Draft Outline of VISTA Hemisphere Survey v3
-------------------------------------------------


Changes since v2 
fixed error in sensitivities
Y 60sec(5sig) changed from 21.0 to 20.6
Add H band sensitivity information.


The current version is here:
http://www.ast.cam.ac.uk/~rgm/vista/vhs/

See also: VISTA Surveys website here:
http://wiki.astrogrid.org/bin/view/VISTA/

A group of us from the UK VISTA consortium propose to submit a
proposal for an ESO Public Survey with VISTA. One medium term 
goals is to provide IR coverage in 4 bands (ZYJK) of the VST 
ATLAS surveyregion as outlined in the ATLAS proposal. The long 
term goal is to provide an IR survey in at least two wavebands 
over the whole Southern Hemisphere to a depth 4magnitudes fainter 
than DENIS and 2MASS at K. The proposal will use the poorer than 
median seeing eg 60-90% seeing i.e 0.8 to 1.4 arc secs.

Some of the science goals and baseline technical specifications
are outlined below.

Science Goals:
--------------

o Galactic Genisis and Archaeology

o Lowest mass stars and the nearest stars 

o Constraints on Dark Energy via the Integrated Sachs-Wolfe effect.

o Luminous High redshift quasars as probes of reionization and the
  baryonic content of the high redshift Universe.

o Legacy value, Serendipity and new classes of object.

o Maximising the science return from ESA missions, XMM-Newton,
  Planck, Herschel and GAIA.

o Synergy with other surveys e.g. VST Atlas, WISE, Astro-F

o Add your own science goal here.

Basline Technical Specification for VHS Survey
-----------------------------------------------

---------------------------------------------------------------
Band| Exp  | Area             Total time on sky
    |      |           (no overheads)  With Overheads(40%)
    |(sec) | deg^2        (hr)             (hr)
---------------------------------------------------------------
Z   | 180  |  7,500       750              987
Y   | 180  |  7,500       750              987
J   |  60  | 20,000       663             1005
Ks  |  60  | 20,000       663             1005
---------------------------------------------------------------
Total time               2826             3984
---------------------------------------------------------------

Note:
(i) If the VISTA Galactic Plane Survey is supported the area of 
20,000 degree decreases by around 10% for the J/K part.
(ii) Similarily, KIDS-IR will reduce the ZYJK by a further 
1000deg at high galactic latitude.


Assuming 60-85% seeing deciles =>520hrs available per year;
so the above is a 7year program. Goal to complete
around the time of launch of GAIA and data release for
WISE.

1.0" seeing; 5sigma limits(in 2arcsec diameter aperture)

             5sigma limit
Band Exp   Vega    AB    mJy
 Z   60    21.3   21.8   6.9
 Y   60    20.6   21.6   7.6
 J   60    20.2   21.1  10.0
 H   60    19.2   20.6  19.0
 Ks  60    18.1   20.0  36.3




 o For 180sec add 0.6mags to depth.

 o For 1.4" seeing in 3.0" diameter aperture, exposures
   time to reach the same limits are 50% longer ie. 90secs in
   J/K.

UKIDSS LAS Survey
----------------

Median limits(5sigma in 2arcsec aperture)
        Vega
 Ks     18.2
 H      18.8
 J      19.6
 Y      20.2