A New Method for Wide-Field Near-IR Imaging with the Hubble Space Telescope

TL;DR

This paper introduces the DASH method, enabling wide-field near-IR imaging with HST by exploiting small drifts during unguided exposures, significantly increasing survey efficiency and area coverage.

Contribution

The paper presents a novel 'drift and shift' technique that allows multiple WFC3-IR pointings per orbit by using gyroscopic guidance and read-shift processing, enhancing survey efficiency.

Findings

DASH method successfully captures 8 pointings per orbit.

Resolution and galaxy structural parameters are preserved.

The method more than triples the surveyed area in the COSMOS field.

Abstract

We present a new technique for wide and shallow observations using the near-infrared channel of Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST). Wide-field near-IR surveys with HST are generally inefficient, as guide star acquisitions make it impractical to observe more than one pointing per orbit. This limitation can be circumvented by guiding with gyros alone, which is possible as long as the telescope has three functional gyros. The method presented here allows us to observe mosaics of eight independent WFC3-IR pointings in a single orbit by utilizing the fact that HST drifts by only a very small amount in the 25 seconds between non-destructive reads of unguided exposures. By shifting the reads and treating them as independent exposures the full resolution of WFC3 can be restored. We use this "drift and shift" (DASH) method in the Cycle 23 COSMOS-DASH program, which will obtain 456 WFC3 $H_{160}$ pointings in 57 orbits, covering an area of 0.6 degree$^2$ in the COSMOS field down to $H_{160} = 25$. When completed, the program will more than triple the area of extra-galactic survey fields covered by near-IR imaging at HST resolution. We demonstrate the viability of the method with the first four orbits (32 pointings) of this program. We show that the resolution of the WFC3 camera is preserved, and that structural parameters of galaxies are consistent with those measured in guided observations.