Point source

About: Point source is a research topic. Over the lifetime, 5077 publications have been published within this topic receiving 94091 citations.

Statistical properties of polarized radio sources at high frequency and their impact on cosmic microwave background polarization measurements

Abstract: We have studied the implications of high-sensitivity polarization measurements of objects from the Wilkinson Microwave Anisotropy Probe (WMAP) point source catalogue made using the Very Large Array (VLA) at 8.4, 22 and 43 GHz. The fractional polarization of sources is almost independent of frequency with a median of ?��2 per cent and an average, for detected sources, of ?��3.5 per cent. These values are also independent of the total intensity over the narrow range of intensity we sample. Using a contemporaneous sample of 105 sources detected at all three VLA frequencies, we have investigated the spectral behaviour as a function of frequency by means of a two-colour diagram. Most sources have power-law spectra in total intensity, as expected. On the other hand, they appear to be almost randomly distributed in the polarized intensity two-colour diagram. This is compatible with the polarized spectra being much less smooth than those in intensity and we speculate on the physical origins of this. We have performed an analysis of the correlations between the fractional polarization and spectral indices including computation of the principal components. We find that there is little correlation between the fractional polarization and the intensity spectral indices. This is also the case when we include polarization measurements at 1.4 GHz from the NRAO VLA Sky Survey (NVSS). In addition we compute 45 rotation measures from polarization position angles which are compatible with a ?� 2 law. We use our results to predict the level of point source confusion noise that contaminates cosmic microwave background polarization measurements aimed at detecting primordial gravitational waves from inflation. We conclude that some level of source subtraction will be necessary to detect r�� 0.1 below 100 GHz and at all frequencies to detect r�� 0.01. We present estimates of the level of contamination expected and the number of sources which need to be subtracted as a function of the imposed cut flux density and frequency.

Protostellar candidates in a sample of bright far-infrared IRAS sources

Abstract: CO and radio continuum emission has been observed in the direction of 39 bright 100-micron sources from the IRAS point source catalog in an attempt to better understand the early stages of star formation. All 39 sources are found to be associated with molecular clouds and are generally characterized by high temperatures (15-40 K) and wide wings in the profiles (up to 34 km/s). Twenty-six of the 39 sources show wide (C-12)O lines, which are interpreted as a result of gas outflow associated with star formation processes. Of the 24 sources for which distances and 6-cm flux densities can be assigned, 11 are premain sequence objects, and 4 others are possibly in this category. Six of the eleven premain sequence sources have associated continuum emission. 30 refs.

Blind and non-blind source detection in WMAP 5-year maps

Abstract: We have analyzed the efficiency in source detection and flux density estimation of blind and non-blind detection techniques exploiting the MHW2 filter applied to the Wilkinson Microwave Anisotropy Probe (WMAP) 5-year maps. A comparison with the AT20G Bright Source Sample (Massardi et al. 2008), with a completeness limit of 0.5 Jy and accurate flux measurements at 20 GHz, close to the lowest frequency of WMAP maps, has allowed us to assess the completeness and the reliability of the samples detected with the two approaches, as well as the accuracy of flux and error estimates, and their variations across the sky. The uncertainties on flux estimates given by our procedure turned out to be about a factor of 2 lower than the rms differences with AT20G measurements, consistent with the smoothing of the fluctuation field yielded by map filtering. Flux estimates were found to be essentially unbiased except that, close to the detection limit, a substantial fraction of fluxes are found to be inflated by the contribution of underlying positive fluctuations. This is consistent with expectations for the Eddington bias associated to the true errors on flux density estimates. The blind and non-blind approaches are found to be complementary: each of them allows the detection of sources missed by the other. Combining results of the two methods on the WMAP 5-year maps we have expanded the non-blindly generated New Extragalactic WMAP Point Source (NEWPS) catalogue (Lopez-Caniego et al. 2007) that was based on WMAP 3-year maps. After having removed the probably spurious objects not identified with known radio sources, the new version of the NEWPS catalogue, NEWPS_5yr comprises 484 sources detected with a signal-to-noise ratio SNR>5.

Chandra & XMM-Newton Observations of NGC5253. Analysis of the X-ray Emission from a Dwarf Starburst Galaxy

Abstract: We present Chandra and XMM-Newton X-ray data of NGC5253, a local starbursting dwarf elliptical galaxy, in the early stages of a starburst episode. Contributions to the X-ray emission come from discrete point sources and extended diffuse emission, in the form of what appear to be multiple superbubbles, and smaller bubbles probably associated with individual star clusters. Chandra detects 17 sources within the optical extent of NGC5253 down to a completeness level corresponding to a luminosity of 1.5E37 erg/s.The slope of the point source X-ray luminosity function is -0.54, similar to that of other nearby dwarf starburst galaxies. Several different types of source are detected within the galaxy, including X-ray binaries and the emission associated with star-clusters. Comparison of the diffuse X-ray emission with the observed Halpha emission shows similarities in their extent. The best spectral fit to the diffuse emission is obtained with an absorbed, two temperature model giving temperatures for the two gas components of ~0.24keV and ~0.75keV.The derived parameters of the diffuse X-ray emitting gas are as follows: a total mass of \~1.4E6 f^{1/2} Msun, where f is the volume filling factor of the X-ray emitting gas, and a total thermal energy content for the hot X-ray emitting gas of \~3.4E54 f^{1/2} erg. The pressure in the diffuse gas is P/k ~ 1E6f^{-1/2}K/cm3. We find that these values are broadly commensurate with the mass and energy injection from the starburst population. Analysis of the kinematics of the starburst region suggest that the stellar ejecta contained within it can escape the gravitational potential well of the galaxy, and pollute the surrounding IGM.