0312-Jaffe Thesis: Foreground Challenge to CMB Polarization: Present Methodologies and New Concepts

Jaffe Thesis: Foreground Challenge to CMB Polarization: Present Methodologies and New Concepts [ CMB ]

ISW effect

the dynamics in the gravitational potential may lead to contribution to CMB temperature anisotropies through the ISW. Such a dynamics happens for example when the equation of state changes in time. Therefore, the ISW effect has contributions both from the early and late time Universe. During recombination, the Universe is almost completely matter dominated;therefore, in Equation 2.21 evolves due to the non-negligible presence of radiation, which gets rapidly diluted (early ISW). Also, at late times, the Universe becomes dark energy dominated, making the gravitational potentials evolving again (late ISW). The two aspects of the ISW appear on the size of the horizon at the relevant time, i.e. a few degrees (early ISW) or the entire sky (late ISW). The effect is now detected with great confidence.

Rees-Sciama Effect

The non-linear regime of ISW, have a very small effect on the temperature of CMB photons and hard to detect.

SZ effect

The tSZ occurs when CMB photons interact with a gas of hot electrons at a temperate TCMB << Tgas which modifies the Planck spectrum. By passing through a hot plasma, the low energy Rayleigh-Jeans regime of the photon spectrum is depleted and the high energy, Wien part is enhanced. An important property of the tSZ effect is that it is independent of the redshift of the galaxy cluster [58]. The kSZ effect arises when the scattering of CMB photons with electrons takes place in a bulk motion of a non-linear perturbation with respect to the CMB. Essentially it is a Doppler term related to electron velocity projected along the line of sight.

Polarized CMB fg

The Galaxy is filled with a large scale Galactic magnetic field, which bends the trajectory of cosmic ray particles, mostly electrons, emitting polarized synchrotron. Also, dust grains heated back by starlight constitutes a quasi-thermal emission, known as thermal dust. They are known to be the ones with largest polarized emission, for obvious reasons for synchrotron, and because the dust grains have a magnetic dipole, which also gets aligned with the local direction of the Galactic magnetic field. In addition, we will also consider the Anomalous Microwave Emission (AME), possibly associated to the spinning dust grains.

synchrotron

By considering the synchrotron spectral index $\beta_s \approx -3$, synchrotron can be polarized up to 70%. The observed value of synchrotron polarization (20%) is lower due to non-uniform magnetic field directions along line of sight.

thermal dust emission

Polarized thermal dust emission [see 65, and references therein] comes from interstellar dust grains which are mostly made of graphites, silicates, and Polycyclic Aromatic Hydrocarbons (PAHs), and they tend to align perpendicularly to the Galactic magnetic field, therefore emitting partially linearly polarized radiation.

AME

In total intensity, the AME has been observed by the Q, U and I Joint Observatory in TEnerife (QUIJOTE) and Planck in the frequency range ⇡ 10-60 GHz.A possible explanation of this emission is represented by the spinning of the dust grains, which rotate at GHz frequencies and emit electric dipole radiation if they have an electric dipole moment [72], or magnetized dust grains and free-floating ferromagnetic material. If the AME is polarized, its polarization fraction must be very small, at the level of a per cent

Component Separation

Parametric fitting

functional form of the frequency scaling for all components is known, and all the prior knowledge and physical modelling of different foregrounds are exploited.

Blind method

ILC

ICA

Template fitting

Status of B mode detection

Lensing B mode was first detected by SPT through cross-correlation, and directly by POLARBEAR.

PAPER

Contribution of Extragalactic Infrared Sources to CMB Foreground Anisotropy arxiv:9603121

Due to its large beam size, COBE was basically unaffected by extragalactic foreground sources. Because the antenna temperature contribution of a point source increases with the inverse of the solid angle of the beam, observations at higher angular resolution are more sensitive to extragalactic foregrounds, including radio sources, the Sunyaev-Zel’dovich effect from galaxy clusters, and the infrared-bright galaxies examined here.

The extragalactic infrared foreground will not be significant in comparison to CMB anisotropies around 100 GHz but will be dominant above 500 GHz.

Contribution of bright extragalactic radio sources to microwave anisotropy arxiv:9811311

For planned CMB anisotropy experiments, an additional concern is that the flatspectrum radio sources can vary by up to a factor of ten in flux since their emission comes from a compact, active core. Typical variations occur on timescales of one month to one year, although the overall spectrum shape is often preserved for a decade or longer (Tornikoski et al. 1993). We use the scatter in the observed fluxes of a source at each frequency to estimate the typical range of variability, which yields an error bar on the source’s flux at that frequency about the mean of all observations. Because the variations are not periodic, there is little more that can be done, unless sources are observed nearly simultaneously at higher resolution and nearby frequencies. GSS looks at the issue of variability in detail, including the possibility of extrapolating long-term drifts in source flux to the next epoch of observation. Radio sources are typically 4-7% polarized, and this polarization is variable (Nartallo et al. 1997), so radio-source foreground subtraction will be an important consideration for CMB polarization observations as well.

The brightest sources will dominate the anisotropy unless they are masked, because uncertainty in their exact fluxes makes subtraction highly inaccurate. After masking, the brightest remaining sources will dominate unless non-Poissonian clustering becomes appreciable.

The results of this investigation motivate an expansion of our catalog so that sources which will contribute to anisotropies on the 1σ level can be masked. It is clear that the current generation of CMB anisotropy experiments must pay close attention to the possibility of radio point source contamination at all frequencies. Masking pixels which contain bright radio galaxies should reduce this foreground to a manageable level.