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18 pages, 2731 KiB

Open AccessArticle

Assessing Galaxy Rotation Kinematics: Insights from Convolutional Neural Networks on Velocity Variations

by Amirmohammad Chegeni, Fatemeh Fazel Hesar, Mojtaba Raouf, Bernard Foing and Fons J. Verbeek

Universe 2025, 11(3), 92; https://doi.org/10.3390/universe11030092 - 8 Mar 2025

Viewed by 245

Abstract

Distinguishing galaxies as either fast or slow rotators plays a vital role in understanding the processes behind galaxy formation and evolution. Standard techniques, which are based on the

λ_{R}

spin parameter obtained from stellar kinematics, frequently face difficulties in classifying fast and [...] Read more.

Distinguishing galaxies as either fast or slow rotators plays a vital role in understanding the processes behind galaxy formation and evolution. Standard techniques, which are based on the

λ_{R}

spin parameter obtained from stellar kinematics, frequently face difficulties in classifying fast and slow rotators accurately. These challenges arise particularly in cases where galaxies have complex interaction histories or exhibit significant morphological diversity. In this paper, we evaluate the performance of a Convolutional Neural Network (CNN) in classifying galaxy rotation kinematics based on stellar kinematic maps from the SAMI survey. Our results show that the optimal CNN architecture achieves an accuracy and precision of approximately 91% and 95%, respectively, on the test dataset. Subsequently, we apply our trained model to classify previously unknown rotator galaxies for which traditional statistical tools have been unable to determine whether they exhibit fast or slow rotation, such as certain irregular galaxies or those in dense clusters. We also used Integrated Gradients (IGs) to reveal the crucial kinematic features that influenced the CNN’s classifications. This research highlights the power of CNNs to improve our comprehension of galaxy dynamics and emphasizes their potential to contribute to upcoming large-scale Integral Field Spectrograph (IFS) surveys. Full article

(This article belongs to the Special Issue Universe: Feature Papers 2024—"Galaxies and Clusters")

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17 pages, 1028 KiB

Open AccessArticle

Unveiling the Dynamics in Galaxy Clusters: The Hidden Role of Low-Luminosity Galaxies in Coma

by Alisson P. Costa, André L. B. Ribeiro, Flavio R. de Morais Neto and Juarez dos Santos Junior

Universe 2025, 11(3), 82; https://doi.org/10.3390/universe11030082 - 1 Mar 2025

Viewed by 269

Abstract

In this work, we study the Coma cluster, one of the richest and most well-known systems at low redshifts, to explore the importance of low-flux objects in the identification of cluster substructures. In addition, we conduct a study of the infall flow around [...] Read more.

In this work, we study the Coma cluster, one of the richest and most well-known systems at low redshifts, to explore the importance of low-flux objects in the identification of cluster substructures. In addition, we conduct a study of the infall flow around Coma, considering the presence or absence of low-flux objects across the projected phase space of the cluster. Our results indicate that low-luminosity galaxies play a fundamental role in understanding the dynamical state of galaxy clusters. These galaxies, often overlooked because of their faint nature, serve as sensitive tracers of substructure dynamics and provide crucial insights into the cluster’s evolutionary history. We show that not considering the low-flux objects present in clusters can lead to significant underestimates of the numbers of substructures, both in most central parts, in the infall regions, and beyond, connecting to the large-scale structure up to a distance of ∼8

R_{200}

from the center of Coma. Full article

(This article belongs to the Special Issue Universe: Feature Papers 2024—"Galaxies and Clusters")

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12 pages, 788 KiB

Open AccessArticle

Issues in the Investigations of the Dark Matter Phenomenon in Galaxies: Parcere Personis, Dicere de Vitiis

by Paolo Salucci

Universe 2025, 11(2), 67; https://doi.org/10.3390/universe11020067 - 17 Feb 2025

Viewed by 536

Abstract

It is always more evident that the kinematics of galaxies provide us with unique information on the Nature of the dark particles and on the properties of the galaxy Dark Matter (DM) halos. However, in investigating this topic, we have to be very [...] Read more.

It is always more evident that the kinematics of galaxies provide us with unique information on the Nature of the dark particles and on the properties of the galaxy Dark Matter (DM) halos. However, in investigating this topic, we have to be very careful about certain issues related to the assumptions that we take or to the practices that we follow. Here, we critically discuss such issues, that, today, result of fundamental importance, in that we have realized that the Nature of the DM will be not provided by “The Theory” but, has to be inferred by reverse engineering the observational scenario. Full article

(This article belongs to the Special Issue Universe: Feature Papers 2024—"Galaxies and Clusters")

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39 pages, 23123 KiB

Open AccessArticle

Core to Cosmic Edge: SIMBA-C’s New Take on Abundance Profiles in the Intragroup Medium at z = 0

by Aviv Padawer-Blatt, Zhiwei Shao, Renier T. Hough, Douglas Rennehan, Ruxin Barré, Vida Saeedzadeh, Arif Babul, Romeel Davé, Chiaki Kobayashi, Weiguang Cui, François Mernier and Ghassem Gozaliasl

Universe 2025, 11(2), 47; https://doi.org/10.3390/universe11020047 - 1 Feb 2025

Viewed by 764

Abstract

We employ the simba-c cosmological simulation to study the impact of its upgraded chemical enrichment model (Chem5) on the distribution of metals in the intragroup medium (IGrM). We investigate the projected X-ray emission-weighted abundance profiles of key elements over two decades in halo [...] Read more.

We employ the simba-c cosmological simulation to study the impact of its upgraded chemical enrichment model (Chem5) on the distribution of metals in the intragroup medium (IGrM). We investigate the projected X-ray emission-weighted abundance profiles of key elements over two decades in halo mass (

10^{13} \leq M_{500} / M_{⊙} \leq 10^{15}

). Typically, simba-c generates lower-amplitude abundance profiles than simba with flatter cores, in better agreement with observations. For low-mass groups, both simulations over-enrich the IGrM with Si, S, Ca, and Fe compared to observations, a trend likely related to inadequate modeling of metal dispersal and mixing. We analyze the 3D mass-weighted abundance profiles, concluding that the lower simba-c IGrM abundances are primarily a consequence of fewer metals in the IGrM, driven by reduced metal yields in Chem5, and the removal of the instantaneous recycling of metals approximation employed by simba. Additionally, an increased IGrM mass in low-mass simba-c groups is likely triggered by changes to the AGN and stellar feedback models. Our study suggests that a more realistic chemical enrichment model broadly improves agreement with observations, but physically motivated sub-grid models for other key processes, like AGN and stellar feedback and turbulent diffusion, are required to realistically reproduce observed group environments. Full article

(This article belongs to the Special Issue Universe: Feature Papers 2024—"Galaxies and Clusters")

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32 pages, 1586 KiB

Open AccessArticle

The Magellanic Clouds Are Very Rare in the IllustrisTNG Simulations

by Moritz Haslbauer, Indranil Banik, Pavel Kroupa, Hongsheng Zhao and Elena Asencio

Universe 2024, 10(10), 385; https://doi.org/10.3390/universe10100385 - 1 Oct 2024

Cited by 2 | Viewed by 895

Abstract

The Large and Small Magellanic Clouds (LMC and SMC) form the closest interacting galactic system to the Milky Way, therewith providing a laboratory to test cosmological models in the local Universe. We quantify the likelihood for the Magellanic Clouds (MCs) to be observed [...] Read more.

The Large and Small Magellanic Clouds (LMC and SMC) form the closest interacting galactic system to the Milky Way, therewith providing a laboratory to test cosmological models in the local Universe. We quantify the likelihood for the Magellanic Clouds (MCs) to be observed within the

Λ

CDM model using hydrodynamical simulations of the IllustrisTNG project. The orbits of the MCs are constrained by proper motion measurements taken by the Hubble Space Telescope and Gaia. The MCs have a mutual separation of

d_{MCs} = 24.5 kpc

and a relative velocity of

v_{MCs} = 90.8 km s^{- 1}

, implying a specific phase-space density of

f_{MCs, obs} \equiv {(d_{MCs} \cdot v_{MCs})}^{- 3} = 9.10 \times 10^{- 11} {km}^{- 3} s^{3} {kpc}^{- 3}

. We select analogues to the MCs based on their stellar masses and distances in MW-like halos. None of the selected LMC analogues have a higher total mass and lower Galactocentric distance than the LMC, resulting in >3.75

σ

tension. We also find that the

f_{MCs}

distribution in the highest resolution TNG50 simulation is in

3.95 σ

tension with observations. Thus, a hierarchical clustering of two massive satellites like the MCs in a narrow phase-space volume is unlikely in

Λ

CDM, presumably because of short merger timescales due to dynamical friction between the overlapping dark matter halos. We show that group infall led by an LMC analogue cannot populate the Galactic disc of satellites (DoS), implying that the DoS and the MCs formed in physically unrelated ways in

Λ

CDM. Since the

20^{\circ}

alignment of the LMC and DoS orbital poles has a likelihood of

P = 0.030

(

2.17 σ

), adding this

χ^{2}

to that of

f_{MCs}

gives a combined likelihood of

P = 3.90 \times 10^{- 5}

(

4.11 σ

). Full article

(This article belongs to the Special Issue Universe: Feature Papers 2024—"Galaxies and Clusters")

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25 pages, 2077 KiB

Open AccessArticle

The Rotation of Classical Bulges in Barred Galaxies in the Presence of Gas

by Rubens E. G. Machado, Kenzo R. Sakamoto, Andressa Wille and Gustavo F. Gonçalves

Universe 2024, 10(5), 223; https://doi.org/10.3390/universe10050223 - 16 May 2024

Cited by 2 | Viewed by 1360

Abstract

Barred galaxies often develop a box/peanut pseudobulge, but they can also host a nearly spherical classical bulge, which is known to gain rotation due to the bar. We aim to explore how the presence of gas impacts the rotation of classical bulges. We [...] Read more.

Barred galaxies often develop a box/peanut pseudobulge, but they can also host a nearly spherical classical bulge, which is known to gain rotation due to the bar. We aim to explore how the presence of gas impacts the rotation of classical bulges. We carried out a comprehensive set of hydrodynamical N-body simulations with different combinations of bulge masses and gas fractions. In these models, both massive bulges and high gas content tend to inhibit the formation of strong bars. For low-mass bulges, the resulting bar is stronger in cases of low gas content. In the stronger bar models, bulges acquire more angular momentum and thus display considerable rotational velocity. Such bulges also develop anisotropic velocity dispersions and become triaxial in shape. We found that the rotation of the bulge becomes less pronounced as the gas fraction is increased from 0 to 30%. These results indicate that the gas content has a significant effect on the dynamics of the classical bulge, because it influences bar strength. Particularly in the case of the low-mass bulges (10% bulge mass fraction), all of the measured rotational and structural properties of the classical bulge depend strongly and systematically on the gas content of the galaxy. Full article

(This article belongs to the Special Issue Universe: Feature Papers 2024—"Galaxies and Clusters")

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26 pages, 17785 KiB

Open AccessArticle

The κ-Model under the Test of the SPARC Database

by Gianni Pascoli

Universe 2024, 10(3), 151; https://doi.org/10.3390/universe10030151 - 21 Mar 2024

Cited by 2 | Viewed by 1429

Abstract

Our main goal here is to conduct a comparative analysis between the well-known MOND theory and a more recent model called the

κ

-model. An additional connection, between the

κ

-model and two other novel MOND-type theories, Newtonian Fractional-Dimension Gravity (NFDG) and Refracted [...] Read more.

Our main goal here is to conduct a comparative analysis between the well-known MOND theory and a more recent model called the

κ

-model. An additional connection, between the

κ

-model and two other novel MOND-type theories, Newtonian Fractional-Dimension Gravity (NFDG) and Refracted Gravity (RG), is likewise presented. All these models are built to overtake the DM paradigm, or at least to strongly reduce the dark matter content. Whereas they rely on different formalisms, however, all four seem to suggest that the universal parameter,

a_{0}

, appearing in MOND theory could intrinsically be correlated to either the sole baryonic mean mass density (RG and

κ

-model) and/or to the dimension of the object under consideration (NFDG and

κ

-model). We then confer to parameter

a_{0}

a more flexible status of multiscale parameter, as required to explain the dynamics together in galaxies and in galaxy clusters. Eventually, the conformal gravity theory (CFT) also seems to have some remote link with the

κ

-model, even though the first one is an extension of general relativity, and the second one is Newtonian in essence. The

κ

-model has been tested on a small sample of spiral galaxies and in galaxy clusters. Now, we test this model on a large sample of galaxies issued from the SPARC database. Full article

(This article belongs to the Special Issue Universe: Feature Papers 2024—"Galaxies and Clusters")

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19 pages, 1623 KiB

Open AccessArticle

Dark Matter in Fractional Gravity III: Dwarf Galaxies Kinematics

by Francesco Benetti, Andrea Lapi, Giovanni Gandolfi, Minahil Adil Butt, Yacer Boumechta, Balakrishna S. Haridasu and Carlo Baccigalupi

Universe 2023, 9(11), 478; https://doi.org/10.3390/universe9110478 - 8 Nov 2023

Cited by 3 | Viewed by 1786

Abstract

Recently, we put forward a framework where the dark matter (DM) component within virialized halos is subject to a non-local interaction originated by fractional gravity (FG) effects. In previous works, we demonstrated that such a framework can substantially alleviate the small-scale issues of [...] Read more.

Recently, we put forward a framework where the dark matter (DM) component within virialized halos is subject to a non-local interaction originated by fractional gravity (FG) effects. In previous works, we demonstrated that such a framework can substantially alleviate the small-scale issues of the standard

Λ

CDM paradigm, without altering the DM mass profile predicted by N-body simulations, and retaining its successes on large cosmological scales. In this paper, we investigate further, to probe FG via the high-quality data of individual dwarf galaxies, by exploiting the rotation velocity profiles inferred from stellar and gas kinematic measurements in eight dwarf irregulars, and the projected velocity dispersion profiles inferred from the observed dynamics of stellar tracers in seven dwarf spheroidals and in the ultra-diffuse galaxy DragonFly 44. We find that FG can reproduce extremely well the rotation and dispersion curves of the analyzed galaxies, performing in most instances significantly better than the standard Newtonian setup. Full article

(This article belongs to the Special Issue Universe: Feature Papers 2024—"Galaxies and Clusters")

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Review

Jump to: Research

38 pages, 1533 KiB

Open AccessReview

The Correlation Luminosity-Velocity Dispersion of Galaxies and Active Galactic Nuclei

by Mauro D’Onofrio, Paola Marziani, Cesare Chiosi and Castalia Alenka Negrete

Universe 2024, 10(6), 254; https://doi.org/10.3390/universe10060254 - 4 Jun 2024

Cited by 2 | Viewed by 1372

Abstract

In this work we discuss the correlation between luminosity L and velocity dispersion

σ

observed in different astrophysical contexts, in particular that of early-type galaxies (ETGs; Faber–Jackson (FJ) law) and that of active galactic nuclei (AGN). Our data for the ETGs confirm the [...] Read more.

In this work we discuss the correlation between luminosity L and velocity dispersion

σ

observed in different astrophysical contexts, in particular that of early-type galaxies (ETGs; Faber–Jackson (FJ) law) and that of active galactic nuclei (AGN). Our data for the ETGs confirm the bending of the FJ at high masses and the existence of similar curvatures in the projections of the Fundamental Plane (FP) approximately at the mass scale of ∼

10^{10} M_{⊙}

. We provide an explanation for such curvatures and for the presence of the Zone of Exclusion (ZoE) in these diagrams. The new prospected theory for the FJ law introduces a new framework to understand galaxy evolution in line with the hierarchical structure of the Universe. The classic analysis carried out for a class of type 1 AGN accreting gas at very high rates, confirms that a FJ law of the form

L = L_{0} σ^{4}

is roughly consistent with the observations, with a slope quite similar to that of ETGs. We discuss the physics behind the FJ law for the AGN in different contexts and also examine the biases affecting both the luminosity and the velocity dispersion, paying particular attention to the effects induced by the spherical symmetry of the emitting sources on the accuracy of the luminosity estimates. Full article

(This article belongs to the Special Issue Universe: Feature Papers 2024—"Galaxies and Clusters")

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