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July - December 2014

Chandrasekhar's Relation and Stellar Rotation in the Kepler Field

J. R. P. Silva1, B. B. Soares, and D. B. de Freitas

According to the statistical law of large numbers, the expected mean of identically distributed random variables of a sample tends toward the actual mean as the sample increases. Under this law, it is possible to test the Chandrasekhar's relation (C ...
Statistical and systematic uncertainties in pixel-based source reconstruction algorithms for gravitational lensing

Tagore, Amitpal S.; Keeton, Charles R.

Gravitational lens modelling of spatially resolved sources is a challenging inverse problem with many observational constraints and model parameters. We examine established pixel-based source reconstruction algorithms for de-lensing the source and c ...
Automatic detection and quantitative assessment of peculiar galaxy pairs in Sloan Digital Sky Survey

Lior Shamir, John Wallin

We applied computational tools for automatic detection of peculiar galaxy pairs. We first detected in SDSS DR7 ∼400,000 galaxy images with i magnitude <18 that had more than one point spread function, and then applied a machine learning algorithm ...
Measuring galaxy morphology at z>1. I - calibration of automated proxies

M. Huertas-Company, S. Kaviraj, S. Mei, R.W. O'Connell, R. Windhorst, S.H. Cohen, .P. Hathi, A.M. Koekemoer, R. Licitra, A. Raichoor, M.J. Rutkowski

New near-infrared surveys, using the HST, offer an unprecedented opportunity to study rest-frame optical galaxy morphologies at z>1 and to calibrate automated morphological parameters that will play a key role in classifying future massive datasets ...
Matched filter optimization of kSZ measurements with a reconstructed cosmological flow field

Li, Ming; Angulo, R. E.; White, S. D. M.; Jasche, J.

We develop and test a new statistical method to measure the kinematic Sunyaev-Zel'dovich (kSZ) effect. A sample of independently detected clusters is combined with the cosmic flow field predicted from a galaxy redshift survey in order to derive a ma ...
Bayesian inferences of galaxy formation from the K-band luminosity and H I mass functions of galaxies: constraining star formation and feedback

Lu, Yu; Mo, H. J.; Lu, Zhankui; Katz, Neal; Weinberg, Martin D.

We infer mechanisms of galaxy formation for a broad family of semi-analytic models (SAMs) constrained by the K-band luminosity function and H I mass function of local galaxies using tools of Bayesian analysis. Even with a broad search in parameter s ...
Fundamental stellar parameters and metallicities from Bayesian spectroscopy: application to low- and high-resolution spectra

Schönrich, Ralph; Bergemann, Maria

We present a unified framework to derive fundamental stellar parameters by combining all available observational and theoretical information for a star. The algorithm relies on the method of Bayesian inference, which for the first time directly inte ...
Direct Minkowski Functional analysis of large redshift surveys: a new high-speed code tested on the luminous red galaxy Sloan Digital Sky Survey-DR7 catalogue

Wiegand, Alexander; Buchert, Thomas; Ostermann, Matthias

As deeper galaxy catalogues are soon to come, it becomes even more important to measure large-scale fluctuations in the catalogues with robust statistics that cover all moments of the galaxy distribution. In this paper, we reinforce a direct analysi ...
Supervised Detection of Anomalous Light Curves in Massive Astronomical Catalogs

Nun, Isadora; Pichara, Karim; Protopapas, Pavlos; Kim, Dae-Won

The development of synoptic sky surveys has led to a massive amount of data for which resources needed for analysis are beyond human capabilities. In order to process this information and to extract all possible knowledge, machine learning technique ...
Exhausting the information: novel Bayesian combination of photometric redshift PDFs

Carrasco Kind, Matias; Brunner, Robert J.

The estimation and utilization of photometric redshift probability density functions (photo-z PDFs) have become increasingly important over the last few years and currently there exist a wide variety of algorithms to compute photo-z's, each with the ...
Estimating cosmological parameter covariance

Taylor, Andy; Joachimi, Benjamin

We investigate the bias and error in estimates of the cosmological parameter covariance matrix due to sampling or modelling the data covariance matrix, for likelihood width and peak scatter estimators. We show that these estimators do not coincide u ...
Removing beam asymmetry bias in precision CMB temperature and polarization experiments

Wallis, Christopher G. R.; Brown, Michael L.; Battye, Richard A.; Pisano, Giampaolo; Lamagna, Luca

Asymmetric beams can create significant bias in estimates of the power spectra from cosmic microwave background (CMB) experiments. With the temperature power spectrum many orders of magnitude stronger than the B-mode power spectrum, any systematic e ...
A new analysis of quasar polarization alignments

Pelgrims, V.; Cudell, J. R.

We propose a new method to analyse the alignment of optical polarization vectors from quasars. This method leads to a definition of intrinsic preferred axes and to a determination of the probability pσ that the distribution of polarization directio ...
A new method of reconstructing VHE γ-ray spectra: the Template Background Spectrum

Virgílio Fernandes, Milton; Horns, Dieter; Kosack, Karl; Raue, Martin; Rowell, Gavin

Context. Very-high-energy (VHE, E > 0.1 TeV) γ-ray emission regions with angular extents comparable to the field-of-view of current imaging air-Cherenkov telescopes (IACT) require additional observations of source-free regions to estimate the backg ...
A deconvolution extraction method for 2D multi-object fibre spectroscopy based on the regularized least-squares QR-factorization algorithm

Yu, Jian; Yin, Qian; Guo, Ping; Luo, A.-li

This paper presents an efficient method for the extraction of astronomical spectra from two-dimensional (2D) multifibre spectrographs based on the regularized least-squares QR-factorization (LSQR) algorithm. We address two issues: we propose a modif ...
Deriving structural parameters of semi-resolved star clusters. FitClust: a program for crowded fields

Narbutis, D.; Semionov, D.; Stonkutė, R.; de Meulenaer, P.; Mineikis, T.; Bridžius, A.; Vansevičius, V.

Context. An automatic tool to derive structural parameters of semi-resolved star clusters located in crowded stellar fields in nearby galaxies is needed for homogeneous processing of archival frames. Aims: We have developed a program that automati ...
SpArcFiRe: Scalable Automated Detection of Spiral Galaxy Arm Segments

Davis, Darren R.; Hayes, Wayne B.

Given an approximately centered image of a spiral galaxy, we describe an entirely automated method that finds, centers, and sizes the galaxy (possibly masking nearby stars and other objects if necessary in order to isolate the galaxy itself) and the ...
Constraining the epoch of reionization with the variance statistic: simulations of the LOFAR case

Patil, Ajinkya H.; Zaroubi, Saleem; Chapman, Emma; Jelić, Vibor; Harker, Geraint; Abdalla, Filipe B.; Asad, Khan M. B.; Bernardi, Gianni; Brentjens, Michiel A.; de Bruyn, A. G.; Bus, Sander; Ciardi, Benedetta; Daiboo, Soobash; Fernandez, Elizabeth R.; Ghosh, Abhik; Jensen, Hannes; Kazemi, Sanaz; Koopmans, Léon V. E.; Labropoulos, Panagiotis; Mevius, Maaijke; Martinez, Oscar; Mellema, Garrelt; Offringa, Andre R.; Pandey, Vishhambhar N.; Schaye, Joop; Thomas, Rajat M.; Vedantham, Harish K.; Veligatla, Vamsikrishna; Wijnholds, Stefan J.; Yatawatta, Sarod

Several experiments are underway to detect the cosmic-redshifted 21-cm signal from neutral hydrogen from the Epoch of Reionization (EoR). Due to their very low signal-to-noise ratio, these observations aim for a statistical detection of the signal b ...
Resolving the mass-anisotropy degeneracy of the spherically symmetric Jeans equation - II. Optimum smoothing and model validation

Diakogiannis, Foivos I.; Lewis, Geraint F.; Ibata, Rodrigo A.

The spherical Jeans equation is widely used to estimate the mass content of stellar systems with apparent spherical symmetry. However, this method suffers from a degeneracy between the assumed mass density and the kinematic anisotropy profile, β(r) ...
Periodic radio variabilities of the blazar 1156+295: harmonic oscillations

Wang, Jun-Yi; An, Tao; Baan, Willem A.; Lu, Xiang-Long

(Quasi)-periodic oscillations of the radio luminosity of a typical blazar 1156+295 were analysed to investigate the dynamic processes associated with the central engine of the active galactic nucleus. Three numerical techniques, the Lomb-Scargle per ...