69 research outputs found
Single or Double Degenerate Progenitors? Searching for Shock Emission in the SDSS-II Type Ia Supernovae
From the set of nearly 500 spectroscopically confirmed type~Ia supernovae and
around 10,000 unconfirmed candidates from SDSS-II, we select a subset of 108
confirmed SNe Ia with well-observed early-time light curves to search for
signatures from shock interaction of the supernova with a companion star. No
evidence for shock emission is seen; however, the cadence and photometric noise
could hide a weak shock signal. We simulate shocked light curves using SN Ia
templates and a simple, Gaussian shock model to emulate the noise properties of
the SDSS-II sample and estimate the detectability of the shock interaction
signal as a function of shock amplitude, shock width, and shock fraction. We
find no direct evidence for shock interaction in the rest-frame -band, but
place an upper limit on the shock amplitude at 9% of supernova peak flux ( mag). If the single degenerate channel dominates type~Ia progenitors,
this result constrains the companion stars to be less than about 6
on the main sequence, and strongly disfavors red giant companions.Comment: 28 pages, 3 figure
Type II-P Supernovae from the SDSS-II Supernova Survey and the Standardized Candle Method
We apply the Standardized Candle Method (SCM) for Type II Plateau supernovae
(SNe II-P), which relates the velocity of the ejecta of a SN to its luminosity
during the plateau, to 15 SNe II-P discovered over the three season run of the
Sloan Digital Sky Survey - II Supernova Survey. The redshifts of these SNe -
0.027 < z < 0.144 - cover a range hitherto sparsely sampled in the literature;
in particular, our SNe II-P sample contains nearly as many SNe in the Hubble
flow (z > 0.01) as all of the current literature on the SCM combined. We find
that the SDSS SNe have a very small intrinsic I-band dispersion (0.22 mag),
which can be attributed to selection effects. When the SCM is applied to the
combined SDSS-plus-literature set of SNe II-P, the dispersion increases to 0.29
mag, larger than the scatter for either set of SNe separately. We show that the
standardization cannot be further improved by eliminating SNe with positive
plateau decline rates, as proposed in Poznanski et al. (2009). We thoroughly
examine all potential systematic effects and conclude that for the SCM to be
useful for cosmology, the methods currently used to determine the Fe II
velocity at day 50 must be improved, and spectral templates able to encompass
the intrinsic variations of Type II-P SNe will be needed.Comment: Accepted for publication by ApJ; data used in this paper can be
downloaded from http://sdssdp47.fnal.gov/sdsssn/photometry/SNIIp.tgz;
citation errors correcte
Type Ia Supernova Properties as a Function of the Distance to the Host Galaxy in the SDSS-II SN Survey
We use type-Ia supernovae (SNe Ia) discovered by the SDSS-II SN Survey to
search for dependencies between SN Ia properties and the projected distance to
the host galaxy center, using the distance as a proxy for local galaxy
properties (local star-formation rate, local metallicity, etc.). The sample
consists of almost 200 spectroscopically or photometrically confirmed SNe Ia at
redshifts below 0.25. The sample is split into two groups depending on the
morphology of the host galaxy. We fit light-curves using both MLCS2k2 and
SALT2, and determine color (AV, c) and light-curve shape (delta, x1) parameters
for each SN Ia, as well as its residual in the Hubble diagram. We then
correlate these parameters with both the physical and the normalized distances
to the center of the host galaxy and look for trends in the mean values and
scatters of these parameters with increasing distance. The most significant (at
the 4-sigma level) finding is that the average fitted AV from MLCS2k2 and c
from SALT2 decrease with the projected distance for SNe Ia in spiral galaxies.
We also find indications that SNe in elliptical galaxies tend to have narrower
light-curves if they explode at larger distances, although this may be due to
selection effects in our sample. We do not find strong correlations between the
residuals of the distance moduli with respect to the Hubble flow and the
galactocentric distances, which indicates a limited correlation between SN
magnitudes after standardization and local host metallicity.Comment: Accepted for publication in The Astrophysical Journal (33 pages, 5
figures, 8 tables
A Mismatch in the Ultraviolet Spectra between Low-Redshift and Intermediate-Redshift Type Ia Supernovae as a Possible Systematic Uncertainty for Supernova Cosmology
We present Keck high-quality rest-frame ultraviolet (UV) through optical
spectra of 21 Type Ia supernovae (SNe Ia) in the redshift range 0.11 < z < 0.37
and a mean redshift of 0.22 that were discovered during the Sloan Digital Sky
Survey-II (SDSS-II) SN Survey. Using the broad-band photometry of the SDSS
survey, we are able to reconstruct the SN host-galaxy spectral energy
distributions (SEDs), allowing for a correction for the host-galaxy
contamination in the SN Ia spectra. Comparison of composite spectra constructed
from a subsample of 17 high-quality spectra to those created from a
low-redshift sample with otherwise similar properties shows that the Keck/SDSS
SNe Ia have, on average, extremely similar rest-frame optical spectra but show
a UV flux excess. This observation is confirmed by comparing synthesized
broad-band colors of the individual spectra, showing a difference in mean
colors at the 2.4 - 4.4 sigma level for various UV colors. We further see a
slight difference in the UV spectral shape between SNe with low-mass and
high-mass host galaxies. Additionally, we detect a relationship between the
flux ratio at 2770 and 2900 A and peak luminosity that differs from that
observed at low redshift. We find that changing the UV SED of an SN Ia within
the observed dispersion can change the inferred distance moduli by ~0.1 mag.
This effect only occurs when the data probe the rest-frame UV. We suggest that
this discrepancy could be due to differences in the host-galaxy population of
the two SN samples or to small-sample statistics.Comment: 28 pages, 21 figures, accepted by AJ, spectra are available at
http://www.cfa.harvard.edu/~rfoley/data
First-year Sloan Digital Sky Survey-II (SDSS-II) Supernova Results: Hubble Diagram and Cosmological Parameters
We present measurements of the Hubble diagram for 103 Type Ia supernovae
(SNe) with redshifts 0.04 < z < 0.42, discovered during the first season (Fall
2005) of the Sloan Digital Sky Survey-II (SDSS-II) Supernova Survey. These data
fill in the redshift "desert" between low- and high-redshift SN Ia surveys. We
combine the SDSS-II measurements with new distance estimates for published SN
data from the ESSENCE survey, the Supernova Legacy Survey, the Hubble Space
Telescope, and a compilation of nearby SN Ia measurements. Combining the SN
Hubble diagram with measurements of Baryon Acoustic Oscillations from the SDSS
Luminous Red Galaxy sample and with CMB temperature anisotropy measurements
from WMAP, we estimate the cosmological parameters w and Omega_M, assuming a
spatially flat cosmological model (FwCDM) with constant dark energy equation of
state parameter, w. For the FwCDM model and the combined sample of 288 SNe Ia,
we find w = -0.76 +- 0.07(stat) +- 0.11(syst), Omega_M = 0.306 +- 0.019(stat)
+- 0.023(syst) using MLCS2k2 and w = -0.96 +- 0.06(stat) +- 0.12(syst), Omega_M
= 0.265 +- 0.016(stat) +- 0.025(syst) using the SALT-II fitter. We trace the
discrepancy between these results to a difference in the rest-frame UV model
combined with a different luminosity correction from color variations; these
differences mostly affect the distance estimates for the SNLS and HST
supernovae. We present detailed discussions of systematic errors for both
light-curve methods and find that they both show data-model discrepancies in
rest-frame -band. For the SALT-II approach, we also see strong evidence for
redshift-dependence of the color-luminosity parameter (beta). Restricting the
analysis to the 136 SNe Ia in the Nearby+SDSS-II samples, we find much better
agreement between the two analysis methods but with larger uncertainties.Comment: Accepted for publication by ApJ
First-Year Spectroscopy for the SDSS-II Supernova Survey
This paper presents spectroscopy of supernovae discovered in the first season
of the Sloan Digital Sky Survey-II Supernova Survey. This program searches for
and measures multi-band light curves of supernovae in the redshift range z =
0.05 - 0.4, complementing existing surveys at lower and higher redshifts. Our
goal is to better characterize the supernova population, with a particular
focus on SNe Ia, improving their utility as cosmological distance indicators
and as probes of dark energy. Our supernova spectroscopy program features
rapid-response observations using telescopes of a range of apertures, and
provides confirmation of the supernova and host-galaxy types as well as precise
redshifts. We describe here the target identification and prioritization, data
reduction, redshift measurement, and classification of 129 SNe Ia, 16
spectroscopically probable SNe Ia, 7 SNe Ib/c, and 11 SNe II from the first
season. We also describe our efforts to measure and remove the substantial host
galaxy contamination existing in the majority of our SN spectra.Comment: Accepted for publication in The Astronomical Journal(47pages, 9
figures
The SDSS-II Supernova Survey: Parameterizing the Type Ia Supernova Rate as a Function of Host Galaxy Properties
Using data from the Sloan Digital Sky Supernova Survey-II, we measure the
rate of Type Ia Supernovae (SNe Ia) as a function of galaxy properties at
intermediate redshift. A sample of 342 SNe Ia with 0.05<z<0.25 is constructed.
Using broad-band photometry we use the PEGASE spectral energy distributions
(SEDs) to estimate host galaxy stellar masses and recent star-formation rates.
We find that the rate of SNe Ia per unit stellar mass is significantly higher
(by a factor of ~30) in highly star-forming galaxies compared to passive
galaxies. When parameterizing the SN Ia rate (SNR_Ia) based on host galaxy
properties, we find that the rate of SNe Ia in passive galaxies is not linearly
proportional to the stellar mass, instead a SNR_Ia proportional to M^0.68 is
favored. However, such a parameterization does not describe the observed SN Ia
rate in star-forming galaxies. The SN Ia rate in star-forming galaxies is well
fit by SNR_Ia = 1.05\pm0.16x10^{-10} M ^{0.68\pm0.01} + 1.01\pm0.09x10^{-3}
SFR^{1.00\pm0.05} (statistical errors only), where M is the host galaxy mass
and SFR is the star-formation rate. These results are insensitive to the
selection criteria used, redshift limit considered and the inclusion of
non-spectroscopically confirmed SNe Ia. We also show there is a dependence
between the distribution of the MLCS light-curve decline rate parameter,
\Delta, and host galaxy type. Passive galaxies host less luminous SNe Ia than
seen in moderately and highly star-forming galaxies, although a population of
luminous SNe is observed in passive galaxies, contradicting previous assertions
that these SNe Ia are only observed in younger stellar systems. The MLCS
extinction parameter, A_V, is similar in passive and moderately star-forming
galaxies, but we find indications that it is smaller, on average, in highly
star-forming galaxies. We confirm these results using the SALT2 light-curve
fitter.Comment: 46 pages, submitted to Ap
The Sloan Digital Sky Survey-II: Photometry and Supernova Ia Light Curves from the 2005 data
We present ugriz light curves for 146 spectroscopically confirmed or
spectroscopically probable Type Ia supernovae from the 2005 season of the
SDSS-II Supernova survey. The light curves have been constructed using a
photometric technique that we call scene modelling, which is described in
detail here; the major feature is that supernova brightnesses are extracted
from a stack of images without spatial resampling or convolution of the image
data. This procedure produces accurate photometry along with accurate estimates
of the statistical uncertainty, and can be used to derive photometry taken with
multiple telescopes. We discuss various tests of this technique that
demonstrate its capabilities. We also describe the methodology used for the
calibration of the photometry, and present calibrated magnitudes and fluxes for
all of the spectroscopic SNe Ia from the 2005 season
- …