## Mission Overview

### A Wide-Field WFC3 Imaging Survey with Grism Spectroscopy in the COSMOS Field ("3D-DASH")

Primary Investigator: Iva Momcheva

HLSP Authors: Lamiya Mowla, Sam Cutler, Gabe Brammer, Iva Momcheva, Kate Whitaker, Pieter van Dokkum

Released: 2022-06-02

Updated: 2022-06-02

Primary Reference(s): Mowla et al. 2022

Source Data:

## Overview

The 3D-Drift And SHift (3D-DASH) program is a Hubble Space Telescope WFC3 F160W imaging and G141 grism survey of the equatorial COSMOS field. 3D-DASH is the widest HST/WFC3 imaging survey in the F160W filter to date, subsuming the COSMOS-DASH pilot survey. 3D-DASH extends the legacy of HST near-infrared imaging and spectroscopy to degree-scale swaths of the sky, enabling the identification and study of distant galaxies (z > 2) that are rare or in short-lived phases of galaxy evolution at rest-frame optical wavelengths. The region covered by the survey spans RA 09:58:00 to 10:02:57 and dec +01:36:00 to +02:51:00 (ICRS).

Observed with the efficient DASH technique, the F160W imaging mosaic comprises 1256 individual WFC3 pointings corresponding to a total area of 1.35 deg2, extending to 1.43 deg2 when combined with ancillary archival data. The total footprint is about twice the area of COSMOS-DASH. 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. 3D-DASH, like 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) for the DASH technique, Mowla et al. (2019) for the pilot COSMOS-DASH image, and Mowla et al. (2022) for the 3D-DASH image. Results from the COSMOS-DASH program showed 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 (see Mowla et al. 2019 and Cutler et al. 2022).

In this first 3D-DASH release, the team presents the reduced F160W imaging mosaic. Grism spectroscopy covering 1.43 deg2 will be made available in a future release.

## Data Products

The initial release of 3D-DASH provides imaging products only. These imaging mosaic products are available at MAST in multiple formats. The mosaic is available as a single, large image (and an accompanying weight map) with the following naming convention:

hlsp_3d-dash_hst_wfc3_<pointings>-cosmos_f160w_<version>_<type>.fits

where:

• <pointings> = the source data from which the mosaic was constructed, either "combined" (DASH pointings combined with ancillary archival data, covering 1.43 deg2) or "dash" (DASH pointings only, covering 1.35 deg2).
• <version> = version, e.g. "v1.0"
• <type> = product type, either "drz-sci" (drizzled, calibrated mosaic image) or "drz-wht" (weight map corresponding to the drz-sci image).

The "combined" mosaic products are also available as smaller tile files from a 16x16 grid of the observed field. Large portions of this grid are empty, and only the 150 tiles containing data are provided here.  These tile files have the following naming convention:

hlsp_3d-dash_hst_wfc3_combined-t<tile>-cosmos_f160w_<version>_<type>.fits

where:

• <tile> = [tile_x].[tile_y], e.g. "01.05". Each tile covers approximately 6.8x6.8 arcmin2 of the sky. A map of the tile grid numbering system is included below.
• Other fields are the same as described above. Only <pointings>="combined" products are available as tiles.

Click the blue [+] below on the right to see the tile map referenced by <tile> in the file names:

Data file types:

 drz-sci.fits drizzled, calibrated 3D-DASH mosaic of the COSMOS field drz-wht.fits weight-map corresponding to the 3D-DASH mosaic

## Data Access

The team has provided a Python Notebook for extracting image cutouts (available on Deepnote and GitHub), as well as an interactive image explorer that includes both 3D-DASH and other surveys. The cutout Notebook and the image explorer are linked here for convenience, but are not owned or maintained by MAST; questions about software should be directed to the authors of Mowla et al. 2022.

Imaging mosaic products from the "combined" 3D-DASH mosaic (including DASH pointings combined with ancillary archival data) are available as small tile files or large single files as follows:

(drz-sci.fits + drz-wht.fits)
Instructions
3D-DASH combined mosaic tiles (bulk download script) 300 Run the shell script in your terminal. The script uses curl, which is likely already installed on your machine (and if not, is freely available as open source software). Total storage space required is approximately 20 GB.
3D-DASH combined mosaic single image (22 GB)
&
3D-DASH combined mosaic single weight map (22 GB)

Imaging mosaic products from the DASH-only mosaic (including DASH pointings only) are available as large single files as follows:

(drz-sci.fits + drz-wht.fits)
Instructions
3D-DASH dash-only mosaic single image (19 GB)
&
3D-DASH dash-only mosaic single weight map (19 GB)