Confirmation of two extended objects along the line of sight to PKS1830-211 with ESO-VLT adaptive optics imaging

We report on new high-resolution near-infrared images of the gravitationally lensed radio source PKS1830-211, a quasar at z=2.507. These adaptive optics observations, taken with the Very Large Telescope (VLT), are further improved through image deconvolution. They confirm the presence of a second object along the line of sight to the quasar, in addition to the previously known spiral galaxy. This additional object is clearly extended in our images. However, its faint luminosity does not allow to infer any photometric redshift. If this galaxy is located in the foreground of PKS1830-211, it complicates the modeling of this system and decreases the interest in using PKS1830-211 as a means to determine H0 via the time delay between the two lensed images of the quasar.Comment: Accepted in A&A Letter

NICMOS and VLA Observations of the Gravitatonally Lensed Ultraluminous BAL Quasar APM~08279+5255: Detection of a Third Image

We present a suite of observations of the recently identified ultraluminous BAL quasar APM 08279+5255, taken both in the infra-red with the NICMOS high resolution camera on board the Hubble Space Telescope, and at 3.5cm with the Very Large Array. With an inferred luminosity of ~5x10^15 Solar luminosities, APM 08279+5255 is apparently the most luminous system known. Extant ground-based images show that APM 08279+5255 is not point-like, but is instead separated into two components, indicative of gravitational lensing. The much higher resolution images presented here also reveal two point sources, A and B, of almost equal brightness (f_B/f_A=0.782 +/- 0.010), separated by 0."378 +/- 0."001, as well as a third, previously unknown, fainter image, C, seen between the brighter images. While the nature of C is not fully determined, several lines of evidence point to it being a third gravitationally lensed image of the quasar, rather than being the lensing galaxy. Simple models which recover the relative image configuration and brightnesses are presented. While proving to be substantially amplified, APM 08279+5255 possesses an intrinsic bolometric luminosity of ~10^14 to 10^15 Solar luminosities and remains amongst the most luminous objects known.Comment: 21 pages, 5 figures (2 as GIF files); accepted for publication in the Astronomical Journa

Photometric monitoring of the doubly imaged quasar UM673: possible evidence for chromatic microlensing

We present the results of two-band CCD photometric monitoring of the gravitationally lensed quasar Q 0142-100 (UM 673).The data, obtained at ESO-La Silla with the 1.54 m Danish telescope in the Gunn i-band (October 1998 - September 1999) and in the Johnson V-band (October 1998 to December 2001), were analyzed using three different photometric methods. The light-curves obtained with all methods show variations, with a peak-to-peak amplitude of 0.14 magnitude in $V$. Although it was not possible to measure the time delay between the two lensed QSO images, the brighter component displays possible evidence for microlensing: it becomes bluer as it gets brighter, as expected under the assumption of differential magnification of a quasar accretion diskComment: Accepted for publication in Astronomy & Astrophysics; 8 pages, 7 figure

COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses VII. Time delays and the Hubble constant from WFI J2033-4723

Gravitationally lensed quasars can be used to map the mass distribution in lensing galaxies and to estimate the Hubble constant H0 by measuring the time delays between the quasar images. Here we report the measurement of two independent time delays in the quadruply imaged quasar WFI J2033-4723 (z = 1.66). Our data consist of R-band images obtained with the Swiss 1.2 m EULER telescope located at La Silla and with the 1.3 m SMARTS telescope located at Cerro Tololo. The light curves have 218 independent epochs spanning 3 full years of monitoring between March 2004 and May 2007, with a mean temporal sampling of one observation every 4th day. We measure the time delays using three different techniques, and we obtain Dt(B-A) = 35.5 +- 1.4 days (3.8%) and Dt(B-C) = 62.6 +4.1/-2.3 days (+6.5%/-3.7%), where A is a composite of the close, merging image pair. After correcting for the time delays, we find R-band flux ratios of F_A/F_B = 2.88 +- 0.04, F_A/F_C = 3.38 +- 0.06, and F_A1/F_A2 = 1.37 +- 0.05 with no evidence for microlensing variability over a time scale of three years. However, these flux ratios do not agree with those measured in the quasar emission lines, suggesting that longer term microlensing is present. Our estimate of H0 agrees with the concordance value: non-parametric modeling of the lensing galaxy predicts H0 = 67 +13/-10 km s-1 Mpc-1, while the Single Isothermal Sphere model yields H0 = 63 +7/-3 km s-1 Mpc-1 (68% confidence level). More complex lens models using a composite de Vaucouleurs plus NFW galaxy mass profile show twisting of the mass isocontours in the lensing galaxy, as do the non-parametric models. As all models also require a significant external shear, this suggests that the lens is a member of the group of galaxies seen in field of view of WFI J2033-4723.Comment: 14 pages, 12 figures, published in A&

MGC2214+3550: A New Binary Quasar

We report the discovery of a binary quasar, MGC2214+3550 A,B, whose components have similar optical spectra at a redshift z=0.88. The quasars are separated on the sky by 3.0", and have a magnitude difference of Delta(m_I)=0.5 mag. The VLA radio map at 3.6 cm shows a single 47mJy radio source with a core-jet morphology that is coincident with the brighter optical quasar A. Gravitational lensing is ruled out by the lack of radio emission from quasar B, and the lack of any visible galaxies to act as the lens. We conclude that MGC 2214+3550 A and B are physically associated. With a projected separation of 12.7h^{-1} kpc (Omega_0=1), MGC 2214+3550 A,B is one of the smallest z>0.5 binary quasars.Comment: 13 pages, 3 .ps figs, submitted to ApJ

Ring-Like Structure in the Radio Lobe of MG0248+0641

We present radio and optical observations of MG0248+0641, which contains a kiloparsec-scale ring-like structure in one of its radio lobes. The radio observations show a typical core-double morphology: a central core between two lobes, each of which has a hotspot. The western radio lobe appears as a nearly continuous ring, with linear polarization electric field vectors which are oriented in a radial direction from the ring center. We consider several different interpretations for the nature of this ring, including gravitational lensing of a normal jet by a foreground galaxy. Even though simple lensing models can describe the ring morphology reasonably well, the high linear polarization seen around the ring cannot be easily explained. The chance interposition of a galactic supernova remnant, nova, planetary nebula, or H II region, has been ruled out. The highly polarized ring of MG0248+0641 is much like the prominent ring seen in 3C219, and the multiple ones in 3C310 and Hercules A, suggesting that similar physical processes are producing shell structures in these radio galaxies. The ring in MG0248+0641 may be caused by the formation of ``bubbles'', as a result of instabilities in the energy flow down the western radio jet. It may also be possible that the required instabilities are triggered by the infall of gas, via tidal interaction of the central source with a nearby galaxy. This scenario may be indicated by our marginal detection of an optical source close to the western hotspot.Comment: 21 pages. Submitted to AJ Aug 15, 1997; Accepted Sep 30, 1997. Minor changes in conten