scholarly journals Detailed study of ELAIS N1 field with the uGMRT – II. Source properties and spectral variation of foreground power spectrum from 300–500 MHz observations

2019 ◽  
Vol 490 (1) ◽  
pp. 243-259 ◽  
Author(s):  
Arnab Chakraborty ◽  
Nirupam Roy ◽  
Abhirup Datta ◽  
Samir Choudhuri ◽  
Kanan K Datta ◽  
...  
Keyword(s):  
Power Spectrum ◽  
Spectral Characteristics ◽  
Low Frequency ◽  
Neutral Hydrogen ◽  
Galactic Nuclei ◽  
Detailed Comparison ◽  
Spectral Variation ◽  
Angular Power Spectrum ◽  
Star Forming ◽  
First Time

ABSTRACT Understanding the low-frequency radio sky in depth is necessary to subtract foregrounds in order to detect the redshifted 21 cm signal of neutral hydrogen from the cosmic dawn, the epoch of reionization and the post-reionization era. In this second paper of the series, we present the upgraded Giant Metrewave Radio Telescope (uGMRT) observation of the ELAIS N1 field made at 300–500 MHz. The image covers an area of ∼1.8 deg2 and has a central background rms noise of ∼ 15 μJy beam−1. We present a radio source catalogue containing 2528 sources (with flux densities > 100 μJy) and normalized source counts derived from that. A detailed comparison of detected sources with previous radio observations is shown. We discuss flux-scale accuracy, positional offsets, spectral index distribution and correction factors in source counts. The normalized source counts are in agreement with previous observations of the same field, as well as model source counts from the Square Kilometre Array Design Study simulation. It shows a flattening below ∼1 mJy that corresponds to a rise in populations of star-forming galaxies and radio-quiet active galactic nuclei. For the first time, we estimate the spectral characteristics of the angular power spectrum or multi-frequency angular power spectrum of diffuse Galactic synchrotron emission over a wide frequency bandwidth of 300–500 MHz from radio interferometric observations. This work demonstrates the improved capabilities of the uGMRT.

scholarly journals Characterizing EoR foregrounds: a study of the Lockman Hole region at 325 MHz

2020 ◽  
Vol 495 (4) ◽  
pp. 4071-4084
Author(s):  
Aishrila Mazumder ◽  
Arnab Chakraborty ◽  
Abhirup Datta ◽  
Samir Choudhuri ◽  
Nirupam Roy ◽  
...  
Keyword(s):  
Power Law ◽  
Galactic Plane ◽  
Low Frequency ◽  
Detailed Comparison ◽  
Data Sets ◽  
Diffuse Emission ◽  
Angular Power Spectrum ◽  
Power Law Index ◽  
First Time ◽  
Lockman Hole

ABSTRACT One of the key science goals for the most sensitive telescopes, both current and upcoming, is the detection of the redshifted 21-cm signal from the Cosmic Dawn and Epoch of Reionization. The success of detection relies on accurate foreground modelling for their removal from data sets. This paper presents the characterization of astrophysical sources in the Lockman Hole region. Using 325-MHz data obtained from the Giant Metrewave Radio Telescope, a 6° × 6° mosaiced map is produced with an rms reaching 50 μJy per beam. A source catalogue containing 6186 sources is created, and the Euclidean normalized differential source counts have been derived from it, consistent with previous observations as well as simulations. A detailed comparison of the source catalogue is also made with previous findings – at both lower and higher frequencies. The angular power spectrum (APS) of the diffuse Galactic synchrotron emission is determined for three different Galactic latitudes using the tapered gridded estimator. The values of the APS lie between ∼1 and ∼100 mK2. Fitting a power law of the form Aℓ−β gives values of A and β varying across the latitudes considered. This paper demonstrates, for the first time, the variation of the power-law index for diffuse emission at very high Galactic locations. It follows the same trend that is seen at locations near the Galactic plane, thus emphasizing the need for low-frequency observations for developing better models of the diffuse emission.

scholarly journals Demonstrating the Tapered Gridded Estimator (TGE) for the Cosmological HI 21-cm Power Spectrum using 150 MHz GMRT observations

2020 ◽  
Author(s):  
Srijita Pal ◽  
Somnath Bharadwaj ◽  
Abhik Ghosh ◽  
Samir Choudhuri
Keyword(s):  
Power Spectrum ◽  
Unbiased Estimate ◽  
Power Spectra ◽  
Neutral Hydrogen ◽  
Statistical Error ◽  
Temperature Fluctuations ◽  
Radio Frequency Interference ◽  
Rectangular Region ◽  
Angular Power Spectrum ◽  
The Mean

Abstract We apply the Tapered Gridded Estimator (TGE) for estimating the cosmological 21-cm power spectrum from 150 MHz GMRT observations which corresponds to the neutral hydrogen (HI) at redshift z = 8.28. Here TGE is used to measure the Multi-frequency Angular Power Spectrum (MAPS) Cℓ(Δν) first, from which we estimate the 21-cm power spectrum P(k⊥, k∥). The data here are much too small for a detection, and the aim is to demonstrate the capabilities of the estimator. We find that the estimated power spectrum is consistent with the expected foreground and noise behaviour. This demonstrates that this estimator correctly estimates the noise bias and subtracts this out to yield an unbiased estimate of the power spectrum. More than $47\%$ of the frequency channels had to be discarded from the data owing to radio-frequency interference, however the estimated power spectrum does not show any artifacts due to missing channels. Finally, we show that it is possible to suppress the foreground contribution by tapering the sky response at large angular separations from the phase center. We combine the k modes within a rectangular region in the ‘EoR window’ to obtain the spherically binned averaged dimensionless power spectra Δ2(k) along with the statistical error σ associated with the measured Δ2(k). The lowest k-bin yields Δ2(k) = (61.47)2 K2 at k = 1.59 Mpc−1, with σ = (27.40)2 K2. We obtain a 2 σ upper limit of (72.66)2 K2 on the mean squared HI 21-cm brightness temperature fluctuations at k = 1.59 Mpc−1.

scholarly journals Validating a novel angular power spectrum estimator using simulated low frequency radio-interferometric data

New Astronomy ◽  
2017 ◽  
Vol 57 ◽  
pp. 94-103 ◽  
Author(s):  
Samir Choudhuri ◽  
Nirupam Roy ◽  
Somnath Bharadwaj ◽  
Sk. Saiyad Ali ◽  
Abhik Ghosh ◽  
...  
Keyword(s):  
Power Spectrum ◽  
Low Frequency ◽  
Angular Power Spectrum

scholarly journals Subtraction of Bright Point Sources from Synthesis Images of the Epoch of Reionization

2011 ◽  
Vol 28 (1) ◽  
pp. 46-57 ◽  
Author(s):  
B. Pindor ◽  
J. S. B. Wyithe ◽  
D. A. Mitchell ◽  
S. M. Ord ◽  
R. B. Wayth ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Dynamic Range ◽  
Low Frequency ◽  
Neutral Hydrogen ◽  
Galactic Nuclei ◽  
Point Sources ◽  
Field Of View ◽  
Bright Point ◽  
Line Of Sight ◽  
Diffuse Background

AbstractBright point sources associated with extragalactic active galactic nuclei and radio galaxies are an important foreground for low-frequency radio experiments aimed at detecting the redshifted 21-cm emission from neutral hydrogen during the epoch of reionization. The frequency dependence of the synthesized beam implies that the sidelobes of these sources will move across the field of view as a function of observing frequency, hence frustrating line-of-sight foreground subtraction techniques. We describe a method for subtracting these point sources from dirty maps produced by an instrument such as the MWA. This technique combines matched filters with an iterative centroiding scheme to locate and characterize point sources in the presence of a diffuse background. Simulations show that this technique can improve the dynamic range of epoch-of-reionization maps by 2—3 orders of magnitude.

scholarly journals Fundamental differences in the radio properties of red and blue quasars: insight from the LOFAR Two-metre Sky Survey (LoTSS)

2020 ◽  
Vol 494 (3) ◽  
pp. 3061-3079 ◽  
Author(s):  
D J Rosario ◽  
V A Fawcett ◽  
L Klindt ◽  
D M Alexander ◽  
L K Morabito ◽  
...  
Keyword(s):  
Star Formation ◽  
Control Sample ◽  
Low Frequency ◽  
Galactic Nuclei ◽  
Sloan Digital Sky Survey ◽  
Stellar Objects ◽  
Radio Detection ◽  
Sky Survey ◽  
Quasi Stellar Objects ◽  
First Time

ABSTRACT Red quasi-stellar objects (QSOs) are a subset of the luminous end of the cosmic population of active galactic nuclei (AGNs), most of which are reddened by intervening dust along the line of sight towards their central engines. In recent work from our team, we developed a systematic technique to select red QSOs from the Sloan Digital Sky Survey, and demonstrated that they have distinctive radio properties using the Faint Images of the Radio Sky at Twenty centimetres radio survey. Here we expand our study using low-frequency radio data from the LOFAR Two-metre Sky Survey (LoTSS). With the improvement in depth that LoTSS offers, we confirm key results: Compared to a control sample of normal ‘blue’ QSOs matched in redshift and accretion power, red QSOs have a higher radio detection rate and a higher incidence of compact radio morphologies. For the first time, we also demonstrate that these differences arise primarily in sources of intermediate radio loudness: Radio-intermediate red QSOs are × 3 more common than typical QSOs, but the excess diminishes among the most radio-loud systems and the most radio-quiet systems in our study. We develop Monte Carlo simulations to explore whether differences in star formation could explain these results, and conclude that, while star formation is an important source of low-frequency emission among radio-quiet QSOs, a population of AGN-driven compact radio sources is the most likely cause for the distinct low-frequency radio properties of red QSOs. Our study substantiates the conclusion that fundamental differences must exist between the red and normal blue QSO populations.

scholarly journals 21-cm power spectrum and ionization bias as a probe of long-mode modulated non-Gaussian sky

2019 ◽  
Vol 488 (4) ◽  
pp. 5941-5951
Author(s):  
Shahram Khosravi ◽  
Amirabbas Ghazizadeh ◽  
Shant Baghram
Keyword(s):  
Power Spectrum ◽  
Background Radiation ◽  
Neutral Hydrogen ◽  
Hydrogen Distribution ◽  
Microwave Background ◽  
Power Asymmetry ◽  
Angular Power Spectrum ◽  
Long Wavelength ◽  
Microwave Background Radiation ◽  
Non Gaussian

ABSTRACT The observed hemispherical power asymmetry in cosmic microwave background radiation can be explained by long-wavelength mode (long-mode) modulation. In this paper, we study the possibility of detecting this effect in the angular power spectrum of the 21-cm brightness temperature. For this task, we study the effect of the neutral hydrogen distribution on the angular power spectrum. This is done by formulating the bias parameter of the ionized fraction to the underlying matter distribution. We also discuss the possibility that the long-mode modulation is accompanied by a primordial non-Gaussianity of local type. In this case, we obtain the angular power spectrum with two effects of primordial non-Gaussianity and long-mode modulation. Finally, we show that the primordial non-Gaussianity enhances the long-mode modulated power of the 21-cm signal via the non-Gaussian scale-dependent bias up to four orders of magnitude. Accordingly, observations of the 21-cm signal with upcoming surveys, such as the Square Kilometer Array (SKA), will probably be capable of detecting hemispherical power asymmetry in the context of long-mode modulation.

scholarly journals Tapering the sky response for angular power spectrum estimation from low-frequency radio-interferometric data

2016 ◽  
Vol 459 (1) ◽  
pp. 151-156 ◽  
Author(s):  
Samir Choudhuri ◽  
Somnath Bharadwaj ◽  
Nirupam Roy ◽  
Abhik Ghosh ◽  
Sk. Saiyad Ali
Keyword(s):  
Power Spectrum ◽  
Low Frequency ◽  
Spectrum Estimation ◽  
Angular Power Spectrum ◽  
Power Spectrum Estimation

scholarly journals A very brief description of LOFAR – the Low Frequency Array

2006 ◽  
Vol 2 (14) ◽  
pp. 386-387 ◽  
Author(s):  
Heino D. Falcke ◽  
Michiel P. van Haarlem ◽  
A. Ger de Bruyn ◽  
Robert Braun ◽  
Huub J.A. Röttgering ◽  
...  
Keyword(s):  
Low Frequency ◽  
Neutral Hydrogen ◽  
High Energy ◽  
Short Term ◽  
First Stars ◽  
High Energy Cosmic Rays ◽  
Radio Detection ◽  
First Time ◽  
X Ray Binaries ◽  
The Universe

AbstractLOFAR (Low Frequency Array) is an innovative radio telescope optimized for the frequency range 30–240 MHz. The telescope is realized as a phased aperture array without any moving parts. Digital beam forming allows the telescope to point to any part of the sky within a second. Transient buffering makes retrospective imaging of explosive short-term events possible. The scientific focus of LOFAR will initially be on four key science projects (KSPs): (i) Detection of the formation of the very first stars and galaxies in the universe during the so-called epoch of reionization by measuring the power spectrum of the neutral hydrogen 21-cm line (Shaver et al. 1999) on the ∼ 5′ scale; (ii) Low-frequency surveys of the sky with of order 108 expected new sources; (iii) All-sky monitoring and detection of transient radio sources such as γ-ray bursts, X-ray binaries, and exo-planets (Farrell et al. 2004); and (iv) Radio detection of ultra-high energy cosmic rays and neutrinos (Falcke & Gorham 2003) allowing for the first time access to particles beyond 1021 eV (Scholten et al. 2006). Apart from the KSPs open access for smaller projects is also planned. Here we give a brief description of the telescope.

scholarly journals A METHOD TO EXTRACT THE ANGULAR POWER SPECTRUM OF THE EPOCH OF REIONIZATION FROM LOW-FREQUENCY RADIO INTERFEROMETERS

2012 ◽  
Vol 758 (1) ◽  
pp. L24 ◽  
Author(s):  
Qian Zheng ◽  
Xiang-Ping Wu ◽  
Jun-Hua Gu ◽  
Jingying Wang ◽  
Haiguang Xu
Keyword(s):  
Power Spectrum ◽  
Low Frequency ◽  
Angular Power Spectrum
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