VISION - Vienna survey in Orion I. VISTA Orion A Survey
  Orion A hosts the nearest massive star factory, thus offering a unique
opportunity to resolve the processes connected with the formation of both low-
and high-mass stars. Here we present the most detailed and sensitive
near-infrared (NIR) observations of the entire molecular cloud to date. With
the unique combination of high image quality, survey coverage, and sensitivity,
our NIR survey of Orion A aims at establishing a solid empirical foundation for
further studies of this important cloud. In this first paper we present the
observations, data reduction, and source catalog generation. To demonstrate the
data quality, we present a first application of our catalog to estimate the
number of stars currently forming inside Orion A and to verify the existence of
a more evolved young foreground population. We used the European Southern
Observatory's (ESO) Visible and Infrared Survey Telescope for Astronomy (VISTA)
to survey the entire Orion A molecular cloud in the NIR $J, H$, and $K_S$
bands, covering a total of $\sim$18.3 deg$^2$. We implemented all data
reduction recipes independently of the ESO pipeline. Estimates of the young
populations toward Orion A are derived via the $K_S$-band luminosity function.
Our catalog (799995 sources) increases the source counts compared to the Two
Micron All Sky Survey by about an order of magnitude. The 90% completeness
limits are 20.4, 19.9, and 19.0 mag in $J, H$, and $K_S$, respectively. The
reduced images have 20% better resolution on average compared to pipeline
products. We find between 2300 and 3000 embedded objects in Orion A and confirm
that there is an extended foreground population above the Galactic field, in
agreement with previous work. The Orion A VISTA catalog represents the most
detailed NIR view of the nearest massive star-forming region and provides a
fundamental basis for future studies of star formation processes toward Orion.
