Context. Various methods have been studied to compute the boosting effects produced by the observer peculiar motion, which modifies and transfers the isotropic monopole frequency spectrum of the ...cosmic background radiation to higher multipoles. Explicit analytical solutions for the spherical harmonic expansion coefficients were already presented and applied to different types of background spectrum, strongly alleviating the computational effort needed for accurate theoretical predictions. The frequency spectra at higher multipoles are inherently led by higher-order derivatives of the monopole spectrum. Provided that it can be well described by analytic or semi-analytic functions, the computation of its transfer is not affected by numerical instabilities when evaluated at the required level of numerical accuracy. Instead, monopole frequency spectra described by tabulated functions are computed with a relatively poor frequency resolution in comparison with the Doppler shift, which necessitates interpolation of the tabular representation. The spectra are also affected by uncertainties related to intrinsic inaccuracies in the modelling or in the related observational data as well as to limited accuracy in their numerical computation. These uncertainties propagate and increase with the derivative order, possibly preventing the trustworthy computation of the transfer to higher multipoles and of the observed monopole. Aims. We study methods to filter the original function or its derivatives and the multipole spectra, to mitigate numerical instabilities, and to derive reliable predictions of the harmonic coefficients for different cosmic background models. Methods. From the analytical solutions, and assuming that the monopole spectrum can be expanded in Taylor’s series, we derive explicit expressions for the harmonic coefficients up to the multipole ℓ max = 6 in terms of monopole spectrum derivatives. We then consider different low-pass filters: prefiltering in Fourier space of the tabular representation; filtering in both real and Fourier space of the numerical derivatives; interpolation approaches; and a dedicated method based on amplification and deamplification of the boosted signal. We study the quality of these methods when applied to suitable analytical approximations of the tabulated functions, possibly polluted with simulated noise. These methods are then applied to the tabulations. Results. We consider two very different types of monopole spectra superimposed to the cosmic microwave background: the (smooth) extragalactic source microwave background signal from radio-loud active galactic nuclei and the (feature-rich) redshifted 21 cm line, and present our results in terms of spherical harmonic coefficients. The direct prediction of these coefficients can be noisy at ℓ > 1 or, depending on the uncertainty level, even at ℓ ≤ 1. Without assuming a functional form for the extragalactic background spectrum, the Gaussian prefiltering coupled to the sequential real-space filtering of derivatives allows us to derive accurate predictions up to ℓ ∼ 6, while a log–log polynomial representation, which is appropriate over several decades, gives accurate solutions at any ℓ . Instead, it is difficult to characterise the 21 cm line model variety, and so it is relevant to work without assumptions about the underlying function. Typically, the prefiltering provides accurate predictions up to ℓ ≃ 3 or 4, while the further sequential filtering of the derivatives or the boosting amplification and deamplification method improves the results up to ℓ = 4, while also allowing reasonable estimations of the spectrum at higher ℓ . Conclusions. The proposed methods can significantly extend the range of realistic cosmic background models manageable with a fast computation, beyond the cases characterised a priori by analytical or semi-analytical functions. These methods require only an affordable increase in computation time compared to the direct calculation via simple interpolation.
The cosmological reionization and thermal history, following the recombination epoch and the dark age, can be studied at radio frequencies through the tomographic view offered by the redshifted 21 cm ...line and the integrated information offered by the diffuse free-free emission, coupled to the Comptonization distortion, which is relevant at higher frequencies. For these types of signals, current theoretical predictions span a wide range of possibilities. The recent EDGES observations of the monopole disagree with the typical standard models and call, if confirmed, for non-standard physical processes and/or for an early population of extragalactic sources producing a remarkable radio background at high redshifts that is almost consistent with the ARCADE 2 claim of a significant excess of cosmic microwave background (CMB) absolute temperature at low frequency. These signatures can be observed both in global (or monopole) signal and fluctuations from very large to small angular scales. The peculiar motion of an observer with respect to an ideal reference frame, at rest with respect to the CMB, produces boosting effects in several observable quantities. They are remarkable in the anisotropy patterns at low multipoles, particularly in the dipole, with frequency spectral behaviours depending on the spectrum of the monopole emission, as previously studied in the context of CMB spectral distortions. We present here a novel investigation of this effect at radio frequencies, aimed at predicting the imprints expected in the redshifted 21 cm line signal and in the diffuse free-free emission plus the Comptonization distortion for several representative models. Furthermore, we consider the same type of signal, but as expected from the cosmological (CMB plus potential astrophysical signals) radio background determining the offset for 21 cm redshifted line. The combination of the four types of signal and their different relevance in the various frequency ranges is studied. This approach of linking monopole and anisotropy analyses, can be applied on all-sky or relatively wide sky coverage surveys as well as to a suitable set of sky patches. By relying only on the quality of interfrequency and relative data calibration, the approach in principle by-passes the need for precise absolute calibration, which is a critical point of current and future radio interferometric facilities.
Context.
The observer peculiar motion produces boosting effects in the anisotropy pattern of the considered background with frequency spectral behaviours related to its frequency spectrum.
Aims.
We ...study how the frequency spectrum of the background isotropic monopole emission is modified and transferred to the frequency spectra at higher multipoles,
ℓ
. We performed the analysis in terms of spherical harmonic expansion up to a certain value of
ℓ
max
, for various models of background radiation, spanning the range between the radio and the far-infrared.
Methods.
We derived a system of linear equations to obtain the spherical harmonic coefficients and provide the explicit solutions up to
ℓ
max
= 6. These are written as linear combinations of the signals at
N
=
ℓ
max
+ 1 colatitudes. We take advantage of the symmetry property of the associated Legendre polynomials with respect to
π
/2, which allows for the separation of the system into two subsystems: (1) for
ℓ
= 0 and even multipoles and (2) for odd multipoles. This improves the accuracy of the solutions with respect to an arbitrary choice of the adopted colatitudes.
Results.
We applied the method to different types of monopole spectra represented in terms of analytical or semi-analytical functions, that is, four types of distortions of the photon distribution function of the cosmic microwave background and four types of extragalactic background signals superimposed onto the cosmic microwave background’s Planckian spectrum, along with several different combinations of these types. We present our results in terms of the spherical harmonic coefficients and of the relationships between the observed and the intrinsic monopole spectra, as well as in terms of the corresponding all-sky maps and angular power spectra. For certain representative cases, we compare the results of the proposed method with those obtained using more computationally demanding numerical integrations or map generation and inversion. The method is generalized to the case of an average map composed by accumulating data taken with sets of different observer velocities, as is necessary when including the effect of the observer motion relative to the Solar System barycentre.
Conclusions.
The simplicity and efficiency of the proposed method can significantly alleviate the computational effort required for accurate theoretical predictions and for the analysis of data derived by future projects across a variety of cases of interest. Finally, we discuss the superposition of the cosmic microwave background intrinsic anisotropies and of the effects induced by the observer peculiar motion, exploring the possibility of constraining the intrinsic dipole embedded in the kinematic dipole in the presence of background spectral distortions.
The density contrast of the Universe, parametrized in terms of the matter power spectrum and its variance, can amplify the signal of the free-free process in the plasma. The damping of fluctuations ...on scales smaller than the dark matter particle free streaming scale corresponds to a suppression of the total matter power spectrum on large wavenumbers k. We derive the time evolution of the variance of the matter power spectrum for various cosmological models and parameters by numerically computing the power spectrum with a modified version of the Boltzmann code camb, for different values of the cut-off parameter k
max. Suitable analytical approximations of the numerical results are presented. We then characterize the cosmic microwave background (CMB) free-free spectral distortion accounting for the amplification effect coming from clumping factor. Indeed, the clumpiness, associated with the density contrast of the intergalactic medium, increases at decreasing redshift. The analysis is carried out for selected astrophysical and phenomenological cosmological reionization histories for which we evaluate the impact of the clumping factor on the free-free distortion and discuss the wavelength dependence of the predicted signal. Finally, we address a comparison with other classes of unavoidable CMB spectral distortions and future observational perspectives. While Comptonization from reionization is dominant at high frequencies, the free-free signal predicted in the considered models contributes to the distortion at a level of few (few tens) per cent at frequencies below ∼25 GHz (∼10 GHz) and represents the main signature below ∼4 GHz. The cosmological signal from the H i 21-cm background is found to prevail over the free-free distortion in a restricted, model-dependent frequency window between ∼0.1 and ∼0.2 GHz.
This Voyage 2050 paper highlights the unique science opportunities using spectral distortions of the cosmic microwave background (CMB). CMB spectral distortions probe many processes throughout the ...history of the Universe, delivering novel information that complements past, present and future efforts with CMB anisotropy and large-scale structure studies. Precision spectroscopy, possible with existing technology, would not only provide key tests for processes expected within the cosmological standard model but also open an enormous discovery space to new physics. This offers unique scientific opportunities for furthering our understanding of inflation, recombination, reionization and structure formation as well as dark matter and particle physics. A dedicated experimental approach could open this new window to the early Universe in the decades to come, allowing us to turn the long-standing upper distortion limits obtained with
COBE
/FIRAS some 25 years ago into clear detections of the expected standard distortion signals and also challenge our current understanding of the laws of nature.
Context. In the last decade, astronomers have found a new type of supernova called superluminous supernovae (SLSNe) due to their high peak luminosity and long light-curves. These hydrogen-free ...explosions (SLSNe-I) can be seen to z ~ 4 and therefore, offer the possibility of probing the distant Universe. Aims. We aim to investigate the possibility of detecting SLSNe-I using ESA’s Euclid satellite, scheduled for launch in 2020. In particular, we study the Euclid Deep Survey (EDS) which will provide a unique combination of area, depth and cadence over the mission. Methods. We estimated the redshift distribution of Euclid SLSNe-I using the latest information on their rates and spectral energy distribution, as well as known Euclid instrument and survey parameters, including the cadence and depth of the EDS. To estimate the uncertainties, we calculated their distribution with two different set-ups, namely optimistic and pessimistic, adopting different star formation densities and rates. We also applied a standardization method to the peak magnitudes to create a simulated Hubble diagram to explore possible cosmological constraints. Results. We show that Euclid should detect approximately 140 high-quality SLSNe-I to z ~ 3.5 over the first five years of the mission (with an additional 70 if we lower our photometric classification criteria). This sample could revolutionize the study of SLSNe-I at z > 1 and open up their use as probes of star-formation rates, galaxy populations, the interstellar and intergalactic medium. In addition, a sample of such SLSNe-I could improve constraints on a time-dependent dark energy equation-of-state, namely w(a), when combined with local SLSNe-I and the expected SN Ia sample from the Dark Energy Survey. Conclusions. We show that Euclid will observe hundreds of SLSNe-I for free. These luminous transients will be in the Euclid data-stream and we should prepare now to identify them as they offer a new probe of the high-redshift Universe for both astrophysics and cosmology.
The shallow, all-sky
Planck
surveys at sub-millimetre wavelengths have detected the brightest strongly gravitationally lensed dusty galaxies in the sky. The combination of their extreme gravitational ...flux-boosting and image-stretching offers the unique possibility of measuring in extraordinary detail the galaxy structure and kinematics in early evolutionary phases through high-resolution imaging and spectroscopic follow-up. This enables us to gain otherwise unaccessible direct information on physical processes in action. However, the extraction of candidate strongly lensed galaxies from
Planck
catalogues is hindered by the fact that they are generally detected with a poor signal-to-noise ratio, except for the few brightest galaxies. Their photometric properties are therefore strongly blurred, which makes them very difficult to single out. We have devised a method capable of increasing the number of identified
Planck
-detected strongly lensed galaxies by a factor of about three to four, although with an unavoidably limited efficiency. Our approach exploits the fact that the sub-millimetre colours of strongly lensed galaxies are definitely colder than those of nearby dusty galaxies, which constitute the overwhelming majority of extragalactic sources detected by
Planck
. The sub-millimetre colours of the 47 confirmed or very likely
Planck
-detected strongly lensed galaxies have been used to estimate the colour range spanned by objects of this type. Moreover, most nearby galaxies and radio sources can be confirmed by cross-matching with the IRAS and PCNT catalogues, respectively. We present samples of lensed candidates selected at 545, 857, and 353 GHz, comprising 177, 97, and 104 sources, respectively. The efficiency of our approach, tested by exploiting data from the SPT survey covering ≃2500 deg
2
, is estimated to be in the range 30%−40%. We also discuss stricter selection criteria to increase the estimated efficiency to ≃50%, at the cost of a somewhat lower completeness. Our analysis of SPT data has identified a dozen galaxies that can reliably be considered previously unrecognized
Planck
-detected strongly lensed galaxies. Extrapolating the number of
Planck
-detected confirmed or very likely strongly lensed galaxies found within the SPT and H-ATLAS survey areas, we expect ≃150 to ≃190 such sources over the full |
b
|> 20° sky.
Euclid preparation Adam, R.; Vannier, M.; Maurogordato, S. ...
Astronomy and astrophysics (Berlin),
07/2019, Letnik:
627
Journal Article
Recenzirano
Odprti dostop
Galaxy cluster counts in bins of mass and redshift have been shown to be a competitive probe to test cosmological models. This method requires an efficient blind detection of clusters from surveys ...with a well-known selection function and robust mass estimates, which is particularly challenging at high redshift. The
Euclid
wide survey will cover 15 000 deg
2
of the sky, avoiding contamination by light from our Galaxy and our solar system in the optical and near-infrared bands, down to magnitude 24 in the
H
-band. The resulting data will make it possible to detect a large number of galaxy clusters spanning a wide-range of masses up to redshift ∼2 and possibly higher. This paper presents the final results of the
Euclid
Cluster Finder Challenge (CFC), fourth in a series of similar challenges. The objective of these challenges was to select the cluster detection algorithms that best meet the requirements of the
Euclid
mission. The final CFC included six independent detection algorithms, based on different techniques, such as photometric redshift tomography, optimal filtering, hierarchical approach, wavelet and friend-of-friends algorithms. These algorithms were blindly applied to a mock galaxy catalog with representative
Euclid
-like properties. The relative performance of the algorithms was assessed by matching the resulting detections to known clusters in the simulations down to masses of
M
200
∼ 10
13.25
M
⊙
. Several matching procedures were tested, thus making it possible to estimate the associated systematic effects on completeness to < 3%. All the tested algorithms are very competitive in terms of performance, with three of them reaching > 80% completeness for a mean purity of 80% down to masses of 10
14
M
⊙
and up to redshift
z
= 2. Based on these results, two algorithms were selected to be implemented in the
Euclid
pipeline, the Adaptive Matched Identifier of Clustered Objects (AMICO) code, based on matched filtering, and the PZWav code, based on an adaptive wavelet approach.
Context. After fundamental ground-based, balloon-born, and space experiments, and, in particular, after the COBE/FIRAS results, confirming that only very small deviations from a Planckian shape can ...be present in the CMB spectrum, current and future CMB absolute temperature experiments aim at discovering very small distortions such as those associated with the cosmological reionization process or that could be generated by different kinds of earlier processes. Aims. Interpretation of future data calls for a continuous improvement in the theoretical modeling of CMB spectrum. In this work we describe the fundamental approach and, in particular, the update to recent NAG versions of a numerical code, KYPRIX, specifically written to solve the Kompaneets equation in a cosmological context. It was first implemented in the years 1989-1991 to accurately compute the CMB spectral distortions under general assumptions. Methods. Specifically, we describe the structure and the main subdivisions of the code and discuss the most relevant aspects of its technical implementation. After a presentation of the equation formalism and of the boundary conditions added to the set of ordinary differential equations derived from the original parabolic partial differential equation, we provide details on the adopted space variable (i.e. dimensionless frequency) and space discretization, on time variables, on the output results, on the accuracy parameters, and on the used auxiliary integration routines. The problem with introducing the time dependence of the ratio between electron and photon temperatures and of the radiative Compton scattering term, both of them introducing integral terms into the Kompaneets equation, is addressed in the specific context of the recent NAG versions. We describe the introduction of the cosmological constant in the terms controlling the general expansion of the Universe in agreement with the current concordance model, of the relevant chemical abundances, and on the ionization history, from recombination to cosmological reionization. The global computational time, the impact of the various aspects of the code on it, and the accuracy of the numerical integration are also discussed. Results. We present some of fundamental tests we carried out to verify the accuracy, reliability, and performance of the code. We focus on some quantitative tests of energy conservation and the time behavior of electron temperature. A comparison of the results obtained with the update and the original version of the code is presented for some representative cases. Finally, we focus on some properties of the free-free distortions relevant for the long wavelength region of the CMB spectrum. Conclusions. All the tests demonstrate the reliability and versatility of the new code version and its accuracy and applicability to the scientific analysis of current CMB spectrum data and of much more precise measurements that will be available in the future. The recipes and tests described in this work can also be useful for implementing accurate numerical codes for other scientific purposes using the same or similar numerical libraries or for verifying the validity of different codes aimed at the same problem or similar ones.
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