## Mission Overview

### 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, Sam Cutler, Katherine Whitaker

Released: 2019-07-01

Updated: 2021-12-01

Primary Reference(s): Mowla et al. (2019), Cutler et al. (2021)

DOI:  10.17909/T96Q5M

Source Data:

## Overview

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.

Towards these ends, the team has also provided the COSMOS-DASH Morphological Catalog, presenting structural measurements from 2D Sersic profile fits to galaxies with SNR>5 in COSMOS-DASH. Early science results from this catalog include evidence for an environment-independent flattening of the galaxy size-mass relation persisting out to z ~ 2 for log M ≲ 10.5. For full details on the morphological catalog, see Cutler et al. (2021).

## Data Products

The main COSMOS-DASH product is a wide H160 imaging mosaic and weight map, currently available as version 1.2.10. The COSMOS-DASH Morphological Catalog was derived from an updated, redrizzled version of these mosaic products containing more archival data (version 1.3, not yet publicly available). Version 0.1 of the mosaic products refers to the preliminary reduction of the first 32 pointings. All COSMOS-DASH file names begin with the following string:

 hlsp_cosmos-dash_hst_wfc3_cosmos_f160w_<ver>_<ext>

where <ver> = version number of the mosaic, 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 morph-cat.txt morphological catalog of galaxies, derived from the version mosaic

For column descriptions and important recommendations on selection filters to use when working with the morphological catalog, see the morphological catalog's README file.

## Data Access

v0.1 Images

(first 32 pointings)

v1.2.10 Images

(full mosaic)

Morphological Catalog

v0.1_drz-sci.fits

v1.2.10_drz-sci.fits

v1.3_morph-cat.txt

v0.1_drz-wht.fits

v1.2.10_drz-wht.fit

Supporting Files Description
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.

## Citations

Please remember to cite the appropriate paper(s) below and the DOI 10.17909/T96Q5M if you use these data in a published work.

Note: These HLSP data products are licensed for use under CC BY 4.0.