| 1. |
- Bianco, Michele, et al.
(författare)
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Deep learning approach for identification of H II regions during reionization in 21-cm observations - II. Foreground contamination
- 2024
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 528:3, s. 5212-5230
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Tidskriftsartikel (refereegranskat)abstract
- The upcoming Square Kilometre Array Observatory will produce images of neutral hydrogen distribution during the epoch of reionization by observing the corresponding 21-cm signal. However, the 21-cm signal will be subject to instrumental limitations such as noise and galactic foreground contamination that pose a challenge for accurate detection. In this study, we present the SegU-Net v2 framework, an enhanced version of our convolutional neural network, built to identify neutral and ionized regions in the 21-cm signal contaminated with foreground emission. We trained our neural network on 21-cm image data processed by a foreground removal method based on Principal Component Analysis achieving an average classification accuracy of 71 per cent between redshift z = 7 and 11. We tested SegU-Net v2 against various foreground removal methods, including Gaussian Process Regression, Polynomial Fitting, and Foreground-Wedge Removal. Results show comparable performance, highlighting SegU-Net v2's independence on these pre-processing methods. Statistical analysis shows that a perfect classification score with AUC = 95 is possible for 8 < z < 10. While the network prediction lacks the ability to correctly identify ionized regions at higher redshift and differentiate well the few remaining neutral regions at lower redshift due to low contrast between 21-cm signal, noise, and foreground residual in images. Moreover, as the photon sources driving reionization are expected to be located inside ionized regions, we show that SegU-Net v2 can be used to correctly identify and measure the volume of isolated bubbles with V-ion > (10cmpc)(3 )at z > 9, for follow-up studies with infrared/optical telescopes to detect these sources.
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| 2. |
- Bruton, Sean, et al.
(författare)
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The Impact of Cosmic Variance on Inferences of Global Neutral Fraction Derived from Lyα Luminosity Functions during Reionization
- 2023
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 953:1
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the impact of field-to -field variation, deriving from cosmic variance, in measured Ly alpha emitter (LAE) luminosity functions (LFs) and this variation's impact on inferences of the neutral fraction of the intergalactic medium (IGM) during reionization. We post-process a z = 7 IGM simulation to populate the dark matter halos with LAEs. These LAEs have realistic UV magnitudes, Ly alpha fluxes, and Ly alpha line profiles. We calculate the attenuation of Ly alpha emission in universes with varying IGM neutral fraction, (x) over bar (H I). In a (x) over bar (H I) = 0.3 simulation, we perform 100 realizations of a mock 2 deg(2) survey with a redshift window Delta z = 0.5 and flux limit f(Ly alpha) > 1 x 10(-17)erg s(-1) cm(-2); such a survey is typical in depth and volume of the largest LAE surveys conducted today. For each realization, we compute the LAE LF and use it to recover the input x(H I). Comparing the inferred values of (x) over bar (H) (I) across the ensemble of the surveys, we find that cosmic variance, deriving from large-scale structure and variation in the neutral gas along the sightline, imposes a floor in the uncertainty of Delta(x) over bar (HI) similar to 0.2 when (x) over bar (H) (I) = 0.3. We explore mitigation strategies to decrease this uncertainty, such as increasing the volume, decreasing the flux limit, or probing the volume with many independent fields. Increasing the area and/or depth of the survey does not mitigate the uncertainty, but composing a survey with many independent fields is effective. This finding highlights the best strategy for LAE surveys aiming at constraining the (x) over bar (HI) of the universe during reionization.
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| 3. |
- Greig, Bradley, et al.
(författare)
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Interpreting LOFAR 21-cm signal upper limits at z ≈ 9.1 in the context of high-z galaxy and reionization observations
- 2021
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 501:1, s. 1-13
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Tidskriftsartikel (refereegranskat)abstract
- Using the latest upper limits on the 21-cm power spectrum at z approximate to 9.1 from the Low Frequency Array (LOFAR), we explore the regions of parameter space which are inconsistent with the data. We use 21CMMC, a Monte Carlo Markov chain sampler of 21CMFAST which directly forward models the three dimensional (3D) cosmic 21-cm signal in a fully Bayesian framework. We use the astrophysical parametrization from 21CMFAST, which includes mass-dependent star formation rates and ionizing escape fractions as well as soft-band X-ray luminosities to place limits on the properties of the high-z galaxies. Further, we connect the disfavoured regions of parameter space with existing observational constraints on the Epoch of Reionization such as ultra-violet (UV) luminosity functions, background UV photoionization rate, intergalactic medium (IGM) neutral fraction, and the electron scattering optical depth. We find that all models exceeding the 21-cm signal limits set by LOFAR at z approximate to 9.1 are excluded at greater than or similar to 2 sigma by other probes. Finally, we place limits on the IGM spin temperature from LOFAR, disfavouring at 95 per cent confidence spin temperatures below similar to 2.6 K across an IGM neutral fraction range of 0.15 less than or similar to (x) over bar (HI) less than or similar to 0.6. Note, these limits are only obtained from 141 h of data in a single redshift bin. With tighter upper limits, across multiple redshift bins expected in the near future from LOFAR, more viable models will be ruled out. Our approach demonstrates the potential of forward modelling tools such as 21CMMC in combining 21-cm observations with other high-z probes to constrain the astrophysics of galaxies.
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| 4. |
- Koopmans, Léon V. E., et al.
(författare)
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Peering into the dark (ages) with low-frequency space interferometers : Using the 21-cm signal of neutral hydrogen from the infant universe to probe fundamental (Astro)physics
- 2021
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Ingår i: Experimental astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 51, s. 1641-1676
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Tidskriftsartikel (refereegranskat)abstract
- The Dark Ages and Cosmic Dawn are largely unexplored windows on the infant Universe (z ~ 200–10). Observations of the redshifted 21-cm line of neutral hydrogen can provide valuable new insight into fundamental physics and astrophysics during these eras that no other probe can provide, and drives the design of many future ground-based instruments such as the Square Kilometre Array (SKA) and the Hydrogen Epoch of Reionization Array (HERA). We review progress in the field of high-redshift 21-cm Cosmology, in particular focussing on what questions can be addressed by probing the Dark Ages at z > 30. We conclude that only a space- or lunar-based radio telescope, shielded from the Earth’s radio-frequency interference (RFI) signals and its ionosphere, enable the 21-cm signal from the Dark Ages to be detected. We suggest a generic mission design concept, CoDEX, that will enable this in the coming decades.
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| 5. |
- Mellema, Garrelt, et al.
(författare)
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Reionization and the Cosmic Dawn with the Square Kilometre Array
- 2013
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Ingår i: Experimental astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 36:1-2, s. 235-318
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Tidskriftsartikel (refereegranskat)abstract
- The Square Kilometre Array (SKA) will have a low frequency component (SKA-low) which has as one of its main science goals the study of the redshifted 21 cm line from the earliest phases of star and galaxy formation in the Universe. This 21 cm signal provides a new and unique window both on the time of the formation of the first stars and accreting black holes and the subsequent period of substantial ionization of the intergalactic medium. The signal will teach us fundamental new things about the earliest phases of structure formation, cosmology and even has the potential to lead to the discovery of new physical phenomena. Here we present a white paper with an overview of the science questions that SKA-low can address, how we plan to tackle these questions and what this implies for the basic design of the telescope.
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| 6. |
- Zackrisson, Erik, et al.
(författare)
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Bubble mapping with the Square Kilometre Array - I. Detecting galaxies with Euclid, JWST, WFIRST, and ELT within ionized bubbles in the intergalactic medium at z > 6
- 2020
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 493:1, s. 855-870
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Tidskriftsartikel (refereegranskat)abstract
- The Square Kilometre Array (SKA) is expected to provide the first tomographic observations of the neutral intergalactic medium at redshifts z > 6 and pinpoint the locations of individual ionized bubbles during early stages of cosmic reionization. In scenarios where star-forming galaxies provide most of the ionizing photons required for cosmic reionization, one expects the first ionized bubbles to be centred on overdensities of such galaxies. Here, we model the properties of galaxy populations within isolated, ionized bubbles that SKA-1 should be able to resolve at z approximate to 7-10, and explore the prospects for galaxy counts within such structures with various upcoming near-infrared telescopes. We find that, for the bubbles that are within reach of SKA-1 tomography, the bubble volume is closely tied to the number of ionizing photons that have escaped from the galaxies within. In the case of galaxy-dominated reionization, galaxies are expected to turn up above the spectroscopic detection threshold of JWST and ELT in even the smallest resolvable bubbles at z <= 10. The prospects of detecting galaxies within these structures in purely photometric surveys with Euclid, WFIRST, JWST, or ELT are also discussed. While spectroscopy is preferable towards the end of reionization to provide a robust sample of bubble members, multiband imaging may be a competitive option for bubbles at z approximate to 10, due to the very small number of line-of-sight interlopers expected at these redshifts.
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| 7. |
- Zhu, Yongda, et al.
(författare)
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Probing Ultralate Reionization: Direct Measurements of the Mean Free Path over 5 z
- 2023
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Ingår i: Astrophysical Journal. - 1538-4357 .- 0004-637X. ; 955:2
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Tidskriftsartikel (refereegranskat)abstract
- The mean free path of ionizing photons, lambda(mfp), is a critical parameter for modeling the intergalactic medium (IGM) both during and after reionization. We present direct measurements of lambda(mfp) from QSO spectra over the redshift range 5 < z < 6, including the first measurements at z similar or equal to 5.3 and 5.6. Our sample includes data from the XQR-30 VLT large program, as well as new Keck/ESI observations of QSOs near z similar to 5.5, for which we also acquire new [C II] 158 mu m redshifts with ALMA. By measuring the Lyman continuum transmission profile in stacked QSO spectra, we find lambda(mfp) = 9.33(-1.80)(+2.06), 5.40(-1.40)(+1.47), 3.31(-1.34)(+2.74), and 0.81(-0.48)(+0.73) pMpc at z = 5.08, 5.31, 5.65, and 5.93, respectively. Our results demonstrate that lambda(mfp) increases steadily and rapidly with time over 5 < z < 6. Notably, we find that lambda(mfp) deviates significantly from predictions based on a fully ionized and relaxed IGM as late as z = 5.3. By comparing our results to model predictions and indirect lambda(mfp) constraints based on IGM Ly alpha opacity, we find that the evolution of lambda(mfp) is consistent with scenarios wherein the IGM is still undergoing reionization and/or retains large fluctuations in the ionizing UV background well below redshift 6.
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