119467715
Radio Observations of the Hubble Deep Field-South Region. III. The 2.5, 5.2, and 8.7 GHz Catalogs and Radio Source Properties
Deep radio observations of a wide region centered on the Hubble Deep Field-South have been performed, providing one of the most sensitive sets of radio observations acquired on the Australia Telescope Compact Array to date. A central rms of ~10 μJy is reached at four frequencies (1.4, 2.5, 5.2, and 8.7 GHz). In this paper the full source catalogs from the 2.5, 5.2, and 8.7 GHz observations are presented to complement Paper II in this series, along with a detailed analysis of image quality and noise. We produce a consolidated catalog by matching sources across all four frequencies of our survey. Radio spectral indices are used to investigate the nature of the radio sources and identify a number of sources with flat or inverted radio spectra, which indicate active galactic nucleus activity. We also find several other interesting sources, including a broad-line-emitting radio galaxy, a giant radio galaxy, and three gigahertz-peaked spectrum sources.
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.
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.
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.
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.
119249502
Gamma rays from top-mediated dark matter annihilations
Lines in the energy spectrum of gamma rays are a fascinating experimental signal, which are often considered ''smoking gun" evidence of dark matter annihilation. The current generation of gamma ray observatories are currently closing in on parameter space of great interest in the context of dark matter which is a thermal relic. We consider theories in which the dark matter's primary connection to the Standard Model is via the top quark, realizing strong gamma ray lines consistent with a thermal relic through the forbidden channel mechanism proposed in the Higgs in Space Model. We consider realistic UV-completions of the Higgs in Space and related theories, and show that a rich structure of observable gamma ray lines is consistent with a thermal relic as well as constraints from dark matter searches and the LHC. Particular attention is paid to the one loop contributions to the continuum gamma rays, which can easily swamp the line signals in some cases, and have been largely overlooked in previous literature.
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.
73704343
WIMP-induced gamma ray spectrum of active Galactic nuclei
As direct and indirect dark matter detection experiments continue to place stringent constraints on WIMP masses and couplings, it becomes imperative to expand the scope of the search for particle dark matter by looking in new and exotic places. One such place may be the core of active galactic nuclei where the density of dark matter is expected to be extremely high. Recently, several groups have explored the possibility of observing signals of dark matter from its interactions with the high-energy jets emanating from these galaxies. In this work, we build upon these analyses by including the other components of the WIMP-induced gamma ray spectrum of active galactic nuclei; namely, (1) the continuum from WIMP annihilation into light standard model states which subsequently radiate and/or decay into photons and (2) the direct (loop-induced) decay into photons. We work in the context of models of universal extra dimensions (in particular, a model with two extra dimensions) and compute all three components of the gamma ray spectrum and compare with current data. We find that the model with two extra dimensions exhibits several interesting features which may be observable with the Fermi gamma ray telescope. We also show that, in conjunction with other measurements, the gamma ray spectrum from AGN can be an invaluable tool for restricting WIMP parameter space.
118462429
Dark matter on top
We consider a simplified model of fermionic dark matter which couples exclusively to the right-handed top quark via a renormalizable interaction with a color-charged scalar. We first compute the relic abundance of this type of dark matter and investigate constraints placed on the model parameter space by the latest direct detection data. We also perform a detailed analysis for the production of dark matter at the LHC for this model. We find several kinematic variables that allow for a clean signal extraction and we show that the parameter space of this model will be well probed during LHC Run-II. Finally, we investigate the possibility of detecting this type of dark matter via its annihilations into gamma rays. We compute the continuum and the line emission (which includes a possible ''Higgs in Space!'' line) and its possible discovery by future gamma-ray telescopes. We find that the annihilation spectrum has distinctive features which may distinguish it from other models.
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.