Statistics
Scientific paper
Oct 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000apj...542l..79g&link_type=abstract
The Astrophysical Journal, Volume 542, Issue 2, pp. L79-L82.
Statistics
43
Cosmology: Observations, Cosmology: Diffuse Radiation, Galaxies: Evolution, Galaxies: Statistics, Surveys, Ultraviolet: Galaxies
Scientific paper
We present galaxy counts in the near-ultraviolet (NUV; 2365 Å) and far-ultraviolet (FUV; 1595 Å) obtained from Space Telescope Imaging Spectrograph observations of portions of the Hubble Deep Field-North (HDF-N), the Hubble Deep Field-South (HDF-S), and a parallel field near the HDF-N. All three fields have deep (AB>29) optical imaging, and we determine magnitudes by taking the ultraviolet flux detected within the limiting optical isophote. An analysis of the UV-optical colors of detected objects, combined with a visual inspection of the UV images, indicates that there are no detectable objects in the UV images that are not also detected in the optical. We determine our detection area and completeness as a function of magnitude with a simulated distribution of galaxies based on the HDF-N Wide Field Planetary Camera 2 (WFPC2) V+I image. The galaxy counts reach to NUVAB=29 and FUVAB=30, which is 1 mag fainter than the HDF-N WFPC2/F300W counts and 7 mag fainter than balloon-based counts. We integrate our measurements in order to present the extragalactic background radiation coming from resolved objects. The NUV galaxy counts show a flattening or turnover beginning at about NUVAB=26.0, which is not predicted either by no-evolution models based on a local luminosity function with a steep faint-end slope or by a semianalytic model in which starbursts are caused by major mergers. The FUV counts also show a flat slope. We argue that the flat slopes could be caused by a short duty cycle for star formation, additional starbursts triggered by minor mergers, and an extended quiescent phase between starburst episodes. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.
Brown Thomas M.
Ferguson Henry C.
Gardner Jonathan P.
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