C. Husillos

The ALHAMBRA Survey: Bayesian photometric redshifts with 23 bands for 3 deg2

The ALHAMBRA (Advance Large Homogeneous Area Medium Band Re dshift Astronomical) survey has observed 8 different regions of the sky, incl uding sections of the COSMOS, DEEP2, ELAIS, GOODS-N, SDSS and Groth fields using a new photometric system with 20 contiguous �300 ˚ A filters covering the optical range, combining them with deep JHKs imaging. The observations, carried out with the Calar Alto 3.5m telescope using the wide field (0.25 deg 2 FOV) optical camera LAICA and the NIR instrument Omega-2000, correspond to �700hrs of on-target science images. The photometric system was specifically designed to maximize the effective depth of the survey in terms of accurate spectral-type and photometric redshift estimation along with the capability of identi fication of relatively faint emission lines. Here we present multicolor photometry and photometric redshifts for �438,000 galaxies, detected in synthetic F814W images, complete down to a magnitude I�24.5AB, carefully taking into account realistic noise estimates, and correct ing by PSF and aperture effects with the ColorPro software. The photometric zeropoints have been calibrated using stellar transformation equations and refined internally, using a new tech nique based on the highly robust photometric redshifts measured for emission line galaxies. We calculate photometric redshifts with the BPZ2.0 code, which includes new empirically calibrated galaxy templates and priors. —

NEAR-INFRARED GALAXY COUNTS AND EVOLUTION FROM THE WIDE-FIELD ALHAMBRA SURVEY*

The ALHAMBRA survey aims to cover 4 deg2 using a system of 20 contiguous, equal width, medium-band filters spanning the range 3500 A-9700 A 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 deg2) 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 0.44 at [17.0, 18.5] to 0.34 at [19.5, 22.0] for the J band; for the H band 0.46 at [15.5, 18.0] to 0.36 at [19.0, 21.0], and in Ks the change is from 0.53 in the range [15.0, 17.0] to 0.33 in the interval [18.0, 20.0]. 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.

The ALHAMBRA survey : evolution of galaxy clustering since z ~ 1.

PA-M was supported by an ERC StG Grant (DEGAS-259586). PN acknowledges the support of the Royal Society through the award of a University Research Fellowship and the European Research Council, through receipt of a Starting Grant (DEGAS-259586). This work was supported by the Science and Technology Facilities Council (grant number ST/F001166/1), by the Generalitat Valenciana (project of excellence Prometeo 2009/064), by the Junta de Andalucia (Excellence Project P08-TIC-3531) and by the SpanishMinistry for Science and Innovation (grantsAYA2010-22111-C03-01 and CSD2007-00060).

The alhambra photometric system

This paper presents the characterization of the optical range of the ALHAMBRA photometric system, a 20 contiguous, equal-width, medium-band CCD system with wavelength coverage from 3500 A to 9700 A. The photometric description of the system is done by presenting the full response curve as a product of the filters, CCD, and atmospheric transmission curves, and using some first- and second-order moments of this response function. We also introduce the set of standard stars that defines the system, formed by 31 classic spectrophotometric standard stars which have been used in the calibration of other known photometric systems, and 288 stars, flux calibrated homogeneously, from the Next Generation Spectral Library (NGSL). Based on the NGSL, we determine the transformation equations between Sloan Digital Sky Survey ugriz photometry and the ALHAMBRA photometric system, in order to establish some relations between both systems. Finally, we develop and discuss a strategy to calculate the photometric zero points of the different pointings in the ALHAMBRA project.

The ALHAMBRA survey: accurate merger fractions derived by PDF analysis of photometrically close pairs

Aims. Our goal is to develop and test a novel methodology to compute accurate close pair fractions with photometric redshifts. Methods. We improve the current methodologies to estimate the merger fraction fm from photometric redshifts by (i) using the full probability distribution functions (PDFs) of the sources in redshift space, (ii) including the variation in the luminosity of the sources with z in both the selection of the samples and in the luminosity ratio constrain, and (iii) splitting individual PDFs into red and blue spectral templates to deal robustly with colour selections. We test the performance of our new methodology with the PDFs provided by the ALHAMBRA photometric survey. Results. The merger fractions and rates from the ALHAMBRA survey are in excellent agreement with those from spectroscopic work, both for the general population and for red and blue galaxies. With the merger rate of bright (MB 20 1:1z) galaxies evolving as (1 + z) n , the power-law index n is larger for blue galaxies (n = 2:7 0:5) than for red galaxies (n = 1:3 0:4), confirming previous results. Integrating the merger rate over cosmic time, we find that the average number of mergers per galaxy since z = 1 is N red m = 0:57 0:05 for red galaxies and N blue m = 0:26 0:02 for blue galaxies. Conclusions. Our new methodology exploits statistically all the available information provided by photometric redshift codes and provides accurate measurements of the merger fraction by close pairs only using photometric redshifts. Current and future photometric surveys will benefit of this new methodology.

Galaxy clusters and groups in the ALHAMBRA survey

Ministerio de Economia y Competitividad AYA2010-22111-C03-02, AYA2010-15169, AYA2012-30789, AYA2013-48623-C2-2, AYA2013-42227-P, AYA2013-40611-P, AYA2011-29517-C03-01, AYA2014-58861-C3-1, AYA2010-15081

The ALHAMBRA survey: reliable morphological catalogue of 22 051 early- and late-type galaxies

This research was supported by the Junta de Andalucia through projects PO8-TIC-03531 and TIC114, the Spanish Ministry of Economy and Competitiveness (MINECO) through projects AYA2006-14046, AYA2010-15169, AYA2010-22111-C03-02, AYA2011-29517-C03-01, and the Generalitat Valenciana through project GV/Prometeo 2009/064. MP acknowledges financial support from JAE-Doc program of the Spanish National Research Council (CSIC), co-funded by the European Social Fund.

Quasi-stellar objects in the ALHAMBRA survey: I. Photometric redshift accuracy based on 23 optical-NIR filter photometry

Context. Even the spectroscopic capabilities of today’s ground and space-based observatories can not keep up with the enormous flow of detections (>10 5 deg −2 ) unveiled in modern cosmological surveys as: i) would be required enormous telescope time to perform the spectroscopic follow-ups and ii) spectra remain unattainable for the fainter detected population. In the past decade, the typical accuracy of photometric redshift (photo-z) determination has drastically improved. Nowdays, it has become a perfect complement to spectroscopy, closing the gap between photometric surveys and their spectroscopic follow-ups. The photo-z precision for active galactic nuclei (AGN) has always lagged behind that for the galaxy population owing to the lack of proper templates and their intrinsic variability. Aims. Our goal is to characterize the ability of the Advanced Large, Homogeneous Area Medium-Band Redshift Astronomical (ALHAMBRA) survey in assigning accurate photo-z’s to broad-line AGN (BLAGN) and quasi-stellar objects (QSOs) based on their ALHAMBRA very-low-resolution optical-near-infrared (NIR) spectroscopy. This will serve as a benchmark for any future compilation of ALHAMBRA selected QSOs and the basis for the statistical analysis required to derive luminosity functions up to z ∼ 5. Methods. We selected a sample of spectroscopically identified BLAGN and QSOs and used a library of templates (including the SEDs of AGN and both normal and starburst galaxies, as well as stars) to fit the 23 photometric data points provided by ALHAMBRA in the optical and NIR (20 medium-band optical filters plus the standard JHKs). Results. We find that the ALHAMBRA photometry is able to provide an accurate photo-z and spectral classification for ∼88% of the 170 spectroscopically identified BLAGN/QSOs over 2.5 deg 2 in different areas of the survey and brighter than m678 = 23.5 (equivalent to rSLOAN ∼ 24.0). The derived photo-z accuracy is below 1% and is comparable to the most recent results in other cosmological fields that use photometric information over a wider wavelength range. The fraction of outliers (∼12%) is mainly caused by the larger photometric errors for the faintest sources and the intrinsic variability of the BLAGN/QSO population. A small fraction of outliers may have an incorrectly assigned spectroscopic redshift. Conclusions. The definition of the ALHAMBRA survey in terms of the number of filters, filter properties, areal coverage, and depth is able to provide photometric redshifts for BLAGN/QSOs with a precision similar to any previous survey that makes use of mediumband optical photometry. In agreement with previous literature results, our analysis also reveals that, in the 0 4). These results are relevant for the design of future optical follow-ups of surveys containing a large fraction of BLAGN, such as many X–ray or radio surveys.

Stellar populations of galaxies in the ALHAMBRA survey up to z ~ 1

Aims. We present MUFFIT, a new generic code optimized to retrieve the main stellar population parameters of galaxies in photometric multi-filter surveys, and check its reliability and feasibility with real galaxy data from the ALHAMBRA survey. Methods. Making use of an error-weighted χ 2 -test, we compare the multi-filter fluxes of galaxies with the synthetic photometry of mixtures of two single stellar populations at different redshifts and extinctions, to provide the most likely range of stellar population parameters (mainly ages and metallicities), extinctions, redshifts, and stellar masses. To improve the diagnostic reliability, MUFFIT identifies and removes from the analysis those bands that are significantly affected by emission lines. The final parameters and their uncertainties are derived by a Monte Carlo method, using the individual photometric uncertainties in each band. Finally, we discuss the accuracies, degeneracies, and reliability of MUFFIT using both simulated and real galaxies from ALHAMBRA, comparing with results from the literature. Results. MUFFIT is a precise and reliable code to derive stellar population parameters of galaxies in ALHAMBRA. Using the results from photometric-redshift codes as input, MUFFIT improves the photometric-redshift accuracy by ∼10–20%. MUFFIT also detects nebular emissions in galaxies, providing physical information about their strengths. The stellar masses derived from MUFFIT show excellent agreement with the COSMOS and SDSS values. In addition, the retrieved age-metallicity locus for a sample of z ≤ 0.22 early-type galaxies in ALHAMBRA at different stellar mass bins are in very good agreement with the ones from SDSS spectroscopic diagnostics. Moreover, a one-to-one comparison between the redshifts, ages, metallicities, and stellar masses derived spectroscopically for SDSS and by MUFFIT for ALHAMBRA reveals good qualitative agreements in all the parameters, hence reinforcing the strengths of multi-filter galaxy data and optimized analysis techniques, like MUFFIT, to conduct reliable stellar population studies.

Stellar populations of galaxies in the ALHAMBRA survey up to z ~ 1 - I. MUFFIT: A multi-filter fitting code for stellar population diagnostics

Aims. We present MUFFIT, a new generic code optimized to retrieve the main stellar population parameters of galaxies in photometric multi-filter surveys, and check its reliability and feasibility with real galaxy data from the ALHAMBRA survey. Methods. Making use of an error-weighted χ 2 -test, we compare the multi-filter fluxes of galaxies with the synthetic photometry of mixtures of two single stellar populations at different redshifts and extinctions, to provide the most likely range of stellar population parameters (mainly ages and metallicities), extinctions, redshifts, and stellar masses. To improve the diagnostic reliability, MUFFIT identifies and removes from the analysis those bands that are significantly affected by emission lines. The final parameters and their uncertainties are derived by a Monte Carlo method, using the individual photometric uncertainties in each band. Finally, we discuss the accuracies, degeneracies, and reliability of MUFFIT using both simulated and real galaxies from ALHAMBRA, comparing with results from the literature. Results. MUFFIT is a precise and reliable code to derive stellar population parameters of galaxies in ALHAMBRA. Using the results from photometric-redshift codes as input, MUFFIT improves the photometric-redshift accuracy by ∼10–20%. MUFFIT also detects nebular emissions in galaxies, providing physical information about their strengths. The stellar masses derived from MUFFIT show excellent agreement with the COSMOS and SDSS values. In addition, the retrieved age-metallicity locus for a sample of z ≤ 0.22 early-type galaxies in ALHAMBRA at different stellar mass bins are in very good agreement with the ones from SDSS spectroscopic diagnostics. Moreover, a one-to-one comparison between the redshifts, ages, metallicities, and stellar masses derived spectroscopically for SDSS and by MUFFIT for ALHAMBRA reveals good qualitative agreements in all the parameters, hence reinforcing the strengths of multi-filter galaxy data and optimized analysis techniques, like MUFFIT, to conduct reliable stellar population studies.