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Universe
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Advances in Studies of Galaxies at High Redshift
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Advances in Studies of Galaxies at High Redshift

A special issue of Universe (ISSN 2218-1997). This special issue belongs to the section "Galaxies and Clusters".

Deadline for manuscript submissions: 31 July 2025 | Viewed by 2559

Special Issue Editor

Dr. Krisztina Éva Gabányi

E-Mail Website
Guest Editor
Department of Astronomy, Institute of Physics and Astronomy, ELTE Eötvös Loránd University, Budapest, Hungary
Interests: radio astronomy; radio interferometry; radio emitting active galactic nuclei

Special Issue Information

Dear Colleagues,

In the last few decades, the meaning of the phrase “high-redshift” went through substantial changes. Roughly 25 years ago, objects at redshifts z>3 were regarded high-redshift sources. Nowadays, thanks to the discoveries made by several new instruments, most recently the James Webb Space Telescope, galaxies at redshifts up to 10 or even higher can be observed and investigated. Thus, the Universe can be studied in its infancy, even when it was less than half a billion years old. The evolution of galaxies, their central supermassive black holes (SMBH), their star-forming activities, feedback processes, and the formation of galaxy clusters can be investigated in more details through a much longer cosmic time. The existence of galaxies and their active nuclei in the very early Universe poses the question how their million to billion solar-mass black holes at their centers formed. What were the properties of seed black holes? What kind of accretion mechanisms have been taking place in the early Universe which made the formation of such objects possible already a few hundred million years after the Big Bang? While it is possible to detect lower-mass SMBH with the most sensitive current instruments even at high redshifts, thus, to observe earlier stages of black hole growth, even studying the close-by Universe via the investigations of isolated, passively evolving galaxies and their central SMBH can provide valuable insights to this field. Last but not least, the huge advancements in computational power in the last decades paved the way to ever-improving numerical simulations on various scales, opening up new perspectives in this topical research field.

Dr. Krisztina Éva Gabányi
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Universe is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • high-redshift galaxies
  • active galaxies
  • quasars
  • supermassive black holes
  • star formation
  • galaxy evolution
  • early universe
  • cosmology
  • observational astronomy
  • simulations

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Published Papers (3 papers)

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Research

16 pages, 10616 KiB  
Article
Superluminal Motion and Jet Parameters in the High-Redshift Blazar J1429+5406
by Dávid Koller and Sándor Frey
Universe 2025, 11(5), 157; https://doi.org/10.3390/universe11050157 - 11 May 2025
Viewed by 820
Abstract
We investigate the relativistic jet of the powerful radio-emitting blazar J1429+5406 at redshift z=3.015. Our understanding of jet kinematics in z≥3 quasars is still rather limited, based on a sample of less than about 50 objects. The blazar [...] Read more.
We investigate the relativistic jet of the powerful radio-emitting blazar J1429+5406 at redshift z=3.015. Our understanding of jet kinematics in z≥3 quasars is still rather limited, based on a sample of less than about 50 objects. The blazar J1429+5406 was observed at a high angular resolution using the method of very long baseline interferometry over more than two decades, between 1994 and 2018. These observations were conducted at five radio frequencies, covering a wide range from 1.7 to 15 GHz. The outer jet components at ∼20–40 milliarcsecond (mas) separations from the core do not show discernible apparent motion. On the other hand, three jet components within the central 10 mas region exhibit significant proper motion in the range of (0.045–0.16) mas year−1, including one that is among the fastest-moving jet components at z≥3 known to date. Based on the proper motion of the innermost jet component and the measured brightness temperature of the core, we estimated the Doppler factor, the bulk Lorentz factor, and the inclination angle of the jet with respect to the line of sight. The core brightness temperature is at least 3.6×1011 K, well exceeding the equipartition limit, indicating Doppler-boosted radio emission. The low jet inclination (≲5.4°) firmly places J1429+5406 into the blazar category. Full article
(This article belongs to the Special Issue Advances in Studies of Galaxies at High Redshift)
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28 pages, 13572 KiB  
Article
High-Redshift Quasars at z ≥ 3—III: Parsec-Scale Jet Properties from Very Long Baseline Interferometry Observations
by Shaoguang Guo, Tao An, Yuanqi Liu, Chuanzeng Liu, Zhijun Xu, Yulia Sotnikova, Timur Mufakharov and Ailing Wang
Universe 2025, 11(3), 91; https://doi.org/10.3390/universe11030091 - 8 Mar 2025
Viewed by 598
Abstract
High-redshift active galactic nuclei (AGN) provide key insights into early supermassive black hole growth and cosmic evolution. This study investigates the parsec-scale properties of 86 radio-loud quasars at z ≥ 3 using very long baseline interferometry (VLBI) observations. Our results show predominantly compact [...] Read more.
High-redshift active galactic nuclei (AGN) provide key insights into early supermassive black hole growth and cosmic evolution. This study investigates the parsec-scale properties of 86 radio-loud quasars at z ≥ 3 using very long baseline interferometry (VLBI) observations. Our results show predominantly compact core and core-jet morphologies, with 35% having unresolved cores, 59% with core–jet structures, and only 6% with core–double jet morphology. Brightness temperatures are generally lower than expected for highly radiative sources. The jets’ proper motions are surprisingly slow compared to those of lower-redshift samples. We observe a high fraction of young and/or confined peak-spectrum sources, providing insights into early AGN evolution in dense environments during early cosmic epochs. The observed trends may reflect genuine evolutionary changes in AGN structure over cosmic time, or selection effects favoring more compact sources at higher redshifts. These results stress the complexity of high-redshift radio-loud AGN populations and emphasize the need for multi-wavelength, high-resolution observations to fully characterize their properties and evolution through cosmic history. Full article
(This article belongs to the Special Issue Advances in Studies of Galaxies at High Redshift)
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12 pages, 1136 KiB  
Article
Prediction of Individual Halo Concentrations Across Cosmic Time Using Neural Networks
by Tianchi Zhang, Tianxiang Mao, Wenxiao Xu and Guan Li
Universe 2025, 11(2), 37; https://doi.org/10.3390/universe11020037 - 26 Jan 2025
Viewed by 744
Abstract
The concentration of dark matter haloes is closely linked to their mass accretion history. We utilize the halo mass accretion histories from large cosmological N-body simulations as inputs for our neural networks, which we train to predict the concentration of individual haloes [...] Read more.
The concentration of dark matter haloes is closely linked to their mass accretion history. We utilize the halo mass accretion histories from large cosmological N-body simulations as inputs for our neural networks, which we train to predict the concentration of individual haloes at a given redshift. The trained model performs effectively in other cosmological simulations, achieving the root mean square error between the actual and predicted concentrations that significantly lower than that of the model by Zhao et al. and Giocoli et al. at any redshift. This model serves as a valuable tool for rapidly predicting halo concentrations at specified redshifts in large cosmological simulations. Full article
(This article belongs to the Special Issue Advances in Studies of Galaxies at High Redshift)
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