2,003 research outputs found
Cosmology from Type Ia Supernovae
This presentation reports on first evidence for a
low-mass-density/positive-cosmological-constant universe that will expand
forever, based on observations of a set of 40 high-redshift supernovae. The
experimental strategy, data sets, and analysis techniques are described. More
extensive analyses of these results with some additional methods and data are
presented in the more recent LBNL report #41801 (Perlmutter et al., 1998;
accepted for publication in Ap.J.), astro-ph/9812133 .
This Lawrence Berkeley National Laboratory reprint is a reduction of a poster
presentation from the Cosmology Display Session #85 on 9 January 1998 at the
American Astronomical Society meeting in Washington D.C. It is also available
on the World Wide Web at http://supernova.LBL.gov/ This work has also been
referenced in the literature by the pre-meeting abstract citation: Perlmutter
et al., B.A.A.S., volume 29, page 1351 (1997).Comment: 9 pages, 8 color figs. Presented at Jan '98 AAS Meeting, also cited
as BAAS,29,1351(1997). Archived here in response to requests; see more
extensive analyses in ApJ paper (astro-ph/9812133
Subaru FOCAS Spectroscopic Observations of High-Redshift Supernovae
We present spectra of high-redshift supernovae (SNe) that were taken with the
Subaru low resolution optical spectrograph, FOCAS. These SNe were found in SN
surveys with Suprime-Cam on Subaru, the CFH12k camera on the
Canada-France-Hawaii Telescope (CFHT), and the Advanced Camera for Surveys
(ACS) on the Hubble Space Telescope (HST). These SN surveys specifically
targeted z>1 Type Ia supernovae (SNe Ia). From the spectra of 39 candidates, we
obtain redshifts for 32 candidates and spectroscopically identify 7 active
candidates as probable SNe Ia, including one at z=1.35, which is the most
distant SN Ia to be spectroscopically confirmed with a ground-based telescope.
An additional 4 candidates are identified as likely SNe Ia from the
spectrophotometric properties of their host galaxies. Seven candidates are not
SNe Ia, either being SNe of another type or active galactic nuclei. When SNe Ia
are observed within a week of maximum light, we find that we can
spectroscopically identify most of them up to z=1.1. Beyond this redshift, very
few candidates were spectroscopically identified as SNe Ia. The current
generation of super red-sensitive, fringe-free CCDs will push this redshift
limit higher.Comment: 19 pages, 26 figures. PASJ in press. see
http://www.supernova.lbl.gov/2009ClusterSurvey/ for additional information
pertaining to the HST Cluster SN Surve
Implications For The Hubble Constant from the First Seven Supernovae at z >= 0.35
The Supernova Cosmology Project has discovered over twenty-eight supernovae
(SNe) at 0.35 <z < 0.65 in an ongoing program that uses Type Ia SNe as
high-redshift distance indicators. Here we present measurements of the ratio
between the locally observed and global Hubble constants, H_0^L/H_0^G, based on
the first 7 SNe of this high-redshift data set compared with 18 SNe at z <= 0.1
from the Calan/Tololo survey. If Omega_M <= 1, then light-curve-width corrected
SN magnitudes yield H_0^L/H_0^G < 1.10 (95% confidence level) in both a
Lambda=0 and a flat universe. The analysis using the SNe Ia as standard candles
without a light-curve-width correction yields similar results. These results
rule out the hypothesis that the discrepant ages of the Universe derived from
globular clusters and recent measurements of the Hubble constant are
attributable to a locally underdense bubble. Using the
Cepheid-distance-calibrated absolute magnitudes for SNe Ia of Sandage (1996},
we can also measure the global Hubble constant, H_0^G. If Omega_M >= 0.2, we
find that H_0^G < 70 km/s/Mpc in a Lambda=0 universe and H_0^G < 78 km/s/Mpc in
a flat universe, correcting the distant and local SN apparent magnitudes for
light curve width. Lower results for H_0^G are obtained if the magnitudes are
not width corrected.Comment: 13 pages, 2 Postscript figures. Preprint also available at
http://www-supernova.lbl.gov . To appear in ApJ Letter
A New Determination of the High Redshift Type Ia Supernova Rates with the Hubble Space Telescope Advanced Camera for Surveys
We present a new measurement of the volumetric rate of Type Ia supernova up
to a redshift of 1.7, using the Hubble Space Telescope (HST) GOODS data
combined with an additional HST dataset covering the North GOODS field
collected in 2004. We employ a novel technique that does not require
spectroscopic data for identifying Type Ia supernovae (although spectroscopic
measurements of redshifts are used for over half the sample); instead we employ
a Bayesian approach using only photometric data to calculate the probability
that an object is a Type Ia supernova. This Bayesian technique can easily be
modified to incorporate improved priors on supernova properties, and it is
well-suited for future high-statistics supernovae searches in which
spectroscopic follow up of all candidates will be impractical. Here, the method
is validated on both ground- and space-based supernova data having some
spectroscopic follow up. We combine our volumetric rate measurements with low
redshift supernova data, and fit to a number of possible models for the
evolution of the Type Ia supernova rate as a function of redshift. The data do
not distinguish between a flat rate at redshift > 0.5 and a previously proposed
model, in which the Type Ia rate peaks at redshift >1 due to a significant
delay from star-formation to the supernova explosion. Except for the highest
redshifts, where the signal to noise ratio is generally too low to apply this
technique, this approach yields smaller or comparable uncertainties than
previous work.Comment: Accepted for publication in Ap
K Corrections For Type Ia Supernovae and a Test for Spatial Variation of the Hubble Constant
Cross-filter K corrections for a sample of "normal" Type Ia supernovae (SNe)
have been calculated for a range of epochs. With appropriate filter choices,
the combined statistical and systematic K correction dispersion of the full
sample lies within 0.05 mag for redshifts z<0.7. This narrow dispersion of the
calculated K correction allows the Type Ia to be used as a cosmological probe.
We use the K corrections with observations of seven SNe at redshifts 0.3 < z
<0.5 to bound the possible difference between the locally measured Hubble
constant (H_L) and the true cosmological Hubble constant (H_0).Comment: 6 pages, 3 Postscript figures, uuencoded uses crckapb.sty and
psfig.sty. To appear in Thermonuclear Supernovae (NATO ASI), eds. R. Canal,
P. Ruiz-LaPuente, and J. Isern. Postscript version is also available at
http://www-supernova.lbl.gov
The distant Type Ia supernova rate
We present a measurement of the rate of distant Type Ia supernovae derived
using 4 large subsets of data from the Supernova Cosmology Project. Within this
fiducial sample, which surveyed about 12 square degrees, thirty-eight
supernovae were detected at redshifts 0.25--0.85. In a spatially-flat
cosmological model consistent with the results obtained by the Supernova
Cosmology Project, we derive a rest-frame Type Ia supernova rate at a mean
redshift of or (1 SNu = 1 supernova per century per
\Lbsun), where the first uncertainty is statistical and the second
includes systematic effects. The dependence of the rate on the assumed
cosmological parameters is studied and the redshift dependence of the rate per
unit comoving volume is contrasted with local estimates in the context of
possible cosmic star formation histories and progenitor models.Comment: 40 pages and 7 figures. Accepted for publication in the Astrophysical
Journal. Preprint also available at http://supernova.lbl.go
Gemini Spectroscopy of Supernovae from SNLS: Improving High Redshift SN Selection and Classification
We present new techiques for improving the efficiency of supernova (SN)
classification at high redshift using 64 candidates observed at Gemini North
and South during the first year of the Supernova Legacy Survey (SNLS). The SNLS
is an ongoing five year project with the goal of measuring the equation of
state of Dark Energy by discovering and following over 700 high-redshift SNe Ia
using data from the Canada-France-Hawaii Telescope Legacy Survey. We achieve an
improvement in the SN Ia spectroscopic confirmation rate: at Gemini 71% of
candidates are now confirmed as SNe Ia, compared to 54% using the methods of
previous surveys. This is despite the comparatively high redshift of this
sample, where the median SN Ia redshift is z=0.81 (0.155 <= z <= 1.01). These
improvements were realized because we use the unprecedented color coverage and
lightcurve sampling of the SNLS to predict whether a candidate is an SN Ia and
estimate its redshift, before obtaining a spectrum, using a new technique
called the "SN photo-z." In addition, we have improved techniques for galaxy
subtraction and SN template chi^2 fitting, allowing us to identify candidates
even when they are only 15% as bright as the host galaxy. The largest
impediment to SN identification is found to be host galaxy contamination of the
spectrum -- when the SN was at least as bright as the underlying host galaxy
the target was identified more than 90% of the time. However, even SNe on
bright host galaxies can be easily identified in good seeing conditions. When
the image quality was better than 0.55 arcsec the candidate was identified 88%
of the time. Over the five-year course of the survey, using the selection
techniques presented here we will be able to add approximately 170 more
confirmed SNe Ia than would be possible using previous methods.Comment: ApJ, accepted, 19 pages, 9 figure
Type Ia Supernovae and Cosmology
I discuss the use of Type Ia supernovae (SNe Ia) for cosmological distance
determinations. Low-redshift SNe Ia (z < 0.1) demonstrate that the Hubble
expansion is linear with H_0 = 72 +/- 8 km/s/Mpc, and that the properties of
dust in other galaxies are generally similar to those of dust in the Milky Way.
The measured luminosity distances of SNe Ia as a function of redshift have
shown that the expansion of the Universe is currently accelerating, probably
due to the presence of repulsive dark energy such as Einstein's cosmological
constant (Lambda). From about 200 SNe Ia, we find that Omega_Lambda - 1.4
Omega_M = 0.35 +/- 0.14. Combining our data with other results, we find a best
fit for Omega_M and Omega_Lambda of 0.28 and 0.72, respectively. A number of
possible systematic effects (dust, supernova evolution) thus far do not seem to
eliminate the need for Omega_Lambda > 0. Recently, analyses of SNe Ia at z =
1.0-1.7 provide further support for current acceleration, and give tentative
evidence for an early epoch of deceleration. The dynamical age of the Universe
is estimated to be 13.1 +/- 1.5 Gyr. According to the most recent data sets,
the SN Ia rate at z > 1 is several times greater than that at low redshifts,
presumably because of higher star formation rates long ago. Moreover, the
typical delay time from progenitor star formation to SNIa explosion appears to
be substantial, ~3 Gyr. Current projects include the measurement of a few
hundred SNe Ia at z = 0.2-0.8 to more accurately determine the
equation-of-state parameter of the dark energy, w = P/(\rho c^2), whose value
is now constrained by SNe Ia to be in the range -1.48 < w < -0.72 at 95%
confidence.Comment: 39 pages, 17 figures, to be published in "White Dwarfs: Probes of
Galactic Structure and Cosmology" ed. E. M. Sion, H. L. Shipman, and S.
Vennes (Kluwer: Dordrecht). Part of the Astrophysics and Space Science
Library Serie
SnoopCGH: software for visualizing comparative genomic hybridization data
Summary: Array-based comparative genomic hybridization (CGH) technology is used to discover and validate genomic structural variation, including copy number variants, insertions, deletions and other structural variants (SVs). The visualization and summarization of the array CGH data outputs, potentially across many samples, is an important process in the identification and analysis of SVs. We have developed a software tool for SV analysis using data from array CGH technologies, which is also amenable to short-read sequence data
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