scholarly journals Quantiles as Robust Probes of Non-Gaussianity in 21-cm Images

2021 ◽  
Author(s):  
Alon Banet ◽  
Rennan Barkana ◽  
Anastasia Fialkov ◽  
Or Guttman
Keyword(s):  
Galactic Halo ◽  
Angular Resolution ◽  
Research Effort ◽  
First Stars ◽  
X Ray ◽  
Global Signal ◽  
Radio Background ◽  
Halo Masses ◽  
The Universe ◽  
Cosmic History

Abstract The epoch in which the first stars and galaxies formed is among the most exciting unexplored eras of the Universe. A major research effort is focused on probing this era with the 21-cm spectral line of hydrogen. While most research focuses on statistics like the 21-cm power spectrum or the sky-averaged global signal, there are other ways to analyze tomographic 21-cm maps, which may lead to novel insights. We suggest statistics based on quantiles as a method to probe non-Gaussianities of the 21-cm signal. We show that they can be used in particular to probe the variance, skewness, and kurtosis of the temperature distribution, but are more flexible and robust than these standard statistics. We test these statistics on a range of possible astrophysical models, including different galactic halo masses, star-formation efficiencies, and spectra of the X-ray heating sources, plus an exotic model with an excess early radio background. Simulating data with angular resolution and thermal noise as expected for the Square Kilometre Array (SKA), we conclude that these statistics can be measured out to redshifts above 20 and offer a promising statistical method for probing early cosmic history.

scholarly journals Tight constraints on the excess radio background at z = 9.1 from LOFAR

2020 ◽  
Vol 498 (3) ◽  
pp. 4178-4191 ◽  
Author(s):  
R Mondal ◽  
A Fialkov ◽  
C Fling ◽  
I T Iliev ◽  
R Barkana ◽  
...  
Keyword(s):  
High Redshift ◽  
Neutral Hydrogen ◽  
Ionization State ◽  
Microwave Background ◽  
X Ray ◽  
Star Forming ◽  
Radio Background ◽  
High Redshift Universe ◽  
The Universe ◽  
High Band

ABSTRACT The ARCADE2 and LWA1 experiments have claimed an excess over the cosmic microwave background (CMB) at low radio frequencies. If the cosmological high-redshift contribution to this radio background is between 0.1 per cent and 22 per cent of the CMB at 1.42 GHz, it could explain the tentative EDGES low-band detection of the anomalously deep absorption in the 21-cm signal of neutral hydrogen. We use the upper limit on the 21-cm signal from the Epoch of Reionization (z = 9.1) based on 141 h of observations with LOFAR to evaluate the contribution of the high-redshift Universe to the detected radio background. Marginalizing over astrophysical properties of star-forming haloes, we find (at 95 per cent CL) that the cosmological radio background can be at most 9.6 per cent of the CMB at 1.42 GHz. This limit rules out strong contribution of the high-redshift Universe to the ARCADE2 and LWA1 measurements. Even though LOFAR places limit on the extra radio background, excess of 0.1–9.6 per cent over the CMB (at 1.42 GHz) is still allowed and could explain the EDGES low-band detection. We also constrain the thermal and ionization state of the gas at z = 9.1, and put limits on the properties of the first star-forming objects. We find that, in agreement with the limits from EDGES high-band data, LOFAR data constrain scenarios with inefficient X-ray sources, and cases where the Universe was ionized by stars in massive haloes only.

scholarly journals Formation and early evolution of massive black holes

2006 ◽  
Vol 2 (S238) ◽  
pp. 73-82
Author(s):  
Piero Madau
Keyword(s):  
Black Holes ◽  
Dark Matter ◽  
Ionization State ◽  
First Stars ◽  
Massive Black Holes ◽  
X Ray ◽  
Hard Radiation ◽  
Low Mass ◽  
The Universe

AbstractThe astrophysical processes that led to the formation of the first seed black holes and to their growth into the supermassive variety that powers bright quasars at z ∼ 6 are poorly understood. In standard ΛCDM hierarchical cosmologies, the earliest massive holes (MBHs) likely formed at redshift z ≳ 15 at the centers of low-mass (M ≳ 5 × 105 M⊙) dark matter “minihalos”, and produced hard radiation by accretion. FUV/X-ray photons from such “miniquasars” may have permeated the universe more uniformly than EUV radiation, reduced gas clumping, and changed the chemistry of primordial gas. The role of accreting seed black holes in determining the thermal and ionization state of the intergalactic medium depends on the amount of cold and dense gas that forms and gets retained in protogalaxies after the formation of the first stars. The highest resolution N-body simulation to date of Galactic substructure shows that subhalos below the atomic cooling mass were very inefficient at forming stars.

scholarly journals Using artificial neural networks to extract the 21-cm global signal from the EDGES data

2021 ◽  
Vol 502 (2) ◽  
pp. 2815-2825
Author(s):  
Madhurima Choudhury ◽  
Atrideb Chatterjee ◽  
Abhirup Datta ◽  
Tirthankar Roy Choudhury
Keyword(s):  
Neutral Hydrogen ◽  
Simulated Data ◽  
Physical Models ◽  
Data Sets ◽  
First Stars ◽  
Global Signal ◽  
Reconstructed Signal ◽  
Radio Background ◽  
Artificial Neural ◽  
Artificial Neural Network Ann

ABSTRACT The redshifted 21-cm signal of neutral hydrogen is a promising probe into the period of evolution of our Universe when the first stars were formed (Cosmic Dawn), to the period where the entire Universe changed its state from being completely neutral to completely ionized (Reionization). The most striking feature of this line of neutral hydrogen is that it can be observed across an entire frequency range as a sky-averaged continuous signature, or its fluctuations can be measured using an interferometer. However, the 21-cm signal is very faint and is dominated by a much brighter Galactic and extragalactic foregrounds, making it an observational challenge. We have used different physical models to simulate various realizations of the 21-cm global signals, including an excess radio background to match the amplitude of the Experiment to Detect the Global EoR Signature (EDGES) 21-cm signal. First, we have used an artificial neural network (ANN) to extract the astrophysical parameters from these simulated data sets. Then, mock observations were generated by adding a physically motivated foreground model and an ANN was used to extract the astrophysical parameters from such data. The R2 score of our predictions from the mock observations is in the range of 0.65–0.89. We have used this ANN to predict the signal parameters giving the EDGES data as the input. We find that the reconstructed signal closely mimics the amplitude of the reported detection. The recovered parameters can be used to infer the physical state of the gas at high redshifts.

scholarly journals A hint on the metal-free star formation rate density from 21-cm-EDGES data

2020 ◽  
Vol 496 (2) ◽  
pp. 1445-1452 ◽  
Author(s):  
Atrideb Chatterjee ◽  
Pratika Dayal ◽  
Tirthankar Roy Choudhury ◽  
Raffaella Schneider
Keyword(s):  
Star Formation ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Monte Carlo Analysis ◽  
Host Galaxies ◽  
X Ray ◽  
Metal Free ◽  
Global Signal ◽  
Radio Background ◽  
X Ray Background

ABSTRACT We aim to provide here the first data-constrained estimate of the metal-free (Population III; Pop III) star formation rate density $\dot{\rho }_{*}^{III}$ required at high redshifts ($z \lower.5ex\hbox{$\,\, \buildrel\gt \over \sim \,\,$}16$) in order to reproduce both the amplitude and the redshift of the EDGES 21-cm global signal. Our model accounts for the Ly α, radio, and X-ray backgrounds from both Pop III and metal-enriched Population II (Pop II) stars. For the latter, we use the star formation rate density estimates (and the Ly α background) from the Delphi semi-analytic model that has been shown to reproduce all key observables for galaxies at $z \lower.5ex\hbox{$\,\, \buildrel\gt \over \sim \,\,$}5$; the radio and X-ray backgrounds are fixed using low-z values. The constraints on the free parameters characterizing the properties of the Pop III stars are obtained using a Markov Chain Monte Carlo analysis. Our results yield a $\dot{\rho }_{*}^{III}$ that while increasing from z ∼ 21 to 16 thereafter shows a sharp decline which is in excellent agreement with the results found by Valiante et al. to simulate the growth of z ∼ 6–7 quasars and their host galaxies, suggesting that the bulk of Pop III star formation occurs in the rarest and most massive metal-poor haloes at z ≲ 20. This allows Pop III stars to produce a rapidly growing Ly α background between z ∼ 21 and 15. Further, Pop III stars are required to provide a radio background that is about 3–4 orders of magnitude higher than that provided by Pop II stars although Pop II stars dominate the X-ray background.

scholarly journals Dust Production around Carbon-Rich Stars: The Role of Metallicity

Universe ◽  
2021 ◽  
Vol 7 (7) ◽  
pp. 233
Author(s):  
Ambra Nanni ◽  
Sergio Cristallo ◽  
Jacco Th. van Loon ◽  
Martin A. T. Groenewegen
Keyword(s):  
Wind Speed ◽  
Galactic Halo ◽  
Magellanic Clouds ◽  
Asymptotic Giant Branch ◽  
Agb Stars ◽  
Circumstellar Envelopes ◽  
Chemical Enrichment ◽  
Wide Range ◽  
The Universe

Background: Most of the stars in the Universe will end their evolution by losing their envelope during the thermally pulsing asymptotic giant branch (TP-AGB) phase, enriching the interstellar medium of galaxies with heavy elements, partially condensed into dust grains formed in their extended circumstellar envelopes. Among these stars, carbon-rich TP-AGB stars (C-stars) are particularly relevant for the chemical enrichment of galaxies. We here investigated the role of the metallicity in the dust formation process from a theoretical viewpoint. Methods: We coupled an up-to-date description of dust growth and dust-driven wind, which included the time-averaged effect of shocks, with FRUITY stellar evolutionary tracks. We compared our predictions with observations of C-stars in our Galaxy, in the Magellanic Clouds (LMC and SMC) and in the Galactic Halo, characterised by metallicity between solar and 1/10 of solar. Results: Our models explained the variation of the gas and dust content around C-stars derived from the IRS Spitzer spectra. The wind speed of the C-stars at varying metallicity was well reproduced by our description. We predicted the wind speed at metallicity down to 1/10 of solar in a wide range of mass-loss rates.

scholarly journals The Voyage of Metals in the Universe from Cosmological to Planetary Scales: the need for a Very High-Resolution, High Throughput Soft X-ray Spectrometer

2021 ◽  
Author(s):  
F. Nicastro ◽  
J. Kaastra ◽  
C. Argiroffi ◽  
E. Behar ◽  
S. Bianchi ◽  
...  
Keyword(s):  
Chemical Composition ◽  
High Resolution ◽  
Deep Understanding ◽  
High Resolution Spectroscopy ◽  
X Ray ◽  
Viable Solution ◽  
Surrounding Space ◽  
Nuclear Processes ◽  
The Universe ◽  
Very High

AbstractMetals form an essential part of the Universe at all scales. Without metals we would not exist, and the Universe would look completely different. Metals are primarily produced via nuclear processes in stars, and spread out through winds or explosions, which pollute the surrounding space. The wanderings of metals in-and-out of astronomical objects are crucial in determining their own evolution and thus that of the Universe as a whole. Detecting metals and assessing their relative and absolute abundances and energetics can thus be used to trace the evolution of these cosmic components. The scope of this paper is to highlight the most important open astrophysical problems that will be central in the next decades and for which a deep understanding of the Universe’s wandering metals, their physical and kinematical states, and their chemical composition represents the only viable solution. The majority of these studies can only be efficiently performed through High Resolution Spectroscopy in the soft X-ray band.

Supermassive Black Hole feedback in early type galaxies

2020 ◽  
Vol 15 (S359) ◽  
pp. 119-125
Author(s):  
W. Forman ◽  
C. Jones ◽  
A. Bogdan ◽  
R. Kraft ◽  
E. Churazov ◽  
...  
Keyword(s):  
Dark Matter Halo ◽  
Scaling Relations ◽  
Radio Sources ◽  
Early Type ◽  
X Ray ◽  
Galaxy Groups ◽  
Sufficient Energy ◽  
The Galaxy ◽  
Simple Scaling ◽  
Halo Masses

AbstractOptically luminous early type galaxies host X-ray luminous, hot atmospheres. These hot atmospheres, which we refer to as coronae, undergo the same cooling and feedback processes as are commonly found in their more massive cousins, the gas rich atmospheres of galaxy groups and galaxy clusters. In particular, the hot coronae around galaxies radiatively cool and show cavities in X-ray images that are filled with relativistic plasma originating from jets powered by supermassive black holes (SMBH) at the galaxy centers. We discuss the SMBH feedback using an X-ray survey of early type galaxies carried out using Chandra X-ray Observatory observations. Early type galaxies with coronae very commonly have weak X-ray active nuclei and have associated radio sources. Based on the enthalpy of observed cavities in the coronae, there is sufficient energy to “balance” the observed radiative cooling. There are a very few remarkable examples of optically faint galaxies that are 1) unusually X-ray luminous, 2) have large dark matter halo masses, and 3) have large SMBHs (e.g., NGC4342 and NGC4291). These properties suggest that, in some galaxies, star formation may have been truncated at early times, breaking the simple scaling relations.

scholarly journals The Hot Universe with XRISM and Athena

2018 ◽  
Vol 14 (S342) ◽  
pp. 29-36
Author(s):  
M. Guainazzi ◽  
M. S. Tashiro
Keyword(s):  
Electromagnetic Radiation ◽  
Large Scale ◽  
Cosmological Evolution ◽  
X Ray ◽  
Hot Gas ◽  
Cosmic Vision ◽  
Esa Cosmic Vision ◽  
The Universe

AbstractX-ray spectroscopy is key to address the theme of “The Hot Universe”, the still poorly understood astrophysical processes driving the cosmological evolution of the baryonic hot gas traceable through its electromagnetic radiation. Two future X-ray observatories: the JAXA-led XRISM (due to launch in the early 2020s), and the ESA Cosmic Vision L-class mission Athena (early 2030s) will provide breakthroughs in our understanding of how and when large-scale hot gas structures formed in the Universe, and in tracking their evolution from the formation epoch to the present day.

scholarly journals The Low-Frequency Array (LOFAR): Opening a New Window on the Universe

2002 ◽  
Vol 199 ◽  
pp. 474-483
Author(s):  
Namir E. Kassim ◽  
T. Joseph W. Lazio ◽  
William C. Erickson ◽  
Patrick C. Crane ◽  
R. A. Perley ◽  
...  
Keyword(s):  
Angular Resolution ◽  
Broad Band ◽  
Low Frequency ◽  
Electromagnetic Spectrum ◽  
Interferometric Imaging ◽  
Very Large Array ◽  
Long Wavelength ◽  
Calibration Techniques ◽  
Long Baselines ◽  
The Universe

Decametric wavelength imaging has been largely neglected in the quest for higher angular resolution because ionospheric structure limited interferometric imaging to short (< 5 km) baselines. The long wavelength (LW, 2—20 m or 15—150 MHz) portion of the electromagnetic spectrum thus remains poorly explored. The NRL-NRAO 74 MHz Very Large Array has demonstrated that self-calibration techniques can remove ionospheric distortions over arbitrarily long baselines. This has inspired the Low Frequency Array (LOFAR)—-a fully electronic, broad-band (15—150 MHz)antenna array which will provide an improvement of 2—3 orders of magnitude in resolution and sensitivity over the state of the art.

scholarly journals Dark stars: a new study of the first stars in the Universe

2009 ◽  
Vol 11 (10) ◽  
pp. 105014 ◽  
Author(s):  
Katherine Freese ◽  
Peter Bodenheimer ◽  
Paolo Gondolo ◽  
Douglas Spolyar
Keyword(s):  
First Stars ◽  
The Universe
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