In order to construct accurate point sources simulations at the frequencies relevant to 21 cm experiments, the angular correlation of radio sources must be taken into account. Using the 74 MHz VLSS survey, we measured the angular 2-point correlation function, w(θ). We obtain the first measurement of clustering at the low frequencies relevant to 21 cm tomography. We find that a single power law with shape w(θ) = A θ^{-γ} fits well the data. For a galactic cut of 10 degrees, with a data cut of δless than -10 degrees, and a flux limit of S = 770 mJy, we obtain a slope of γ= (-1.2 +/- 0.35). This value of γis consistent with that measured from other radio catalogues at the millimeter wavelengths. The amplitude of clustering has a length of 0.2 degrees - 0.6 degrees, and it is independent of the flux-density threshold.
Studying the spatial distribution of extragalactic source populations is vital in understanding the matter distribution in the Universe. It also enables understanding the cosmological evolution of dark matter density fields and the relationship between dark matter and luminous matter. Clustering studies are also required for EoR foreground studies since it affects the relevant angular scales. This paper investigates the angular and spatial clustering properties and the bias parameter of radio-selected sources in the Lockman Hole field at 325 MHz. The data probes sources with fluxes $\gtrsim$0.…
We study the angular clustering of point sources in The GMRT (Giant Meter Wave Telescope) Sky Survey (TGSS). The survey at 150 MHz with delta > -53.5 degrees has a sky coverage of 3.6 pi steradians, i.e., 90% of the whole sky. We created subsamples by applying different total flux thresholds limit (S >> 5 sigma) for good completeness and measured the angular correlation function omega(theta) of point sources at large scales ( >= 1 degree). We find that the amplitude of angular clustering is higher for brighter subsamples, this indicates that higher threshold flux samples are hosted by massive …
The first direct measurement of gravitational waves by the LIGO and Virgo collaborations has opened up new avenues to explore our Universe. This white paper outlines the challenges and gains expected in gravitational wave searches at frequencies above the LIGO/Virgo band, with a particular focus on Ultra High-Frequency Gravitational Waves (UHF-GWs), covering the MHz to GHz range. The absence of known astrophysical sources in this frequency range provides a unique opportunity to discover physics beyond the Standard Model operating both in the early and late Universe, and we highlight some of th…
In recent years, the level of the extragalactic radio background has become a point of considerable interest, with some lines of argument pointing to an entirely new cosmological synchrotron background. The contribution of the known discrete source population to the sky temperature is key to this discussion. Because of the steep spectral index of the excess over the cosmic microwave background, it is best studied at low frequencies where the signal is strongest. The Low-Frequency Array (LOFAR) wide and deep sky surveys give us the best constraints yet on the contribution of discrete extragalac…
Radio synchrotron emission from the bridges of low-density gas connecting galaxy clusters and groups is a challenge for particle acceleration processes. In this work, we analyse the Coma radio bridge using new LOw Frequency ARray (LOFAR) observations at 144 MHz. LOFAR detects the bridge and its substructures with unprecedented sensitivity and resolution. We find that the radio emission peaks on the NGC 4839 group. Towards the halo, in front of the NGC 4839 group, the radio brightness decreases and streams of radio emission connect the NGC 4839 group to the radio relic. Using X-ray observations…
Tracing Large-scale Structure with the MeerKLASS On-the-Fly Survey: Angular Clustering of Radio Sources at 816 MHz
The University of Manchester（曼彻斯特大学）；University of the Western Cape（西开普大学）；University of Portsmouth（朴茨茅斯大学）；LMU Faculty of Physics（慕尼黑大学物理学院）；South African Radio Astronomy Observatory (SARAO)（南非射电天文观测台）
We present a new analysis of the widely used relation between cavity power and radio luminosity in clusters of galaxies with evidence for strong AGN feedback. We study the correlation at low radio frequencies using two new surveys - the First Alternative Data Release of the TIFR GMRT Sky Survey (TGSS ADR1) at 148 MHz and LOFAR's first all-sky survey, the Multifrequency Snapshot Sky Survey (MSSS) at 140 MHz. We find a scaling relation $P_{\rm cav} \propto L_{148}^β$, with a logarithmic slope of $β= 0.51 \pm 0.14$, which is in good agreement with previous results based on data at 327 MHz. The la…
We present the first wide area (19 deg$^2$), deep ($\approx120-150$ μJy beam$^{-1}$), high resolution ($5.6 \times 7.4$ arcsec) LOFAR High Band Antenna image of the Boötes field made at 130-169 MHz. This image is at least an order of magnitude deeper and 3-5 times higher in angular resolution than previously achieved for this field at low frequencies. The observations and data reduction, which includes full direction-dependent calibration, are described here. We present a radio source catalogue containing 6276 sources detected over an area of $19$\,deg$^2$, with a peak flux density threshold o…
We show that the spectral energy distribution of relic gravitons mildly increases for frequencies smaller than the $μ$Hz and then flattens out whenever the refractive index of the tensor modes is dynamical during a quasi-de Sitter stage of expansion. For a conventional thermal history the high-frequency plateau ranges between the mHz and the audio band but it is supplemented by a spike in the GHz region if a stiff post-inflationary phase precedes the standard radiation-dominated epoch. Even though the slope is blue at intermediate frequencies, it may become violet in the MHz window. For a vari…
We report on a spectral study at radio frequencies of the giant radio halo in A2142 (z=0.0909), which we performed to explore its nature and origin. A2142 is not a major merger and the presence of a giant radio halo is somewhat surprising. We performed deep radio observations with the GMRT at 608 MHz, 322 MHz, and 234 MHz and with the VLA in the 1-2 GHz band. We obtained high-quality images at all frequencies in a wide range of resolutions. The radio halo is well detected at all frequencies and extends out to the most distant cold front in A2142. We studied the spectral index in two regions: t…
We present new low-frequency ($ν= 88$-216 MHz) observations of the complex merging galaxy cluster Abell 3266. These new observations are taken with the Murchison Widefield Array (MWA) in its Phase II 'extended', long-baseline configuration, offering the highest-resolution low-frequency view of the cluster to date. We report on the detection of four steep spectrum ($α\lesssim -1$ for $S_ν\propto ν^α$) extended radio sources within the cluster. We confirm the detection of a $\sim 570$ kpc radio relic to the south of the cluster, and a possible bridge of emission connecting the relic to the clust…
The galaxy cluster Abell 2256 hosts one of the most intriguing examples in the class of radio relics. It has been found that this radio relic has a rather flat integrated spectrum at low frequencies that would imply an injection spectral index for the electrons that is inconsistent with the flattest allowed by the test particle diffusive shock acceleration (DSA). We performed new high-frequency observations at 2273, 2640, and 4850 MHz. Combining these new observations with images available in the literature, we constrain the radio integrated spectrum of the radio relic in Abell 2256 over the w…
