5,470 research outputs found
First results of the NEMO3 experiment
The objective of the NEMO Collaboration is to search for neutrinoless double beta decay and thus to investigate physics beyond the Standard Model. The expected sensitivity for the effective neutrino mass is on the order of 0.1 eV. The NEMO-3 detector has been operating in the Fréjus Underground Laboratory and has been collecting data since February of 2003. The half-life of two-neutrino double beta decay has been measured for 100Mo and 82Se. Constraints on the background for neutrinoless double beta decay have been set.
PACS: 23.40.-s Beta decay; double beta decay; electron and muon capture – 14.60.Pq Neutrino mass and mixin
Results from the search for neutrinoless double beta decay with NEMO-3 and The SuperNEMO project
International audienceThe NEMO-3 experiment located in the Modane Underground Laboratory (LSM) is searching for neutrinoless double beta decay. The experiment has been taking data since 2003 with a range of isotopes. The main isotopes are ~ 7 kg of 100Mo and ~ 1 kg of 82Se. Since no evidence for neutrinoless double beta decay has been found, a 90% Confidence Level lower limit on the half-life of this process is derived. From this we determine an upper limit on the effective Majorana neutrino mass. New results using 150Nd, an isotope of special interest due to its potential use in future experiments, will also be presented. The data are also interpreted in terms of alternative models, such as weak right-handed currents or Majoron emission. NEMO-3 has also performed precision measurements of the standard model double beta decay process for several isotopes. Measurements of this process are important for reducing the uncertainties on nuclear matrix elements. A precise measurement of the half-life for the double beta decay of 130Te and a comparison with the conflicting results from geochemical experiments has also been performed. The most recent experimental results of NEMO-3 will be presented
Bulge plus disc and S\'ersic decomposition catalogues for 16,908 galaxies in the SDSS Stripe 82 co-adds: A detailed study of the structural measurements
Quantitative characterization of galaxy morphology is vital in enabling
comparison of observations to predictions from galaxy formation theory.
However, without significant overlap between the observational footprints of
deep and shallow galaxy surveys, the extent to which structural measurements
for large galaxy samples are robust to image quality (e.g., depth, spatial
resolution) cannot be established. Deep images from the Sloan Digital Sky
Survey (SDSS) Stripe 82 co-adds provide a unique solution to this problem -
offering magnitudes improvement in depth with respect to SDSS Legacy
images. Having similar spatial resolution to Legacy, the co-adds make it
possible to examine the sensitivity of parametric morphologies to depth alone.
Using the Gim2D surface-brightness decomposition software, we provide public
morphology catalogs for 16,908 galaxies in the Stripe 82 co-adds. Our
methods and selection are completely consistent with the Simard et al. (2011)
and Mendel et al. (2014) photometric decompositions. We rigorously compare
measurements in the deep and shallow images. We find no systematics in total
magnitudes and sizes except for faint galaxies in the -band and the
brightest galaxies in each band. However, characterization of bulge-to-total
fractions is significantly improved in the deep images. Furthermore, statistics
used to determine whether single-S\'ersic or two-component (e.g., bulge+disc)
models are required become more bimodal in the deep images. Lastly, we show
that asymmetries are enhanced in the deep images and that the enhancement is
positively correlated with the asymmetries measured in Legacy images.Comment: 27 pages, 14 figures. MNRAS accepted. Our catalogs are available in
TXT and SQL formats at
http://orca.phys.uvic.ca/~cbottrel/share/Stripe82/Catalogs
Stellar mass functions of galaxies, disks and spheroids at z~0.1
We present the stellar mass functions (SMF) and mass densities of galaxies,
and their spheroid and disk components in the local (z~0.1) universe over the
range 8.9 <= log(M/M_solar) <= 12 from spheroid+disk decompositions and
corresponding stellar masses of a sample of over 600,000 galaxies in the
SDSS-DR7 spectroscopic sample. The galaxy SMF is well represented by a single
Schechter function (M* = 11.116+/-0.011, alpha = -1.145+/-0.008), though with a
hint of a steeper faint end slope. The corresponding stellar mass densities are
(2.670+/-0.110), (1.687+/-0.063) and (0.910+/-0.029)x10^8 M_solar Mpc^-3 for
galaxies, spheroids and disks respectively. We identify a crossover stellar
mass of log(M/M_solar) = 10.3+/-0.030 at which the spheroid and disk SMFs are
equal. Relative contributions of four distinct spheroid/disk dominated
sub-populations to the overall galaxy SMF are also presented. The mean
disk-to-spheroid stellar mass ratio shows a five fold disk dominance at the low
mass end, decreasing monotonically with a corresponding increase in the
spheroidal fraction till the two are equal at a galaxy stellar mass,
log(M/M_solar)=10.479+/-0.013, the dominance of spheroids then grows with
increasing stellar mass. The relative numbers of composite disk and spheroid
dominated galaxies show peaks in their distributions, perhaps indicative of a
preferred galaxy mass. Our characterization of the low redshift galaxy
population provides stringent constraints for numerical simulations to
reproduce.Comment: 30 pages, 18 figures, 5 tables (2 online), Accepted for publication
in MNRA
The signature of dissipation in the mass-size relation: are bulges simply spheroids wrapped in a disc?
The relation between the stellar mass and size of a galaxy's structural
subcomponents, such as discs and spheroids, is a powerful way to understand the
processes involved in their formation. Using very large catalogues of
photometric bulge+disc structural decompositions and stellar masses from the
Sloan Digital Sky Survey Data Release Seven, we carefully define two large
subsamples of spheroids in a quantitative manner such that both samples share
similar characteristics with one important exception: the 'bulges' are embedded
in a disc and the 'pure spheroids' are galaxies with a single structural
component. Our bulge and pure spheroid subsample sizes are 76,012 and 171,243
respectively. Above a stellar mass of ~ M, the mass-size
relations of both subsamples are parallel to one another and are close to lines
of constant surface mass density. However, the relations are offset by a factor
of 1.4, which may be explained by the dominance of dissipation in their
formation processes. Whereas the size-mass relation of bulges in discs is
consistent with gas-rich mergers, pure spheroids appear to have been formed via
a combination of 'dry' and 'wet' mergers.Comment: Accepted for publication in MNRAS, 6 pages, 3 figure
Pluralism as a Bias Mitigation Strategy
An agnostic pluralist approaches inquiry with the assumption that it is possible for more than one account of the phenomenon in question to be correct. A monist approaches inquiry with the assumption that only one account of the phenomenon in question is correct. The purpose of my paper is to support the claim that agnostic pluralists are less susceptible to a sort of bias that I call dialectical bias than monists
On deductivism : a critical survey of deductivism in informal logic
The aim of this thesis is to understand and critically evaluate deductivism as a theory of inferential sufficiency in informal logic. I distinguish three different types of deductivism: strong normative deductivism, weak normative deductivism, and reconstructive deductivism. I also discuss some potential justificatory strategies that might be invoked in an attempt to justify strong normative deductivism and reconstructive deductivism. I apply this categorization scheme to develop an interpretation of Leo Groarke\u27s version of reconstructive deductivism. I then evaluate some of the criticisms of deductivism raised in the informal logic literature. I focus in particular on the criticisms of Ralph Johnson and Trudy Govier. I follow up this evaluation by raising some problems for the justificatory strategies used to support deductivism. I also show how these problems apply to Groarke\u27s reconstructive deductivism
Clues to the Origin of the Mass-Metallicity Relation: Dependence on Star Formation Rate and Galaxy Size
We use a sample of 43,690 galaxies selected from the Sloan Digital Sky Survey
Data Release 4 to study the systematic effects of specific star formation rate
(SSFR) and galaxy size (as measured by the half light radius, r_h) on the
mass-metallicity relation. We find that galaxies with high SSFR or large r_h
for their stellar mass have systematically lower gas phase-metallicities (by up
to 0.2 dex) than galaxies with low SSFR or small r_h. We discuss possible
origins for these dependencies, including galactic winds/outflows, abundance
gradients, environment and star formation rate efficiencies.Comment: Accepted by ApJ Letter
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