Stella Seitz

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We reformulate the transport equation which determines the size, shape and orientation of innnitesimal light beams in arbitrary spacetimes. The behaviour of such light beams near vertices and conjugate points is investigated, with special attention to the singular behaviour of the optical scalars. We then specialize the general transport equation to the(More)
Re-ionization of the intergalactic medium occurred in the early Universe at redshift z ≈ 6-11, following the formation of the first generation of stars. Those young galaxies (where the bulk of stars formed) at a cosmic age of less than about 500 million years (z ≲ 10) remain largely unexplored because they are at or beyond the sensitivity limits of existing(More)
Gravitational light deeection can distort the images of distant sources by its tidal eeects. The population of faint blue galaxies is at suuciently high redshift so that their images are distorted near foreground clusters, with giant luminous arcs being the most spectacular evidence for this eeect. Much weaker distortions, however, can observationally be(More)
  • Jochen Heidt, Immo Appenzeller, Armin Gabasch, Klaus Jäger, Stella Seitz, Ralf Bender +18 others
  • 2002
The FORS Deep Field project is a multi-colour, multi-object spectroscopic investigation of a ∼ 7 ′ × 7 ′ region near the south galactic pole based mostly on observations carried out with the FORS instruments attached to the VLT telescopes. It includes the QSO Q 0103-260 (z = 3.36). The goal of this study is to improve our understanding of the formation and(More)
We present a new method for reconstructing two-dimensional mass maps of galaxy clusters from the image distortion of background galaxies. In contrast to most previous approaches , which directly convert locally averaged image ellip-ticities to mass maps (direct methods), our entropy-regularized maximum-likelihood method is an inverse approach. Albeit(More)
We present a catalog of 25 definite and 11 probable strong galaxy–galaxy gravitational lens systems with lens redshifts 0.4 z 0.7, discovered spectroscopically by the presence of higher-redshift emission lines within the Baryon Oscillation Spectroscopic Survey (BOSS) of luminous galaxies, and confirmed with high-resolution Hubble Space Telescope (HST)(More)
We present a novel method to reconstruct the mass distribution of galaxy clusters from their gravitational lens effect on background galaxies. The method is based on a least-␹ 2 fit of the two-dimensional gravitational cluster potential. The method combines information from shear and magnification by the cluster lens and is designed to easily incorporate(More)
We present a novel method to recontruct the mass distribution of galaxy clusters from their gravitational lens effect on background galaxies. The method is based on a least-χ 2 fit of the two-dimensional gravitational cluster potential. The method combines information from shear and magnification by the cluster lens and is designed to easily incorporate(More)
Accepted —-. Received —-; in original form —-. ABSTRACT We present an analysis of a general machine learning technique called 'stacking' for the estimation of photometric redshifts. Stacking techniques can feed the photometric redshift estimate, as output by a base algorithm, back into the same algorithm as an additional input feature in a subsequent(More)
We introduce an ordinal classification algorithm for photometric redshift estimation, which significantly improves the reconstruction of photometric redshift probability density functions (PDFs) for individual galaxies and galaxy samples. As a use case we apply our method to CFHTLS galaxies. The ordinal classification algorithm treats distinct redshift bins(More)