428 research outputs found
The SuperNova Legacy Survey: cosmological results from the first year data set
International audienceThe first cosmological results from the SuperNova Legacy Survey are presented. The recipe to obtain the deep, homogenous and complete set of 71 identified type Ia supernovae is described. The construction of the Hubble diagram is supported by precise distance measurement. The steps to obtain this distance are good differential photometry, precise calibration and light-curve modelling. All steps are detailled to present the Hubble diagram. finally the cosmological parameters are fitted from this diagram. A full error estimation (statistical and systematical) is presented
On the determination of the deceleration parameter from Supernovae data
Supernovae searches have shown that a simple matter-dominated and
decelerating universe should be ruled out. However a determination of the
present deceleration parameter through a simple kinematical description
is not exempt of possible drawbacks. We show that, with a time dependent
equation of state for the dark energy, a bias is present for : models
which are very far from the so-called Concordance Model can be accommodated by
the data and a simple kinematical analysis can lead to wrong conclusions. We
present a quantitative treatment of this bias and we present our conclusions
when a possible dynamical dark energy is taken into account.Comment: 4 pages, 3 figures, submitte
CNN photometric redshifts in the SDSS at
We release photometric redshifts, reaching 0.7, for 14M galaxies
at in the 11,500 deg of the SDSS north and south galactic caps.
These estimates were inferred from a convolution neural network (CNN) trained
on stamp images of galaxies labelled with a spectroscopic redshift from
the SDSS, GAMA and BOSS surveys. Representative training sets of 370k
galaxies were constructed from the much larger combined spectroscopic data to
limit biases, particularly those arising from the over-representation of
Luminous Red Galaxies. The CNN outputs a redshift classification that offers
all the benefits of a well-behaved PDF, with a width efficiently signaling
unreliable estimates due to poor photometry or stellar sources. The dispersion,
mean bias and rate of catastrophic failures of the median point estimate are of
order , , on a representative test sample at ,
out-performing currently published estimates. The distributions in narrow
intervals of magnitudes of the redshifts inferred for the photometric sample
are in good agreement with the results of tomographic analyses. The inferred
redshifts also match the photometric redshifts of the redMaPPer galaxy clusters
for the probable cluster members. The CNN input and output are available at:
https://deepdip.iap.fr/treyer+2023.Comment: Submitted to MNRA
Making things better: the Case of Corporate Social Responsibility versus Social Entrepreneurship
This paper is concerned with varying market cracks and gaps, which have the potential to impact both environmental and social fields detrimentally. Instead of focusing on how international bodies and regulation could tackle such problems, this paper focuses on how business could decrease or repair the damages it causes. Thus, the potential of two recent fields: Corporate Social Responsibility (CSR) and Social Entrepreneurship are investigated, addressing the extent to which they can tackle market cracks and gaps. To have a better understanding of what solutions they provide, as well as what problems they encounter, case study research is employed.
The research demonstrates the clear positive impact created by such ventures, without underestimating the main debates surrounding those approaches. Yet as positive outcomes remain prevalent, the paper calls for a convergence between the two fields of CSR and Social Entrepreneurship, through the development of partnerships and other innovative initiatives
MIMAC: MIcro-tpc MAtrix of Chambers for dark matter directional detection
Directional detection of non-baryonic Dark Matter is a promising search
strategy for discriminating WIMP events from neutrons, the ultimate background
for dark matter direct detection. This strategy requires both a precise
measurement of the energy down to a few keV and 3D reconstruction of tracks
down to a few mm. The MIMAC (MIcro-tpc MAtrix of Chambers) collaboration has
developed in the last years an original prototype detector based on the direct
coupling of large pixelized micromegas with a special developed fast
self-triggered electronics showing the feasibility of a new generation of
directional detectors. The first bi-chamber prototype has been installed at
Modane, underground laboratory in June 2012. The first undergournd background
events, the gain stability and calibration are shown. The first spectrum of
nuclear recoils showing 3D tracks coming from the radon progeny is presented.Comment: Proceedings of the 4th International Conference on Directional Dark
Matter Detection CYGNUS2013, held in Toyoma (Japan), June 201
SiFTO: An Empirical Method for Fitting SNe Ia Light Curves
We present SiFTO, a new empirical method for modeling type Ia supernovae (SNe
Ia) light curves by manipulating a spectral template. We make use of
high-redshift SN observations when training the model, allowing us to extend it
bluer than rest frame U. This increases the utility of our high-redshift SN
observations by allowing us to use more of the available data. We find that
when the shape of the light curve is described using a stretch prescription,
applying the same stretch at all wavelengths is not an adequate description.
SiFTO therefore uses a generalization of stretch which applies different
stretch factors as a function of both the wavelength of the observed filter and
the stretch in the rest-frame B band. We compare SiFTO to other published
light-curve models by applying them to the same set of SN photometry, and
demonstrate that SiFTO and SALT2 perform better than the alternatives when
judged by the scatter around the best fit luminosity distance relationship. We
further demonstrate that when SiFTO and SALT2 are trained on the same data set
the cosmological results agree.Comment: Modified to better match published version in Ap
Two superluminous supernovae from the early universe discovered by the Supernova Legacy Survey
We present spectra and lightcurves of SNLS 06D4eu and SNLS 07D2bv, two
hydrogen-free superluminous supernovae discovered by the Supernova Legacy
Survey. At z = 1.588, SNLS 06D4eu is the highest redshift superluminous SN with
a spectrum, at M_U = -22.7 is one of the most luminous SNe ever observed, and
gives a rare glimpse into the restframe ultraviolet where these supernovae put
out their peak energy. SNLS 07D2bv does not have a host galaxy redshift, but
based on the supernova spectrum, we estimate it to be at z ~ 1.5. Both
supernovae have similar observer-frame griz lightcurves, which map to restframe
lightcurves in the U-band and UV, rising in ~ 20 restframe days or longer, and
declining over a similar timescale. The lightcurves peak in the shortest
wavelengths first, consistent with an expanding blackbody starting near 15,000
K and steadily declining in temperature. We compare the spectra to theoretical
models, and identify lines of C II, C III, Fe III, and Mg II in the spectrum of
SNLS 06D4eu and SCP 06F6, and find that they are consistent with an expanding
explosion of only a few solar masses of carbon, oxygen, and other trace metals.
Thus the progenitors appear to be related to those suspected for SNe Ic. A high
kinetic energy, 10^52 ergs, is also favored. Normal mechanisms of powering
core- collapse or thermonuclear supernovae do not seem to work for these
supernovae. We consider models powered by 56Ni decay and interaction with
circumstellar material, but find that the creation and spin-down of a magnetar
with a period of 2ms, magnetic field of 2 x 10^14 Gauss, and a 3 solar mass
progenitor provides the best fit to the data.Comment: ApJ, accepted, 43 pages, 15 figure
Probing Dark Energy with Supernovae : a concordant or a convergent model?
We present a revised interpretation of recent analysis of supernovae data. We
evaluate the effect of the priors on the extraction of the dark energy equation
of state. We find that the conclusions depend strongly on the prior
value and on its uncertainty, and show that a biased fitting procedure applied
on non concordant simulated data can converge to the "concordance model".
Relaxing the prior on points to other sets of solutions, which are
not excluded by observational data.Comment: 1+4 pages, 6 figures, submitted to Phys. Re
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