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Register a new userHST imaging of four gravitationally lensed quasars
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We present new HST WFPC3 imaging of four gravitationally lensed quasars: MG 0414+0534; RXJ 0911+0551; B 1422+231; WFI J2026-4536. In three of these systems we detect wavelength-dependent microlensing, which we use to place constraints on the sizes and temperature profiles of the accretion discs in each quasar. Accretion disc radius is assumed to vary with wavelength according to the power-law relationship $rpropto lambda^p$, equivalent to a radial temperature profile of $Tpropto r^{-1/p}$. The goal of this work is to search for deviations from standard thin disc theory, which predicts that radius goes as wavelength to the power $p=4/3$. We find a wide range of power-law indices, from $p=1.4^{+0.5}_{-0.4}$ in B 1422+231 to $p=2.3^{+0.5}_{-0.4}$ in WFI J2026-4536. The measured value of $p$ appears to correlate with the strength of the wavelength-dependent microlensing. We explore this issue with mock simulations using a fixed accretion disc with $p=1.5$, and find that cases where wavelength-dependent microlensing is small tend to under-estimate the value of $p$. This casts doubt on previous ensemble single-epoch measurements which have favoured low values using samples of lensed quasars that display only moderate chromatic effects. Using only our systems with strong chromatic microlensing we prefer $p>4/3$, corresponding to shallower temperature profiles than expected from standard thin disc theory.
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We present spectroscopic confirmation of three new two-image gravitationally lensed quasars, compiled from existing strong lens and X-ray catalogs. Images of HSC J091843.27$-$022007.5 show a red galaxy with two blue point sources at either side, separated by 2.26 arcsec. This system has a source and a lens redshifts $z_s=0.804$ and $z_{ell}=0.459$, respectively, as obtained by our follow-up spectroscopic data. CXCO J100201.50$+$020330.0 shows two point sources separated by 0.85 arcsec on either side of an early-type galaxy. The follow-up spectroscopic data confirm the fainter quasar has the same redshift with the brighter quasar from the SDSS fiber spectrum at $z_s=2.016$. The deflecting foreground galaxy is a typical early-type galaxy at a redshift of $z_{ell}=0.439$. SDSS J135944.21$+$012809.8 has two point sources with quasar spectra at the same redshift $z_s=1.096$, separated by 1.05 arcsec, and fits to the HSC images confirm the presence of a galaxy between these. These discoveries demonstrate the power of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP)s deep imaging and wide sky coverage. Combined with existing X-ray source catalogues and follow-up spectroscopy, the HSC-SSP provides us unique opportunities to find multiple-image quasars lensed by a foreground galaxy.
We present deep spectroscopic observations of a Lyman-break galaxy candidate (hereafter MACS1149-JD) at $zsim9.5$ with the $textit{Hubble}$ Space Telescope ($textit{HST}$) WFC3/IR grisms. The grism observations were taken at 4 distinct position angles, totaling 34 orbits with the G141 grism, although only 19 of the orbits are relatively uncontaminated along the trace of MACS1149-JD. We fit a 3-parameter ($z$, F160W mag, and Ly$alpha$ equivalent width) Lyman-break galaxy template to the three least contaminated grism position angles using an MCMC approach. The grism data alone are best fit with a redshift of $z_{mathrm{grism}}=9.53^{+0.39}_{-0.60}$ ($68%$ confidence), in good agreement with our photometric estimate of $z_{mathrm{phot}}=9.51^{+0.06}_{-0.12}$ ($68%$ confidence). Our analysis rules out Lyman-alpha emission from MACS1149-JD above a $3sigma$ equivalent width of 21 AA{}, consistent with a highly neutral IGM. We explore a scenario where the red $textit{Spitzer}$/IRAC $[3.6] - [4.5]$ color of the galaxy previously pointed out in the literature is due to strong rest-frame optical emission lines from a very young stellar population rather than a 4000 AA{} break. We find that while this can provide an explanation for the observed IRAC color, it requires a lower redshift ($zlesssim9.1$), which is less preferred by the $textit{HST}$ imaging data. The grism data are consistent with both scenarios, indicating that the red IRAC color can still be explained by a 4000 AA{} break, characteristic of a relatively evolved stellar population. In this interpretation, the photometry indicate that a $340^{+29}_{-35}$ Myr stellar population is already present in this galaxy only $sim500~mathrm{Myr}$ after the Big Bang.
Thanks to its sharp view, HST has significantly improved our knowledge of tens of gravitationally lensed quasars in four different respects: (1) confirming their lensed nature; (2) detecting the lensing galaxy responsible for the image splitting; (3) improving the astrometric accuracy on the positions of the unresolved QSO images and of the lens; (4) resolving extended lensed structures from the QSO hosts into faint NIR or optical rings or arcs. These observations have helped to break some degeneracies on the lens potential, to probe the galaxy evolution and to reconstruct the true shape of the QSO host with an increased angular resolution.
We present the discovery of four gravitationally lensed quasars selected from the spectroscopic quasar catalog of the Sloan Digital Sky Survey. We describe imaging and spectroscopic follow-up observations that support the lensing interpretation of the following four quasars: SDSS J0832+0404 (image separation theta=1.98, source redshift z_s=1.115, lens redshift z_l=0.659); SDSS J1216+3529 (theta=1.49, z_s=2.012); SDSS J1322+1052 (theta=2.00, z_s=1.716); and SDSS J1524+4409 (theta=1.67, z_s=1.210, z_l=0.320). Each system has two lensed images. We find that the fainter image component of SDSS J0832+0404 is significantly redder than the brighter component, perhaps because of differential reddening by the lensing galaxy. The lens potential of SDSS J1216+3529 might be complicated by the presence of a secondary galaxy near the main lensing galaxy.
Cadenced optical imaging surveys in the next decade will be capable of detecting time-varying galaxy-scale strong gravitational lenses in large numbers, increasing the size of the statistically well-defined samples of multiply-imaged quasars by two orders of magnitude, and discovering the first strongly-lensed supernovae. We carry out a detailed calculation of the likely yields of several planned surveys, using realistic distributions for the lens and source properties and taking magnification bias and image configuration detectability into account. We find that upcoming wide-field synoptic surveys should detect several thousand lensed quasars. In particular, the LSST should find 8000 lensed quasars, 3000 of which will have well-measured time delays, and also ~130 lensed supernovae, which is compared with ~15 lensed supernovae predicted to be found by the JDEM. We predict the quad fraction to be ~15% for the lensed quasars and ~30% for the lensed supernovae. Generating a mock catalogue of around 1500 well-observed double-image lenses, we compute the available precision on the Hubble constant and the dark energy equation parameters for the time delay distance experiment (assuming priors from Planck): the predicted marginalised 68% confidence intervals are sigma(w_0)=0.15, sigma(w_a)=0.41, and sigma(h)=0.017. While this is encouraging in the sense that these uncertainties are only 50% larger than those predicted for a space-based type-Ia supernova sample, we show how the dark energy figure of merit degrades with decreasing knowledge of the the lens mass distribution. (Abridged)
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