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Adriano Agnello
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The Southern Hemisphere has just recently begun to be charted by wide-field surveys, with a sufficient depth and image quality to enable the discovery of strongly lensed quasars. The quadruply imaged quasar WG0214-2105 (r.a.=02:14:16.37, dec.=-21:05:35.3) is a previously unknown lens, with `blue mid-IR colors and high UV deficit, found in the intersection of three survey footprints: the Dark Energy Survey public DR1 (DES, Abbott et al. 2018), The VST-ATLAS (Shanks et al. 2015) and Pan-STARRS (Chambers et al. 2016). Its discovery relied on high spatial resolution from the Gaia mission (Lindegren et al. 2016) and mid-IR color preselection in the WISE catalog (Wright et al. 2010).
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We report the discovery of the quadruply lensed quasar J1433+6007, mined in the SDSS DR12 photometric catalogues using a novel outlier-selection technique, without prior spectroscopic or UV excess information. Discovery data obtained at the Nordic Optical telescope (NOT, La Palma) show nearly identical quasar spectra at $z_s=2.74$ and four quasar images in a fold configuration, one of which sits on a blue arc. The deflector redshift is $z_{l}=0.407,$ from Keck-ESI spectra. We describe the selection procedure, discovery and follow-up, image positions and $BVRi$ magnitudes, and first results and forecasts from simple lens models.
We present Keck Cosmic Web Imager spectroscopy of the four putative images of the lensed quasar candidate J014709+463037 recently discovered by Berghea et al. (2017). The data verify the source as a quadruply lensed, broad absorption-line quasar having z_S = 2.377 +/- 0.007. We detect intervening absorption in the FeII 2586, 2600, MgII 2796, 2803, and/or CIV 1548, 1550 transitions in eight foreground systems, three of which have redshifts consistent with the photometric-redshift estimate reported for the lensing galaxy (z_L ~ 0.57). By virtue of their positions on the sky, the source images probe these absorbers over transverse physical scales of ~0.3-21 kpc, permitting assessment of the variation in metal-line equivalent width W_r as a function of sight-line separation. We measure differences in W_r,2796 of <40% across all sight-line pairs subtending 7-21 kpc, suggestive of a high degree of spatial coherence for MgII-absorbing material. W_r,2600 is observed to vary by >50% over the same scales across the majority of sight-line pairs, while CIV absorption exhibits a wide range in W_r,1548 differences of ~5-80% within transverse distances less than ~3 kpc. J014709+463037 is one of only a handful of z > 2 quadruply lensed systems for which all four source images are very bright (r = 15.4-17.7 mag) and are easily separated in ground-based seeing conditions. As such, it is an ideal candidate for higher-resolution spectroscopy probing the spatial variation in the kinematic structure and physical state of intervening absorbers.
We report the quadruple nature of the source WISE 025942.9-163543 as observed in the VST-ATLAS survey. Spectra of the two brightest images show quasar emission lines at z=2.16. The system was discovered by splitting ATLAS cutouts of WISE sources with W1-W2 > 0.7, when possible, into three components. Followup Magellan images were used to obtain astrometry and g and i photometry, with i=18.78 and 19.73, respectively, for the brightest and faintest components. Absorption lines are observed at z=0.905 but there is little evidence for a lensing galaxy after PSF fitting and subtraction. Saha and Williams (2003) would classify ATLAS 0259-1635 as a short-axis quad. The larger and smaller diameters are 1.57 and 1.32 arcseconds, respectively. Modeling the lensing galaxy as a singular isothermal sphere with external shear, the largest and smallest predicted magnifications are 10.8 and 6.4 respectively.
Among known strongly lensed quasar systems, ~25% have gravitational potentials sufficiently flat (and sources sufficiently well aligned) to produce four images rather than two. The projected flattening of the lensing galaxy and tides from neighboring galaxies both contribute to the potentials quadrupole. Witts hyperbola and Wynnes ellipse permit determination of the overall quadrupole from the positions of the quasar images. The position of the lensing galaxy resolves the distinct contributions of intrinsic ellipticity and tidal shear to that quadrupole. Among 31 quadruply lensed quasars systems with statistically significant decompositions, 15 are either reliably ($2sigma$) or provisionally ($1sigma$) shear-dominated and 11 are either reliably or provisionally ellipticity-dominated. For the remaining 8, the two effects make roughly equal contributions to the combined cross section (newly derived here) for quadruple lensing. This observational result is strongly at variance with the ellipticity-dominated forecast of Oguri & Marshall (2010).
We present new measurements of the time delays of WFI2033-4723. The data sets used in this work include 14 years of data taken at the 1.2m Leonhard Euler Swiss telescope, 13 years of data from the SMARTS 1.3m telescope at Las Campanas Observatory and a single year of high-cadence and high-precision monitoring at the MPIA 2.2m telescope. The time delays measured from these different data sets, all taken in the R-band, are in good agreement with each other and with previous measurements from the literature. Combining all the time-delay estimates from our data sets results in Dt_AB = 36.2-0.8+0.7 days (2.1% precision), Dt_AC = -23.3-1.4+1.2 days (5.6%) and Dt_BC = -59.4-1.3+1.3 days (2.2%). In addition, the close image pair A1-A2 of the lensed quasars can be resolved in the MPIA 2.2m data. We measure a time delay consistent with zero in this pair of images. We also explore the prior distributions of microlensing time-delay potentially affecting the cosmological time-delay measurements of WFI2033-4723. There is however no strong indication in our measurements that microlensing time delay is neither present nor absent. This work is part of a H0LiCOW series focusing on measuring the Hubble constant from WFI2033-4723.
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