980 research outputs found
Study of thermometers for measuring a microcanonical phase transition in nuclear fragmentation
The aim of this work is to study how the thermodynamic temperature is related
to the known thermometers for nuclei especially in view of studying the
microcanonical phase transition. We find within the MMMC-model that the
"S-shape" of the caloric equation of state e^*(T) which is the signal of a
phase transition in a system with conserved energy, can be seen in the
experimentally accessible slope temperatures T_slope for different particle
types and also in the isotopic temperatures T_He-Li. The isotopic temperatures
T_H-He are weaker correlated to the shape of the thermodynamic temperature and
therefore are less favorable to study the signal of a microcanonical phase
transition. We also show that the signal is very sensitive to variations in
mass of the source
Automated reliability assessment for spectroscopic redshift measurements
We present a new approach to automate the spectroscopic redshift reliability
assessment based on machine learning (ML) and characteristics of the redshift
probability density function (PDF).
We propose to rephrase the spectroscopic redshift estimation into a Bayesian
framework, in order to incorporate all sources of information and uncertainties
related to the redshift estimation process, and produce a redshift posterior
PDF that will be the starting-point for ML algorithms to provide an automated
assessment of a redshift reliability.
As a use case, public data from the VIMOS VLT Deep Survey is exploited to
present and test this new methodology. We first tried to reproduce the existing
reliability flags using supervised classification to describe different types
of redshift PDFs, but due to the subjective definition of these flags, soon
opted for a new homogeneous partitioning of the data into distinct clusters via
unsupervised classification. After assessing the accuracy of the new clusters
via resubstitution and test predictions, unlabelled data from preliminary mock
simulations for the Euclid space mission are projected into this mapping to
predict their redshift reliability labels.Comment: Submitted on 02 June 2017 (v1). Revised on 08 September 2017 (v2).
Latest version 28 September 2017 (this version v3
On the galaxy luminosity function in the central regions of the Coma cluster
We have obtained new redshifts for 265 objects in the central
48~~25~arcmin region of the Coma cluster. When supplemented with
literature data, our redshift sample is 95~\% complete up to a magnitude
b=18.0 (the magnitudes are taken from the photometric sample of Godwin
et al. 1983). Using redshift-confirmed membership for 205 galaxies, and the
location in the colour-magnitude diagram for another 91 galaxies, we have built
a sample of cluster members which is complete up to b=20.0. We show
that the Coma cluster luminosity function cannot be adequately fitted by a
single Schechter (1976) function, because of a dip in the magnitude
distribution at b17. The superposition of an Erlang (or a Gauss)
and a Schechter function provides a significantly better fit. We compare the
luminosity function of Coma to those of other clusters, and of the field.
Luminosity functions for rich clusters look similar, with a maximum at , while the Virgo and the field luminosity
functions show a nearly monotonic behaviour. These differences may be produced
by physical processes related to the environment which affect the luminosities
of a certain class of cluster galaxies.Comment: 7 pages, uuencoded postscript file (figures included) Accepted for
publication on A&
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&
Isoscaling and the symmetry energy in spectator fragmentation
Isoscaling and its relation to the symmetry energy in the fragmentation of
excited residues produced at relativistic energies were studied in two
experiments conducted at the GSI laboratory. The INDRA multidetector has been
used to detect and identify light particles and fragments with Z <= 5 in
collisions of 12C on 112,124Sn at incident energies of 300 and 600 MeV per
nucleon. Isoscaling is observed, and the deduced parameters decrease with
increasing centrality. Symmetry term coefficients, deduced within the
statistical description of isotopic scaling, are near gamma = 25 MeV for
peripheral and gamma < 15 MeV for central collisions.
In a very recent experiment with the ALADIN spectrometer, the possibility of
using secondary beams for reaction studies at relativistic energies has been
explored. Beams of 107Sn, 124Sn, 124La, and 197Au were used to investigate the
mass and isospin dependence of projectile fragmentation at 600 MeV per nucleon.
The decrease of the isoscaling parameters is confirmed and extended over the
full fragmentation regime covered in these reactions.Comment: Proceedings of the IWM2005, Catania, Italy, Nov 200
Accurate photometric redshifts for the CFHT Legacy Survey calibrated using the VIMOS VLT Deep Survey
We present photometric redshifts for an uniquely large and deep sample of
522286 objects with i'_{AB}<25 in the Canada-France Legacy Survey ``Deep
Survey'' fields, which cover a total effective area of 3.2 deg^2. We use 3241
spectroscopic redshifts with 0<z<5 from the VIMOS VLT Deep Survey as a
calibration to derive these photometric redshifts. We devise a robust
calibration method which removes systematic trends in the photometric redshifts
and significantly reduces the fraction of catastrophic errors. We use our
unique spectroscopic sample to present a detailed assessment of the robustness
of the photometric redshift sample. For a sample selected at i'_{AB}<24, we
reach a redshift accuracy of \sigma_{\Delta z/(1+z)}=0.037 with \eta=3.7% of
catastrophic error. The reliability of our photometric redshifts is lower for
fainter objects: we find \sigma_{\Delta z/(1+z)}=0.029, 0.043 and \eta=1.7%,
5.4% for samples selected at i'_{AB}=17.5-22.5 and 22.5-24 respectively. We
find that the photometric redshifts of starburst galaxies in our sample are
less reliable: although these galaxies represent only 18% of the spectroscopic
sample they are responsible for 54% of the catastrophic errors. We find an
excellent agreement between the photometric and the VVDS spectroscopic redshift
distributions at i'_{AB}<24. Finally, we compare the redshift distributions of
i' selected galaxies on the four CFHTLS deep fields, showing that cosmic
variance is already present on fields of 0.8 deg^2.Comment: 19 pages, 17 figures, submitted to A&A. The photometric redshifts
described in this paper will be made publicly available from 1st may 2006 at
http://terapix.iap.fr and http://cencosw.oamp.fr
Giant Anisotropy of Spin-Orbit Splitting at the Bismuth Surface
We investigate the bismuth (111) surface by means of time and angle resolved
photoelectron spectroscopy. The parallel detection of the surface states below
and above the Fermi level reveals a giant anisotropy of the Spin-Orbit (SO)
spitting. These strong deviations from the Rashba-like coupling cannot be
treated in perturbation theory. Instead, first
principle calculations could accurately reproduce the experimental dispersion
of the electronic states. Our analysis shows that the giant anisotropy of the
SO splitting is due to a large out-of plane buckling of the spin and orbital
texture.Comment: 5 pages, 4 figure
The Star Formation Rate Density and Dust Attenuation Evolution over 12 Gyr with the VVDS Surveys
[Abridged] We investigate the global galaxy evolution over 12 Gyr
(0.05<z<4.5), from the star formation rate density (SFRD), combining the VVDS
Deep (17.5<=I<=24.0) and Ultra-Deep (23.00<=i<=24.75) surveys. We obtain a
single homogeneous spectroscopic redshift sample, totalizing about 11000
galaxies. We estimate the rest-frame FUV luminosity function (LF) and
luminosity density (LD), extract the dust attenuation of the FUV radiation
using SED fitting, and derive the dust-corrected SFRD. We find a constant and
flat faint-end slope alpha in the FUV LF at z1.7, we set alpha
steepening with (1+z). The absolute magnitude M*_FUV brightens in the entire
range 02 it is on average brighter than in the literature,
while phi* is smaller. Our total LD shows a peak at z=2, present also when
considering all sources of uncertainty. The SFRD history peaks as well at z=2.
It rises by a factor of 6 during 2 Gyr (from z=4.5 to z=2), and then decreases
by a factor of 12 during 10 Gyr down to z=0.05. This peak is mainly produced by
a similar peak within the population of galaxies with -21.5<=M_FUV<=-19.5 mag.
As times goes by, the total SFRD is dominated by fainter and fainter galaxies.
The presence of a clear peak at z=2 and a fast rise at z>2 of the SFRD is
compelling for models of galaxy formation. The mean dust attenuation A_FUV of
the global galaxy population rises by 1 mag during 2 Gyr from z=4.5 to z=2,
reaches its maximum at z=1 (A_FUV=2.2 mag), and then decreases by 1.1 mag
during 7 Gyr down to z=0. The dust attenuation maximum is reached 2 Gyr after
the SFRD peak, implying a contribution from the intermediate-mass stars to the
dust production at z<2.Comment: 23 pages, 15 figures, accepted for publication in A&
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