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Posts: 131433
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Einstein Cross
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Title: The Einstein Cross: constraint on dark matter from stellar dynamics and gravitational lensing
Authors: Glenn van de Ven (1 and 2), Jesus Falcon-Barroso (3 and 4), Richard M. McDermid (5), Michele Cappellari (6), Bryan W. Miller (7), P. Tim de Zeeuw (8 and 9) ((1) MPIA, Heidelberg, (2) IAS, Princeton, (3) IAC, Tenerife, (4) ESA/ESTEC, (5) Gemini Observatory, Hawaii, (6) University of Oxford, (7) Gemini Observatory, Chile (8) ESO, Garching, (9) Sterrewacht Leiden)
(Version v2)

We present two-dimensional line-of-sight stellar kinematics of the lens galaxy in the Einstein Cross, obtained with the GEMINI 8m telescope, using the GMOS integral-field spectrograph. The velocity map shows regular rotation up to ~100 km/s around the minor axis of the bulge, consistent with axisymmetry. The velocity dispersion map shows a weak gradient increasing towards a central (R<1") value of sigma_0=1709 km/s. We deproject the observed surface brightness from HST imaging to obtain a realistic luminosity density of the lens galaxy, which in turn is used to build axisymmetric dynamical models that fit the observed kinematic maps. We also construct a gravitational lens model that accurately fits the positions and relative fluxes of the four quasar images. We find that the resulting luminous and total mass distribution are nearly identical around the Einstein radius R_E = 0.89", with a slope that is close to isothermal, but which becomes shallower towards the center if indeed mass follows light. The dynamical model fits to the observed kinematic maps result in a total mass-to-light ratio (M/L)_dyn=3.70.5 M_sun/L_sun,I (in the I-band). This is consistent with the Einstein mass M_E = 1.54 x 10^10 M_sun divided by the (projected) luminosity within R_E, which yields a total mass-to-light ratio of (M/L)_E=3.4 M_sun/L_sun,I, with an error of at most a few per cent. We estimate from stellar populations model fits to colours of the lens galaxy a stellar mass-to-light ratio (M/L)_* from 2.8 to 4.1 M_sun/L_sun,I. Although a constant dark matter fraction of 20 per cent is not excluded, dark matter may play no significant role in the bulge of this ~L* early-type spiral galaxy.

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Posts: 131433
Date:
QSO 2237+0305
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Title: Spitzer observations of a gravitationally lensed quasar, QSO 2237+0305
Authors: Eric Agol (UW), Stephanie Gogarten (UW), Varoujan Gorjian (JPL), Amy Kimball (UW)

The four-image gravitationally lensed quasar QSO 2237+0305 is microlensed by stars in the lens galaxy. The amplitude of microlensing variability can be used to infer the relative size of the quasar as a function of wavelength; this provides a test of quasar models. Toward this end, we present Spitzer Space Telescope Infrared Spectrograph and Infrared Array Camera (IRAC) observations of QSO 2237+0305, finding the following. (1) The infrared (IR) spectral energy distribution (SED) is similar to that of other bright radio-quiet quasars, contrary to an earlier claim. (2) A dusty torus model with a small opening angle fits the overall shape of the IR SED well, but the quantitative agreement is poor due to an offset in wavelength of the silicate feature. (3) The flux ratios of the four lensed images can be derived from the IRAC data despite being unresolved. We find that the near-IR fluxes are increasingly affected by microlensing toward shorter wavelengths. (4) The wavelength dependence of the IRAC flux ratios is consistent with the standard quasar model in which an accretion disk and a dusty torus both contribute near 1 micron in the rest frame. This is also consistent with recent IR spectropolarimetry of nearby quasars.

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Posts: 131433
Date:
Einstein Cross
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The team of astronomers from Europe and the US studied the "Einstein Cross", a famous cosmic mirage. This cross-shaped configuration consists of four images of a single very distant source. The multiple images are a result of gravitational lensing by a foreground galaxy, an effect that was predicted by Albert Einstein as a consequence of his theory of general relativity. The light source in the Einstein Cross is a quasar approximately ten billion light-years away, whereas the foreground lensing galaxy is ten times closer. The light from the quasar is bent in its path and magnified by the gravitational field of the lensing galaxy. (December 2008)



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Posts: 131433
Date:
The Einstein Cross
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The Einstein Cross or QSO 2237+0305 is a gravitationally lensed quasar that sits directly behind ZW 2237+030, Huchra's Lens. It is quadruply imaged, hence its name, Einstein Cross, forming a nearly perfect cross, with the lensing galaxy at its center.
The quasar is located about 8 billion light years from Earth, while the lensing galaxy is located at a distance of 400 million light years.
The Einstein Cross can be found in Pegasus at 22h40m30.3s +3d21m31s.

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Posts: 131433
Date:
QSO 2237+0305
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Microlensing variability in the gravitationally lensed quasar QSO 2237+0305 = the Einstein Cross.

Astronomers Dissect a Supermassive Black Hole with Natural Magnifying Glasses
Combining a double natural "magnifying glass" with the power of ESO's Very Large Telescope, astronomers have scrutinised the inner parts of the disc around a supermassive black hole 10 billion light-years away. They were able to study the disc with a level of detail a thousand times better than that of the best telescopes in the world, providing the first observational confirmation of the prevalent theoretical models of such discs.
The team of astronomers from Europe and the US studied the "Einstein Cross", a famous cosmic mirage. This cross-shaped configuration consists of four images of a single very distant source. The multiple images are a result of gravitational lensing by a foreground galaxy, an effect that was predicted by Albert Einstein as a consequence of his theory of general relativity. The light source in the Einstein Cross is a quasar approximately ten billion light-years away, whereas the foreground lensing galaxy is ten times closer. The light from the quasar is bent in its path and magnified by the gravitational field of the lensing galaxy.

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