Gravitational Lens B1608+656. I. V-, I-, and H‐Band Hubble Space Telescope Imaging

We present a multiwavelength analysis of high-resolution observations of the quadruple lens B1608+656 from the Hubble Space Telescope archive, acquired with WFPC2 through filters F606W (V band) and F814W (I band) and with NIC1 in filter F160W (H band). In the three bands, the observations show extended emission from the four images of the source in a ringlike configuration that surrounds the two resolved, ensing galaxies. B1608+656 was discovered as a double-lobed radio source and later identified as a poststarburst galaxy in the optical. Based on photometry and optical spectroscopy we estimate that the stellar population of the source has an age of ~500 Myr. This provides a model for the spectrum of the source that extends over spectral regions where no observations are available and is used to generate Tiny Tim point-spread functions (PSFs) for the filters. Deconvolutions performed with the Lucy-Richardson method are presented, and the limitations of these restorations are discussed. V-I and I-H color maps show evidence of extinction by dust associated with one of the lensing galaxies, a late-type galaxy presumably disrupted after its close encounter with the other lens, an elliptical galaxy. The extinction affects the two lens galaxies and two of the four multiple images. The diagnostic of wavelength-dependent effects in the images shows that corrections for contamination with light from the lenses, extinction, and PSF convolution need to be applied before using the extended structure in the images as a constraint on lens models. We will present the restoration of the images in a subsequent paper

The Gravitational Lens B1608+656: I. V, I, and H-band HST Imaging

We present a multi-wavelength analysis of high-resolution observations of the quadruple lens B1608+656 from the HST archive, acquired with WFPC2 through filters F606W (V-band) and F814W (I-band), and with NIC1 in filter F160W (H-band). In the three bands, the observations show extended emission from the four images of the source in a ring-like configuration that surrounds the two, resolved, lensing galaxies. B1608+656 was discovered as a double-lobed radio source, and later identified as a post-starburst galaxy in the optical. Based on photometry and optical spectroscopy we estimate that the stellar population of the source has an age of $\sim$ 500 Myr. This provides a model for the spectrum of the source that extends over spectral regions where no observations are available, and is used to generate Tiny Tim PSFs for the filters. Deconvolutions performed with the Lucy-Richardson method are presented, and the limitations of these restorations is discussed. V$-$I and I$-$H color maps show evidence of extinction by dust associated with one of the lensing galaxies, a late type galaxy presumably disrupted after its close encounter with the other lens, an elliptical galaxy. The extinction affects the two lens galaxies and two of the four multiple images. The diagnostic of wavelength-dependent effects in the images shows that corrections for contamination with light from the lenses, extinction, and PSF convolution need to be applied before using the extended structure in the images as a constraint on lens models. We will present the restoration of the images in a subsequent paper.Comment: 29 pages. Submitted to Ap

In-Depth NMR Investigation of the Magnetic Hardening in Co Thin Films Induced by the Interface with Molecular Layers

The hybridization of the surface orbitals of thin ferromagnetic layers with molecular orbitals represents a soft but efficient technology that is able to induce in ferromagnetic component radical modifications of the key magnetic parameters, such as magnetization, magnetic anisotropy, and others. These effects are investigated in 7 nm thick polycrystalline Co films interfaced with C-60 and Gaq(3) molecular layers by combining Co-59 Ferromagnetic nuclear resonance spectroscopy (FNR) and magneto-optic kerr effect (MOKE) techniques. It is demonstrated that the surface hybridization produces a significant magnetic hardening with respect to a reference Co/Al system and that the molecule-induced effects modify the magnetic properties of entire Co layer, propagating for several nm from the interface. The FNR spectroscopy also reveals a reconstruction of the magnetic environment at the cobalt surface, whose observation in polycrystalline films is especially intriguing. The results shed new and unexpected light on the interfacial physics in such systems, whose understanding necessitates further experimental and theoretical research

The Hubble Constant from the Gravitational Lens B1608+656

We present a refined gravitational lens model of the four-image lens system B1608+656 based on new and improved observational constraints: (i) the three independent time-delays and flux-ratios from VLA observations, (ii) the radio-image positions from VLBA observations, (iii) the shape of the deconvolved Einstein Ring from optical and infrared HST images, (iv) the extinction-corrected lens-galaxy centroids and structural parameters, and (v) a stellar velocity dispersion, sigma_ap=247+-35 km/s, of the primary lens galaxy (G1), obtained from an echelle spectrum taken with the Keck--II telescope. The lens mass model consists of two elliptical mass distributions with power-law density profiles and an external shear, totaling 22 free parameters, including the density slopes which are the key parameters to determine the value of H_0 from lens time delays. This has required the development of a new lens code that is highly optimized for speed. The minimum-chi^2 model reproduces all observations very well, including the stellar velocity dispersion and the shape of the Einstein Ring. A combined gravitational-lens and stellar dynamical analysis leads to a value of the Hubble Constant of H_0=75(+7/-6) km/s/Mpc (68 percent CL; Omega_m=0.3, Omega_Lambda=0.7. The non-linear error analysis includes correlations between all free parameters, in particular the density slopes of G1 and G2, yielding an accurate determination of the random error on H_0. The lens galaxy G1 is ~5 times more massive than the secondary lens galaxy (G2), and has a mass density slope of gamma_G1=2.03(+0.14/-0.14) +- 0.03 (68 percent CL) for rho~r^-gamma', very close to isothermal (gamma'=2). (Abridged)Comment: 17 pages, 6 figures, 5 tables; revised version with correct fig.6 and clarified text based on referee report; conclusions unchange

Galaxy-Galaxy Lensing by Non-Spherical Haloes I:Theoretical Considerations

We use Monte Carlo simulations to investigate the theory of galaxy-galaxy lensing by non-spherical dark matter haloes. The simulations include a careful accounting of the effects of multiple deflections. In a typical data set where the mean tangential shear of sources with redshifts zs ~ 0.6 is measured with respect to the observed symmetry axes of foreground galaxies with redshifts zl ~ 0.3, the signature of anisotropic galaxy-galaxy lensing differs substantially from the expectation that one would have in the absence of multiple deflections. The observed ratio of the mean tangential shears, g+/g-, is strongly suppressed compared to the function that one would measure if the intrinsic symmetry axes of the foreground galaxies were known. Depending upon the characteristic masses of the lenses, the observed ratio of the mean tangential shears may be consistent with an isotropic signal (despite the fact that the lenses are non-spherical), or it may even be reversed from the expected signal (i.e., the mean tangential shear for sources close to the observed minor axes of the lenses may exceed the mean tangential shear for sources close to the observed major axes of the lenses). These effects are caused primarily by the fact that the lens galaxies have, themselves, been lensed and therefore the observed symmetry axes of the lenses differ from their intrinsic symmetry axes. The effects of lensing of the foreground galaxies on the observed function g+/g- cannot be eliminated by the rejection of foreground galaxies with small image ellipticities, nor by focusing the analysis on sources that are located very close to the observed symmetry axes of the foreground galaxies. We conclude that any attempt to use a measurement of g+/g- to constrain the shapes of dark matter galaxy haloes must include Monte Carlo simulations that take multiple deflections properly into account.Comment: 15 pages, 17 figures, submitted to MNRAS, full manuscript with high-resolution version of Fig. 4 can be found at http://firedrake.bu.edu/preprints/preprints.htm

Weak-Lensing by Large-Scale Structure and the Polarization Properties of Distant Radio-Sources

We estimate the effects of weak lensing by large-scale density inhomogeneities and long-wavelength gravitational waves upon the polarization properties of electromagnetic radiation as it propagates from cosmologically distant sources. Scalar (density) fluctuations do not rotate neither the plane of polarization of the electromagnetic radiation nor the source image. They produce, however, an appreciable shear, which distorts the image shape, leading to an apparent rotation of the image orientation relative to its plane of polarization. In sources with large ellipticity the apparent rotation is rather small, of the order (in radians) of the dimensionless shear. The effect is larger at smaller source eccentricity. A shear of 1% can induce apparent rotations of around 5 degrees in radio sources with the smallest eccentricity among those with a significant degree of integrated linear polarization. We discuss the possibility that weak lensing by shear with rms value around or below 5% may be the cause for the dispersion in the direction of integrated linear polarization of cosmologically distant radio sources away from the perpendicular to their major axis, as expected from models for their magnetic fields. A rms shear larger than 5% would be incompatible with the observed correlation between polarization properties and source orientation in distant radio galaxies and quasars. Gravity waves do rotate both the plane of polarization as well as the source image. Their weak lensing effects, however, are negligible.Comment: 23 pages, 2 eps figures, Aastex 4.0 macros. Final version, as accepted by ApJ. Additional references and some changes in the introduction and conclusion

Gravitational Lens Time Delays and Gravitational Waves

Using Fermat's principle, we analyze the effects of very long wavelength gravitational waves upon the images of a gravitationally lensed quasar. We show that the lens equation in the presence of gravity waves is equivalent to that of a lens with different alignment between source, deflector, and observer in the absence of gravity waves. Contrary to a recent claim, we conclude that measurements of time delays in gravitational lenses cannot serve as a method to detect or constrain a stochastic background of gravitational waves of cosmological wavelengths, because the wave-induced time delay is observationally indistinguishable from an intrinsic time delay due to the lens geometry.Comment: 22 pages in REVTEX 3.0 (previous versions may not have TeXed due to Unix mailer problems

Reconstruction of the Primordial Power Spectrum using Temperature and Polarisation Data from Multiple Experiments

We develop a method to reconstruct the primordial power spectrum, P(k), using both temperature and polarisation data from the joint analysis of a number of Cosmic Microwave Background (CMB) observations. The method is an extension of the Richardson-Lucy algorithm, first applied in this context by Shafieloo & Souradeep. We show how the inclusion of polarisation measurements can decrease the uncertainty in the reconstructed power spectrum. In particular, the polarisation data can constrain oscillations in the spectrum more effectively than total intensity only measurements. We apply the estimator to a compilation of current CMB results. The reconstructed spectrum is consistent with the best-fit power spectrum although we find evidence for a `dip' in the power on scales k ~ 0.002 Mpc^-1. This feature appears to be associated with the WMAP power in the region 18 < l < 26 which is consistently below best--fit models. We also forecast the reconstruction for a simulated, Planck-like survey including sample variance limited polarisation data.Comment: 8 pages, 5 figures, comments welcom

Interpretation of the Global Anisotropy in the Radio Polarizations of Cosmologically Distant Sources

We present a detailed statistical study of the observed anisotropy in radio polarizations from distant extragalactic objects. This anisotropy was earlier found by Birch (1982) and reconfirmed by Jain and Ralston (1999) in a larger data set. A very strong signal was seen after imposing the cut $|RM-\bar{RM}|>6$ rad/m$^2$, where $RM$ is the rotation measure and $\bar{RM}$ its mean value. In this paper we show that there are several indications that this anisotropy cannot be attributed to bias in the data. We also find that a generalized statistic shows a very strong signal in the entire data without imposing the RM dependent cut. Finally we argue that an anisotropic background pseudoscalar field can explain the observations.Comment: 13 pages, 6 figure