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Galaxies
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Challenges in Our Understanding of Dwarf Galaxies
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Challenges in Our Understanding of Dwarf Galaxies

A special issue of Galaxies (ISSN 2075-4434).

Deadline for manuscript submissions: closed (30 September 2021) | Viewed by 16950

Special Issue Editors

Dr. Behnam Javanmardi

E-Mail Website
Guest Editor
Institute for Genomic Statistics and Bioinformatics, University of Bonn, 53127 Bonn, Germany
Interests: extragalactic astronomy and cosmology
Dr. Yanbin Yang

E-Mail
Guest Editor
CNRS / Paris Observatory, 75016 Paris, France
Interests: dynamics of galaxy formation

Special Issue Information

Dear Colleagues,

Dwarf galaxies are the most numerous type of galaxies in the Universe and are considered as rich laboratories for testing different astrophysical and cosmological models and theories. During the past years, the increasingly precise observations of the dwarf galaxies in the Local Group and the deep observations of dwarf galaxies in distant groups have provided exciting insights into the properties of these objects. Additionally, the progress in theoretical studies and the improvements in computer simulations have been advancing our understanding of the physical processes involved in the formation and evolution of dwarf galaxies and their relations to their environments.

Nevertheless, there are still unsolved puzzles in our understanding of dwarf galaxies, and the purpose of this Special Issue is to focus on and become a reference for these challenges and possible research paths towards their solution. To this end, both review papers and focused research papers, especially on the following key topics, are welcomed:

  • Past, current, and future dwarf galaxy surveys.
  • Dwarf galaxies in the Local Group and beyond.
  • Dwarf galaxies and the standard model of cosmology.
  • Missing satellites, too-big-to-fail, and disk-of-satellites problems.
  • Dynamical properties of dwarf galaxies, dark matter, and modified gravity.
  • Dwarf galaxies in computer simulations.
  • Star formation in dwarf galaxies.
  • Influence of different environments on the properties of dwarf galaxies.
  • Tidal dwarf galaxies and primordial dwarf galaxies.

Dr. Behnam Javanmardi
Dr. Yanbin Yang
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. Galaxies is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1400 CHF (Swiss Francs). 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

  • galaxies: dwarf
  • galaxies: evolution
  • galaxies: formation
  • Local Group
  • dark matter
  • galaxies: kinematics and dynamics

Published Papers (5 papers)

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Research

Jump to: Review

31 pages, 2533 KiB  
Article
The Interstellar Medium of Dwarf Galaxies
by Christian Henkel, Leslie K. Hunt and Yuri I. Izotov
Galaxies 2022, 10(1), 11; https://0-doi-org.brum.beds.ac.uk/10.3390/galaxies10010011 - 12 Jan 2022
Cited by 8 | Viewed by 3278
Abstract
Dwarf galaxies are by far the most numerous galaxies in the Universe, showing properties that are quite different from those of their larger and more luminous cousins. This review focuses on the physical and chemical properties of the interstellar medium of those dwarfs [...] Read more.
Dwarf galaxies are by far the most numerous galaxies in the Universe, showing properties that are quite different from those of their larger and more luminous cousins. This review focuses on the physical and chemical properties of the interstellar medium of those dwarfs that are known to host significant amounts of gas and dust. The neutral and ionized gas components and the impact of the dust will be discussed, as well as first indications for the existence of active nuclei in these sources. Cosmological implications are also addressed, considering the primordial helium abundance and the similarity of local Green Pea galaxies with young, sometimes protogalactic sources in the early Universe. Full article
(This article belongs to the Special Issue Challenges in Our Understanding of Dwarf Galaxies)
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33 pages, 1307 KiB  
Article
Review of Solutions to the Cusp-Core Problem of the ΛCDM Model
by Antonino Del Popolo and Morgan Le Delliou
Galaxies 2021, 9(4), 123; https://0-doi-org.brum.beds.ac.uk/10.3390/galaxies9040123 - 18 Dec 2021
Cited by 12 | Viewed by 4270
Abstract
This review aims at proposing to the field an overview of the Cusp-core problem, including a discussion of its advocated solutions, assessing how each can satisfactorily provide a description of central densities. Whether the Cusp-core problem reflects our insufficient grasp on the nature [...] Read more.
This review aims at proposing to the field an overview of the Cusp-core problem, including a discussion of its advocated solutions, assessing how each can satisfactorily provide a description of central densities. Whether the Cusp-core problem reflects our insufficient grasp on the nature of dark matter, of gravity, on the impact of baryonic interactions with dark matter at those scales, as included in semi-analytical models or fully numerical codes, the solutions to it can point either to the need for a paradigm change in cosmology, or to to our lack of success in ironing out the finer details of the ΛCDM paradigm. Full article
(This article belongs to the Special Issue Challenges in Our Understanding of Dwarf Galaxies)
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15 pages, 565 KiB  
Article
Are Disks of Satellites Comprised of Tidal Dwarf Galaxies?
by Michal Bílek, Ingo Thies, Pavel Kroupa and Benoit Famaey
Galaxies 2021, 9(4), 100; https://0-doi-org.brum.beds.ac.uk/10.3390/galaxies9040100 - 10 Nov 2021
Cited by 8 | Viewed by 2325
Abstract
It was found that satellites of nearby galaxies can form flattened co-rotating structures called disks of satellites or planes of satellites. Their existence is not expected by the current galaxy formation simulations in the standard dark matter-based cosmology. On the contrary, modified gravity [...] Read more.
It was found that satellites of nearby galaxies can form flattened co-rotating structures called disks of satellites or planes of satellites. Their existence is not expected by the current galaxy formation simulations in the standard dark matter-based cosmology. On the contrary, modified gravity offers a promising alternative: the objects in the disks of satellites are tidal dwarf galaxies, that is, small galaxies that form from tidal tails of interacting galaxies. After introducing the topic, we review here our work on simulating the formation of the disks of satellites of the Milky Way and Andromeda galaxies. The initial conditions of the simulation were tuned to reproduce the observed positions, velocities and disk orientations of the galaxies. The simulation showed that the galaxies had a close flyby 6.8 Gyr ago. One of the tidal tails produced by the Milky Way was captured by Andromeda. It formed a cloud of particles resembling the disk of satellites at Andromeda by its size, orientation, rotation and mass. A hint of a disk of satellites was formed at the Milky Way too. In addition, the encounter induced a warp in the disk of the simulated Milky Way that resembles the real warp by its magnitude and orientation. We present here, for the first time, the proper motions of the members of the disk of satellites of Andromeda predicted by our simulation. Finally, we point out some of the remaining open questions which this hypothesis, for the formation of disks of satellites, brings up. Full article
(This article belongs to the Special Issue Challenges in Our Understanding of Dwarf Galaxies)
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Review

Jump to: Research

38 pages, 18692 KiB  
Review
The Cusp–Core Problem in Gas-Poor Dwarf Spheroidal Galaxies
by Pierre Boldrini
Galaxies 2022, 10(1), 5; https://0-doi-org.brum.beds.ac.uk/10.3390/galaxies10010005 - 30 Dec 2021
Cited by 13 | Viewed by 2688
Abstract
This review deals with the inconsistency of inner dark matter density profiles in dwarf galaxies, known as the cusp–core problem. In particular, we aim to focus on gas-poor dwarf galaxies. One of the most promising solutions to this cold dark matter small-scale issue [...] Read more.
This review deals with the inconsistency of inner dark matter density profiles in dwarf galaxies, known as the cusp–core problem. In particular, we aim to focus on gas-poor dwarf galaxies. One of the most promising solutions to this cold dark matter small-scale issue is the stellar feedback, but it seems to be only designed for gas-rich dwarfs. However, in the regime of classical dwarfs, this core mechanism becomes negligible. Therefore, it is required to find solutions without invoking these baryonic processes as dark matter cores tend to persist even for these dwarfs, which are rather dark-matter-dominated. Here, we have presented two categories of solutions. One consists of creating dark matter cores from cusps within cold dark matter by altering the dark matter potential via perturbers. The second category gathers solutions that depict the natural emergence of dark matter cores in alternative theories. Given the wide variety of solutions, it becomes necessary to identify which mechanism dominates in the central region of galaxies by finding observational signatures left by them in order to highlight the true nature of dark matter. Full article
(This article belongs to the Special Issue Challenges in Our Understanding of Dwarf Galaxies)
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30 pages, 4785 KiB  
Review
Phase-Space Correlations among Systems of Satellite Galaxies
by Marcel S. Pawlowski
Galaxies 2021, 9(3), 66; https://0-doi-org.brum.beds.ac.uk/10.3390/galaxies9030066 - 13 Sep 2021
Cited by 21 | Viewed by 2958
Abstract
Driven by the increasingly complete observational knowledge of systems of satellite galaxies, mutual spatial alignments and relations in velocities among satellites belonging to a common host have become a productive field of research. Numerous studies have investigated different types of such phase-space correlations [...] Read more.
Driven by the increasingly complete observational knowledge of systems of satellite galaxies, mutual spatial alignments and relations in velocities among satellites belonging to a common host have become a productive field of research. Numerous studies have investigated different types of such phase-space correlations and were met with varying degrees of attention by the community. The Planes of Satellite Galaxies issue is maybe the best-known example, with a rich field of research literature and an ongoing, controversial debate on how much of a challenge it poses to the ΛCDM model of cosmology. Another type of correlation, the apparent excess of close pairs of dwarf galaxies, has received considerably less attention despite its reported tension with ΛCDM expectations. With the fast expansion of proper motion measurements in recent years, largely driven by the Gaia mission, other peculiar phase-space correlations have been uncovered among the satellites of the Milky Way. Examples are the apparent tangential velocity excess of satellites compared to cosmological expectations, and the unexpected preference of satellites to be close to their pericenters. At the same time, other kinds of correlations have been found to be more in line with cosmological expectations—specifically, lopsided satellite galaxy systems and the accretion of groups of satellite galaxies. The latter has mostly been studied in cosmological simulations thus far, but it offers the potential to address some of the other issues by providing a way to produce correlations among the orbits of a group’s satellite galaxy members. This review is the first to provide an introduction to the highly active field of phase-space correlations among satellite galaxy systems. The emphasis is on summarizing existing, recent research and highlighting interdependencies between the different, currently almost exclusively individually considered types of correlations. Future prospects in light of upcoming observational facilities and our ever-expanding knowledge of satellite galaxy systems beyond the Local Group are also briefly discussed. Full article
(This article belongs to the Special Issue Challenges in Our Understanding of Dwarf Galaxies)
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