We describe a simulation for the distribution of galaxies focusing on the atomic Hydrogen content. We aim to make predictions for surveys of galaxies using the redshifted 21 cm line emission. We take the expected distribution of HI masses, circular velocities, sizes of galaxies and orientations into account for this simulation. We use the sensitivity of ASKAP and MeeKAT radio telescopes to estimate the number of detections of HI galaxies in upcoming surveys. We validate our simulation with earlier estimates carried out by using some of these considerations. We show that unlike earlier simulations that take some of the factors into account, the predicted number of galaxies and their distribution across masses changes significantly when all of these are accounted for. We describe our predictions for the MIGHTEE-HI and WALLABY surveys for blind detection of galaxies using the redshifted 21 cm radiation. We study the dependence of the predicted number of detections on the HI mass function. We also describe our future plans for improving the simulation.
Single-dish HI Intensity Mapping with the SKAO: Precursor Progress with MeerKAT's Large Area Synoptic Survey (MeerKLASS)
University of Portsmouth（朴茨茅斯大学）；The University of Manchester（曼彻斯特大学）；Shanghai Astronomical Observatory, Chinese Academy of Sciences（中国科学院上海天文台）；University of the Western Cape（西开普敦大学）；Institute for Fundamental Physics of the Universe（宇宙基础物理研究所）；The University of Edinburgh（爱丁堡大学）；University of Cambridge（剑桥大学）；Northeastern University（东北大学）；Observatoire de la Côte d’Azur（蔚蓝海岸天文台）
This present article is dedicated to thoroughly exploring the competency of the synergy of the upcoming Cosmic Microwave Background (CMB) missions and Square Kilometre Array (SKA) surveys in detecting features in the primordial power spectrum. Features are by definition specific scale-dependent modifications to the minimal power-law power spectrum. The functional form of the features depends on the inflationary scenarios taken into consideration. The identification of any conclusive deviation from the feature-less power-law power spectrum will allow us to largely fathom out the microphysics of…
It has been proposed recently that the SKA1-MID could be used to conduct an HI intensity mapping survey that could rival upcoming Stage IV dark energy surveys. However, measuring the weak HI signal is expected to be very challenging due to contaminations such as residual Galactic emission, RFI, and instrumental 1/f noise. Modelling the effects of these contaminants on the cosmological HI signal requires numerical end-to-end simulations. Here we present how 1/f noise within the receiver can double the effective uncertainty of an SKA-like survey to HI on large angular scales (l < 50).
Studying the cosmic dawn and the epoch of reionization through the redshifted 21 cm line are among the major science goals of the SKA1. Their significance lies in the fact that they are closely related to the very first stars in the universe. Interpreting the upcoming data would require detailed modelling of the relevant physical processes. In this article, we focus on the theoretical models of reionization that have been worked out by various groups working in India with the upcoming SKA in mind. These models include purely analytical and semi-numerical calculations as well as fully numerical…
Hydroxyl ($\rm OH$) is known to form efficiently in cold gas ($T\sim 100$K) along with the molecule $\rm H_2$ and can be used as an efficient tracer of the diffuse molecular gas in the interstellar medium (ISM). Using a simple formalism describing the $\rm H\,I/H_2$ transition and a reduced network of major chemical reactions, we present a semi-analytical prescription to estimate the abundances of O-bearing molecules in the diffuse ISM. We show that predictions based on our prescription are in good agreement with the estimates obtained using the MEUDON PDR code which utilizes the full reaction…
The intergalactic medium (IGM) plays an important role in the formation and evolution of galaxies. Recent developments in upcoming radio telescopes are starting to open up the possibility of making a first direct detection of the 21 cm signal of neutral hydrogen (HI) from the warm gas of the IGM in large-scale filaments. The cosmological hydrodynamical EAGLE simulation is used to estimate the typical IGM filament signal. Assuming the same average signal for all filaments, a prediction is made for the detectability of such a signal with the upcoming mid-frequency array of the Square Kilometer A…
In this paper we use radiative transfer + N-body simulations to explore the feasibility of measurements of cross-correlations between the 21cm field observed by the Square Kilometer Array (SKA) and high-z Lyman Alpha Emitters (LAEs) detected in galaxy surveys with the Subaru Hyper Supreme Cam (HSC), Subaru Prime Focus Spectrograph (PFS) and Wide Field Infrared Survey Telescope (WFIRST). 21cm-LAE cross-correlations are in fact a powerful probe of the epoch of reionization as they are expected to provide precious information on the progress of reionization and the typical scale of ionized region…
Interferometric HI Intensity Mapping of the Late Time Universe with SKA-Mid
The University of Manchester（曼彻斯特大学）；The University of Edinburgh（爱丁堡大学）；University of the Western Cape（西开普敦大学）；Tsinghua University（清华大学）；Université Paris-Saclay（巴黎萨克雷大学）；Université Paris Cité（巴黎西岱大学）
It is usually assumed that we will need to wait until next-generation surveys like Euclid, LSST and SKA, in order to improve on the current best constraints on primordial non-Gaussianity from the Planck experiment. We show that two contemporary surveys, with the SKA precursor MeerKAT and the Dark Energy Survey (DES), can be combined using the multi-tracer technique to deliver an accuracy on measurement of $f_{\rm NL}$ that is up to three times better than Planck.
Simulations of the 21cm emission line for upcoming large-scale HI galaxy surveys
ETH Zürich（苏黎世联邦理工学院）；Observatoire de la Côte d’Azur, Laboratoire J-L Lagrange（蔚蓝海岸天文台J-L拉格朗日实验室）；University of the Western Cape（西开普敦大学）；INAF - Astronomical Observatory of Trieste（意大利国家天体物理研究所的里雅斯特天文台）；IFPU - Institute for Fundamental Physics of the Universe（宇宙基础物理研究所）；Centre for Astrophysics Research, University of Hertfordshire（赫特福德大学天体物理学研究中心）；EPFL - Institute of Physics, Laboratory for Galaxy Evolution（洛桑联邦理工学院物理系星系演化实验室）；Tianjin Normal University（天津师范大学）
The substantial decrease in star formation density from z=1 to the present day is curious given the relatively constant neutral gas density over the same epoch. Future radio astronomy facilities, including the SKA and pathfinder telescopes, will provide pioneering measures of both the gas content of galaxies and star formation activity over cosmological timescales. Here we investigate the commensalities between neutral atomic gas (HI) and radio continuum observations, as well as the complementarity of the data products. We start with the proposed HI and continuum surveys to be undertaken with …
Observatoire de la Côte d’Azur（蔚蓝海岸天文台）；University of the Western Cape（西开普敦大学）；Cardiff University（卡迪夫大学）；University of Manchester（曼彻斯特大学）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；University of Chinese Academy of Sciences（中国科学院大学）
We explore the potential use of the Radio Continuum (RC) survey conducted by the Square Kilometre Array (SKA) to remove (delens) the lensing-induced B-mode polarization and thus enhance future cosmic microwave background (CMB) searches for inflationary gravitational waves. Measurements of large-scale B-modes of the CMB are considered to be the best method for probing gravitational waves from the cosmic inflation. Future CMB experiments will, however, suffer from contamination by non-primordial B-modes, one source of which is the lensing B-modes. Delensing, therefore, will be required for furth…
The light-cone (LC) effect causes the mean as well as the statistical properties of the redshifted 21-cm signal $T_{\rm b}(\hat{\bf n},ν)$ to change with frequency $ν$ (or cosmic time). Consequently, the statistical homogeneity (ergodicity) of the signal along the line of sight (LoS) direction is broken. This is a severe problem particularly during the Epoch of Reionization (EoR) when the mean neutral hydrogen fraction ($\bar{x}_{\rm HI}$) changes rapidly as the universe evolves. This will also pose complications for large bandwidth observations. These effects imply that the 3D power spectrum …
Detection of the redshifted 21-cm signal of neutral hydrogen from the Cosmic Dawn and the Epoch of Reionization is one of the final frontiers of modern observational cosmology. The inherently faint signal makes it susceptible to contamination by several sources like astrophysical foregrounds and instrumental systematics. Nevertheless, developments achieved in the recent times will combine to make signal detection possible with the upcoming Square Kilometer Array (SKA), both statistically and via tomography. This review describes an indigenously developed end-to-end pipeline that simulates sens…
Sensitivity toward dark matter annihilation imprints on 21-cm signal with SKA-Low: A convolutional neural network approach
Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences (HIAS-UCAS)（中国科学院大学杭州高等研究院）；University of Chinese Academy of Sciences（中国科学院大学）；International Centre for Theoretical Physics Asia-Pacific (ICTP-AP)（亚太理论物理中心）；Gifu Shotoku Gakuen University（岐阜女子大学）；Institute for Advanced Research, and Kobayashi Maskawa Institute, Nagoya University（名古屋大学先进研究院及小林–益川研究所）
HI Simulations for Cosmology with the SKA Observatory
INAF -- Institute of Radioastronomy (IRA)（意大利国家天体物理研究所射电天文学研究所）；ETH Zurich -- Institute for Particle Physics and Astrophysics（苏黎世联邦理工学院粒子物理与天体物理研究所）；University of Geneva（日内瓦大学）；IFPU: Institute for Fundamental Physics of the Universe（宇宙基础物理研究所）；Tianjin Normal University（天津师范大学）；Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, The University of Manchester（曼彻斯特大学物理与天文学系乔德雷尔银行天体物理学中心）；Department of Physics, National Institute of Technology Calicut（卡利卡特国立技术学院物理系）；Department of Physics and Astronomy, Johns Hopkins University（约翰斯·霍普金斯大学物理与天文学系）；School of Natural Sciences, Institute for Advanced Study（高等研究院自然科学学院）；Centre for Astrophysics Research, University of Hertfordshire（赫特福德大学天体物理学研究中心）
Probing the large-scale structure with 21cm-galaxy cross-bispectrum: Estimates from simulations and forecasts for upcoming cosmological surveys
Indian Institute of Technology Indore（印度印多尔理工学院）；SISSA - International School for Advanced Studies（国际高等研究院）；IFPU - Institute for Fundamental Physics of the Universe（宇宙基础物理研究所）；INAF - Osservatorio Astronomico di Trieste（的里雅斯特天文台）；INFN - Sezione di Trieste（意大利国家核物理研究所的里雅斯特分部）；Observatoire de la Côte d’Azur, Laboratoire Lagrange（蔚蓝海岸天文台拉格朗日实验室）
The late-time integrated Sachs-Wolfe (ISW) signal in the CMB temperature anisotropies is an important probe of dark energy when it can be detected by cross-correlation with large-scale structure surveys. Because of their huge sky area, surveys in the radio are well-suited to ISW detection. We show that 21cm intensity mapping and radio continuum surveys with the SKA in Phase~1 promise a $\sim5σ$ detection if we use tomography, with a similar forecast for the precursor EMU survey. In SKA Phase~2, the 21cm galaxy redshift survey and the continuum survey could deliver a $\sim6σ$ detection. Our ana…
The SKA era is set to revolutionize our understanding of neutral hydrogen (HI) in individual galaxies out to redshifts of z~0.8; and in the z > 6 intergalactic medium through the detection and imaging of cosmic reionization. Direct HI number density constraints will, nonetheless, remain relatively weak out to cosmic noon (z~2) - the epoch of peak star formation and black hole accretion - and beyond. However, as was demonstrated from the 1990s with molecular line observations, this can be overcome by utilising the natural amplification afforded by strong gravitational lensing, which results in …
Neutral hydrogen (HI) intensity mapping traces the large-scale distribution of matter in the Universe and therefore should correlate with the gamma-ray emission originated from particle dark matter annihilation or from active galactic nuclei and star-forming galaxies, since the related processes occur in the same cosmic structures hosting HI. In this paper, we derive the cross-correlation signal between the brightness temperature of the 21-cm line emission of the HI spin-flip transition in the Universe and the unresolved gamma-ray background. Specifically, we derive forecasts for the cross-cor…
We present a phenomenological method for predicting the number of Flat Spectrum Radio Quasars (FSRQs) that should be detected by upcoming Square Kilometer Array (SKA) SKA1-MID Wide Band 1 and Medium-Deep band 2 surveys. We use the Fermi Blazar Sequence and mass estimates of Fermi FSRQs, and gamma-ray emitting Narrow Line Seyfert 1 galaxies, to model the radio emission of FSRQs as a function of mass alone, assuming a near-Eddington accretion rate, which is suggested by current quasar surveys at z > 6. This is used to determine the smallest visible black hole mass as a function of redshift in tw…
The upcoming Square Kilometre Array (SKA-Low) will map the distribution of neutral hydrogen during reionization, and produce a tremendous amount of 3D tomographic data. These images cubes will be subject to instrumental limitations, such as noise and limited resolution. Here we present SegU-Net, a stable and reliable method for identification of neutral and ionized regions in these images. SegU-Net is a U-Net architecture based convolutional neural network (CNN) for image segmentation. It is capable of segmenting our image data into meaningful features (ionized and neutral regions) with greate…
Next generation observatories will enable us to study the first billion years of our Universe in unprecedented detail. Foremost among these are 21-cm interferometry with the HERA and the SKA, and high-$z$ galaxy observations with the James Webb Space Telescope (JWST). Taking a basic galaxy model, in which we allow the star formation rates and ionizing escape fractions to have a power-law dependence on halo mass with an exponential turnover below some threshold, we quantify how observations from these instruments can be used to constrain the astrophysics of high-$z$ galaxies. For this purpose, …
