Title: Radio Galaxy Zoo: Cosmological Alignment of Radio Sources,
Abstract: We study the mutual alignment of radio sources within two surveys, FIRST and
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 $7\,000$ and $17\,000$ square degrees. The
identification of the sources in the FIRST sample was performed in advance by
volunteers of the Radio Galaxy Zoo 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 $2.5°$ 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 $1.5°$ the alignment is maximal. For one third of the sources,
the Radio Galaxy Zoo volunteers identified an optical counterpart. Assuming a
flat $\Lambda$CDM cosmology with $\Omega_m = 0.31, \Omega_\Lambda = 0.69$, 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 $1.4$
deg$^2$ 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.