program. Bicep3 began observing at the South Pole in 2015. Spider, which is a balloon-borne telescope, had its first flight in January 2015. Detailed discussion of Bicep3 and Spider is beyond the scope of this thesis.
The design of Bicep2/KeckArray, which are derivative of the Bicep1 instrument , is contrary to the usual design of most science quality telescopes in operation today, which boast very large mirrors and very fine angular resolution. Instead, the Bicep2/KeckArray strategy is to use small-aperture refractors for a deliberately coarse angular resolution, with beams as wide as ∼ 0.5° FWHM at 150 GHz and ∼ 0.8° FWHM at 95 GHz. Since an IGW B-mode signal would be expected to peak at degree angular scales, the required resolution need not be much finer than that. As a refractor, the optical chain can remain cylindrically symmetric, reducing any polarized systematic effects that could arise if there were an asymmetry. By keeping the telescope small, it is much easier to rotate the telescope around its boresight. The deck rotation modulates the antenna axis between Stokes Q and U and helps remove the effect of instrument polarization from the receivers.
The VLA data were edited and calibrated with standard AIPS tools. Data edits substantially reduced the body of monitoring data; these edits can be grouped based on the reach of the underlying problem—some problems affected the entire the array, while others affected individual antennas or baselines. External factors, particularly bad weather, compelled the rejection of all data for five of the thirteen runs: high winds at the site rendered four runs useless, and a control system crash during the run eliminated another. The wind-based edits resulted in a substan- tial loss of data, and these edits are discussed in detail in Section 4.3.2. Most antenna-based edits arose from pointing calibration failures, which are noted in the referenced pointing solutions; and from gain instabilities, which were apparent in the uncalibrated visibilities. Failure to reject the antennas with no pointing solutions for 3C286 on 05apr00, for example, biases the K band 3C279 flux up- ward by 10%. Finally, bad correlations in one of RR, RL, LR & LL for either IF prompted the rejection of all visibilities for that integration. Together these edits reduced the data from the subset of good antennas in the eight remaining runs by 30% at K band and 15% at Q band.
ter output versus FRM bias current, displays the same hysteresis as illustrated in Figure 2.6 when the telescope observes a polarized source.
Although the FRMs are successful polarization modulation devices with suffi- ciently low instrumental polarization, the death sentence for FRMs in B ICEP came in a noise performance showdown between FRM-demodulated and PSB-differenced data. Stability data taken shortly before deploying the instrument indicated that the FRMs introduced excess white noise, and the power spectral densities of the FRM-demodulated bolometer timestreams were significantly higher than those from differenced PSBs. As a result, all but six FRMs were removed from the B ICEP focal plane for the 2006 observing season, and the remaining six were removed during the 2006–2007 Austral summer. The simple, yet effective, PSB differenc- ing strategy has worked extremely well for B ICEP . Upcoming CMB polarization experiments seeking to probe lower tensor-to-scalar limits may benefit from polar- ization modulation, as systematics become dominant limiting factors. B ICEP 2 and S PIDER , which are both small-aperture experiments, plan to use a rotating wave- plate at the aperture so that only polarized emission from the sky is modulated.
Bicep3 follows the Bicep2/KeckArray strategy of compact, on-axis, two-refractor optical design to target the degree-scale primordial B-mode CMB polarization. It has an aperture of 520 mm and beam width given by the Gaussian radius σ ∼ 8.9 0 . Both of the lenses, and most of the filters, are held at cryogenic temperatures inside of the cryostat receiver in order to minimize excess in-band photon load. Only the HDPE plastic cryostat window and the stack of IR filters directly behind it are mounted at room-temperature. Together with faster optics design, and doubling the aperture diameter, Bicep3 achieves ∼10× higher optical throughput and detector count compared to a single KeckArray receiver at the same frequency. Table 3.1 shows the optical design parameters as compared to the previous generation Bi- cep2/KeckArray receivers.
High accuracy CMB spectrum space experiments, such DIMES 9 (0.5 ∼ λ ∼ <
15 cm) and FIRAS II 10 (λ ∼ 1 cm), were proposed to constrain energy exchanges <
up to 100 times better than FIRAS. Dissipation processes at early times (z ∼ 10 > 5 ), like the ones DIMES is able to probe, result in Bose-Einstein (BE)-like distortions, 11 while late epochs mechanisms (z ∼ 10 < 4 ) before or after the recombination era gen- erate Comptonization and FF distortions. 12 New space missions were proposed to investigate the cosmic origin and its evolution by observing CMB temperature and polarization anisotropies with ∼ degree resolution, as in PIXIE 13 and LiteBird, c or
3.3.1 Array Module
The silicon wafers that compose each detector array, along with its feedhorns and first stage readout electronics, are contained within a single compact array module made of OFHC copper. These modules, which are cooled to ∼ 100 mK by the receiver’s cryogenic systems, not only help shield the detectors from stray energetic photons and unwanted thermal radiation, but also provide critical mechanical support for the instrument’s most sensitive components. A thick copper ring forms the base of each module assembly and serves as its primary mounting surface. The array’s silicon feedhorn stack is suspended on the interior of this ring using six beryllium-copper 20 L brackets that have been custom-designed to absorb the stress resulting from differential thermal contraction of the joined materials. A short extension tube, which is capped off by the final filter in the array’s LPE filter stack, is mounted to the skyward side of the copper ring to form a partially closed optical cavity around the feedhorn entrance apertures.
Figure 1. E-mode and B-mode polarization power spectra. The diamonds, triangles, stars, and squares show the WMAP seven-year data (Larson et al.
2011), the QUaD final data (Brown et al. 2009), the BICEP two-year data (Chiang et al. 2010), and the QUIET 43 GHz data (QUIET Collaboration 2010), respectively. The upper solid line shows the scalar E-mode power spectrum of the WMAP seven-year best-fit model. The dashed lines show the primordial B-mode power spectra with the tensor-to-scalar ratio of r = 0.24, which corresponds to the current 95% upper limit (Komatsu et al. 2011) as well as of r = 0.03 and 0.003. These lines are linearly proportional to r. The dotted line shows the secondary B-mode power spectrum expected to be generated by the weak gravitational lensing effect converting E modes to B modes (Zaldarriaga &
missions focusing on this challenging measurement, from the ground, from stratospheric balloons, and from space (see e.g. ).
During their long travel, crossing half of the observable cosmos, CMB photons interact with the large scale structure of the universe. These secondary interactions provide additional precision ob- servables of the CMB. Gravitational lensing of CMB photons provide a way to study the development of dark matter structures in the earliest phases of the structure formation process, exploiting the re- sulting distortion of the CMB anisotropy map (see e.g. ). This same e ff ect produces B-modes of the CMB polarization field at small angular scales (see e.g.  and references therein). In addition, ionized structures in the universe (clusters of galaxies, filaments) produce inverse Compton scattering in CMB photons (the Sunyaev-Zeldovich effect, [19, 20]), which can be isolated exploiting its well defined and characteristic spectral distortion.
scalar ratio, denoted as r remains at the forefront of CMB polarization studies, and requires the measurement of the BB power spectrum, which, as yet, has been undetected, though measurements of the TT, TE, and EE power spectra have been made and results for the ACTPol instrument will be presented later in this work, along with a description of the implications of inflationary cosmology and some of the next-generation instruments that seek to confirm this model through the measurement of B-modes. If confirmed, inflationary cosmology would extend our understanding of ΛCDM cosmology and would help to explain the measured spatial curvature of the Universe as well as to explain how quantum mechani- cal density fluctuations in the primordial Universe could be stretched to large scales during inflation, preserving apparent thermal equilibrium between areas of the CMB that should not be in causal contact, which is often described as the so-called horizon problem (Car- roll and Ostlie 2007). It should also be noted that the CMB temperature and polarization anisotropies described in this section are not the only anisotropic features that experimental cosmology platforms observing the CosmicMicrowaveBackground measure, since what we are describing here are ideal CMB temperature and polarization signals detected without interaction with any structure throughout the expansion history of the Universe, so-called primary anisotropies. There are also secondary anisotropies, associated with small-angular scale measurements of the CMB, that describe eﬀects on temperature and polarization sig- nal following interaction with structures in the Universe, including gravitational lensing of CMB temperature signal, and E-mode polarization that is induced to B-mode polarization from gravitational lensing from large scale structure. In the next section, we will briefly describe another such source of secondary anisotropy, describing the Sunyaev-Zel‘dovich eﬀect resulting from the interaction of CMB radiation with ionized gas in galaxy clusters.
indeed, AdvACTPol, BICEP-Keck, Simons Array and SPT-3G plan to. Here, we model all channels flying at altitude to avoid having to select a particular observatory to optimize against. We assume all experiments considered can scan half the sky and access multi- poles in the range 20 ≤ ≤ 2500 unless otherwise stated. We do not explicitly treat systematic effects, which are highly experiment-
interest: the optical power absorbed by the detector. A thick-grill filter (TGF) is a sheet of metal with a closely spaced array of holes of fixed diameter. The sheet will block wavelengths above the waveguide cutoff determined by the hole diameter. For a TGF cutoff above the band-pass of a perfect filter stack, the thick-grill filter would look exactly like an unbroken metal sheet. The optical signal should vanish when either one is placed in front of the dewar window. Any residual signal is evidence for a leak. The frequency of a leak can be pinned down by using thick-grill filters with different frequency cutoffs. The experimental setup is very similar to the optical time constant measurement with the substitution of a much brighter, chopped thermal source. A digital lockin is used to maximize the signal-to-noise of the measurement at the chop frequency. The measurement is repeated with the window open, blocked by each thick grill filter, and blanked off. The three data points yield the total signal, the out-of-band signal, and a zero point. In the final set of thick grill tests before putting ACBAR on the telescope, we measured total signal voltages of 800 to 1000 mV and out-of-band signal voltages of 0.1-0.5 mV for rejection level in power of
The leading paradigm for the generation of these primordial density perturbations is inflation[1, 2, 3, 4], a period of nearly exponential expansion of the Universe. This expansion not only generates density perturbations, but in addition creates gravitational waves. These gravitational waves persist and become imprinted in the CMB temperature and polarization anisotropies. Unlike density perturbations, the gravitational waves produce a polarization pat- tern with a curl component, commonly referred to as “B-mode” polarization. The amplitude of the signal is proportional to the expansion rate so that the strength of the B-mode signal would provide a measurement of the expansion rate during inflation. In addition, because general relativity relates the expansion rate to the energy density, a detection would allow us to infer one of the most basic properties of inflation, its energy scale.
Another major breakthrough followed with the 2003, 2007 and 2008 data releases from another NASA satellite experiment, WMAP (the data are publicly available on the web site http://lambda.gsfc.nasa.gov/). Such data releases yielded measurement of the correlation structure of the random field up to a resolution of about 0.22 degrees, that is, approximately 30 times better than COBE (7–10 degrees). Another major boost in data analysis is expected from the ESA satellite mission Planck, which is now scheduled to be launched on October 31, 2008; data releases for the public are expected in the following 3–5 years. Planck is planned to provide datasets of nearly 5 × 10 10 observations, and this will allow to settle many open questions with CMB temperature data. New challenging questions are expected to arise at a faster and faster pace over the next decades; for instance, Planck will pro- vide high quality for so-called polarization data, which will set the agenda for the experiments to come. Polarization data can be viewed as tensor-valued, rather than scalar, observations—that is, what we observe are not measure- ments of a scalar quantity such as the temperature, but random quadratic forms. As such, this entails an entirely new field of statistical research, which is still in its infancy and will not be discussed in the present paper.
We find that, for all four of the maps, the preferred axes of the quadrupole all point in the same direction, within our measurement precision. However, the preferred axis of the octopole of the uncorrelated polarization map does not align with the one of the quadrupole. The same holds for the correlated temperature map. In order to assess our result, we ask the following question. We take the axes measured in the temperature map as given, and assume that the axes of the uncorrelated polarization map are distributed isotropically and independently of each other. We then ask how likely it is that at least one of these axes lies such that the axis of the temperature map lies inside its 1σ region. This probability amounts to about 50 per cent for currently available polarization data. This high probability is due to the large uncertainties we have in the axes of the uncorrelated polarization map. The main contribution of this uncertainty comes from the high noise-level in the polarization data rather than from the mask. We can therefore hope that the Planck polarization data (Tauber 2000) will yield much stronger constraints on the axes than the WMAP data.
For those first 300,000 years, the pho- tonsofthebackgroundradiationwere bound up in a broiling plasma. Be- cause of random fluctuations gener- ated by cosmic inflation in the first split second, some regions happened to be denser. Their gravity sucked in material, whereupon the pressure im- partedbythephotonspushedthatma- terial apart again. The ensuing battle between pressure and inertia caused the plasma to oscillate between com- pression and rarefaction—vibrations characteristic of sound waves. As the universe aged, coherent oscillations developed on ever larger scales, filling theheavenswithadeepeningroar.But whentheplasmacooledandcondensed intohydrogengas,thephotonswent their separate ways, and the universe abruptly went silent. The fine detail inthebackgroundradiationisasnap- shot of the sound waves at this in- stant (283:14, parenthetical items inorig.,emp.added).
described in Nolta et al. (2009), at each multipole the conditional likelihoods are computed as a function of C EE , with all other multipoles held ﬁxed, for 2 < < 7. The results are consistent, although this analysis ﬁnds more power at = 4 and 5. Computing the likelihood as a function of τ we ﬁnd τ = 0.090 ± 0.019 for the Gibbs-sampled maps outside the P06 mask, which is consistent with the results obtained through template cleaning, which give τ = 0.086 ± 0.016 for the KaQV data combination. Obtained using a different methodology and accounting for foreground marginalization, this adds conﬁdence in the detection of the CMB E-mode polarization signal. The spatially varying synchrotron index appears not to cause a signiﬁcant difference, as we obtain a similar mean when the