Cluster Coadd Data

Note: updated co-add catalogs covering 2 deg x 2 deg for these fields are also available.

Data of cluster fields taken toward the end of the SV period were processed using v7 of the standalone pipeline. Coadds were made, covering approximately a 1 deg^2 region (or 14000x14000 pixels exactly) centered on each cluster. These data were taken under good seeing conditions and should be useful for tests of galaxy photometry, star/galaxy separation, weak lensing, etc. Typically there were 10x90 sec exposures done in each filter.

Some notes on the processing:
  • No crosstalk corrections were applied.
  • Astrometry was done using Scamp, with 2MASS as the reference catalog.
  • Relative CCD-by-CCD photometric calibration was done by comparing SExtractor MAG_AUTO relative to a fiducial pointing (typically the first pointing in the dither sequence). The data generally look photometric except for a few pointings of RXJ 2248-4431, where some care was taken to check the relative pointing-by-pointing zeropoint offsets before choosing the fiducial pointing.
  • Photometric calibration of the fiducial pointing was done by simply applying the CCD-by-CCD zeropoints derived using previous DECam Stripe 82 data (star flat sequences from 20121102,20121104). Those zeropoints came from comparing SExtractor MAG_AUTO against SDSS griz modelmag of Stripe 82 coadd stars, or against Y-band AB magnitudes of UKIDSS standards provided by Douglas Tucker.
  • Flux scaling values derived from the relative photometry were applied to the remapped images before coadding.
  • The coadds were done as medians of the input images, using Swarp. These coadds do not have any PSF homogenization.
  • PSFEx was used to model the PSF in the coadded images and enable subsequent model fitting photometry.
  • SExtractor was run in dual-image mode, using the i or r band as the detection image, as these were the deepest filters.
  • Was used the default SExtractor MAG_ZEROPOINT = 25. So, the SEXMGZPT is given by 25 + offset (see table bellow).
The following offsets should be added to the cataloged magnitudes to obtain approximately calibrated AB magnitudes, using
  • calibrated magnitude = SExtractor magnitude in catalog + offset
filter     offset
g 5.04
r 5.24
i 5.18
z 4.80
Y 3.05
  • No airmass-dependent extinction corrections were applied.
  • The overall photometric zeropoints (as given in the above table) probably are not much better than about 5%; we'll want to improve on this by, say, checking with stellar locus regression.

Stellar locus regression update (Keith):
Zeropoint shift maps are now available for DES griz for the SPTW field (see attachments). The maps are stored in fits files as HEALPix maps (NSIDE = 256 -> ~14 arcmin resolution, EQUATORIAL coordinates, RING ordering scheme) with a column for each DES filter. The values in the maps should be added to the magnitudes in the coadd object catalogs. The maps cover the whole sky, and tiles without fitted stars have the large negative healpy.UNSEEN value. The zeropoint shift maps are based on the procedure described in There are zeropoint maps using only DES colors (z magnitudes fixed), and also with absolute magnitude calibration against J-band magnitudes of matched 2MASS stars.

The Fermilab locations of the coadd images and catalogs for each cluster are as follows:

SPT-CL J2332-5358 (z = 0.40)

  • grizY data from 20121116,20121117,20121118
  • coadd images: /data/des10.b/data/hlin/standalone_pipeline_tests/v7/swarp_tests/sptw/[grizY]/sptw_[grizY].fits
  • coadd weight maps: /data/des10.b/data/hlin/standalone_pipeline_tests/v7/swarp_tests/sptw/[grizY]/sptw_weight_[grizY].fits
  • coadd catalogs: /data/des10.b/data/hlin/standalone_pipeline_tests/v7/swarp_tests/sptw/[grizY]/sptw_[grizY]_detr_cat.fits
    • r band is detection image
  • spectroscopic redshift from Song et al. The NED redshift of 0.32 is incorrect.
Preliminary stellar locus regression zeropoint shift maps are available for griz in the attachments, and at Fermilab:
  • /data/des10.a/data/bechtol/projects/dust_maps/cluster_fields/sptw/sptw_slr_zeropoint_shiftmap_DES_griz_EQUATORIAL_NSIDE_256_RING_without2MASS.fits
  • /data/des10.a/data/bechtol/projects/dust_maps/cluster_fields/sptw/sptw_slr_zeropoint_shiftmap_DES_griz_EQUATORIAL_NSIDE_256_RING_with2MASS.fits

Bullet Cluster (z = 0.30)

  • rizY data from 20121123,20121124
  • coadd images: /data/des09.a/data/hlin/standalone_pipeline_tests/v7/swarp_tests/bullet_cluster/[rizY]/bulletcluster_[rizY].fits
  • coadd weight maps: /data/des09.a/data/hlin/standalone_pipeline_tests/v7/swarp_tests/bullet_cluster/[rizY]/bulletcluster_weight_[rizY].fits
  • coadd catalogs: /data/des09.a/data/hlin/standalone_pipeline_tests/v7/swarp_tests/bullet_cluster/[riz]/bulletcluster_[riz]_deti_cat.fits
    • i band is detection image
    • problem with Y band catalog generation, so not available (yet)

RXJ 2248-4431 (z = 0.35; is a CLASH cluster)

  • rizY data from 20121124
  • coadd images: /data/des10.b/data/hlin/standalone_pipeline_tests/v7/swarp_tests/rxj2248/[rizY]/rxj2248_[rizY].fits
  • coadd weight maps: /data/des10.b/data/hlin/standalone_pipeline_tests/v7/swarp_tests/rxj2248/[rizY]/rxj2248_weight_[rizY].fits
  • coadd catalogs: /data/des10.b/data/hlin/standalone_pipeline_tests/v7/swarp_tests/rxj2248/[rizY]/rxj2248_[rizY]_deti_cat.fits
  • r data from 20121207: coadd catalog: /data/des10.b/data/hlin/standalone_pipeline_tests/v7/swarp_tests/rxj2248/r2/rxj2248_r2_deti_cat.fits
  • preliminary photo-z catalog: rxj2248_photoz.etbl
    • trained on DES SN X3/VVDS Deep 02 hr data (see here)
    • ascii file, with row-by-row the same objects as coadd catalogs
    • first column is photo-z
    • second column is photo-z error
    • known issue: redshift distribution looks bimodal fainter than about i-band MAG_AUTO > 23

El Gordo (z = 0.87; ACT-CL J0102-4915)

  • rizY data from 20121124
  • coadd images: /data/des10.b/data/hlin/standalone_pipeline_tests/v7/swarp_tests/el_gordo/[rizY]/elgordo_[rizY].fits
  • coadd weight maps: /data/des10.b/data/hlin/standalone_pipeline_tests/v7/swarp_tests/el_gordo/[rizY]/elgordo_weight_[rizY].fits
  • coadd catalogs: /data/des10.b/data/hlin/standalone_pipeline_tests/v7/swarp_tests/el_gordo/[rizY]/elgordo_[rizY]_deti_cat.fits
    • i band is detection image

Color images

  • From Nikolay Kuropatkin, here are high-resolution png images of regions near the centers of each of the coadds. The images are about 35-40 MB in size and are suitable for viewing at full resolution with a large monitor:
  • A very big (400 MB) high-resolution color png (made by Nikolay Kuropatkin) of the full ~1 deg^2 coadd area of SPT-CL J2332-5358
    is available at Fermilab at /blue-sim/kuropat/astroimage/SPT/imageRGB_SPT_sqrt.png
  • Here is a smaller image of the central portion of the g,r,i coadd of SPT-CL J2332-5358, showing the cluster in the middle as well as the big spiral NGC 7689 toward the bottom left: