Time-Dependent Corrections to the Ly-alpha Escape Probability During Cosmological Hydrogen Recombination

We consider the effects connected with the detailed radiative transfer during the epoch of cosmological recombination on the ionization history of our Universe. We focus on the escape of photons from the hydrogen Lyman-alpha resonance at redshifts 600<~ z <~ 2000, one of two key mechanisms defining the rate of cosmological recombination. We approach this problem within the standard formulation, and corrections due to two-photon interactions are deferred to another paper. As a main result we show here that within a non-stationary approach to the escape problem, the resulting correction in the free electron fraction, N_e, is about ~1.6-1.8% in the redshift range 800<~z<~1200. Therefore the discussed process results in one of the largest modifications to the ionization history close to the maximum of Thomson-visibility function at z~1100 considered so far. We prove our results both numerically and analytically, deriving the escape probability, and considering both Lyman-alpha line emission and line absorption in a way different from the Sobolev approximation. In particular, we give a detailed derivation of the Sobolev escape probability during hydrogen recombination, and explain the underlying assumptions. We then discuss the escape of photons for the case of coherent scattering in the lab frame, solving this problem analytically in the quasi-stationary approximation and also in the time-dependent case. We show here that during hydrogen recombination the Sobolev approximation for the escape probability is not valid at the level of DP/P~5-10%. This is because during recombination the ionization degree changes significantly over a characteristic time Dz/z~10%, so that at percent level accuracy the photon distribution is not evolving (abridged)Comment: 18 pages, 12 figures, accepted versio

Evolution of low-frequency features in the CMB spectrum due to stimulated Compton scattering and Doppler-broadening

We discuss a new solution of the Kompaneets-equation for physical situations in which low frequency photons, forming relatively narrow spectral details, are Compton scattered in an isotropic, infinite medium with an intense ambient blackbody field that is very close to full thermodynamic equilibrium with the free electrons. In this situation the background-induced stimulated Compton scattering slows down the motion of photons toward higher frequencies by a factor of 3 in comparison with the solution that only takes into account Doppler-broadening and boosting. This new solution is important for detailed computations of cosmic microwave background spectral distortions arising due to uncompensated atomic transitions of hydrogen and helium in the early Universe. In addition we derive another analytic solution that only includes the background-induced stimulated Compton scattering and is valid for power-law ambient radiation fields. This solution might have interesting applications for radio lines arising inside of bright extra-galactic radio source, where according to our estimates line shifts because of background-induced stimulated scattering could be amplified and even exceed the line broadening due to the Doppler-effect.Comment: 5 pages, 2 figures, submitted to A&

«Bellezas atroces». Fundamentos del juicio crítico sobre la calidad tipográfica

This paper collects a compilation of critical statements linked to typographic taste. The analysis has been considered based on two positions: criticism of poorly designed or bad taste fonts and the recommendation to use good or well considered fonts. Based on the results obtained from this compilation, a list of twelve variables that intervene in the definition of the typographic criterion is proposed. &nbsp;Este artículo es una revisión de las manifestaciones críticas vinculadas a las prescripciones relacionadas con el supuesto gusto tipográfico. El análisis se ha considerado en base a dos posiciones: la crítica sobre tipografías no recomendadas (o de mal gusto) y la recomendación de uso de tipografías entendidas como buenas tipografías (o de buen gusto). En base a los resultados obtenidos de dicha recopilación, se plantea una lista de doce variables que intervienen en la definición del criterio tipográfico

Ly alpha escape during cosmological hydrogen recombination: the 3d-1s and 3s-1s two-photon processes

We give a formulation of the radiative transfer equation for Lyman alpha photons which allows us to include the two-photon corrections for the 3s-1s and 3d-1s decay channels during cosmological hydrogen recombination. We use this equation to compute the corrections to the Sobolev escape probability for Lyman alpha photons during hydrogen recombination, which then allow us to calculate the changes in the free electron fraction and CMB temperature and polarization power spectra. We show that the effective escape probability changes by DP/P ~+ 11% at z~1400 in comparison with the one obtained using the Sobolev approximation. This speeds up of hydrogen recombination by DN_e/N_e ~- 1.6% at z~1190, implying |DC_l/C_l| ~1%-3% at l >~ 1500 with shifts in the positions of the maxima and minima in the CMB power spectra. These corrections will be important for the analysis of future CMB data. The total correction is the result of the superposition of three independent processes, related to (i) time-dependent aspects of the problem, (ii) corrections due to quantum mechanical deviations in the shape of the emission and absorption profiles in the vicinity of the Lyman alpha line from the normal Lorentzian, and (iii) a thermodynamic correction factor, which occurs to be very important. All these corrections are neglected in the Sobolev-approximation, but they are important in the context of future CMB observations. All three can be naturally obtained in the two-photon formulation of the Lyman alpha absorption process. However, the corrections (i) and (iii) can also be deduced in the normal '1+1' photon language, without necessarily going to the two-photon picture. Therefore only (ii) is really related to the quantum mechanical aspects of the two-photon process (abridged)Comment: 30 pages, 21 figures, submitted to A&

Discovery of a massive supercluster system at z∼0.47z \sim 0.47

Superclusters are the largest relatively isolated systems in the cosmic web. Using the SDSS BOSS survey we search for the largest superclusters in the redshift range $0.43<z<0.71$. We generate a luminosity-density field smoothed over $8 h^{-1}\mathrm{Mpc}$ to detect the large-scale over-density regions. Each individual over-density region is defined as single supercluster in the survey. We define the superclusters in the way that they are comparable with the superclusters found in the SDSS main survey. We found a system we call the BOSS Great Wall (BGW), which consists of two walls with diameters 186 and 173 $h^{-1}$Mpc, and two other major superclusters with diameters of 64 and 91 $h^{-1}$Mpc. As a whole, this system consists of 830 galaxies with the mean redshift 0.47. We estimate the total mass to be approximately $2\times10^{17}h^{-1}M_\odot$. The morphology of the superclusters in the BGW system is similar to the morphology of the superclusters in the Sloan Great Wall region. The BGW is one of the most extended and massive system of superclusters yet found in the Universe.Comment: 4 pages, accepted as a letter in A&

COSMOSOMAS Observations of the CMB and Galactic Foregrounds at 11 GHz: Evidence for anomalous microwave emission at high Galactic Latitude

We present observations with the new 11 GHz radiometer of the COSMOSOMAS experiment at the Teide Observatory (Tenerife). The sky region between 0 deg <= RA <= 360 deg and 26 deg <= DEC 49 deg (ca. 6500 square degrees) was observed with an angular resolution of 0.9 deg. Two orthogonal independent channels in the receiving system measured total power signals from linear polarizations with a 2 GHz bandwidth. Maps with an average sensitivity of 50 microK per beam have been obtained for each channel. At high Galactic latitude (|b|>30deg) the 11 GHz data are found to contain the expected cosmic microwave background as well as extragalactic radiosources, galactic synchrotron and free-free emission, and a dust-correlated component which is very likely of galactic origin. At the angular scales allowed by the window function of the experiment, the dust-correlated component presents an amplitude \Delta T aprox. 9-13 microK while the CMB signal is of order 27 microK. The spectral behaviour of the dust-correlated signal is examined in the light of previous COSMOSOMAS data at 13-17 GHz and WMAP data at 22-94 GHz in the same sky region. We detect a flattening in the spectral index of this signal below 20 GHz which rules out synchrotron radiation as being responsible for the emission. This anomalous dust emission can be described by a combination of free-free emission and spinning dust models with a flux density peaking around 20 GHz.Comment: 17 pages, 10 tables, 20 figures. Details on the COSMOSOMAS experiment can be found at http://www.iac.es/project/cmb/cosmosomas

La tipografía como conector de la cultura visual y los procesos de diseño gráfico

Este artículo estudia la relación entre la tipografía y los procesos de apropiación de la identidad en un territorio en particular, como resultado del desarrollo de su cultura visual. El estudio se enfoca en un análisis de caso específico, el desarrollo de la tipografía Granaína. Se profundiza en su origen gráfico, basado en la cerámica autóctona de Granada, que inspiró la creación de sus formas tipográficas. Además se describen los procesos de diseño y difusión de la tipografía estructurados en un análisis sintáctico, semántico y pragmático que finaliza con la reflexión sobre las aplicaciones que se sucedieron tras su distribución con una licencia gratuita de libre uso (Creative Commons)

Cosmological Hydrogen Recombination: influence of resonance and electron scattering

In this paper we consider the effects of resonance and electron scattering on the escape of Lyman alpha photons during cosmological hydrogen recombination. We pay particular attention to the influence of atomic recoil, Doppler boosting and Doppler broadening using a Fokker-Planck approximation of the redistribution function describing the scattering of photons on the Lyman alpha resonance of moving hydrogen atoms. We extend the computations of our recent paper on the influence of the 3d/3s-1s two-photon channels on the dynamics of hydrogen recombination, simultaneously including the full time-dependence of the problem, the thermodynamic corrections factor, leading to a frequency-dependent asymmetry between the emission and absorption profile, and the quantum-mechanical corrections related to the two-photon nature of the 3d/3s-1s emission and absorption process on the exact shape of the Lyman alpha emission profile. We show here that due to the redistribution of photons over frequency hydrogen recombination is sped up by DN_e/N_e~-0.6% at z~900. For the CMB temperature and polarization power spectra this results in |DC_l/C_l|~0.5%-1% at l >~ 1500, and therefore will be important for the analysis of future CMB data in the context of the PLANCK Surveyor, SPT and ACT. The main contribution to this correction is coming from the atomic recoil effect (DN_e/N_e~-1.2% at z~900), while Doppler boosting and Doppler broadening partially cancel this correction, again slowing hydrogen recombination down by DN_e/N_e~0.6% at z~900. The influence of electron scattering close to the maximum of the Thomson visibility function at z~1100 can be neglected. (abridged)Comment: 11 pages, 13 figures, submitted to A&