1812.06191
Why chromatic imaging matters
Sanchez-Bermudez, et al
During the last two decades, the fist generation of beam combiners at the VLT Interferometer has proved the importance of optical interferometry for high-angular resolution astrophysical studies in the near- and mid-infrared. With the advent of 4-beam combiners at the VLTI, the u-v coverage per pointing increases significantly, providing an opportunity to use reconstructed images as powerful scientific tools. Therefore, interferometric imaging is already a key feature of the new generation of VLTI instruments, as well as for other interferometric facilities like CHARA and JWST. It is thus imperative to account for the current image reconstruction capabilities and their expected evolutions in the coming years. Here, present a general overview of the current situation of optical interferometric image reconstruction with a focus on new wavelength-dependent information, highlighting its main advantages and limitations. As an Appendix, include several cookbooks describing the usage and installation of several state-of-the art image reconstruction packages. To illustrate the current capabilities of the software available to the community, recover chromatic images, from simulated MATISE data, using the MCMC software SQUEEZE. With these images, aim at showing the importance of selecting good regularization functions and their impact on the reconstruction.
1812.06618
Ultrahigh-energy cosmic rays
Mariazzi
UHECRs arrive at Earth from the most energetic astrophysical accelerators in the universe. They collide with atoms in the upper atmosphere with energies about 10 times higher than any man-made accelerator, and produce gigantic cascades of secondary particles, called extensive air showers (EAS). EASs can be detected spreading particle detectors over a large area to record the interactions of secondary particles. The Pierre Auger Observatory has been designed to investigate the origin and nature of UHECRs using the combination of information from a surface array, measuring the lateral distributions of secondary particles at the ground, and fluorescence telescopes, observing the longitudinal profile of the EM component of EAS, providing an enhanced reconstruction capability. In this contribution, the status and prospects of understanding the physics of UHECRs will be reviewed, focusing on the progress made thanks to the measurements of the Pierre Auger Observatory. Physics results form the UHECR data collected with the PAO opened new perspectives and motivated an upgrade of the Observatory, AugerPrime, whose main characteristics are also presented.
1812.06918
Environmental dependence of ellipticity correlation functions of intrinsic alignments
Reischke, Schäfer
Investigate the environmental dependence of the IA in cosmic shear surveys. Use the quadratic and linear alignment model to describe the contributions by spiral and elliptical galaxies, respectively. The density field is in both cases described by a Gaussian random field and ellipticity correlation functions that are conditional on the environment of the galaxies are constructed by sampling random values for the tidal tensor and inertial tensor. The covariance of the Gaussian random process from which the tensor entries are drawn is decomposed by means of a spherical Fourier-Bessel transformation of the density field. The dependence on environment is modeled by the number of positive eigenvalues of the tidal tensor, which allows a differentiation between voids, sheets, filaments and superclusters. Find that elliptical galaxies align strongest in elongated structures such as sheets and filaments with an amplitude almost an order of magnitude higher compared to the alignment in clusters or voids. In contrast to this, spiral galaxies align equally strong in all environments. Cross-alignments between different environments are smaller than the respective auto-correlations subject to the Cauchy-Schwartz inequality which is an effective bound on their amplitude. Furthermore, find misalignment between inertial and tidal tensor to be stronger in anisotropic regions compared to clusters or voids. While the imprint of WL on galaxy ellipticities is agnostic about the environment, using environment information can help to distinguish between lensing and the IA signal.
1812.06922
Influence of the local Universe on weak gravitational lensing surveys
Reischke, et al
Observations of the LSS implicitly assume an ideal FLRW observer with the ambient structure having no influence on the observer. However, due to correlations in the LSS, cosmological observables are dependent on the position of an observer. Investigate this influence in full generality for a weakly non-Gaussian random field, for which expressions are derived for angular spectra of large-scale structure observables conditional on a property of the LSS that is typical for the observer's location. As an application, apply to the formalism to angular spectra of the WL effect and provide numerical estimates for the resulting change on the spectra using linear structure formation. For angular WL spectra, find the effect to be of order of a few percent, for instance estimate for an overdensity of delta=0.5 and multipoles up to ell=100 the change in the WL spectra to be approximately 4%. Show that without accounting for correlation between the density at observer's location and the WL spectra, the values of the parameters Omega_m and sigma_8 are underestimated by a few %. Thus, this effect will be important when analyzing data from future surveys such as Euclid, which aim at the %-level precision. The effect is difficult to capture in simulations, as estimates of the number of numerical simulations necessary to quantify the effect are high.
Why chromatic imaging matters
Sanchez-Bermudez, et al
During the last two decades, the fist generation of beam combiners at the VLT Interferometer has proved the importance of optical interferometry for high-angular resolution astrophysical studies in the near- and mid-infrared. With the advent of 4-beam combiners at the VLTI, the u-v coverage per pointing increases significantly, providing an opportunity to use reconstructed images as powerful scientific tools. Therefore, interferometric imaging is already a key feature of the new generation of VLTI instruments, as well as for other interferometric facilities like CHARA and JWST. It is thus imperative to account for the current image reconstruction capabilities and their expected evolutions in the coming years. Here, present a general overview of the current situation of optical interferometric image reconstruction with a focus on new wavelength-dependent information, highlighting its main advantages and limitations. As an Appendix, include several cookbooks describing the usage and installation of several state-of-the art image reconstruction packages. To illustrate the current capabilities of the software available to the community, recover chromatic images, from simulated MATISE data, using the MCMC software SQUEEZE. With these images, aim at showing the importance of selecting good regularization functions and their impact on the reconstruction.
1812.06618
Ultrahigh-energy cosmic rays
Mariazzi
UHECRs arrive at Earth from the most energetic astrophysical accelerators in the universe. They collide with atoms in the upper atmosphere with energies about 10 times higher than any man-made accelerator, and produce gigantic cascades of secondary particles, called extensive air showers (EAS). EASs can be detected spreading particle detectors over a large area to record the interactions of secondary particles. The Pierre Auger Observatory has been designed to investigate the origin and nature of UHECRs using the combination of information from a surface array, measuring the lateral distributions of secondary particles at the ground, and fluorescence telescopes, observing the longitudinal profile of the EM component of EAS, providing an enhanced reconstruction capability. In this contribution, the status and prospects of understanding the physics of UHECRs will be reviewed, focusing on the progress made thanks to the measurements of the Pierre Auger Observatory. Physics results form the UHECR data collected with the PAO opened new perspectives and motivated an upgrade of the Observatory, AugerPrime, whose main characteristics are also presented.
1812.06918
Environmental dependence of ellipticity correlation functions of intrinsic alignments
Reischke, Schäfer
Investigate the environmental dependence of the IA in cosmic shear surveys. Use the quadratic and linear alignment model to describe the contributions by spiral and elliptical galaxies, respectively. The density field is in both cases described by a Gaussian random field and ellipticity correlation functions that are conditional on the environment of the galaxies are constructed by sampling random values for the tidal tensor and inertial tensor. The covariance of the Gaussian random process from which the tensor entries are drawn is decomposed by means of a spherical Fourier-Bessel transformation of the density field. The dependence on environment is modeled by the number of positive eigenvalues of the tidal tensor, which allows a differentiation between voids, sheets, filaments and superclusters. Find that elliptical galaxies align strongest in elongated structures such as sheets and filaments with an amplitude almost an order of magnitude higher compared to the alignment in clusters or voids. In contrast to this, spiral galaxies align equally strong in all environments. Cross-alignments between different environments are smaller than the respective auto-correlations subject to the Cauchy-Schwartz inequality which is an effective bound on their amplitude. Furthermore, find misalignment between inertial and tidal tensor to be stronger in anisotropic regions compared to clusters or voids. While the imprint of WL on galaxy ellipticities is agnostic about the environment, using environment information can help to distinguish between lensing and the IA signal.
1812.06922
Influence of the local Universe on weak gravitational lensing surveys
Reischke, et al
Observations of the LSS implicitly assume an ideal FLRW observer with the ambient structure having no influence on the observer. However, due to correlations in the LSS, cosmological observables are dependent on the position of an observer. Investigate this influence in full generality for a weakly non-Gaussian random field, for which expressions are derived for angular spectra of large-scale structure observables conditional on a property of the LSS that is typical for the observer's location. As an application, apply to the formalism to angular spectra of the WL effect and provide numerical estimates for the resulting change on the spectra using linear structure formation. For angular WL spectra, find the effect to be of order of a few percent, for instance estimate for an overdensity of delta=0.5 and multipoles up to ell=100 the change in the WL spectra to be approximately 4%. Show that without accounting for correlation between the density at observer's location and the WL spectra, the values of the parameters Omega_m and sigma_8 are underestimated by a few %. Thus, this effect will be important when analyzing data from future surveys such as Euclid, which aim at the %-level precision. The effect is difficult to capture in simulations, as estimates of the number of numerical simulations necessary to quantify the effect are high.
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