497 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
Early-type Galaxies in the Hubble Deep Field. The <mu_e>-r_e relation and the lack of large galaxies at high redshift
We present the results of the detailed surface photometry of a sample of
early-type galaxies in the Hubble Deep Field. Effective radii, surface
brightnesses and total V_606 magnitudes have been obtained, as well as U_300,
B_450, I_814, J, H and K colors, which are compared with the predictions of
chemical-spectrophotometric models of population synthesis. Spectroscopic
redshifts are available for 23 objects. For other 25 photometric redshifts are
given. In the -r_e plane the early-type galaxies of the HDF, once the
appropriate K+E corrections are applied, turn out to follow the `rest frame'
Kormendy relation. This evidence, linked to the dynamical information gathered
by Steidel et al.(1996), indicates that these galaxies, even at z~2-3, lie in
the Fundamental Plane, in a virial equilibrium condition. At the same redshifts
a statistically significant lack of large galaxies [i.e. with Log r_e(kpc) >
0.2] is observed.Comment: 30 pages, LaTeX with aasms4.sty macros, 9 embedded postscript figures
+ 1 postscript Table. To appear in the Astronomical Journa
Comparing the Evolution of the Galaxy Disk Sizes with CDM Models: The Hubble Deep Field
The intrinsic sizes of the field galaxies with I<26 in the Hubble and ESO-NTT
Deep Fields are shown as a function of their redshifts and absolute magnitudes
using photometric redshifts derived from the multicolor catalogs and are
compared with the CDM predictions. Extending to lower luminosities and to
higher z our previous analysis performed on the NTT field alone, we find that
the distribution of the galaxy disk sizes at different cosmic epochs is within
the range predicted by typical CDM models. However, the observed size
distribution of faint (M_B>-19) galaxies is skewed with respect to the CDM
predictions and an excess of small-size disks (R_d<2 kpc) is already present at
z~ 0.5. The excess persists up to z~3 and involves brighter galaxies . Such an
excess may be reduced if luminosity-dependent effects, like starburst activity
in interacting galaxies, are included in the physical mechanisms governing the
star formation history in CDM models.Comment: 9 pages, 3 figures, ApJ Letters in pres
ESO Imaging survey: Optical Deep Public Survey
This paper presents new five passbands (UBVRI) optical wide-field imaging
data accumulated as part of the DEEP Public Survey (DPS) carried out as a
public survey by the ESO Imaging Survey (EIS) project. Out of the 3 square
degrees originally proposed, the survey covers 2.75 square degrees, in at least
one band (normally R), and 1.00 square degrees in five passbands. The median
seeing, as measured in the final stacked images, is 0.97", ranging from 0.75"
to 2.0". The median limiting magnitudes (AB system, 2" aperture, 5 sigma
detection limit) are U_(AB)=25.65, B_(AB)=25.54, V_(AB)=25.18, R_(AB) = 24.8
and I_(AB)=24.12 mag, consistent with those proposed in the original survey
design. The paper describes the observations and data reduction using the EIS
Data Reduction System and its associated EIS/MVM library. The quality of the
individual images were inspected, bad images discarded and the remaining used
to produce final image stacks in each passband, from which sources have been
extracted. Finally, the scientific quality of these final images and associated
catalogs was assessed qualitatively by visual inspection and quantitatively by
comparison of statistical measures derived from these data with those of other
authors as well as model predictions, and from direct comparison with the
results obtained from the reduction of the same dataset using an independent
(hands-on) software system. Finally to illustrate one application of this
survey, the results of a preliminary effort to identify sub-mJy radio sources
are reported. To the limiting magnitude reached in the R and I passbands the
success rate ranges from 66 to 81% (depending on the fields). These data are
publicly available at CDS.Comment: 24 pages, 26 figures. Accepted for pubblication in A&
ESO Imaging Survey. Deep Public Survey: Multi-Color Optical Data for the Chandra Deep Field South
This paper presents multi-passband optical data obtained from observations of
the Chandra Deep Field South (CDF-S), located at alpha ~ 3h 32m, delta ~ -27d
48m. The observations were conducted at the ESO/MPG 2.2m telescope at La Silla
using the 8kx8k Wide-Field Imager (WFI). This data set, taken over a period of
one year, represents the first field to be completed by the ongoing Deep Public
Survey (DPS) being carried out by the ESO Imaging Survey (EIS) project. This
paper describes the optical observations, the techniques employed for
un-supervised pipeline processing and the general characteristics of the final
data set. The paper includes data taken in six different filters U'UBVRI. The
data cover an area of about 0.25 square degrees reaching 5 sigma limiting
magnitudes of U'_AB=26.0, U_AB=25.7, B_AB=26.4$, V_AB=25.4, R_AB=25.5 and I_AB=
24.7 mag, as measured within a 2xFWHM aperture. The optical data covers the
area of ~ 0.1Comment: 13 pages, 19 postscript figures, Figure 3,4,7,10 are available in
jpeg format, use aa.cls style. The full postscript of the paper is available
at http://www.eso.org/science/eis/eis_pub/eis_pub.htm
Why Optically--Faint AGN Are Faint: The Spitzer Perspective
Optically--faint X-ray sources (those with f_X/f_R > 10) constitute about 20%
of X-ray sources in deep surveys, and are potentially highly obscured and/or at
high redshift. Their faint optical fluxes are generally beyond the reach of
spectroscopy. For a sample of 20 optically--faint sources in CDFS, we compile
0.4--24 um photometry, relying heavily on Spitzer. We estimate photometric
redshifts for 17 of these 20 sources. We find that these AGN are
optically--faint both because they lie at significantly higher redshifts
(median z ~ 1.6) than most X-ray--selected AGN, and because their spectra are
much redder than standard AGN. They have 2--8 keV X-ray luminosities in the
Seyfert range, unlike the QSO--luminosities of optically--faint AGN found in
shallow, wide--field surveys. Their contribution to the X-ray Seyfert
luminosity function is comparable to that of z>1 optically--bright AGN.Comment: Accepted for publication in the Astrophysical Journa
The First VLT FORS1 spectra of Lyman-break candidates in the HDF-S and AXAF Deep Field
We report on low-resolution multi-object spectroscopy of 30 faint targets (R
\~ 24-25) in the HDF-S and AXAF deep field obtained with the VLT Focal
Reducer/low dispersion Spectrograph (FORS1). Eight high-redshift galaxies with
2.75< z < 4 have been identified. The spectroscopic redshifts are in good
agreement with the photometric ones with a dispersion at z<2
and at z>2. The inferred star formation rates of the
individual objects are moderate, ranging from a few to a few tens solar masses
per year. Five out of the eight high-z objects do not show prominent emission
lines. One object has a spectrum typical of an AGN. In the AXAF field two
relatively close pairs of galaxies have been identified, with separations of
8.7 and 3.1 proper Mpc and mean redshifts of 3.11 and 3.93, respectively.Comment: 5 pages Latex, with 2 PostScript figures. Astronomy and Astrophysics,
in pres
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