ASSESSING THE SIGNIFICANCE OF APPARENT CORRELATIONS BETWEEN RADIO AND GAMMA-RAY BLAZAR FLUXES

• Published in: The Astrophysical journal Vol. 751; no. 2; pp. 1 - 13
• Main Authors: PAVLIDOU, V, RICHARDS, J. L, ZENSUS, J. A, GIROLETTI, M, REIMER, A, HEALEY, S. E, ROMANI, R. W, SHAW, M. S, MAX-MOERBECK, W, KING, O. G, PARSON, T. J, READHEAD, A. C. S, REEVES, R, STEVENSON, M. A, ANGELAKIS, E, FUHRMANN, L
• Format: Journal Article
• Language: English
• Published: Bristol IOP 01-06-2012
• Subjects: Astronomy; ASTROPHYSICS; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; Bins; Blazars; Correlation; CORRELATIONS; COSMIC GAMMA SOURCES; COSMOLOGY; Density; Earth, ocean, space; Exact sciences and technology; FLUX DENSITY; Fluxes; GAMMA RADIATION; LUMINOSITY; QUASARS; Radio; RADIO GALAXIES; RED SHIFT; VARIATIONS; Red shift; Radio galaxies; Luminosity; Blazar; Continuum; Active galaxies; Statistical method; methods: statistical; Gamma radiation; Flux density; galaxies: active; Correlations; Cosmic radio sources; gamma rays: galaxies; Luminosity function; radio continuum: galaxies
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1088/0004-637X/751/2/149

Whether or not a correlation exists between the radio and gamma-ray flux densities of blazars is a long-standing question, and one that is difficult to answer confidently because of various observational biases, which may either dilute or apparently enhance any intrinsic correlation between radio and gamma-ray luminosities. The novelty of the method lies in a combination of data randomization in luminosity space (to ensure that the randomized data are intrinsically, and not just apparently, uncorrelated) and significance assessment in flux space (to explicitly avoid Malmquist bias and automatically account for the limited dynamical range in both frequencies). We show that for a smaller number of redshift bins, the method yields a worse significance, and in this way it is conservative: although it may fail to confirm an existing intrinsic correlation in a small sample that cannot be split into many redshift bins, it will not assign a stronger, artificially enhanced significance.