Jan Hartlap
Current Organizations / Institutes
The organizations/institutes from the scholar's latest article
Research Subjects
Jan Hartlap has a total of 9 co-authors. Here are the top co-authors by number of shared publications:
P. Schneider
Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
4 shared publicationsP. Simon
The Scottish Universities Physics Alliance (SUPA), Institute for Astronomy, School of Physics, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
2 shared publicationsPeter Schneider
Argelander-Institut für Astronomie Universität Bonn Auf dem Hügel 71 D-53121 Bonn Germany
2 shared publicationsHendrik Hildebrandt
Leiden Observatory Leiden University Niels Bohrweg 2 NL-2333 CA Leiden the Netherlands
1 shared publication- Hendrik Hildebrandt
Ruhr University Bochum, Faculty of Physics and Astronomy, Astronomical Institute (AIRUB), German Centre for Cosmological Lensing (GCCL)
1 shared publication - Jörg P. Dietrich
Department of Physics, Ludwig-Maximilians-Universität, Scheinerstr. 1, D-81679 München, Germany
1 shared publication
Latest Publications
- 28 February 2011
- Published by EDP Sciences in Astronomy & Astrophysics
- Vol. 528, A51
A bias in cosmic shear from galaxy selection: results from ray-tracing simulations
Astronomy & Astrophysics (A&A) is an international journal which publishes papers on all aspects of astronomy and astrophysics
- 28 February 2011
- Published by EDP Sciences in Astronomy & Astrophysics
- Vol. 528, A51
A bias in cosmic shear from galaxy selection: results from ray-tracing simulations
Astronomy & Astrophysics (A&A) is an international journal which publishes papers on all aspects of astronomy and astrophysics
- Open Access
A bias in cosmic shear from galaxy selection: results from ray-tracing simulations
We identify and study a previously unknown systematic effect on cosmic shear measurements, caused by the selection of galaxies used for shape measurement, in particular the rejection of close (blended) galaxy pairs. We use ray-tracing simulations based on the Millennium Simulation and a semi-analytical model of galaxy formation to create realistic galaxy catalogues. From these, we quantify the bias in the shear correlation functions by comparing measurements made from galaxy catalogues with and without removal of close pairs. A likelihood analysis is used to quantify the resulting shift in estimates of cosmological parameters. The filtering of objects with close neighbours (a) changes the redshift distribution of the galaxies used for correlation function measurements, and (b) correlates the number density of sources in the background with the density field in the foreground. This leads to a scale-dependent bias of the correlation function of several percent, translating into biases of cosmological parameters of similar amplitude. This makes this new systematic effect potentially harmful for upcoming and planned cosmic shear surveys. As a remedy, we propose and test a weighting scheme that can significantly reduce the bias.
Open AccessA bias in cosmic shear from galaxy selection: results from ray-tracing simulations
We identify and study a previously unknown systematic effect on cosmic shear measurements, caused by the selection of galaxies used for shape measurement, in particular the rejection of close (blended) galaxy pairs. We use ray-tracing simulations based on the Millennium Simulation and a semi-analytical model of galaxy formation to create realistic galaxy catalogues. From these, we quantify the bias in the shear correlation functions by comparing measurements made from galaxy catalogues with and without removal of close pairs. A likelihood analysis is used to quantify the resulting shift in estimates of cosmological parameters. The filtering of objects with close neighbours (a) changes the redshift distribution of the galaxies used for correlation function measurements, and (b) correlates the number density of sources in the background with the density field in the foreground. This leads to a scale-dependent bias of the correlation function of several percent, translating into biases of cosmological parameters of similar amplitude. This makes this new systematic effect potentially harmful for upcoming and planned cosmic shear surveys. As a remedy, we propose and test a weighting scheme that can significantly reduce the bias.
- Open Access
- 2 February 2010
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 402 (2) , 1049-1058
Cosmology with the shear-peak statistics
- 2 February 2010
- Published by Oxford University Press (OUP) in Monthly Notices of the Royal Astronomical Society
- Vol. 402 (2) , 1049-1058
Open AccessCosmology with the shear-peak statistics
- Open Access
- 16 July 2009
- Published by EDP Sciences in Astronomy & Astrophysics
- Vol. 504 (3) , 705-717
Constrained correlation functions
Astronomy & Astrophysics (A&A) is an international journal which publishes papers on all aspects of astronomy and astrophysics
- 16 July 2009
- Published by EDP Sciences in Astronomy & Astrophysics
- Vol. 504 (3) , 705-717
Open AccessConstrained correlation functions
Astronomy & Astrophysics (A&A) is an international journal which publishes papers on all aspects of astronomy and astrophysics
- Open Access
- 9 July 2009
- Published by EDP Sciences in Astronomy & Astrophysics
- Vol. 504 (3) , 689-703
The non-Gaussianity of the cosmic shear likelihood or how odd is theChandraDeep Field South?
Astronomy & Astrophysics (A&A) is an international journal which publishes papers on all aspects of astronomy and astrophysics
- 9 July 2009
- Published by EDP Sciences in Astronomy & Astrophysics
- Vol. 504 (3) , 689-703
Open AccessThe non-Gaussianity of the cosmic shear likelihood or how odd is theChandraDeep Field South?
Astronomy & Astrophysics (A&A) is an international journal which publishes papers on all aspects of astronomy and astrophysics
- Open Access
Constrained correlation functions
We show that correlation functions have to satisfy contraint relations, owing to the non-negativity of the power spectrum of the underlying random process. Specifically, for any statistically homogeneous and (for more than one spatial dimension) isotropic random field with correlation function $\xi(x)$, we derive inequalities for the correlation coefficients $r_n\equiv \xi(n x)/\xi(0)$ (for integer $n$) of the form $r_{n{\rm l}}\le r_n\le r_{n{\rm u}}$, where the lower and upper bounds on $r_n$ depend on the $r_j$, with $j<n$. Explicit expressions for the bounds are obtained for arbitrary $n$. These constraint equations very significantly limit the set of possible correlation functions. For one particular example of a fiducial cosmic shear survey, we show that the Gaussian likelihood ellipsoid has a significant spill-over into the forbidden region of correlation functions, rendering the resulting best-fitting model parameters and their error region questionable, and indicating the need for a better description of the likelihood function. We conduct some simple numerical experiments which explicitly demonstrate the failure of a Gaussian description for the likelihood of $\xi$. Instead, the shape of the likelihood function of the correlation coefficients appears to follow approximately that of the shape of the bounds on the $r_n$, even if the Gaussian ellipsoid lies well within the allowed region. For more than one spatial dimension of the random field, the explicit expressions of the bounds on the $r_n$ are not optimal. We outline a geometrical method how tighter bounds may be obtained in principle. We illustrate this method for a few simple cases; a more general treatment awaits future work.Open AccessConstrained correlation functions
We show that correlation functions have to satisfy contraint relations, owing to the non-negativity of the power spectrum of the underlying random process. Specifically, for any statistically homogeneous and (for more than one spatial dimension) isotropic random field with correlation function $\xi(x)$, we derive inequalities for the correlation coefficients $r_n\equiv \xi(n x)/\xi(0)$ (for integer $n$) of the form $r_{n{\rm l}}\le r_n\le r_{n{\rm u}}$, where the lower and upper bounds on $r_n$ depend on the $r_j$, with $j<n$. Explicit expressions for the bounds are obtained for arbitrary $n$. These constraint equations very significantly limit the set of possible correlation functions. For one particular example of a fiducial cosmic shear survey, we show that the Gaussian likelihood ellipsoid has a significant spill-over into the forbidden region of correlation functions, rendering the resulting best-fitting model parameters and their error region questionable, and indicating the need for a better description of the likelihood function. We conduct some simple numerical experiments which explicitly demonstrate the failure of a Gaussian description for the likelihood of $\xi$. Instead, the shape of the likelihood function of the correlation coefficients appears to follow approximately that of the shape of the bounds on the $r_n$, even if the Gaussian ellipsoid lies well within the allowed region. For more than one spatial dimension of the random field, the explicit expressions of the bounds on the $r_n$ are not optimal. We outline a geometrical method how tighter bounds may be obtained in principle. We illustrate this method for a few simple cases; a more general treatment awaits future work. - Top Cited PapersOpen Access
- 5 December 2006
- Published by EDP Sciences in Astronomy & Astrophysics
- Vol. 464 (1) , 399-404
Why your model parameter confidences might be too optimistic. Unbiased estimation of the inverse covariance matrix
Astronomy & Astrophysics (A&A) is an international journal which publishes papers on all aspects of astronomy and astrophysics
- 5 December 2006
- Published by EDP Sciences in Astronomy & Astrophysics
- Vol. 464 (1) , 399-404
Top Cited PapersOpen AccessWhy your model parameter confidences might be too optimistic. Unbiased estimation of the inverse covariance matrix
Astronomy & Astrophysics (A&A) is an international journal which publishes papers on all aspects of astronomy and astrophysics