Examinando por Autor "Fassnacht, C."

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    Double dark matter vision: Twice the number of compact-source lenses with narrow-line lensing and the WFC3 grism
    (Oxford University Press, 2020) Nierenberg, A.; Gilman, D.; Treu, T.; Brammer, G.; Birrer, S.; Moustakas, L.; Agnello, A.; Anguita, T.; Fassnacht, C.; Motta, V.; Peter, A.; Sluse, D.
    The magnifications of compact-source lenses are extremely sensitive to the presence of lowmass darkmatter haloes along the entire sightline from the source to the observer. Traditionally, the study of darkmatter structure in compact-source strong gravitational lenses has been limited to radio-loud systems, as the radio emission is extended and thus unaffected by microlensing which can mimic the signal of dark matter structure. An alternate approach is to measure quasar nuclear-narrow-line emission, which is free from microlensing and present in virtually all quasar lenses. In this paper, we double the number of systems which can be used for gravitational lensing analyses by presenting measurements of narrow-line emission from a sample of eight quadruply imaged quasar lens systems, WGD J0405-3308, HS 0810+2554, RX J0911+0551, SDSS J1330+1810, PS J1606-2333, WFI 2026-4536, WFI 2033-4723, and WGD J2038-4008. We describe our updated grism spectral modelling pipeline, which we use to measure narrow-line fluxes with uncertainties of 2-10 per cent, presented here. We fit the lensed image positions with smooth mass models and demonstrate that these models fail to produce the observed distribution of image fluxes over the entire sample of lenses. Furthermore, typical deviations are larger than those expected from macromodel uncertainties. This discrepancy indicates the presence of perturbations caused by small-scale dark matter structure. The interpretation of this result in terms of dark matter models is presented in a companion paper.
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    The STRong lensing Insights into the dark energy survey (STRIDES) 2017/2018 follow-up campaign: Discovery of 10 lensed quasars and 10 quasar pairs
    (Oxford University Press, 2020) Lemon, C.; Auger, M.; Anguita, T.; McMahon, R.; Apostolovski, Y.; Chen, G.; Fassnacht, C.; Melo, A.; Motta, V.; Shajib, A.; Treu, T.; Agnello, A.; Buckley-Geer, E; Schechter, P.; Birrer, S.; Collett, T.; Courbin, F.; Rusu, C.; Abbott, T.; Allam, S.; Annis, J.; Avila, S.; Bertin, E.; Brooks, D.; Burke, D.; Carnero Rosell, A.; Carrasco Kind, M.; Carretero, J.; Costanzi, M.; Costa, L.; De Vicente, J.; Desai, S.; Eifler, T.; Flaugher, B.; Frieman, J.; Garcia-Bellido, J.; Gaztanaga, E.; Gerdes, D.; Gruen, D.; Gruendl, R.; Gschwend, J.; Gutierrez, G.; Honscheid, K.; James, D.; Kim, A.; Krause, E.; Kuehn, K.; Kuropatkin, N.; Lahav, O.; Lima, M.; Lin, H.; Maia, M.; March, M.; Marshall, J.; Menanteau, F.; Miquel, R.; Palmese, A.; Paz-Chinchon, F.; Plazas, A.; Roodman, A.; Sanchez, E.; Schubnell, M.; Serrano, S.; Smith, M.; Soares-Santos, M.; Suchyta, E.; Tarle, G.; Walker, A.
    We report the results of the STRong lensing Insights into the Dark Energy Survey (STRIDES) follow-up campaign of the late 2017/early 2018 season. We obtained spectra of 65 lensed quasar candidates with ESO Faint Object Spectrograph and Camera 2 on the NTT and Echellette Spectrograph and Imager onKeck, confirming 10 newlensed quasars and 10 quasar pairs. Eight lensed quasars are doubly imaged with source redshifts between 0.99 and 2.90, one is triply imaged (DESJ0345.2545, z = 1.68), and one is quadruply imaged (quad: DESJ0053.2012, z = 3.8). Singular isothermal ellipsoid models for the doubles, based on high-resolution imaging from SAMI on Southern Astrophysical Research Telescope or Near InfraRed Camera 2 on Keck, give total magnifications between 3.2 and 5.6, and Einstein radii between 0.49 and 1.97 arcsec. After spectroscopic follow-up, we extract multi-epoch grizY photometry of confirmed lensed quasars and contaminant quasar+star pairs from DES data using parametric multiband modelling, and compare variability in each system's components. By measuring the reduced χ2 associated with fitting all epochs to the samemagnitude, we find a simple cut on the less variable component that retains all confirmed lensed quasars, while removing 94 per cent of contaminant systems. Based on our spectroscopic follow-up, this variability information improves selection of lensed quasars and quasar pairs from 34-45 per cent to 51-70 per cent, with most remaining contaminants being star-forming galaxies. Using mock lensed quasar light curves we demonstrate that selection based only on variability will over-represent the quad fraction by 10 per cent over a complete DES magnitude-limited sample, explained by the magnification bias and hence lower luminosity/more variable sources in quads.