611 research outputs found
Clustering at high redshift
The addition of deep near infrared images to the database provided by the
HDF-S WFPC2 is essential to monitor the SEDs of the objects on a wide baseline
and address a number of key issues including the total stellar content of
baryonic mass, the effects of dust extinction, the dependence of morphology on
the rest frame wavelength, the photometric redshifts, the detection and nature
of extremely red objects (EROs). For these reasons deep near infrared images
were obtained with the ISAAC instrument at the ESO VLT in the Js, H and Ks
bands reaching, respectively, 23.5, 22.0, 22.0 limiting Vega-magnitude. A
multi-color (F300, F450, F606, F814, Js, H, Ks) photometric catalog of the
HDF-S has been produced. Photometric redshifts have been generated both fitting
templates to the observed SEDs and with neural network techniques.
Spectroscopic observations of the 9 candidates with I_AB <24.25 have confirmed
all of them to be galaxies with 2<z<3.5. The photometric redshifts for all the
galaxies brighter than I_AB< 27.5 have been used to study the evolution of
galaxy clustering in the interval 0<z<4.5.Comment: 2 pages Latex, To appear in the proceedings of "The mass of galaxies
at low and high redshift", Venice, Oct 24-26, 2001,eds. R. Bender and A.
Renzini (ESO Astrophysics Symposia, Springer-Verlag
The assembly of massive galaxies from NIR observations of the Hubble Deep Field South
We use a deep K(AB)<25 galaxy sample in the Hubble Deep Field South to trace
the evolution of the cosmological stellar mass density from z~ 0.5 to z~3. We
find clear evidence for a decrease of the average stellar mass density at high
redshift, 2<z<3.2, that is 15^{+25}_{-5}% of the local value, two times higher
than what observed in the Hubble Deep Field North. To take into account for the
selection effects, we define a homogeneous subsample of galaxies with
10^{10}M_\odot \leq M_* \leq 10^{11}M_\odot: in this sample, the mass density
at z>2 is 20^{+20}_{-5} % of the local value. In the mass--limited subsample at
z>2, the fraction of passively fading galaxies is at most 25%, although they
can contribute up to about 40% of the stellar mass density. On the other hand,
star--forming galaxies at z>2 form stars with an average specific rate at least
~4 x10^{-10} yr, 3 times higher than the z<~1 value. This
implies that UV bright star--forming galaxies are substancial contributors to
the rise of the stellar mass density with cosmic time. Although these results
are globally consistent with --CDM scenarios, the present rendition of
semi analytic models fails to match the stellar mass density produced by more
massive galaxies present at z>2.Comment: Accepted for publication on ApJLetter
The Great Observatories Origins Deep Survey - VLT/VIMOS Spectroscopy in the GOODS-South Field: Part II
We present the full data set of the VIMOS spectroscopic campaign of the
ESO/GOODS program in the CDFS, which complements the FORS2 ESO/GOODS
spectroscopic campaign. The GOODS/VIMOS spectroscopic campaign is structured in
two separate surveys using two different VIMOS grisms. The VIMOS Low Resolution
Blue (LR-Blue) and Medium Resolution (MR) orange grisms have been used to cover
different redshift ranges. The LR-Blue campaign is aimed at observing galaxies
mainly at 1.8<z<3.5, while the MR campaign mainly aims at galaxies at z<1 and
Lyman Break Galaxies (LBGs) at z>3.5. The full GOODS/VIMOS spectroscopic
campaign consists of 20 VIMOS masks. This release adds 8 new masks to the
previous release (12 masks, Popesso et al. 2009). In total we obtained 5052
spectra, 3634 from the 10 LR-Blue masks and 1418 from the 10 MR masks. A
significant fraction of the extracted spectra comes from serendipitously
observed sources: ~21% in the LR-Blue and ~16% in the MR masks. We obtained
2242 redshifts in the LR-Blue campaign and 976 in the MR campaign for a total
success rate of 62% and 69% respectively, which increases to 66% and 73% if
only primary targets are considered. The typical redshift uncertainty is
estimated to be ~0.0012 (~255 km/s) for the LR-Blue grism and ~0.00040 (~120
km/s) for the MR grism. By complementing our VIMOS spectroscopic catalog with
all existing spectroscopic redshifts publicly available in the CDFS, we
compiled a redshift master catalog with 7332 entries, which we used to
investigate large scale structures out to z~3.7. We produced stacked spectra of
LBGs in a few bins of equivalent width (EW) of the Ly-alpha and found evidence
for a lack of bright LBGs with high EW of the Ly-alpha. Finally, we obtained
new redshifts for 12 X-ray sources of the CDFS and extended-CDFS.Comment: 22 pages, 20 figures, accepted for publication on Astronomy and
Astrophysics, catalogs and data products are available at
http://archive.eso.org/cms/eso-data/data-packages/goods-vimos-spectroscopy-data-release-version-2.0/,
for ESO-GOODS related material consult
http://www.eso.org/sci/activities/projects/goods
Quantum versus classical instability of scalar fields in curved backgrounds
General-relativistic stable spacetimes can be made unstable under the
presence of certain nonminimally coupled free scalar fields. In this paper, we
analyze the evolution of linear scalar-field perturbations in spherically
symmetric spacetimes and compare the classical stability analysis with a
recently discussed quantum field one. In particular, it is shown that vacuum
fluctuations lead to natural seeds for the unstable phase, whereas in the
classical framework the presence of such seeds in the initial conditions must
be assumed.Comment: 5 pages, 1 figure; condensed and revised version matching published
on
Instability of nonminimally coupled scalar fields in the spacetime of slowly rotating compact objects
Nonminimally coupled free scalar fields may be unstable in the spacetime of
compact objects. Such instability can be triggered by classical seeds or, more
simply, by quantum fluctuations giving rise to the so-called {\em vacuum
awakening effect}. Here, we investigate how the parameter space which
characterizes the instability is affected when the object gains some rotation.
For this purpose, we focus on the stability analysis of nonminimally coupled
scalar fields in the spacetime of slowly spinning matter shells.Comment: 11 pages, 6 figure
Awaking the vacuum with spheroidal shells
It has been shown that well-behaved spacetimes may induce the vacuum
fluctuations of some nonminimally coupled free scalar fields to go through a
phase of exponential growth. Here, we discuss this mechanism in the context of
spheroidal thin shells emphasizing the consequences of deviations from
spherical symmetry.Comment: 10 pages, 7 figures. Minor changes, version published on Phys. Rev.
The Luminosity Function of high-redshift QSOs - A combined analysis of GOODS and SDSS
Aims: In this work the luminosity function of QSOs is measured in the
redshift range 3.5<z<5.2 for the absolute magnitude interval -21<M_{145}<-28.
The determination of the faint end of the luminosity function at these
redshifts provides important constraints on models of joint evolution of
galaxies and AGNs. Methods: We have defined suitable criteria to select faint
QSOs in the GOODS fields, checking in detail their effectiveness and
completeness. Spectroscopic follow-up of the resulting QSO candidates has been
carried out. The confirmed sample of faint QSOs is compared with a brighter one
derived from the SDSS. We have used a Monte-Carlo technique to estimate the
properties of the luminosity function, checking various parameterizations for
its shape and evolution. Results: Models based on Pure Density Evolution show
better agreement with observation than models based on Pure Luminosity
Evolution. However a different break magnitude with respect to z~2.1 is
required at 3.5<z<5.2. Models with a steeper faint end score a higher
probability. We do not find any evidence for a flattening of the bright end at
redshift z>3.5. Conclusions: The estimated space density evolution of QSOs
indicates a suppression of the formation and/or feeding of Supermassive Black
Holes at these redshifts. The QSO contribution to the UV background is
insufficient to ionize the IGM at 3.5<z<5.2.Comment: 17 pages, 13 ps figures, A&A accepted. Updated to journal versio
Analytic Evaluation of the Decay Rate for Accelerated Proton
We evaluate the decay rate of the uniformly accelerated proton. We obtain an
analytic expression for inverse beta decay process caused by the acceleration.
We evaluate the decay rate both from the inertial frame and from the
accelerated frame where we should consider thermal radiation by Unruh effect.
We explicitly check that the decay rates obtained in both frame coincide with
each other.Comment: 11 page
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