The Optical Identification of a Primeval Galaxy at z >~ 4.4

We have obtained with the SUSI CCD camera on the ESO 3.5m NTT deep images in the BVRI bands of the field centered on the QSO BRI 1202-0725 ($z_{\it em}=4.694$). In the final combined frames the stellar images have FWHM of 1,1,0.6 and 0.65 arcsec respectively. The R and I images show clearly a galaxy $2.2''$ from the QSO, corresponding to $13h^{-1}_{50}$ kpc at $z\sim 4.5$. Possible identification with the metal absorption systems seen in the line of sight to the QSO, including the highest redshift damped system known to date at $z=4.383$, are discussed. We conclude that its colours can be reconciled only with the spectrum of a primeval galaxy at z >~ 4.4, making it the most distant galaxy detected so far. From its magnitudes and models of young galaxy evolution we deduce that it is forming stars at a rate $\sim 30 M_{\odot}$ yr$^{-1}$ and has an estimated age of the order of $10^8$ yr or less, implying that the bulk of the stellar population formed at $z < 6$.Comment: 5 pages, 1 b/w + 1 color Postcript figure (6.5 Mb after decompression). Uses mn.sty (included). To appear in MNRAS Letter

Measuring the Redshift Evolution of Clustering: the Hubble Deep Field South

We present an analysis of the evolution of galaxy clustering in the redshift interval 0<z<4.5 in the HDF-S. The HST optical data are combined with infrared ISAAC/VLT observations, and photometric redshifts are used for all the galaxies brighter than I_AB<27.5. The clustering signal is obtained in different redshift bins using two different approaches: a standard one, which uses the best redshift estimate of each object, and a second one, which takes into account the redshift probability function of each object. This second method makes it possible to improve the information in the redshift intervals where contamination from objects with insecure redshifts is important. With both methods, we find that the clustering strength up to z~3.5 in the HDF-S is consistent with the previous results in the HDF-N. While at redshift lower than z~1 the HDF galaxy population is un/anti-biased (b<1) with respect to the underlying dark matter, at high redshift the bias increases up to b~2-3, depending on the cosmological model. These results support previous claims that, at high redshift, galaxies are preferentially located in massive haloes, as predicted by the biased galaxy formation scenario. The impact of cosmic errors on our analyses has been quantified, showing that errors in the clustering measurements in the HDF surveys are indeed dominated by shot-noise in most regimes. Future observations with instruments like the ACS on HST will improve the S/N by at least a factor of two and more detailed analyses of the errors will be required. In fact, pure shot-noise will give a smaller contribution with respect to other sources of errors, such as finite volume effects or non-Poissonian discreteness effects.Comment: 17 pages Latex, with 12 PostScript figures, Accepted for publication in MNRA

Speckle statistics in adaptive optics images at visible wavelengths

Residual speckles in adaptive optics (AO) images represent a well-known limitation on the achievement of the contrast needed for faint source detection. Speckles in AO imagery can be the result of either residual atmospheric aberrations, not corrected by the AO, or slowly evolving aberrations induced by the optical system. We take advantage of the high temporal cadence (1 ms) of the data acquired by the System for Coronagraphy with High-order Adaptive Optics from R to K bands-VIS forerunner experiment at the Large Binocular Telescope to characterize the AO residual speckles at visible wavelengths. An accurate knowledge of the speckle pattern and its dynamics is of paramount importance for the application of methods aimed at their mitigation. By means of both an automatic identification software and information theory, we study the main statistical properties of AO residuals and their dynamics. We therefore provide a speckle characterization that can be incorporated into numerical simulations to increase their realism and to optimize the performances of both real-time and postprocessing techniques aimed at the reduction of the speckle noise

High redshift evolution of optically and IR-selected galaxies: a comparison with CDM scenarios

A combination of ground-based (NTT and VLT) and HST (HDF-N and HDF-S) public imaging surveys have been used to collect a sample of 1712 I-selected and 319 $K\leq 21$ galaxies. Photometric redshifts have been obtained for all these galaxies. The results have been compared with the prediction of an analytic rendition of the current CDM hierarchical models for galaxy formation. We focus in particular on two observed quantities: the galaxy redshift distribution at K<21 and the evolution of the UV luminosity density. The derived photometric redshift distribution is in agreement with the hierarchical CDM prediction, with a fraction of only 5% of galaxies detected at z>2. This result strongly supports hierarchical scenarios where present-day massive galaxies are the result of merging processes. The observed UV luminosity density in the I-selected sample is confined within a factor of 4 over the whole range 0<z<4.5. CDM models in a critical Universe are not able to produce the density of UV photons that is observed at z>3. CDM models in $\Lambda$-dominated universe are in better agreement at 3<z<4.5, but predict a pronounced peak at z~1.5 and a drop by a factor of 8 from z=1.5 to z=4 that is not observed in the data. We conclude that improvements are required in the treatment of the physical processes directly related to the SFR, e.g. the starbust activity in merger processes and/or different feedback to the star formation activity.Comment: Figures 2 and 3 modified to match the published versio

Multicolor observations of the Hubble Deep Field South

We present a deep multicolor (UBVIJsHKs) catalog of galaxies in the HDF-S, based on observations obtained with the HST WFPC2 in 1998 and VLT-ISAAC in 1999. The photometric procedures were tuned to derive a catalog optimized for the estimation of photometric redshifts. In particular we adopted a ``conservative'' detection threshold which resulted in a list of 1611 objects. The behavior of the observed source counts is in general agreement with the result of Casertano et al. (2000) in the HDF-S and Williams et al. (1996) in the HDF-N, while the corresponding counts in the HDF-N provided by Fernandez-Soto et al. (1999) are systematically lower by a factor 1.5 beyond I_AB=26. After correcting for the incompleteness of the source counts, the object surface density at I_AB<27.5 is estimated to be 220 per square arcmin, providing an estimate of the Extragalactic Background Light in the I band consistent with the work of Madau & Pozzetti(2000). The comparison between the median V-I color in the HDF-North and South shows a significant difference around I_AB~26, possibly due to the presence of large scale structure at z~1 in the HDF-N. High-z galaxy candidates (90 U dropout and 17 B dropout) were selected by means of color diagrams, down to a magnitude I_AB=27, with a surface density of (21+-1) and (3.9+-0.9) per square arcmin, respectively. 11 EROs (with (I-K)_AB>2.7) were selected down to K_AB=24, plus 3 objects whose upper limit to the Ks flux is still compatible with the selection criterion. The corresponding surface density of EROs is (2.5+-0.8) per sq.arcmin ((3.2+-0.9) per sq.arcmin if we include the three Ks upper limits). They show a remarkably non-uniform spatial distribution and are classified with roughly equal fractions in the categories of elliptical and starburst galaxies.Comment: 36 pages Latex, with 12 PostScript figures. Accepted for publication in Astronomical Journa

Photometric redshifts and selection of high redshift galaxies in the NTT and Hubble Deep Fields

We present and compare in this paper new photometric redshift catalogs of the galaxies in three public fields: the NTT Deep Field, the HDF-N and the HDF-S. Photometric redshifts have been obtained for thewhole sample, by adopting a $\chi^2$ minimization technique on a spectral library drawn from the Bruzual and Charlot synthesis models, with the addition of dust and intergalactic absorption. The accuracy, determined from 125 galaxies with known spectroscopic redshifts, is $\sigma_z\sim 0.08 (0.3)$ in the redshift intervals $z=0-1.5 (1.5-3.5)$. The global redshift distribution of I-selected galaxies shows a distinct peak at intermediate redshifts, z~0.6 at I_{AB}<26 and z~0.8 at I_{AB}<27.5 followed by a tail extending to z~6. We also present for the first time the redshift distribution of the total IR-selected sample to faint limits ($Ks \leq 21$ and $J\leq22$). It is found that the number density of galaxies at 1.25<z<1.5 is ~ 0.1 /arcmin^22 at J<=21 and ~1./arcmin^2} at J<22, and drops to 0.3/arcmin^2 (at J<22) at 1.5<z<2. The HDFs data sets are used to compare the different results from color selection criteria and photometric redshifts in detecting galaxies in the redshift range 3.5<z<4.5 Photometric redshifts predict a number of high z candidates in both the HDF-N and HDF-S that is nearly 2 times larger than color selection criteria, and it is shown that this is primarily due to the inclusion of dusty models that were discarded in the original color selection criteria by Madau et al 1998. In several cases, the selection of these objects is made possible by the constraints from the IR bands. Finally, it is shown that galactic M stars may mimic z>5 candidates in the HDF filter set and that the 4 brightest candidates at $z>5$ in the HDF-S are indeed most likely M stars. (ABRIDGED)Comment: Version accepted on July, 20, 2000. To appear on Astronomical Journal, Nov 2000. The data and photometric redshift catalogs presented here are available on line at http://www.mporzio.astro.it/HIGH

Ultra-deep Large Binocular Camera U-band Imaging of the GOODS-North Field: Depth vs. Resolution

We present a study of the trade-off between depth and resolution using a large number of U-band imaging observations in the GOODS-North field (Giavalisco et al. 2004) from the Large Binocular Camera (LBC) on the Large Binocular Telescope (LBT). Having acquired over 30 hours of data (315 images with 5-6 mins exposures), we generated multiple image mosaics, starting with the best atmospheric seeing images (FWHM $\lesssim$0.8"), which constitute $\sim$10% of the total data set. For subsequent mosaics, we added in data with larger seeing values until the final, deepest mosaic included all images with FWHM $\lesssim$1.8" ($\sim$94% of the total data set). From the mosaics, we made object catalogs to compare the optimal-resolution, yet shallower image to the lower-resolution but deeper image. We show that the number counts for both images are $\sim$90% complete to $U_{AB}$ $\lesssim26$. Fainter than $U_{AB}$$\sim$ 27, the object counts from the optimal-resolution image start to drop-off dramatically (90% between $U_{AB}$ = 27 and 28 mag), while the deepest image with better surface-brightness sensitivity ($\mu^{AB}_{U}$$\lesssim$ 32 mag arcsec$^{-2}$) show a more gradual drop (10% between $U_{AB}$ $\simeq$ 27 and 28 mag). For the brightest galaxies within the GOODS-N field, structure and clumpy features within the galaxies are more prominent in the optimal-resolution image compared to the deeper mosaics. Finally, we find - for 220 brighter galaxies with $U_{AB}$$\lesssim$ 24 mag - only marginal differences in total flux between the optimal-resolution and lower-resolution light-profiles to $\mu^{AB}_{U}$$\lesssim$ 32 mag arcsec$^{-2}$. In only 10% of the cases are the total-flux differences larger than 0.5 mag. This helps constrain how much flux can be missed from galaxy outskirts, which is important for studies of the Extragalactic Background Light.Comment: 24 pages, 14 figures, submitted to PASP, comments welcom

A deep Large Binocular Telescope view of the Canes Venatici I dwarf galaxy

We present the first deep color-magnitude diagram of the Canes Venatici I (CVnI) dwarf galaxy from observations with the wide field Large Binocular Camera on the Large Binocular Telescope. Reaching down to the main-sequence turnoff of the oldest stars, it reveals a dichotomy in the stellar populations of CVnI: it harbors an old (> 10 Gyr), metal-poor ([Fe/H] ~ -2.0) and spatially extended population along with a much younger (~ 1.4-2.0 Gyr), 0.5 dex more metal-rich, and spatially more concentrated population. These young stars are also offset by 64_{-20}^{+40} pc to the East of the galaxy center. The data suggest that this young population, which represent ~ 3-5 % of the stellar mass of the galaxy within its half-light radius, should be identified with the kinematically cold stellar component found by Ibata et al. (2006). CVnI therefore follows the behavior of the other remote MW dwarf spheroidals which all contain intermediate age and/or young populations: a complex star formation history is possible in extremely low-mass galaxies.Comment: 4 pages, 3 figures, accepted for publication in ApJL. Minor changes, conclusions unchange

Asteroid Distributions in the Ecliptic

We present analysis of the asteroid surface density distribution of main belt asteroids (mean perihelion $\Delta \simeq 2.404$ AU) in five ecliptic latitude fields, -17 \gtsimeq \beta(\degr) \ltsimeq +15, derived from deep \textit{Large Binocular Telescope} (LBT) $V-$band (85% completeness limit $V = 21.3$ mag) and \textit{Spitzer Space Telescope} IRAC 8.0 \micron (80% completeness limit $\sim 103 \mu$Jy) fields enabling us to probe the 0.5--1.0 km diameter asteroid population. We discovered 58 new asteroids in the optical survey as well as 41 new bodies in the \textit{Spitzer} fields. The derived power law slopes of the number of asteroids per square degree are similar within each $\sim 5$\degr{} ecliptic latitude bin with a mean value of $-0.111 \pm 0.077$. For the 23 known asteroids detected in all four IRAC channels mean albedos range from $0.24 \pm 0.07$ to $0.10 \pm 0.05$. No low albedo asteroids ($p_{V}$ \ltsimeq 0.1) were detected in the \textit{Spitzer} FLS fields, whereas in the SWIRE fields they are frequent. The SWIRE data clearly samples asteroids in the middle and outer belts providing the first estimates of these km-sized asteroids' albedos. Our observed asteroid number densities at optical wavelengths are generally consistent with those derived from the Standard Asteroid Model within the ecliptic plane. However, we find an over density at \beta \gtsimeq 5\degr{} in our optical fields, while the infrared number densities are under dense by factors of 2 to 3 at all ecliptic latitudes.Comment: 35 pages including 5 figures, accepted to The Astronomical Journa