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Register a new userAn absolutely calibrated survey of polarized emission from the northern sky at 1.4 GHz
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A new polarization survey of the northern sky at 1.41 GHz is presented. The observations were carried out using the 25.6m telescope at the Dominion Radio Astrophysical Observatory in Canada, with an angular resolution of 36 arcmin. The data are corrected for ground radiation to obtain Stokes U and Q maps on a well-established intensity scale tied to absolute determinations of zero levels, containing emission structures of large angular extent, with an rms noise of 12 mK. Survey observations were carried out by drift scanning the sky between -29 degr and +90 degr declination. The fully sampled drift scans, observed in steps of 0.25 degr to 2.5 degr in declination, result in a northern sky coverage of 41.7% of full Nyquist sampling. The survey surpasses by a factor of 200 the coverage, and by a factor of 5 the sensitivity, of the Leiden/Dwingeloo polarization survey (Spoelstra 1972) that was until now the most complete large-scale survey. The temperature scale is tied to the Effelsberg scale. Absolute zero-temperature levels are taken from the Leiden/Dwingeloo survey after rescaling those data by the factor of 0.94. The paper describes the observations, data processing, and calibration steps. The data are publicly available at http://www.mpifr-bonn.mpg.de/div/konti/26msurvey or http://www.drao.nrc.ca/26msurvey.
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We present results from simulations of the extragalactic polarized sky at 1.4 GHz. As the basis for our polarization models, we use a semi-empirical simulation of the extragalactic total intensity (Stokes I) continuum sky developed at the University of Oxford (http://scubed.physics.ox.ac.uk) under the European SKA Design Study (SKADS) initiative, and polarization distributions derived from analysis of polarization observations. By considering a luminosity dependence for the polarization of AGN, we are able to fit the 1.4 GHz polarized source counts derived from the NVSS and the DRAO ELAIS N1 deep field survey down to approximately 1 mJy. This trend is confirmed by analysis of the polarization of a complete sample of bright AGN. We are unable to fit the additional flattening of the polarized source counts from the deepest observations of the ELAIS N1 survey, which go down to ~0.5 mJy. Below 1 mJy in Stokes I at 1.4 GHz, starforming galaxies become an increasingly important fraction of all radio sources. We use a spiral galaxy integrated polarization model to make realistic predictions of the number of polarized sources at microJy levels in polarized flux density and hence, realistic predictions of what the next generation radio telescopes such as ASKAP, other SKA pathfinders and the SKA itself will see.
Polarized diffuse emission observations at 1.4-GHz in a high Galactic latitude area of the northern Celestial hemisphere are presented. The 3.2 X 3.2 deg^2 field, centred at RA = 10h 58m, Dec = +42deg 18 (B1950), has Galactic coordinates l~172deg, b~+63deg and is located in the region selected as northern target of the BaR-SPOrt experiment. Observations have been performed with the Effelsberg 100-m telescope. We find that the angular power spectra of the E- and B-modes have slopes of beta_E = -1.79 +/- 0.13 and beta_B = -1.74 +/- 0.12, respectively. Because of the very high Galactic latitude and the smooth emission, a weak Faraday rotation action is expected, which allows both a fair extrapolation to Cosmic Microwave Background Polarization (CMBP) frequencies and an estimate of the contamination by Galactic synchrotron emission. We extrapolate the E-mode spectrum up to 32-GHz and confirm the possibility to safely detect the CMBP E-mode signal in the Ka band found in another low emission region (Carretti et al. 2005b). Extrapolated up to 90-GHz, the Galactic synchrotron B-mode looks to compete with the cosmic signal only for models with a tensor-to-scalar perturbation power ratio T/S < 0.001, which is even lower than the T/S value of 0.01 found to be accessible in the only other high Galactic latitude area investigated to date. This suggests that values as low as T/S = 0.01 might be accessed at high Galactic latitudes. Such low emission values can allow a significant red-shift of the best frequency to detect the CMBP B-mode, also reducing the contamination by Galactic dust, and opening interesting perspectives to investigate Inflation models.
We present high sensitivity and absolutely calibrated images of diffuse radio polarisation at a resolution of about 10 arcmin covering the range 10 degr <l<34 degr and |b|<5 degr at 2.3 GHz from the S-band Parkes All Sky Survey and at 4.8 GHz from the Sino-German 6 cm polarisation survey of the Galactic plane. Strong depolarisation near the Galactic plane is seen at 2.3 GHz, which correlates with strong Halpha emission. We ascribe the depolarisation to spatial Faraday rotation measure fluctuations of about 65 rad/m2 on scales smaller than 6-9 pc. We argue that most (about 90%) of the polarised emission seen at 4.8 GHz originates from a distance of 3-4 kpc in the Scutum arm and that the random magnetic field dominates the regular field there. A branch extending from the North Polar Spur towards lower latitudes can be identified from the polarisation image at 4.8 GHz but only partly from the polarised image at 2.3 GHz, implying the branch is at a distance larger than 2-3 kpc. We show that comparison of structure functions of complex polarised intensity with those of polarised intensity can indicate whether the observed polarised structures are intrinsic or caused by Faraday screens. The probability distribution function of gradients from the polarisation images at 2.3 GHz indicates the turbulence in the warm ionised medium is transonic.
We have searched the Faint Images of the Radio Sky at Twenty centimeters (FIRST) and the NRAO VLA Sky Survey (NVSS) 1.4 GHz radio surveys for sources that are coincident with emission-line galaxy (ELG) candidates from the KPNO International Spectroscopic Survey (KISS). A total of 207 of the 2157 KISS ELGs (~10%) in the first two H-alpha-selected survey lists were found to possess radio detections in FIRST and/or NVSS. Follow-up spectra exist for all of the radio detections, allowing us to determine the activity type (star-forming vs. AGN) for the entire sample. We explore the properties of the radio-detected KISS galaxies in order to gain a better insight into the nature of radio-emitting galaxies in the local universe (z < 0.1). No dwarf galaxies were detected, despite the large numbers of low-luminosity galaxies present in KISS, suggesting that lower mass, lower luminosity objects do not possess strong galaxian-scale magnetic fields. Due to the selection technique used for KISS, our radio ELGs represent a quasi-volume-limited sample, which allows us to develop a clearer picture of the radio galaxy population at low redshift. Nearly 2/3rds of the KISS radio galaxies are starburst/star-forming galaxies, which is in stark contrast to the results of flux-limited radio surveys that are dominated by AGNs and elliptical galaxies (i.e., classic radio galaxies). While there are many AGNs among the KISS radio galaxies, there are no objects with large radio powers in our local volume. We derive a radio luminosity function (RLF) for the KISS ELGs that agrees very well with previous RLFs that adequately sample the lower-luminosity radio population.
We report on an Arecibo 4.5-GHz polarimetric single-pulse survey of the brightest pulsars at high frequency within its sky. The high frequency profiles are accompanied by a collection of both previously published and unpublished high quality 1.4- and 0.33-GHz observations. Here our analyses and discussion primarily involve the average and statistical properties of the 46 pulsars polarimetric pulse sequences, profile classification and frequency evolution, and polarimetric profiles and peak-occurrence histograms. In most cases both the fractional linear polarization and profile widths decrease with frequency as expected, but there are some exceptions. Similarly, we were able to review and/or extend the profile classifications for this population of pulsars and work out their beaming characteristics quantitatively showing that almost all show properties compatible with the core/double-cone emission beam model. The entirety of these observations average profiles are accessible for download.
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