NICMOS UDF images and catalogues


Summary:
This page presents images and catalogs for the NICMOS Ultra Deep Field. The data are of 4 types:
  • Space-based infrared (NICMOS)
  • Space-based optical (ACS)
  • Ground-based infrared (ISAAC)
  • Ground-based optical (EIS)
In all, there are 15 photometric bands. Photometric redshifts have been calculated with the space-based photometry.
ZJH composite image. Go here for the full size (1600x1600) version including clickable map access to the data.


Data sources:
  • Space-based infrared (NICMOS) This data was taken as part of the HST Ultra Deep Field. The images were retreived from the CADC. They were used "as is". There are two photometric bands: F110W (~J) and. F160W (~H)
  • Space-based optical (ACS) The NICMOS UDF is imbedded in the larger optical UDF. The UDF optical images were resampled with SWarp to be perfectly registered with NICMOS images. The SWarp parameter file is here. There are four bands: F435W (~B), F606W (somewhere between V and R), F775W (~I) and (F850LP) (~Z).
  • Ground-based infrared (ISAAC) These images were taken as part of the GOODS survey with ISAAC on VLT. The image were released as 6 mosaic tiles in each band. This tiles were resampled into to match the NICMOS images. The SWarp parameter file is here. There are three bands: JHK'
  • Ground-based optical (EIS) These are taken from the ESO imaging survey. These images were retreived from ESO database and resampled to the image area of the NICMOS images. The registration is close, but not perfect as the WCS in the EIS images is slightly off. The SWarp parameter file is here. There are 6 bands: U'UBVRI (U' is slightly bluer than U)


The images:
The images are all registered to each other. They measure 1600x1600 pixels or 2.4 arcminutes on a side (0.09''/pixel) This slightly undersamples the high-resolution space-based optical images, while greatly over sampling the ground-based images. The zero-points are defined in the following way:
magAB=-2.5 * log10(flux in DU) + zero-point
The filter curves for all 15 filters can be found in this directory


Photometric catalog:

SExtractor was run in double-image mode on all the images in all the bands. The SExtractor parameter file is given here. The NICMOS F160W (H-band) image was used as the reference image. The catalog is thus H-band selected. The limiting magnitude is HAB=26.5. The resulting catalog can be found here: The columns are labelled:
  • Ra and Dec are given in decimal degrees.
  • X,Y refer to the any of the images.
  • The photometry is given in AB magnitudes. A value of 99.00 is given when their is no detection or the magnitude is below the limiting magnitude in that band.
  • HLR stands for "Half-Light Radius". It is given in units of pixels with a plate-scale is 0.09''/pixel.


Photometric redshift catalog:

Photometric redshifts were calculated for all the objects in the field. The usual chi-squared minimization method was used. Only the 6 HST filters (roughly BVIZJH) were used to calculated the photometric redshifts: The other bands (particularly the EIS bands) are considerably shallower and are only useful for the brightest galaxies anyway. They are given in the following catalog This catalog contains all the columns in NICMOS.UDF.phot plus:
  • z_phot the photometric redshift
  • z_type the galaxy spectral type. The types are explained here
  • z_low the probable lower bound (66% level) of the photometric redshift. The redshift at which the reduced chi-squared increases to 1 above the minimum.
  • z_high the probable lower bound (66% level) of the photometric redshift calculated in the same manner.
  • chi_sq The minimum chi-squred.
There are roughly forty spectroscopic redshifts in the NICMOS UDF. The redshifts were taken from this compilation and compared to the photometric redshifts. The results are shown at right.


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Send comments/suggestions/problems to

gwyn@uvastro.phys.uvic.ca