The distortion of distant galaxy images by large-scale structure

Inhomogeneity in the distribution of mass in the universe on scales ≲ 100 Mpc can generate a coherent shear distortion or polarization of the images of background galaxies. This distortion may be measurable over patches of the sky up to a few square degrees in size. If this distortion is measured, or conversely, if its magnitude is limited, it should help us understand the degree to which luminosity traces the underlying mass over cosmological scales. A prescription is given for quantifying the galaxy distortion and a propagation equation for its evolution in an inhomogeneous universe is derived. The creation of shear by inhomogeneity is illustrated using model kinematic universes comprising random distributions of point masses, spheres and circular discs designed to simulate the superclusters, voids and ‘walls’ reported in galaxy velocity surveys. Using these simulations, we estimate that an rms induced ellipticity of |p|_(rms) ˜ 0.2Ω_(LSS) (where Ω_(LSS) is the fraction of the mass of the universe clustered on the large scale) will be produced. The angular correlation length is ˜ 1.6°. In an alternative prescription, the universe is modelled using a power spectrum of density fluctuations and the mean correlation function is computed both analytically and numerically. In these simulations we find that |p|_(rms) ˜0.02 for biased cold dark matter models of an Einslein–De Sitter universe, and the effective correlation length is θ_(1/2) ˜ 0.5^ΰ. For a hot dark matter dominated universe the correlation length is θ_(1/2) ˜ 0.7^ΰ. The faint, blue galaxies discovered by Tyson and collaborators have a surface density of ˜ 3 × 10^5 deg^(−2) and should provide an ideal set of sources for measuring this effect

The distortion of distant galaxy images by large-scale structure

Inhomogeneity in the distribution of mass in the universe on scales ≲ 100 Mpc can generate a coherent shear distortion or polarization of the images of background galaxies. This distortion may be measurable over patches of the sky up to a few square degrees in size. If this distortion is measured, or conversely, if its magnitude is limited, it should help us understand the degree to which luminosity traces the underlying mass over cosmological scales. A prescription is given for quantifying the galaxy distortion and a propagation equation for its evolution in an inhomogeneous universe is derived. The creation of shear by inhomogeneity is illustrated using model kinematic universes comprising random distributions of point masses, spheres and circular discs designed to simulate the superclusters, voids and ‘walls’ reported in galaxy velocity surveys. Using these simulations, we estimate that an rms induced ellipticity of |p|_(rms) ˜ 0.2Ω_(LSS) (where Ω_(LSS) is the fraction of the mass of the universe clustered on the large scale) will be produced. The angular correlation length is ˜ 1.6°. In an alternative prescription, the universe is modelled using a power spectrum of density fluctuations and the mean correlation function is computed both analytically and numerically. In these simulations we find that |p|_(rms) ˜0.02 for biased cold dark matter models of an Einslein–De Sitter universe, and the effective correlation length is θ_(1/2) ˜ 0.5^ΰ. For a hot dark matter dominated universe the correlation length is θ_(1/2) ˜ 0.7^ΰ. The faint, blue galaxies discovered by Tyson and collaborators have a surface density of ˜ 3 × 10^5 deg^(−2) and should provide an ideal set of sources for measuring this effect

Quasar Image Shifts due to Gravitational Microlensing

Gravitational microlensing of quasars by stars in external galaxies can introduce fluctuations in the centroid of the ``point-like'' macro--images. The induced shifts are extremely small, on micro--arcsecond scales, below the limits of current optical observations. However, such shifts will become measurable with the proposed ``Space Interferometry'' mission, due to fly in 2005. The degree of the centroid shifts and their application as probes of both quasar structure and the stellar mass function in the lensing galaxy are discussed.Comment: 16 Pages, 4 Figures. Accepted for publication in The Astrophysical Journa

Keck Mid-Infrared Imaging of the QSO 2237+0305

Using the Long Wavelength Spectrometer on Keck I, we have imaged the gravitationally lensed radio quiet quasi-stellar object (QSO) 2237+0305 at 8.9 and 11.7 microns for the first time. The mid-infrared flux ratios are inconsistent with the optical flux ratios, but agree with the radio flux ratios and with some published gravitational lens models. These flux ratios indicate that the infrared emission is not affected by microlensing, which rules out the synchrotron emission model. The infrared emission is likely produced by hot dust extended on a length scale of more than 0.03 parsecs. The spectral energy distribution further implies a narrow range of dust temperatures, suggesting that the dust may be located in a shell extending between ~1 to 3 parsecs from the nucleus, and intercepting about half of the QSO luminosity.Comment: Accepted to ApJ, 8 pages, 3 figures (1 color). Please email [email protected] if you have any comments or questions about this pape

Radio Astronomy

Contains table of contents for Section 4 and reports on seven research projects.National Science Foundation Grant AST 92-24191MIT Class of 1948/Career Development ChairNational Science Foundation Presidential Young Investigator AwardDavid and Lucile Packard FellowshipMIT Lincoln Laboratory Agreement BX-4975National Aeronautics and Space Administration/Goddard Space Flight Center Grant NAS5-31276National Aeronautics and Space Administration/Goddard Space Flight Center Grant NAG5-10MIT Leaders for Manufacturing Progra

XQ-100: A legacy survey of one hundred 3.5 ≲ z ≲ 4.5 quasars observed with VLT/X-shooter

We describe the execution and data reduction of the European Southern Observatory Large Programme "Quasars and their absorption lines: a legacy survey of the high-redshift Universe with VLT/X-shooter" (hereafter "XQ-100"). XQ-100 has produced and made publicly available a homogeneous and high-quality sample of echelle spectra of 100 quasars (QSOs) at redshifts z ≃ 3.5-4.5 observed with full spectral coverage from 315 to 2500 nm at a resolving power ranging from R ̃. 4000 to 7000, depending on wavelength. The median signal-to-noise ratios are 33, 25 and 43, as measured at rest-frame wavelengths 1700, 3000 and 3600 Å, respectively. This paper provides future users of XQ-100 data with the basic statistics of the survey, along with details of target selection, data acquisition and data reduction. The paper accompanies the public release of all data products, including 100 reduced spectra. XQ-100 is the largest spectroscopic survey to date of high-redshift QSOs with simultaneous rest-frame UV/optical coverage, and as such enables a wide range of extragalactic research, from cosmology and galaxy evolution to AGN astrophysics. © 2016 ESO

XQ-100: A legacy survey of one hundred 3.5 72 z 72 4.5 quasars observed with VLT/X-shooter

We describe the execution and data reduction of the European Southern Observatory Large Programme "Quasars and their absorption lines: a legacy survey of the high-redshift Universe with VLT/X-shooter" (hereafter "XQ-100"). XQ-100 has produced and made publicly available a homogeneous and high-quality sample of echelle spectra of 100 quasars (QSOs) at redshifts z 43 3.5-4.5 observed with full spectral coverage from 315 to 2500 nm at a resolving power ranging from R \u303. 4000 to 7000, depending on wavelength. The median signal-to-noise ratios are 33, 25 and 43, as measured at rest-frame wavelengths 1700, 3000 and 3600 \uc5, respectively. This paper provides future users of XQ-100 data with the basic statistics of the survey, along with details of target selection, data acquisition and data reduction. The paper accompanies the public release of all data products, including 100 reduced spectra. XQ-100 is the largest spectroscopic survey to date of high-redshift QSOs with simultaneous rest-frame UV/optical coverage, and as such enables a wide range of extragalactic research, from cosmology and galaxy evolution to AGN astrophysics. \ua9 2016 ESO

Spectral variations of Lyman alpha emission within strongly lensed sources observed with MUSE

We present an analysis of HI Lyman-alpha emission in deep VLT/MUSE observations of two highly magnified and extended galaxies at z=3.5 and 4.03, including a newly discovered, almost complete Einstein ring. While these Lyman-alpha haloes are intrinsically similar to the ones typically seen in other MUSE deep fields, the benefits of gravitational lensing allows us to construct exceptionally detailed maps of Lyman-alpha line properties at sub-kpc scales. By combining all multiple images, we are able to observe complex structures in the Lyman-alpha emission and uncover small (~ 120 km/s in Lyman-alpha peak shift), but significant at > 4 sigma, systematic variations in the shape of the Lyman-alpha line profile within each halo. Indeed, we observe a global trend for the line peak shift to become redder at large radii, together with a strong correlation between the peak wavelength and line width. This systematic intrahalo variation is markedly similar to the object-to-object variations obtained from the integrated properties of recent large samples. Regions of high surface brightness correspond to relatively small line shifts, which could indicate that Lyman-alpha emission escapes preferentially from regions where the line profile has been less severely affected by scattering of Lyman-alpha photons.Comment: 9 pages, 4 figures, accepted for publication in MNRA