125 research outputs found
Measuring the properties of extragalactic dust and implications for the Hubble diagram
Scattering and absorption of light by a homogeneous distribution of
intergalactic large dust grains has been proposed as an alternative,
non-cosmological explanation for the faintness of Type Ia supernovae at z\s im
0.5. We investigate the differential extinction for high-redshift sources
caused by extragalactic dust along the line of sight.
Future observations of Type Ia supernovae up to , e.g. by the
proposed SNAP satellite, will allow the measurement of the properties of dust
over cosmological distances. We show that 1% {\em relative} spectrophotometric
accuracy (or broadband photometry) in the wavelength interval 0.7--1.5 m
is required to measure the extinction caused by ``grey'' dust down to magnitudes.
We also argue that the presence of grey dust is not necessarily inconsistent
with the recent measurement of the brightness of a supernova at (SN
1997ff), in the absence of accurate spectrophotometric information of the
supernova.Comment: Accepted by A&
Limiting the dimming of distant type Ia supernovae
Distant supernovae have been observed to be fainter than what is expected in
a matter dominated universe. The most likely explanation is that the universe
is dominated by an energy component with negative pressure -- dark energy.
However, there are several astrophysical processes that could, in principle,
affect the measurements and in order to be able to take advantage of the
growing supernova statistics, the control of systematic effects is crucial. We
discuss two of these; extinction due to intergalactic grey dust and dimming due
to photon-axion oscillations and show how their effect on supernova
observations can be constrained using observed quasar colours and spectra. For
a wide range of intergalactic dust models, we are able to rule out any dimming
larger than 0.2 magnitudes for a type Ia supernova at z=1. The corresponding
limit for intergalactic Milky Way type dust is 0.03 mag. For the more
speculative model of photons mixing with axions, we find that the effect is
independent of photon energy for certain combinations of parameter values and a
dimming as large as 0.6 magnitudes cannot be ruled out. These effects can have
profound implications for the possibility of constraining dark energy
properties using supernova observations.Comment: 19 pages, 11 figures Matches version accepted in JCAP. Some
corrections due to minor bug in simulations, major conclusions unchange
Tentative detection of the gravitational magnification of type Ia supernovae
The flux from distant type Ia supernovae (SN) is likely to be amplified or
de-amplified by gravitational lensing due to matter distributions along the
line-of-sight. A gravitationally lensed SN would appear brighter or fainter
than the average SN at a particular redshift. We estimate the magnification of
26 SNe in the GOODS fields and search for a correlation with the residual
magnitudes of the SNe. The residual magnitude, i.e. the difference between
observed and average magnitude predicted by the "concordance model" of the
Universe, indicates the deviation in flux from the average SN. The linear
correlation coefficient for this sample is r=0.29. For a similar, but
uncorrelated sample, the probability of obtaining a correlation coefficient
equal to or higher than this value is ~10%, i.e. a tentative detection of
lensing at ~90% confidence level. Although the evidence for a correlation is
weak, our result is in accordance with what could be expected given the small
size of the sample.Comment: 7 pages, 2 figure
SNOC: a Monte-Carlo simulation package for high-z supernova observations
We present a Monte-Carlo package for simulation of high-redshift supernova
data, SNOC. Optical and near-infrared photons from supernovae are ray-traced
over cosmological distances from the simulated host galaxy to the observer at
Earth. The distances to the sources are calculated from user provided
cosmological parameters in a Friedmann-Lemaitre universe, allowing for
arbitrary forms of ``dark energy''. The code takes into account gravitational
interactions (lensing) and extinction by dust, both in the host galaxy and in
the line-of-sight. The user can also choose to include exotic effects like a
hypothetical attenuation due to photon-axion oscillations. SNOC is primarily
useful for estimations of cosmological parameter uncertainties from studies of
apparent brightness of Type Ia supernovae vs redshift, with special emphasis on
potential systematic effects. It can also be used to compute standard
cosmological quantities like luminosity distance, lookback time and age of the
universe in any Friedmann-Lemaitre model with or without quintessence.Comment: 16 pages, 3 figure
Cosmic distance-duality as probe of exotic physics and acceleration
In cosmology, distances based on standard candles (e.g. supernovae) and
standard rulers (e.g. baryon oscillations) agree as long as three conditions
are met: (1) photon number is conserved, (2) gravity is described by a metric
theory with (3) photons travelling on unique null geodesics. This is the
content of distance-duality (the reciprocity relation) which can be violated by
exotic physics. Here we analyse the implications of the latest cosmological
data sets for distance-duality. While broadly in agreement and confirming
acceleration we find a 2-sigma violation caused by excess brightening of SN-Ia
at z > 0.5, perhaps due to lensing magnification bias. This brightening has
been interpreted as evidence for a late-time transition in the dark energy but
because it is not seen in the d_A data we argue against such an interpretation.
Our results do, however, rule out significant SN-Ia evolution and extinction:
the "replenishing" grey-dust model with no cosmic acceleration is excluded at
more than 4-sigma despite this being the best-fit to SN-Ia data alone, thereby
illustrating the power of distance-duality even with current data sets.Comment: 6 pages, 4 colour figures. Version accepted as a Rapid Communication
in PR
Near-IR search for lensed supernovae behind galaxy clusters: III. Implications for cluster modeling and cosmology
Massive galaxy clusters at intermediate redshifts act as gravitational lenses
that can magnify supernovae (SNe) occurring in background galaxies. We assess
the possibility to use lensed SNe to put constraints on the mass models of
galaxy clusters and the Hubble parameter at high redshift. Due to the standard
candle nature of Type Ia supernovae (SNe Ia), observational information on the
lensing magnification from an intervening galaxy cluster can be used to
constrain the model for the cluster mass distribution. A statistical analysis
using parametric cluster models was performed to investigate the possible
improvements from lensed SNe Ia for the accurately modeled galaxy cluster A1689
and the less well constrained cluster A2204. Time delay measurements obtained
from SNe lensed by accurately modeled galaxy clusters can be used to measure
the Hubble parameter. For a survey of A1689 we estimate the expected rate of
detectable SNe Ia and of multiply imaged SNe. The velocity dispersion and core
radius of the main cluster potential show strong correlations with the
predicted magnifications and can therefore be constrained by observations of
SNe Ia in background galaxies. This technique proves especially powerful for
galaxy clusters with only few known multiple image systems. The main
uncertainty for measurements of the Hubble parameter from the time delay of
strongly lensed SNe is due to cluster model uncertainties. For the extremely
well modeled cluster A1689, a single time delay measurement could be used to
determine the Hubble parameter with a precision of ~ 10%. We conclude that
observations of SNe Ia behind galaxy clusters can be used to improve the mass
modeling of the large scale component of galaxy clusters and thus the
distribution of dark matter. Time delays from SNe strongly lensed by accurately
modeled galaxy clusters can be used to measure the Hubble constant at high
redshifts.Comment: 10 pages, 8 figures, 3 tables. Accepted for publication in A&
Constraining dark matter halo properties using lensed SNLS supernovae
This paper exploits the gravitational magnification of SNe Ia to measure
properties of dark matter haloes. The magnification of individual SNe Ia can be
computed using observed properties of foreground galaxies and dark matter halo
models. We model the dark matter haloes of the galaxies as truncated singular
isothermal spheres with velocity dispersion and truncation radius obeying
luminosity dependent scaling laws. A homogeneously selected sample of 175 SNe
Ia from the first 3-years of the Supernova Legacy Survey (SNLS) in the redshift
range 0.2 < z < 1 is used to constrain models of the dark matter haloes
associated with foreground galaxies. The best-fitting velocity dispersion
scaling law agrees well with galaxy-galaxy lensing measurements. We further
find that the normalisation of the velocity dispersion of passive and star
forming galaxies are consistent with empirical Faber-Jackson and Tully-Fisher
relations, respectively. If we make no assumption on the normalisation of these
relations, we find that the data prefer gravitational lensing at the 92 per
cent confidence level. Using recent models of dust extinction we deduce that
the impact of this effect on our results is very small. We also investigate the
brightness scatter of SNe Ia due to gravitational lensing. The gravitational
lensing scatter is approximately proportional to the SN Ia redshift. We find
the constant of proportionality to be B = 0.055 +0.039 -0.041 mag (B < 0.12 mag
at the 95 per cent confidence level). If this model is correct, the
contribution from lensing to the intrinsic brightness scatter of SNe Ia is
small for the SNLS sample.Comment: 11 pages, 7 figures, accepted for publication in MNRA
An investigation of gravitational lens determinations of H_o in quintessence cosmologies
There is growing evidence that the majority of the energy density of the
universe is not baryonic or dark matter, rather it resides in an exotic
component with negative pressure. The nature of this `quintessence' influences
our view of the universe, modifying angular diameter and luminosity distances.
Here, we examine the influence of a quintessence component upon gravitational
lens time delays. As well as a static quintessence component, an evolving
equation of state is also considered. It is found that the equation of state of
the quintessence component and its evolution influence the value of the
Hubble's constant derived from gravitational lenses. However, the differences
between evolving and non-evolving cosmologies are relatively small. We
undertake a suite of Monte Carlo simulations to examine the potential
constraints that can be placed on the universal equation of state from the
monitoring of gravitational lens system, and demonstrate that at least an order
of magnitude more lenses than currently known will have to be discovered and
analysed to accurately probe any quintessence component.Comment: 8pages, accepted for publication in MNRA
Near-IR Search for Lensed Supernovae Behind Galaxy Clusters - II. First Detection and Future Prospects
Powerful gravitational telescopes in the form of massive galaxy clusters can
be used to enhance the light collecting power over a limited field of view by
about an order of magnitude in flux. This effect is exploited here to increase
the depth of a survey for lensed supernovae at near-IR wavelengths. A pilot SN
search program conducted with the ISAAC camera at VLT is presented. Lensed
galaxies behind the massive clusters A1689, A1835 and AC114 were observed for a
total of 20 hours split into 2, 3 and 4 epochs respectively, separated by
approximately one month to a limiting magnitude J<24 (Vega). Image subtractions
including another 20 hours worth of archival ISAAC/VLT data were used to search
for transients with lightcurve properties consistent with redshifted
supernovae, both in the new and reference data. The feasibility of finding
lensed supernovae in our survey was investigated using synthetic lightcurves of
supernovae and several models of the volumetric Type Ia and core-collapse
supernova rates as a function of redshift. We also estimate the number of
supernova discoveries expected from the inferred star formation rate in the
observed galaxies. The methods consistently predict a Poisson mean value for
the expected number of SNe in the survey between N_SN=0.8 and 1.6 for all
supernova types, evenly distributed between core collapse and Type Ia SN. One
transient object was found behind A1689, 0.5" from a galaxy with photometric
redshift z_gal=0.6 +- 0.15. The lightcurve and colors of the transient are
consistent with being a reddened Type IIP SN at z_SN=0.59. The lensing model
predicts 1.4 magnitudes of magnification at the location of the transient,
without which this object would not have been detected in the near-IR ground
based search described in this paper (unlensed magnitude J~25). (abridged)Comment: Accepted by AA, matches journal versio
- âŠ