We discuss the properties of 137 cataclysmic variables (CVs) which are included in the Sloan Digital Sky Survey (SDSS) spectroscopic data base, and for which accurate orbital periods have been ...measured. 92 of these systems are new discoveries from SDSS and were followed-up in more detail over the past few years. 45 systems were previously identified as CVs because of the detection of optical outbursts and/or X-ray emission, and subsequently re-identified from the SDSS spectroscopy. The period distribution of the SDSS CVs differs dramatically from that of all the previously known CVs, in particular it contains a significant accumulation of systems in the orbital period range 80–86 min. We identify this feature as the elusive ‘period minimum spike’ predicted by CV population models, which resolves a long-standing discrepancy between compact binary evolution theory and observations. We show that this spike is almost entirely due to the large number of CVs with very low accretion activity identified by SDSS. The optical spectra of these systems are dominated by emission from the white dwarf photosphere, and display little or no spectroscopic signature from the donor stars, suggesting very low mass companion stars. We determine the average absolute magnitude of these low-luminosity CVs at the period minimum to be 〈Mg〉= 11.6 ± 0.7. Comparison of the SDSS CV sample to the CVs found in the Hamburg Quasar Survey and the Palomar Green Survey suggests that the depth of SDSS is the key ingredient resulting in the discovery of a large number of intrinsically faint short-period systems.
We present the results of CANDELSz7, a European Southern Observatory (ESO) Large Program aimed at spectroscopically confirming a homogeneous sample of z ≃ 6 and z ≃ 7 star forming galaxies. The ...candidates were selected in the GOODS-South, UDS, and COSMOS fields using the official CANDELS catalogs based on H160-band detections. Standard color criteria, which were tailored depending on the ancillary multi-wavelength data available for each field, were applied to select more than 160 candidate galaxies at z ≃ 6 and z ≃ 7. Deep, medium-resolution FORS2 spectroscopic observations were then conducted with integration times ranging from 12 to 20 h to reach a Lyα flux limit of approximately 1 − 3 × 10−18 erg s−1 cm−2 at 3σ. We could determine a spectroscopic redshift for about 40% of the galaxies, mainly through the detection of a single emission line that we interpret as Lyα emission, or for some of the brightest objects (H160 ≤ 25.5) from the presence of faint continuum and a sharp drop that we interpret as a Lyα break. In this paper we present the redshifts and main properties of 65 newly confirmed high-redshift galaxies. Adding previous proprietary and archival data we assemble a sample of ≃260 galaxies that we use to explore the evolution of the Lyα fraction in Lyman break galaxies and the change in the shape of the emission line between z ∼ 6 and z ∼ 7. We also discuss the accuracy of the CANDELS photometric redshifts in this redshift range.
Aims. Cosmic reionization is an important process occurring in the early epochs of the Universe. However, because of observational limitations due to the opacity of the intergalactic medium to Lyman ...continuum photons, the nature of ionizing sources is still not well constrained. While high-redshift star-forming galaxies are thought to be the main contributors to the ionizing background at z> 6, it is impossible to directly detect their ionizing emission. Therefore, looking at intermediate redshift analogues (z ~ 2−4) can provide useful hints about cosmic reionization. Methods. We investigate the physical properties of one of the best Lyman continuum emitter candidate at z = 3.212 found in the GOODS-S/CANDELS field with photometric coverage from the U to the MIPS 24 μm band and VIMOS/VLT and MOSFIRE/Keck spectroscopy. These observations allow us to derive physical properties such as stellar mass, star formation rate, age of the stellar population, dust attenuation, metallicity, and ionization parameter, and to determine how these parameters are related to the Lyman continuum emission. Results. Investigation of the UV spectrum confirms a direct spectroscopic detection of the Lyman continuum emission with S/N> 5. Non-zero Lyα flux at the systemic redshift and high Lyman-α escape fraction (fesc(Lyα) ≥ 0.78) suggest a low H i column density. The weak C and Si low-ionization absorption lines are also consistent with a low covering fraction along the line of sight. The subsolar abundances are consistent with a young and extreme starburst. The O iiiλλ4959,5007+Hβ equivalent width (EW) is one of the largest reported for a galaxy at z> 3 (EW( O iii λλ4959,5007 + Hβ) ≃ 1600 Å, rest-frame; 6700 Å observed-frame) and the near-infrared spectrum shows that this is mainly due to an extremely strong O iii emission. The large observed O iii/O ii ratio (>10) and high ionization parameter are consistent with prediction from photoionization models in the case of a density-bounded nebula scenario. Furthermore, the EW(O iiiλλ4959,5007+Hβ) is comparable to recent measurements reported at z ~ 7−9, in the reionization epoch. We also investigate the possibility of an AGN contribution to explain the ionizing emission but most of the AGN identification diagnostics suggest that stellar emission dominates instead. Conclusions. This source is currently the first high-z example of a Lyman continuum emitter exhibiting indirect and direct evidences of a Lyman continuum leakage and having physical properties consistent with theoretical expectation from Lyman continuum emission from a density-bounded nebula. A low H i column density, low covering fraction, compact star formation activity, and a possible interaction/merging of two systems may contribute to the Lyman continuum photon leakage.
The fraction of Lyman-α emitters (LAEs) among the galaxy population has been found to increase from z ~ 0 to z ~ 6 and drop dramatically at z> 6. This drop has been interpreted as an effect of an ...increasingly neutral intergalactic medium (IGM) with increasing redshift, while a Lyman continuum escape fraction evolving with redshift and/or a sudden change of galaxy physical properties can also contribute to the decreasing LAE fraction. We report the result of a large VLT/FORS2 program aiming to confirm spectroscopically a large galaxy sample at z ≥ 6 that has been selected in several independent fields through the Lyman break technique. Combining those data with archival data, we create a large and homogeneous sample of z ~ 6 galaxies (N = 127), complete in terms of Lyα detection at > 95% for Lyα equivalent width EW(Lyα) ≥ 25 Å. We use this sample to derive a new measurement of the LAE fraction at z ~ 6 and derive the physical properties of these galaxies through spectral energy distribution (SED) fitting. We find a median LAE fraction at z ~ 6 lower than in previous studies, while our sample exhibits typical properties for z ~ 6 galaxies in terms of UV luminosity and UVβ slope. The comparison of galaxy physical properties between LAEs and non-LAEs is comparable to results at lower redshift: LAEs with the largest EW(Lyα) exhibit bluer UV slopes, are slightly less massive and less star-forming. The main difference between LAEs and non-LAEs is that the latter are significantly dustier. Using predictions of our SED fitting code accounting for nebular emission, we find an effective Lyα escape fraction fesceff(Lyα) = 0.23-0.17+0.36 remarkably consistent with the value derived by comparing UV luminosity function with Lyα luminosity function. We conclude that the drop in the LAE fraction from z ~ 6 to z> 6 is less dramatic than previously found and the effect of an increasing IGM neutral fraction is possibly observed at 5 <z< 6. The processes driving the escape of Lyα photons at z ~ 6 are similar to those at lower redshifts and based on our derived fesceff(Lyα), we find that the IGM has a relatively small impact on Lyα photon visibility at z ~ 6, with a lower limit for the IGM transmission to Lyα photons, TIGM ≳ 0.20, likely due to the presence of outflows.
ABSTRACT We use a sample of 149 spectroscopically confirmed UV-selected galaxies at z ∼ 2 to investigate the relative dust attenuation of the stellar continuum and the nebular emission lines. For ...each galaxy in the sample, at least one rest-frame optical emission line (H /N ii λ6583 or O iii λ5007) measurement has been taken from the litterature, and 41 galaxies have additional Spitzer/MIPS 24 m observations that are used to infer infrared luminosities. We use a spectral energy distribution (SED) fitting code that predicts nebular line strengths when fitting the stellar populations of galaxies in our sample, and we perform comparisons between the predictions of our models and the observed/derived physical quantities. We find that on average our code is able to reproduce all the physical quantities (e.g., UV β slopes, infrared luminosities, emission line fluxes), but we need to apply a higher dust correction to the nebular emission compared to the stellar emission for the largest star formation rate (SFR) (log SFR/M yr−1 > 1.82, Salpeter initial mass function). We find a correlation between SFR and the difference in nebular and stellar color excesses, which could resolve the discrepant results regarding nebular dust correction at z ∼ 2 from previous studies.
Over the last two decades, the repair of existing engineering structures using fiber reinforced polymer composites has attracted a great attention by aerospace industry, as it is more economical than ...replacing new. With an increased use of composite material in aerospace field, it is thus essential to restore the structural integrity by repair of damaged part. Concerns regarding the long term durability of composite repair bonded joints have been a major obstacle for critical component of aerospace structures. This paper reviews the current research on the environmental durability of adhesive bonded repair of composite structures to focus on the durability concerns and suggestion on the research needed in this area. The most important environmental factors (moisture and temperature) are reviewed thoroughly and also combined environmental effect. Finite element methods used to predict the environmental influence on the composite bonded joints are briefly reviewed. Finally, the paper concludes with key findings, opportunities and future research topics in order to develop cost effective, better quality and reliable composite repair bonded joints.
ABSTRACT Several Lyman Continuum (Ly C) emitters have been detected so far, but their observed ionizing spectra sometimes differ from attenuated stellar spectra predicted by stellar population ...synthesis modelling. This discrepancy may be due to a significant contribution of Ly C nebular emission. We aim to quantify the importance this emission in Ly C leakers: its contribution to the ionizing photons budget, and to measurements of Ly C escape. To estimate the nebular contribution to the Ly C spectra of galaxies, we run photoionization models with Cloudy for a range of Binary Population and Spectral Synthesis templates, varying the column density of the surrounding gas, from density-bounded (NH i = 1016 cm−2) to ionization-bounded (NH i = 1019 cm−2) regimes. In the limits of very optically thin (fesc = 1), or thick configurations (fesc = 0), there is no nebular contribution to the emergent Ly C spectra. This contribution matters only at intermediate Ly C opacities (0 < fesc < 1), where it alters the shape of the Ly C spectrum chromatically, so that escape fractions estimates are highly sensitive to the wavelength range over which they are calculated. We propose a formula to estimate integrated escape fractions using Fλ700/Fλ1100 flux ratios, since this wavelength range is not affected by nebular emission. Regarding simulations, the boost of hydrogen ionizing photons escaping galaxies is inversely proportional to the stellar escape fractions, but since typical simulated escape fractions are low, Ly C photons escape is important. Nebular Ly C is a non-negligible additional source of ionizing photons from galaxies, whose contribution has been overlooked so far in observations and in cosmic reionization simulations.
The brewer's spent grain (BSG) is a byproduct of the brewing industry produced in large quantities and with few ecological disposal options. The use of this low-cost residue was investigated for the ...removal of methylene blue (MB) and tartrazine yellow (TY) dyes. The BSG has been extensively characterized to obtain its physicochemical characteristics. Batch experiments were conducted to investigate the effects of biosorption parameters: initial pH, kinetics, equilibrium isotherms and adsorption thermodynamics. The characterization showed high carbon content and heterogeneous morphology with the presence of meso and macropores. The best experimental conditions were obtained as pH 11 for MB and pH 2 for TY. Kinetics resulted in an equilibrium time of 240 min for MB and 300 min for TY and was best represented by the pseudo-second order model. Different interaction mechanisms were suggested, such as electrostatic interactions, electron donors and electron acceptors, hydrogen bonds, π-π dispersion interactions and the dye molecules aggregation. Equilibrium data were better represented by Langmuir isotherm. The maximum adsorbed amount of MB and TY was 284.75 and 26.18 mg/g, respectively, in each better experimental condition. Through the thermodynamic analysis, it was observed that the adsorption of the dyes was spontaneous and favourable. MB is preferentially retained through chemisorption, whereas TY followed a physical process. Considering the characteristics and results found compared to the recent literature, it was verified that BSG can be used as an effective and innovative biosorbent for removal purposes of dyeing effluent.
We have obtained the first complete ultraviolet (UV) spectrum of a strong Lyman continuum (LyC) emitter at low redshift – the compact, low-metallicity, star-forming galaxy J1154+2443 – with a Lyman ...continuum escape fraction of 46% discovered recently. The Space Telescope Imaging Spectrograph spectrum shows strong Lyα and C III λ1909 emission, as well as O III λ1666. Our observations show that strong LyC emitters can have UV emission lines with a high equivalent width (e.g. EW(C III) = 11.7 ± 2.9 Å rest-frame), although their equivalent widths should be reduced due to the loss of ionizing photons. The intrinsic ionizing photon production efficiency of J1154+2443 is high, log(ξ0ion = 25.56 erg−1 Hz) log ( ξ ion 0 ) = 25.56 erg − 1 Hz $ {\rm log}{(\xi_\text{ion}^0)}=25.56\text{erg}^{-1}\text{Hz} $ , comparable to that of other recently discovered z ~ 0.3−0.4 LyC emitters. Combining our measurements and earlier determinations from the literature, we find a trend of increasing ξ0ion ξ ion 0 $ \xi_\text{ion}^0 $ with increasing C III λ1909 equivalent width, which can be understood by a combination of decreasing stellar population age and metallicity. Simple ionization and density-bounded photoionization models can explain the main observational features including the UV spectrum of J1154+2443.
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