Deep UBVRI observations of a field within ELAIS-S1: the Stockholm VIMOS Supernova Survey III
(English)Manuscript (preprint) (Other academic)
Context. The Stockholm VIMOS Supernova Survey (SVISS) is an optical broad-band photometry survey, aimed at the search fordistant (redshifts z~0.7) supernovae, which are detected by means of monthly imaging in R and I bands with the VIMOS instrumenton the ESO VLT. The distances of the supernovae are estimated using photometric redshifts facilitated by additional U, B and V imaging also with VIMOS. In this paper we present the deep stacked imaging data in all these bands and a catalogue of galaxiesextending to very faint magnitudes.
Aims. We discuss the various steps followed to create a galaxy catalog, including the reduction and stacking of the data, astrometricand photometric calibration and source detections.We derived completeness, corrected number counts and color selected Lyman breakgalaxies. Raw number counts are also calculated. Finally, making use of a template fitting code, photometric redshifts are derived.
Methods. UBVRI deep imaging of a 4x56 sq. arcmin field within the ELAIS-S1 field is presented in this paper. The data reduction has been done with a dedicated MIDAS pipeline. The final images have been weighted by their seeing, which was found to optimise depth and spatial resolution. Source detection and phortometry was done using SExtractor. The photometric accuracy was tested by comparing the colors of the sources to stellar libraries and redshifted galaxy templates. A mixture of synthetic point-like andextended sources are simulated in order to estimate completeness. Derived number counts have been compared to the results ofsimilar surveys. Lyman break galaxy candidates were selected using color criteria: UBR, BRI, BVI and VRI, and their numbers computed and compared to other surveys.We have obtained photometric redshifts by spectral energy distribution template fitting. The photometric redshifts were calibrated using a sample of galaxies in the HDF-S with available spectroscopic redshifts that have also been observed with the same filter set as used here.
Results. Using a seeing weighted method to combine the science frames resulted in an increase of the number of faint objects detectedand minimizing the photometric errors. The astrometric accuracy is 0.400 arcsec with respect to 2MASS and 5 sigma limiting magnitudes for UBVRI are 28.2, 29.3, 28.3, 28.5 and 27.2 respectively (Vega). The computed galaxy number counts are in good agreement with previous works, with the U band counts of this survey being one of the deepest ever obtained. The raw number counts from broadband color selected Lyman break galaxies show a good agreement for the U and B dropouts with other surveys. Photometric redshifts have a scatter of dz=0.085 with a 9.1% fraction of outliers.
Conclusions. We derive deep number counts which are found to be consistent with previous works, reproducing the bright and faintends. Especially, the stacked deep U and I band data are found to present a comptetetive combination of depth and area, comparableto HDF observations. As well as V band, comparable to Subaru and the Lockman hole observations. Our U and B dropouts are within the expected redshift range, with mean values of 3 and 3.8 respectively.
imaging surveys, techniques: image processing, galaxies: photometry, photometric redshifts, lyman break galaxies
Astronomy, Astrophysics and Cosmology
Research subject Astronomy
IdentifiersURN: urn:nbn:se:su:diva-56789OAI: oai:DiVA.org:su-56789DiVA: diva2:413078