Paper pool 2 » History » Version 4
Version 3 (Robert Suhada, 11/27/2012 11:34 AM) → Version 4/7 (Robert Suhada, 12/03/2012 09:34 AM)
h1. Paper pool 2
Interesting papers that are off-topic, controversial or for other reasons not suitable for journal club. We can still discuss them over coffee!
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h2. Cosmology and clusters
h3. A Stacked Analysis of Brightest Cluster Galaxies Observed with the Fermi Large Area Telescope
K. L. Dutson, R. J. White, A. C. Edge, J. A. Hinton, M. T. Hogan
(Submitted on 27 Nov 2012)
We present the results of a search for high-energy gamma-ray emission from a large sample of galaxy clusters sharing the properties of three existing Fermi-LAT detections (in Perseus, Virgo and Abell 3392), namely a powerful radio source within their brightest cluster galaxy (BCG). From a parent, X-ray flux-limited sample of clusters, we select 114 systems with a core-dominated BCG radio flux above 50 or 75 mJy, stacking data from the first 45 months of the Fermi mission, to determine statistical limits on the gamma-ray fluxes of the ensemble of candidate sources. For a >300 MeV selection, the distribution of detection significance across the sample is consistent with that across control samples for significances <3 sigma, but has a tail extending to higher values, including three >4 sigma signals which are not associated with previously identified gamma-ray emission. Modelling of the data in these fields results in the detection of four non-2FGL Fermi sources, though none appear to be unambiguously associated with the BCG candidate. A search at energies >3 GeV hints at emission from the BCG in A 2055, which hosts a BL Lac object. There is no evidence for a signal in the stacked data, and the upper limit derived on the gamma-ray flux of an average radio-bright BCG in the sample is an order-of-magnitude more constraining than that calculated for individual objects. F(1 GeV)/F(1.4 GHz) <15, compared with ~120 for NGC 1275 in Perseus, which might indicate a special case for those objects detected at high energies; that beamed emission from member galaxies comprise the dominant bright gamma-ray sources in clusters.
h3. Excess ellipticity of hot and cold spots in the WMAP data?
Eirik Berntsen, Frode K. Hansen
(Submitted on 22 Nov 2012)
We investigate claims of excess ellipticity of hot and cold spots in the WMAP data (Gurzadyan et al. 2005, 2007). Using the cosmic microwave background data from 7 years of observations by the WMAP satellite, we find, contrary to previous claims of a 10 sigma detection of excess ellipticity in the 3-year data, that the ellipticity of hot and cold spots are perfectly consistent with simulated CMB maps based on the concordance cosmology. We further test for excess obliquity and excess skewness/kurtosis of ellipticity and obliquity and find the WMAP7 data consistent with Gaussian simulated maps.
http://arxiv.org/abs/1211.5275
h2. General interest: Astrophysics
h3. The imminent detection of gravitational waves from massive black-hole binaries with pulsar timing arrays
Sean T. McWilliams, Jeremiah P. Ostriker, Frans Pretorius
(Submitted on 19 Nov 2012)
Recent observations of massive galaxies indicate that they double in mass and quintuple in size between redshift z = 1 and the present, despite undergoing very little star formation, suggesting that galaxy mergers drive the evolution. Since these galaxies will contain supermassive black holes, this suggests a larger black hole merger rate, and therefore a larger gravitational-wave signal, than previously expected. We calculate the merger-driven evolution of the mass function, and find that merger rates are 10 to 30 times higher and gravitational waves are 3 to 5 times stronger than previously estimated, so that the gravitational-wave signal may already be detectable with existing data from pulsar timing arrays. We also provide an explanation for the disagreement with past estimates that were based on dark matter halo simulations.
http://arxiv.org/abs/1211.4590
h2. General interest: Physics
h2. Other
Interesting papers that are off-topic, controversial or for other reasons not suitable for journal club. We can still discuss them over coffee!
{{toc}}
h2. Cosmology and clusters
h3. A Stacked Analysis of Brightest Cluster Galaxies Observed with the Fermi Large Area Telescope
K. L. Dutson, R. J. White, A. C. Edge, J. A. Hinton, M. T. Hogan
(Submitted on 27 Nov 2012)
We present the results of a search for high-energy gamma-ray emission from a large sample of galaxy clusters sharing the properties of three existing Fermi-LAT detections (in Perseus, Virgo and Abell 3392), namely a powerful radio source within their brightest cluster galaxy (BCG). From a parent, X-ray flux-limited sample of clusters, we select 114 systems with a core-dominated BCG radio flux above 50 or 75 mJy, stacking data from the first 45 months of the Fermi mission, to determine statistical limits on the gamma-ray fluxes of the ensemble of candidate sources. For a >300 MeV selection, the distribution of detection significance across the sample is consistent with that across control samples for significances <3 sigma, but has a tail extending to higher values, including three >4 sigma signals which are not associated with previously identified gamma-ray emission. Modelling of the data in these fields results in the detection of four non-2FGL Fermi sources, though none appear to be unambiguously associated with the BCG candidate. A search at energies >3 GeV hints at emission from the BCG in A 2055, which hosts a BL Lac object. There is no evidence for a signal in the stacked data, and the upper limit derived on the gamma-ray flux of an average radio-bright BCG in the sample is an order-of-magnitude more constraining than that calculated for individual objects. F(1 GeV)/F(1.4 GHz) <15, compared with ~120 for NGC 1275 in Perseus, which might indicate a special case for those objects detected at high energies; that beamed emission from member galaxies comprise the dominant bright gamma-ray sources in clusters.
h3. Excess ellipticity of hot and cold spots in the WMAP data?
Eirik Berntsen, Frode K. Hansen
(Submitted on 22 Nov 2012)
We investigate claims of excess ellipticity of hot and cold spots in the WMAP data (Gurzadyan et al. 2005, 2007). Using the cosmic microwave background data from 7 years of observations by the WMAP satellite, we find, contrary to previous claims of a 10 sigma detection of excess ellipticity in the 3-year data, that the ellipticity of hot and cold spots are perfectly consistent with simulated CMB maps based on the concordance cosmology. We further test for excess obliquity and excess skewness/kurtosis of ellipticity and obliquity and find the WMAP7 data consistent with Gaussian simulated maps.
http://arxiv.org/abs/1211.5275
h2. General interest: Astrophysics
h3. The imminent detection of gravitational waves from massive black-hole binaries with pulsar timing arrays
Sean T. McWilliams, Jeremiah P. Ostriker, Frans Pretorius
(Submitted on 19 Nov 2012)
Recent observations of massive galaxies indicate that they double in mass and quintuple in size between redshift z = 1 and the present, despite undergoing very little star formation, suggesting that galaxy mergers drive the evolution. Since these galaxies will contain supermassive black holes, this suggests a larger black hole merger rate, and therefore a larger gravitational-wave signal, than previously expected. We calculate the merger-driven evolution of the mass function, and find that merger rates are 10 to 30 times higher and gravitational waves are 3 to 5 times stronger than previously estimated, so that the gravitational-wave signal may already be detectable with existing data from pulsar timing arrays. We also provide an explanation for the disagreement with past estimates that were based on dark matter halo simulations.
http://arxiv.org/abs/1211.4590
h2. General interest: Physics
h2. Other