K_(s) number counts in the Groth and Coppi fields

We have used William Herschel Telescope/INGRID K_(s) images on two high-latitude fields, the Coppi and Groth strips, to obtain galaxy number counts over similar to 180 arcmin^(2), to a depth of K_(s) similar to 21.0. Detection efficiency corrections as a function of object size have been calculated on each pointing. We have used a signal-to-noise threshold in two complementary half-exposure images to remove spurious detections. Our data cover the range from K_(s) = 14.5 to K_(s) = 21.0, so they are useful for investigating a previously reported change in the number count slope (d log N/dm) at K similar to 17. We find a slope gamma(b) = 0.54 0.63 for K 17.5. A total contribution from galaxies to the extragalactic background light (EBL) in the K band of nuI(nu) = 10.5 nW m^(-2) sr^(-1) has been calculated. This K-band EBL coming from galaxies accounts for only similar to 50% of the recent measurements of the diffuse EBL. Standard number count models fail to reproduce the observed slope change at K similar to 17.5 unless elliptical and spiral formation is pushed to z less than or similar to 2

K-s number counts in the Groth and Coppi fields

We have used William Herschel Telescope/INGRID K_(s) images on two high-latitude fields, the Coppi and Groth strips, to obtain galaxy number counts over ~ 180 arcmin^(2), to a depth of K_(s) ~ 21:0. Detection efficiency corrections as a function of object size have been calculated on each pointing. We have used a signalto-noise threshold in two complementary half-exposure images to remove spurious detections. Our data cover the range from K_(s) = 14.5 to K_(s) = 21.0, so they are useful for investigating a previously reported change in the number count slope (d log N/dm) at K ~ 17. We find a slope ϒ_(b)= 0:54- 0:63 for K 17.5. A total contribution from galaxies to the extragalactic background light (EBL) in the K band of νI_(ν)=10.5 nW m^(-2) sr^(-1) has been calculated. This K-band EBL coming from galaxies accounts for only ~50% of the recent measurements of the diffuse EBL. Standard number count models fail to reproduce the observed slope change at K ~ 17.5 unless elliptical and spiral formation is pushed to z<̱̱̰2

Evolutionary paths among different red galaxy types at 0.3 < z < 1.5 and the late buildup of massive E-S0's through major mergers

Some recent observations seem to disagree with hierarchical theories of galaxy formation about the role played by major mergers in the late buildup of massive E-S0s. We re-address this question by analysing the morphology, structural distortion level and star formation enhancement of a sample of massive galaxies (M_* > 5x10^10M_⨀) lying on the Red Sequence and its surroundings at 0.3 10^11 M_⨀ at z = 0 through gas-rich major mergers has frozen since z similar to 0.6. All these facts support that major mergers have played a dominant role in the definitive buildup of present-day E-S0s with M-* > 10(11) M-circle dot at 0.6 < z < 1.2, in good agreement with hierarchical scenarios of galaxy formation

ELDAR, a new method to identify AGN in multi-filter surveys: the ALHAMBRA test-case

International audienceWe present eldar, a new method that exploits the potential of medium- and narrow-band filter surveys to securely identify active galactic nuclei (AGN) and determine their redshifts. Our methodology improves on traditional approaches by looking for AGN emission lines expected to be identified against the continuum, thanks to the width of the filters. To assess its performance, we apply eldar to the data of the ALHAMBRA (Advance Large Homogeneous Area Medium Band Redshift Astronomical) survey, which covered an effective area of 2.38 deg^2 with 20 contiguous medium-band optical filters down to F814W ≃ 24.5. Using two different configurations of  eldar in which we require the detection of at least two and three emission lines, respectively, we extract two catalogues of type-I AGN. The first is composed of 585 sources (79  per cent of them spectroscopically unknown) down to  F814W = 22.5 at z_phot > 1, which corresponds to a surface density of 209 deg^−2. In the second, the 494 selected sources (83  per cent of them spectroscopically unknown) reach F814W = 23 at z_phot > 1.5, for a corresponding number density of 176 deg^−2. Then, using samples of spectroscopically known AGN in the ALHAMBRA fields, for the two catalogues we estimate a completeness of 73  per cent and 67  per cent, and a redshift precision of 1.01  per cent and 0.86  per cent (with outliers fractions of 8.1  per cent and 5.8  per cent). At z > 2, where our selection performs best, we reach 85  per cent and 77  per cent completeness and we find no contamination from galaxies