Nicmos Scientific Rationale:
NICMOS UDF parallels are being obtained in F110W (J) and F160W (H). These parallels should be especially useful for searching for Lyman Break galaxies (LBGs) at z ~ 4 - 6, and provide a natural extension to the selected set of ACS filters. These two filters should also allow the discovery of any "hyper" red (J-band dropout) objects such as the one discovered by Dickinson et al. (ApJ 2000, 531, 624) in the HDF-N.
Both pairs of NICMOS parallel fields fall outside the GOODS field, but both fall within the area covered by the GEMS survey which surrounds it.
Since there are two slightly different ORIENT or roll angles during each of the two UDF epochs of observing, the NICMOS parallel fields resulting from this will both be deepest in the center and somewhat less deep in the outer edges. Both of the NICMOS parallel fields will have the essential appearance of two squares which overlap over a corner of their individual fields, with the area of intersection (roughly 1/4 the size of a full NIC3 field) containing the greatest amount of exposure time, thus being the deepest. We did not move the FOM due to uncertainties in the exact repeatability of the position and calibration issues related to this. We instead relied on the dithering of the primary ACS observations for our NICMOS dithering.
The pointings for these two pairs of overlapping fields are essentially as follows, with the first set of coordinates representing the approximate NIC3 aperture reference location and the second set representing the approximate center of the NIC3 field of view:
Epoch 1, ORIENT 310 RA (J2000)= 03 33 02.7 DEC (J2000)= -27 40 47.9 ~NIC3 03 33 02.6 -27 40 50.1 ~center Epoch 1, ORIENT 314 RA (J2000)= 03 33 04.7 DEC (J2000)= -27 41 10.7 ~NIC3 03 33 04.6 -27 41 12.8 ~center Approximate center of deepest overlap region in Epoch 1: RA (J2000)= 03 33 03.65 DEC (J2000)= -27 41 01.5 Epoch 2, ORIENT 40 RA (J2000)= 03 33 09.3 DEC (J2000)= -27 52 43.6 ~NIC3 03 33 09.0 -27 52 43.2 ~center Epoch 2, ORIENT 44 RA (J2000)= 03 33 07.5 DEC (J2000)= -27 53 10.6 ~NIC3 03 33 07.3 -27 53 08.9 ~center Approximate center of deepest overlap region in Epoch 2: RA (J2000)= 03 33 08.2 DEC (J2000)= -27 52 56.1
F110W (J) and F160W (H).
Although we could not a priori know exactly the amount of exposure time we would receive at either ORIENT in each of the two bands, we could estimate some depths which we hoped to achieve based on a given number of orbits and total exposure time, per filter.
By having at least approximately 50 orbits worth of exposure time, we may exceed a S/N of ~20 for a model LBG galaxy with a basic power law spectrum of fnu ~ lambda**0.8 normalized to an AB magnitude of 26 at rest-frame wavelength of 1500 Angstroms. Including IGM absorption from Madau (ApJ 1995, 441, 18), the normalization should make the model comparable to an L* galaxy at z ~3. Even when the model is redshifted out to z = 4.5, 5.5, and 6.3, the S/N should still exceed 20. At the low end, it could in principle yield a S/N of ~3 for a 0.1L* galaxy at z ~6 in both filters.
All data for both Epochs have been obtained.