The ALHAMBRA (Advance Large Homogeneous Area Medium Band Redshift Astronomical) survey has observed 8 different regions of the sky, including sections of the COSMOS, DEEP2, ELAIS, GOODS-N, SDSS and Groth fields using a new photometric system with 20 optical, contiguous ∼300Å filters plus the JHKs bands. The filter system is designed to optimize the effective photometric redshift depth of the survey, while having enough wavelength resolution for the identification of faint emission lines. The observations, carried out with the Calar Alto 3.5m telescope using the wide field optical camera LAICA and the NIR instrument Omega-2000, represent a total of ∼700hrs of on-target science images. Here we present multicolor PSF-corrected photometry and photometric redshifts for ∼438,000 galaxies, detected in synthetic F 814W images. The catalogs are complete down to a magnitude I∼24.5AB and cover an effective area of 2.79 deg 2 . Photometric zeropoints were calibrated using stellar transformation equations and refined internally, using a new technique based on the highly robust photometric redshifts measured for emission line galaxies. We calculate Bayesian photometric redshifts with the BPZ2.0 code, obtaining a precision of δ z /(1+z s )=1% for I<22.5 and δ z /(1+z s )=1.4% for 22.5=0.56 for I<22.5 AB and =0.86 for I<24.5 AB. Given its depth and small cosmic variance, ALHAMBRA is a unique dataset for galaxy evolution studies.

Here we describe the first results of the ALHAMBRA survey which provides cosmic tomography of the evolution of the contents of the Universe over most of Cosmic history. Our novel approach employs 20 contiguous, equal-width, medium-band filters covering from 3500Å to 9700Å, plus the standard JHK s near-infrared bands, to observe a total area of 4 square degrees on the sky. The -2optical photometric system has been designed to maximize the number of objects with accurate classification by Spectral Energy Distribution type and redshift, and to be sensitive to relatively faint emission features in the spectrum. The observations are being carried out with the Calar Alto 3.5m telescope using the wide field cameras in the optical, LAICA, and in the NIR, Omega-2000. The first data confirm that we are reaching the expected magnitude limits (for a total of 100 ksec integration time per pointing) of AB ≤ 25 mag (for an unresolved object, S/N = 5) in the optical filters from the blue to 8300Å, and from AB = 24.7 to 23.4 for the redder ones. The limit in the NIR, for a total of 15 ks exposure time per pointing, is (in the Vega system) K s ≈ 20 mag, H ≈ 21 mag, J≈ 22 mag. Some preliminary results are presented here to illustrate the capabilities of the ongoing survey. We expect to obtain accurate redshift values, ∆z/(1 + z) ≤ 0.03 for about 5 ×10 5 galaxies with I≤ 25 (60% completeness level), and z med = 0.74. This accuracy, together with the homogeneity of the selection function, will allow for the study of the redshift evolution of the large scale structure, the galaxy population and its evolution with redshift, the identification of clusters of galaxies, and many other studies, without the need for any further followup. It will also provide targets for detailed studies with 10m-class telescopes. Given its area, spectral coverage and its depth, apart from those main goals, the ALHAMBRA-Survey will also produce valuable data for galactic studies.

This paper describes the Second Public Data Release (DR2) of the Calar Alto Legacy Integral Field Area (CALIFA) survey. The data for 200 objects are made public, including the 100 galaxies of the First Public Data Release (DR1). Data were obtained with the integral-field spectrograph PMAS/PPak mounted on the 3.5 m telescope at the Calar Alto observatory. Two different spectral setups are available for each galaxy, (i) a lowresolution V500 setup covering the wavelength range 3745-7500 Å with a spectral resolution of 6.0 Å (FWHM); and (ii) a medium-resolution V1200 setup covering the wavelength range 3650-4840 Å with a spectral resolution of 2.3 Å (FWHM). The sample covers a redshift range between 0.005 and 0.03, with a wide range of properties in the color-magnitude diagram, stellar mass, ionization conditions, and morphological types. All the cubes in the data release were reduced with the latest pipeline, which includes improved spectrophotometric calibration, spatial registration, and spatial resolution. The spectrophotometric calibration is better than 6% and the median spatial resolution is 2. 4. In total, the second data release contains over 1.5 million spectra.

In the next years, several cosmological surveys will rely on imaging data to estimate the redshift of galaxies, using traditional filter systems with 4 − 5 optical broad bands; narrower filters improve the spectral resolution, but strongly reduce the total system throughput. We explore how photometric redshift performance depends on the number of filters n f , characterizing the survey depth by the fraction of galaxies with unambiguous redshift estimates. For a combination of total exposure time and telescope imaging area of 270 hrs m 2 , 4 − 5 filter systems perform significantly worse, both in completeness depth and precision, than systems with n f 8 filters. Our results suggest that for low n f , the color-redshift degeneracies overwhelm the improvements in photometric depth, and that even at higher n f , the effective photometric redshift depth decreases much more slowly with filter width than naively expected from the reduction in S/N . Adding near-IR observations improves the performance of low n f systems, but still the system which maximizes the photometric redshift completeness is formed by 9 filters with logarithmically increasing bandwidth (constant resolution) and half-band overlap, reaching ∼ 0.7 mag deeper, with 10% better redshift precision, than 4 − 5 filter systems. A system with 20 constant-width, non-overlapping filters reaches only ∼ 0.1 mag shallower than 4 − 5 filter systems, but has a precision almost 3 times better, δz = 0.014(1 + z) vs δz = 0.042(1 + z). We briefly discuss a practical implementation of such a photometric system: the ALHAMBRA survey.

The ALHAMBRA survey aims to cover 4 deg 2 using a system of 20 contiguous, equal width, medium-band filters spanning the range 3500 Å-9700 Å plus the standard JHKs filters. Here we analyze deep near-IR number counts of one of our fields (ALH08) for which we have a relatively large area (0.5 deg 2 ) and faint photometry (J = 22.4, H = 21.3, and K = 20.0 at the 50% of recovery efficiency for point-like sources). We find that the logarithmic gradient of the galaxy counts undergoes a distinct change to a flatter slope in each band: from 0. . These observations together with faint optical counts are used to constrain models that include density and luminosity evolution of the local type-dependent luminosity functions. Our models imply a decline in the space density of evolved early-type galaxies with increasing redshift, such that only 30%-50% of the bulk of the present day red ellipticals was already in place at z ∼ 1.