scholarly journals The Kaiser-Rocket effect: three decades and counting

2021 ◽  
Vol 2021 (11) ◽  
pp. 027
Author(s):  
Benedict Bahr-Kalus ◽  
Daniele Bertacca ◽  
Licia Verde ◽  
Alan Heavens
Keyword(s):  
Cosmological Parameters ◽  
Cosmological Parameter ◽  
Selection Function ◽  
Systematic Effect ◽  
Parameter Inference ◽  
Sky Survey ◽  
Peculiar Motion ◽  
Rocket Effect ◽  
Do So

Abstract The peculiar motion of the observer, if not accurately accounted for, is bound to induce a well-defined clustering signal in the distribution of galaxies. This signal is related to the Kaiser rocket effect. Here we examine the amplitude and form of this effect, both analytically and numerically, and discuss possible implications for the analysis and interpretation of forthcoming cosmological surveys. For an idealistic cosmic variance dominated full-sky survey with a Gaussian selection function peaked at z ∼ 1.5 it is a > 5σ effect and it can in principle bias very significantly the inference of cosmological parameters, especially for primordial non-Gaussianity. For forthcoming surveys, with realistic masks and selection functions, the Kaiser rocket is not a significant concern for cosmological parameter inference except perhaps for primordial non-Gaussianity studies. However, it is a systematic effect, whose origin, nature and imprint on galaxy maps are well known and thus should be subtracted or mitigated. We present several approaches to do so.

scholarly journals Observing Galaxy Clusters with eROSITA: Simulations

10.14311/1466 ◽  
2011 ◽  
Vol 51 (6) ◽  
Author(s):  
J. Hölzl ◽  
J. Wilms ◽  
I. Kreykenbohm ◽  
Ch. Schmid ◽  
Ch. Grossberger ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Dark Matter ◽  
Dark Energy ◽  
Galaxy Clusters ◽  
Cosmological Parameters ◽  
Mass Function ◽  
Angular Diameter ◽  
Monte Carlo Code ◽  
X Rays ◽  
Sky Survey

The eROSITA instrument on board the Russian Spectrum Roentgen Gamma spacecraft, which will be launched in 2013,will conduct an all sky survey in X-rays. A main objective of the survey is to observe galaxy clusters in order to constrain cosmological parameters and to obtain further knowledge about dark matter and dark energy. For the simulation of the eROSITA survey we present a Monte-Carlo code generating a mock catalogue of galaxy clusters distributed accordingto the mass function of [1]. The simulation generates the celestial coordinates as well as the cluster mass and redshift. From these parameters, the observed intensity and angular diameter are derived. These are used to scale Chandra cluster images as input for the survey-simulation.

scholarly journals Void Dynamics

2014 ◽  
Vol 11 (S308) ◽  
pp. 530-537
Author(s):  
Nelson D. Padilla ◽  
Dante Paz ◽  
Marcelo Lares ◽  
Laura Ceccarelli ◽  
Diego Garcí a Lambas ◽  
...  
Keyword(s):  
Dark Matter ◽  
Correlation Functions ◽  
Cross Correlation ◽  
Cosmological Parameters ◽  
Matter Field ◽  
Sloan Digital Sky Survey ◽  
Density Profiles ◽  
Peculiar Velocities ◽  
Sky Survey ◽  
Space Data

AbstractCosmic voids are becoming key players in testing the physics of our Universe. Here we concentrate on the abundances and the dynamics of voids as these are among the best candidates to provide information on cosmological parameters. Cai, Padilla & Li (2014) use the abundance of voids to tell apart Hu & Sawicki f(R) models from General Relativity. An interesting result is that even though, as expected, voids in the dark matter field are emptier in f(R) gravity due to the fifth force expelling away from the void centres, this result is reversed when haloes are used to find voids. The abundance of voids in this case becomes even lower in f(R) compared to GR for large voids. Still, the differences are significant and this provides a way to tell apart these models. The velocity field differences between f(R) and GR, on the other hand, are the same for halo voids and for dark matter voids. Paz et al. (2013), concentrate on the velocity profiles around voids. First they show the necessity of four parameters to describe the density profiles around voids given two distinct void populations, voids-in-voids and voids-in-clouds. This profile is used to predict peculiar velocities around voids, and the combination of the latter with void density profiles allows the construction of model void-galaxy cross-correlation functions with redshift space distortions. When these models are tuned to fit the measured correlation functions for voids and galaxies in the Sloan Digital Sky Survey, small voids are found to be of the void-in-cloud type, whereas larger ones are consistent with being void-in-void. This is a novel result that is obtained directly from redshift space data around voids. These profiles can be used to remove systematics on void-galaxy Alcock-Pacinsky tests coming from redshift-space distortions.

Right on Time: An Electoral Audit for the Publication of Vote Results

2019 ◽  
Vol 10 (2) ◽  
pp. 137-186
Author(s):  
Leonardo Antenangeli ◽  
Francisco Cantú
Keyword(s):  
Presidential Election ◽  
Counting Process ◽  
Time Span ◽  
Systematic Effect ◽  
Potential Bias ◽  
Electoral Outcome ◽  
Administrative Capacity ◽  
Electoral Outcomes ◽  
The Moment ◽  
Do So

Abstract The publication of electoral results in real time is a common practice in contemporary democracies. However, delays in the reporting of electoral outcomes often stir up skepticism and suspicion in the vote-counting process. This issue urges us to construct a systematic test to distinguish delays attributable to manipulation to those resulting from a limited administrative capacity. This paper proposes a method to assess the potential sorting of the electoral results given the moment at which polling stations publish their vote totals. To do so, we model the time span for a polling station to report its electoral results, to identify those observations whose reported times are poorly explained by the model, and to assess a potential bias in the candidates’ vote trends. We illustrate this method by analyzing the 2006 Presidential Election in Mexico, a contest that aroused suspicion from opposition parties and public opinion alike regarding how the electoral results were reported. The results suggest that polling stations’ time logs mostly respond to their specific geographic, logistic, and sociodemographic features. Moreover, those observations that took longer than expected to report their returns had no systematic effect on the electoral outcome. The proposed method can be used as an additional post-election audit to help officials and party representatives evaluate the integrity of an election.

Combining simulations and physical observations to estimate cosmological parameters

2018 ◽  
Author(s):  
Dave Higdon ◽  
Katrin Heitmann ◽  
Charles Nakhleh ◽  
Salman Habib
Keyword(s):  
Cold Dark Matter ◽  
Cosmological Parameters ◽  
Sloan Digital Sky Survey ◽  
Microwave Background ◽  
Statistical Framework ◽  
Sky Survey ◽  
Simulation Results ◽  
Computationally Intensive ◽  
Diverse Data ◽  
The Universe

This article focuses on the use of a Bayesian approach that combines simulations and physical observations to estimate cosmological parameters. It begins with an overview of the Λ-cold dark matter (CDM) model, the simplest cosmological model in agreement with the cosmic microwave background (CMB) and largescale structure analysis. The CDM model is determined by a small number of parameters which control the composition, expansion and fluctuations of the universe. The present study aims to learn about the values of these parameters using measurements from the Sloan Digital Sky Survey (SDSS). Computationally intensive simulation results are combined with measurements from the SDSS to infer about a subset of the parameters that control the CDM model. The article also describes a statistical framework used to determine a posterior distribution for these cosmological parameters and concludes by showing how it can be extended to include data from diverse data sources.

scholarly journals Synthetic simulations of the extragalactic sky seen by eROSITA

2018 ◽  
Vol 617 ◽  
pp. A92 ◽  
Author(s):  
N. Clerc ◽  
M. E. Ramos-Ceja ◽  
J. Ridl ◽  
G. Lamer ◽  
H. Brunner ◽  
...  
Keyword(s):  
Galaxy Clusters ◽  
Detection Efficiency ◽  
Photon Emission ◽  
Cosmological Parameters ◽  
Galaxy Cluster ◽  
Selection Function ◽  
Selection Effects ◽  
Source Detection ◽  
Telescope Array ◽  
X Ray

Context. Studies of galaxy clusters provide stringent constraints on models of structure formation. Provided that selection effects are under control, large X-ray surveys are well suited to derive cosmological parameters, in particular those governing the dark energy equation of state. Aims. We forecast the capabilities of the all-sky eROSITA (extended ROentgen Survey with an Imaging Telescope Array) survey to be achieved by the early 2020s. We bring special attention to modelling the entire chain from photon emission to source detection and cataloguing. Methods. The selection function of galaxy clusters for the upcoming eROSITA mission is investigated by means of extensive and dedicated Monte-Carlo simulations. Employing a combination of accurate instrument characterisation and a state-of-the-art source detection technique, we determine a cluster detection efficiency based on the cluster fluxes and sizes. Results. Using this eROSITA cluster selection function, we find that eROSITA will detect a total of approximately 105 clusters in the extra-galactic sky. This number of clusters will allow eROSITA to put stringent constraints on cosmological models. We show that incomplete assumptions on selection effects, such as neglecting the distribution of cluster sizes, induce a bias in the derived value of cosmological parameters. Conclusions. Synthetic simulations of the eROSITA sky capture the essential characteristics impacting the next-generation galaxy cluster surveys and they highlight parameters requiring tight monitoring in order to avoid biases in cosmological analyses.

scholarly journals Cosmological Parameters from Eigenmode Analysis of Sloan Digital Sky Survey Galaxy Redshifts

2005 ◽  
Vol 216 ◽  
pp. 129-139
Author(s):  
Alexander Szalay ◽  
Adrian Pope ◽  
Takahiko Matsubara ◽  
Michael R. Blanton ◽  
Daniel J. Eisenstein ◽  
...  
Keyword(s):  
Maximum Likelihood ◽  
Power Spectrum ◽  
Linear Theory ◽  
Excellent Agreement ◽  
Cosmological Parameters ◽  
Density Fluctuations ◽  
Sloan Digital Sky Survey ◽  
Sky Survey ◽  
Eigenmode Analysis ◽  
Karhunen Loeve Transform

We present estimates of cosmological parameters from the application of the Karhunen-Loève transform to the analysis of the 3D power spectrum of density fluctuations using Sloan Digital Sky Survey galaxy redshifts. We use Ωmh and fb = Ωb/Ωm to describe the shape of the power spectrum, σL8g for the (linearly extrapolated) normalization, and β to parametrize linear theory redshift space distortions. on scales k ≤ 0.16hMpc--1, our maximum likelihood values are Ωmh = 0.264 ± 0.043, fb = 0.286 ± 0.065, σL8g = 0.966 ± 0.048, and β = 0.45 ± 0.12. When we take a prior on Ωb from WMAP, we find Ωmh = 0.207 ± 0.030, which is in excellent agreement with WMAP and 2dF. This indicates that we have reasonably measured the gross shape of the power spectrum but we have difficulty breaking the degeneracy between and Ωmh and fb because the baryon oscillations are not resolved in the current spectroscopic survey window function.

scholarly journals Far-IR Galaxy Counts Expected in the Iris Survey

1999 ◽  
Vol 186 ◽  
pp. 486-486
Author(s):  
T.T. Takeuchi ◽  
H. Hirashita ◽  
T. G. Hattori ◽  
K. Ohta ◽  
H. Shibai
Keyword(s):  
Simple Model ◽  
Galaxy Evolution ◽  
Infrared Imaging ◽  
Cosmological Parameters ◽  
Flux Limit ◽  
Sky Survey

Infrared Imaging Surveyor (IRIS, officially Astro-F) is a satellite which will be launched in the winter of 2003. The main purpose of the IRIS mission is an all sky survey in the mid- and far-IR with a flux limit much deeper than that of IRAS. In order to examine the performance of the survey and to find a suitable set of bandpasses for tracing galaxy evolution and picking up protogalaxy candidates as effective as possible using IRIS, we estimated the FIR galaxy counts based on a simple model with various sets of cosmological parameters and evolution types.

On the connection between cosmological parameters and peculiar motion in a G2 massless scalar field spacetime

2021 ◽  
pp. 2150099
Author(s):  
Daniele Gregoris
Keyword(s):  
Scalar Field ◽  
Turning Point ◽  
Cosmological Parameters ◽  
Energy Scale ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Peculiar Velocity ◽  
Astronomical Object ◽  
Peculiar Motion ◽  
Matter Flow

The geodesic motion of a massive test particle in a [Formula: see text] massless scalar field universe is investigated. The time evolution of the peculiar velocity is connected to the values of the cosmological parameters, and it is quantified how the spacetime shearing effects affect the deviations from the asymptotic value of comoving matter flow at late epochs. On the other hand, it is shown that the energy scale of the cosmic fluid does not affect the evolution of the peculiar velocity. The existence of a turning point in the motion of the astronomical object is identified. The potential astrophysical relevance of this study in the modeling of cosmic filaments and Large Quasar Groups is briefly discussed.

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