2,164 research outputs found

### Lensing reconstruction of cluster-mass cross-correlation with cosmic microwave background polarization

We extend our maximum likelihood method for reconstructing the cluster-mass
cross-correlation from cosmic microwave background (CMB) temperature
anisotropies and develop new estimators that utilize six different quadratic
combinations of CMB temperature and polarization fields. Our maximum likelihood
estimators are constructed with delensed CMB temperature and polarization
fields by using an assumed model of the convergence field and they can be
iteratively applied to a set of clusters, approaching to the optimal condition
for the lensing reconstruction as the assumed initial model is refined. Using
smoothed particle hydrodynamics simulations, we create a catalog of realistic
clusters obtainable from the current Sunyaev-Zel'dovich (SZ) surveys, and we
demonstrate the ability of the maximum likelihood estimators to reconstruct the
cluster-mass cross-correlation from the massive clusters. The iTT temperature
estimator provides a signal-to-noise ratio of a factor 3 larger than the iEB
polarization estimator, unless the detector noise for measuring polarization
anisotropies is controlled under 3 microK.Comment: 10 pages, 6 figures, accepted for publication in Physical Review

### Large scale motions in superclusters: their imprint in the CMB

We identify high density regions of supercluster size in high resolution
N-body simulations of a representative volume of three Cold Dark Matter
Universes. By assuming that (1) the density and peculiar velocities of baryons
trace those of the dark matter, and (2) the temperature of plasma is
proportional to the velocity dispersion of the dark matter particles in regions
where the crossing times is smaller than the supercluster free-fall time, we
investigate how thermal motions of electrons in the intra-cluster medium and
peculiar velocity of clusters can affect the secondary anisotropies in the
cosmic microwave background (CMB). We show that the thermal effect dominates
the kinematic effect and that the largest thermal decrements are associated
with the most massive clusters in superclusters. Thus, searching for the
presence of two or more close large CMB decrements represents a viable strategy
for identifying superclusters at cosmological distances. Moreover, maps of the
kinematic effect in superclusters are characterized by neighboring large peaks
of opposite signs. These peaks can be as high as ~ 10 microK at the arcminute
angular resolution. Simultaneous pointed observations of superclusters in the
millimeter and submillimeter bands with upcoming sensitive CMB experiments can
separate between the thermal and kinematic effect contributions and constrain
the evolution of the velocity field in large overdense regions.Comment: 4 pages, 5 figures, ApJ Letters, in press; revised version according
to referee's comment

### Scaling Laws in High-Energy Inverse Compton Scattering. II. Effect of Bulk Motions

We study the inverse Compton scattering of the CMB photons off high-energy
nonthermal electrons. We extend the formalism obtained by the previous paper to
the case where the electrons have non-zero bulk motions with respect to the CMB
frame. Assuming the power-law electron distribution, we find the same scaling
law for the probability distribution function P_{1,K}(s) as P_{1}(s) which
corresponds to the zero bulk motions, where the peak height and peak position
depend only on the power-index parameter. We solved the rate equation
analytically. It is found that the spectral intensity function also has the
same scaling law. The effect of the bulk motions to the spectral intensity
function is found to be small. The present study will be applicable to the
analysis of the X-ray and gamma-ray emission models from various astrophysical
objects with non-zero bulk motions such as radio galaxies and astrophysical
jets.Comment: 10 pages, 3 figures, accepted version by Physical Review

### Two-photon transitions in hydrogen and cosmological recombination

We study the two-photon process for the transitions ns --> 1s and nd --> 1s
in hydrogen up to large n. For n<=20 we provide simple analytic fitting
formulae to describe the non-resonant part of the two-photon emission profiles.
Combining these with the analytic form of the cascade-term yields a simple and
accurate description of the full two-photon decay spectrum, which only involves
a sum over a few intermediate states. We demonstrate that the cascade term
naturally leads to a nearly Lorentzian shape of the two-photon profiles in the
vicinity of the resonances. However, due to quantum-electrodynamical
corrections, the two-photon emission spectra deviate significantly from the
Lorentzian shape in the very distant wings of the resonances. We investigate up
to which distance the two-photon profiles are close to a Lorentzian and discuss
the role of the interference term. We then analyze how the deviation of the
two-photon profiles from the Lorentzian shape affects the dynamics of
cosmological hydrogen recombination. Since in this context the escape of
photons from the Lyman-alpha resonance plays a crucial role, we concentrate on
the two-photon corrections in the vicinity of the Lyman-alpha line. Our
computations show that the changes in the ionization history due to the
additional two-photon process from high shell (n>2) likely do not reach the
percent-level. For conservative assumptions we find a correction DN_e/N_e~-0.4%
at redshift z~1160. This is numerically similar to the result of another recent
study; however, the physics leading to this conclusion is rather different. In
particular, our calculations of the effective two-photon decay rates yield
significantly different values, where the destructive interference of the
resonant and non-resonant terms plays a crucial role in this context (abridged)Comment: 20 pages, 13 figures, 4 tables, accepted versio

### The evolution of CMB spectral distortions in the early Universe

The energy spectrum of the cosmic microwave background (CMB) allows
constraining episodes of energy release in the early Universe. In this paper we
revisit and refine the computations of the cosmological thermalization problem.
For this purpose a new code, called CosmoTherm, was developed that allows
solving the coupled photon-electron Boltzmann equation in the expanding,
isotropic Universe for small spectral distortion in the CMB. We explicitly
compute the shape of the spectral distortions caused by energy release due to
(i) annihilating dark matter; (ii) decaying relict particles; (iii) dissipation
of acoustic waves; and (iv) quasi-instantaneous heating. We also demonstrate
that (v) the continuous interaction of CMB photons with adiabatically cooling
non-relativistic electrons and baryons causes a negative mu-type CMB spectral
distortion of DI_nu/I_nu ~ 10^{-8} in the GHz spectral band. We solve the
thermalization problem including improved approximations for the double Compton
and Bremsstrahlung emissivities, as well as the latest treatment of the
cosmological recombination process. At redshifts z <~ 10^3 the matter starts to
cool significantly below the temperature of the CMB so that at very low
frequencies free-free absorption alters the shape of primordial distortions
significantly. In addition, the cooling electrons down-scatter CMB photons
introducing a small late negative y-type distortion at high frequencies. We
also discuss our results in the light of the recently proposed CMB experiment
Pixie, for which CosmoTherm should allow detailed forecasting. Our current
computations show that for energy injection because of (ii) and (iv) Pixie
should allow to improve existing limits, while the CMB distortions caused by
the other processes seem to remain unobservable with the currently proposed
sensitivities and spectral bands of Pixie.Comment: 22 pages, 19 figures, 1 table, accepted by MNRA

### (No) dimming of X-ray clusters beyond z~1 at fixed mass: crude redhshifts and masses from raw X-ray and SZ data

Scaling relations in the LCDM Cosmology predict that for a given mass the
clusters formed at larger redshift are hotter, denser and therefore more
luminous in X-rays than their local z~0 counterparts. This effect overturns the
decrease in the observable X-ray flux so that it does not decrease at z > 1,
similar to the SZ signal. Provided that scaling relations remain valid at
larger redshifts, X-ray surveys will not miss massive clusters at any redshift,
no matter how far they are. At the same time, the difference in scaling with
mass and distance of the observable SZ and X-ray signals from galaxy clusters
at redshifts $z\lesssim 2$ offers a possibility to crudely estimate the
redshift and the mass of a cluster. This might be especially useful for
preselection of massive high-redshift clusters and planning of optical
follow-up for overlapping surveys in X-ray (e.g., by SRG/eRosita) and SZ (e.g.
Planck, SPT and ACT).Comment: 7 pages, 5 figures, MNRAS accepte

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