Unveiling radio halos in galaxy clusters in the LOFAR era

Giant radio halos are mega-parsec scale synchrotron sources detected in a fraction of massive and merging galaxy clusters. Radio halos provide one of the most important pieces of evidence for non-thermal components in large scale structure. Statistics of their properties can be used to discriminate among various models for their origin. Therefore, theoretical predictions of the occurrence of radio halos are important as several new radio telescopes are about to begin to survey the sky at low frequencies with unprecedented sensitivity. In this paper we carry out Monte Carlo simulations to model the formation and evolution of radio halos in a cosmological framework. We extend previous works on the statistical properties of radio halos in the context of the turbulent re-acceleration model. First we compute the fraction of galaxy clusters that show radio halos and derive the luminosity function of radio halos. Then, we derive differential and integrated number count distributions of radio halos at low radio frequencies with the main goal to explore the potential of the upcoming LOFAR surveys. By restricting to the case of clusters at redshifts <0.6, we find that the planned LOFAR all sky survey at 120 MHz is expected to detect about 350 giant radio halos. About half of these halos have spectral indices larger than 1.9 and substantially brighten at lower frequencies. If detected they will allow for a confirmation that turbulence accelerates the emitting particles. We expect that also commissioning surveys, such as MSSS, have the potential to detect about 60 radio halos in clusters of the ROSAT Brightest Cluster Sample and its extension (eBCS). These surveys will allow us to constrain how the rate of formation of radio halos in these clusters depends on cluster mass.Comment: 12 pages, 12 figures, accepted for publication in Astronomy and Astrophysic

Space charge effects in a vacuum thermionic diode

Temperature effects on thermionic diode with space charge model including emitter and accumulator electrode emission

Pressure measuring systems for closed cycle liquid metal facilities Ninth quarterly report, Mar. 1 - May 31, 1966

Thermionic diode pressure transducer for liquid metal application

Pressure measuring systems for closed cycle liquid metal facilities fifth quarterly report, 1 mar. - 31 may 1965

Pressure transducer system with thermionic diode sensor for closed cycle liquid metal applicatio

Pressure measuring systems for closed cycle liquid metal facilities Final report

Thermionic diode pressure sensor for liquid, vapor, and two phase potassium flow measurements at high temperature

Pressure measuring systems for closed cycle liquid metal facilities Seventh quarterly report, 1 Sep. - 30 Nov. 1965

Thermionic diode pressure transducer for closed cycle liquid metal application

Pressure measuring systems for closed cycle liquid metal facilities Eighth quarterly report, 1 Dec. 1965 - 28 Feb. 1966

Thermionic diode pressure transducer for liquid metal applications and thermionic sensor desig

Pressure measuring systems for closed cycle liquid metal facilities fourth quarterly report, 1 dec. 1964 - 28 feb. 1965

Pressure transducer system for liquid metal applications - fabrication of test pressure capsules, and deflection tests using optical measurement techniqu

Is the Sunyaev-Zeldovich effect responsible for the observed steepening in the spectrum of the Coma radio halo ?

The spectrum of the radio halo in the Coma cluster is measured over almost two decades in frequency. The current radio data show a steepening of the spectrum at higher frequencies, which has implications for models of the radio halo origin. There is an on-going debate on the possibility that the observed steepening is not intrinsic to the emitted radiation, but is instead caused by the SZ effect. Recently, the Planck satellite measured the SZ signal and its spatial distribution in the Coma cluster allowing to test this hypothesis. Using the Planck results, we calculated the modification of the radio halo spectrum by the SZ effect in three different ways. With the first two methods we measured the SZ-decrement within the aperture radii used for flux measurements of the halo at the different frequencies. First we adopted the global compilation of data from Thierbach et al. and a reference aperture radius consistent with those used by the various authors. Second we used the available brightness profiles of the halo at different frequencies to derive the spectrum within two fixed apertures, and derived the SZ-decrement using these apertures. As a third method we used the quasi-linear correlation between the y and the radio-halo brightness at 330 MHz discovered by Planck to derive the modification of the radio spectrum by the SZ-decrement in a way that is almost independent of the adopted aperture radius. We found that the spectral modification induced by the SZ-decrement is 4-5 times smaller than that necessary to explain the observed steepening. Consequently a break or cut-off in the spectrum of the emitting electrons is necessary to explain current data. We also show that, if a steepening is absent from the emitted spectrum, future deep observations at 5 GHz with single dishes are expected to measure a halo flux in a 40 arcmin radius that would be 7-8 times higher than currently seen.Comment: 8 pages, 6 figures, accepted in Astronomy and Astrophysics (date of acceptance 19/08/2013

2008 Report for the project entitled: A Comprehensive Modeling Approach Towards Understanding and Prediction of the Alaskan Coastal System Response to Changes in an Ice-diminished Arctic

LONG-TERM GOALS: Our research combines state-of-the-art regional modeling of sea ice, ocean, atmosphere and ecosystem to provide a system approach to advance the knowledge and predictive capability of the diverse impacts of changing sea ice cover on the bio-physical marine environment of coastal Alaska and over the larger region of the western Arctic Ocean. The focus of this project on seasonally ice-free Alaskan coasts and shelves is in direct support of the ‘Coastal Effects of a Diminished-ice Arctic Ocean’ and littoral studies of interest to the U.S. Navy. Given the continued warming and summer sea ice cover decrease in the Arctic during the past decades, this research will have broader and long-term impacts by facilitating studies of the potential increased exploration of natural resources along the seasonally ice-free northern Alaskan coasts and shelves and of the use of northern sea routes from the Pacific Ocean to Europe. Such activities will change the strategic importance of the entire pan-Arctic region. The research will allow a better understanding and planning of current and future operational needs in support of the continued US commercial and tactical interests in the region.Award Number: N0001407WR2029