96 research outputs found
Type Ia supernova constraints on compact object dark matter
The nature of dark matter (DM) is an open question in cosmology, despite its
abundance in the universe. While elementary particles have been posited to
explain DM, compact astrophysical objects such as black holes formed in the
early universe offer a theoretically appealing alternate route. Here, we
constrain the fraction of DM that can be made up of primordial black holes
(PBHs) with masses , using the Type Ia supernova Hubble
diagram. Utilizing the Dyer-Roeder distance relation, where the homogeneous
matter fraction is parameterized with , we find a maximum fractional
amount of DM in compact objects () of 0.50 at 95\% confidence level
(C.L.), in the flat CDM model and 0.49 when marginalising over a
constant dark energy equation of state. These limits do not change when
marginalising over cosmic curvature, demonstrating the robustness to the
cosmological model. When allowing for the prior on to include , we derive at 95 C.L., showing that the prior assumption of
gives a conservative upper limit on . When including Cepheid
calibrated supernovae, the 95\% C.L. constraints improve to . We
find that the estimate for the Hubble constant in our inference is consistent
with the homogeneous case, showing that inhomogeneities in the form of compact
dark matter cannot account for the observed Hubble tension. In conclusion, we
strongly exclude the possibility that PBHs with stellar masses and above form a
dominant fraction of the dark matter.Comment: to be submitted to MNRAS Letter
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
Growth Histories in Bimetric Massive Gravity
We perform cosmological perturbation theory in Hassan-Rosen bimetric gravity
for general homogeneous and isotropic backgrounds. In the de Sitter
approximation, we obtain decoupled sets of massless and massive scalar
gravitational fluctuations. Matter perturbations then evolve like in Einstein
gravity. We perturb the future de Sitter regime by the ratio of matter to dark
energy, producing quasi-de Sitter space. In this more general setting the
massive and massless fluctuations mix. We argue that in the quasi-de Sitter
regime, the growth of structure in bimetric gravity differs from that of
Einstein gravity.Comment: 28 pages + appendix, 11 figure
Constraining dark energy fluctuations with supernova correlations
We investigate constraints on dark energy fluctuations using type Ia
supernovae. If dark energy is not in the form of a cosmological constant, that
is if the equation of state is not equal to -1, we expect not only temporal,
but also spatial variations in the energy density. Such fluctuations would
cause local variations in the universal expansion rate and directional
dependences in the redshift-distance relation. We present a scheme for relating
a power spectrum of dark energy fluctuations to an angular covariance function
of standard candle magnitude fluctuations. The predictions for a
phenomenological model of dark energy fluctuations are compared to
observational data in the form of the measured angular covariance of Hubble
diagram magnitude residuals for type Ia supernovae in the Union2 compilation.
The observational result is consistent with zero dark energy fluctuations.
However, due to the limitations in statistics, current data still allow for
quite general dark energy fluctuations as long as they are in the linear
regime.Comment: 18 pages, 6 figures, matches the published versio
Spectral Signatures of Photon-Particle Oscillations from Celestial Objects
We give detailed predictions for the spectral signatures arising from
photon-particle oscillations in astrophysical objects. The calculations include
quantum electrodynamic effects as well as those due to active relativistic
plasma. We show that, by studying the spectra of compact sources, it may be
possible to directly detect (pseudo-)scalar particles, such as the axion, with
much greater sensitivity, by roughly three orders of magnitude, than is
currently achievable by other methods. In particular, if such particles exist
with masses m_a<0.01[eV] and coupling constant to the electromagnetic field,
g>1e-13[1/GeV], then their oscillation signatures are likely to be lurking in
the spectra of magnetars, pulsars, and quasars.Comment: 29 pages (reduced resolution for figs. 3, 4b, 7
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
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
Near-IR search for lensed supernovae behind galaxy clusters: I. Observations and transient detection efficiency
Massive galaxy clusters at intermediate redshift can magnify the flux of
distant background sources by several magnitudes and we exploit this effect to
search for lensed distant supernovae that may otherwise be too faint to be
detected. A supernova search was conducted at near infrared wavelengths using
the ISAAC instrument at the VLT. The galaxy clusters Abell 1689, Abell 1835 and
AC114 were observed at multiple epochs of 2 hours of exposure time, separated
by a month. Image-subtraction techniques were used to search for transient
objects with light curve properties consistent with supernovae, both in our new
and archival ISAAC/VLT data. The limiting magnitude of the individual epochs
was estimated by adding artificial stars to the subtracted images. Most of the
epochs reach 90% detection efficiency at SZ(J) ~= 23.8-24.0 mag (Vega). Two
transient objects, both in archival images of Abell 1689 and AC114, were
detected. The transient in AC114 coincides - within the position uncertainty -
with an X-ray source and is likely to be a variable AGN at the cluster
redshift. The transient in Abell 1689 was found at SZ=23.24 mag, ~0.5 arcsec
away from a galaxy with photometric redshift z=0.6 +/-0.15. The light curves
and the colors of the transient are consistent with a reddened Type IIP
supernova at redshift z=0.59 +/- 0.05. The lensing model of Abell 1689 predicts
~1.4 mag of magnification at the position of the transient, making it the most
magnified supernova ever found and only the second supernova found behind a
galaxy cluster. Our pilot survey has demonstrated the feasibility to find
distant gravitationally magnified supernovae behind massive galaxy clusters.
One likely supernova was found behind Abell 1689, in accordance with the
expectations for this survey, as shown in an accompanying analysis paper.Comment: Language-edited version, 9 pages, 6 figures, accepted by A&
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