119371788
The properties of extragalactic radio sources selected at 20 GHz
We present some first results on the variability, polarization and general properties of radio sources selected at 20 GHz, the highest frequency at which a sensitive radio survey has been carried out over a large area of sky. Sources with flux densities above 100 mJy in the Australia
117999125
Space Densities for Powerful Radio Sources in the Light of Unification
As radio survey frequency is raised the proportion of flat-spectrum sources increases in bright fiux-limited samples (eg Wall 1994, Aust J Phys 47, 625). Differential source counts show a corresponding broadening of the central maximum due to the increasing proportion of flat-spectrum sources. Orr & Browne (1982, MNRAS 200, 1067) modelled this change in shape of the source count by proposing a unifying scheme which states that the core-dominated, flat-spectrum radio sources are the steep-spectrum sources with their cores Doppler-boosted due to the alignment of the jets with the line of sight.
14097040
Extragalactic radio source evolution&unification: clues to the demographics of blazars
In this paper we discuss the demographics of the radio blazar population: (i) what are their parent ('unbeamed') sources and (ii) what magnitude and/or type of evolution have they undergone ? The discussion is based on models of radio source evolution and beaming based on a 'dual population' unification paradigm. These models, developed from radio blazar properties in bright samples, predict blazar demographic trends at the lower flux-density levels; samples from deep mJy-level surveys (e.g. NVSS and FIRST) may now provide direct tests of these predictions. All galaxies are radio galaxies in a sense. The scale of activity ranges from 'normal' galaxies (like our own) whose radio emission emanates from supernova remnants. At higher radio powers are the 'starburst' galaxies, greatly-enhanced stellar activity resulting in stronger radio emission. At similar radio powers are the Seyfert galaxies with their small-scale radio core-jet structures and with clear indication of AGN activity. At the top end of the scale are the powerful radio galaxies, together with BL Lacs and quasars, the latter two being collectively termed blazars. Radio galaxies tend to have steep radio spectra and therefore dominate low radio-frequency (ν < 0.5 GHz) surveys. The structures are predominantly double-lobed; Fanaroff & Riley (1974) compared the distances between central maxima of the radio structures to overall size and discovered a dichotomy. Sources with regions of maximum brightness separated by more than 0.5 times the overall source size are edge-brightened (FRII), while when the regions of maximum brightness lies within this limit the source has diffuse outer lobes (FRI) (centrally concentrated); and the highest radio power objects are predominantly FRIIs whilst those of lower radio power are usually FRIs. The overlap between the classes at middling radio powers is seen in the local radio luminos-ity function (Figure 1), and the division is known to be a function of optical luminosity as well as radio (Owen and Ledlow 1993).
15937671
The Parkes quarter-Jansky flat-spectrum sample: III. Space density and evolution of QSOs
We analyze the Parkes quarter-Jansky flat-spectrum sample of QSOs in terms of space density, including the redshift distribution, the radio luminosity function, and the evidence for a redshift cutoff. With regard to the luminosity function, we note the strong evolution in space density from the present day to epochs corresponding to redshifts ∼1. We draw attention to a selection effect due to spread in spectral shape that may have misled other investigators to consider the apparent similarities in shape of luminosity functions in different redshift shells as evidence for luminosity evolution. To examine the evolution at redshifts beyond 3, we develop a model-independent method based on the Vmax test using each object to predict expectation densities beyond z = 3. With this we show that a diminution in space density at z > 3 is present at a significance level >4σ. We identify a severe bias in such determinations from using flux-density measurements at epochs significantly later than that of the finding survey. The form of the diminution is estimated, and is shown to be very similar to that found for QSOs selected in X-ray and optical wavebands. The diminution is also compared with the current estimates of star-formation evolution, with less conclusive results. In summary we suggest that the reionization epoch is little influenced by powerful flat-spectrum QSOs, and that dust obscuration does not play a major role in our view of the QSO population selected at radio, optical or X-ray wavelengths. © ESO 2005.
18615828
Radio Sources in the 2dF Galaxy Redshift Survey. I. Radio source populations
We present the first results from a study of the radio continuum properties of galaxies in the 2dF Galaxy Redshift Survey, (2dFGRS) based on thirty 2dF fields covering a total area of about 100 deg2. About 1.5% of galaxies with b_J < 19.4 mag. are detected as radio continuum sources in the NRAO VLA Sky Survey (NVSS). Of these, roughly 40% are star-forming galaxies and 60% are active galaxies (mostly low-power radio galaxies and a few Seyferts). The combination of 2dFGRS and NVSS will eventually yield a homogeneous set of around 4000 radio-galaxy spectra, which will be a powerful tool for studying the distribution and evolution of both AGN and starburst galaxies out to z ~ 0.3.
119069361
Radio Observations of the Hubble Deep Field South region: I. Survey Description and Initial Results
This paper is the first of a series describing the results of the Australia Telescope Hubble Deep Field–South radio survey. The survey was conducted at four wavelengths, 20, 11, 6, and 3 cm, over a 4 year period and achieves an rms sensitivity of about 10 μJy at each wavelength. We describe the observations and data reduction processes and present data on radio sources close to the center of the Hubble Deep Field–South. We discuss in detail the properties of a subset of these sources. The sources include both starburst galaxies and galaxies powered by an active galactic nucleus and range in redshift from 0.1 to 2.2. Some of them are characterized by unusually high radio-to-optical luminosities, presumably caused by dust extinction.
118342809
Gamma ray lines from a universal extra dimension
Indirect Dark Matter searches are based on the observation of secondary particles produced by the annihilation or decay of Dark Matter. Among them, gamma-rays are perhaps the most promising messengers, as they do not suffer deflection or absorption on Galactic scales, so their observation would directly reveal the position and the energy spectrum of the emitting source. Here, we study the detailed gamma-ray energy spectrum of Kaluza-Klein Dark Matter in a theory with 5 Universal Extra Dimensions. We focus in particular on the two body annihilation of Dark Matter particles into a photon and another particle, which produces monochromatic photons, resulting in a line in the energy spectrum of gamma rays. Previous calculations in the context of the five dimensional UED model have computed the line signal from annihilations into ??, but we extend these results to include ?Z and ?H final states. We find that these spectral lines are subdominant compared to the predicted ?? signal, but they would be important as follow-up signals in the event of the observation of the ?? line, in order to distinguish the 5d UED model from other theoretical scenarios.
3163182
Higgs-Pair Production and Measurement of the Triscalar Coupling at LHC(8,14)
Abstract We simulate the measurement of the triscalar Higgs coupling at LHC ( 8 , 14 ) via pair production of h (125 GeV). We find that the most promising hh final state is b b ¯ γ γ . We account for deviations of the triscalar coupling from its SM value and study the effects of this coupling on the hh cross-section and distributions with cut-based and multivariate methods. Our fit to the hh production matrix element at LHC(14) with 3 ab − 1 yields a 30% uncertainty on this coupling in the SM and a range of 20–60% uncertainties for non-SM values.
18512510
Higgs boson production with one bottom quark including higher-order soft-gluon corrections
A Higgs boson produced in association with one or more bottom quarks is of great theoretical and experimental interest to the high-energy community. A precise prediction of its total and differential cross section can have a great impact on the discovery of a Higgs boson with large bottom-quark Yukawa coupling, like the scalar (h{sup 0} and H{sup 0}) and pseudoscalar (A{sup 0}) Higgs bosons of the minimal supersymmetric standard model in the region of large tan{beta}. In this paper we apply the threshold resummation formalism to determine both differential and total cross sections for bg{yields}b{phi} (where {phi}=h{sup 0},H{sup 0}), including up to next-to-next-to-next-to-leading order soft plus virtual QCD corrections at next-to-leading logarithmic accuracy. We present results for both the Fermilab Tevatron and the CERN Large Hadron Collider.
121807969
Dark matter search with PICASSO
PICASSO at SNOLAB searches primarily for spin-dependent WIMP interactions on 19F using the superheated droplet technique. This technique is based on the bubble chamber principle, where phase transitions in superheated liquid droplets can be triggered by WIMP induced nuclear recoils. The physics of the detection process allows a highly efficient suppression of backgrounds from cosmic muons, γ- and β-rays. We will discuss qualitatively recent progress in PICASSO and its sensitivity reach for spin-dependent and spin-independent WIMP searches.
119997511
Probing the mechanism of neutrinoless double beta decay with SuperNEMO
Abstract The SuperNEMO experiment is being designed to search for neutrinoless double beta decay. Its experimental technique of tracking and calorimetry provides the means to discriminate different underlying mechanisms for neutrinoless double beta decay by measuring the angular and energy distributions of electrons. The results of a study by the SuperNEMO Collaboration and F. Deppisch (in preparation)  [7] for identifying light Majorana neutrino exchange and right-handed currents are presented.