7, the value of f_H2 peaks and ranges between 0.5-0.9 for intermediate mass LAEs with stellar mass M_* ~ 10^{9-10} solar mass, decreasing for both smaller and larger galaxies. However, the largest value of the H2 mass is found in the most luminous LAEs. These trends also hold at z\sim6.6, although, due to a lower dust content, f_H2(z=6.6)\sim0.5 f_H2(z=5.7) when averaged over all LAEs; they arise due to the interplay between the H2 formation/shielding controlled by dust and the intensity of the ultraviolet (UV) Lyman-Werner photo-dissociating radiation produced by stars. We then predict the carbon monoxide (CO) luminosities for such LAEs and check that they are consistent with the upper limits found by Wagg et al. (2009) for two z>6 LAEs. At z\sim(5.7, 6.6), the lowest CO rotational transition observable for both samples with the actual capabilities of Atacama Large Millimeter Array (ALMA) is the CO(6-5). We find that at z\sim5.7, about 1-2% of LAEs, i.e., those with an observed Lyman Alpha luminosity larger than 10^{43.2} erg/s would be detectable with an integration time of 5-10 hours (S/N=5); at z\sim6.6 none of the LAEs would be detectable in CO, even with an ALMA integration time of 10 hours. We also build the CO `flux function', i.e., the number density of LAEs as a function of the line-integrated CO flux, S_CO, and show that it peaks at S_CO = 0.1 mJy at z\sim5.7, progressively shifting to lower values at higher redshifts. We end by discussing the model uncertainties.
Lyman Alpha Emitters at Redshift z=5.7  [PDF]
James E. Rhoads,Sangeeta Malhotra
Physics , 2001, DOI: 10.1086/338477
Abstract: Lyman alpha galaxies at high redshifts offer a powerful probe of both the formation of galaxies and the reionization of the intergalactic medium. Lyman alpha line emission is an efficient tool for identifying young galaxies at high redshift, because it is strong in systems with young stars and little or no dust-- properties expected in galaxies undergoing their first burst of star-formation. Lyman alpha galaxies also provide a robust test of the reionization epoch that is independent of Gunn-Peterson trough observations in quasar spectra and is better able to distinguish line center optical depths tau=5 from tau=10^5. This is because neutral gas scatters Lyman alpha photons, dramatically ``blurring'' images of Lyman alpha galaxies embedded in a neutral intergalactic medium and rendering them undetectable. We present a photometrically selected sample of z=5.7 Lyman alpha emitters derived from the Large Area Lyman Alpha survey. The presence of these low-luminosity Lyman alpha sources at z=5.7 immediately implies that the reionization redshift was > 5.7. Comparing these objects to our earlier z=4.5 sample, we find that the number of z=5.7 emitters at fixed line luminosity marginally exceeds the no-evolution expectation, but falls well short of published model predictions. The equivalent width distribution is similar at the two redshifts. The large equivalent widths of the Lyman alpha line indicate young galaxies undergoing their first star formation.
Discovery of 9 Ly alpha emitters at redshift z~3.1 using narrow-band imaging and VLT spectroscopy  [PDF]
R. P. Kudritzki,R. H. Mendez,J. J. Feldmeier,R. Ciardullo,G. H. Jacoby,K. C. Freeman,M. Arnaboldi,M. Capaccioli,O. Gerhard,H. C. Ford
Physics , 2000, DOI: 10.1086/308925
Abstract: Narrow-band imaging surveys aimed at detecting the faint emission from the 5007 [O III] line of intracluster planetary nebulae in Virgo also probe high redshift z=3.1 Ly alpha emitters. Here we report on the spectroscopic identification of 9 Ly alpha emitters at z=3.13, obtained with the FORS spectrograph at Unit 1 of the ESO Very Large Telescope (VLT UT1). The spectra of these high redshift objects show a narrow, isolated Ly alpha emission with very faint (frequently undetected) continuum, indicating a large equivalent width. No other features are visible in our spectra. Our Ly alpha emitters are quite similar to those found by Hu (1998), Cowie & Hu (1998) and Hu et al. (1998). Using simple population synthesis models, on the assumption that these sources are regions of star formation, we conclude that the nebulae are nearly optically thick and must have a very low dust content, in order to explain the high observed Ly alpha equivalent widths. For the cosmological and star formation parameters we adopted, the total stellar mass produced would seem to correspond to the formation of rather small galaxies, some of which are perhaps destined to merge. The implied star formation density in our sampled comoving volume is probably somewhat smaller than, but of the same order of magnitude as the star formation density at z=3 derived by other authors from Lyman-break galaxy surveys. This result agrees with the expectation that the Ly alpha emitters are a low-metallicity (or low-dust) tail in a distribution of star forming regions at high redshifts. Finally, the Ly alpha emitters may contribute as many H-ionizing photons as QSOs at z=3.
Models for High-Redshift Lyman Alpha Emitters  [PDF]
Zoltan Haiman,Marco Spaans
Physics , 1998, DOI: 10.1063/1.58635
Abstract: We present models for dusty high-redshift Lyman alpha emitting galaxies by combining the Press-Schechter formalism with a treatment of inhomogeneous dust distribution inside galaxies. These models reproduce the surface density of emitters inferred from recent observations, and also agree with previous non-detections. Although a detailed determination of the individual model parameters is precluded by uncertainties, we find that (i) the dust content of primordial galaxies builds up in no more than 5x10^8 years, (ii) the galactic HII regions are inhomogeneous with a cloud covering factor of order unity, and (iii) the overall star formation efficiency is at least 5 percent. Future observations should be able to detect Lyman alpha galaxies upto redshifts of about z=8. If the universe is reionized at z(reion)<8, the corresponding decline in the number of Lyman alpha emitters at z>z(reion) could prove to be a useful probe of the reionization epoch.
Detecting Lyman Alpha Emitters in the Sub-millimeter  [PDF]
Pratika Dayal,Hiroyuki Hirashita,Andrea Ferrara
Physics , 2009, DOI: 10.1111/j.1365-2966.2009.16164.x
Abstract: Using the results from a previously developed Lyman Alpha/continuum production/transmission and dust enrichment model for Lyman Alpha Emitters (LAEs), based on cosmological SPH simulations, we assess the detectability of their dust-reprocessed sub-millimeter (submm) radiation. As supernovae (rather than evolved stars) control dust formation and destruction processes, LAEs are relatively dust-poor with respect to local galaxies: they have low dust-to-gas ratios (0.05 times the dust-to-gas ratio of the Milky Way) in spite of their relatively high metallicity, which is approximately 10-50% of the solar value. Using the derived escape fraction of ultraviolet (UV) continuum photons we compute the UV luminosity absorbed by dust and re-emitted in the far infrared. The LAE submm fluxes correlate with their Lyman Alpha luminosity: about (3%, 1%) at z=(5.7, 6.6) of the LAEs in our simulated sample (those with with Log L_\alpha > 43.1) would have fluxes at 850 micrometer (the optimal band for detection) in excess of 0.12 mJy and will be therefore detectable at 5 sigma with ALMA with an integration time of only 1 hour. Such detections would open a new window on the physical conditions prevailing in these most distant galaxies.
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