21 research outputs found
The distortion of distant galaxy images by large-scale structure
Inhomogeneity in the distribution of mass in the universe on scales âČ 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 âwallsâ reported in galaxy velocity surveys. Using these simulations, we estimate that an rms induced ellipticity of |p|_(rms) Ë 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 Ë 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) Ë0.02 for biased cold dark matter models of an EinsleinâDe Sitter universe, and the effective correlation length is Ξ_(1/2) Ë 0.5^ΰ. For a hot dark matter dominated universe the correlation length is Ξ_(1/2) Ë 0.7^ΰ.
The faint, blue galaxies discovered by Tyson and collaborators have a surface density of Ë 3 Ă 10^5 deg^(â2) and should provide an ideal set of sources for measuring this effect
The MUSE-Wide Survey: A first catalogue of 831 emission line galaxies
We present a first instalment of the MUSE-Wide survey, covering an area of
22.2 arcmin (corresponding to 20% of the final survey) in the
CANDELS/Deep area of the Chandra Deep Field South. We use the MUSE integral
field spectrograph at the ESO VLT to conduct a full-area spectroscopic mapping
at a depth of 1h exposure time per 1 arcmin pointing. We searched for
compact emission line objects using our newly developed LSDCat software based
on a 3-D matched filtering approach, followed by interactive classification and
redshift measurement of the sources. Our catalogue contains 831 distinct
emission line galaxies with redshifts ranging from 0.04 to 6. Roughly one third
(237) of the emission line sources are Lyman emitting galaxies with , only four of which had previously measured spectroscopic redshifts.
At lower redshifts 351 galaxies are detected primarily by their [OII] emission
line (), 189 by their [OIII] line (), and 46 by their H line (). Comparing our spectroscopic redshifts to photometric redshift estimates
from the literature, we find excellent agreement for with a median
of only and an outlier rate of 6%, however a
significant systematic offset of and an outlier rate of 23%
for Ly emitters at . Together with the catalogue we also release
1D PSF-weighted extracted spectra and small 3D datacubes centred on each of the
831 sources.Comment: 24 pages, 14 figures, accepted for publication in A&A, data products
are available for download from http://muse-vlt.eu/science/muse-wide-survey/
and later via the CD
The distortion of distant galaxy images by large-scale structure
Inhomogeneity in the distribution of mass in the universe on scales âČ 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 âwallsâ reported in galaxy velocity surveys. Using these simulations, we estimate that an rms induced ellipticity of |p|_(rms) Ë 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 Ë 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) Ë0.02 for biased cold dark matter models of an EinsleinâDe Sitter universe, and the effective correlation length is Ξ_(1/2) Ë 0.5^ΰ. For a hot dark matter dominated universe the correlation length is Ξ_(1/2) Ë 0.7^ΰ.
The faint, blue galaxies discovered by Tyson and collaborators have a surface density of Ë 3 Ă 10^5 deg^(â2) and should provide an ideal set of sources for measuring this effect
The MUSE-Wide Survey: Survey Description and First Data Release
We present the MUSE-Wide survey, a blind, 3D spectroscopic survey in the
CANDELS/GOODS-S and CANDELS/COSMOS regions. Each MUSE-Wide pointing has a depth
of 1 hour and hence targets more extreme and more luminous objects over 10
times the area of the MUSE-Deep fields (Bacon et al. 2017). The legacy value of
MUSE-Wide lies in providing "spectroscopy of everything" without photometric
pre-selection. We describe the data reduction, post-processing and PSF
characterization of the first 44 CANDELS/GOODS-S MUSE-Wide pointings released
with this publication. Using a 3D matched filtering approach we detected 1,602
emission line sources, including 479 Lyman- (Lya) emitting galaxies
with redshifts . We cross-match the emission line
sources to existing photometric catalogs, finding almost complete agreement in
redshifts and stellar masses for our low redshift (z < 1.5) emitters. At high
redshift, we only find ~55% matches to photometric catalogs. We encounter a
higher outlier rate and a systematic offset of z0.2 when
comparing our MUSE redshifts with photometric redshifts. Cross-matching the
emission line sources with X-ray catalogs from the Chandra Deep Field South, we
find 127 matches, including 10 objects with no prior spectroscopic
identification. Stacking X-ray images centered on our Lya emitters yielded no
signal; the Lya population is not dominated by even low luminosity AGN. A total
of 9,205 photometrically selected objects from the CANDELS survey lie in the
MUSE-Wide footprint, which we provide optimally extracted 1D spectra of. We are
able to determine the spectroscopic redshift of 98% of 772 photometrically
selected galaxies brighter than 24th F775W magnitude. All the data in the first
data release - datacubes, catalogs, extracted spectra, maps - are available on
the website https://musewide.aip.de. [abridged]Comment: 25 pages 15+1 figures. Accepted, A&A. Comments welcom
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
XQ-100: A legacy survey of one hundred 3.5 âČ z âČ 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 â 3.5-4.5 observed with full spectral coverage from 315 to 2500 nm at a resolving power ranging from R Ì. 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 Ă
, 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
The MUSE-Wide survey: a measurement of the Ly α emitting fraction among z > 3 galaxies
Large scale structure and cosmolog
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 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