Optimal identification of H ii regions during reionization in 21-cm observations

Giri, Sambit K.; Mellema, Garrelt; Ghara, Raghunath

doi:10.1093/mnras/sty1786

Cited by 62 publications

(54 citation statements)

References 53 publications

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“…In Giri et al (2018b), we presented a method to identify the ionized region in noisy 21-cm observation during the EoR, called superpixels. Below we briefly describe the procedure to create the superpixels and the criteria used to identify superpixels containing ionized regions.…”

Section: Structure Identificationmentioning

confidence: 99%

Neutral island statistics during reionization from 21-cm tomography

Giri

Mellema

Aldheimer

et al. 2019

Monthly Notices of the Royal Astronomical Society

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We present the prospects of extracting information about the Epoch of Reionization by identifying the remaining neutral regions, referred to as islands, in tomographic observations of the redshifted 21-cm signal. Using simulated data sets we show that at late times the 21-cm power spectrum is fairly insensitive to the details of the reionization process but that the properties of the neutral islands can distinguish between different reionization scenarios. We compare the properties of these islands with those of ionized bubbles. At equivalent volume filling fractions, neutral islands tend to be fewer in number but larger compared to the ionized bubbles. In addition, the evolution of the size distribution of neutral islands is found to be slower than that of the ionized bubbles and also their percolation behaviour differs substantially. Even though the neutral islands are relatively rare, they will be easier to identify in observations with the low frequency component of the Square Kilometre Array (SKA-Low) due to their larger size and the lower noise levels at lower redshifts. The size distribution of neutral islands at the late stages of reionization is found to depend on the source properties, such as the ionizing efficiency of the sources and their minimum mass. We find the longest line of sight through a neutral region to be more than 100 comoving Mpc until very late stages (90-95 per cent reionized), which may have relevance for the long absorption trough at z = 5.6 − 5.8 in the spectrum of quasar ULAS J0148+0600.

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Section: Structure Identificationmentioning

confidence: 99%

Neutral island statistics during reionization from 21-cm tomography

Giri

Mellema

Aldheimer

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…(12) In order to enhance the convergence of MCMC chains, we set the amplitudes of all the independent peaks in the power spectrum equal to the maximum amplitude and set the amplitudes of combination frequencies and noise to be zero. Since the peaks are generally clustered into groups, we analysed them with a 1-D k-means clustering algorithm (MacQueen 1967;Wu 2010), which is a common and powerful clustering algorithm used in unsupervised machine learning (see two applications in Giri et al 2018;Rahmani et al 2018). We used six frequency groups and in each group we included the pattern around the highest peak if the number of independent frequencies within the group was larger than four, since there are three free parameters in Equ 8 (P0, ∆P0, and Σ).…”

Section: Cross-correlation and Mcmcmentioning

confidence: 99%

Period spacings of γ Doradus pulsators in theKeplerfield: detection methods and application to 22 slow rotators

Bedding

Murphy

et al. 2018

Monthly Notices of the Royal Astronomical Society

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In γ Doradus stars, the g-mode period spacing shows an approximately linear relation with period. The slope is a new asteroseismic diagnostic, related to the rotation rate and the azimuthal order m. We report two automated methods, the 'moving-window Fourier transform' and the 'cross-correlation', to detect and measure the period spacings based on four-year light curves from the Kepler satellite. The results show that the cross-correlation method performs better at detecting the period spacings and their slopes. In this paper, we apply our method to 22 γ Dor stars with g-mode multiplets split by rotation. The rotation periods are similar to the g-mode period spacings, causing the multiplets to overlap. To clarify the overlapping patterns, we use theéchelle diagram and introduce a 'copy-shift' diagram to discern and measure the splittings. The first observational relation between slopes and splittings is shown. The slope deviates from zero when the splitting increases, as the theory predicts. We found that what appears to be rotational splittings in two stars is in fact caused by two nearly-identical overlapping patterns from binaries.

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“…We follow the method given in Ghara et al (2017) and Giri et al (2018) to simulate the expected noise from the first generation of SKA-Low (hereafter SKA1-Low). Even though the construction of SKA1-Low has not started, the distribution of antennae is being planned.…”

Section: Telescope Noisementioning

confidence: 99%

Redshift-space distortions in simulations of the 21-cm signal from the cosmic dawn

Ross

Giri

Mellema

et al. 2021

Monthly Notices of the Royal Astronomical Society

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The 21-cm signal from the Cosmic Dawn (CD) is likely to contain large fluctuations, with the most extreme astrophysical models on the verge of being ruled out by observations from radio interferometers. It is therefore vital that we understand not only the astrophysical processes governing this signal, but also other inherent processes impacting the signal itself, and in particular line-of-sight effects. Using our suite of fully numerical radiative transfer simulations, we investigate the impact on the redshifted 21-cm from the CD from one of these processes, namely the redshift-space distortions (RSDs). When RSDs are added, the resulting boost to the power spectra makes the signal more or equally detectable for our models for all redshifts, further strengthening hopes that a power spectra measurement of the CD will be possible. RSDs lead to anisotropy in the signal at the beginning and end of the CD, but not while X-ray heating is underway. The inclusion of RSDs, however, decreases detectability of the non-Gaussianity of fluctuations from inhomogeneous X-ray heating as measured by the skewness and kurtosis. On the other hand, mock observations created from all our simulations that include telescope noise corresponding to 1000 hours of observation with the Square Kilometre Array telescope show that we may be able image the CD for all heating models considered and suggest RSDs dramatically boost fluctuations coming from the inhomogeneous Ly-α background.

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Optimal identification of H ii regions during reionization in 21-cm observations

Cited by 62 publications

References 53 publications

Neutral island statistics during reionization from 21-cm tomography

Neutral island statistics during reionization from 21-cm tomography

Period spacings of γ Doradus pulsators in theKeplerfield: detection methods and application to 22 slow rotators

Redshift-space distortions in simulations of the 21-cm signal from the cosmic dawn

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