The wide-field imager probes large angular scales where first-light fluctuations are expected to peak, and where they can best be separated from galaxy clustering and shot noise. The imager data will be combined with shallow Spitzer and Akari survey fields to allow us to detect and remove galaxies in the camera images. CIBER complements these facilities by virtue of its much wider FOV, providing sensitivity to fluctuations on large angular scales, and shorter wavelength coverage, crucial for discriminating a first-light component.
Instrumentation
The wide-field imager consists of dual 11-cm refracting telescopes cooled to 77 K, imaging onto two 1024 x 1024 focal plane arrays. All-spherical refracting optics provide diffraction-limited performance from 0.75 to 2.2 μm over a 2° x 2° field of view. The spatial resolution is determined by the 7" pixel size, not aberrations or diffraction.
The pixel size of 7" reduces the local-galaxy clustering signal, giving us a sufficient density of pixels to remove sources down to I = 21, H = 20 with modest data loss. CIBER itself reaches a limiting point source sensitivity of I = 18.4 and H = 18.2 mag (3σ); several times deeper than 2MASS. We quote a 3σ threshold because we are only interested in rejecting point sources from the data, not extracting and cataloging them. Source confusion, using deep galaxy counts, is 2-3 times below the instrument noise.
The 1024 detector arrays are sampled continuously every 1.8 s, providing background-limited performance. We use an off-chip JFET follower to eliminate multiplexer glow. In order to minimize dark current associated with temperature drifts, the array is mounted on a thermally isolated stage, which is monitored with sensitive dcstabilized thermometry and thermally regulated. A cold shutter placed just above the array allows us to record dark frames prior to launch, and on ascent and descent.
