5 research outputs found
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
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 in the redshift intervals . 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
( and ). 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 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
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
UVES observations of QSO 0000-2620: oxygen and zinc abundances in the Damped Ly-alpha galaxy at z_abs=3.3901
Observations of the QSO 0000-2620 with UVES spectrograph at the 8.2m ESO
KUEYEN telescope are used for abundance analysis of the damped Ly-alpha system
at z_{abs}=3.3901. Several Oxygen lines are identified in the Ly_alpha forest
and a measure for the oxygen abundance is obtained at [O/H]=-1.85 +/- 0.1 by
means of the unsaturated OI 925 A and OI 950 A lines. This represents the most
accurate O measurement in a damped Ly_alpha galaxy so far. We have also
detected ZnII 2026 A and CrII 2056, 2062 A redshifted at about 8900 A and found
abundances [Zn/H] = -2.07 +/- 0.1 and [Cr/H]=-1.99 +/- 0.1. Furthermore,
previous measurements of Fe, Si, Ni and N have been refined yielding
[Fe/H]=-2.04 +/- 0.1, [Si/H]=-1.90 +/- 0.1, [Ni/H]=-2.27 +/- 0.1, and
[N/H]=-2.68 +/- 0.1. The abundance of the non-refractory element zinc is the
lowest among the damped Ly-alpha systems showing that the associated
intervening galaxy is indeed in the early stages of its chemical evolution. The
fact that the Zn abundance is identical to that of the refractory elements Fe
and Cr suggests that dust grains have not formed yet. In this Damped Ly-alpha
system the observed [O,S,Si/Zn,Fe,Cr] ratios, in whatever combination are
taken, are close to solar (i.e 0.1-0.2 dex) and do not show the
[alpha-element/Fe] enhancement observed in Milky Way stars of comparable
metallicity. The observed behavior supports a galaxy evolution model
characterized by either episodic or low star formation rate rather than a
Milky-Way-type evolutionary model.Comment: Accepted by Ap
Molecular hydrogen, deuterium and metal abundances in the damped Ly-alpha system at z = 3.025 toward QSO 0347-3819
We have detected in high resolution spectra of the quasar Q0347--3819
obtained with the UVES spectrograph at the VLT/Kueyen telescope over 80
absorption features in the Lyman and Werner H2 bands at the redshift of a
damped Ly-alpha system at z = 3.025. The z = 3.025 system spans over 80 km/s
and exhibits a multicomponent velocity structure in the metal lines. The main
component at z = 3.024855 shows a total H2 column density N(H2) =
(4.10\pm0.21)*10^{14} cm^{-2} and a fractional molecular abundance f(H2) =
(1.94\pm0.10)*10^{-6} derived from the H2 lines arising from J=0 to 5
rotational levels of the ground electronic-vibrational state. For the first
time we unambiguously reveal a pronounced [alpha-element/iron-peak] enhancement
of [O,Si/Zn] = 0.6\pm0.1 (6 sigma c.l.) at high redshift. The simultaneous
analysis of metal and hydrogen lines leads to D/H = (3.75\pm0.25)*10^{-5}. This
value is consistent with standard big bang nucleosynthesis if the
baryon-to-photon ratio, eta, lies within the range 4.37*10^{-10} <= eta <=
5.32*10^{-10}, implying 0.016 <= Omega_b h^2_100 <= 0.020.Comment: 32 pages, 16 ps figures, accepted to Ap
A High-Redshift Damped Ly-α System at z_(abs) = 4.466 Towards APM BR J0307-4945
We present the results of the analysis of the chemical abundances and kinematics in a high-redshift damped Ly-α (DLA) system towards the quasar APM BR J0307-4945 observed during the Commissioning of UVES on the 8.2m ESO VLT Kueyen telescope at Cerro Paranal Observatory. With a redshift z_(abs) = 4.466 and a total neutral hydrogen column density log N(H I) = 20.67±0.09, it is the most distant DLA system known to the present date, observed when the Universe was as young as 1.3 Gyr