Georgios Zacharegkas
A5064381218- Astrophysics and Cosmic Phenomena
- Galaxies: Formation, Evolution, Phenomena
- Solar and Space Plasma Dynamics
- Ionosphere and magnetosphere dynamics
- Cosmology and Gravitation Theories
- Gamma-ray bursts and supernovae
- Astronomy and Astrophysical Research
- Radio Astronomy Observations and Technology
- CCD and CMOS Imaging Sensors
- Adaptive optics and wavefront sensing
- Dark Matter and Cosmic Phenomena
- Astronomical Observations and Instrumentation
- Computational Physics and Python Applications
- Neutrino Physics Research
- Geomagnetism and Paleomagnetism Studies
University of Chicago
2020-2024
University of Hawaii System
2023
Fermi National Accelerator Laboratory
2023
Aristotle University of Thessaloniki
2016
We constrain cosmological and galaxy-bias parameters using the combination of galaxy clustering galaxy-galaxy lensing measurements from Dark Energy Survey Year-3 data. describe our modeling framework, choice scales analyzed, validating their robustness to theoretical uncertainties in small-scale by analyzing simulated Using a linear bias model redMaGiC sample, we obtain constraints on matter density be $\Omega_{\rm m} = 0.325^{+0.033}_{-0.034}$. also implement non-linear probe smaller that...
We present and characterize the galaxy-galaxy lensing signal measured using first three years of data from Dark Energy Survey (DES Y3) covering 4132 deg$^2$. These measurements are used in DES Y3 3$\times$2pt cosmological analysis, which combines weak galaxy clustering information. use two lens samples: a magnitude-limited sample redMaGic sample, span redshift range $\sim 0.2-1$ with 10.7 M 2.6 galaxies respectively. For source catalog, we Metacalibration shape consisting $\simeq$100...
Abstract The nonresonant streaming instability (Bell instability) plays a pivotal role in the acceleration and confinement of cosmic rays (CRs), yet exact mechanism responsible for its saturation magnitude final amplified magnetic field have not been assessed from first principles. Using survey hybrid simulations (with kinetic ions fluid electrons), we study evolution Bell as function parameters CR population. We find that at saturation, pressure is comparable with initial anisotropic...
Using the first three years of data from Dark Energy Survey, we use ratios small-scale galaxy-galaxy lensing measurements around same lens sample to constrain source redshift uncertainties, intrinsic alignments and other nuisance parameters our model. Instead using a simple geometric approach for ratios, full modeling measurements, including corresponding integration over power spectrum contributions magnification. We perform extensive testing shear ratio (SR) by studying impact different...
We develop estimators of agreement and disagreement between correlated cosmological data sets. These account for correlations when computing the significance both tensions excess confirmation while remaining statistically optimal. discuss thoroughly characterize different approaches commenting on ones that have best behavior in practical applications. complement calculation their statistical distribution within Gaussian model with one estimator takes non-Gaussianities fully into account. To...
Galaxy-galaxy lensing is a powerful probe of the connection between galaxies and their host dark matter halos, which important both for galaxy evolution cosmology. We extend measurement modeling galaxy-galaxy signal in recent Dark Energy Survey Year 3 cosmology analysis to highly nonlinear scales ($\sim 100$ kpc). This extension enables us study galaxy-halo via Halo Occupation Distribution (HOD) framework two lens samples used analysis: luminous red sample (redMaGiC) magnitude-limited...
ABSTRACT We cross-correlate positions of galaxies measured in data from the first three years Dark Energy Survey with Compton-y maps generated using South Pole Telescope (SPT) and Planck mission. model this cross-correlation measurement together galaxy autocorrelation to constrain distribution gas Universe. measure hydrostatic mass bias or, equivalently, mean halo bias-weighted electron pressure 〈bhPe 〉, large-scale information. find 〉 be...
Recent cosmological analyses with large-scale structure and weak lensing measurements, usually referred to as 3$\times$2pt, had discard a lot of signal-to-noise from small scales due our inability accurately model non-linearities baryonic effects. Galaxy-galaxy lensing, or the position-shear correlation between lens source galaxies, is one three two-point functions that are included in such analyses, estimated mean tangential shear. However, shear measurements at given angular scale $\theta$...
The limitation of the Quasilinear Theory (QLT) to describe diffusion electrons and ions in velocity space when interacting with a spectrum large amplitude electrostatic Langmuir, Upper Lower hybrid waves, is analyzed. We analytically numerically estimate threshold for waves above which QLT breaks down, using test particle code. evolution distribution, velocity-space coefficients, driven current, heating particles are investigated, interaction small that is, both regimes, where valid it clearly down.
The nonresonant cosmic ray instability, predicted by Bell (2004), is thought to play an important role in the acceleration and confinement of rays (CRs) close supernova remnants. Despite its importance, exact mechanism responsible for saturation instability has not been determined, there no first-principle prediction amplitude saturated magnetic field. Using a survey self-consistent kinetic hybrid simulations (with ions fluid electrons), we study non-resonant streaming as function parameters...
The nonresonant cosmic ray instability, predicted by Bell (2004), is thought to play an important role in the acceleration and confinement of rays (CR) close supernova remnants. Despite its importance, exact mechanism responsible for saturation instability has not been determined, there no first-principle prediction amplitude saturated magnetic field. Using a survey self-consistent hybrid simulations (with kinetic ions fluid electrons), we study non-linear evolution as function parameters CR...
The nonresonant cosmic ray instability, predicted by Bell (2004), is thought to play an important role in the acceleration and confinement of rays (CRs) close supernova remnants. Despite its importance, exact mechanism responsible for saturation instability has not been determined, there no first-principle prediction amplitude saturated magnetic field. Using a survey self-consistent kinetic hybrid simulations (with ions fluid electrons), we study non-resonant streaming as function parameters...
The nonresonant streaming instability (Bell instability) plays a pivotal role in the acceleration and confinement of cosmic rays (CRs); yet, exact mechanism responsible for its saturation magnitude final amplified magnetic field have not been assessed from first-principles. Using survey hybrid simulations (with kinetic ions fluid electrons), we study evolution Bell as function parameters CR population. We find that, at saturation, pressure is comparable with initial anisotropic pressure,...
The non-resonant (Bell) streaming instability driven by energetic particles is crucial for producing amplified magnetic fields that are key to the acceleration of cosmic rays (CRs) in supernova remnants, around Galactic and extra-galactic CR sources, transport. We present a covariant theory saturation Bell instability, substantiated self-consistent kinetic simulations, can be applied arbitrary distributions discuss its implications several heliospheric astrophysical contexts.
The non-resonant (Bell) streaming instability driven by energetic particles is crucial for producing amplified magnetic fields that are key to the acceleration of cosmic rays (CRs) in supernova remnants, around Galactic and extra-galactic CR sources, transport. We present a covariant theory saturation Bell instability, substantiated self-consistent kinetic simulations, can be applied arbitrary distributions discuss its implications several heliospheric astrophysical contexts.
The nonresonant cosmic ray instability, predicted by Bell (2004), is thought to play an important role in the acceleration and confinement of rays (CR) close supernova remnants. Despite its importance, exact mechanism responsible for saturation instability has not been determined, there no first-principle prediction amplitude saturated magnetic field. Using a survey self-consistent hybrid simulations (with kinetic ions fluid electrons), we study non-linear evolution as function parameters CR...