Iskanje po repozitoriju

A+ | A- | | SLO | ENG

Opis: Galaxies, and clusters of galaxies, can act as gravitational lenses and magnify the light of objects behind them. The effect enables observations of very distant supernovae, that otherwise would be too faint to be detected by existing telescopes, and allows studies of the frequency and properties of these rare phenomena when the universe was young. Under the right circumstances, multiple images of the lensed supernovae can be observed, and due to the variable nature of the objects, the difference between the arrival times of the images can be measured. Since the images have taken different paths through space before reaching us, the time-differences are sensitive to the expansion rate of the universe. One class of supernovae, Type Ia, are of particular interest to detect. Their well known brightness can be used to determine the magnification, which can be used to understand the lensing systems. I will also report our discovery of the first resolved multiply-imaged gravitationally lensed supernova Type Ia.
Ključne besede: lensed supernovae, strong lensing
Objavljeno v RUNG: 03.05.2018; Ogledov: 3945; Prenosov: 0
Gradivo ima več datotek! Več...

Opis: Aims. Strong lensing by massive galaxy clusters can provide magnification of the flux and even multiple images of the galaxies that lie behind them. This phenomenon allows one to observe high-redshift supernovae (SNe), that otherwise would remain undetected. Type Ia supernovae (SNe Ia) detections are of particular interest because of their standard brightness, since they can be used to improve either cluster lensing models or cosmological parameter measurements. Methods. We present a ground-based, near-infrared search for lensed SNe behind the galaxy cluster Abell 370. Our survey was based on 15 epochs of J-band observations with the HAWK-I instrument on the Very Large Telescope (VLT). We use Hubble Space Telescope (HST) photometry to infer the global properties of the multiply-imaged galaxies. Using a recently published lensing model of Abell 370, we also present the predicted magnifications and the time-delays between the images. Results. In our survey, we did not discover any live SNe from the 13 lensed galaxies with 47 multiple images behind Abell 370. This is consistent with the expectation of 0.09 ± 0.02 SNe calculated based on the measured star formation rate. We compare the expectations of discovering strongly lensed SNe in our survey and that performed with HST during the Hubble Frontier Fields (HFF) program. We also show the expectations of search campaigns that can be conducted with future facilities, such as the James Webb Space Telescope (JWST) or the Wide-Field Infrared Survey Telescope (WFIRST). We show that NIRCam instrument aboard the JWST will be sensitive to most SN multiple images in the strongly-lensed galaxies and thus able to measure their time-delays if observations are scheduled accordingly.
Ključne besede: JWST, WFIRST, lensed supernovae, transient search
Objavljeno v RUNG: 29.01.2018; Ogledov: 3720; Prenosov: 0
Gradivo ima več datotek! Več...

Opis: Gravitational lenses such as galaxies and galaxy clusters, can magnify the flux of background galaxies. These galaxies at high redshift can host supernovae (SNe) which, thanks to the magnification boost due to lensing, can be observed, otherwise too faint to be detected by current telescopes. Under the right circumstances, the background galaxies may also have multiple images due to the strong lensing. Of particular interest is to detect lensed supernovae of type Ia (SNe Ia), because of their standard brightness. They could help improve lensing models and, if multiple images are observed, the Hubble constant can be measured independently. In this thesis, we use galaxy clusters as gravitational telescopes to search for lensed SNe at high redshift. We performed ground-based, near-infrared and optical search campaigns towards the massive clusters Abell 1689 and 370, which are among the most powerful gravitational telescopes known. Our search resulted in the discovery of five photometrically classified, core- collapse SNe at redshifts of 0.671 < z < 1.703 with significant magnification from the cluster. Owing to the power of the lensing cluster, we calculated the volumetric core-collapse SN rates for 0.4  z < 2.9, and find good agreement with previous estimates and predictions from cosmic star formation history. During our survey, we also discovered two SNe Ia in A1689 cluster members, which allowed us to determine the cluster Ia rate. Furthermore, we discuss the expectations of finding lensed SNe at high redshift in simulated search campaigns that can be conducted with upcoming ground- and space-based telescopes. Magnification from a galaxy lens also allows for detailed studies of the SN properties at high redshift that otherwise would not be possible. Spec- troscopic observations of lensed high-redshift SNe Ia are of particular interest since they can be used to test for evolution of the standard candle nature of these objects. However, if systematic redshift-dependent properties are found, their utility for future surveys could be challenged. We investigate whether the properties of the strongly lensed and very distant SN Ia PS1- 10afx at z = 1.4, deviates from the well-studied nearby and intermediate populations of normal SNe Ia. In other study, we report the discovery of the first resolved multiply-imaged gravitationally lensed SN Ia.
Ključne besede: supernovae, gravitational telescopes, galaxy clusters, lensed supernovae, strong lensing, astronomical surveys and telescopes
Objavljeno v RUNG: 23.01.2018; Ogledov: 4625; Prenosov: 0
Gradivo ima več datotek! Več...