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, $5^\circ$, and $15^\circ$. Our data, combined with an
earlier measurement by Granett et al 2010, are consistent with a large $R_{\rm
void}=(192 \pm 15)h^{-1} Mpc $ $(2\sigma)$ supervoid with $\delta \simeq -0.13
\pm 0.03$ centered at $z=0.22\pm0.01$. Such a supervoid, constituting a
$\sim3.5 \sigma$ fluctuation in the $\Lambda CDM$ model, is a plausible cause
for the Cold Spot.Comment: 4 pages, 2 figures, Proceedings of IAU 306 Symposium: Statistical
  Challenges in 21st Century Cosmolog

Burgett, Will

Cole, Shaun

Draper, Peter W.

Farrow, Daniel J.

Frei, Zsolt

Granett, Benjamin R.

Kaiser, Nicholas

Kovács, András

Magnier, Eugene A.

Metcalfe, Nigel

Morgan, Jeffrey S.

Price, Paul

Silk, Joseph

Szapudi, István

Tonry, John

Wainscoat, Richard

English

arXiv

AbstractWe 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 Rvoid=(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.</jats:p

András Kovács

István Szapudi

Benjamin R. Granett

Zsolt Frei

Joseph Silk

Will Burgett

Shaun Cole

Peter W. Draper

Daniel J. Farrow

Nicholas Kaiser

Eugene A. Magnier

Nigel Metcalfe

Jeffrey S. Morgan

Paul Price

John Tonry

Richard Wainscoat

Crossref

Proceedings of the International Astronomical Union

Supervoid Origin of the Cold Spot in the Cosmic Microwave Background

Granett, Benjamin R

Draper, Peter W

Farrow, Daniel J

Magnier, Eugene A

Morgan, Jeffrey S

ELTE Digital Institutional Repository (EDIT)

arXiv:1407.1470v1  [astro-ph.CO]  6 Jul 2014Statistical Challenges in 21st Century CosmologyProceedings IAU Symposium No. 306, 2014A.C. Editor, B.D. Editor & C.E. Editor, eds.c© 2014 International Astronomical UnionDOI: 00.0000/X000000000000000XSupervoid Origin of the Cold Spot in theCosmic Microwave BackgroundAndrás Kovács1,2, István Szapudi3, Benjamin R. Granett4, ZsoltFrei1,2, Joseph Silk5, Will Burgett3, Shaun Cole6, Peter W. Draper6,Daniel J. Farrow6, Nicholas Kaiser3, Eugene A. Magnier3, NigelMetcalfe6, Jeffrey S. Morgan3, Paul Price7, John Tonry3, RichardWainscoat31 Institute of Physics, Eötvös Loránd University, 1117 Pázmány Péter sétány 1/A Budapest,Hungary2 MTA-ELTE EIRSA ”Lendület” Astrophysics Research Group, 1117 Pázmány Péter sétány1/A Budapest, Hungary3 Institute for Astronomy, University of Hawaii 2680 Woodlawn Drive, Honolulu, HI, 96822,USA4INAF OA Brera, Via E. Bianchi 46, Merate, Italy5Department of Physics and Astronomy, The Johns Hopkins University, Baltimore MD 21218,USA6Department of Physics, Durham University, South Road, Durham DH1 3LE, UK7Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544Abstract. We use a WISE-2MASS-Pan-STARRS1 galaxy catalog to search for a supervoid inthe direction of the Cosmic Microwave Background Cold Spot. We obtain photometric redshiftsusing our multicolor data set to create a tomographic map of the galaxy distribution. Theradial density profile centred on the Cold Spot shows a large low density region, extendingover 10’s of degrees. Motivated by previous Cosmic Microwave Background results, we testfor underdensities within two angular radii, 5◦, and 15◦. Our data, combined with an earliermeasurement by Granett et al. 2010, are consistent with a large Rvoid = (192±15)h−1Mpc (2σ)supervoid with δ ≃ −0.13 ± 0.03 centered at z = 0.22 ± 0.01. Such a supervoid, constituting a∼ 3.5σ fluctuation in the ΛCDM model, is a plausible cause for the Cold Spot.Keywords. cosmic microwave background, observations, large-scale structure of universe1. IntroductionThe Cosmic Microwave Background (CMB) Cold Spot (CS) is an exceptionally coldarea centered on on (l, b) ≃ (209◦,−57◦) and was first detected in the Wilkinson Mi-crowave Anisotropy Probe (Bennett et al. 2012) at ≃ 3σ significance using wavelet fil-tering (Vielva et al. 2003). The CS is perhaps the most significant among the anomaliesrecently confirmed by Planck (Planck 2013 results. XXIII.). These physical anomalies aresignificant enough to motivate further studies. Some of the models include exotic physics,e.g., cosmic textures (Cruz et al. 2008), while e.g. Inoue and Silk 2007 claim that the CS,and possibly other anomalies, are caused by the Integrated Sachs-Wolfe effect (ISW) ofthe decaying gravitational potentials, which in turn is caused by Dark Energy. The latterexplanation would require of a large,∼> 200h−1Mpc supervoid centered on the CS, readilydetectable in large scale structure surveys.The supervoid model has been constrained by using radio galaxies of the NVSS survey,Canada-France-Hawaii Telescope (CFHT) imaging of the CS region, redshift survey datausing the VIMOS spectrograph on the VLT, and the relatively shallow 2MASS galaxy12 András Kovács, István Szapudi, Benjamin R. Granett et al.catalogue. See Szapudi et al. 2014, and references therein for review. Although theseworks report a possible underdense region at redshifts z < 0.3, they either run out ofobjects at low redshift, or have no redshifts for tomographic imaging. Note that althoughno void has been found that could fully explain the CS anomaly, there is strong,∼> 4.4σ,statistical evidence that superstructures imprint on the CMB as cold and hot spots(Granett et al. 2008).2. Analysis of WISE-2MASS-PS1 galaxy countsNext we describe some of our methods and procedures, while Szapudi et al. 2014and Finelli et al. 2014 can be consulted for further details. We probe the z ≃ 0.3 red-shift range, unconstrained by previous studies, using the WISE-2MASS galaxy catalog(Kovács and Szapudi 2014) with zmed ≃ 0.14, and 21,200 square degrees of coverage.The catalog contains sources to flux limits of W1WISE 6 15.2 mag and J2MASS 6 16.5mag, resulting in a galaxy sample deeper than 2MASS (Skrutskie et al. 2006) and moreuniform than WISE (Wright et al. 2010).In this projected catalog, we detect an underdensity centred on the Cold Spot. Inparticular, we find signal-to-noise ratios S/N ∼ 12 for rings at our pre-determinedradii, 5◦ and 15◦, and an extended underdensity to ∼ 20◦ with∼> 5σ significance. Atlarger radii, the radial profile is consistent with a supervoid surrounded by a gentlecompensation that converges to the average galaxy density at ∼ 50◦. The supervoid ap-pears to contain an extra depression in its centre, with its own compensation at around≃ 8◦. The projected underdensity in WISE-2MASS is modeled with a ΛLTB model(Garcia-Bellido and Haugbølle 2008) by Finelli et al. 2014.We then set out to create a detailed map of the CS region in three dimensions. There-fore, WISE-2MASS galaxies have been matched with Pan-STARRS1 (Kaiser 2004, PS1)objects within a 50◦ × 50◦ area centred on the CS, except for a Dec > −28.0 cut toconform to the PS1 boundary. We used PV1.2 reprocessing of PS1 in an area of 1,300square degrees. For PS1, we required a proper measurement of Kron and PSF magnitudesin gP1, rP1 and iP1 bands that were used to construct photometric redshifts (photo-z’s)with a Support Vector Machine algorithm. The training and control sets were createdmatching WISE-2MASS, PS1, and the Galaxy and Mass Assembly Driver et al. 2011(GAMA) redshift survey. Our three dimensional catalog of WISE-2MASS-PS1 galaxiescontains photo-z’s with an estimated error of σz ≈ 0.034. We count galaxies as a func-tion of redshift in disks centred on the CS using the two pre-determined angular radii,R = 5◦, and 15◦. The galaxy density calculated from the average redshift distribution isshown in the upper panel of Fig. 1. Note that the larger disk is not fully contained in ourphoto-z catalog due to the limited PS1 footprint. In photo-z bins of width of ∆z = 0.035,we found S/N ∼ 5 and S/N ∼ 6 for the deepest under-density bins, respectively. Themeasurement errors are due to Poisson fluctuations in the redshift bins. To extend ouranalysis to higher redshifts, we add a previous measurement (Granett et al. 2010) in aphoto-z bin centred at z = 0.4.For a rudimentary understanding of our counts, we build toy models from top-hat voidsin the z direction convolved with the photo-z errors. This model has three parameters,redshift (zvoid), radius (Rvoid), and depth (δg). We carry out the χ2-based maximumlikelihood parameter estimation for R = 15◦, using our first 10 bins combined with theextra bin measured by Granett et al. 2010 for n = 11 data points. We find χ20 = 92.4 forthe null hypothesis of no void. The marginalized results for the parameters of our toymodel are zvoid = 0.22±0.01 (2σ), Rvoid = (192±15)h−1Mpc (2σ), and δg = −0.18±0.01(2σ) finding χ2min = 5.97. We take the bg = 1.41 ± 0.07 galaxy bias of the catalog intoSupervoid at the CMB Cold Spot 30 200 400 600 800 1000Comoving dis ance (h−1 Mpc)−0.6−0.4−0.20.00.2δ gRv=192h−1Mpc, δg=−0.18, z=0.22Rv=250h−1Mpc, δg=−0.20, z=0.25Rv=5◦Rv=15◦Grane   e  al. (2010)0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40Redshif Figure 1. Our measurements of the galaxy density in the line-of-sight using the ∆z = 0.035photo-z bins we defined. We detected a significant depression in galaxy density in r = 5◦ and15◦ test circles. We used our simple modeling tool to examine the effects of photo-z errors, andtest the consistency of simple top-hat voids with our measurements. The last bin (shown ingrey) was excluded from the analysis, and a data point by Granett et al (2010) accounts for thehigher redshift part of the measurement. See text for details.190 195 200 205 210 215 220 225ℓ−75−70−65−60−55−50−45−40b60 µK60 µK60 µKz<0.09−0.24−0.16−0.080.000.080.160.240.32190 195 200 205 210 215 220 225ℓ−75−70−65−60−55−50−45−4060 µK60 µK60 µK0.11<z<0.14−0.24−0.16−0.080.000.080.160.240.320.40190 195 200 205 210 215 220 225ℓ−75−70−65−60−55−50−45−4060 µK60 µK60 µK0.17<z<0.22−0.24−0.16−0.080.000.080.160.240.32Figure 2. Tomographic view of the CS region. Below z < 0.09 appears to show the frontcompensation (higher density area) of the large void, although there is an under dense structureto the right. The slice at 0.11 < z < 0.14 cuts into front of the supervoid, and the ring roundrepresents a slice of the compensation. Finally the slice 0.17 < z < 0.22 cuts into the front halfof the supervoid with compensation around it. Note that the left side of the images reflects themask of the PS1 data set.account finding an average depth of δ = δg/bg ≃ −0.13 ± 0.03 (2σ). While the toymodel quantifies the properties of the void, careful inspection of the Figures reveals acomplex structure. There appears to be a compensation in front of the supervoid ataround z ≃ 0.05 − 0.08, and the significantly deeper counts at the smaller radii showthat the void is deeper at the centre. An approximate tomographic imaging of the CSregion is presented in Fig. 2. in three slices of z < 0.09, 0.11 < z < 0.14, 0.17 < z < 0.22and smoothed at 2◦ scales. The Planck SMICA CMB temperature map is over-plot withcontours. While we characterized the profile in radial bins, the geometry of the supervoidis more complex. It is noteworthy that deepest part of the void is close to the centre ofthe CS in the middle slice. Given the enormous size, the rich structure is expected: thesupervoid contains voids, their compensations, filaments, and appears to have its owncompensation.4 András Kovács, István Szapudi, Benjamin R. Granett et al.3. ConclusionsWe have found strong statistical evidences for a supervoid at redshift z = 0.22± 0.01with radius R = (192± 15)h−1Mpc and depth of δ = −0.13± 0.03 (Szapudi et al. 2014).These parameters are in excellent agreement with the projected density analysis resultsby Finelli et al. 2014, with the redshift slightly closer. We estimated the linear ISWeffect due to such an underdensity from a simple approximation. We found that it couldsignificantly affect the CMB, of order −20 µK, falling short of a full explanation of theCS anomaly. However, a non-linear LTB supervoid based on the projected profile in theWISE-2MASS catalog matches well the profile observed on the CMB (Finelli et al. 2014).The observed alignment and morphological similarity to a compensation is noteworthy.We estimate that the supervoid we detected corresponds to a rare, at least∼> 3.5σ,density fluctuation in ΛCDM; thus chance alignment with another rare structure, theCS, is negligible.AcknowledgmentsWe acknowledge the support of NASA grants NNX12AF83G and NNX10AD53G. AK and ZFacknowledge support from OTKA through grant no. 101666. In addition, AK acknowledges sup-port from the Campus Hungary fellowship program. We make use of HEALPix Gorski et al. 2005software in our project. The Pan-STARRS1 Surveys (PS1) have been made possible through con-tributions by the Institute for Astronomy, the University of Hawaii, the Pan-STARRS ProjectOffice, the Max-Planck Society and its participating institutes, the Max Planck Institute forAstronomy, Heidelberg and the Max Planck Institute for Extraterrestrial Physics, Garching,The Johns Hopkins University, Durham University, the University of Edinburgh, the Queen’sUniversity Belfast, the Harvard-Smithsonian Center for Astrophysics, the Las Cumbres Ob-servatory Global Telescope Network Incorporated, the National Central University of Taiwan,the Space Telescope Science Institute, and the National Aeronautics and Space Administrationunder Grant No. NNX08AR22G issued through the Planetary Science Division of the NASAScience Mission Directorate, the National Science Foundation Grant No. AST-1238877, and theUniversity of Maryland, and Eotvos Lorand University (ELTE).ReferencesInoue, K. T. & Silk, J. 2006, ApJ, 648, 23-30Szapudi, I. and Kovács, A., Granett, B. R., et al. 2014, arXiv:1405.1566Finelli, F., Garcia-Bellido, J., Kovacs, A., Paci, F., and Szapudi, I. 2014, arXiv:1405.1555Kovács, A. and Szapudi, I. 2014, arXiv:1401.0156Garcia-Bellido, J. and Haugbølle, T. 2008, JCAP, 4:3K. M. Gorski, E. Hivon and et al. 2005, Apj, 622:759–771E. L. Wright et al. 2010, AJ, 140:1868–1881B. R. Granett, M. C. Neyrinck, and I. Szapudi 2008, ApjL, 683:L99–L102B. R. Granett, I. Szapudi, and M. C. Neyrinck 2010, Apj, 714:825–833M. F. Skrutskie, R. M. Cutri, R. Stiening, and et al. 2006, AJ, 131:1163–1183C. L. Bennett, D. Larson, and J. L et al. Weiland. 2012 ArXiv e-printsP. Vielva et al. 2004, Apj, 609:22–34.M. Cruz et al. 2008, MNRAS, 390:913–919S. P. Driver, D. T. Hill, and et al. 2011 MNRAS, 413:971–995Planck 2013 results. XXIII. 2013 ArXiv e-printsN. Kaiser. SPIE Conference Series, 2004.

Supervoid Origin of the Cold Spot in the Cosmic Microwave Background

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