GOYA Survey: U and B Number Counts in the Groth-Westphal Strip

Eliche-Moral, M. Carmen; Balcells, Marc; Prieto, Mercedes; García-Dabó, César E.; Erwin, Peter; Cristóbal-Hornillos, David
Bibliographical reference

The Astrophysical Journal, Volume 639, Issue 2, pp. 644-671.

Advertised on:
3
2006
Number of authors
6
IAC number of authors
6
Citations
30
Refereed citations
25
Description
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 dlogN/dm=0.50+/-0.02 for B=21.0-24.5 and dlogN/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 Ks, using a Λ-dominated cosmology and SDSS local luminosity functions. Only by setting a recent zf~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 (τB=0.6) for all galaxy types ensures that the recent formation for elliptical galaxies 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. Based on observations made with the Isaac Newton Telescope operated on the island of La Palma by the Isaac Newton Group of Telescopes in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.