CERN Accelerating science

{\bf Top}: The radio sky zero level in radiometric temperature units, reproduced from \citet{DT18}, as measured by several different instruments or surveys reporting an absolute zero-level calibration. The spectrum has power-law at frequencies below $\sim$10 GHz above the CMB level. Results are shown for ARCADE~2 at 3--10 GHz \citep{Fixsen11}, \citet{RR86} at 1.4 GHz, \citet{Haslam} at 408 MHz, \citet{Maeda99} at 45 MHz, and \citet{Roger99} at 22 MHz, as well as several points reported by \citet{DT18}. {\bf Bottom}: The photon backgrounds in the universe in units of spectral energy surface brightness density. Reproduced from \citet{CP1}.

{\bf Top}: The radio sky zero level in radiometric temperature units, reproduced from \citet{DT18}, as measured by several different instruments or surveys reporting an absolute zero-level calibration. The spectrum has power-law at frequencies below $\sim$10 GHz above the CMB level. Results are shown for ARCADE~2 at 3--10 GHz \citep{Fixsen11}, \citet{RR86} at 1.4 GHz, \citet{Haslam} at 408 MHz, \citet{Maeda99} at 45 MHz, and \citet{Roger99} at 22 MHz, as well as several points reported by \citet{DT18}. {\bf Bottom}: The photon backgrounds in the universe in units of spectral energy surface brightness density. Reproduced from \citet{CP1}.

Some photos of relevant instrumentation for the 310~MHz absolute map project. The top photo shows the custom high edge-taper feed which will be mounted at the prime focus of the GBT, while the bottom photo shows the custom balanced correlation receiver mounted in a spare GBT prime focus receiver box. The 310~MHz map will have an absolutely calibrated zero level and polarization information, which will be valuable for CMB, 21-cm, and other studies as discussed in \S \ref{GBTsec}.

Some photos of relevant instrumentation for the 310~MHz absolute map project. The top photo shows the custom high edge-taper feed which will be mounted at the prime focus of the GBT, while the bottom photo shows the custom balanced correlation receiver mounted in a spare GBT prime focus receiver box. The 310~MHz map will have an absolutely calibrated zero level and polarization information, which will be valuable for CMB, 21-cm, and other studies as discussed in \S \ref{GBTsec}.

Diagram of the balanced correlation receiver design. `LNA' is low-noise amplifier, `BPF' is band pass filter, and `ADC' is analog-to-digital conversion. There is one independent receiver chain as visualized here for each polarization.

Measured anisotropy power spectrum of the radio sky centered at 140~MHz with an RMS noise of 720 $\mu$Jy. Shown are curves for the full bandwidth of the coldest patch field (field A) and the secondary field (field B), as well as for 12 four MHz wide sub-bands of field A. The anisotropy in field A deduced by considering the average noise per beam in the image with the synthesized beam tapered to 30\arcsec\ FWHM is also shown and agrees at the relevant angular scale. We also show comparison levels inferred by the noise per beam at 8.7~GHz, 8.4~GHz, and 4.9~GHz in different fields as calculated by \citet{Holder14} and scaled here to 140~MHz assuming a synchrotron power law of -2.6 in radiometric temperature units. The amount of angular power is $\sim$1.4 times higher for field B compared to field A (in K$^2$ units) across a range of angular scales. All angular powers are expressed here in the $\left({\Delta T} \right)_\ell^2$ normalization. Reproduced from \citet{LF21}

C-BASS North maps of total intensity (\textit{top}) and polarized intensity (\textit{bottom}) in Galactic coordinates using a mollweide projection. The total intensity map color scale has been saturated along the Galactic plane and includes the locations of well-known radio loops \citep{Vidal2015}. The polarized intensity map has the projected B-field direction overlaid using line-integral convolution.

C-BASS North maps of total intensity (\textit{top}) and polarized intensity (\textit{bottom}) in Galactic coordinates using a mollweide projection. The total intensity map color scale has been saturated along the Galactic plane and includes the locations of well-known radio loops \citep{Vidal2015}. The polarized intensity map has the projected B-field direction overlaid using line-integral convolution.

$\sqrt{D/2}$ vs. separation $\Delta\theta$ for the high-latitude C-BASS polarization angles, where $D$ is the structure function, so $\sqrt{D/2}$ would equal the standard deviation, on scales large enough that pixel pairs are uncorrelated.

Measured cross spectrum $\kappa g$ of TGSS -- CMB lensing (red dots) and NVSS -- CMB lensing (black diamonds). Error bars represent the $1\sigma$ uncertainties obtained assuming Gaussian statistics. Blue curves represent model predictions obtained using different prescriptions for the bias, $b(z)$, while the T-RECS $N(z)$ distribution of \cite{Bonaldi18} is used (see \citet{Piccirilli22} for a detailed description).

Spectral distortion signals created by free-free-type soft photon injection from a decaying DM particle with lifetime $t_X\simeq 10^{12}$ (top) and $10^{15}$ s (bottom). In each case it is assumed that a fraction $\epsilon_{\rm soft}$ of the total energy (as labeled) is injected as soft photons. The injection frequency, $x_{\rm inj, 0}=h\nu_{\rm inj, 0}/k T_0$ is also varied with some of the cases shown coming intriguingly close to the ARCADE RSB level (figures provided by Sandeep Acharya).

Spectral distortion signals created by free-free-type soft photon injection from a decaying DM particle with lifetime $t_X\simeq 10^{12}$ (top) and $10^{15}$ s (bottom). In each case it is assumed that a fraction $\epsilon_{\rm soft}$ of the total energy (as labeled) is injected as soft photons. The injection frequency, $x_{\rm inj, 0}=h\nu_{\rm inj, 0}/k T_0$ is also varied with some of the cases shown coming intriguingly close to the ARCADE RSB level (figures provided by Sandeep Acharya).

Differential number counts used to create the training set discussed in \S \ref{Todarello}.

Reconstruction residuals. The red star marks the image having the differential source count $n_{T-RECS}(s)$.

{\bf Top}: Picture of the AAVS2 station with a close-up view of the log-periodic antennas. Adapted from \cite{Macario22}. {\bf Middle}: Examples of all-sky images taken with the AAVS2 station at 110 MHz (panel A) and 70 MHz (panel B). Both orthogonal polarizations, $XX$ and $YY$, are displayed. Units are Jy~beam$^{-1}$. Adapted from \cite{Macario22}. {\bf Bottom}: Mean value (gray solid line) and standard deviation (gray area) of the foreground spectral index as a function of LST. Black lines represent prediction extrapolated from other measurements (see \citealt{Spinelli21} for details). The yellow region indicates measurement taken during daytime. Reproduced from \cite{Spinelli21}.

{\bf Top}: Picture of the AAVS2 station with a close-up view of the log-periodic antennas. Adapted from \cite{Macario22}. {\bf Middle}: Examples of all-sky images taken with the AAVS2 station at 110 MHz (panel A) and 70 MHz (panel B). Both orthogonal polarizations, $XX$ and $YY$, are displayed. Units are Jy~beam$^{-1}$. Adapted from \cite{Macario22}. {\bf Bottom}: Mean value (gray solid line) and standard deviation (gray area) of the foreground spectral index as a function of LST. Black lines represent prediction extrapolated from other measurements (see \citealt{Spinelli21} for details). The yellow region indicates measurement taken during daytime. Reproduced from \cite{Spinelli21}.

{\bf Top}: Picture of the AAVS2 station with a close-up view of the log-periodic antennas. Adapted from \cite{Macario22}. {\bf Middle}: Examples of all-sky images taken with the AAVS2 station at 110 MHz (panel A) and 70 MHz (panel B). Both orthogonal polarizations, $XX$ and $YY$, are displayed. Units are Jy~beam$^{-1}$. Adapted from \cite{Macario22}. {\bf Bottom}: Mean value (gray solid line) and standard deviation (gray area) of the foreground spectral index as a function of LST. Black lines represent prediction extrapolated from other measurements (see \citealt{Spinelli21} for details). The yellow region indicates measurement taken during daytime. Reproduced from \cite{Spinelli21}.

The net background temperature $(T_\mathrm{r}=T_{\mathrm{b}} +T_{\mathrm{CMB}})$ generated by radio emission due to accretion onto supermassive PBHs. For $\lambda=0.5, f_{\mathrm{X}}=0.1, f_{\mathrm{duty}}=0.05$ and $f_{\mathrm{PBH}}=10^{-4}$ (solid blue) we can explain the RSB observed (dotted blue). For $\lambda=0.1, f_{\mathrm{duty}}=0.01$ we get (solid red) 5\% of ARCADE~2 (dotted red) radio emission necessary to get the EDGES result \citep{Mittal_JCAP}. The CMB temperature is shown in dashed black for reference. The gray shaded region roughly covers the frequency range over which an RSB has been seen.

Synthetic radio sky with a mean magnetic field of 1.6~nT at 3.3~GHz (except: bottom right). The resolution is 12$^\circ$ matching that of the ARCADE~2 radiometer. The top row shows the distribution of the antenna temperature. The bottom row shows the fractional polarization for the corresponding image. The left column is for a complete Kolmogorov power spectrum. The middle (right) one is for a model with the 20 (85) percent largest modes set to zero. Bottom right: Predicted radio synchrotron emission for the Local Bubble for the 85 percent largest modes set to zero and different mean magnetic field strengths between 0.16~nT and 10~nT. Measurements are from \citet{Seiffert11} and \citet{DT18}. Reproduced from \citet{KH21}.

Polarization intensity $P$ (top) and fractional polarization $P/I$ (bottom) from Planck evaluated at 30 GHz. Despite the high degree of depolarization, the polarization angle (white bars) shows little scatter.

MIST instrument conducting test observations in Deep Springs, California (top), and in Death Valley, Nevada (bottom) in May 2022. MIST is a single-antenna total-power radiometer without a metal ground plane. The antenna is a blade dipole of $2.4$ m tip-to-tip length and the measurements span the $25-125$~MHz range. These test measurements are currently being analyzed to understand the diffuse synchrotron emission in the northern hemisphere as well as the effect of the ground on the sky measurements.

MIST instrument conducting test observations in Deep Springs, California (top), and in Death Valley, Nevada (bottom) in May 2022. MIST is a single-antenna total-power radiometer without a metal ground plane. The antenna is a blade dipole of $2.4$ m tip-to-tip length and the measurements span the $25-125$~MHz range. These test measurements are currently being analyzed to understand the diffuse synchrotron emission in the northern hemisphere as well as the effect of the ground on the sky measurements.

Point-wise posterior for $T_{\rm exc}$ within our proposed model, showing the middle-68\% and 95\% regions (dark and light blue regions, respectively). We include the contribution from unresolved extragalactic sources $T_{\rm eg}$~\citep[dashed grey --][]{Gervasi:2008rr} for completeness. The spectrum for a single point in parameter space is shown in pink. Radio data, plotted as $T - T_0^{\rm FIRAS}$, include measurements from ARCADE~2, shown in red~\citep{Fixsen11}, with results from other telescopes shown in black. The pink dashed line shows a fit to the ARCADE~2 data only assuming no stimulated emission.

Limits on the cross section as a function of the DM mass. Comparison with limits from: autocorrelation of gamma rays (dashed red for Fermi \citet{Fermi_2018}, light purple dashed for Fermissimo), intensity of the gamma-ray flux (yellow for Fermi \citet{Fermi_2015}, black for Fermissimo) and dwarf spheroidal galaxies \citep{Dwarfs_2017}.

Example morphology of the DM synchrotron polarization amplitude at $30$~GHz for $m_{\rm DM}=50$~GeV annihilating in $\mu^+ \mu^-$ pairs with a thermal cross section, and Psh+11 GMF model.

Upper limits on the DM annihilation cross section from the intensity and polarization data at $30$~GHz. Left: effect of the GMF modeling for the $\bar{b} b$ channel. Right: constraints for different annihilation channels for the Psh+11 GMF. Also shown for comparison are the constraints obtained from \textit{Planck} CMB data \citep{Planck:2018vyg}.

Upper limits on the DM annihilation cross section from the intensity and polarization data at $30$~GHz. Left: effect of the GMF modeling for the $\bar{b} b$ channel. Right: constraints for different annihilation channels for the Psh+11 GMF. Also shown for comparison are the constraints obtained from \textit{Planck} CMB data \citep{Planck:2018vyg}.