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- Amanullah, R., et al.
(författare)
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A HIGHLY MAGNIFIED SUPERNOVA AT z=1.703 BEHIND THE MASSIVE GALAXY CLUSTER A1689
- 2011
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Ingår i: ASTROPHYS J LETT. - 2041-8205. ; 742:1, s. L7-
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Tidskriftsartikel (refereegranskat)abstract
- Our ability to study the most remote supernova explosions, crucial for the understanding of the evolution of the high-redshift universe and its expansion rate, is limited by the light collection capabilities of telescopes. However, nature offers unique opportunities to look beyond the range within reach of our unaided instruments thanks to the light-focusing power of massive galaxy clusters. Here we report on the discovery of one of the most distant supernovae ever found, at redshift z = 1.703. Due to a lensing magnification factor of 4.3 +/- 0.3, we are able to measure a light curve of the supernova, as well as spectroscopic features of the host galaxy with a precision comparable to what would otherwise only be possible with future generation telescopes.
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| 2. |
- Goobar, Ariel, et al.
(författare)
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Near-IR search for lensed supernovae behind galaxy clusters. II. First detection and future prospects
- 2009
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 507:1, s. 71-83
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Tidskriftsartikel (refereegranskat)abstract
- Aims: 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. Methods: We present a pilot supernova search programme conducted with the ISAAC camera at VLT. Lensed galaxies behind the massive clusters A1689, A1835, and AC114 were observed for a total of 20 h divided into 2, 3, and 4 epochs respectively, separated by approximately one month to a limiting magnitude J ≲ 24 (Vega). Image subtractions including another 20 h 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. Results: 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 supernovae in the survey of between N_SN = 0.8 and 1.6 for all supernova types, evenly distributed between core collapse and type Ia supernovae. One transient object was found behind A1689, 0.5 arcsec 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 supernova at z_SN = 0.59. The lensing model predicts 1.4 mag 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). We perform a feasibility study of the potential for lensed supernovae discoveries with larger and deeper surveys and conclude that the use of gravitational telescopes is a very exciting path for new discoveries. For example, a monthly rolling supernova search of a single very massive cluster with the HAWK-I camera at VLT would yield ≳ 10 lensed supernova lightcurves per year, where type Ia supernovae would constitute about half of the expected sample. Based on observations made with ESO telescopes at the La Silla Paranal Observatory under programme ID 079.A-0192 and ID 081.A-0734.
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| 4. |
- Holopainen, Janne, et al.
(författare)
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An analytical model of surface mass densities of cold dark matter haloes - with an application to MACHO microlensing optical depths
- 2008
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 383:2, s. 720-728
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Tidskriftsartikel (refereegranskat)abstract
- The cold dark matter (CDM) scenario generically predicts the existence of triaxial dark matter haloes which contain notable amounts of substructure. However, analytical halo models with smooth, spherically symmetric density profiles are routinely adopted in the modelling of light propagation effects through such objects. In this paper, we address the biases introduced by this procedure by comparing the surface mass densities of actual N-body haloes against the widely used analytical model suggested by Navarro, Frenk and White (NFW). We conduct our analysis in the redshift range of 0.0-1.5. In cluster-sized haloes, we find that triaxiality can cause scatter in the surface mass density of the haloes up to sigma(+) = +60 per cent and sigma(-) = -70 per cent, where the 1 sigma limits are relative to the analytical NFW model given value. Subhaloes can increase this scatter to sigma(+) = +70 per cent and sigma(-) = -80 per cent. In galaxy-sized haloes, the triaxial scatter can be as high as sigma(+) = +80 per cent and sigma(-) = -70 per cent, and with subhaloes the values can change to sigma(+) = +40 per cent and sigma(-) = -80 per cent. We present an analytical model for the surface mass density scatter as a function of distance to the halo centre, halo redshift and halo mass. The analytical description enables one to investigate the reliability of results obtained with simplified halo models. Additionally, it provides the means to add simulated surface density scatter to analytical density profiles. As an example, we discuss the impact of our results on the calculation of microlensing optical depths for massive astrophysical compact halo objects in CDM haloes.
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| 6. |
- Riehm, Teresa, 1982-
(författare)
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Investigating the Dark Universe through Gravitational Lensing
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A variety of precision observations suggest that the present universe is dominated by some unknown components, the so-called dark matter and dark energy. The distribution and properties of these components are the focus of modern cosmology and we are only beginning to understand them. Gravitational lensing, the bending of light in the gravitational field of a massive object, is one of the predictions of the general theory of relativity. It has become an ever more important tool for investigating the dark universe, especially with recent and coming advances in observational data. This thesis studies gravitational lensing effects on scales ranging over ten orders of magnitude to probe very different aspects of the dark universe. Implementing a matter distribution following the predictions of recent simulations, we show that microlensing by a large population of massive compact halo objects (MACHOs) is unlikely to be the source of the observed long-term variability in quasars. We study the feasibility of detecting the so far elusive galactic dark matter substructures, the so-called “missing satellites”, via millilensing in galaxies close to the line-of-sight to distant light sources. Finally, we utilise massive galaxy clusters, some of the largest structures known in the universe, as gravitational telescopes in order to detect distant supernovae, thereby gaining insight into the expansion history of the universe. We also show, how such observations can be used to put constraints on the dark matter component of these galaxy clusters.
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| 7. |
- Riehm, Teresa, et al.
(författare)
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Near-IR search for lensed supernovae behind galaxy clusters III. Implications for cluster modeling and cosmology
- 2011
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 536, s. A94-
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Tidskriftsartikel (refereegranskat)abstract
- Context. Massive galaxy clusters at intermediate redshifts act as gravitational lenses that can magnify supernovae (SNe) occurring in background galaxies. Aims. We assess the possibility of using lensed SNe to constraint the mass models of galaxy clusters and the Hubble parameter at high redshift. Methods. Owing to the standard candle nature of Type Ia supernovae (SNe Ia), observational information on the lensing magnification by 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 provided by lensed SNe Ia to the analysis of the accurately modeled galaxy cluster A1689 and the less well-modeled 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 rates of detectable SNe Ia and multiply imaged SNe. Results. The velocity dispersion and core radius of the main cluster potential follow 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 a few known multiple image systems. The main uncertainty in measurements of the Hubble parameter from the time delay of strongly lensed SNe is caused by 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 similar to 10%. Conclusions. 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.
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