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Impact of the 3D source geometry on time-delay measurements of lensed type-Ia supernovae
摘要： It has recently been proposed that gravitationally lensed type-Ia supernovae can provide microlensing-free time-delay measurements provided that the measurement is taken during the achromatic expansion phase of the explosion and that color light curves are used rather than single-band light curves. If verified, this would provide both precise and accurate time-delay measurements, making lensed type-Ia supernovae a new golden standard for time-delay cosmography. However, the 3D geometry of the expanding shell can introduce an additional bias that has not yet been fully explored. In this work, we present and discuss the impact of this effect on time-delay cosmography with lensed supernovae and find that on average it leads to a bias of a few tenths of a day for individual lensed systems. This is negligible in view of the cosmological time delays predicted for typical lensed type-Ia supernovae but not for the specific case of the recently discovered type-Ia supernova iPTF16geu, whose time delays are expected to be smaller than a day.
关键词： gravitational lensing: strong,cosmological parameters,supernovae: general
更新于2025-09-23 15:23:52
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Bright lenses are easy to find: spectroscopic confirmation of lensed quasars in the Southern Sky
摘要： Gravitationally lensed quasars are valuable, but extremely rare, probes of observational cosmology and extragalactic astrophysics. Progress in these fields has been limited just by the paucity of systems with good ancillary data. Here we present a first spectroscopic confirmation of lenses discovered in the Southern Sky from the DES and KiDS-DR3 footprints. We have targeted seven high-graded candidates, selected with new techniques, with NTT-EFOSC2, and confirmed five of them. We provide source spectroscopic redshifts, image separations, gri photometry, and first lens model parameters. The success rate of ～70 per cent confirms our forecasts, based on the comparison between the number of candidate doubles and quadruplets in our searches over a ≈5000 deg2 footprint and theoretical predictions.
关键词： gravitational lensing: strong,Galaxies: formation,surveys
更新于2025-09-23 15:23:52
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Testing the validity of the ray-tracing code GYOTO
摘要： Context. In the next few years, the near-infrared interferometer GRAVITY will be able to observe the Galactic center. Astrometric data will be obtained with an anticipated accuracy of 10 μas. To analyze these future data, we have developed a code called GYOTO to compute orbits and ray-trace images. Aims. We want to assess the validity and accuracy of GYOTO in a variety of contexts, in particular for stellar astrometry in the Galactic center. Furthermore, we want to tackle and complete a study made on the astrometric displacements that are due to lensing effects of a star of the central parsec with GYOTO. Methods. We first validate GYOTO in the weak-deflection limit (WDL) by studying primary caustics and primary critical curves obtained for a Kerr black hole. We compare GYOTO results to available analytical approximations and estimate GYOTO errors using an intrinsic estimator. In the strong-deflection limit (SDL), we choose to compare null geodesics computed by GYOTO and the ray-tracing code named Geokerr. Finally, we use GYOTO to estimate the apparent astrometric displacements of a star for different angles from Sagittarius A* (Sgr A*). Results. In the WDL, we find a good coherence between GYOTO results and approximations. The maximal difference is around 10?5 μas. Our intrinsic estimator finds a conservative uncertainty estimate also around 10?5 μas. In the SDL, both ray-tracing codes find the same photon’s coordinates with a maximal difference of about 10?3 μas. The shift of a star located behind the plane of sky containing Sgr A* is consistent with the current study. In addition, the effect of lensing on any star in this plane of sky is a radial shift by 5 μas, independent of the distance from Sgr A* up to a very large distance. Conclusions. We have demonstrated that GYOTO is accurate to a very high level, orders of magnitude better than the GRAVITY requirements. GYOTO is also valid in weak- and strong-deflection regimes and for very long integrations. At the astrometric precision that GRAVITY is aiming for, lensing effects must always be taken into account when fitting stellar orbits in the central parsec of the Galaxy.
关键词： gravitational lensing: weak,gravitational lensing: strong,black hole physics,Galaxy: center
更新于2025-09-23 15:21:21
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A Window on the Earliest Star Formation: Extreme Photoionization Conditions of a High-ionization, Low-metallicity Lensed Galaxy at <i>z</i> ～ 2*
摘要： We report new observations of SL2S J021737–051329, a lens system consisting of a bright arc at z = 1.84435, magnified ～17× by a massive galaxy at z = 0.65. SL2S0217 is a low-mass (M < 109 Me), low-metallicity (Z ～ 1/20 Ze) galaxy, with extreme star-forming conditions that produce strong nebular UV emission lines in the absence of any apparent outflows. Here we present several notable features from rest-frame UV Keck/LRIS spectroscopy: (1) Very strong narrow emission lines are measured for C IV λλ1548, 1550, He II λ1640, O III] λλ1661, 1666, Si III] λλ1883, 1892, and C III] λλ1907, 1909. (2) Double-peaked Lyα emission is observed with a dominant blue peak and centered near the systemic velocity. (3) The low- and high-ionization absorption features indicate very little or no outflowing gas along the sight line to the lensed galaxy. The relative emission-line strengths can be reproduced with a very high ionization, low-metallicity starburst with binaries, with the exception of He II, which indicates that an additional ionization source is needed. We rule out large contributions from active galactic nuclei and shocks to the photoionization budget, suggesting that the emission features requiring the hardest radiation field likely result from extreme stellar populations that are beyond the capabilities of current models. Therefore, SL2S0217 serves as a template for the extreme conditions that are important for reionization and thought to be more common in the early universe.
关键词： first stars,galaxies: abundances,reionization,gravitational lensing: strong,galaxies: evolution,dark ages,galaxies: ISM
更新于2025-09-10 09:29:36
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Accurate spectroscopic redshift of the multiply lensed quasar PSOJ0147 from the Pan-STARRS survey
摘要： Context. The gravitational lensing time delay method provides a one-step determination of the Hubble constant (H0) with an uncertainty level on par with the cosmic distance ladder method. However, to further investigate the nature of the dark energy, a H0 estimate down to 1% level is greatly needed. This requires dozens of strongly lensed quasars that are yet to be delivered by ongoing and forthcoming all-sky surveys. Aims. In this work we aim to determine the spectroscopic redshift of PSOJ0147, the first strongly lensed quasar candidate found in the Pan-STARRS survey. The main goal of our work is to derive an accurate redshift estimate of the background quasar for cosmography. Methods. To obtain timely spectroscopically follow-up, we took advantage of the fast-track service programme that is carried out by the Nordic Optical Telescope. Using a grism covering 3200?9600 ?, we identified prominent emission line features, such as Lyα, N V, O I, C II, Si IV, C IV, and [C III] in the spectra of the background quasar of the PSOJ0147 lens system. This enables us to determine accurately the redshift of the background quasar. Results. The spectrum of the background quasar exhibits prominent absorption features bluewards of the strong emission lines, such as Lyα, N V, and C IV. These blue absorption lines indicate that the background source is a broad absorption line (BAL) quasar. Unfortunately, the BAL features hamper an accurate determination of redshift using the above-mentioned strong emission lines. Nevertheless, we are able to determine a redshift of 2.341 ± 0.001 from three of the four lensed quasar images with the clean forbidden line [C III]. In addition, we also derive a maximum outflow velocity of ～9800 km s?1 with the broad absorption features bluewards of the C IV emission line. This value of maximum outflow velocity is in good agreement with other BAL quasars.
关键词： gravitational lensing: strong,quasars: general,cosmology: observations
更新于2025-09-04 15:30:14
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The elliptical power law profile lens
摘要： The de?ection, potential, shear and magni?cation of a gravitational lens following an elliptical power law mass model are investigated. This mass model is derived from the circular power law pro?le through a rescaling of the axes, similar to the case of a singular isothermal ellipsoid. The resulting de?ection can be calculated explicitly and given in terms of the Gaussian hypergeometric function. Analytic expressions for the remaining lensing properties are found as well. Because the power law pro?le lens contains a number of well-known lens models as special cases, the equivalence of the new expressions with known results is checked. Finally, it is shown how these results naturally lead to a fast and accurate numerical scheme for computing the de?ection and other lens quantities, making this method a useful tool for realistically modelling observed lenses.
关键词： gravitational lensing: strong,methods: analytical
更新于2025-09-04 15:30:14
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THE BOSS EMISSION-LINE LENS SURVEY. IV. SMOOTH LENS MODELS FOR THE BELLS GALLERY SAMPLE
摘要： We present Hubble Space Telescope F606W-band imaging observations of 21 galaxy-Lyα emitter lens candidates in the Baryon Oscillation Spectroscopic Survey Emission-Line Lens Survey (BELLS) for the GALaxy-Lyα EmitteR sYstems (BELLS GALLERY) survey. Seventeen systems are confirmed to be definite lenses with unambiguous evidence of multiple imaging. The lenses are primarily massive early-type galaxies (ETGs) at redshifts of approximately 0.55, while the lensed sources are Lyα emitters (LAEs) at redshifts from two to three. Although most of the lens systems are well fit by smooth lens models consisting of singular isothermal ellipsoids in an external shear field, a thorough exploration of dark substructures in the lens galaxies is required. The Einstein radii of the BELLS GALLERY lenses are, on average, 60% larger than those of the BELLS lenses because of the much higher source redshifts. This will allow for a detailed investigation of the radius evolution of the mass profile in ETGs. With the aid of the average ～13× lensing magnification, the LAEs are frequently resolved into individual star-forming knots with a wide range of properties. They have characteristic sizes from less than 100 pc to several kiloparsecs, rest-frame far-UV apparent AB magnitudes from 29.6 to 24.2, and typical projected separations of 500 pc to 2 kpc.
关键词： galaxies: elliptical and lenticular, cD,gravitational lensing: strong,dark matter,techniques: image processing
更新于2025-09-04 15:30:14