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The WIRCam Ultra Deep Survey (WUDS)
摘要： The aim of this paper is to introduce the WIRCam Ultra Deep Survey (WUDS), a near-IR photometric survey carried out at the CFH Telescope in the field of the CFHTLS-D3 field (Groth Strip). WUDS includes four near-IR bands (Y, J, H and Ks) over a field of view of ～400 arcmin2. The typical depth of WUDS data reaches between ～26.8 in Y and J, and ～26 in H and Ks (AB, 3σ in 1.3'' aperture), whereas the corresponding depth of the CFHTLS-D3 images in this region ranges between 28.6 and 29 in ugr, 28.2 in i and 27.1 in z (same S/N and aperture). The area and depth of this survey were specifically tailored to set strong constraints on the cosmic star formation rate and the luminosity function brighter or around L* in the z ～ 6?10 redshift domain, although these data are also useful for a variety of extragalactic projects. This first paper is intended to present the properties of the public WUDS survey in details: catalog building, completeness and depth, number counts, photometric redshifts, and global properties of the galaxy population. We have also concentrated on the selection and characterization of galaxy samples at z ～ [4.5?7] in this field. For these purposes, we include an adjacent shallower area of ～1260 arcmin2 in this region, extracted from the WIRCam Deep Survey (WIRDS), and observed in J, H and Ks bands. UV luminosity functions were derived at z ～ 5 and z ～ 6 taking advantage from the fact that WUDS covers a particularly interesting regime at intermediate luminosities, which allows a combined determination of M* and Φ* with increased accuracy. Our results on the luminosity function are consistent with a small evolution of both M* and Φ* between z = 5 and z = 6, irrespective of the method used to derive them, either photometric redshifts applied to blindly-selected dropout samples or the classical Lyman Break Galaxy color-preselected samples. Our results lend support to higher Φ* determinations at z = 6 than usually reported. The selection and combined analysis of different galaxy samples at z ≥ 7 will be presented in a forthcoming paper, as well as the evolution of the UV luminosity function between z ～ 4.5 and 9. WUDS is intended to provide a robust database in the near-IR for the selection of targets for detailed spectroscopic studies, in particular for the EMIR/GTC GOYA Survey.
关键词： surveys,first stars,reionization,galaxies: high-redshift,dark ages
更新于2025-09-23 15:22:29
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Neutral gas properties of Lyman continuum emitting galaxies: Column densities and covering fractions from UV absorption lines
摘要： Context. The processes allowing the escape of ionizing photons from galaxies into the intergalactic medium are poorly known. Aims. To understand how Lyman continuum (LyC) photons escape galaxies, we constrain the H I covering fractions and column densities using ultraviolet (UV) H I and metal absorption lines of 18 star-forming galaxies that have Lyman series observations. Nine of these galaxies are confirmed LyC emitters. Methods. We fit the stellar continuum, dust attenuation, metal, and H I properties to consistently determine the UV attenuation, as well as the column densities and covering factors of neutral hydrogen and metals. We used synthetic interstellar absorption lines to explore the systematics of our measurements. Then we applied our method to the observed UV spectra of low-redshift and z ~ 3 galaxies. Results. The observed H I lines are found to be saturated in all galaxies. An indirect approach using O I column densities and the observed O/H abundances yields H I column densities of log(NH I) ~ 18.6 - 20 cm^{-2}. These columns are too high to allow the escape of ionizing photons. We find that the known LyC leakers have H I covering fractions less than unity. Ionizing photons escape through optically thin channels in a clumpy interstellar medium. Our simulations confirm that the H I covering fractions are accurately recovered. The Si II and H I covering fractions scale linearly, in agreement with observations from stacked Lyman break galaxy spectra at z ~ 3. Thus, with an empirical correction, the Si II absorption lines can also be used to determine the H I coverage. Finally, we show that a consistent fitting of dust attenuation, continuum, and absorption lines is required to properly infer the covering fraction of neutral gas and subsequently to infer the escape fraction of ionizing radiation. Conclusions. These measurements can estimate the LyC escape fraction, as we demonstrate in a companion paper.
关键词： ISM: abundances,dark ages, reionization, first stars,ultraviolet: ISM,ISM: lines and bands,dust, extinction,galaxies: ISM
更新于2025-09-23 15:22:29
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QUANTIFYING DISTRIBUTIONS OF THE LYMAN CONTINUUM ESCAPE FRACTION
摘要： Simulations have indicated that most of the escaped Lyman continuum (LyC) photons escape through a minority of solid angles with near complete transparency, with the remaining majority of the solid angles largely opaque, resulting in a very broad and skewed probability distribution function (PDF) of the escape fraction when viewed at different angles. Thus, the escape fraction of LyC photons of a galaxy observed along a line of sight merely represents the properties of the interstellar medium along that line of sight, which may be an ill-representation of the true escape fraction of the galaxy averaged over its full sky. Here we study how LyC photons escape from galaxies at z = 4–6, utilizing high-resolution large-scale cosmological radiation-hydrodynamic simulations. We compute the PDF of the mean escape fraction (?f_esc?) averaged over mock observational samples, as a function of the sample size, compared to the true mean (if an infinite sample size is used). We find that, when the sample size is small, the apparent mean skews to the low end. For example, for a true mean of 6.7%, an observational sample of (2,10,50) galaxies at z = 4 would have a 2.5% probability of obtaining the sample mean lower than (0.007%, 1.8%, 4.1%) and a 2.5% probability of obtaining the sample mean greater than (43%, 18%, 11%). Our simulations suggest that at least ～100 galaxies should be stacked in order to constrain the true escape fraction within 20% uncertainty.
关键词： dark ages, reionization, first stars,cosmic background radiation,galaxies: high-redshift,ultraviolet: galaxies,radiative transfer,large-scale structure of universe
更新于2025-09-19 17:15:36
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A Window on the Earliest Star Formation: Extreme Photoionization Conditions of a High-ionization, Low-metallicity Lensed Galaxy at <i>z</i> ～ 2*
摘要： We report new observations of SL2S J021737–051329, a lens system consisting of a bright arc at z = 1.84435, magnified ～17× by a massive galaxy at z = 0.65. SL2S0217 is a low-mass (M < 109 Me), low-metallicity (Z ～ 1/20 Ze) galaxy, with extreme star-forming conditions that produce strong nebular UV emission lines in the absence of any apparent outflows. Here we present several notable features from rest-frame UV Keck/LRIS spectroscopy: (1) Very strong narrow emission lines are measured for C IV λλ1548, 1550, He II λ1640, O III] λλ1661, 1666, Si III] λλ1883, 1892, and C III] λλ1907, 1909. (2) Double-peaked Lyα emission is observed with a dominant blue peak and centered near the systemic velocity. (3) The low- and high-ionization absorption features indicate very little or no outflowing gas along the sight line to the lensed galaxy. The relative emission-line strengths can be reproduced with a very high ionization, low-metallicity starburst with binaries, with the exception of He II, which indicates that an additional ionization source is needed. We rule out large contributions from active galactic nuclei and shocks to the photoionization budget, suggesting that the emission features requiring the hardest radiation field likely result from extreme stellar populations that are beyond the capabilities of current models. Therefore, SL2S0217 serves as a template for the extreme conditions that are important for reionization and thought to be more common in the early universe.
关键词： first stars,galaxies: abundances,reionization,gravitational lensing: strong,galaxies: evolution,dark ages,galaxies: ISM
更新于2025-09-10 09:29:36