We study the mutual alignment of radio sources within two surveys, Faint Images of the Radio Sky at Twenty-centimetres (FIRST) and TIFR GMRT Sky Survey (TGSS). This is done by producing two position angle catalogues containing the preferential directions of respectively 30 059 and 11 674 extended sources distributed over more than 7000 and 17 000 deg2. The identification of the sources in the FIRST sample was performed in advance by volunteers of the RadioGalaxy Zoo (RGZ) project, while for the TGSS sample it is the result of an automated process presented here. After taking into account systematic effects, marginal evidence of a local alignment on scales smaller than 2.5 deg is found in the FIRST sample. The probability of this happening by chance is found to be less than 2 per cent. Further study suggests that on scales up to 1.5 deg the alignment is maximal. For one third of the sources, the RGZ volunteers identified an optical counterpart. Assuming a flat Λ cold dark matter cosmology with Ωm = 0.31,ΩΛ = 0.69, we convert the maximum angular scale on which alignment is seen into a physical scale in the range [19, 38] Mpc h 70 -1. This result supports recent evidence reported by Taylor and Jagannathan of radio jet alignment in the 1.4 deg2 ELAIS N1 field observed with the Giant Metrewave Radio Telescope. The TGSS sample is found to be too sparsely populated to manifest a similar signal.
Bibliographical noteFunding Information:
This publication has been made possible by the participation of more than 7000 volunteers in the Radio Galaxy Zoo project. The data in this paper are the result of the efforts of the Radio Galaxy Zoo volunteers. Their efforts are individually acknowledged at http://rgzauthors.galaxyzoo.org. This publication makes use of data product from the Karl G. Jansky Very Large Array. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. This publication makes use of data products from the Wide-field Infrared Survey Explorer (WISE) and the Spitzer Space Telescope. The WISE is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration. SWIRE is supported by NASA through the SIRTF Legacy Program under contract 1407 with the Jet Propulsion Laboratory. We also thank the staffof the GMRT that made possible the observations TGSS is based upon. GMRT is run by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research. FdG is supported by the VENI research programme with project number 1808, which is financed by the Netherlands Organisation for Scientific Research (NWO). Partial support for LR comes from US National Science Foundation grants AST-1211595 and AST-1714205 to the University of Minnesota. HA benefitted from grant DAIP 980/2016-2017 of the University of Guanajuato. Parts of this research were conducted by the Australian Research Council Centre of Excellence for All-sky Astrophysics (CAASTRO), through project number CE110001020
© 2017 The Authors.
- Cosmology: observations
- Galaxies: jets
- Galaxies: statistics
- Large-scale structure of Universe
- Radio continuum: galaxies