159 research outputs found
Optical Photometry of the Type Ia SN 1999ee and the Type Ib/c SN 1999ex in IC 5179
We present UBVRIz lightcurves of the Type Ia SN 1999ee and the Type Ib/c SN
1999ex, both located in the galaxy IC 5179. SN 1999ee has an extremely well
sampled lightcurve spanning from 10 days before Bmax through 53 days after
peak. Near maximum we find systematic differences ~0.05 mag in photometry
measured with two different telescopes, even though the photometry is reduced
to the same local standards around the supernova using the specific color terms
for each instrumental system. We use models for our bandpasses and
spectrophotometry of SN 1999ee to derive magnitude corrections (S-corrections)
and remedy this problem. This exercise demonstrates the need of accurately
characterizing the instrumental system before great photometric accuracies of
Type Ia supernovae can be claimed. It also shows that this effect can have
important astrophysical consequences since a small systematic shift of 0.02 mag
in the B-V color can introduce a 0.08 mag error in the extinction corrected
peak B magnitudes of a supernova and thus lead to biased cosmological
parameters. The data for the Type Ib/c SN 1999ex present us with the first ever
observed shock breakout of a supernova of this class. These observations show
that shock breakout occurred 18 days before Bmax and support the idea that Type
Ib/c supernovae are due to core collapse of massive stars rather than
thermonuclear disruption of white dwarfs.Comment: 55 pages, 15 figures, accepted by the Astronomical Journa
SN Refsdal: Classification as a Luminous and Blue SN 1987A-like Type II Supernova
We have acquired Hubble Space Telescope (HST) and Very Large Telescope
near-infrared spectra and images of supernova (SN) Refsdal after its discovery
as an Einstein cross in Fall 2014. The HST light curve of SN Refsdal matches
the distinctive, slowly rising light curves of SN 1987A-like supernovae (SNe),
and we find strong evidence for a broad H-alpha P-Cygni profile in the HST
grism spectrum at the redshift (z = 1.49) of the spiral host galaxy. SNe IIn,
powered by circumstellar interaction, could provide a good match to the light
curve of SN Refsdal, but the spectrum of a SN IIn would not show broad and
strong H-alpha absorption. From the grism spectrum, we measure an H-alpha
expansion velocity consistent with those of SN 1987A-like SNe at a similar
phase. The luminosity, evolution, and Gaussian profile of the H-alpha emission
of the WFC3 and X-shooter spectra, separated by ~2.5 months in the rest frame,
provide additional evidence that supports the SN 1987A-like classification. In
comparison with other examples of SN 1987A-like SNe, SN Refsdal has a blue B-V
color and a high luminosity for the assumed range of potential magnifications.
If SN Refsdal can be modeled as a scaled version of SN 1987A, we estimate it
would have an ejecta mass of 20+-5 solar masses. The evolution of the light
curve at late times will provide additional evidence about the potential
existence of any substantial circumstellar material (CSM). Using MOSFIRE and
X-shooter spectra, we estimate a subsolar host-galaxy metallicity (8.3+-0.1 dex
and <8.4 dex, respectively) near the explosion site.Comment: Submitted to ApJ; 26 page
Dust in the Host Galaxies of Supernovae
We present Spitzer/MIPS 24 micron observations of 50 supernova host galaxies
at 0.1<z<1.7 in the Great Observatories Origins Deep Survey (GOODS) fields. We
also discuss the detection of SN host galaxies in SCUBA/850 micron observations
of GOODS-N and Spitzer/Infrared Spectrograph (IRS) 16 micron observations of
GOODS-S. About 60% of the host galaxies of both Type Ia and core-collapse
supernovae are detected at 24 microns, a detection rate which is a factor of
1.5 higher than the field galaxy population. Among the 24 micron detected
hosts, 80% have far-infrared luminosities that are comparable to or greater
than the optical luminosity indicating the presence of substantial amounts of
dust in the hosts. The median bolometric luminosity of the Type Ia SN hosts is
\~10^10.5 L_sun, very similar to that of core-collapse SN hosts. Using the high
resolution Hubble/ACS data, we have studied the variation of rest-frame
optical/ultraviolet colors within the 24 micron detected galaxies at z<1 to
understand the origin of the dust emission. The 24 micron detected galaxies
have average colors which are redder by ~0.1 mag than the 24 micron undetected
hosts while the latter show greater scatter in internal colors. This suggests
that a smooth distribution of dust is responsible for the observed mid- and
far-infrared emission. 70% of supernovae that have been detected in the GOODS
fields are located within the half-light radius of the hosts where dust
obscuration effects are significant. Although the dust emission that we detect
cannot be translated into a line of sight A_V, we suggest that the factor of
2-3 larger scatter in the peak B-V colors that is seen in the high-z Type Ia
supernova sample relative to the low-z supernovae might be partially due to the
dust that we detect in the hosts.Comment: 22 pages, 4 figures, 4 tables; ApJ 635, Dec 20, 2005 issu
Clues to AGN Growth from Optically Variable Objects in the Hubble Ultra Deep Field
We present a photometric search for objects with point-source components that
are optically variable on timescales of weeks--months in the Hubble Ultra Deep
Field (HUDF) to i'(AB)=28.0 mag. The data are split into four sub-stacks of
approximately equal exposure times. Objects exhibiting the signature of optical
variability are selected by studying the photometric error distribution between
the four different epochs, and selecting 622 candidates as 3.0 sigma outliers
from the original catalog of 4644 objects. Of these, 45 are visually confirmed
as free of contamination from close neighbors or various types of image
defects. Four lie within the positional error boxes of Chandra X-ray sources,
and two of these are spectroscopically confirmed AGN. The photometric redshift
distribution of the selected variable sample is compared to that of field
galaxies, and we find that a constant fraction of ~1% of all field objects show
variability over the range of 0.1<z<4.5. Combined with other recent HUDF
results, as well as those of recent state-of-the-art numerical simulations, we
discuss a potential link between the hierarchical merging of galaxies and the
growth of AGN.Comment: 9 pages, 6 figures, accepted for publication in Astrophysical
Journal, minor changes to reference
The Distance to SN 1999em from the Expanding Photosphere Method
We present optical and IR spectroscopy of the first two months of evolution
of the Type II SN 1999em. We combine these data with high-quality optical/IR
photometry beginning only three days after shock breakout, in order to study
the performance of the ``Expanding Photosphere Method'' (EPM) in the
determination of distances. With this purpose we develop a technique to measure
accurate photospheric velocities by cross-correlating observed and model
spectra. The application of this technique to SN 1999em shows that we can reach
an average uncertainty of 11% in velocity from an individual spectrum. Our
analysis shows that EPM is quite robust to the effects of dust. In particular,
the distances derived from the VI filters change by only 7% when the adopted
visual extinction in the host galaxy is varied by 0.45 mag. The superb time
sampling of the BVIZJHK light-curves of SN 1999em permits us to study the
internal consistency of EPM and test the dilution factors computed from
atmosphere models for Type II plateau supernovae. We find that, in the first
week since explosion, the EPM distances are up to 50% lower than the average,
possibly due the presence of circumstellar material. Over the following 65
days, on the other hand, our tests lend strong credence to the atmosphere
models, and confirm previous claims that EPM can produce consistent distances
without having to craft specific models to each supernova. This is particularly
true for the VI filters which yield distances with an internal consistency of
4%. From the whole set of BVIZJHK photometry, we obtain an average distance of
7.5+/-0.5 Mpc, where the quoted uncertainty (7%) is a conservative estimate of
the internal precision of the method obtained from the analysis of the first 70
days of the supernova evolution.Comment: 68 pages, 15 tables, 22 figures, to appear in Ap
Dynamical dark energy: Current constraints and forecasts
We consider how well the dark energy equation of state as a function of
red shift will be measured using current and anticipated experiments. We
use a procedure which takes fair account of the uncertainties in the functional
dependence of on , as well as the parameter degeneracies, and avoids the
use of strong prior constraints. We apply the procedure to current data from
WMAP, SDSS, and the supernova searches, and obtain results that are consistent
with other analyses using different combinations of data sets. The effects of
systematic experimental errors and variations in the analysis technique are
discussed. Next, we use the same procedure to forecast the dark energy
constraints achieveable by the end of the decade, assuming 8 years of WMAP data
and realistic projections for ground-based measurements of supernovae and weak
lensing. We find the constraints on the current value of to be
, and on (between and ) to be
. Finally, we compare these limits to other
projections in the literature. Most show only a modest improvement; others show
a more substantial improvement, but there are serious concerns about
systematics. The remaining uncertainty still allows a significant span of
competing dark energy models. Most likely, new kinds of measurements, or
experiments more sophisticated than those currently planned, are needed to
reveal the true nature of dark energy.Comment: 24 pages, 20 figures. Added SN systematic uncertainties, extended
discussio
High Redshift Supernova Rates
We use a sample of 42 supernovae detected with the Advanced Camera for
Surveys on-board the Hubble Space Telescope as part of the Great Observatories
Origins Deep Survey to measure the rate of core collapse supernovae to z~0.7
and type Ia supernovae to z~1.6. This significantly increases the redshift
range where supernova rates have been estimated from observations.
The rate of core collapse supernovae can be used as an independent probe of
the cosmic star formation rate. Based on the observations of 17 core collapse
supernovae, we measure an increase in the core collapse supernova rate by a
factor of 1.6 in the range 0.3<z<0.7, and an overall increase by a factor of 7
to z~0.7 in comparison to the local core collapse supernova rate. The increase
in the rate in this redshift range in consistent with recent measurements of
the star formation rate derived from UV-luminosity densities and IR datasets.
Based on 25 type Ia supernovae, we find a SN Ia rate that is a factor 3-5
higher at z~1 compared to earlier estimates at lower redshifts (z<0.5),
implying that the type Ia supernova rate traces a higher star formation rate at
redshifts z>1 compared to low redshift. At higher redshift (z>1), we find a
suggested decrease in the type Ia rate with redshift. This evolution of the Ia
rate with redshift is consistent with a type Ia progenitor model where there is
a substantial delay between the formation of the progenitor star and the
explosion of the supernova. Assuming that the type Ia progenitor stars have
initial main sequence masses 3-8 M_Sun, we find that 5-7% of the available
progenitors explode as type Ia supernovae.Comment: 16 pages, 3 figures, accepted for publication in the Astrophysical
Journa
Q-LET - Quick Lensing Estimation Tool - An application to SN2003es
Q-LET is a FORTRAN 77 code that enables a quick estimate of the gravitational
lensing effects on a point- or an extended source. The user provided input
consists of the redshifts, angular positions relative to the source, mass or
velocity dispersion estimate and halo type for the lens galaxies. The
considered halo types are the Navarro-Frenk-White and the Singular Isothermal
Sphere. The code uses the so-called multiple lens-plane method to find the
magnification and intrinsic shape of the source. This method takes into account
the multiple deflections that may arise when several mass accumulations are
situated at different redshifts close to the line-of-sight.
The Q-LET code is applied to the recently discovered supernova, SN2003es,
which is likely to be of Type Ia as its host galaxy is classified as an
elliptical. We find that SN2003es is likely to have been significantly
magnified by gravitational lensing and that this should be considered in high-z
studies if this SN is to be used to determine the cosmological parameters.
Q-LET was motivated by the supernova searches, where lensing can be a
problem, but it can also be applied to any simple lens system where a quick
estimate is wanted, e.g. the single lens case.Comment: 16 pages, 5 figures. Submitted to JCAP. Software available at
http://www.physto.se/~cg/qlet/qlet.ht
Supernova rates from the Southern inTermediate Redshift ESO Supernova Search (STRESS)
To measure the supernova (SN) rates at intermediate redshift we performed the
Southern inTermediate Redshift ESO Supernova Search (STRESS). Unlike most of
the current high redshift SN searches, this survey was specifically designed to
estimate the rate for both type Ia and core collapse (CC) SNe. We counted the
SNe discovered in a selected galaxy sample measuring SN rate per unit blue band
luminosity. Our analysis is based on a sample of ~43000 galaxies and on 25
spectroscopically confirmed SNe plus 64 selected SN candidates. Our approach is
aimed at obtaining a direct comparison of the high redshift and local rates and
at investigating the dependence of the rates on specific galaxy properties,
most notably their colour. The type Ia SN rate, at mean redshift z=0.3, amounts
to 0.22^{+0.10+0.16}_{-0.08 -0.14} h_{70}^2 SNu, while the CC SN rate, at
z=0.21, is 0.82^{+0.31 +0.30}_{-0.24 -0.26} h_{70}^2 SNu. The quoted errors are
the statistical and systematic uncertainties. With respect to local value, the
CC SN rate at z=0.2 is higher by a factor of ~2 already at redshift, whereas
the type Ia SN rate remains almost constant. This implies that a significant
fraction of SN Ia progenitors has a lifetime longer than 2-3 Gyr. We also
measured the SN rates in the red and blue galaxies and found that the SN Ia
rate seems to be constant in galaxies of different colour, whereas the CC SN
rate seems to peak in blue galaxies, as in the local Universe. SN rates per
unit volume were found to be consistent with other measurements showing a
steeper evolution with redshift for CC SNe with respect to SNe Ia. Finally we
have exploited the link between star formation (SF) and SN rates to predict the
evolutionary behaviour of the SN rates and compare it with the path indicated
by observations.Comment: Accepted for publication in A&A; 25 pages (including on line
material), 13 figure
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