Browsing by Author "Moya Sierralta, Cristóbal Andrés"

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    Depthwise convolutional neural network for multiband automatic quasars classification in ATLAS
    (2023) San Martín Jiménez, Astrid Elizabeth; Pichara Baksai, Karim Elías; Barrientos, Luis Felipe; Rojas Henríquez, Felipe Ignacio; Moya Sierralta, Cristóbal Andrés
    In recent years, the astronomical scientific community has made significant efforts to automate quasars' detection. Automatic classification of these objects is challenging since they are very distant and appear as point sources, outnumbered by other sources. Thus, performing automatic morphological classification is not straightforward; colour dimension seems better as a key concept. Previous work using machine learning tools has proposed classifiers that use features such as magnitude and colour, working only for quasar representation, which requires high-quality observational data that is not always available. Those features are computationally costly in extensive image surveys like VST ATLAS (Shanks et al. 2015). With the continuous developments in deep-learning architectures, we find a powerful tool to perform automatic classification from images, where capturing information from different bands takes relevance in this kind of approach. In this work, we developed a new quasar selection method that we hope to apply to the complete ATLAS survey in subsequent papers, where the completeness and efficiency of depthwise architecture will be compared to more standard methods such as selection on the colour-colour diagrams and machine-learning feature-based methods. This automatic quasar classification tool uses images in u, g, i, z bands available in ATLAS, heading towards new survey requirements facing the big data era. We propose a deep-learning architecture based on depthwise convolutional units that work directly with ATLAS images, reduced by the VST pipeline. Our model reaches an accuracy of 96.53 per cent with a quasar classification f1-score of 96.49 per cent, a very competitive benchmark compared to previous unscalable approaches....
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    Galaxy Protoclusters as Drivers of Cosmic Reionization: I. Bubble Overlap at Redshift z ∼ 7 in LAGER-z7OD1
    (2026) Martin, Crystal L.; Hu, Weida; Wold, Isak G. B.; Faisst, Andreas; Moya Sierralta, Cristóbal Andrés; Malhotra, Sangeeta; Rhoads, James E.; Barrientos Parra, Luis Felipe; Harikane, Yuichi; Infante Lira, Leopoldo; Koekemoer, Anton M.; González López, Jorge; Ouchi, Masami; Xu, Junyan; Yang, Jiayang; Yung, L. Y. Aaron; Weaver, John R.; McCracken, Henry; Zheng, Zhenya; Wang, Junxian
    Since the launch of JWST, the sample size of reionization-era Lyα emitters (LAEs) has been steadily growing; yet inferences about the neutral hydrogen fraction in the intergalactic medium exhibit increasing variance at redshift z ≈ 7, possibly indicating significant field-to-field fluctuations in the progression of cosmic reionization. In this paper, we present new JWST/NIRSpec and Keck/LRIS spectra of nine LAEs in the redshift z ∼ 7 protocluster LAGER-z7OD1. Measurements of Lyα transmission and Lyα velocity offset along multiple sight lines map the Lyα damping wing optical depth across the galaxy overdensity. In the standard context of inside-out ionization, we estimate the radii of ionized bubbles, 0.69 Mpc (physical), based on the distance from each LAE to the first neutral patch along the sight line. The resulting 3D topology reveals three distinct subclusters where the ionized bubbles are approaching overlap. Five of the nine LAEs plausibly ionized their bubbles, where a few bursts of star formation and a modest escape fraction are sufficient. We demonstrate, however, that the actual ionized volumes are likely larger, at least = 0.42–1.29 Mpc (physical), based on an empirical model for interstellar attenuation of Lyα. Modeling galactic attenuation of Lyα significantly increases the inferred intergalactic transmission (thus enlarging the ionized path length). The error bars on the reddening correction allow fully overlapping bubbles, and our results are consistent with accelerated reionization in the protocluster.