150 research outputs found
The supernova CSS121015:004244+132827: a clue for understanding super-luminous supernovae
We present optical photometry and spectra of the super luminous type II/IIn
supernova CSS121015:004244+132827 (z=0.2868) spanning epochs from -30 days
(rest frame) to more than 200 days after maximum. CSS121015 is one of the more
luminous supernova ever found and one of the best observed. The photometric
evolution is characterized by a relatively fast rise to maximum (~40 days in
the SN rest frame), and by a linear post-maximum decline. The light curve shows
no sign of a break to an exponential tail. A broad Halpha is first detected at
~ +40 days (rest-frame). Narrow, barely-resolved Balmer and [O III] 5007 A
lines, with decreasing strength, are visible along the entire spectral
evolution. The spectra are very similar to other super luminous supernovae
(SLSNe) with hydrogen in their spectrum, and also to SN 2005gj, sometimes
considered a type Ia interacting with H-rich CSM. The spectra are also similar
to a subsample of H-deficient SLSNe. We propose that the properties of
CSS121015 are consistent with the interaction of the ejecta with a massive,
extended, opaque shell, lost by the progenitor decades before the final
explosion, although a magnetar powered model cannot be excluded. Based on the
similarity of CSS121015 with other SLSNe (with and without H), we suggest that
the shocked-shell scenario should be seriously considered as a plausible model
for both types of SLSN.Comment: 17 pages, 10 figures and 5 tables. In press to MNRAS. This version
matches the accepted one. Main conclusions are unchange
Improving Cosmological Distance Measurements Using Twin Type Ia Supernovae
We introduce a method for identifying "twin" Type Ia supernovae, and using
them to improve distance measurements. This novel approach to Type Ia supernova
standardization is made possible by spectrophotometric time series observations
from the Nearby Supernova Factory (SNfactory). We begin with a well-measured
set of supernovae, find pairs whose spectra match well across the entire
optical window, and then test whether this leads to a smaller dispersion in
their absolute brightnesses. This analysis is completed in a blinded fashion,
ensuring that decisions made in implementing the method do not inadvertently
bias the result. We find that pairs of supernovae with more closely matched
spectra indeed have reduced brightness dispersion. We are able to standardize
this initial set of SNfactory supernovae to 0.083 +/- 0.012 magnitudes,
implying a dispersion of 0.072 +/- 0.010 magnitudes in the absence of peculiar
velocities. We estimate that with larger numbers of comparison SNe, e.g, using
the final SNfactory spectrophotometric dataset as a reference, this method will
be capable of standardizing high-redshift supernovae to within 0.06-0.07
magnitudes. These results imply that at least 3/4 of the variance in Hubble
residuals in current supernova cosmology analyses is due to previously
unaccounted-for astrophysical differences among the supernovaeComment: 37 pages, 9 figures, 5 tables. Accepted for publication in ApJ. Fixed
typo in arXiv abstrac
The Extinction Properties of and Distance to the Highly Reddened Type Ia Supernova SN 2012cu
Correction of Type Ia Supernova brightnesses for extinction by dust has
proven to be a vexing problem. Here we study the dust foreground to the highly
reddened SN 2012cu, which is projected onto a dust lane in the galaxy NGC 4772.
The analysis is based on multi-epoch, spectrophotometric observations spanning
3,300 - 9,200 {\AA}, obtained by the Nearby Supernova Factory. Phase-matched
comparison of the spectroscopically twinned SN 2012cu and SN 2011fe across 10
epochs results in the best-fit color excess of (E(B-V), RMS) = (1.00, 0.03) and
total-to-selective extinction ratio of (RV , RMS) = (2.95, 0.08) toward SN
2012cu within its host galaxy. We further identify several diffuse interstellar
bands, and compare the 5780 {\AA} band with the dust-to-band ratio for the
Milky Way. Overall, we find the foreground dust-extinction properties for SN
2012cu to be consistent with those of the Milky Way. Furthermore we find no
evidence for significant time variation in any of these extinction tracers. We
also compare the dust extinction curve models of Cardelli et al. (1989),
O'Donnell (1994), and Fitzpatrick (1999), and find the predictions of
Fitzpatrick (1999) fit SN 2012cu the best. Finally, the distance to NGC4772,
the host of SN 2012cu, at a redshift of z = 0.0035, often assigned to the Virgo
Southern Extension, is determined to be 16.61.1 Mpc. We compare this
result with distance measurements in the literature.Comment: 48 pages, 13 figures. Accepted for publication in The Astrophysical
Journal. The spectral time series data presented in this article can be found
at http://snfactory.lbl.gov/snf/data
SCALA: In situ calibration for integral field spectrographs
International audienceThe scientific yield of current and future optical surveys is increasingly limited by systematic uncertainties in the flux calibration. This is the case for Type Ia supernova (SN Ia) cosmology programs, where an improved calibration directly translates into improved cosmological constraints. Current methodology rests on models of stars. Here we aim to obtain flux calibration that is traceable to state-of-the-art detector-based calibration. We present the SNIFS Calibration Apparatus (SCALA), a color (relative) flux calibration system developed for the SuperNova Integral Field Spectrograph (SNIFS), operating at the University of Hawaii 2.2 m (UH 88) telescope. By comparing the color trend of the illumination generated by SCALA during two commissioning runs, and to previous laboratory measurements, we show that we can determine the light emitted by SCALA with a long-term repeatability better than 1%. We describe the calibration procedure necessary to control for system aging. We present measurements of the SNIFS throughput as estimated by SCALA observations. The SCALA calibration unit is now fully deployed at the UH\,88 telescope, and with it color-calibration between 4000 {\AA} and 9000 {\AA} is stable at the percent level over a one-year baseline
Dark Energy Survey Year 3 results: Curved-sky weak lensing mass map reconstruction
We present reconstructed convergence maps, mass maps, from the Dark Energy Survey (DES) third year (Y3) weak gravitational lensing data set. The mass maps are weighted projections of the density field (primarily dark matter) in the foreground of the observed galaxies. We use four reconstruction methods, each is a maximum a posteriori estimate with a different model for the prior probability of the map: Kaiser-Squires, null B-mode prior, Gaussian prior, and a sparsity prior. All methods are implemented on the celestial sphere to accommodate the large sky coverage of the DES Y3 data. We compare the methods using realistic \u39bCDM simulations with mock data that are closely matched to the DES Y3 data. We quantify the performance of the methods at the map level and then apply the reconstruction methods to the DES Y3 data, performing tests for systematic error effects. The maps are compared with optical foreground cosmic-web structures and are used to evaluate the lensing signal from cosmic-void profiles. The recovered dark matter map covers the largest sky fraction of any galaxy weak lensing map to date
Dark Energy Survey Year 3 results: Magnification modeling and impact on cosmological constraints from galaxy clustering and galaxy-galaxy lensing
We study the effect of magnification in the Dark Energy Survey Year 3
analysis of galaxy clustering and galaxy-galaxy lensing, using two different
lens samples: a sample of Luminous red galaxies, redMaGiC, and a sample with a
redshift-dependent magnitude limit, MagLim. We account for the effect of
magnification on both the flux and size selection of galaxies, accounting for
systematic effects using the Balrog image simulations. We estimate the impact
of magnification on the galaxy clustering and galaxy-galaxy lensing cosmology
analysis, finding it to be a significant systematic for the MagLim sample. We
show cosmological constraints from the galaxy clustering auto-correlation and
galaxy-galaxy lensing signal with different magnifications priors, finding
broad consistency in cosmological parameters in CDM and CDM.
However, when magnification bias amplitude is allowed to be free, we find the
two-point correlations functions prefer a different amplitude to the fiducial
input derived from the image simulations. We validate the magnification
analysis by comparing the cross-clustering between lens bins with the
prediction from the baseline analysis, which uses only the auto-correlation of
the lens bins, indicating systematics other than magnification may be the cause
of the discrepancy. We show adding the cross-clustering between lens redshift
bins to the fit significantly improves the constraints on lens magnification
parameters and allows uninformative priors to be used on magnification
coefficients, without any loss of constraining power or prior volume concerns.Comment: 21 pages, 13 figures, See this
https://www.darkenergysurvey.org/des-year-3-cosmology-results-papers/ URL for
the full DES Y3 cosmology releas
Beyond the 3rd moment: A practical study of using lensing convergence CDFs for cosmology with DES Y3
Widefield surveys of the sky probe many clustered scalar fields -- such as
galaxy counts, lensing potential, gas pressure, etc. -- that are sensitive to
different cosmological and astrophysical processes. Our ability to constrain
such processes from these fields depends crucially on the statistics chosen to
summarize the field. In this work, we explore the cumulative distribution
function (CDF) at multiple scales as a summary of the galaxy lensing
convergence field. Using a suite of N-body lightcone simulations, we show the
CDFs' constraining power is modestly better than that of the 2nd and 3rd
moments of the field, as they approximately capture the information from all
moments of the field in a concise data vector. We then study the practical
aspects of applying the CDFs to observational data, using the first three years
of the Dark Energy Survey (DES Y3) data as an example, and compute the impact
of different systematics on the CDFs. The contributions from the point spread
function are 2-3 orders of magnitude below the cosmological signal, while those
from reduced shear approximation contribute to the signal.
Source clustering effects and baryon imprints contribute . Enforcing
scale cuts to limit systematics-driven biases in parameter constraints degrades
these constraints a noticeable amount, and this degradation is similar for the
CDFs and the moments. We also detect correlations between the observed
convergence field and the shape noise field at . We find that the
non-Gaussian correlations in the noise field must be modeled accurately to use
the CDFs, or other statistics sensitive to all moments, as a rigorous cosmology
tool.Comment: 21 pages, 12 figure
Dark Energy Survey year 3 results: point spread function modelling
We introduce a new software package for modelling the point spread function (PSF) of astronomical images, called PIFF (PSFs
In the Full FOV), which we apply to the first three years (known as Y3) of the Dark Energy Survey (DES) data. We describe
the relevant details about the algorithms used by PIFF to model the PSF, including how the PSF model varies across the field
of view (FOV). Diagnostic results show that the systematic errors from the PSF modelling are very small over the range of
scales that are important for the DES Y3 weak lensing analysis. In particular, the systematic errors from the PSF modelling are
significantly smaller than the corresponding results from the DES year one (Y1) analysis. We also briefly describe some planned
improvements to PIFF that we expect to further reduce the modelling errors in future analyses
The Dark Energy Survey Year 3 and eBOSS: constraining galaxy intrinsic alignments across luminosity and colour space
We present direct constraints on galaxy intrinsic alignments using the Dark
Energy Survey Year 3 (DES Y3), the Extended Baryon Oscillation Spectroscopic
Survey (eBOSS) and its precursor, the Baryon Oscillation Spectroscopic Survey
(BOSS). Our measurements incorporate photometric red sequence (redMaGiC)
galaxies from DES with median redshift , luminous red galaxies
(LRGs) from eBOSS at , and also a SDSS-III BOSS CMASS sample at
. We measure two point intrinsic alignment correlations, which we fit
using a model that includes lensing, magnification and photometric redshift
error. Fitting on scales Mpc, we make a detection of
intrinsic alignments in each sample, at (assuming a simple
one parameter model for IAs). Using these red samples, we measure the
IA-luminosity relation. Our results are statistically consistent with previous
results, but offer a significant improvement in constraining power,
particularly at low luminosity. With this improved precision, we see detectable
dependence on colour between broadly defined red samples. It is likely that a
more sophisticated approach than a binary red/blue split, which jointly
considers colour and luminosity dependence in the IA signal, will be needed in
future. We also compare the various signal components at the best fitting point
in parameter space for each sample, and find that magnification and lensing
contribute of the total signal. As precision continues to improve,
it will certainly be necessary to account for these effects in future direct IA
measurements. Finally, we make equivalent measurements on a sample of Emission
Line Galaxies (ELGs) from eBOSS at . We report a null detection,
constraining the IA amplitude (assuming the nonlinear alignment model) to be
( at CL).Comment: Submitted to MNRAS; 22 pages, 11 figure
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