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The shape of the curves defined by the counts of radio sources per unit area as a function of their flux density was one of the earliest cosmological probes. Radio source counts continue to be an area of interest, used to study the relative populations of galaxy types in the Universe (as well as investigate any cosmological evolution in luminosity functions). They are a vital consideration for determining how source confusion may limit the depth of a radio interferometer observation, and are essential for characterising extragalactic foregrounds in CMB experiments. There is currently no consensus as to the relative populations of the faintest (sub-mJy) source types, where the counts turn-up. Most of the source counts in this regime are gathered from multiple observations that each use a deep, single pointing with a radio interferometer. These independent measurements show large amounts of scatter (factors ~ a few) that significantly exceeds their stated uncertainties. In this article we use a simulation of the extragalactic radio continuum emission to assess the level at which sample variance may be the cause of the scatter. We find that the scatter induced by sample variance in the simulated counts decreases towards lower flux density bins as the raw source counts increase. The field-to-field variations are significant, and could even be the sole cause at >100 {mu}Jy. We present a method for evaluating the flux density limit that a survey must reach in order to reduce the count uncertainty induced by sample variance to a specific value. We also derive a method for correcting Poisson errors on counts in order to include the uncertainties due to the cosmological clustering of sources. An empirical constraint on the effect of sample variance at these low luminosities is unlikely to arise until the completion of new large-scale surveys with next-generation radio telescopes.
Infrared-faint radio sources (IFRS) are objects that have flux densities of several mJy at 1.4GHz, but that are invisible at 3.6um when using sensitive Spitzer observations with uJy sensitivities. Their nature is unclear and difficult to investigate
We present the multiwavelength properties of 266 cataloged radio sources identified with 20 and 6 cm VLA deep observations of the CDFS at a flux density limit of 42 mu Jy at the field centre at 1.4 GHz. These new observations probe the faint end of b
MOJAVE is a VLBI program which monitors a statistically complete, radio-selected sample of 135 relativistically beamed, flat-spectrum active galactic nuclei for over more than a decade. In order to understand the high-energy behavior of this radio co
It has been speculated that low luminosity radio-loud AGN have the potential to serve as an important source of AGN feedback, and may be responsible for suppressing star-formation activity in massive elliptical galaxies at late times. As such the cos
Binary merging constitutes a complementary mode of galaxy evolution to the canonical hierarchical clustering theory. This merger-driven evolution not only influences the galaxy mass distribution function, but may drive the main galactic activity cycl