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Kovacs A.,Eötvös Loránd University | Kovacs A.,MTA ELTE EIRSA Lendulet Astrophysics Research Group | Szapudi I.,University of Hawaii at Manoa | Granett B.R.,National institute for astrophysics | And 14 more authors.
Proceedings of the International Astronomical Union | Year: 2015

We use a WISE-2MASS-Pan-STARRS1 galaxy catalog to search for a supervoid in the direction of the Cosmic Microwave Background Cold Spot. We obtain photometric redshifts using our multicolor data set to create a tomographic map of the galaxy distribution. The radial density profile centred on the Cold Spot shows a large low density region, extending over 10's of degrees. Motivated by previous Cosmic Microwave Background results, we test for underdensities within two angular radii, 5°, and 15°. Our data, combined with an earlier measurement by Granett et al. 2010, are consistent with a large R void=(192 ± 15)h-1 Mpc (2σ) supervoid with δ ≃ -0.13 ± 0.03 centered at z=0.22 ± 0.01. Such a supervoid, constituting a ∼3.5 σ fluctuation in the ΛCDM model, is a plausible cause for the Cold Spot. © International Astronomical Union 2015.


Szapudi I.,University of Hawaii at Manoa | Kovacs A.,Eötvös Loránd University | Kovacs A.,MTA ELTE EIRSA Lendulet Astrophysics Research Group | Kovacs A.,Autonomous University of Barcelona | And 15 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2015

We use the WISE-2MASS infrared galaxy catalogue matched with Pan-STARRS1 (PS1) galaxies to search for a supervoid in the direction of the cosmic microwave background (CMB) cold spot (CS). Our imaging catalogue has median redshift z ≃ 0.14, and we obtain photometric redshifts from PS1 optical colours to create a tomographic map of the galaxy distribution. The radial profile centred on the CS shows a large low-density region, extending over tens of degrees. Motivated by previous CMB results, we test for underdensities within two angular radii, 5°, and 15°. The counts in photometric redshift bins show significantly low densities at high detection significance, ≳5σ and ≳6σ, respectively, for the two fiducial radii. The line-of-sight position of the deepest region of the void is z ≃ 0.15-0.25. Our data, combined with an earlier measurement by Granett, Szapudi & Neyrinck, are consistent with a large Rvoid = (220 ± 50)h-1 Mpc supervoid with δm ≃ -0.14 ± 0.04 centred at z = 0.22 ± 0.03. Such a supervoid, constituting at least a ≃ 3.3σ fluctuation in a Gaussian distribution of the Λ cold dark matter model, is a plausible cause for the CS. © 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Raffai P.,Columbia University | Raffai P.,Eötvös Loránd University | Raffai P.,MTA ELTE EIRSA Lendulet Astrophysics Research Group | Gondan L.,Eötvös Loránd University | And 7 more authors.
Classical and Quantum Gravity | Year: 2013

We aim to find the optimal site locations for a hypothetical network of 1-3 triangular gravitational-wave telescopes. We define the following N-telescope figures of merit (FoMs) and construct three corresponding metrics: (a) capability of reconstructing the signal polarization; (b) accuracy in source localization; and (c) accuracy in reconstructing the parameters of a standard binary source. We also define a combined metric that takes into account the three FoMs with practically equal weight. After constructing a geomap of possible telescope sites, we give the optimal 2-telescope networks for the four FoMs separately in example cases where the location of the first telescope has been predetermined. We found that based on the combined metric, placing the first telescope to Australia provides the most options for optimal site selection when extending the network with a second instrument. We suggest geographical regions where a potential second and third telescope could be placed to get optimal network performance in terms of our FoMs. Additionally, we use a similar approach to find the optimal location and orientation for the proposed LIGO-India detector within a five-detector network with Advanced LIGO (Hanford), Advanced LIGO (Livingston), Advanced Virgo, and KAGRA. We found that the FoMs do not change greatly in sites within India, though the network can suffer a significant loss in reconstructing signal polarizations if the orientation angle of an L-shaped LIGO-India is not set to the optimal value of ∼58.2°( + k × 90°) (measured counterclockwise from East to the bisector of the arms). © 2013 IOP Publishing Ltd.


Hu Y.-M.,University of Glasgow | Raffai P.,Columbia University | Raffai P.,Eötvös Loránd University | Raffai P.,MTA ELTE EIRSA Lendulet Astrophysics Research Group | And 8 more authors.
Classical and Quantum Gravity | Year: 2015

We consider the optimal site selection of future generations of gravitational wave (GW) detectors. Previously, Raffai et al optimized a two-detector network with a combined figure of merit (FoM). This optimization was extended to networks with more than two detectors in a limited way by first fixing the parameters of all other component detectors. In this work we now present a more general optimization that allows the locations of all detectors to be simultaneously chosen. We follow the definition of Raffai et al on the metric that defines the suitability of a certain detector network. Given the locations of the component detectors in the network, we compute a measure of the network's ability to distinguish the polarization, constrain the sky localization and reconstruct the parameters of a GW source. We further define the 'flexibility index' for a possible site location, by counting the number of multi-detector networks with a sufficiently high FoM that include that site location. We confirm the conclusion of Raffai et al, that in terms of the flexibility index as defined in this work, Australia hosts the best candidate site to build a future generation GW detector. This conclusion is valid for either a three-detector network or a five-detector network. For a three-detector network, site locations in Northern Europe display a comparable flexibility index to sites in Australia. However, for a five-detector network, Australia is found to be a clearly better candidate than any other location. © 2015 IOP Publishing Ltd.


Kovacs A.,Eötvös Loránd University | Kovacs A.,MTA ELTE EIRSA Lendulet Astrophysics Research Group | Carron J.,University of Hawaii at Manoa | Szapudi I.,University of Hawaii at Manoa
Monthly Notices of the Royal Astronomical Society | Year: 2013

The recent data release of ESA's Planck mission together with earlier Wilkinson Microwave Anisotropy Probe (WMAP) releases provide the first opportunity to compare high-resolution full sky cosmic microwave background (CMB) temperature anisotropy maps. To quantify the coherence of these maps beyond the power spectrum, we introduce Generalized Phases in the sense of SO(3), unit vectors in the 2l + 1 dimensional representation spaces. For an isotropic Gaussian distribution, Generalized Phases point to random directions and if there is non-Gaussianity, they represent most of the non-Gaussian information. The alignment of these unit vectors from two maps can be characterized by their angle, 0° expected for full coherence, and 90° for random vectors. We analyse maps from both missions with the same mask and Nside = 512 resolution, and compare both power spectra and Generalized Phases.We find excellent agreement of the Generalized Phases of Planck Spectral Matching Independent Component Analysis map with that of the WMAP Q, V, W maps, rejecting the null hypothesis of no correlations at 5σ for l < 700, l < 900 and l < 1100, respectively, except perhaps for l < 10. Using foreground reduced maps for WMAP increases the phase-coherence. The observed coherence angles can be explained with a simple assumption of Gaussianity and a WMAP noise model neglecting Planck noise, except for low-intermediate l values there is a slight, but significant offset, depending on the WMAP band. On the same scales WMAP power spectrum is about 2.6 per cent higher at a very high significance, while at higher l ranges there appears to be no significant bias. Using our theoretical tools, we predict the phase alignment of Planck with a hypothetical perfect noiseless CMB experiment, finding decoherence at l ≠ 2900; below this value Planck can be used most efficiently to constrain non-Gaussianity. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Kovacs A.,Eötvös Loránd University | Kovacs A.,MTA ELTE EIRSA Lendulet Astrophysics Research Group | Szapudi I.,University of Hawaii at Manoa | Szapudi I.,MTA ELTE EIRSA Lendulet Astrophysics Research Group | And 2 more authors.
Astronomische Nachrichten | Year: 2013

We performed a comprehensive statistical analysis using complex phases of the alm coefficients computed from the most recent data of the Wilkinson Microwave Anisotropy Probe (WMAP). Our alm was to confirm or constrain the presence of non-Gaussianities in the data. We found phase correlations - that suggest non-Gaussianity - at high l in alm coefficients by applying various statistical tests. Most of all, we detected a non-Gaussian signal reaching a significance of 4.7σ using random walk statistics and simulations. However, our conclusion is that the non-Gaussian behavior is due to contamination from galactic foregrounds that show up in small scales only. When masked out the contaminated regions, we found no significant non-Gaussianity. Furthermore, we constrained the fNL parameter using CMB simulations that mimic primordial non-Gaussianity. Our estimate is fNL = 40 ± 200, in agreement with previous measurements and inflationary expectations. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Kovacs A.,Eötvös Loránd University | Kovacs A.,MTA ELTE EIRSA Lendulet Astrophysics Research Group | Szapudi I.,University of Hawaii at Manoa | Granett B.R.,National institute for astrophysics | And 2 more authors.
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2013

We measured the cross-correlation of the Wilkinson Microwave Anisotropy Probe (WMAP) 7-year temperature map and the full sky data release of the Wide-field Infrared Survey Explorer galaxy map. Using careful map-making and masking techniques we find a positive crosscorrelation signal. The results are fully consistent with a λCDM universe, although not statistically significant. Our findings are robust against changing the Galactic latitude cut from |b| > 10° to |b| > 20° and no colour dependence was detected when we used WMAP Q, V or W maps.We confirm higher significance correlations found in the preliminary data release. The change in significance is consistent with cosmic variance. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


Kovacs A.,Autonomous University of Barcelona | Kovacs A.,MTA ELTE EIRSA Lendulet Astrophysics Research Group | Szapudi I.,University of Hawaii at Manoa
Monthly Notices of the Royal Astronomical Society | Year: 2015

We combine photometric information of the Wide-Field Infrared Survey Explorer (WISE) and Two Micron All Sky Survey (2MASS) all-sky infrared data bases, and demonstrate how to produce clean and complete galaxy catalogues for future analyses. Adding 2MASS colours to WISE photometry improves star-galaxy separation efficiency substantially at the expense of losing a small fraction of the galaxies. We find that 93 per cent of the WISE objects within W1 < 15.2 mag have a 2MASS match, and that a class of supervised machine learning algorithms, support vector machines (SVM), are efficient classifiers of objects in our multicolour data set. We constructed a training set from the Sloan Digital Sky Survey PhotoObj table with known star-galaxy separation, and determined redshift distribution of our sample from the Galaxy and Mass Assembly spectroscopic survey. Varying the combination of photometric parameters input into our algorithm we show that W1WISE - J2MASS is a simple and effective star-galaxy separator, capable of producing results comparable to the multidimensional SVM classification. We present a detailed description of our star-galaxy separation methods, and characterize the robustness of our tools in terms of contamination, completeness, and accuracy. We explore systematics of the full sky WISE-2MASS galaxy map, such as contamination from moon glow. We show that the homogeneity of the full sky galaxy map is improved by an additional J2MASS < 16.5 mag flux limit. The all-sky galaxy catalogue we present in this paper covers 21 200 deg2 with dusty regions masked out, and has an estimated stellar contamination of 1.2 per cent and completeness of 70.1 per cent among 2.4 million galaxies with zmed ≈ 0.14. WISE-2MASS galaxy maps with well controlled stellar contamination will be useful for spatial statistical analyses, including cross-correlations with other cosmological random fields, such as the cosmic microwave background. The same techniques also yield a statistically controlled sample of stars as well. © 2015 The Authors.


Raffai P.,Eötvös Loránd University | Raffai P.,MTA ELTE EIRSA Lendulet Astrophysics Research Group | Haiman Z.,Columbia University | Frei Z.,Eötvös Loránd University | Frei Z.,MTA ELTE EIRSA Lendulet Astrophysics Research Group
Monthly Notices of the Royal Astronomical Society | Year: 2016

We propose an observational test for gravitationally recoiling supermassive black holes (BHs) in active galactic nuclei, based on a correlation between the velocities of BHs relative to their host galaxies, |Δv|, and their obscuring dust column densities, Σdust (both measured along the line of sight).We use toy models for the distribution of recoil velocities, BHtrajectories, and the geometry of obscuring dust tori in galactic centres, to simulate 2.5 × 105 random observations of recoiling quasars. BHs with recoil velocities comparable to the escape velocity from the galactic centre remain bound to the nucleus, and do not fully settle back to the centre of the torus due to dynamical friction in a typical quasar lifetime. We find that |Δv| and Σdust for these BHs are positively correlated. For obscured (Σdust > 0) and for partially obscured (0 < Σdust ≲ 2.3 gm-2) quasars with |Δv| ≥ 45 km s-1, the sample correlation coefficient between log10(|Δv|) and Σdust is r45 = 0.28 ± 0.02 and r45 = 0.13 ± 0.02, respectively. Allowing for random ±100 km s-1 errors in |Δv| unrelated to the recoil dilutes the correlation for the partially obscured quasars to r45 = 0.026 ± 0.004 measured between |Δv| and Σdust. A random sample of ≳ 3500 obscured quasars with |Δv| = 45 km s-1 would allow rejection of the no-correlation hypothesis with 3s significance 95 per cent of the time. Finally, we find that the fraction of obscured quasars, Fobs (|Δv|), decreases with |Δv| from Fobs (<10 km s-1) ≳ 0.8 to Fobs (>103 km s-1) ≲ 0.4. This predicted trend can be compared to the observed fraction of type II quasars, and can further test combinations of recoil, trajectory, and dust torus models. © 2015 The Authors.

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