We compute the spectral distortions of the cosmic microwave background (CMB) arising during the epoch of cosmological hydrogen recombination within the standard cosmological (concordance) model for ...frequencies in the range 1-3500 GHz. We follow the evolution of the populations of the hydrogen levels including states up to principle quantum number n= 30 in the redshift range 500 ≤z≤ 3500. All angular momentum substates are treated individually, resulting in a total number of 465 hydrogen levels. The evolution of the matter temperature and the fraction of electrons coming from He ii are also included. We present a detailed discussion of the distortions arising from the main dipolar transitions, for example Lyman and Balmer series, as well as the emission due to the two-photon decay of the hydrogen 2s level. Furthermore, we investigate the robusteness of the results against changes in the number of shells considered. The resulting spectral distortions have a characteristic oscillatory behaviour, which might allow experimentalists to separate them from other backgrounds. The relative distortion of the spectrum exceeds a value of 10−7 at wavelengths longer than 21 cm. Our results also show the importance of detailed follow-up of the angular momentum substates, and their effect on the amplitude of the lines. The effect on the residual electron fraction is only moderate, and mainly occurs at low redshifts. The CMB angular power spectrum is changed by less than 1 per cent. Finally, our computations show that if the primordial radiation field is described by a pure blackbody, then there is no significant emission from any hydrogen transition at redshifts greater than z∼ 2000. This is in contrast to some earlier works, where the existence of a 'pre-recombination' peak was claimed.
We report the development of new bioactive coatings of biomaterials based on the alternate deposition of oppositely charged polyelectrolytes. We selected polylysine (PLL) and poly(glutamic acid) ...(PGA) for the polyelectrolytes and murine melanoma cells as a biological test model system. These cells respond specifically to a small peptide hormone, α-melanocortin, which is a potent stimulator of melanogenesis. We show that a synthetic α-melanocortin derivative, covalently coupled to PLL forming the outer layer of a multilayer film remains as biologically active as the free hormone. Furthermore, the long time activity of the hormone is maintained when embedded in multilayer architectures whereas its short time activity depends on integration depth. The embedding of bioactive molecules not only anchors them irreversibly on the biomaterial, but opens also the possibility to control their activity. In comparison to conventional coating methods, polyelectrolyte multilayers are easy to prepare and retain their biological activity after storage as dry material. These very flexible systems allow broad medical applications for implant and tissue engineering.
We present results for the spectral distortions of the cosmic microwave background (CMB) arising due to bound–bound transitions during the epoch of cosmological hydrogen recombination at frequencies ...down to ν∼100 MHz. We extend our previous treatment of the recombination problem now including the main collisional processes and following the evolution of all the hydrogen angular momentum substates for up to 100 shells. We show that, due to the low baryon density of the Universe, even within the highest considered shell full statistical equilibrium (SE) is not reached and that at low frequencies the recombination spectrum is significantly different when assuming full SE for n > 2. We also directly compare our results for the ionization history to the output of the recfast code, showing that especially at low redshifts rather big differences arise. In the vicinity of the Thomson visibility function the electron fraction differs by roughly −0.6 per cent which affects the temperature and polarization power spectra by ≲ 1 per cent. Furthermore, we shortly discuss the influence of free–free absorption and line broadening due to electron scattering on the bound–bound recombination spectrum and the generation of CMB angular fluctuations due to scattering of photons within the high shells.
The physical processes affecting the thermalization of cosmic microwave background spectral distortions are very simple and well understood. This allows us to make precise predictions for the ...distortions signals caused by various energy release scenarios, where the theoretical uncertainty is largely dominated by the physical ingredients that are used for the calculation. Here, we revisit various approximations for the distortion visibility function - defined using the fraction of the released energy that does not thermalize -- and early μ-type distortions. Our approach is based on a perturbative expansion, which allows us to identify and clarify the origin of different improvements over earlier approximations. It provides a better than ...0.1-1 per cent description of our numerical results over a wide range of parameters. In particular, we are able to capture the high-frequency part of the ...-distortion, which directly depends on the time derivative of the electron temperature. We also include lowest order double Compton and Compton scattering relativistic corrections, finding that because of cancellation they increase the thermalization efficiency in the tail of the distortion visibility function by only ...10 per cent (at z ... 6 x 10...), although individually their effect can reach ...20-40 per cent. (ProQuest: ... denotes formulae/symbols omitted.)
Aims.We provide simple and accurate analytic approximations for the low frequency double Compton emission coefficient that are applicable in a broad range of physical situations up to mildly ...relativistic temperatures. These approximations may be useful for checking in which circumstances the double Compton process is important. Methods.We perform series expansions of the double Compton emission integral for low energies of the incident photon and electron and compare the derived analytic expressions with the results obtained by numerical integrations of the full double Compton cross section. Results.We explicitly derived analytic approximations to the low frequency double Compton emission coefficient for initial monochromatic photons and Wien spectra. We show that combining the analytic approximations given in this paper, an accuracy of better than 5% over a very broad range of temperatures and under various physical conditions can be achieved. The double Compton emissivity strongly depends on the ratio of the incoming photon and electron energies: for hard photons and cold electrons the emission is strongly suppressed compared to the case of similar photon and electron energy, whereas in the opposite situation, i.e. hot electrons and soft initial photons, the emission is enhanced. For photons and electrons close to thermodynamic equilibrium the double Compton emissivity increases less rapidly with temperature than in the Lightman-Thorne approximation and the corrections exceed ∼10% for temperatures above $4\,$keV.
We show how the temperature and the polarization of the cosmic microwave background are affected by bulk rotation of clusters of galaxies owing to the kinetic Sunyaev-Zeldovich effect. The main ...effects of rotation are (i) a shift of the position of the peak of the temperature fluctuation relative to the center of the cluster by a few percent of the core radius and (ii) a tilt of the direction of the plane of linear polarization by several degrees.
We present RICO, a code designed to compute the ionization fraction of the universe during the epoch of hydrogen and helium recombination with an unprecedented combination of speed and accuracy. This ...is accomplished by training the machine learning code PICO on the calculations of a multilevel cosmological recombination code which self-consistently includes several physical processes that were neglected previously. After training, RICO is used to fit the free electron fraction as a function of the cosmological parameters. While, for example, at low redshifts (z 900), much of the net change in the ionization fraction can be captured by lowering the hydrogen fudge factor in RECFAST by about 3%, RICO provides a means of effectively using the accurate ionization history of the full recombination code in the standard cosmological parameter estimation framework without the need to add new or refined fudge factors or functions to a simple recombination model. Within the new approach presented here, it is easy to update RICO whenever a more accurate full recombination code becomes available. Once trained, RICO computes the cosmological ionization history with negligible fitting error in ~10 ms, a speedup of at least 106 over the full recombination code that was used here. Also RICO is able to reproduce the ionization history of the full code to a level well below 0.1%, thereby ensuring that the theoretical power spectra of cosmic microwave background (CMB) fluctuations can be computed to sufficient accuracy and speed for analysis from upcoming CMB experiments like Planck. Furthermore, it will enable cross-checking different recombination codes across cosmological parameter space, a comparison that will be very important in order to assure the accurate interpretation of future CMB data.
We discuss a new analytic 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 Doppler broadening and boosting into account. This new solution is important for detailed computations of cosmic microwave background spectral distortions arising from uncompensated atomic transitions of hydrogen and helium in the early Universe. It also clearly shows that the broadening of weak lines in this situation only depends on the Compton y-parameter defined by Te, even though the evolution of the ambient CMB blackbody spectrum itself is described by $y\propto T_{\rm e}-T_{\gamma}$. 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 sources, 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.
We consider the changes of the SZ cluster brightness, flux and number counts induced by the motion of the Solar System with respect to the frame defined by the cosmic microwave background (CMB). ...These changes are connected to the Doppler effect and aberration and exhibit a strong spectral and spatial dependence. The correction to the SZ cluster brightness and flux has an amplitude and spectral dependence, which is similar to the first order cluster peculiar velocity correction to the thermal SZ effect and hence may lead to a ∼10% correction to the kinetic SZ effect. Due to the change in the received cluster CMB flux, the motion of the Solar System induces a dipolar asymmetry in the observed number of clusters above a given flux level. Similar effects were discussed for γ-ray bursts and radio galaxies, but here, due to the very peculiar frequency-dependence of the thermal SZ effect, the number of observed clusters in one direction of the sky can be both decreased or increased depending on the frequency band.
The change of physical conditions across the turbulent and magnetized interstellar medium induces a 3D spatial variation of the properties of Galactic polarized emission. The observed signal results ...from the averaging of different spectral energy distributions (SEDs) and polarization angles along and between lines of sight. As a consequence, the total Stokes parameters
Q
and
U
will have different frequency dependencies, both departing from the canonical emission law, so that the polarization angle becomes frequency dependent. In the present work, we show how this phenomenon similarly induces a different, distorted SED for the three polarized angular power spectra
EE
,
BB
, and
EB
, implying a variation of the
EE
/
BB
ratio with frequency. We demonstrate how the previously introduced “spin-moment” formalism provides a natural framework to grasp these effects and enables us to derive analytical predictions for the spectral behaviors of the polarized spectra, focusing here on the example of thermal dust polarized emission. After a quantitative discussion based on a model combining emission from a filament with its background, we further reveal that the spectral complexity implemented in the dust models commonly used by the cosmic microwave background (CMB) community includes different distortions for the three polarized power-spectra. This new understanding is crucial for CMB component separation, in which extreme accuracy is required for the modeling of the dust signal to allow for the search of the primordial imprints of inflation or cosmic birefringence. For the latter, as long as the dust
E
B
signal is not measured accurately, great caution is required regarding the assumptions made to model its spectral behavior, as it may not be inferred from the other dust angular power spectra.
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