Wide and deep near-UV (360nm) galaxy counts and the extragalactic background light with the Large Binocular Camera

TL;DR

This study presents deep near-UV galaxy counts over 0.4 sq. deg. using the Large Binocular Camera, providing new constraints on galaxy evolution and the extragalactic background light in the near-UV band.

Contribution

First deep near-UV galaxy counts over a large area with high completeness, constraining galaxy evolution models and the contribution to the extragalactic background light.

Findings

Galaxy counts follow a double power-law shape.

The counts suggest the near-UV EBL contribution is over 70% of recent upper limits.

Results are consistent with hierarchical CDM galaxy formation models.

Abstract

Deep multicolour surveys are the main tool to explore the formation and evolution of the faint galaxies which are beyond the spectroscopic limit with the present technology. The photometric properties of these faint galaxies are usually compared with current renditions of semianalytical models to provide constraints on the fundamental physical processes involved in galaxy formation and evolution, namely the mass assembly and the star formation. Galaxy counts over large sky areas in the near-UV band are important because they are difficult to obtain given the low efficiency of near-UV instrumentation, even at 8m class telescopes. A large instrumental field of view helps in minimizing the biases due to the cosmic variance. We have obtained deep images in the 360nm U band provided by the blue channel of the Large Binocular Camera at the prime focus of the Large Binocular Telescope. We have derived over an area of ~0.4 sq. deg. the galaxy number counts down to U=27 in the Vega system (corresponding to U=27.86 in the AB system) at a completeness level of 30% reaching the faintest current limit for this wavelength and sky area. The shape of the galaxy counts in the U band can be described by a double power-law, the bright side being consistent with the shape of shallower surveys of comparable or greater areas. The slope bends over significantly at U>23.5 ensuring the convergence of the contribution by star forming galaxies to the EBL in the near-UV band to a value which is more than 70% of the most recent upper limits derived for this band. We have jointly compared our near-UV and K band counts collected from the literature with few selected hierarchical CDM models emphasizing critical issues in the physical description of the galaxy formation and evolution.