arXiv subjects

Joachim Wambsganss

Publications and source records attributed to Joachim Wambsganss.

58 records · Page 4Linked to original sources

arXiv1996

ROSAT/HRI study of the optically rich, lensing cluster CL0500-24

An analysis of a ROSAT/HRI observation of the optically rich, gravitationally lensing galaxy cluster CL0500-24 (or Abell S0506) is presented. We show that the X-ray luminosity of this supposedly rich cluster is relatively low at $1.1^{+0.2}_{-0.1}\times10^{44}$ erg/s in the ROSAT band, the bolometric X-ray luminosity is $2.0^{+1.5}_{-0.7}\times 10^{44}$ erg/s. The X-ray emission is strongly correlated with the northern subconcentration of the cluster galaxies at redshift $z = 0.327$. The derived total mass of the (sub-)cluster within 1 Mpc is $(1.5\pm 0.8) \times 10^{14}$M$_\odot$, with an upper limit to the gas mass of about $0.5\times 10^{14}$M$_\odot$, corresponding to a gas mass fraction of $\le 30^{+30}_{-10}$\%. The X-ray luminosity and the morphology of the extended X-ray emission supports the view that CL0500-24 consists of two clusters at a velocity difference of $Δv \approx 3200$ km/s that happen to lie along the line of sight.

astro-ph↗

arXiv1995

Gravitational Microlensing by Random Motion of Stars: Analysis of Light Curves

We present a quantitative analysis of the effect of microlensing caused by random motion of individual stars in the galaxy which is lensing a background quasar. We calculate a large number of magnification patterns for positions of the stars slightly offset from one frame to the next, and in this way obtain light curves for fixed quasar and galaxy positions, only due to the change in the relative star positions. These light curves are analyzed to identify micro- lensing events, which are classified according to height, duration, and slope. We find that microlensing events produced by random motion of stars are shorter, steeper, and more frequent than bulk motion events. This difference is caused by the fact that in the case of random motion, caustics can move with arbitrarily high velocity, producing very short events. An accompanying video illustrates these results. For three different values of the surface mass density kappa, it shows time sequences of 1000 magnification patterns for slowly changing lens positions, together with the positions and velocity vectors of the microlensing stars. Short sequences of the video are available as MPEG movie by anonymous ftp at ftp://astro.princeton.edu/jkw/microlensing/moving_stars .

astro-ph↗

arXiv1994

Testing Cosmogonic Models with Gravitational Lensing

Gravitational lensing provides a strict test of cosmogonic models. Detailed numerical propagation of light rays through a universe having a distribution of inhomogeneities derived from the standard CDM (cold dark matter) scenario with the aid of massive, fully nonlinear computer simulations is used to test the model. It predicts that we should have seen far more widely split quasar images than have been found. These and other inconsistencies rule out the COBE normalized CDM model with $Ω=1$ and $H_0=50$km/s/Mpc; but variants of this model might be constructed, which could pass the stringent tests provided by strong gravitational lensing.

astro-ph↗

arXiv1994

Parameter degeneracy in models of the quadruple lens system Q2237+0305

The geometry of the quadruple lens system Q2237+0305 is modeled with a simple astigmatic lens: a power-law mass distribution: m \propto r^βwith an external shear γ. The image positions can be reproduced with an accuracy better than 0.01 arcsec for any 0.0 < β< 1.85 and the corresponding value of γ= 0.1385 - 0.0689 β. This is a factor of about 4 more precise than what can be achieved by the best constant M/L lens models. The image intensity ratios and the time delay ratios are almost constant along our one parameter family of models, but the total magnification varies from 8 to > 1000, and the maximum time delay (between leading image B and trailing image C) for H_0 of 75 km/sec/Mpc varies from more than 20 hours to about 1.5 hours, while βincreases from 0.0 to 1.85.

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