We estimate the impact of the dipole straylight contamination (DSC) for the Planck satellite on the alignments of vectors associated with the low multipoles of the pattern of the cosmic microwave ...background (CMB) anisotropies. In particular we study how the probability distributions of 18 estimators for the alignments change when DSC is taken into account. We find that possible residual DSC should leave a non-negligible impact on low multipole alignments for effective values of the fractional far sidelobe integrated response, p, larger than ∼ few × 10−3. The effect is strongly dependent on the intrinsic sky amplitude and weakly dependent on the considered scanning strategy. We find a decrease of the alignment probability between the quadrupole and the dipole and an increase of the alignment probability between the hexadecapole and the dipole (larger is the intrinsic sky amplitude and lower is the contamination). The remaining estimators do not exhibit clear signatures, except, in some cases, considering the largest values of p and the lowest sky amplitudes. Provided that the real sidelobes of the Planck receivers in flight conditions will correspond to p≲ few × 10−3, as realistically expected at least in the cosmological frequency channels, and will be known with accuracies better than ∼ few × 10 per cent allowing for a suitable cleaning during data reduction, Planck will be very weakly affected from DSC on the alignments of low multipoles.
We present an analysis of the dipole straylight contamination (DSC) for spinning space missions designed to measure cosmic microwave background (CMB) anisotropies. Although this work is mainly ...devoted to the Planck project, it is relatively general and allows us to focus on the most relevant DSC implications. We first study a simple analytical model for the DSC in which the pointing direction of the main spillover can be assumed parallel or not to the spacecraft spin axis direction and compute the time-ordered data and map. The map is then analysed paying particular attention to the DSC of the low-multipole coefficients of the map. Through dedicated numerical simulations, we verify the analytical results and extend the analysis to higher multipoles and to more complex (and realistic) cases by relaxing some of the simple assumptions adopted in the analytical approach. We find that the systematic effect averages out in an even number of surveys, except for a contamination of the dipole itself that survives when spin axis and spillover directions are not parallel and for a contamination of the other multipoles in the case of complex scanning strategies. In particular, the observed quadrupole can be affected by the DSC in an odd number of surveys or in the presence of survey uncompleteness or overcompleteness. Various aspects relevant in CMB space projects (such as implications for calibration, impact on polarization measurements, accuracy requirement in the far beam knowledge for data analysis applications and scanning strategy dependence) are discussed.
We compute the imprints left on the cosmic microwave background (CMB) by two cosmic reionization models consistent with current observations but characterized by alternative radiative feedback ...prescriptions (suppression and filtering) resulting in a different suppression of star formation in low-mass haloes. The models imply different ionization and thermal histories and 21-cm background signals. The derived Comptonization, u, and free–free distortion, yB, parameters are below current observational limits for both models. However, the value of u≃ 1.69 × 10−7 (≃9.65 × 10−8) for the suppression (filtering) model is in the detectability range of the next generation of CMB spectrum experiments. Through, the dedicated Boltzmann code cmbfast, modified to include the above ionization histories, we compute the CMB angular power spectrum (APS) of the TT, TE and EE modes. For the EE mode, the differences between these models are significantly larger than the cosmic and sampling variance over the multipole range ℓ∼ 5–15, leaving a good chance of discriminating between these feedback mechanisms with forthcoming/future CMB polarization experiments. The main limitations come from foreground contamination: it should be subtracted at per cent level in terms of APS, a result potentially achievable by novel component separation techniques and mapping of Galactic foreground.
Planck 2018 results Akrami, Y.; Ashdown, M.; Aumont, J. ...
Astronomy and astrophysics (Berlin),
09/2020, Letnik:
641
Journal Article
Recenzirano
Odprti dostop
Analysis of the
Planck
2018 data set indicates that the statistical properties of the cosmic microwave background (CMB) temperature anisotropies are in excellent agreement with previous studies using ...the 2013 and 2015 data releases. In particular, they are consistent with the Gaussian predictions of the ΛCDM cosmological model, yet also confirm the presence of several so-called “anomalies” on large angular scales. The novelty of the current study, however, lies in being a first attempt at a comprehensive analysis of the statistics of the polarization signal over all angular scales, using either maps of the Stokes parameters,
Q
and
U
, or the
E
-mode signal derived from these using a new methodology (which we describe in an appendix). Although remarkable progress has been made in reducing the systematic effects that contaminated the 2015 polarization maps on large angular scales, it is still the case that residual systematics (and our ability to simulate them) can limit some tests of non-Gaussianity and isotropy. However, a detailed set of null tests applied to the maps indicates that these issues do not dominate the analysis on intermediate and large angular scales (i.e.,
ℓ
≲ 400). In this regime, no unambiguous detections of cosmological non-Gaussianity, or of anomalies corresponding to those seen in temperature, are claimed. Notably, the stacking of CMB polarization signals centred on the positions of temperature hot and cold spots exhibits excellent agreement with the ΛCDM cosmological model, and also gives a clear indication of how
Planck
provides state-of-the-art measurements of CMB temperature and polarization on degree scales.
Detectable signatures of cosmic radiative feedback Schneider, R.; Salvaterra, R.; Choudhury, T. Roy ...
Monthly Notices of the Royal Astronomical Society,
March 2008, Letnik:
384, Številka:
4
Journal Article
Recenzirano
Odprti dostop
We use a semi-analytical model to study the impact of reionization, and the associated radiative feedback, on galaxy formation. Two feedback models have been considered: (i) a standard prescription, ...according to which star formation is totally suppressed in galaxies with circular velocity below a critical threshold (model CF06) and (ii) a characterization based on the filtering scale (model G00), allowing for a gradual reduction of the gas available for star formation in low-mass galaxies. In model CF06, reionization starts at z≲ 15–20 and is 85 per cent complete by z∼ 10; at the same z, the ionized fraction is 16 per cent in model G00. The models match SDSS constraints on the evolution of the neutral hydrogen fraction at z < 7, but predict different Thomson optical depths, τe= 0.1017 (CF06) and 0.0631 (G00); such values are within 1σ of the Wilkinson Microwave Anisotropy Probe three-year determination. Both models are in remarkable good agreement with additional existing data evolution of Lyman-limit systems, cosmic star formation history, high-z galaxy counts, intergalactic medium (IGM) thermal history, which therefore cannot be used to discriminate among different feedback models. Deviations among radiative feedback prescriptions emerge when considering the expected H i 21-cm background signal, where a ∼15 mK absorption feature in the range 75–100 MHz is present in model G00 and a global shift of the emission feature preceding reionization towards larger frequencies occurs in the same model. Single dish observations with existing or forthcoming low-frequency radio telescopes can achieve mK sensitivity, allowing the identification of these features provided that foregrounds can be accurately subtracted.
ABSTRACT
We present a new, updated version of the EuclidEmulator (called EuclidEmulator2), a fast and accurate predictor for the nonlinear correction of the matter power spectrum. 2 per cent level ...accurate emulation is now supported in the eight-dimensional parameter space of w0waCDM+∑mν models between redshift z = 0 and z = 3 for spatial scales within the range $0.01 \, h\, {\rm Mpc}^{-1}\le k \le 10\, h\, {\rm Mpc}^{-1}$. In order to achieve this level of accuracy, we have had to improve the quality of the underlying N-body simulations used as training data: (i) we use self-consistent linear evolution of non-dark matter species such as massive neutrinos, photons, dark energy, and the metric field, (ii) we perform the simulations in the so-called N-body gauge, which allows one to interpret the results in the framework of general relativity, (iii) we run over 250 high-resolution simulations with 30003 particles in boxes of 1(h−1 Gpc)3 volumes based on paired-and-fixed initial conditions, and (iv) we provide a resolution correction that can be applied to emulated results as a post-processing step in order to drastically reduce systematic biases on small scales due to residual resolution effects in the simulations. We find that the inclusion of the dynamical dark energy parameter wa significantly increases the complexity and expense of creating the emulator. The high fidelity of EuclidEmulator2 is tested in various comparisons against N-body simulations as well as alternative fast predictors such as HALOFIT, HMCode, and CosmicEmu. A blind test is successfully performed against the Euclid Flagship v2.0 simulation. Nonlinear correction factors emulated with EuclidEmulator2 are accurate at the level of $1{{\ \rm per\ cent}}$ or better for $0.01 \, h\, {\rm Mpc}^{-1}\le k \le 10\, h\, {\rm Mpc}^{-1}$ and z ≤ 3 compared to high-resolution dark-matter-only simulations. EuclidEmulator2 is publicly available at https://github.com/miknab/EuclidEmulator2.
We analyse the implications of future observations of the cosmic microwave background (CMB) absolute temperature at centimetre and decimetre wavelengths, where both ground, balloon and space ...experiments are currently under way to complement the accurate COBE/FIRAS data available at λ≲ 1 cm. Our analysis shows that forthcoming ground and balloon measurements will allow a better understanding of free–free distortions but will not be able to significantly improve the constraints already provided by the FIRAS data on the possible energy exchanges in the primeval plasma. The same holds even for observations with sensitivities up to ∼10 times better than those of forthcoming experiments. Thus, we have studied the impact of very high-quality data, such as those, in principle, achievable with a space experiment such as the Diffuse Microwave Emission Survey (DIMES) planned to measure the CMB absolute temperature at 0.5 ≲λ∼ 15 cm with a sensitivity of ∼0.1 mK, close to that of FIRAS. We have demonstrated that such high-quality data would improve by a factor of ∼50 the FIRAS results on the fractional energy exchanges, Δε/εi, associated with dissipation processes possibly occurred in a wide range of cosmic epochs, at intermediate and high redshifts (yh≳ 1), and that the energy dissipation epoch could also be significantly constrained. By jointly considering two dissipation processes occurring at different epochs, we demonstrated that the sensitivity and frequency coverage of a DIMES-like experiment would allow one to accurately recover the epoch and the amount of energy possibly injected into the radiation field at early and intermediate epochs even in the presence of a possible late distortion, while the constraints on the energy possibly dissipated at late epochs can be improved by a factor of ≃2. In addition, such measurements can provide an independent and very accurate cross-check of FIRAS calibration. Finally, a DIMES-like experiment will be able to provide indicative independent estimates of the baryon density: the product ΩbH20 can be recovered within a factor of ∼2–5 even in the case of (very small) early distortions with Δε/εi∼ (5–2) × 10−6. On the other hand, for Ωb (H0/50)2≲ 0.2, an independent baryon density determination with an accuracy at ∼ per cent level, comparable to that achievable with CMB anisotropy experiments, would require an accuracy of ∼1 mK or better in the measurement of possible early distortions but up to a wavelength from ∼ few × dm to ∼7 dm, according to the baryon density value.
Planck 2018 results Akrami, Y.; Ashdown, M.; Aumont, J. ...
Astronomy and astrophysics (Berlin),
09/2020, Letnik:
641
Journal Article
Recenzirano
Odprti dostop
We present full-sky maps of the cosmic microwave background (CMB) and polarized synchrotron and thermal dust emission, derived from the third set of
Planck
frequency maps. These products have ...significantly lower contamination from instrumental systematic effects than previous versions. The methodologies used to derive these maps follow closely those described in earlier papers, adopting four methods (
Commander
,
NILC
,
SEVEM
, and
SMICA
) to extract the CMB component, as well as three methods (
Commander
,
GNILC
, and
SMICA
) to extract astrophysical components. Our revised CMB temperature maps agree with corresponding products in the
Planck
2015 delivery, whereas the polarization maps exhibit significantly lower large-scale power, reflecting the improved data processing described in companion papers; however, the noise properties of the resulting data products are complicated, and the best available end-to-end simulations exhibit relative biases with respect to the data at the few percent level. Using these maps, we are for the first time able to fit the spectral index of thermal dust independently over 3° regions. We derive a conservative estimate of the mean spectral index of polarized thermal dust emission of
β
d
= 1.55 ± 0.05, where the uncertainty marginalizes both over all known systematic uncertainties and different estimation techniques. For polarized synchrotron emission, we find a mean spectral index of
β
s
= −3.1 ± 0.1, consistent with previously reported measurements. We note that the current data processing does not allow for construction of unbiased single-bolometer maps, and this limits our ability to extract CO emission and correlated components. The foreground results for intensity derived in this paper therefore do not supersede corresponding
Planck
2015 products. For polarization the new results supersede the corresponding 2015 products in all respects.
The subject of this paper is beam deconvolution in small angular scale CMB experiments. The beam effect is reversed using the Jacobi iterative method, which was designed to solved systems of ...algebraic linear equations. The beam is a non circular one which moves according to the observational strategy. A certain realistic level of Gaussian instrumental noise is assumed. The method applies to small scale CMB experiments in general (cases A and B), but we have put particular attention on Planck mission at 100 GHz (cases C and D). In cases B and D, where noise is present, deconvolution allows to correct the main beam distortion effect and recover the initial angular power spectrum up to the end of the fifth acoustic peak. An encouraging result whose importance is analyzed in detail. More work about deconvolution in the presence of other systematics is in progress. This paper is related to the Planck LFI activities.
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