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Field Selection

RA = 3  32 28.0 ,   DEC= -27  48 30        (J2000)



The selection of the field was mainly driven by the need of low  HI column density in order to maximize the depth of the CDFS, especially a low energies.  The Leiden/Dwingeloo Survey (Hartmann & Burton, 1997) covers the entire sky with DEC> -30o on a half-degree grid. Since surveys of HI around the SGP are not readily available, the search was limited to the area covered by the Dwingeloo survey.

A quick look at the all-sky HI colour map (Fig.1) shows a South Galactic Hole (SGH), at b=50o  with NH values comparable to the those
in the Lockman Hole (~0.7x1020 cm2).
 
 

Fig.1 - Leiden/Dwingeloo HI Survey in galactic coordinates.





Fig.2 shows NH contours in a 5x5 degrees area around the SGH. These values are consistent with those provided by the Galactic NH Tool ``Colden" at the AXAF Science Center. A 2x2 degree area around the SGH has been scanned with 9 DSS plates to search for a 16 arcmin field not contaminated by bright (m<12) stars.
 
 

Fig.2 -  NH values in units of  1020 cm2 around the South Galactic Hole (blue) and DSS scans (red). The cross indicates the selected field.


Visual inspection of the 9 DSS plates lead to the selection of four candidate fields. After a short optical campaign in Feb 1998, we have selected the following field center (aim point of ACIS-I and ACIS-S):
 
 
RA = 3  32 28.0 ,   DEC= -27  48 30        (J2000)

The field contains stars fainter than 14th mag and has optimal visibility in Chile from September through January (peak in November). The NED database does not yield any relevant sources in the field. Moreover, no X-ray sources from the ROSAT ALL-Sky Survey Catalogue are found.