A template of atmospheric O2 circularly polarized emission for CMB experiments

We compute the circularly polarized signal from atmospheric molecular oxygen. Polarization of O2 rotational lines is caused by Zeeman effect in the Earth magnetic field. We evaluate the circularly polarized emission for various sites suitable for CMB measurements: South Pole and Dome C (Antarctica), Atacama (Chile) and Testa Grigia (Italy). An analysis of the polarized signal is presented and discussed in the framework of future CMB polarization experiments. We find a typical circularly polarized signal (V Stokes parameter) of ~ 50 - 300 {mu}K at 90 GHz looking at the zenith. Among the other sites Atacama shows the lower polarized signal at the zenith. We present maps of this signal for the various sites and show typical elevation and azimuth scans. We find that Dome C presents the lowest gradient in polarized temperature: ~ 0.3 {mu}K/circ at 90 GHz. We also study the frequency bands of observation: around { u} simeq 100 GHz and { u} simeq 160 GHz we find the best conditions because the polarized signal vanishes. Finally we evaluate the accuracy of the templates and the signal variability in relation with the knowledge and the variability of the Earth magnetic field and the atmospheric parameters.

TRIS II: search for CMB spectral distortions at 0.60, 0.82 and 2.5 GHz

With the TRIS experiment we have performed absolute measurements of the sky brightness in a sky circle at $delta = +42^{circ}$ at the frequencies $ u =$ 0.60, 0.82 and 2.5 GHz. In this paper we discuss the techniques used to separate the different contributions to the sky emission and give an evaluation of the absolute temperature of the Cosmic Microwave Background. For the black-body temperature of the CMB we get: $T_{cmb}^{th}=(2.837 pm 0.129 pm 0.066)K$ at $ u=0.60$ GHz; $T_{cmb}^{th}=(2.803 pm 0.051 ^{+0.430} _{-0.300})K$ at $ u=0.82$ GHz; $T_{cmb}^{th}=(2.516 pm 0.139 pm 0.284)K$ at $ u=2.5$ GHz. The first error bar is statistic (1$sigma$) while the second one is systematic. These results represent a significant improvement with respect to the previous measurements. We have also set new limits to the free-free distortions, $ -6.3 times 10^{-6} < Y_{ff} < 12.6 times 10^{-6}$, and slightly improved the Bose-Einstein upper limit, $|mu| < 6 times 10^{-5}$, both at 95% confidence level.

TRIS III: the diffuse galactic radio emission at $delta=+42^{circ}$

We present values of temperature and spectral index of the galactic diffuse radiation measured at 600 and 820 MHz along a 24 hours right ascension circle at declination $delta = +42^{circ}$. They have been obtained from a subset of absolute measurements of the sky temperature made with TRIS, an experiment devoted to the measurement of the Cosmic Microwave Background temperature at decimetric-wavelengths with an angular resolution of about $20^{circ}$. Our analysis confirms the preexisting picture of the galactic diffuse emission at decimetric wavelength and improves the accuracy of the measurable quantities. In particular, the signal coming from the halo has a spectral index in the range $2.9-3.1$ above 600 MHz, depending on the sky position. In the disk, at TRIS angular resolution, the free-free emission accounts for the 11% of the overall signal at 600 MHz and 21% at 1420 MHz. The polarized component of the galactic emission, evaluated from the survey by Brouw and Spoelstra, affects the observations at TRIS angular resolution by less than 3% at 820 MHz and less than 2% at 600 MHz. Within the uncertainties, our determination of the galactic spectral index is practically unaffected by the correction for polarization. Since the overall error budget of the sky temperatures measured by TRIS at 600 MHz, that is 66 mK(systematic)$+$18 mK (statistical), is definitely smaller than those reported in previous measurements at the same frequency, our data have been used to discuss the zero levels of the sky maps at 150, 408, 820 and 1420 MHz in literature. Concerning the 408 MHz survey, limiting our attention to the patch of sky corresponding to the region observed by TRIS, we suggest a correction of the base-level of $(+3.9pm 0.6)$K.

TRIS I: Absolute Measurements of the Sky Brightness Temperature at 0.6, 0.82 and 2.5 GHz

At frequencies close to 1 GHz the sky diffuse radiation is a superposition of radiation of Galactic origin, the 3 K Relic or Cosmic Microwave Background Radiation, and the signal produced by unresolved extragalactic sources. Because of their different origin and space distribution the relative importance of the three components varies with frequency and depends on the direction of observation. With the aim of disentangling the components we built TRIS, a system of three radiometers, and studied the temperature of the sky at $ u =0.6$, $ u = 0.82$ and $ u = 2.5$ GHz using geometrically scaled antennas with identical beams (HPBW = $18^{circ} times 23^{circ}$). Observations included drift scans along a circle at constant declination $delta=+42^{circ}$ which provided the dependence of the sky signal on the Right Ascension, and absolute measurement of the sky temperature at selected points along the same scan circle. TRIS was installed at Campo Imperatore (lat. = $42^{circ}~26$ N, long.= $13^{circ}~33$, elevation = 2000 m a.s.l.) in Central Italy, close to the Gran Sasso Laboratory.

The contribution of the Unresolved Extragalactic Radio Sources to the Brightness Temperature of the sky

The contribution of the Unresolved Extragalactic Radio Sources to the diffuse brightness of the sky was evaluated using the source number - flux measurements available in literature. We first optimized the fitting function of the data based on number counts distribution. We then computed the brightness temperature at various frequencies from 151 MHz to 8440 MHz and derived its spectral dependence. As expected the frequency dependence can be described by a power law with a spectral index $gamma simeq -2.7$, in agreement with the flux emitted by the {it steep spectrum} sources. The contribution of {it flat spectrum} sources becomes relevant at frequencies above several GHz. Using the data available in literature we improved our knowledge of the brightness of the unresolved extragalactic radio sources. The results obtained have general validity and they can be used to disentangle the various contributions of the sky brightness and to evaluate the CMB temperature.