Contours of the Galactic nH column density at |b| < 40 deg in units of 10^(20) cm^(-2) (Dickey & Lockman 1990). Note the large regions of relatively low absorption, nH < 5 x 10^(21) cm^(-2), well inside the traditional zone of avoidance of optically selected cluster samples at |b| < 20 deg (marked by the dashed lines).

Move mouse over image to see the CIZA sample:
The colored bullets mark the locations of the 101 CIZA clusters spectroscopically confirmed as of Dec 2000. Systems relevant for LSS studies of the local universe (z < 0.075) are shown in yellow; more distant clusters are shown in blue. The green line denotes the part of the sky that is not easily observable from Mauna Kea; CIZA follow-up observations in this area are pursued from CTIO.