Authors: Arnab Mishra, Kanan K. Datta, Chandra Shekhar Murmu, Samir Choudhuri, Iffat Nasreen, Snehasish Saha
First author institution: Center for Relativity and Cosmology Research, Department of Physics, Jadavpur University, India.
Status: Available on ArXiv
In the early universe, gravitational forces allowed clumps of matter to collapse to form the first stars and galaxies. The radiation from these first stars and galaxies formed and can be observed today in distant parts of the universe marked an era called “.”cosmic dawn‘. The high-energy photons of the first stars in the universe ionized the neutral atoms (such as hydrogen) around them. This process is explained as follows: “Reionization” (look Figure 1 of this byte for explanation).
The dawn and reionization of the universe (also known as the Era of Reionization, or EoR) is of great interest to scientists. Studying EoR signatures It helps you learn about the first stars that formed, the formation of the first galaxies, and changes in the intergalactic medium. It informs our understanding of cosmology and helps us understand the presence and abundance of dark matter and dark energy in the universe.
Since the existence of radiation from the beginning of the universe, redshifted This signal actually needs to be searched at a long (radio) wavelength (because the wavelength has been stretched). telescope like square kilometer array (SKA) This is currently in the early stages of development, using two radio telescopes – the SKA-low array in Western Australia and the SKA-mid in South Africa – to measure radiation from the early Universe and allow us to see the signature of EoR. The idea is 21cm radiation (redshifted to radio wavelengths) It originates from cold, neutral hydrogen gas. This radioactive hydrogen gas is ionized during EoR and a bubble-like region grows. This example has been studied in the literature and a nice video is shown. here.
The authors of today’s paper attempt to address the challenges that are expected to arise when measuring signals from these bubbles. All telescopes produce instrument noise, which makes detection difficult. process such as synchrotron Radiation that occurs within our galaxy (particles are accelerated by magnetic fields and emit high-frequency radiation) can affect our ability to discern weak EoR signals (commonly, radiation from our galaxy is called the galactic foreground). The authors study the capabilities of an algorithm called . matched filter We attempt to detect the expected EoR signal from these affected noisy data.
Studying the efficiency of matched filter algorithms
The authors focus on creating simulations of observations by the radio interferometer SKA-low (this Click here for video (This is a nice visual example of how this works). They create mock grids in a simulation box and study different configurations of the telescope. The telescope under construction will have multiple “stations” (clusters of antennas) spread across the globe. Murchison Desert. Depending on the station being used or the configuration of stations available, Fourier space The information sampled by the telescopes is different and affects the ability to measure the EoR signal. In general, the more observation points, the better. Some of the antenna configurations that will exist during the construction phase are shown in Figure 1 below.
The authors create simulations of different “scenarios” of ionized gas “bubbles” forming during EoR. They study cases where bubbles of ionized gas form around them. quasaranother scenario where a bubble forms around galaxy cluster And another quasar scenario, but in a more speckled bubble environment. These incorporate the influence of galactic foregrounds and radio-radiated point sources into simulated data. Their inclusion ensures that the effects of these contaminants are included in the analysis. Noise from the instruments is also included using the studied sensitivity and noise of the SKA-low telescope.
of matched filter estimator calculate cross-correlation the rest visibility signal Use expected EoR signal encoded with matched filter (These visibilities are the Fourier transform of the sky radiation intensity after the EoR signal has been separated). The visibility data collected from the telescope can be compared to a matched filter template of the EoR signal and an attempt can be made to maximize the signal-to-noise ratio of the cross-correlation. This depends on variables such as bubble radius that can be changed to change the template signal.
Computational efficiency, detectability, and parameter estimation
Because a large number of data points are collected from the SKA-low configuration, computing the matched filter estimator can be computationally expensive. To address this, the authors map the modes in the data onto a grid and use this to compute matched filter estimators. This approach results in a slightly lower signal-to-noise ratio for the measurements. However, we found that this approach allows us to obtain a maximum signal-to-noise ratio corresponding to the expected bubble size in the different scenarios studied. Some results of applying this approach are shown in Figure 2. Despite the low signal-to-noise ratio, this approach performs reasonably well and saves computational costs. They also compare new and improved approaches to remove the galactic foreground that obscures the EoR signal.
This estimator not only works well to obtain the accurate peak of the signal-to-noise ratio, but also reaches an acceptable threshold for the detection of ionized bubbles. They also show that a new and improved approach to dealing with the galactic foreground improves the signal-to-noise ratio. They also study relationships and provide relationships that relate things like bubble size to signal-to-noise ratio for fast retrieval.
The authors MCMC algorithm (These algorithms allow us to estimate probability distributions of parameters from our data by constraining bubble properties (such as size and redshift) for different scenarios. They show that bubble properties can indeed be constrained by the SKA-low configuration and determine appropriate scaling relationships.
summary
The authors showed that the SKA-low telescope can detect ionized bubbles as a signature of EoR. Primarily, as the telescope configuration becomes more developed, it will be possible to detect these bubbles in just about 100 hours of observation time with the telescope. The scaling relationships they derived can also help scientists better plan their observations.
Editor: Sokya Shanbhog
Featured image credit: Galaxies during the reionization era of the early universe (simulation), by M. Alvarez (http://www.cita.utoronto.ca/~malvarez), R. Kaehler, and T. Abel, CC BY 4.0
