A Wide-Field WFC3 Imaging Survey in the COSMOS Field (COSMOS-DASH)
Primary Investigator: Pieter van Dokkum
HLSP Authors: Lamiya Mowla, Ivelina Momcheva, Gabriel Brammer
Primary Reference(s): Mowla et al. (2019)
Citations: See ADS Statistics
COSMOS-Drift And SHift (COSMOS-DASH) is a Hubble Space Telescope WFC3 imaging survey of the COSMOS field in the F160W filter, comprising 456 WFC3 pointings covering an area of 0.49 deg2, giving 0.66 deg2 of total data in the archive. By taking advantage of the unique Drift And SHift (DASH) observing mode, COSMOS-DASH is the widest HST/WFC3 imaging survey in F160W, tripling the extragalactic survey area in the near-infrared at HST resolution. Generally, guide star acquisitions make it impractical to observe multiple pointings per orbit, so very wide near-IR surveys with HST are inefficient. However, this limitation can be overcome by guiding with gyros alone, which is possible when HST operates with three gyros. COSMOS-DASH observed eight independent WFC3-IR pointings per orbit, taking advantage of the fact that HST drifts by only a very small amount in the 25 seconds between non-destructive reads of unguided exposures. Because the DASH method leads to shifts during exposures, reducing DASH data is more complex than for guided exposures. For full details, see Momcheva et al. (2017) and Appendix A1 of Mowla et al. (2019). Results from the COSMOS-DASH program show that with appropriate data reduction methods, the DASH technique preserves the WFC3 spatial resolution, and that galaxy structural parameters are consistent with those measured from guided surveys.
The science goals of COSMOS-DASH include a study of the relation between the star formation rate and structure of massive galaxies; the identification of the star forming progenitors of massive compact galaxies; an analysis of the merger rate using close pairs; and an analysis of structures of other rare objects such as post-starburst galaxies.
The main COSMOS-DASH product is a wide H160 imaging mosaic and weight map. Version 0.1 of the products refers to the preliminary reduction of the first 32 pointings. All COSMOS-DASH file names begin with the following string:
where <ver> = version number of the data product, and <ext> is one of the following extensions:
|drz-sci.fits||drizzled, calibrated mosaic of the COSMOS field in F160W|
|drz-wht.fits||weight map corresponding to the COSMOS-DASH mosaic in F160W|
|v0.1 Images (first 32 pointings)||v1.2.10 Images (full mosaic)|
|pointings-info.txt||A list of all FLT files that were used in the mosaics with information extracted from the headers and sky background value calculated during reduction.|
|shifts.tar.gz||A folder containing shifts and rotations calculated for each image during alignment relative to the external catalogs.|
|pointings-reg.txt||DS9 regions file of the footprints of all pointings.|
|drizzled-psf.tar.gz||A folder containing cutouts of all the stars used to construct a PSF. Also included is a CSV file listing all the stars used in the PSF.|