Characterization of unresolved and unclassified sources detected in
  radio continuum surveys of the Galactic plane
  The continuum emission from 1 to 2 GHz of The HI/OH/Recombination line survey
of the inner Milky Way (THOR) at $\lesssim$18" resolution covers $\sim 132$
square degrees of the Galactic plane and detects 10387 sources. Similarly, the
first data release of the Global View of Star Formation in the Milky Way
(GLOSTAR) surveys covers $\sim 16$ square degrees of the Galactic plane from
4-8 GHz at 18" resolution and detects 1575 sources. However, a large fraction
of the unresolved discrete sources detected in these radio continuum surveys of
the Galactic plane remain unclassified. Here, we study the Euclidean-normalized
differential source counts of unclassified and unresolved sources detected in
these surveys and compare them with simulated extragalactic radio source
populations as well as previously established source counts. We find that the
differential source counts for THOR and GLOSTAR surveys are in excellent
agreement with both simulation and previous observations. We also estimate the
angular two-point correlation function of unclassified and unresolved sources
detected in THOR survey. We find a higher clustering amplitude in comparison
with the Faint Images of the Radio Sky at Twenty-cm (FIRST) survey up to the
angular separation of $5^{\circ}$. The decrease in angular correlation with
increasing flux cut and the excellent agreement of clustering pattern of
sources above 1 mJy with high $z$ samples ($z >0.5$) of the FIRST survey
indicates that these sources might be high $z$ extragalactic compact objects.
The similar pattern of one-point and two-point statistics of unclassified and
compact sources with extragalactic surveys and simulations confirms the
extragalactic origin of these sources.
