Podcasts about cosmic microwave background cmb

Study on the filters of atmospheric contamination in ground based CMB observation by Yi-Wen Wu et al. on Tuesday 18 October The atmosphere is one of the most important contamination sources in the ground-based Cosmic Microwave Background (CMB) observations. In this paper, we study three kinds of filters, which are polynomial filter, high-pass filter, and Wiener filter, to investigate their ability for removing atmospheric noise, as well as their impact on the data analysis process through the end-to-end simulations of CMB experiment. We track their performance by analyzing the response of different components of the data, including both signals and noise. In the time domain, the calculation shows that the high-pass filter has the smallest root mean square error and can achieve high filtering efficiency, followed by the Wiener filter and polynomial filter. We then perform map-making with the filtered time ordered data (TOD) to trace the effects from filters on the map domain, and the results show that the polynomial filter gives high noise residual at low frequency, which gives rise to serious leakage to small scales in map domain during the map-making process, while the high-pass filter and Wiener filter do not have such significant leakage. Then we estimate the angular power spectra of residual noise, as well as those of the input signal for comparing the filter effects in the power spectra domain. Finally, we estimate the standard deviation of the filter corrected power spectra to compare the effects from different filters, and the results show that, at low noise level, the three filters give almost comparable standard deviations on the medium and small scales, but at high noise level, the standard deviation of the polynomial filter is significantly larger. These studies can be used for the reduction of atmospheric noise in future ground-based CMB data processing. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2210.09711v1

Tracer-Field Cross-Correlations with k -Nearest Neighbor Distributions by Arka Banerjee et al. on Tuesday 11 October In astronomy and cosmology, significant effort is devoted to characterizing and understanding spatial cross-correlations between points - e.g. galaxy positions, high energy neutrino arrival directions, X-ray and AGN sources, and continuous field - e.g. weak lensing and Cosmic Microwave Background (CMB) maps. Recently, we introduced the $k$-nearest neighbor formalism to better characterize the clustering of discrete (point) datasets. Here we extend it to the point-field cross-correlation analysis. It combines $k$NN measurements of the point data set with measurements of the field smoothed on many scales. The resulting statistics are sensitive to all orders in the joint clustering of the points and the field. We demonstrate that this approach, unlike the 2-pt cross-correlation, can measure the statistical dependence of two datasets even when there are no linear (Gaussian) correlations. We further demonstrate that this framework is far more effective than the two-point function in detecting cross-correlations when the continuous field is contaminated by high levels of noise. For a particularly high level of noise, the cross-correlations between halos and the underlying matter field in a cosmological simulation, between $10h^{-1}{rm Mpc}$ and $30h^{-1}{rm Mpc}$, is detected at $>5sigma$ significance using the technique presented here, when the two-point cross-correlation significance is $sim 1sigma$. Finally, we show that the $k$NN cross-correlations of halos and the matter field can be well-modeled on quasilinear scales by the Hybrid Effective Field Theory (HEFT) framework, with the same set of bias parameters as are used for the two-point cross-correlations. The substantial improvement in the statistical power of detecting cross-correlations with this method makes it a promising tool for various cosmological applications. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2210.05140v1

Detection and estimation of the cosmic dipole with the Einstein Telescope and Cosmic Explorer by S. Mastrogiovanni et al. on Monday 26 September One of the open issues of the standard cosmological model is the value of the cosmic dipole measured from the Cosmic Microwave Background (CMB), as well as from the number count of quasars and radio sources. These measurements are currently in tension, with the number count dipole being 2-5 times larger than expected from CMB measurements. This discrepancy has been pointed out as a possible indication that the cosmological principle is not valid. In this paper, we explore the possibility of detecting and estimating the cosmic dipole with gravitational waves (GWs) from compact binary mergers detected by the future next-generation detectors Einstein Telescope and Cosmic Explorer. We model the expected signal and show that for binary black holes, the dipole amplitude in the number count of detections is independent of the characteristics of the population and provides a systematic-free tool to estimate the observer velocity. We introduce techniques to detect the cosmic dipole from number counting of GW detections and estimate its significance. We show that a GW dipole consistent with the amplitude of the dipole in radio galaxies would be detectable with $>3sigma$ significance with a few years of observation ($10^6$ GW detections) and estimated with a $16%$ precision, while a GW dipole consistent with the CMB one would require at least $10^7$ GW events for a confident detection. We also demonstrate that a total number $N_{rm tot}$ of GW detections would be able to detect a dipole with amplitude $v_o/c simeq1/sqrt{N_{rm tot}}$. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2209.11658v1

Detection and estimation of the cosmic dipole with the Einstein Telescope and Cosmic Explorer by S. Mastrogiovanni et al. on Monday 26 September One of the open issues of the standard cosmological model is the value of the cosmic dipole measured from the Cosmic Microwave Background (CMB), as well as from the number count of quasars and radio sources. These measurements are currently in tension, with the number count dipole being 2-5 times larger than expected from CMB measurements. This discrepancy has been pointed out as a possible indication that the cosmological principle is not valid. In this paper, we explore the possibility of detecting and estimating the cosmic dipole with gravitational waves (GWs) from compact binary mergers detected by the future next-generation detectors Einstein Telescope and Cosmic Explorer. We model the expected signal and show that for binary black holes, the dipole amplitude in the number count of detections is independent of the characteristics of the population and provides a systematic-free tool to estimate the observer velocity. We introduce techniques to detect the cosmic dipole from number counting of GW detections and estimate its significance. We show that a GW dipole consistent with the amplitude of the dipole in radio galaxies would be detectable with $>3sigma$ significance with a few years of observation ($10^6$ GW detections) and estimated with a $16%$ precision, while a GW dipole consistent with the CMB one would require at least $10^7$ GW events for a confident detection. We also demonstrate that a total number $N_{rm tot}$ of GW detections would be able to detect a dipole with amplitude $v_o/c simeq1/sqrt{N_{rm tot}}$. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2209.11658v1

Scalar induced gravitational waves from primordial black hole Poisson fluctuations in f R gravity by Theodoros Papanikolaou et al. on Monday 19 September The gravitational potential of a gas of initially randomly distributed primordial black holes (PBH) can induce a stochastic gravitational-wave (GW) background through second-order gravitational effects. This GW background can be abundantly generated in a cosmic era dominated by ultralight primordial black holes, with masses $m_mathrm{PBH}

Wide Field High Cadence CMB Survey Designs for Chilean Telescopes by Haruki Ebina et al. on Wednesday 14 September We present new wide field survey strategies for Chilean Large Aperture Telescopes (LAT) measuring the Cosmic Microwave Background (CMB), which we call Sinusoidal Modulated High Cadence Survey Strategies. The strategies were developed during the process of optimizing LAT measurements for the CMB-S4, Simons Observatory, and CCAT-prime collaborations. Observing more than $f_{sky} sim 0.5$, the telescope consistently achieves high observation efficiency, even with Sun-avoidance enabled. Classical azimuthal scan survey strategies observing fields of equal size suffer from problems of observation depth non-uniformity relative to declination and lack of crosslinking. The new survey strategies described here significantly improve both uniformity and crosslinking while also enabling higher cadence observations for time-domain astrophysics. Uniformity and crosslinking are improved by modulation of azimuthal angular velocity and sinusoidal elevation nods, respectively. In particular, there is nearly uniform observation depth and crosslinking is improved from total lack of crosslinking near -40 degree declination to clearing the strictest thresholds for crosslinking across the entire field. The simulated strategies are compared to the strategies used for the Atacama Cosmology Telescope and previously studied Simons Observatory survey strategies. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2208.10070v2

CMB lensing from Planck PR4 maps by Julien Carron et al. on Monday 12 September We reconstruct the Cosmic Microwave Background (CMB) lensing potential on the latest Planck CMB PR4 (NPIPE) maps, which include slightly more data than the 2018 PR3 release, and implement quadratic estimators using more optimal filtering. We increase the reconstruction signal to noise by almost $20%$, constraining the amplitude of the CMB-marginalized lensing power spectrum in units of the Planck 2018 best-fit to $1.004 pm 0.024$ ($68%$ limits), which is the tightest constraint on the CMB lensing power spectrum to date. For a base $Lambda$CDM cosmology we find $sigma_8 Omega_m^{0.25} = 0.599pm 0.016$ from CMB lensing alone in combination with weak priors and element abundance observations. Combination with baryon acoustic oscillation data gives tight $68%$ constraints on individual $Lambda$CDM parameters $sigma_8 = 0.814pm 0.016$, $H_0 = 68.1^{+1.0}_{-1.1}$km s$^{-1}$ Mpc$^{-1}$, $Omega_m = 0.313^{+0.014}_{-0.016}$. Planck polarized maps alone now constrain the lensing power to $7%$. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2206.07773v2

A grounded perspective on New Early Dark Energy using ACT, SPT, and BICEP Keck by Juan S. Cruz et al. on Wednesday 07 September We examine further the ability of the New Early Dark Energy model (NEDE) to resolve the current tension between the Cosmic Microwave Background (CMB) and local measurements of $H_0$ and the consequences for inflation. We perform new Bayesian analyses, including the current datasets from the ground-based CMB telescopes Atacama Cosmology Telescope (ACT), the South Pole Telescope (SPT), and the BICEP/Keck telescopes, employing an updated likelihood for the local measurements coming from the S$H_0$ES collaboration. Using the S$H_0$ES prior on $H_0$, the combined analysis with Baryonic Acoustic Oscillations (BAO), Pantheon, Planck and ACT improves the best-fit by $Deltachi^2 = -15.9$ with respect to $Lambda$CDM, favors a non-zero fractional contribution of NEDE, $f_{rm NEDE} > 0$, by $4.8sigma$, and gives a best-fit value for the Hubble constant of $H_0 = 72.09$ km/s/Mpc (mean $71.48_{-0.81}^{+0.79}$ with $68%$ C.L.). A similar analysis using SPT instead of ACT yields consistent results with a $Delta chi^2 = - 23.1$ over $Lambda$CDM, a preference for non-zero $f_{rm NEDE}$ of $4.7sigma$ and a best-fit value of $H_0=71.77$ km/s/Mpc (mean $71.43_{-0.84}^{+0.84}$ with $68%$ C.L.). We also provide the constraints on the inflation parameters $r$ and $n_s$ coming from NEDE, including the BICEP/Keck 2018 data, and show that the allowed upper value on the tensor-scalar ratio is consistent with the $Lambda$CDM bound, but, as also originally found, with a more blue scalar spectrum implying that the simplest curvaton model is now favored over the Starobinsky inflation model. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2209.02708v1

For thousands of years, humans have been trying to figure out the universe and determine its true extent. And there have been a lot of assumptions and theories. during the 1960s, astronomers became aware of microwave background radiation that was detectable in all directions. Known as the Cosmic Microwave Background (CMB), the existence of this radiation has helped to hone our understanding of how the Universe began. The cosmic microwave background (CMB, CMBR) is faint electromagnetic radiation that is a remnant from an early stage of the universe, filling all space. It represents the heat leftover from the Big Bang and radiation is most visible in the microwave part of the electromagnetic spectrum hence the name CMB.

The Big Bang Afterglow is known as the Cosmic Microwave Background (CMB). Discover how combining CMB data with galactic observations is unlocking the secret of galaxy formation. This episode is also available as a blog post: http://daretoknow.ca/2021/03/19/big-bang-afterglow-showing-how-galaxies-form/ --- Send in a voice message: https://anchor.fm/david-morton-rintoul/message

A brief description of the Cosmic Microwave Background (CMB) also known as the Primordial Background Radiation.

Through a Lens. In the show this time, we talk to Hugo Messias about Gravitational lensing [34:50 - 1:01:41], Bob Watson tells us about Three decades of Cosmic Microwave Background(CMB) in this month's JodBite. [00:52 - 34:43], and your astronomy questions are answered by George Bendo in Ask an Astronomer [1:23:02 - 1:32:27].

Through a Lens. In the show this time, we talk to Hugo Messias about Gravitational lensing [34:50 - 1:01:41], Bob Watson tells us about Three decades of Cosmic Microwave Background(CMB) in this month's JodBite. [00:52 - 34:43], and your astronomy questions are answered by George Bendo in Ask an Astronomer [1:23:02 - 1:32:27].

Galaxy clusters, the massive systems host hundreds of galaxies, are invaluable cosmological probes and astrophysical laboratories. Besides these fascinating galaxies, the concentration of dark matter creates a deep gravitational potential well, where even light passing by is bended and the background image is distorted. The baryonic gas falling into the potential well is heated up to more than 10^7 K that free electrons start to emitting in X-ray. Observing those phenomena leads to a throughout understanding of gravity, particle physics and hydrodynamics. In addition, residing on the top of the density perturbations, clusters are sensitive to the initial condition of the Universe, such that they are complimentary tools for cosmology studies. In this thesis we first introduce the basic framework of the Universe and supporting observational evidence. Following that, we sketch the principle to use clusters for cosmology study via their redshift and mass distribution. However cluster mass is not a direct observable, so we need to estimate it by other channels. We briefly exhibit cluster observations in optical, X-ray and microwave bands and discuss the challenges in estimating the underlying cluster mass with them. After this introduction, we present our results on three aspects of the cluster cosmology study. First, we present a study of Planck Sunyaev-Zel’dovich effect (SZE) selected galaxy cluster candidates using Panoramic Survey Telescope & Rapid Response System (Pan-STARRS) imaging data. To fulfil the strength of SZE survey, the redshifts of clusters are required. In this work we examine 237 Planck cluster candidates that have no redshift in the Planck source catalogue. Among them, we confirmed 60 galaxy clusters and measure their redshifts. For the remaining sample, 83 candidates are so heavily contaminated by stars due to their location near the Galactic plane that we do not identify galaxy members and assign reliable redshifts. For the rest 94 candidates we find no optical counterparts. By examining with 150 Planck confirmed clusters with spectroscopy redshifts, our redshift estimations have an accuracy of σ_{z/(1+z)}~0.022. Scaling for the already published Planck sample, we expect the majority of the unconfirmed candidates to be noise fluctuations, except a few at high redshift that the Pan-STARRS1 (PS1) data are not sufficiently deep for confirmation. Thus we use the depth of the optical imaging for each candidate together with a model of the expected galaxy population for a massive cluster to estimate a redshift lower limit, beyond which we would not have expected to detect the optical counterpart. Second, we use 95GHz, 150GHz, and 220GHz observations from South Pole Telescope (SPT) to study the SZE signatures of a sample of 46 X-ray selected groups and clusters drawn from ~6 deg^2 of the XMM-Newton Blanco Cosmology Survey (XMM-BCS). The wide redshift range and low masses make this analysis complementary to previous studies. We develop an analysis tool that using X-ray luminosity as a mass proxy to extract selection-bias corrected constraints on the SZE significance- and Y_{SZ}-mass relations. The SZE significance- mass relation is in good agreement with an extrapolation of the relation obtained from high mass clusters. However, the fit to the Y_{SZ}-mass relation at low masses, while in agreement with the extrapolation from high mass SPT sample, is in tension at 2.8σ with the constraints from the Planck sample. We examine the tension with the Planck relation, discussing sample differences and biases that could contribute. We also analyse the radio galaxy point source population in this ensemble of X-ray selected systems. We find 18 of our systems have 1 GHz Sydney University Molonglo Sky Survey (SUMSS) sources within 2 arcmin of the X-ray centre, and three of these are also detected at significance >4 by SPT. Among these three, two are associated with the brightest cluster galaxies, and the third is a likely unassociated quasar candidate. We examined the impact of these point sources on our SZE scaling relation result and find no evidence of biases. We also examined the impact of dusty galaxies. By stacking the 220 GHz data, we found 2.8σ significant evidence of flux excess, which would correspond to an average underestimate of the SZE signal that is (17±9) % in this sample of low mass systems. Finally we predict a factor of four to five improvements on these SZE mass-observable relation constraints based on future data from SPTpol and XMM-XXL. In the end we present a study using clusters as tools to probe deviations from adiabatic evolution of the Cosmic Microwave Background (CMB) temperature. The expected adiabatic evolution is a key prediction of standard cosmology. We measure the deviation of the form T(z)=T_0(1+z)^{1-α} using measurements of the spectrum of the SZE with SPT. We present a method using the ratio of the SZE signal measured at 95 and 150 GHz in the SPT data to constrain the temperature of the CMB. We validate that this approach provides unbiased results using mock observations of cluster from a new set of hydrodynamical simulations. Applying this method to a sample of 158 SPT-selected clusters, we measure α=0.017^{+0.030}_{−0.028} consistent with the standard model prediction of α=0. Combining with other published results, we find α=0.005±0.012, an improvement of ~ 10% over published constraints. This measurement also provides a strong constraint on the effective equation of state, w_{eff}=−0.994±0.010, which is presented in models of decaying dark energy.

The tremendous impact of Cosmic Microwave Background (CMB) radiation experiments on our understanding of the history and evolution of the universe is based on a tight connection between the observed fluctuations and the physical processes taking place in the very early universe. According to the prevalent paradigm, the anisotropies were generated during the era of inflation. The simplest inflationary models predict almost perfectly Gaussian primordial perturbations, but competitive theories can naturally be constructed, allowing for a wide range in primordial non-Gaussianity. For this reason, the test for non-Gaussianity becomes a fundamental means to probe the physical processes of inflation. The aim of the project is to develop a Bayesian formalism to infer the level of non-Gaussianity of local type. Bayesian statistics attaches great importance to a consistent formulation of the problem and properly calculates the error bounds of the measurements on the basis of the actual data. As a first step, we develop an exact algorithm to generate simulated temperature and polarization CMB maps containing arbitrary levels of local non-Gaussianity. We derive an optimization scheme that allows us to predict and actively control the simulation accuracy. Implementing this strategy, the code outperforms existing algorithms in computational efficiency by an order of magnitude. Then, we develop the formalism to extend the Bayesian approach to the calculation of the amplitude of non-Gaussianity. We implement an exact Hamiltonian Monte Carlo sampling algorithm to generate samples from the target probability distribution. These samples allow to construct the full posterior distribution of the level of non-Gaussianity given the data. The applicability of the scheme is demonstrated by means of a simplified data model. Finally, we fully implement the necessary equations considering a realistic CMB experiment dealing with partial sky coverage and anisotropic noise. A direct comparison between the traditional frequentist estimator and the exact Bayesian approach shows the advantage of the newly developed method. For a significant detection of non-Gaussianity, the former suffers from excess variance whereas the Bayesian scheme always provides optimal error bounds.

Measurements of the Cosmic Microwave Background (CMB) emission with increasingly high resolution and sensitivity are now becoming available, and even higher quality data are expected from the ongoing Planck mission and future experiments. Dealing with the Galactic foreground contamination, however, is still problematic, due to our poor knowledge of the physics of the Interstellar Medium at microwave frequencies. This contamination biases the CMB observations and needs to be removed before using the data for cosmological studies. In this thesis the problem of component separation for the CMB is considered and a highly focused study of a specific implementation of Independent Component Analysis (ICA), called FastICA, is presented. This algorithm has been used to perform a foreground analysis of the WMAP three and five-year data and subsequently to investigate the properties of the main sources of diffuse Galactic emission (e.g. synchrotron, dust and free-free emission). The foreground contamination in the WMAP data is quantified in terms of coupling coefficients between the data and various templates, which are observations of the sky emission at frequencies where only one physical component is likely to dominate. The coefficients have been used to extract the frequency spectra of the Galactic components, with particular attention paid to the free-free frequency spectrum. Our results favour the existence of a spectral ‘bump’, interpreted as a signature of emission by spinning dust grains in the Warm Ionised Medium, which spatially correlates with the Hα radiation used to trace the free-free emission. The same coupling coefficients have been used to clean the WMAP observations, which have then been further analysed using FastICA. This iterative step in the analysis provides a powerful tool for cleaning the CMB data of any residuals not traced by the adopted templates. In practice, it is a unique way to potentially reveal new physical emission components. In this way, we detected a residual spatially concentrated emission component around the Galactic center, consistent with the so-called WMAP Haze. In order to take into account the actual spatial properties of the Galactic foreground emission, we proposed an analysis of theWMAP data on patches of the sky, both using FastICA and the Internal Linear Combination (ILC). Since the temperature power spectrum is reasonably insensitive to the fine details of the foreground corrections except on the largest scales (low l), the two methods are compared by means of non-Gaussianity tests, used to trace the presence of possible residuals. While the performance of FastICA improves only for particular cases with a small number of regions, the ILC CMB estimation generally ameliorates significantly if the number of patches is increased. Moreover, FastICA plays a key role in establishing a partitioning that realistically traces the features of the sky, a requirement we have shown to be paramount for a successful regional analysis.

Recent measurements of the Cosmic Microwave Background (CMB) have allowed the most accurate determinations yet of the parameters of the standard CDM model, but the data also contain intriguing anomalies that are inconsistent with the assumptions of statistical isotropy and Gaussianity. This work investigates possible sources of such anomalies by studying the morphology of the CMB. An unexpected correlation is found between the CMB anisotropies and a temperature pattern generated in a Bianchi Type VIIh universe, i.e., an anisotropic universe allowing a universal rotation or vorticity. This model is found to be incompatible with other observations of the cosmological parameters, but correcting for such a component can serendipitously remove many of the anomalies from the WMAP sky. This result indicates that an alternative cosmological model producing such a morphology may be needed. A similar cross-correlation method applied to the microwave foregrounds studies the variation of the spectral behaviours of the Galactic emission processes across the sky. The results shed light on the unexpectedly low free-free emission amplitude as well as the nature of the anomalous dust-correlated emission that dominates at low frequencies. As a complementary method, phase statistics apply to situations where no a priori knowledge of the spatial structure informs the search for a non-Gaussian signal. Such statistics are applied to compact topological models as well as to foreground residuals, and a preliminary analysis shows that these may prove powerful tools in the study of non-Gaussianity and anisotropy.

During the last ten to fifteen years cosmology has turned from a data-starved to a data-driven science. Several key parameters of the Universe have now been measured with an accuracy better than 10%. Surprisingly, it has been found that instead of slowing down, the expansion of the Universe proceeds at an ever increasing rate. From this we infer the existence of a negative pressure component -- the so-called Dark Energy (DE) -- that makes up more than two thirds of the total matter-energy content of our Universe. It is generally agreed amongst cosmologists and high energy physicists that understanding the nature of the DE poses one of the biggest challenges for the modern theoretical physics. Future cosmological datasets, being superior in both quantity and quality to currently existing data, hold the promise for unveiling many of the properties of the mysterious DE component. With ever larger datasets, as the statistical errors decrease, one needs to have a very good control over the possible systematic uncertainties. To make progress, one has to concentrate the observational effort towards the phenomena that are theoretically best understood and also least ``contaminated'' by complex astrophysical processes or several intervening foregrounds. Currently by far the cleanest cosmological information has been obtained through measurements of the angular temperature fluctuations of the Cosmic Microwave Background (CMB). The typical angular size of the CMB temperature fluctuations is determined by the distance the sound waves in the tightly coupled baryon-photon fluid can have traveled since the Big Bang until the epoch of recombination. A similar scale is also expected to be imprinted in the large-scale matter distribution as traced by, for instance, galaxies or galaxy clusters. Measurements of the peaks in the CMB angular power spectrum fix the physical scale of the sound horizon with a high precision. By identifying the corresponding features in the low redshift matter power spectrum one is able to put constraints on several cosmological parameters. In this thesis we have investigated the prospects for the future wide-field SZ cluster surveys to detect the acoustic scale in the matter power spectrum, specifically concentrating on the possibilities for constraining the properties of the DE. The core part of the thesis is concerned with a power spectrum analysis of the SDSS Luminous Red Galaxy (LRG) sample. We have been able to detect acoustic features in the redshift-space power spectrum of LRGs down to scales of ~ 0.2 hMpc^{-1}, which approximately corresponds to the seventh peak in the CMB angular spectrum. Using this power spectrum measurement along with the measured size of the sound horizon, we have carried out the maximum likelihood cosmological parameter estimation using Markov chain Monte Carlo techniques. The precise measurement of the low redshift sound horizon in combination with the CMB data has enabled us to measure, under some simplifying assumptions, the Hubble constant with a high precision: H_0 = 70.8 {+1.9} {-1.8} km/s/Mpc. Also we have shown that a decelerating expansion of the Universe is ruled out at more than 5-sigma confidence level.

The main purpose of the work presented in this thesis is to investigate the phenomenon of resonant scattering of the Cosmic Microwave Background (CMB) photons by atoms and molecules. The fine-structure transitions of the various atoms and ions of Carbon, Nitrogen, Oxygen and other common metals have wavelengths in the far-infrared regions, which are particularly suitable for scattering the CMB photons at high redshifts ($2 lesssim z lesssim 30$). Since the CMB photons are released at redshifts $zsimeq 1100$, they must interact with all the intervening matter before reaching us at $z=0$. Therefore scattering of these photons in the far-IR fine-structure lines of various atoms and ions provide a plausible way to couple the radiation with the matter at those redshifts and to study the enrichment and ionization history of the universe. Moreover, rotational transitions of diatomic molecules like the CO have wavelengths extending into the sub-millimeter wavebands, and hence they can scatter the CMB photons at very low redshifts. Studying the very low density gas of nearby galaxies in CO lines can yield a definitive signature of resonant scattering of the CMB photons through a decrement in the background intensity of the microwave sky. Observation of this scattering signal from any object in the sky will tell us about its radial velocity in the CMB rest frame. In this work we first derive the detailed formalism for the scattering effect in presence of the peculiar motion of the scatterer. Then we investigate the possibility to detect individual objects at different redshifts through scattering and try to find applications for this effect. Our main example is the possibility to find the peculiar motions of nearby galaxies in the CMB rest frame through observation of the scattering signal, which we explore in detail. Next we discuss the density limits in which scattering effect can dominate over the line emission in individual objects. We describe three types of critical densities, and show that detection of single objects through scattering requires very low density, whereas observation of the integrated scattering signal coming from many unresolved objects in the sky will permit us to probe higher densities. We discuss this effect subsequently, as we compute the change in the angular fluctuations of the CMB sky temperature through resonant scattering. We found that the scattering signal gets strong enhancement due to a non-zero correlation existing between the density perturbations at the last scattering surface, where CMB anisotropies are generated, and at the epoch of scattering. This opens up a new way to study the ionization and enrichment history of the universe, and we investigate various enrichment scenarios and the temperature fluctuations that might be caused by them. The resulting signal is already within the sensitivity limits of some upcoming space- and ground-based CMB experiments, and we show upto what extent they shall be able to put constraints on different enrichment histories. Finally we analyze the effect of line and dust emission in the same frequency range that we used for the detection of scattering signal. These emissions are coming from very high density objects where active star formation is taking place, and due to the compactness of their size as well as absence of any velocity dependence the emission signal is significantly suppressed at large angular scales, where scattering will be dominant. We present some detailed analytic expressions for the scattering signal and also a method to solve for the detailed statistical balance equations in a multi-level system in the appendix.

The Cosmic Microwave Background (CMB) is a vast curtain of energy left over from the Big Bang. It is the oldest, most distant feature of the observable Universe. Since the discovery of the CMB in the mid-1960s, cosmology—the study of the origin and evolution of the Universe—has experienced an explosion of activity. The field has changed from a purely theoretical enterprise to the empirical study of what populates the physical Universe. "Cosmologists are right at the cusp," says the University of Chicago's Michael Turner. "We have these fantastic ideas about the Universe, and we now have the technology and the instruments to test them." This feature travels to the U.S. Amundsen-Scott South Pole Station in Antarctica, where an instrument called DASI measures the CMB, and to the University of Chicago, where DASI’s results are analyzed.