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Universe
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The Physical Properties of the Groups of Galaxies
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The Physical Properties of the Groups of Galaxies

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

Deadline for manuscript submissions: closed (31 March 2021) | Viewed by 18751

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editors

Dr. Lorenzo Lovisari

E-Mail Website
Guest Editor
INAF, Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, via Pietro Gobetti 93/3, 40129 Bologna, Italy
Interests: groups and clusters of galaxies; intracluster medium; X-ray; cosmology
Dr. Stefano Ettori

E-Mail Website
Guest Editor
INAF, Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, via Pietro Gobetti 93/3, 40129 Bologna, Italy
Interests: galaxy clusters; intracluster medium; X-ray; dark matter; cosmology

Special Issue Information

Dear Colleagues,

Galaxy groups consist of a few tens of galaxies bound in a common gravitational potential and contain a significant fraction of the overall universal baryon budget. Therefore, they are key to our understanding of how the bulk of matter in the Universe accretes and forms hierarchical structures and how different sources of feedback affect their gravitational collapse. However, despite their crucial role in cosmic structure formation and evolution, galaxy groups have received less attention compared to massive clusters. This is perhaps in part due to their rarity in being observed and properly characterized. With the advent of eROSITA, many thousands of galaxy groups will be detected by X-ray, complementing optical and SZ coverage.

It is time to collect and organize the latest developments in our understanding of these systems and present future prospects from both observational and theoretical points of view.

This Special Issue aims to foster progress in the field of the physical properties of galaxy groups, facilitating effective cross-communication between observers, theorists, and simulators. Topics of interest to this Special Issue include (but are most certainly not limited to) multi-wavelength observations of single objects and samples, hydrodynamical simulations of cosmic structures, fossil/compact groups, the physics of the intragroup plasma and the distribution of the metals, and the scaling relations and their impact on cosmology.


Dr. Lorenzo Lovisari
Dr. Stefano Ettori
Guest Editors

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

  • observations
  • numerical simulations
  • cosmology
  • plasmas
  • galaxies

Published Papers (6 papers)

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Editorial

Jump to: Review

2 pages, 164 KiB  
Editorial
The Physical Properties of the Groups of Galaxies
by Lorenzo Lovisari and Stefano Ettori
Universe 2021, 7(8), 254; https://doi.org/10.3390/universe7080254 - 21 Jul 2021
Cited by 4 | Viewed by 1338
Abstract
Galaxy groups consist of a few tens of galaxies bound in a common gravitational potential [...] Full article
(This article belongs to the Special Issue The Physical Properties of the Groups of Galaxies)

Review

Jump to: Editorial

63 pages, 8934 KiB  
Review
Simulating Groups and the IntraGroup Medium: The Surprisingly Complex and Rich Middle Ground between Clusters and Galaxies
by Benjamin D. Oppenheimer, Arif Babul, Yannick Bahé, Iryna S. Butsky and Ian G. McCarthy
Universe 2021, 7(7), 209; https://doi.org/10.3390/universe7070209 - 24 Jun 2021
Cited by 54 | Viewed by 3047
Abstract
Galaxy groups are more than an intermediate scale between clusters and halos hosting individual galaxies, they are crucial laboratories capable of testing a range of astrophysics from how galaxies form and evolve to large scale structure (LSS) statistics for cosmology. Cosmological hydrodynamic simulations [...] Read more.
Galaxy groups are more than an intermediate scale between clusters and halos hosting individual galaxies, they are crucial laboratories capable of testing a range of astrophysics from how galaxies form and evolve to large scale structure (LSS) statistics for cosmology. Cosmological hydrodynamic simulations of groups on various scales offer an unparalleled testing ground for astrophysical theories. Widely used cosmological simulations with ∼(100 Mpc)3 volumes contain statistical samples of groups that provide important tests of galaxy evolution influenced by environmental processes. Larger volumes capable of reproducing LSS while following the redistribution of baryons by cooling and feedback are the essential tools necessary to constrain cosmological parameters. Higher resolution simulations can currently model satellite interactions, the processing of cool (T≈104−5 K) multi-phase gas, and non-thermal physics including turbulence, magnetic fields and cosmic ray transport. We review simulation results regarding the gas and stellar contents of groups, cooling flows and the relation to the central galaxy, the formation and processing of multi-phase gas, satellite interactions with the intragroup medium, and the impact of groups for cosmological parameter estimation. Cosmological simulations provide evolutionarily consistent predictions of these observationally difficult-to-define objects, and have untapped potential to accurately model their gaseous, stellar and dark matter distributions. Full article
(This article belongs to the Special Issue The Physical Properties of the Groups of Galaxies)
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48 pages, 2461 KiB  
Review
The Metal Content of the Hot Atmospheres of Galaxy Groups
by Fabio Gastaldello, Aurora Simionescu, Francois Mernier, Veronica Biffi, Massimo Gaspari, Kosuke Sato and Kyoko Matsushita
Universe 2021, 7(7), 208; https://doi.org/10.3390/universe7070208 - 24 Jun 2021
Cited by 24 | Viewed by 2700
Abstract
Galaxy groups host the majority of matter and more than half of all the galaxies in the Universe. Their hot (107 K), X-ray emitting intra-group medium (IGrM) reveals emission lines typical of many elements synthesized by stars and supernovae. Because their [...] Read more.
Galaxy groups host the majority of matter and more than half of all the galaxies in the Universe. Their hot (107 K), X-ray emitting intra-group medium (IGrM) reveals emission lines typical of many elements synthesized by stars and supernovae. Because their gravitational potentials are shallower than those of rich galaxy clusters, groups are ideal targets for studying, through X-ray observations , feedback effects, which leave important marks on their gas and metal contents. Here, we review the history and present status of the chemical abundances in the IGrM probed by X-ray spectroscopy. We discuss the limitations of our current knowledge, in particular due to uncertainties in the modeling of the Fe-L shell by plasma codes, and coverage of the volume beyond the central region. We further summarize the constraints on the abundance pattern at the group mass scale and the insight it provides to the history of chemical enrichment. Parallel to the observational efforts, we review the progress made by both cosmological hydrodynamical simulations and controlled high-resolution 3D simulations to reproduce the radial distribution of metals in the IGrM, the dependence on system mass from group to cluster scales, and the role of AGN and SN feedback in producing the observed phenomenology. Finally, we highlight future prospects in this field, where progress will be driven both by a much richer sample of X-ray emitting groups identified with eROSITA, and by a revolution in the study of X-ray spectra expected from micro-calorimeters onboard XRISM and ATHENA. Full article
(This article belongs to the Special Issue The Physical Properties of the Groups of Galaxies)
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58 pages, 5339 KiB  
Review
Feedback from Active Galactic Nuclei in Galaxy Groups
by Dominique Eckert, Massimo Gaspari, Fabio Gastaldello, Amandine M. C. Le Brun and Ewan O’Sullivan
Universe 2021, 7(5), 142; https://doi.org/10.3390/universe7050142 - 11 May 2021
Cited by 67 | Viewed by 5215
Abstract
The co-evolution between supermassive black holes and their environment is most directly traced by the hot atmospheres of dark matter halos. The cooling of the hot atmosphere supplies the central regions with fresh gas, igniting active galactic nuclei (AGN) with long duty cycles. [...] Read more.
The co-evolution between supermassive black holes and their environment is most directly traced by the hot atmospheres of dark matter halos. The cooling of the hot atmosphere supplies the central regions with fresh gas, igniting active galactic nuclei (AGN) with long duty cycles. Outflows from the central engine tightly couple with the surrounding gaseous medium and provide the dominant heating source preventing runaway cooling by carving cavities and driving shocks across the medium. The AGN feedback loop is a key feature of all modern galaxy evolution models. Here, we review our knowledge of the AGN feedback process in the specific context of galaxy groups. Galaxy groups are uniquely suited to constrain the mechanisms governing the cooling–heating balance. Unlike in more massive halos, the energy that is supplied by the central AGN to the hot intragroup medium can exceed the gravitational binding energy of halo gas particles. We report on the state-of-the-art in observations of the feedback phenomenon and in theoretical models of the heating-cooling balance in galaxy groups. We also describe how our knowledge of the AGN feedback process impacts galaxy evolution models and large-scale baryon distributions. Finally, we discuss how new instrumentation will answer key open questions on the topic. Full article
(This article belongs to the Special Issue The Physical Properties of the Groups of Galaxies)
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39 pages, 1448 KiB  
Review
Scaling Properties of Galaxy Groups
by Lorenzo Lovisari, Stefano Ettori, Massimo Gaspari and Paul A. Giles
Universe 2021, 7(5), 139; https://doi.org/10.3390/universe7050139 - 10 May 2021
Cited by 55 | Viewed by 2706
Abstract
Galaxy groups and poor clusters are more common than rich clusters, and host the largest fraction of matter content in the Universe. Hence, their studies are key to understand the gravitational and thermal evolution of the bulk of the cosmic matter. Moreover, because [...] Read more.
Galaxy groups and poor clusters are more common than rich clusters, and host the largest fraction of matter content in the Universe. Hence, their studies are key to understand the gravitational and thermal evolution of the bulk of the cosmic matter. Moreover, because of their shallower gravitational potential, galaxy groups are systems where non-gravitational processes (e.g., cooling, AGN feedback, star formation) are expected to have a higher impact on the distribution of baryons, and on the general physical properties, than in more massive objects, inducing systematic departures from the expected scaling relations. Despite their paramount importance from the astrophysical and cosmological point of view, the challenges in their detection have limited the studies of galaxy groups. Upcoming large surveys will change this picture, reassigning to galaxy groups their central role in studying the structure formation and evolution in the Universe, and in measuring the cosmic baryonic content. Here, we review the recent literature on various scaling relations between X-ray and optical properties of these systems, focusing on the observational measurements, and the progress in our understanding of the deviations from the self-similar expectations on groups’ scales. We discuss some of the sources of these deviations, and how feedback from supernovae and/or AGNs impacts the general properties and the reconstructed scaling laws. Finally, we discuss future prospects in the study of galaxy groups. Full article
(This article belongs to the Special Issue The Physical Properties of the Groups of Galaxies)
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28 pages, 3217 KiB  
Review
Properties of Fossil Groups of Galaxies
by J. Alfonso L. Aguerri and Stefano Zarattini
Universe 2021, 7(5), 132; https://doi.org/10.3390/universe7050132 - 4 May 2021
Cited by 13 | Viewed by 1938
Abstract
We review the formation and evolution of fossil groups and clusters from both the theoretical and the observational points of view. In the optical band, these systems are dominated by the light of the central galaxy. They were interpreted as old systems that [...] Read more.
We review the formation and evolution of fossil groups and clusters from both the theoretical and the observational points of view. In the optical band, these systems are dominated by the light of the central galaxy. They were interpreted as old systems that had enough time to merge all the M* galaxies within the central one. During the last two decades, many observational studies were performed to prove the old and relaxed state of fossil systems. The majority of these studies that spans a wide range of topics including halos global scaling relations, dynamical substructures, stellar populations, and galaxy luminosity functions seem to challenge this scenario. The general picture that can be obtained by reviewing all the observational works is that the fossil state could be transitional. Indeed, the formation of the large magnitude gap observed in fossil systems could be related to internal processes rather than an old formation. Full article
(This article belongs to the Special Issue The Physical Properties of the Groups of Galaxies)
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