Mission Overview


Primary Investigator:  Pieter van Dokkum

HLSP Authors: Lamiya Mowla, Ivelina Momcheva, Gabriel Brammer

Released: 2019-07-01

Updated: 2019-07-01

Primary Reference(s): Mowla et al. (2019)

DOI:  10.17909/T96Q5M

Citations: See ADS Statistics

Read Me

Source Data:

Figure 1
Figure 1: The COSMOS-DASH H160 mosaic (Mowla et al. 2019). The science image is shown in the main figure, along with the exposure map in the colored inset. Zoomed-in portions of the science image are shown as well. The area contributed by COSMOS-DASH is 0.49 deg2; the total area with H160 data (including the deeper CANDELS imaging and various other archival data sets listed in Table 4) is 0.66 deg2. The dark blue outline shows the 1.64 degree2 covered by ACS I814.


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.

Figure 2
Figure 2: Comparison with ground based photometry. Images of massive galaxies at z~1.5 observed with UltraVISTA (top panel; H+i) and COSMOS-DASH (bottom panel; H160 + I814). Many single objects observed from the ground reveal more complex structures in high resolution HST images which allow for proper analysis of galaxy structures, close-pair fraction, etc.


Figure 3
Figure 3: Grid of random galaxy images from the COSMOS-DASH survey (6”x6”; H160+I814).


Data Products

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

Data Access

v0.1 Images (first 32 pointings) v1.2.10 Images (full mosaic)
v0.1_drz-sci.fits v1.2.10_drz-sci.fits
v0.1_drz-wht.fits v1.2.10_drz-wht.fits


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.



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.