Clustering properties of TGSS radio sources
  We investigate the clustering properties of radio sources in the Alternative
Data Release 1 of the TIFR GMRT Sky Survey (TGSS), focusing on large angular
scales, where previous analyses have detected a large clustering signal. After
appropriate data selection, the TGSS sample we use contains ~110,000 sources
selected at 150 MHz over ~70% of the sky. The survey footprint is largely
superimposed on that of the NRAO VLA Sky Survey (NVSS) with the majority of
TGSS sources having a counterpart in the NVSS sample. These characteristics
make TGSS suitable for large-scale clustering analyses and facilitate the
comparison with the results of previous studies. In this analysis we focus on
the angular power spectrum, although the angular correlation function is also
computed to quantify the contribution of multiple-component radio sources. We
find that on large angular scales, corresponding to multipoles $2 \leq \ell
\leq 30$, the amplitude of the TGSS angular power spectrum is significantly
larger than that of the NVSS. We do not identify any observational systematic
effects that may explain this mismatch. We have produced a number of physically
motivated models for the TGSS angular power spectrum and found that all of them
fail to match observations, even when taking into account observational and
theoretical uncertainties. The same models provide a good fit to the angular
spectrum of the NVSS sources. These results confirm the anomalous nature of the
TGSS large-scale power, which has no obvious physical origin and seems to
indicate that unknown systematic errors are present in the TGSS dataset.
