-
[show abstract]
[hide abstract]
ABSTRACT: The Galileon model is a modified gravity theory that may provide an
explanation for the accelerated expansion of the Universe. This model does not
suffer from instabilities or ghost problems (normally associated with
higher-order derivative theories), restores local General Relativity -- thanks
to the Vainshtein screening effect -- and predicts late time acceleration of
the expansion. In this paper, we derive a new definition of the Galileon
parameters that allows us to avoid having to choose initial conditions for the
Galileon field, and then test this model against precise measurements of the
cosmological distances and the rate of growth of cosmic structures. We observe
a small tension between the constraints set by growth data and those from
distances. However, we find that the Galileon model remains consistent with
current observations and is still competitive with the \Lambda CDM model,
contrary to what was concluded in recent publications.
02/2013;
-
M. Betoule,
J. Marriner,
N. Regnault,
J. -C. Cuillandre, P. Astier,
J. Guy,
C. Balland,
P. El Hage,
D. Hardin,
R. Kessler,
L. Le Guillou,
J. Mosher,
R. Pain,
P. -F. Rocci,
M. Sako,
K. Schahmaneche
[show abstract]
[hide abstract]
ABSTRACT: We present a combined photometric calibration of the SNLS and the SDSS
supernova survey, which results from a joint effort of the SDSS and the SNLS
collaborations. We deliver fluxes calibrated to the HST spectrophotometric star
network for large sets of tertiary stars that cover the science fields of both
surveys in all photometric bands. We also cross-calibrate directly the two
surveys and demonstrate their consistency. For each survey the flat-fielding is
revised based on the analysis of dithered star observations. The calibration
transfer from the HST spectrophotometric standard stars to the multi-epoch
tertiary standard star catalogs in the science fields follows three different
paths: observations of primary standard stars with the SDSS PT telescope;
observations of Landolt secondary standard stars with SNLS MegaCam instrument
at CFHT; and direct observation of faint HST standard stars with MegaCam. In
addition, the tertiary stars for the two surveys are cross-calibrated using
dedicated MegaCam observations of stripe 82. This overlap enables the
comparison of these three calibration paths and justifies using their
combination to improve the calibration accuracy. Flat-field corrections have
improved the uniformity of each survey as demonstrated by the comparison of
photometry in overlapping fields: the rms of the difference between the two
surveys is 3 mmag in gri, 4 mmag in z and 8 mmag in u. We also find a
remarkable agreement (better than 1%) between the SDSS and the SNLS calibration
in griz. The cross-calibration and the introduction of direct calibration
observations bring redundancy and strengthen the confidence in the resulting
calibration. We conclude that the surveys are calibrated to the HST with a
precision of about 0.4% in griz. This precision is comparable to the external
uncertainty affecting the color of the HST primary standard stars.
12/2012;
-
K. Perrett,
M. Sullivan,
A. Conley,
S. Gonzalez-Gaitan,
R. Carlberg,
D. Fouchez,
P. Ripoche,
J. D. Neill, P. Astier,
D. Balam, [......],
R. Pain,
N. Palanque-Delabrouille,
C. Pritchet,
N. Regnault,
J. Rich,
V. Ruhlmann-Kleider,
S. Baumont,
C. Lidman,
S. Perlmutter,
E. S. Walker
[show abstract]
[hide abstract]
ABSTRACT: We present a measurement of the volumetric Type Ia supernova (SN Ia) rate
(SNR_Ia) as a function of redshift for the first four years of data from the
Canada-France-Hawaii Telescope (CFHT) Supernova Legacy Survey (SNLS). This
analysis includes 286 spectroscopically confirmed and more than 400 additional
photometrically identified SNe Ia within the redshift range 0.1<z<1.1. The
volumetric SNR_Ia evolution is consistent with a rise to z~1.0 that follows a
power-law of the form (1+z)^alpha, with alpha=2.11+/-0.28. This evolutionary
trend in the SNLS rates is slightly shallower than that of the cosmic
star-formation history over the same redshift range. We combine the SNLS rate
measurements with those from other surveys that complement the SNLS redshift
range, and fit various simple SN Ia delay-time distribution (DTD) models to the
combined data. A simple power-law model for the DTD (i.e., proportional to
t^-beta) yields values from beta=0.98+/-0.05 to beta=1.15+/-0.08 depending on
the parameterization of the cosmic star formation history. A two-component
model, where SNR_Ia is dependent on stellar mass (Mstellar) and star formation
rate (SFR) as SNR_Ia(z)=AxMstellar(z) + BxSFR(z), yields the coefficients
A=1.9+/-0.1 SNe/yr/M_solar and B=3.3+/-0.2 SNe/yr/(M_solar/yr). More general
two-component models also fit the data well, but single Gaussian or exponential
DTDs provide significantly poorer matches. Finally, we split the SNLS sample
into two populations by the light curve width (stretch), and show that the
general behavior in the rates of faster-declining SNe Ia (0.8<s<1.0) is
similar, within our measurement errors, to that of the slower objects
(1.0<s<1.3) out to z~0.8.
06/2012;
-
C. Lidman,
V. Ruhlmann-Kleider,
M. Sullivan,
J. Myzska,
P. Dobbie,
K. Glazebrook,
J. Mould, P. Astier,
C. Balland,
M. Betoule, [......],
J. Guy,
D. Hardin,
I. Hook,
D. A. Howell,
R. Pain,
N. Palanque-Delabrouille,
K. Perrett,
C. Pritchet,
N. Regnault,
J. Rich
[show abstract]
[hide abstract]
ABSTRACT: We use the wide-field capabilities of the 2dF fibre positioner and the
AAOmega spectrograph on the Anglo-Australian Telescope (AAT) to obtain
redshifts of galaxies that hosted supernovae during the first three years of
the Supernova Legacy Survey (SNLS). With exposure times ranging from 10 to 60
ksec per galaxy, we were able to obtain redshifts for 400 host galaxies in two
SNLS fields, thereby substantially increasing the total number of SNLS
supernovae with host galaxy redshifts. The median redshift of the galaxies in
our sample that hosted photometrically classified Type Ia supernovae (SNe Ia)
is 0.77, which is 25% higher than the median redshift of spectroscopically
confirmed SNe Ia in the three-year sample of the SNLS. Our results demonstrate
that one can use wide-field fibre-fed multi-object spectrographs on 4m
telescopes to efficiently obtain redshifts for large numbers of supernova host
galaxies over the large areas of sky that will be covered by future
high-redshift supernova surveys, such as the Dark Energy Survey.
05/2012;
-
S. González-Gaitán,
A. Conley,
F. B. Bianco,
D. A. Howell,
M. Sullivan,
K. Perrett,
R. Carlberg, P. Astier,
D. Balam,
C. Balland, [......],
J. Guy,
D. Hardin,
I. M. Hook,
C. Lidman,
R. Pain,
N. Palanque-Delabrouille,
C. J. Pritchet,
N. Regnault,
J. Rich,
and V. Ruhlmann-Kleider
[show abstract]
[hide abstract]
ABSTRACT: We calculate the average stretch-corrected rise time of Type Ia supernovae (SNe Ia) in the Supernova Legacy Survey. We use the aggregate light curves of spectroscopic and photometrically identified SNe Ia to fit the rising part of the light curve with a simple quadratic model. We obtain a light curve shape corrected, i.e., stretch-corrected, fiducial rise time of 17.02+0.18 – 0.28 (stat) days. The measured rise time differs from an earlier finding by the SNLS (Conley et al.) due to the use of different SN Ia templates. We compare it to nearby samples using the same methods and find no evolution in the early part of the light curve of SNe Ia up to z = 1. We search for variations among different populations, particularly subluminous objects, by dividing the sample in stretch. Bright and slow decliners (s > 1.0) have consistent stretch-corrected rise times compared to fainter and faster decliners (0.8 < s ≤ 1.0); they are shorter by 0.57+0.47 – 0.50 (stat) days. Subluminous SNe Ia (here defined as objects with s ≤ 0.8), although less constrained, are also consistent, with a rise time of 18.03+0.81 – 1.37 (stat) days. We study several systematic biases and find that the use of different fiducial templates may affect the average rise time but not the intrinsic differences between populations. Based on our results, we estimate that subluminous SNe Ia are powered by 0.05-0.35 M ☉ of 56Ni synthesized in the explosion. Our conclusions are the same for the single-stretch and two-stretch parameterizations of the light curve.
The Astrophysical Journal 12/2011; 745(1):44. · 6.02 Impact Factor
-
R. Laureijs,
J. Amiaux,
S. Arduini,
J. L. Auguères,
J. Brinchmann,
R. Cole,
M. Cropper,
C. Dabin,
L. Duvet,
A Ealet, [......],
S. Spiro,
M Sullivan,
A Tilquin,
R. Trotta,
L. Verde,
Y Wang,
G. Williger,
G Zhao,
J. Zoubian,
E. Zucca
[show abstract]
[hide abstract]
ABSTRACT: Euclid is a space-based survey mission from the European Space Agency
designed to understand the origin of the Universe's accelerating expansion. It
will use cosmological probes to investigate the nature of dark energy, dark
matter and gravity by tracking their observational signatures on the geometry
of the universe and on the cosmic history of structure formation. The mission
is optimised for two independent primary cosmological probes: Weak
gravitational Lensing (WL) and Baryonic Acoustic Oscillations (BAO). The Euclid
payload consists of a 1.2 m Korsch telescope designed to provide a large field
of view. It carries two instruments with a common field-of-view of ~0.54 deg2:
the visual imager (VIS) and the near infrared instrument (NISP) which contains
a slitless spectrometer and a three bands photometer. The Euclid wide survey
will cover 15,000 deg2 of the extragalactic sky and is complemented by two 20
deg2 deep fields. For WL, Euclid measures the shapes of 30-40 resolved galaxies
per arcmin2 in one broad visible R+I+Z band (550-920 nm). The photometric
redshifts for these galaxies reach a precision of dz/(1+z) < 0.05. They are
derived from three additional Euclid NIR bands (Y, J, H in the range 0.92-2.0
micron), complemented by ground based photometry in visible bands derived from
public data or through engaged collaborations. The BAO are determined from a
spectroscopic survey with a redshift accuracy dz/(1+z) =0.001. The slitless
spectrometer, with spectral resolution ~250, predominantly detects Ha emission
line galaxies. Euclid is a Medium Class mission of the ESA Cosmic Vision
2015-2025 programme, with a foreseen launch date in 2019. This report (also
known as the Euclid Red Book) describes the outcome of the Phase A study.
10/2011;
-
F. B. Bianco,
D. A. Howell,
M. Sullivan,
A. Conley,
D. Kasen,
S. González-Gaitán,
J. Guy, P. Astier,
C. Balland,
R. G. Carlberg, [......],
I. Hook,
C. Lidman,
R. Pain,
N. Palanque-Delabrouille,
S. Perlmutter,
K. M. Perrett,
C. J. Pritchet,
N. Regnault,
J. Rich,
and V. Ruhlmann-Kleider
[show abstract]
[hide abstract]
ABSTRACT: While it is generally accepted that Type Ia supernovae are the result of the explosion of a carbon-oxygen white dwarf accreting mass in a binary system, the details of their genesis still elude us, and the nature of the binary companion is uncertain. Kasen points out that the presence of a non-degenerate companion in the progenitor system could leave an observable trace: a flux excess in the early rise portion of the light curve caused by the ejecta impact with the companion itself. This excess would be observable only under favorable viewing angles, and its intensity depends on the nature of the companion. We searched for the signature of a non-degenerate companion in three years of Supernova Legacy Survey data by generating synthetic light curves accounting for the effects of shocking and comparing true and synthetic time series with Kolmogorov-Smirnov tests. Our most constraining result comes from noting that the shocking effect is more prominent in the rest-frame B than V band: we rule out a contribution from white dwarf-red giant binary systems to Type Ia supernova explosions greater than 10% at the 2σ, and greater than 20% at the 3σ level.
The Astrophysical Journal 10/2011; 741(1):20. · 6.02 Impact Factor
-
G. Bazin,
V Ruhlmann-Kleider,
N. Palanque-Delabrouille,
J. Rich,
E. Aubourg, P. Astier,
C. Balland,
S. Basa,
R. G. Carlberg,
A. Conley, [......],
K. Perrett,
C. J. Pritchet,
N. Regnault,
M Sullivan,
N. Fourmanoit,
S. Gonzalez-Gaitan,
C. Lidman,
S. Perlmutter,
P. Ripoche,
E. S. Walker
[show abstract]
[hide abstract]
ABSTRACT: We present a sample of 485 photometrically identified Type Ia supernova
candidates mined from the first three years of data of the CFHT SuperNova
Legacy Survey (SNLS). The images were submitted to a deferred processing
independent of the SNLS real-time detection pipeline. Light curves of all
transient events were reconstructed in the g_M, r_M, i_M and z_M filters and
submitted to automated sequential cuts in order to identify possible
supernovae. Pure noise and long-term variable events were rejected by light
curve shape criteria. Type Ia supernova identification relied on event
characteristics fitted to their light curves assuming the events to be normal
SNe Ia. The light curve fitter SALT2 was used for this purpose, assigning host
galaxy photometric redshifts to the tested events. The selected sample of 485
candidates is one magnitude deeper than that allowed by the SNLS spectroscopic
identification. The contamination by supernovae of other types is estimated to
be 4%. Testing Hubble diagram residuals with this enlarged sample allows us to
measure the Malmquist bias due to spectroscopic selections directly. The result
is fully consistent with the precise Monte Carlo based estimate used to correct
SN Ia distance moduli in the SNLS 3-year cosmological analyses. This paper
demonstrates the feasibility of a photometric selection of high redshift
supernovae with known host galaxy redshifts, opening interesting prospects for
cosmological analyses from future large photometric SN Ia surveys.
09/2011;
-
F. B. Bianco,
D. A. Howell,
M Sullivan,
A. Conley,
D. Kasen,
S. Gonzalez-Gaitan,
J Guy, P. Astier,
C. Balland,
R. G. Carlberg, [......],
I. Hook,
C. Lidman,
R Pain,
N. Palanque-Delabrouille,
S. Perlmutter,
K. M. Perrett,
C. J. Pritchet,
N. Regnault,
J. Rich,
V Ruhlmann-Kleider
[show abstract]
[hide abstract]
ABSTRACT: While it is generally accepted that Type Ia supernovae are the result of the
explosion of a carbon-oxygen White Dwarf accreting mass in a binary system, the
details of their genesis still elude us, and the nature of the binary companion
is uncertain. Kasen (2010) points out that the presence of a non-degenerate
companion in the progenitor system could leave an observable trace: a flux
excess in the early rise portion of the lightcurve caused by the ejecta impact
with the companion itself. This excess would be observable only under favorable
viewing angles, and its intensity depends on the nature of the companion. We
searched for the signature of a non-degenerate companion in three years of
Supernova Legacy Survey data by generating synthetic lightcurves accounting for
the effects of shocking and comparing true and synthetic time series with
Kolmogorov-Smirnov tests. Our most constraining result comes from noting that
the shocking effect is more prominent in rest-frame B than V band: we rule out
a contribution from white dwarf-red giant binary systems to Type Ia supernova
explosions greater than 10% at 2 sigma, and than 20% at 3 sigma level.
06/2011;
-
A. Conley,
J Guy,
M Sullivan,
N. Regnault, P. Astier,
C. Balland,
S. Basa,
R. G. Carlberg,
D Fouchez,
D. Hardin, [......],
M. J. Hudson,
E. Hsiao,
T. Kronborg,
C. Lidman,
A. M. Mourao,
J. D. Neill,
S. Perlmutter,
P. Ripoche,
N Suzuki,
E. S. Walker
[show abstract]
[hide abstract]
ABSTRACT: We combine high redshift Type Ia supernovae from the first 3 years of the
Supernova Legacy Survey (SNLS) with other supernova (SN) samples, primarily at
lower redshifts, to form a high-quality joint sample of 472 SNe (123 low-$z$,
93 SDSS, 242 SNLS, and 14 {\it Hubble Space Telescope}). SN data alone require
cosmic acceleration at >99.9% confidence, including systematic effects. For the
dark energy equation of state parameter (assumed constant out to at least
$z=1.4$) in a flat universe, we find $w = -0.91^{+0.16}_{-0.20}(\mathrm{stat})
^{+0.07}_{-0.14} (\mathrm{sys})$ from SNe only, consistent with a cosmological
constant. Our fits include a correction for the recently discovered
relationship between host-galaxy mass and SN absolute brightness. We pay
particular attention to systematic uncertainties, characterizing them using a
systematics covariance matrix that incorporates the redshift dependence of
these effects, as well as the shape-luminosity and color-luminosity
relationships. Unlike previous work, we include the effects of systematic terms
on the empirical light-curve models. The total systematic uncertainty is
dominated by calibration terms. We describe how the systematic uncertainties
can be reduced with soon to be available improved nearby and
intermediate-redshift samples, particularly those calibrated onto
USNO/SDSS-like systems.
04/2011;
-
M Sullivan,
J Guy,
A. Conley,
N. Regnault, P. Astier,
C. Balland,
S. Basa,
R. G. Carlberg,
D Fouchez,
D. Hardin, [......],
M. J. Hudson,
E. Hsiao,
T. Kronborg,
C. Lidmam,
A. M. Mourao,
J. D. Neill,
S. Perlmutter,
P. Ripoche,
N Suzuki,
E. S. Walker
[show abstract]
[hide abstract]
ABSTRACT: We present observational constraints on the nature of dark energy using the
Supernova Legacy Survey three year sample (SNLS3) of Guy et al. (2010) and
Conley et al. (2011). We use the 472 SNe Ia in this sample, accounting for
recently discovered correlations between SN Ia luminosity and host galaxy
properties, and include the effects of all identified systematic uncertainties
directly in the cosmological fits. Combining the SNLS3 data with the full WMAP7
power spectrum, the Sloan Digital Sky Survey luminous red galaxy power
spectrum, and a prior on the Hubble constant H0 from SHOES, in a flat universe
we find omega_m=0.269+/-0.015 and w=-1.061+0.069-0.068 -- a 6.5% measure of the
dark energy equation-of-state parameter w. The statistical and systematic
uncertainties are approximately equal, with the systematic uncertainties
dominated by the photometric calibration of the SN Ia fluxes -- without these
calibration effects, systematics contribute only a ~2% error in w. When
relaxing the assumption of flatness, we find omega_m=0.271+/-0.015,
omega_k=-0.002+/-0.006, and w=-1.069+0.091-0.092. Parameterizing the time
evolution of w as w(a)=w_0+w_a(1-a), gives w_0=-0.905+/-0.196,
w_a=-0.984+1.094-1.097 in a flat universe. All of our results are consistent
with a flat, w=-1 universe. The size of the SNLS3 sample allows various tests
to be performed with the SNe segregated according to their light curve and host
galaxy properties. We find that the cosmological constraints derived from these
different sub-samples are consistent. There is evidence that the coefficient,
beta, relating SN Ia luminosity and color, varies with host parameters at
>4sigma significance (in addition to the known SN luminosity--host relation);
however this has only a small effect on the cosmological results and is
currently a sub-dominant systematic.
04/2011;
-
S. González-Gaitán,
K. Perrett,
M. Sullivan,
A. Conley,
D. A. Howell,
R. G. Carlberg, P. Astier,
D. Balam,
C. Balland,
S. Basa,
D. Fouchez,
J. Guy,
D. Hardin,
I. M. Hook,
R. Pain,
C. J. Pritchet,
N. Regnault,
J. Rich,
and C. Lidman
[show abstract]
[hide abstract]
ABSTRACT: The rate evolution of subluminous Type Ia supernovae (SNe Ia) is presented using data from the Supernova Legacy Survey. This sub-sample represents the faint and rapidly declining light curves of the observed SN Ia population here defined by low-stretch values (s ≤ 0.8). Up to redshift z = 0.6, we find 18 photometrically identified subluminous SNe Ia, of which six have spectroscopic redshift (and three are spectroscopically confirmed SNe Ia). The evolution of the subluminous volumetric rate is constant or slightly decreasing with redshift, in contrast to the increasing SN Ia rate found for the normal stretch population, although a rising behavior is not conclusively ruled out. The subluminous sample is mainly found in early-type galaxies with little or no star formation, so that the rate evolution is consistent with a galactic mass-dependent behavior: r(z) = A × Mg , with A = (1.1 ± 0.3) × 10–14 SNe yr–1 M –1 ☉.
The Astrophysical Journal 01/2011; 727(2):107. · 6.02 Impact Factor
-
A. Conley,
J. Guy,
M. Sullivan,
N. Regnault, P. Astier,
C. Balland,
S. Basa,
R. G. Carlberg,
D. Fouchez,
D. Hardin, [......],
M. J. Hudson,
E. Hsiao,
T. Kronborg,
C. Lidman,
A. M. Mourao,
J. D. Neill,
S. Perlmutter,
P. Ripoche,
N. Suzuki,
and E. S. Walker
[show abstract]
[hide abstract]
ABSTRACT: We combine high-redshift Type Ia supernovae from the first three years of the Supernova Legacy Survey (SNLS) with other supernova (SN) samples, primarily at lower redshifts, to form a high-quality joint sample of 472 SNe (123 low-z, 93 SDSS, 242 SNLS, and 14 Hubble Space Telescope). SN data alone require cosmic acceleration at >99.999% confidence, including systematic effects. For the dark energy equation of state parameter (assumed constant out to at least z = 1.4) in a flat universe, we find w = –0.91+0.16 –0.20(stat)+0.07 –0.14(sys) from SNe only, consistent with a cosmological constant. Our fits include a correction for the recently discovered relationship between host-galaxy mass and SN absolute brightness. We pay particular attention to systematic uncertainties, characterizing them using a systematic covariance matrix that incorporates the redshift dependence of these effects, as well as the shape-luminosity and color-luminosity relationships. Unlike previous work, we include the effects of systematic terms on the empirical light-curve models. The total systematic uncertainty is dominated by calibration terms. We describe how the systematic uncertainties can be reduced with soon to be available improved nearby and intermediate-redshift samples, particularly those calibrated onto USNO/SDSS-like systems.
The Astrophysical Journal Supplement Series 12/2010; 192(1):1. · 13.46 Impact Factor
-
J Guy,
M Sullivan,
A. Conley,
N. Regnault, P. Astier,
C. Balland,
S. Basa,
R. G. Carlberg,
D Fouchez,
D. Hardin, [......],
S. Gonzalez-Gaitan,
M. L. Graham,
E. Hsiao,
T. Kronborg,
C. Lidman,
A. M. Mourao,
S. Perlmutter,
P. Ripoche,
N Suzuki,
E. S. Walker
[show abstract]
[hide abstract]
ABSTRACT: We present photometric properties and distance measurements of 252 high redshift Type Ia supernovae (0.15 < z < 1.1) discovered during the first three years of the Supernova Legacy Survey (SNLS). These events were detected and their multi-colour light curves measured using the MegaPrime/MegaCam instrument at the Canada-France-Hawaii Telescope (CFHT), by repeatedly imaging four one-square degree fields in four bands. Follow-up spectroscopy was performed at the VLT, Gemini and Keck telescopes to confirm the nature of the supernovae and to measure their redshifts. Systematic uncertainties arising from light curve modeling are studied, making use of two techniques to derive the peak magnitude, shape and colour of the supernovae, and taking advantage of a precise calibration of the SNLS fields. A flat LambdaCDM cosmological fit to 231 SNLS high redshift Type Ia supernovae alone gives Omega_M = 0.211 +/- 0.034(stat) +/- 0.069(sys). The dominant systematic uncertainty comes from uncertainties in the photometric calibration. Systematic uncertainties from light curve fitters come next with a total contribution of +/- 0.026 on Omega_M. No clear evidence is found for a possible evolution of the slope (beta) of the colour-luminosity relation with redshift. Comment: (The SNLS Collaboration) 40 pages, 32 figures, Accepted in A&A
10/2010;
-
[show abstract]
[hide abstract]
ABSTRACT: We present a forecast of dark energy constraints that could be obtained from a large sample of distances to Type Ia supernovae detected and measured from space. We simulate the supernova events as they would be observed by a EUCLID-like telescope with its two imagers, assuming those would be equipped with 4 visible and 3 near infrared swappable filters. We account for known systematic uncertainties affecting the cosmological constraints, including those arising through the training of the supernova model used to fit the supernovae light curves. Using conservative assumptions and Planck priors, we find that a 18 month survey would yield constraints on the dark energy equation of state comparable to the cosmic shear approach in EUCLID: a variable two-parameter equation of state can be constrained to ~0.03 at z~0.3. These constraints are derived from distances to about 13,000 supernovae out to z=1.5, observed in two cones of 10 and 50 deg^2. These constraints do not require measuring a nearby supernova sample from the ground. Provided swappable filters can be accommodated on EUCLID, distances to supernovae can be measured from space and contribute to obtain the most precise constraints on dark energy properties. Comment: 14 pages, 2 figures, accepted in A&A
10/2010;
-
E. S. Walker,
I. M. Hook,
M Sullivan,
D. A. Howell, P. Astier,
C. Balland,
S. Basa,
T. J. Bronder,
R. Carlberg,
A. Conley, [......],
C. Pritchet,
N. Regnault,
J. Rich,
G. Aldering,
H. K. Fakhouri,
T. Kronborg,
N. Palanque-Delabrouille,
S. Perlmutter,
V Ruhlmann-Kleider,
T. Zhang
[show abstract]
[hide abstract]
ABSTRACT: GMOS optical long-slit spectroscopy at the Gemini-North telescope was used to classify targets from the Supernova Legacy Survey (SNLS) from July 2005 and May 2006 - May 2008. During this time, 95 objects were observed. Where possible the objects' redshifts (z) were measured from narrow emission or absorption features in the host galaxy spectrum, otherwise they were measured from the broader supernova features. We present spectra of 68 confirmed or probable SNe Ia from SNLS with redshifts in the range 0.17 \leq z \leq 1.02. In combination with earlier SNLS Gemini and VLT spectra, we used these new observations to measure pseudo-equivalent widths (EWs) of three spectral features - CaII H&K, SiII and MgII - in 144 objects and compared them to the EWs of low-redshift SNe Ia from a sample drawn from the literature. No signs of changes with z are seen for the CaII H&K and MgII features. Systematically lower EW SiII is seen at high redshift, but this can be explained by a change in demographics of the SNe Ia population within a two-component model combined with an observed correlation between EW SiII and photometric lightcurve stretch. Comment: 49 pages including 2 online-only appendices, accepted for publication in MNRAS
08/2010;
-
K. Perrett,
D. Balam,
M. Sullivan,
C. Pritchet,
A. Conley,
R. Carlberg, P. Astier,
C. Balland,
S. Basa,
D. Fouchez,
J. Guy,
D. Hardin,
I. M. Hook,
D. A. Howell,
R. Pain,
and N. Regnault
[show abstract]
[hide abstract]
ABSTRACT: The Supernova Legacy Survey (SNLS) has produced a high-quality, homogeneous sample of Type Ia supernovae (SNe Ia) out to redshifts greater than z = 1. In its first four years of full operation (to 2007 June), the SNLS discovered more than 3000 transient candidates, 373 of which have been spectroscopically confirmed as SNe Ia. Use of these SNe Ia in precision cosmology critically depends on an analysis of the observational biases incurred in the SNLS survey due to the incomplete sampling of the underlying SN Ia population. This paper describes our real-time supernova detection and analysis procedures, and uses detailed Monte Carlo simulations to examine the effects of Malmquist bias and spectroscopic sampling. Such sampling effects are found to become apparent at z ~ 0.6, with a significant shift in the average magnitude of the spectroscopically confirmed SN Ia sample toward brighter values for z 0.75. We describe our approach to correct for these selection biases in our three-year SNLS cosmological analysis (SNLS3) and present a breakdown of the systematic uncertainties involved.
The Astronomical Journal 06/2010; 140(2):518. · 4.03 Impact Factor
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R. Amanullah,
C. Lidman,
D. Rubin,
G. Aldering, P. Astier,
K. Barbary,
M. S. Burns,
A. Conley,
K. S. Dawson,
S. E. Deustua, [......],
N. Panagia,
S. Perlmutter,
J. Raux,
P. Ruiz-Lapuente,
A. L. Spadafora,
M. Strovink,
N. Suzuki,
L. Wang,
W. M. Wood-Vasey,
N. Yasuda
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ABSTRACT: We report on work to increase the number of well-measured Type Ia supernovae (SNe Ia) at high redshifts. Light curves, including high signal-to-noise Hubble Space Telescope data, and spectra of six SNe Ia that were discovered during 2001, are presented. Additionally, for the two SNe with z > 1, we present ground-based J-band photometry from Gemini and the Very Large Telescope. These are among the most distant SNe Ia for which ground-based near-IR observations have been obtained. We add these six SNe Ia together with other data sets that have recently become available in the literature to the Union compilation. We have made a number of refinements to the Union analysis chain, the most important ones being the refitting of all light curves with the SALT2 fitter and an improved handling of systematic errors. We call this new compilation, consisting of 557 SNe, the Union2 compilation. The flat concordance ΛCDM model remains an excellent fit to the Union2 data with the best-fit constant equation-of-state parameter w = –0.997+0.050 –0.054(stat)+0.077 –0.082(stat + sys together) for a flat universe, or w = –1.038+0.056 –0.059(stat)+0.093 –0.097(stat + sys together) with curvature. We also present improved constraints on w(z). While no significant change in w with redshift is detected, there is still considerable room for evolution in w. The strength of the constraints depends strongly on redshift. In particular, at z 1, the existence and nature of dark energy are only weakly constrained by the data.
The Astrophysical Journal 05/2010; 716(1):712. · 6.02 Impact Factor
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R. Amanullah,
C. Lidman,
D. Rubin,
G. Aldering, P. Astier,
K. Barbary,
M. S. Burns,
A. Conley,
K. S. Dawson,
S. E. Deustua, [......],
N. Panagia,
S. Perlmutter,
J. Raux,
P. Ruiz-Lapuente,
A. L. Spadafora,
M Strovink,
N Suzuki,
L Wang,
W. M. Wood-Vasey,
N Yasuda
[show abstract]
[hide abstract]
ABSTRACT: We report on work to increase the number of well-measured Type Ia supernovae
(SNe Ia) at high redshifts. Light curves, including high signal-to-noise HST
data, and spectra of six SNe Ia that were discovered during 2001 are presented.
Additionally, for the two SNe with z>1, we present ground-based J-band
photometry from Gemini and the VLT. These are among the most distant SNe Ia for
which ground based near-IR observations have been obtained. We add these six
SNe Ia together with other data sets that have recently become available in the
literature to the Union compilation (Kowalski et al. 2008). We have made a
number of refinements to the Union analysis chain, the most important ones
being the refitting of all light curves with the SALT2 fitter and an improved
handling of systematic errors. We call this new compilation, consisting of 557
supernovae, the Union2 compilation. The flat concordance LambdaCDM model
remains an excellent fit to the Union2 data with the best fit constant equation
of state parameter w=-0.997^{+0.050}_{-0.054} (stat) ^{+0.077}_{-0.082}
(stat+sys\ together) for a flat universe, or w=-1.035^{+0.055}_{-0.059}
(stat)^{+0.093}_{-0.097} (stat+sys together) with curvature. We also present
improved constraints on w(z). While no significant change in w with redshift is
detected, there is still considerable room for evolution in w. The strength of
the constraints depend strongly on redshift. In particular, at z > 1, the
existence and nature of dark energy are only weakly constrained by the data.
04/2010;
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M Sullivan,
A. Conley,
D. A. Howell,
J. D. Neill, P. Astier,
C. Balland,
S. Basa,
R. G. Carlberg,
D Fouchez,
J Guy, [......],
C. J. Pritchet,
N. Regnault,
J. Rich,
V Ruhlmann-Kleider,
S. Baumont,
E. Hsiao,
T. Kronborg,
C. Lidman,
S. Perlmutter,
E. S. Walker
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ABSTRACT: (Abridged) Precision cosmology with Type Ia supernovae (SNe Ia) makes use of the fact that SN Ia luminosities depend on their light-curve shapes and colours. Using Supernova Legacy Survey (SNLS) and other data, we show that there is an additional dependence on the global characteristics of their host galaxies: events of the same light-curve shape and colour are, on average, 0.08mag (~4.0sigma) brighter in massive host galaxies (presumably metal-rich) and galaxies with low specific star-formation rates (sSFR). SNe Ia in galaxies with a low sSFR also have a smaller slope ("beta") between their luminosities and colours with ~2.7sigma significance, and a smaller scatter on SN Ia Hubble diagrams (at 95% confidence), though the significance of these effects is dependent on the reddest SNe. SN Ia colours are similar between low-mass and high-mass hosts, leading us to interpret their luminosity differences as an intrinsic property of the SNe and not of some external factor such as dust. If the host stellar mass is interpreted as a metallicity indicator, the luminosity trends are in qualitative agreement with theoretical predictions. We show that the average stellar mass, and therefore the average metallicity, of our SN Ia host galaxies decreases with redshift. The SN Ia luminosity differences consequently introduce a systematic error in cosmological analyses, comparable to the current statistical uncertainties on parameters such as w. We show that the use of two SN Ia absolute magnitudes, one for events in high-mass (metal-rich) galaxies, and one for events in low-mass (metal-poor) galaxies, adequately corrects for the differences. Cosmological fits incorporating these terms give a significant reduction in chi^2 (3.8-4.5sigma). We conclude that future SN Ia cosmological analyses should use a correction of this (or similar) form to control demographic shifts in the galaxy population. Comment: Accepted for publication in MNRAS.
03/2010;
