Detalles de publicación
PP 05050
GOYA Survey: U and B Number Counts in the Groth-Westphal Strip
(1) Instituto de Astrofisica de Canarias, Spain, (2) Departamento de Astrofisica de la Universidad de La Laguna, Spain
We present U and B galaxy differential number counts from a field of ~900
arcmin2, based on GOYA Survey imaging of the HST Groth-Westphal strip. Source
detection efficiency corrections as a function of the object size have been
applied. A variation of the half-exposure image method has been devised to
identify and remove spurious detections. Achieved 50% detection efficiencies
are 24.8 mag in U and 25.5 mag in B in the Vega system. Number count slopes are
d log (N)/dm = 0.50 ± 0.02 for B=21.0-24.5, and d log (N)/dm = 0.48 ± 0.03
for U=21.0-24.0. Simple number count models are presented that simultaneously
reproduce the counts over 15 mag in U and B,and over 10 mag in K_s, using a
Lambda-dominated cosmology and SDSS local luminosity functions. Only by setting
a recent z_f ~ 1.5 formation redshift for early-type, red galaxies do the
models reproduce the change of slope observed at Ks = 17.5 in NIR counts. A
moderate optical depth (tau_B = 0.6) for all galaxy types ensures that the
recent formation for ellipticals does not leave a signature in the U or B
number counts, which are featureless at intermediate magnitudes. No ad-hoc
disappearing populations are needed to explain the counts if number evolution
is introduced using an observationally-based z-evolution of the merger
fraction.
arcmin2, based on GOYA Survey imaging of the HST Groth-Westphal strip. Source
detection efficiency corrections as a function of the object size have been
applied. A variation of the half-exposure image method has been devised to
identify and remove spurious detections. Achieved 50% detection efficiencies
are 24.8 mag in U and 25.5 mag in B in the Vega system. Number count slopes are
d log (N)/dm = 0.50 ± 0.02 for B=21.0-24.5, and d log (N)/dm = 0.48 ± 0.03
for U=21.0-24.0. Simple number count models are presented that simultaneously
reproduce the counts over 15 mag in U and B,and over 10 mag in K_s, using a
Lambda-dominated cosmology and SDSS local luminosity functions. Only by setting
a recent z_f ~ 1.5 formation redshift for early-type, red galaxies do the
models reproduce the change of slope observed at Ks = 17.5 in NIR counts. A
moderate optical depth (tau_B = 0.6) for all galaxy types ensures that the
recent formation for ellipticals does not leave a signature in the U or B
number counts, which are featureless at intermediate magnitudes. No ad-hoc
disappearing populations are needed to explain the counts if number evolution
is introduced using an observationally-based z-evolution of the merger
fraction.