IRAC Ultra Deep Field (IUDF) Data release of the science images, exposure time maps, and PSF maps Data reduction v0.9 Data release version 1 (April 2015) Readme version: 17 April 2015 Survey Paper: Labbe et al. 2015, ApJS 1. Summary: The IRAC Ultradeep Field (IUDF) combines all ultradeep data ever taken with the Spitzer Infrared Array Camera (IRAC) at 3.6μm and 4.5μm over GOODS-South and the HUDF (+ two HUDF parallel fields). The deepest observations come from the IRAC Ultra Deep Field (IUDF, ID 70145, PI Labbé) and IRAC Legacy over GOODS (IGOODS, PID 10076, PI Oesch) programs, combined with a number of archival IRAC legacy programs. The data release includes reduced image maps, PSF maps, and reduced maps of all individual AORs. 2. General information: Instrument: Spitzer IRAC Filters: Channel 1 (3.6μm) and 2 (4.5μm). Field location: 03:32:29.460 -27:48:18.32 Area: 23.1 x 28.4 arcmin Contributing Programs: PID Title PI 70145 IUDF I. Labbé 10076 IGOODS P. Oesch 194 GOODS M. Dickinson 70204 ERS G. Fazio 80217 S-CANDELS G. Fazio 60022 SEDS G. Fazio 30866 UDF2 R. Bouwens 3. Data reduction The data reduction is described in Labbe et al. (2015) and follows the procedures used in Damen et al. 2011 (SIMPLE survey). Briefly, the starting point for the reduction are the BCD frames produced by SSC pipeline. Subsequently, the data are post-processed by subtracting a median sky, correcting for column pull down and muxbleed and muxstriping, masking pixels affected by persistence caused by bright sources, and rejecting cosmic rays. The astrometry is calibrated by minimizing the position residuals of sources in common with the deep WFC3 catalogs of 3D-HST (Skelton et al. 2014). The rms residuals are < 0.1 arcsec. The post-processed frames of each AOR of all programs are drizzled (Fruchter & Hook 2002) onto a reference grid and averaged. The reference grid is a tangent plane defined by the CANDELS (Koekemoer, A. M. et al., 2011, ApJS, 197, 36), using the same tangent point (orientation: north up, east left), with a pixel scale of 0.3 arcsec/pixel. In addition to a full stack of all data, the release also includes separate stacks for each AOR (on the same grid). These are useful to study the reliability or variability of sources. The image quality is a constant FWHM=1.49" over the field. The units of the final science images are counts/sec, where a count rate of 1 DN/sec corresponds to a flux density 34.04 microJy or 20.07 AB magnitudes. The units of the exposure time maps are seconds. The exposure time maps are created by multiplying, at each position, the number of bcd-frames that contributed to each pixel by the integration time of the frames. The exposure map thus reflects the exposure time in seconds on that position of the sky, not the average exposure time per final output pixel. To facilitate prior-based WFC3+IRAC photometry, this release contains high signal-to-noise PSFs, created from the data, and the information needed to reconstruct the spatial variation of the PSF due to survey geometry. First, a constant "super PSF" is construct from bright stars in all the AORs. This serves as a very high SNR template created from the data on the same pixel scale as the science image. Second, a map is created which records the weight and rotation angle of all AORs that contributed to the final image. The effective PSF at each position of the final image can then be reconstructed by rotating and weighting the super PSF according to that map. 4. Data products The IUDF data release consists of three main data products: 1) the combined science images and exposure time maps, 2) spatially varying PSF maps, 3) reduced images of all individual AORs. IUDF_CH1_v0.9_sci.fits - science image at 3.6μm [AB = 20.07] IUDF_CH1_v0.9_exp.fits - exposure time map at 3.6μm [sec] IUDF_CH2_v0.9_sci.fits - science image at 4.5μm [AB = 20.07] IUDF_CH2_v0.9_exp.fits - exposure time map at 4.5μm [sec] The PSF maps are supplied in a multi-extension fits file. The first extension is the "super PSF". The second extension contains a 4-dimensional array, containing the weights and rotation angle of all AORs recorded on a a rectangular grid in RA and Dec. IUDF_CH1_v0.9_psf.fits - PSF map at 3.6μm IUDF_CH2_v0.9_psf.fits - PSF map at 4.5μm Reduced images of all individual 272 AORs, are registered and drizzled onto the same grid as the full stack science image. The naming convention is: r[XXX]_CH[Y]_v0.9_[ZZZ].fits.gz where XXX is the aor key, Y is the channel number (1 for 3.6μm and 2 for 4.5μm), and ZZZ is sci (for science image) or exp (for exposure time map). A download script is provided which uses the command line tool curl to download the entire dataset and which can be edited to download only the files needed.