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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

DOI: 10.17909/srcz-2b67

Citations: See ADS Statistics

Read Me

Source Data:



Full image of the 3D-DASH mosaic, with highly detailed panels zoomed in on specific galaxies.
The 3D-DASH F160W Mosaic

The area contributed by 3D-DASH is 1.35 deg2; the total area with all ancillary F160W data in the COSMOS field, including the deeper CANDELS imaging and various other archival data is 1.43 deg2. The zoomed-in panels reveal the wealth of bright objects that can be studied in this high resolution shallow tier of the extragalactic wedding cake.

Animated gif showing the image building up.
The Observations

Observed with the efficient DASH technique, the 3D-DASH F160W imaging mosaic comprises over a thousand individual WFC3 pointings built up over the course of years.

3D-DASH is much larger than the moon, shallower but slightly larger than COSMOS-Web, and shallower but much larger than other surveys.
Comparison of Surveys

Area vs. depth for WFC3/F160W imaging surveys. The area of the thumbnails is proportional to the area of the surveys

Map of the depth of 3D-DASH pointings. The DASH contributions are relatively shallow, while the ancillary data are deep.
Depth Map

The 3D-DASH H160 point source depth map. The area contributed by 3D-DASH is 1.35 deg2 shown by the blue pointings. The total area is 1.43 deg2 and includes all ancillary data in the COSMOS field shown by black to orange pointings, including the deeper CANDELS imaging and various other archival data sets.

100 stamp images of galaxies showing a wide range of morphologies.
Galaxy Images

The wide imaging area, combined with grism spectroscopy, gives a census of the morphology of star-forming regions of the rare massive star-forming galaxies in the last 5 Gyrs. These stamps show the most massive star-forming galaxies in the 3D-DASH field with high star formation rate and low redshift from the UVISTA catalog. The galaxies are sorted by their redshift, which are shown in the top left corner. Each stamp is 40 kpc x 40 kpc, and are created using DASH-area only WFC3/F160W and ACS/F814W images.


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. Each mosaic is available as a single, large image (and an accompanying weight map) with the following naming convention:   



  • <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 grid of the observed field. Portions of this grid are empty, and only the 150 tiles containing data are provided here.  These tile files have the following naming convention:



  • <tile> = [tile_x].[tile_y], e.g. "01.05". Each tile covers approximately 6.9x6.9 arcmin2 of the sky. 
  • Other fields are the same as described above. Only <pointings>="combined" products are available as tiles.


Data file types:

drz-sci.fits drizzled, calibrated 3D-DASH mosaic of the COSMOS field

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) and 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.  

The tile files (both drz-sci.fits and drz-wht.fits) of the "combined" mosaic are available in the MAST Portal (web-based, cross-mission search interface) and Astroquery (Python package to search for and download files from Python scripts you write). In contrast, the large single mosaic files are available only via direct download links in the table below. Set the Provenance Name filter to 3D-DASH in the Portal Advanced Search to find all or individual tiles. Each observation in the Portal contains a single tile. Both the drz-sci and drz-wht products of each tile are selected as minimum recommended products. The tiles can be retrieved programmatically by using the astroquery.mast module. See a code example below for retrieving and downloading all tiles. 

from astroquery.mast import Observations
all_obs = Observations.query_criteria(provenance_name="3d-dash")
data_products = Observations.get_product_list(all_obs)

For those who want to download all tile files, we also provide a bulk download script in the table below.

  • A web-based interface for cross-mission searches of data at MAST or the Virtual Observatory
  • Search for and retrieve 3D-DASH data products programmatically.

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:

Download Links File Count
(drz-sci.fits + drz-wht.fits)
3D-DASH combined mosaic tiles (bulk download script, 20GB) 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). The 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)
2 Two direct download links. The total storage space required is approximately 50 GB.

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

Download links File Count
(drz-sci.fits + drz-wht.fits)
3D-DASH dash-only mosaic single image (19 GB)
3D-DASH dash-only mosaic single weight map (19 GB)
2 Two direct download links. Total storage space required is approximately 40 GB.



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

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