76 research outputs found
Dinosaur tracks from the Kilmaluag Formation (Bathonian, Middle Jurassic) of Score Bay, Isle of Skye, Scotland, UK
Tracks of a juvenile theropod dinosaur with footprint lengths of between 2 and 9 cm as well as adults of the same ichnospecies with footprints of about 15–25 cm in length were found in the Bathonian (Middle Jurassic) Kilmaluag Formation of Score Bay, northwestern Trotternish Peninsula, Isle of Skye, Scotland, UK. Two footprint sizes occur together on the same bedding plane in the central portion of Score Bay, both in situ and on loose blocks. Another horizon containing footprints above this was also identified. The footprints from the lowest horizon were produced in a desiccated silty mud that was covered with sand. A close association of both adults and juveniles with similar travel direction indicated by the footprints may suggest post-hatching care in theropod dinosaurs. Other footprints, produced on a rippled sandy substrate, have been found on the slightly higher bedding plane at this locality. Loose blocks found 130 m to the northeast in the central part of Score Bay have not been correlated with any in situ sediments, but were preserved in a similar manner to those from the higher bedding plane. These tracks represent the youngest dinosaur remains yet found in Scotland
The VIMOS VLT Deep Survey - Evolution of the luminosity functions by galaxy type up to z=1.5 from first epoch data
From the first epoch observations of the VVDS up to z=1.5 we have derived
luminosity functions (LF) of different spectral type galaxies. The VVDS data,
covering ~70% of the life of the Universe, allow for the first time to study
from the same sample and with good statistical accuracy the evolution of the
LFs by galaxy type in several rest frame bands from a purely magnitude selected
sample. The magnitude limit of the VVDS allows the determination of the faint
end slope of the LF with unprecedented accuracy. Galaxies have been classified
in four spectral classes, using their colours and redshift, and LFs have been
derived in the U, B, V, R and I rest frame bands from z=0.05 to z=1.5. We find
a significant steepening of the LF going from early to late types. The M*
parameter is significantly fainter for late type galaxies and this difference
increases in the redder bands. Within each of the galaxy spectral types we find
a brightening of M* with increasing redshift, ranging from =< 0.5 mag for early
type galaxies to ~1 mag for the latest type galaxies, while the slope of the LF
of each spectral type is consistent with being constant with redshift. The LF
of early type galaxies is consistent with passive evolution up to z~1.1, while
the number of bright early type galaxies has decreased by ~40% from z~0.3 to
z~1.1. We also find a strong evolution in the normalization of the LF of latest
type galaxies, with an increase of more than a factor 2 from z~0.3 to z~1.3:
the density of bright late type galaxies in the same redshift range increases
of a factor ~6.6. These results indicate a strong type-dependent evolution and
identifies the latest spectral types as responsible for most of the evolution
of the UV-optical luminosity function out to z=1.5.Comment: 18 pages with encapsulated figures, revised version after referee's
comments, accepted for publication in A&
The evolution of the luminosity functions in the FORS Deep Field from low to high redshift: I. The blue bands
We use the very deep and homogeneous I-band selected dataset of the FORS Deep
Field (FDF) to trace the evolution of the luminosity function over the redshift
range 0.5 < z < 5.0. We show that the FDF I-band selection down to I(AB)=26.8
misses of the order of 10 % of the galaxies that would be detected in a K-band
selected survey with magnitude limit K(AB)=26.3 (like FIRES). Photometric
redshifts for 5558 galaxies are estimated based on the photometry in 9 filters
(U, B, Gunn g, R, I, SDSS z, J, K and a special filter centered at 834 nm). A
comparison with 362 spectroscopic redshifts shows that the achieved accuracy of
the photometric redshifts is (Delta z / (z_spec+1)) < 0.03 with only ~ 1 %
outliers. This allows us to derive luminosity functions with a reliability
similar to spectroscopic surveys. In addition, the luminosity functions can be
traced to objects of lower luminosity which generally are not accessible to
spectroscopy. We investigate the evolution of the luminosity functions
evaluated in the restframe UV (1500 Angstroem and 2800 Angstroem), u', B, and
g' bands. Comparison with results from the literature shows the reliability of
the derived luminosity functions. Out to redshifts of z ~ 2.5 the data are
consistent with a slope of the luminosity function approximately constant with
redshift, at a value of -1.07 +- 0.04 in the UV (1500 Angstroem, 2800
Angstroem) as well as u', and -1.25 +- 0.03 in the blue (g', B). We do not see
evidence for a very steep slope (alpha < -1.6) in the UV at z ~ 3.0 and z ~ 4.0
favoured by other authors. There may be a tendency for the faint-end slope to
become shallower with increasing redshift but the effect is marginal. We find a
brightening of M_star and a decrease of Phi_star with redshift for all analyzed
wavelengths. [abridged]Comment: 30 pages, re-submitted to A&A after referee comments have been taken
into account, full-resolution version available at
http://www.usm.uni-muenchen.de/people/gabasch/publications/gabasch_lfblue.p
The WiggleZ Dark Energy Survey: the transition to large-scale cosmic homogeneity
We have made the largest-volume measurement to date of the transition to
large-scale homogeneity in the distribution of galaxies. We use the WiggleZ
survey, a spectroscopic survey of over 200,000 blue galaxies in a cosmic volume
of ~1 (Gpc/h)^3. A new method of defining the 'homogeneity scale' is presented,
which is more robust than methods previously used in the literature, and which
can be easily compared between different surveys. Due to the large cosmic depth
of WiggleZ (up to z=1) we are able to make the first measurement of the
transition to homogeneity over a range of cosmic epochs. The mean number of
galaxies N(<r) in spheres of comoving radius r is proportional to r^3 within
1%, or equivalently the fractal dimension of the sample is within 1% of D_2=3,
at radii larger than 71 \pm 8 Mpc/h at z~0.2, 70 \pm 5 Mpc/h at z~0.4, 81 \pm 5
Mpc/h at z~0.6, and 75 \pm 4 Mpc/h at z~0.8. We demonstrate the robustness of
our results against selection function effects, using a LCDM N-body simulation
and a suite of inhomogeneous fractal distributions. The results are in
excellent agreement with both the LCDM N-body simulation and an analytical LCDM
prediction. We can exclude a fractal distribution with fractal dimension below
D_2=2.97 on scales from ~80 Mpc/h up to the largest scales probed by our
measurement, ~300 Mpc/h, at 99.99% confidence.Comment: 21 pages, 16 figures, accepted for publication in MNRA
Three-dimensional Topology-Independent Methods to Look for Global Topology
The space-like hypersurface of the Universe at the present cosmological time
is a three-dimensional manifold. A non-trivial global topology of this
space-like hypersurface would imply that the apparently observable universe
(the sphere of particle horizon radius) could contain several images of the
single, physical Universe. Recent three-dimensional techniques for constraining
and/or detecting this topology are reviewed. Initial applications of these
techniques using X-ray bright clusters of galaxies and quasars imply (weak)
candidates for a non-trivial topology.Comment: minor revision; 7 pages, 1 figure, accepted by Classical and Quantum
Gravit
Can the Universe Create Itself?
The question of first-cause has troubled philosophers and cosmologists alike.
Now that it is apparent that our universe began in a Big Bang explosion, the
question of what happened before the Big Bang arises. Inflation seems like a
very promising answer, but as Borde and Vilenkin have shown, the inflationary
state preceding the Big Bang must have had a beginning also. Ultimately, the
difficult question seems to be how to make something out of nothing. This paper
explores the idea that this is the wrong question --- that that is not how the
Universe got here. Instead, we explore the idea of whether there is anything in
the laws of physics that would prevent the Universe from creating itself.
Because spacetimes can be curved and multiply connected, general relativity
allows for the possibility of closed timelike curves (CTCs). Thus, tracing
backwards in time through the original inflationary state we may eventually
encounter a region of CTCs giving no first-cause. This region of CTCs, may well
be over by now (being bounded toward the future by a Cauchy horizon). We
illustrate that such models --- with CTCs --- are not necessarily inconsistent
by demonstrating self-consistent vacuums for Misner space and a multiply
connected de Sitter space in which the renormalized energy-momentum tensor does
not diverge as one approaches the Cauchy horizon and solves Einstein's
equations. We show such a Universe can be classically stable and
self-consistent if and only if the potentials are retarded, giving a natural
explanation of the arrow of time. Some specific scenarios (out of many possible
ones) for this type of model are described. For example: an inflationary
universe gives rise to baby universes, one of which turns out to be itself.
Interestingly, the laws of physics may allow the Universe to be its own mother.Comment: 48 pages, 8 figure
Spherically Symmetric Non Linear Structures
We present an analytical method to extract observational predictions about
non linear evolution of perturbations in a Tolman Universe. We assume no a
priori profile for them. We solve perturbatively a Hamilton - Jacobi equation
for a timelike geodesic and obtain the null one as a limiting case in two
situations: for an observer located in the center of symmetry and for a non -
centered one. In the first case we find expressions to evaluate the density
contrast and the number count and luminosity distance vs redshift relationships
up to second order in the perturbations. In the second situation we calculate
the CMBR anisotropies at large angular scales produced by the density contrast
and by the asymmetry of the observer's location, up to first order in the
perturbations. We develope our argument in such a way that the formulae are
valid for any shape of the primordial spectrum.Comment: 27 pages, uses RevTex. Modified in response to referee's Comments
(submitted to PRD
A small non-vanishing cosmological constant from vacuum energy: physically and observationally desirable
Increasing improvements in the independent determinations of the Hubble
constant and the age of the universe now seem to indicate that we need a small
non-vanishing cosmological constant to make the two independent observations
consistent with each other. The cosmological constant can be physically
interpreted as due to the vacuum energy of quantized fields. To make the
cosmological observations consistent with each other we would need a vacuum
energy density, today ( in the cosmological
units ). It is argued in this article that such a vacuum energy
density is natural in the context of phase transitions linked to massive
neutrinos. In fact, the neutrino masses required to provide the right vacuum
energy scale to remove the age Vs Hubble constant discrepancy are consistent
with those required to solve the solar neutrino problem by the MSW mechanism.Comment: 25 pages, latex, revised version to appear in Phys. Rev. D52 (1995):
contains an expanded and clarified discussion of the particle physics model
and connected issue
The Large Scale Structure in the Universe: From Power-Laws to Acoustic Peaks
The most popular tools for analysing the large scale distribution of galaxies
are second-order spatial statistics such as the two-point correlation function
or its Fourier transform, the power spectrum. In this review, we explain how
our knowledge of cosmic structures, encapsulated by these statistical
descriptors, has evolved since their first use when applied on the early galaxy
catalogues to the present generation of wide and deep redshift surveys,
incorporating the most challenging discovery in the study of the galaxy
distribution: the detection of Baryon Acoustic Oscillations.Comment: 20 pages, 12 figures, to appear in "Data Analysis in Cosmology",
Lecture Notes in Physics, 2008, eds. V. J. Martinez, E. Saar, E.
Martinez-Gonzalez, and M.J. Pons-Borderia, Springer-Verla
Galaxy luminosity function per morphological type up to z=1.2
We have computed the evolution of the rest-frame B-band luminosity function
(LF) for bulge and disk-dominated galaxies since z=1.2. We use a sample of 605
spectroscopic redshifts with I_{AB}<24 in the Chandra Deep Field South from the
VIMOS-VLT Deep Survey, 3555 galaxies with photometric redshifts from the
COMBO-17 multi-color data, coupled with multi-color HST/ACS images from the
Great Observatories Origin Deep Survey. We split the sample in bulge- and
disk-dominated populations on the basis of asymmetry and concentration
parameters measured in the rest-frame B-band. We find that at z=0.4-0.8, the LF
slope is significantly steeper for the disk-dominated population (\alpha=-1.19
\pm 0.07) compared to the bulge-dominated population (\alpha=-0.53 \pm 0.13).
The LF of the bulge-dominated population is composed of two distinct
populations separated in rest-frame color: 68% of red (B-I)_{AB}>0.9 and bright
galaxies showing a strongly decreasing LF slope \alpha=+0.55 \pm 0.21, and 32%
of blue (B-I)_{AB}<0.9 and more compact galaxies which populate the LF
faint-end. We observe that red bulge-dominated galaxies are already well in
place at z~1, but the volume density of this population is increasing by a
factor 2.7 between z~1 and z~0.6. It may be related to the building-up of
massive elliptical galaxies in the hierarchical scenario. In addition, we
observe that the blue bulge-dominated population is dimming by 0.7 magnitude
between z~1 and z~0.6. Galaxies in this faint and more compact population could
possibly be the progenitors of the local dwarf spheroidal galaxies.Comment: 9 pages, 4 figures, 2 tables, accepted for publication in Astronomy
and Astrophysic
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