Large-scale clustering amongst Fermi blazars; evidence for axis alignments?

Abstract

We find evidence for large-scale clustering amongst Fermi-selected BL Lac objects but not amongst Fermi-selected FSRQs. Using two-point correlation functions we have investigated the clustering properties of different classes of objects from the Fermi LAT 4FGL catalogue. We wanted to test the idea based on optical polarization observations that there might be large volumes of space in which AGN axes are aligned. To do this we needed a clean sample of blazars as these are objects with their jet axes pointing towards the observer and Fermi sources provide such a sample. We find that high latitude Fermi sources taken as a whole show a significant clustering signal on scales up to 30 degrees. To investigate if all blazars behave in the same way we used the machine learning classifications of Kovacevic, et al. (2020), which are based only on gamma-ray information, to separate BL Lac-like objects from FSRQ-like objects. A possible explanation for the clustering signal we find amongst the BL Lac-like objects is that there are indeed large volumes of space in which AGN axes are aligned. This signal might be washed out in FSRQs since they occupy a much larger volume of space. Thus our results support the idea that large scale polarization alignments could originate from coherent alignments of AGN axes. We speculate that these axis alignments may be related to the well-known intrinsic alignments of galaxy optical position angles.

References in corpus (43)

• Unified Schemes for Radio-Loud Active Galactic Nuclei
• The Large Area Telescope on the Fermi Gamma-ray Space Telescope Mission
• Fermi Large Area Telescope Fourth Source Catalog
• Statistical Analysis of Galaxy Surveys - I. Robust error estimation for 2-point clustering statistics
• Galaxy alignments: An overview
• A Test of the Cosmological Principle with Quasars
• Mapping extreme-scale alignments of quasar polarization vectors
• A halo model for intrinsic alignments of galaxy ellipticities
• A structure in the early universe at z ~ 1.3 that exceeds the homogeneity scale of the R-W concordance cosmology
• Intrinsic alignments of galaxies in the Horizon-AGN cosmological hydrodynamical simulation
• The Cosmic Radio Dipole: Estimators and Frequency Dependence
• Fractal Dimension as a measure of the scale of Homogeneity
• Alignment of quasar polarizations with large-scale structures
• Possible structure in the GRB sky distribution at redshift two
• Quantifying angular clustering in wide-area radio surveys
• Alignments of Radio Galaxies in Deep Radio Imaging of ELAIS N1
• A giant ring-like structure at 0.78<z<0.86 displayed by GRBs
• New data support the existence of the Hercules-Corona Borealis Great Wall
• Angular correlation function of 1.5 million LRGs: clustering evolution and a search for BAO
• Power spectrum of halo intrinsic alignments in simulations
• Unveiling the Intrinsic Alignment of Galaxies with Self-Calibration and DECaLS DR3 data
• Large Scale Structure of the Universe
• The polarization in the JVAS/CLASS flat-spectrum radio sources: II. A search for aligned radio polarizations
• Evaluating the optical classification of Fermi BCUs using machine learning
• Radio and optical orientations of galaxies
• Intrinsic alignment statistics of density and velocity fields at large scales: Formulation, modeling, and baryon acoustic oscillation features
• Angular clustering in the SUMSS radio survey
• Radio Galaxy Zoo: Cosmological Alignment of Radio Sources
• The clustering of gamma-ray bursts in the Hercules-Corona Borealis Great Wall: the largest structure in the Universe?
• Polarization alignments of radio quasars in JVAS/CLASS surveys
• Evidence for the alignment of quasar radio polarizations with large quasar group axes
• Measuring the cosmic homogeneity scale with SDSS-IV DR16 Quasars
• Classification of Blazar Candidates of Uncertain Type from the Fermi LAT 8-Year Source Catalog with an Artificial Neural Network
• Evolutionary Map of the Universe: Tracing Clusters to High Redshift
• Angular clustering of point sources at 150 MHz in the TGSS survey
• The clustering of X-ray AGN at 0.5 < z < 4.5: host galaxies dictate dark matter halo mass
• Evidence of isotropy at large-scale from polarizations of radio sources
• Clustering of gamma-ray selected 2LAC Fermi Blazars
• Alignment of Radio Galaxy Axes using FIRST Catalogue
• Compatibility of the Large Quasar Groups with the Concordance Cosmological Model
• Alignment in the orientation of LOFAR radio sources
• Galaxy Alignments with Surrounding Structure in the Sloan Digital Sky Survey
• Testing the Alignment Tendency of Some Polarized Radio Sources

Cited by in corpus (7)

• Is the Observable Universe Consistent with the Cosmological Principle?
• A Giant Arc on the Sky
• Analysis of spin directions of galaxies in the DESI Legacy Survey
• The Scale of Homogeneity in the $R_h=ct$ Universe
• Analysis of $\sim 10^6$ spiral galaxies from four telescopes shows large-scale patterns of asymmetry in galaxy spin directions
• Large-scale asymmetry in the distribution of galaxy spin directions -- analysis and reproduction
• Scanning the Universe for Large-Scale Structures using Gamma-Ray Bursts