skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: CROSS-CORRELATING THE γ-RAY SKY WITH CATALOGS OF GALAXY CLUSTERS

Abstract

In this article, we report the detection of a cross-correlation signal between Fermi Large Area Telescope diffuse γ-ray maps and catalogs of clusters. In our analysis, we considered three different catalogs: WHL12, redMaPPer, and PlanckSZ. They all show a positive correlation with different amplitudes, related to the average mass of the objects in each catalog, which also sets the catalog bias. The signal detection is confirmed by the results of a stacking analysis. The cross-correlation signal extends to rather large angular scales, around 1°, that correspond, at the typical redshift of the clusters in these catalogs, to a few to tens of megaparsecs, i.e., the typical scale-length of the large-scale structures in the universe. Most likely this signal is contributed by the cumulative emission from active galactic nuclei (AGNs) associated with the filamentary structures that converge toward the high peaks of the matter density field in which galaxy clusters reside. In addition, our analysis reveals the presence of a second component, more compact in size and compatible with a point-like emission from within individual clusters. At present, we cannot distinguish between the two most likely interpretations for such a signal, i.e., whether it is produced by AGNs inside clusters ormore » if it is a diffuse γ-ray emission from the intracluster medium. Lastly, we argue that this latter, intriguing, hypothesis might be tested by applying this technique to a low-redshift large-mass cluster sample.« less

Authors:
ORCiD logo [1]; ORCiD logo [2];  [3]; ORCiD logo [4]; ORCiD logo [4];  [5];  [6]
  1. Universita degli Studi Roma Tre (Italy); INFN, Sezione di Roma Tre (Italy); INAF Osservatorio Astronomico di Roma, Osservatorio Astronomico di Roma (Italy)
  2. The University of Manchester, Alan Turing Building (United Kingdom). Jodrell Bank Centre for Astrophysics
  3. RWTH Aachen University (Germany). Institute for Theoretical Particle Physics and Cosmology
  4. Universita di Torino (Italy). Dipartimento di Fisica; Istituto Nazionale di Fisica Nucleare, Sezione di Torino (Italy)
  5. INAF Osservatorio Astronomico di Trieste (Italy); SISSA-International School for Advanced Studies, Trieste (Italy); INFN, Sezione di Trieste (Italy)
  6. Beijing Normal University (China). Department of Astronomy
Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE
Contributing Org.:
Fermi LAT Collaboration
OSTI Identifier:
1355746
Grant/Contract Number:
AC02-76SF00515
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
The Astrophysical Journal. Supplement Series (Online)
Additional Journal Information:
Journal Name: The Astrophysical Journal. Supplement Series (Online); Journal Volume: 228; Journal Issue: 1; Journal ID: ISSN 1538-4365
Publisher:
American Astronomical Society/IOP
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; cosmology; observations; theory; gamma-rays; diffuse backgrounds; large-scale structure of universe

Citation Formats

Branchini, Enzo, Camera, Stefano, Cuoco, Alessandro, Fornengo, Nicolao, Regis, Marco, Viel, Matteo, and Xia, Jun-Qing. CROSS-CORRELATING THE γ-RAY SKY WITH CATALOGS OF GALAXY CLUSTERS. United States: N. p., 2017. Web. doi:10.3847/1538-4365/228/1/8.
Branchini, Enzo, Camera, Stefano, Cuoco, Alessandro, Fornengo, Nicolao, Regis, Marco, Viel, Matteo, & Xia, Jun-Qing. CROSS-CORRELATING THE γ-RAY SKY WITH CATALOGS OF GALAXY CLUSTERS. United States. doi:10.3847/1538-4365/228/1/8.
Branchini, Enzo, Camera, Stefano, Cuoco, Alessandro, Fornengo, Nicolao, Regis, Marco, Viel, Matteo, and Xia, Jun-Qing. Wed . "CROSS-CORRELATING THE γ-RAY SKY WITH CATALOGS OF GALAXY CLUSTERS". United States. doi:10.3847/1538-4365/228/1/8. https://www.osti.gov/servlets/purl/1355746.
@article{osti_1355746,
title = {CROSS-CORRELATING THE γ-RAY SKY WITH CATALOGS OF GALAXY CLUSTERS},
author = {Branchini, Enzo and Camera, Stefano and Cuoco, Alessandro and Fornengo, Nicolao and Regis, Marco and Viel, Matteo and Xia, Jun-Qing},
abstractNote = {In this article, we report the detection of a cross-correlation signal between Fermi Large Area Telescope diffuse γ-ray maps and catalogs of clusters. In our analysis, we considered three different catalogs: WHL12, redMaPPer, and PlanckSZ. They all show a positive correlation with different amplitudes, related to the average mass of the objects in each catalog, which also sets the catalog bias. The signal detection is confirmed by the results of a stacking analysis. The cross-correlation signal extends to rather large angular scales, around 1°, that correspond, at the typical redshift of the clusters in these catalogs, to a few to tens of megaparsecs, i.e., the typical scale-length of the large-scale structures in the universe. Most likely this signal is contributed by the cumulative emission from active galactic nuclei (AGNs) associated with the filamentary structures that converge toward the high peaks of the matter density field in which galaxy clusters reside. In addition, our analysis reveals the presence of a second component, more compact in size and compatible with a point-like emission from within individual clusters. At present, we cannot distinguish between the two most likely interpretations for such a signal, i.e., whether it is produced by AGNs inside clusters or if it is a diffuse γ-ray emission from the intracluster medium. Lastly, we argue that this latter, intriguing, hypothesis might be tested by applying this technique to a low-redshift large-mass cluster sample.},
doi = {10.3847/1538-4365/228/1/8},
journal = {The Astrophysical Journal. Supplement Series (Online)},
number = 1,
volume = 228,
place = {United States},
year = {Wed Jan 18 00:00:00 EST 2017},
month = {Wed Jan 18 00:00:00 EST 2017}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record

Citation Metrics:
Cited by: 3works
Citation information provided by
Web of Science

Save / Share:
  • We report the detection of a cross-correlation signal between Fermi Large Area Telescope diffuse γ -ray maps and catalogs of clusters. In our analysis, we considered three different catalogs: WHL12, redMaPPer, and PlanckSZ. They all show a positive correlation with different amplitudes, related to the average mass of the objects in each catalog, which also sets the catalog bias. The signal detection is confirmed by the results of a stacking analysis. The cross-correlation signal extends to rather large angular scales, around 1°, that correspond, at the typical redshift of the clusters in these catalogs, to a few to tens ofmore » megaparsecs, i.e., the typical scale-length of the large-scale structures in the universe. Most likely this signal is contributed by the cumulative emission from active galactic nuclei (AGNs) associated with the filamentary structures that converge toward the high peaks of the matter density field in which galaxy clusters reside. In addition, our analysis reveals the presence of a second component, more compact in size and compatible with a point-like emission from within individual clusters. At present, we cannot distinguish between the two most likely interpretations for such a signal, i.e., whether it is produced by AGNs inside clusters or if it is a diffuse γ -ray emission from the intracluster medium. We argue that this latter, intriguing, hypothesis might be tested by applying this technique to a low-redshift large-mass cluster sample.« less
  • Building on our previous cross-correlation analysis (Xia et al. 2011) between the isotropic γ-ray background (IGRB) and different tracers of the large-scale structure of the universe, we update our results using 60 months of data from the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope (Fermi). For this study, we perform a cross-correlation analysis both in configuration and spherical harmonics space between the IGRB and objects that may trace the astrophysical sources of the IGRB: QSOs in the Sloan Digital Sky Survey (SDSS) DR6, the SDSS DR8 Main Galaxy Sample, luminous red galaxies (LRGs) in the SDSS catalog, infrared-selected galaxies in the Two Micron All Sky Survey (2MASS), and radio galaxies in the NRAO VLA Sky Survey (NVSS). The benefit of correlating the Fermi-LAT signal with catalogs of objects at various redshifts is to provide tomographic information on the IGRB, which is crucial in separating the various contributions and clarifying its origin. The main result is that, unlike in our previous analysis, we now observe a significant (>3.5σ) cross-correlation signal on angular scales smaller than 1° in the NVSS, 2MASS, and QSO cases and, at lower statistical significance (~3.0σ), with SDSS galaxies. The signal is stronger in two energy bands, E > 0.5 GeV and E > 1 GeV, but it is also seen at E > 10 GeV. No cross-correlation signal is detected between Fermi data and the LRGs. These results are robust against the choice of the statistical estimator, estimate of errors, map cleaning procedure, and instrumental effects. Finally, we test the hypothesis that the IGRB observed by Fermi-LAT originates from the summed contributions of three types of unresolved extragalactic sources: BL Lacertae objects (BL Lacs), flat spectrum radio quasars (FSRQs), and star-forming galaxies (SFGs). Finally, we find that a model in which the IGRB is mainly produced by SFGs (more » $$72_{-37}^{+23}$$% with 2σ errors), with BL Lacs and FSRQs giving a minor contribution, provides a good fit to the data. We also consider a possible contribution from misaligned active galactic nuclei, and we find that, depending on the details of the model and its uncertainty, they can also provide a substantial contribution, partly degenerate with the SFG one.« less
  • The data in the Zwicky and Abell galaxy catalogs are inhomogeneous because the observing conditions vary from plate to plate. A simple statistical method is developed for analyzing this inhomogeneity by comparing the fluctuations in the count of clusters within a plate and the analogous fluctuations in the count from one plate to the next. Examination of samples drawn from the two catalogs shows that inhomogeneity of the data contributes significantly to the dispersion in the counts of clusters. In previous research, neglect of this fact and inadequate allowance for irregular absorption has led to the erroneous inference that manymore » clusters belong to superclusters of galaxies. There is evidence for appreciable inhomogeneity in the magnitude estimates of Zwicky galaxies with m in the range 15/sup m/.4--15/sup m/.7. The problem of inhomogeneous data within a single plate is discussed briefly.« less
  • We present our measurement of the 'bulk flow' using the kinetic Sunyaev-Zel'dovich (kSZ) effect in the Wilkinson Microwave Anisotropy Probe (WMAP) seven-year data. As the tracer of peculiar velocities, we use Planck Early Sunyaev-Zel'dovich Detected Cluster Catalog and a compilation of X-ray-detected galaxy cluster catalogs based on ROSAT All-Sky Survey. We build a full-sky kSZ template and fit it to the WMAP data in W band. Using a Wiener filter we maximize the signal-to-noise ratio of the kSZ cluster signal in the data. We find no significant detection of the bulk flow, and our results are consistent with the {Lambda}CDMmore » prediction.« less
  • We compare the measured angular cross-correlation between the Fermi-Large Area Telescope γ-ray sky and catalogs of extragalactic objects with the expected signal induced by weakly interacting massive particle (WIMP) dark matter (DM). We include a detailed description of the contribution of astrophysical γ-ray emitters such as blazars, misaligned active galactic nucleus (AGN), and star-forming galaxies, and perform a global fit to the measured cross-correlation. Five catalogs are considered: Sloan Digital Sky Survey (SDSS)-DR6 quasars, Two Micron All Sky Survey galaxies, NRAO VLA Sky Survey radio galaxies, SDSS-DR8 Luminous Red Galaxies, and the SDSS-DR8 main galaxy sample. To model the cross-correlation signal,more » we use the halo occupation distribution formalism to estimate the number of galaxies of a given catalog in DM halos and their spatial correlation properties. We discuss uncertainties in the predicted cross-correlation signal arising from the DM clustering and WIMP microscopic properties, which set the DM γ-ray emission. The use of different catalogs probing objects at different redshifts significantly reduces, though not completely, the degeneracy among the different γ-ray components. We find that the presence of a significant WIMP DM signal is allowed by the data but not significantly preferred by the fit, although this is mainly due to a degeneracy with the misaligned AGN component. With modest substructure boost, the sensitivity of this method excludes thermal annihilation cross sections at 95% level for WIMP masses up to few tens of GeV. Constraining the low-redshift properties of astrophysical populations with future data will further improve the sensitivity to DM.« less