240 research outputs found
A Calibration of NICMOS Camera 2 for Low Count-Rates
NICMOS 2 observations are crucial for constraining distances to most of the
existing sample of z > 1 SNe Ia. Unlike the conventional calibration programs,
these observations involve long exposure times and low count rates. Reciprocity
failure is known to exist in HgCdTe devices and a correction for this effect
has already been implemented for high and medium count-rates. However
observations at faint count-rates rely on extrapolations. Here instead, we
provide a new zeropoint calibration directly applicable to faint sources. This
is obtained via inter-calibration of NIC2 F110W/F160W with WFC3 in the low
count-rate regime using z ~ 1 elliptical galaxies as tertiary calibrators.
These objects have relatively simple near-IR SEDs, uniform colors, and their
extended nature gives superior signal-to-noise at the same count rate than
would stars. The use of extended objects also allows greater tolerances on PSF
profiles. We find ST magnitude zeropoints (after the installation of the NICMOS
cooling system, NCS) of 25.296 +- 0.022 for F110W and 25.803 +- 0.023 for
F160W, both in agreement with the calibration extrapolated from count-rates
1,000 times larger (25.262 and 25.799). Before the installation of the NCS, we
find 24.843 +- 0.025 for F110W and 25.498 +- 0.021 for F160W, also in agreement
with the high-count-rate calibration (24.815 and 25.470). We also check the
standard bandpasses of WFC3 and NICMOS 2 using a range of stars and galaxies at
different colors and find mild tension for WFC3, limiting the accuracy of the
zeropoints. To avoid human bias, our cross-calibration was "blinded" in that
the fitted zeropoint differences were hidden until the analysis was finalized.Comment: Accepted for Publication in the Astronomical Journal. New version
contains added referenc
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
Standardizing Type Ia Supernova Absolute Magnitudes Using Gaussian Process Data Regression
We present a novel class of models for Type Ia supernova time-evolving
spectral energy distributions (SED) and absolute magnitudes: they are each
modeled as stochastic functions described by Gaussian processes. The values of
the SED and absolute magnitudes are defined through well-defined regression
prescriptions, so that data directly inform the models. As a proof of concept,
we implement a model for synthetic photometry built from the spectrophotometric
time series from the Nearby Supernova Factory. Absolute magnitudes at peak
brightness are calibrated to 0.13 mag in the -band and to as low as 0.09 mag
in the blueshifted -band, where the dispersion includes
contributions from measurement uncertainties and peculiar velocities. The
methodology can be applied to spectrophotometric time series of supernovae that
span a range of redshifts to simultaneously standardize supernovae together
with fitting cosmological parameters.Comment: 47 pages, 15 figures, accepted for publication by Astrophysical
Journa
Atmospheric extinction properties above Mauna Kea from the Nearby Supernova Factory spectro-photometric data set
We present a new atmospheric extinction curve for Mauna Kea spanning
3200--9700 \AA. It is the most comprehensive to date, being based on some 4285
standard star spectra obtained on 478 nights spread over a period of 7 years
obtained by the Nearby SuperNova Factory using the SuperNova Integral Field
Spectrograph. This mean curve and its dispersion can be used as an aid in
calibrating spectroscopic or imaging data from Mauna Kea, and in estimating the
calibration uncertainty associated with the use of a mean extinction curve. Our
method for decomposing the extinction curve into physical components, and the
ability to determine the chromatic portion of the extinction even on cloudy
nights, is described and verified over the wide range of conditions sampled by
our large dataset. We demonstrate good agreement with atmospheric science data
obtain at nearby Mauna Loa Observatory, and with previously published
measurements of the extinction above Mauna Kea.Comment: 22 pages, 24 figures, 6 table
Host Galaxy Properties and Hubble Residuals of Type Ia Supernovae from the Nearby Supernova Factory
We examine the relationship between Type Ia Supernova (SN Ia) Hubble
residuals and the properties of their host galaxies using a sample of 115 SNe
Ia from the Nearby Supernova Factory (SNfactory). We use host galaxy stellar
masses and specific star-formation rates fitted from photometry for all hosts,
as well as gas-phase metallicities for a subset of 69 star-forming (non-AGN)
hosts, to show that the SN Ia Hubble residuals correlate with each of these
host properties. With these data we find new evidence for a correlation between
SN Ia intrinsic color and host metallicity. When we combine our data with those
of other published SN Ia surveys, we find the difference between mean SN Ia
brightnesses in low and high mass hosts is 0.077 +- 0.014 mag. When viewed in
narrow (0.2 dex) bins of host stellar mass, the data reveal apparent plateaus
of Hubble residuals at high and low host masses with a rapid transition over a
short mass range (9.8 <= log(M_*/M_Sun) <= 10.4). Although metallicity has been
a favored interpretation for the origin of the Hubble residual trend with host
mass, we illustrate how dust in star-forming galaxies and mean SN Ia progenitor
age both evolve along the galaxy mass sequence, thereby presenting equally
viable explanations for some or all of the observed SN Ia host bias.Comment: 20 pages, 11 figures, accepted for publication in Ap
The Hubble Space Telescope Cluster Supernova Survey: VI. The Volumetric Type Ia Supernova Rate
We present a measurement of the volumetric Type Ia supernova (SN Ia) rate out
to z ~ 1.6 from the Hubble Space Telescope Cluster Supernova Survey. In
observations spanning 189 orbits with the Advanced Camera for Surveys we
discovered 29 SNe, of which approximately 20 are SNe Ia. Twelve of these SNe Ia
are located in the foregrounds and backgrounds of the clusters targeted in the
survey. Using these new data, we derive the volumetric SN Ia rate in four broad
redshift bins, finding results consistent with previous measurements at z > 1
and strengthening the case for a SN Ia rate that is equal to or greater than
~0.6 x 10^-4/yr/Mpc^3 at z ~ 1 and flattening out at higher redshift. We
provide SN candidates and efficiency calculations in a form that makes it easy
to rebin and combine these results with other measurements for increased
statistics. Finally, we compare the assumptions about host-galaxy dust
extinction used in different high-redshift rate measurements, finding that
different assumptions may induce significant systematic differences between
measurements.Comment: 11 pages, 7 figures. Submitted to the Astrophysical Journal. Revised
version following referee comments. See the HST Cluster SN Survey website at
http://supernova.lbl.gov/2009ClusterSurvey for control time simulations in a
machine-readable table and a complete listing of transient candidates from
the surve
Measuring cosmic bulk flows with Type Ia Supernovae from the Nearby Supernova Factory
Context. Our Local Group of galaxies appears to be moving relative to the
cosmic microwave background with the source of the peculiar motion still
uncertain. While in the past this has been studied mostly using galaxies as
distance indicators, the weight of type Ia supernovae (SNe Ia) has increased
recently with the continuously improving statistics of available low-redshift
supernovae.
Aims. We measured the bulk flow in the nearby universe ()
using 117 SNe Ia observed by the Nearby Supernova Factory, as well as the
Union2 compilation of SN Ia data already in the literature.
Methods. The bulk flow velocity was determined from SN data binned in
redshift shells by including a coherent motion (dipole) in a cosmological fit.
Additionally, a method of spatially smoothing the Hubble residuals was used to
verify the results of the dipole fit. To constrain the location and mass of a
potential mass concentration (e.g., the Shapley supercluster) responsible for
the peculiar motion, we fit a Hubble law modified by adding an additional mass
concentration.
Results. The analysis shows a bulk flow that is consistent with the direction
of the CMB dipole up to , thereby doubling the volume over which
conventional distance measures are sensitive to a bulk flow. We see no
significant turnover behind the center of the Shapley supercluster. A simple
attractor model in the proximity of the Shapley supercluster is only marginally
consistent with our data, suggesting the need for another, more distant source.
In the redshift shell , we constrain the bulk flow velocity to
(68% confidence level) for the direction of the CMB
dipole, in contradiction to recent claims of the existence of a large-amplitude
dark flow.Comment: 12 pages, 5 figures, added corrigendum
(http://adsabs.harvard.edu/abs/2015A%26A...578C...1F
Host Galaxies of Type Ia Supernovae from the Nearby Supernova Factory
We present photometric and spectroscopic observations of galaxies hosting
Type Ia supernovae (SNe Ia) observed by the Nearby Supernova Factory
(SNfactory). Combining GALEX UV data with optical and near infrared photometry,
we employ stellar population synthesis techniques to measure SN Ia host galaxy
stellar masses, star-formation rates (SFRs), and reddening due to dust. We
reinforce the key role of GALEX UV data in deriving accurate estimates of
galaxy SFRs and dust extinction. Optical spectra of SN Ia host galaxies are
fitted simultaneously for their stellar continua and emission lines fluxes,
from which we derive high precision redshifts, gas-phase metallicities, and
Halpha-based SFRs. With these data we show that SN Ia host galaxies present
tight agreement with the fiducial galaxy mass-metallicity relation from SDSS
for stellar masses log(M_*/M_Sun)>8.5 where the relation is well-defined. The
star-formation activity of SN Ia host galaxies is consistent with a sample of
comparable SDSS field galaxies, though this comparison is limited by systematic
uncertainties in SFR measurements. Our analysis indicates that SN Ia host
galaxies are, on average, typical representatives of normal field galaxies.Comment: 25 pages, 13 figures, accepted for publication in Ap
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
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