Galaxies

40 pages, 2191 KB

Open AccessArticle

Comparing Measures of the Hubble and BAO Tensions in ΛCDM and Possible Solutions in f(Q) Gravity

by José Antonio Nájera, Indranil Banik, Harry Desmond and Vasileios Kalaitzidis

Galaxies 2026, 14(2), 19; https://doi.org/10.3390/galaxies14020019 - 9 Mar 2026

We test whether

f (Q)

symmetric teleparallel gravity theories can solve the Hubble tension consistently with DESI DR2 BAO. We consider three

f (Q)

functional forms: logarithmic, exponential, and hyperbolic tangent. We extend these models by allowing a cosmological [...] Read more.

We test whether

f (Q)

symmetric teleparallel gravity theories can solve the Hubble tension consistently with DESI DR2 BAO. We consider three

f (Q)

functional forms: logarithmic, exponential, and hyperbolic tangent. We extend these models by allowing a cosmological constant, and compare to phenomenological models with a flexible exponential, hyperbolic secant, and polynomial decay addition to the standard

Λ

CDM

H (z)

. We test these models against DESI DR2 BAO, CMB (Planck 2018 + SPT-3G + ACT DR6), local

H_{0}

, and Cosmic Chronometer data. The logarithmic and hyperbolic tangent

f (Q)

models do not provide an adequate solution, but the exponential model does. Furthermore, it slightly reduces the

(Ω_{m}, H_{0} r_{d})

parameter space tension between CMB and BAO datasets to

2.56 σ

, down from

2.65 σ

for

Λ

CDM. Although

Λ

CDM faces only

1.66 σ

tension in DESI data space, the

1 σ

higher tension in parameter space suggests a real anomaly. The models assisted by the cosmological constant perform slightly better still, at the cost of undermined theoretical motivation. They also perform poorly once local

H_{0}

measurements are included. The phenomenological models fit all data reasonably well, yet the best-fitting models predict isotropically averaged BAO distances exceeding the DESI DR2 measurements at all redshifts. This highlights the difficulties of finding a theoretically motivated solution to the Hubble tension while remaining consistent with BAO data. Full article

(This article belongs to the Special Issue Theoretical and Observational Approaches to the Hubble Tension in Cosmology)

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21 pages, 6304 KB

Open AccessArticle

Enhancing Gravitational Lens Study with Deep Learning: A Study on Effects of Dropout Regularization

by Juan Jordi Ancona-Flores, Alberto Hernández-Almada and Verónica Motta

Galaxies 2026, 14(2), 18; https://doi.org/10.3390/galaxies14020018 - 6 Mar 2026

Abstract

Strong gravitational lensing provides valuable insights into the mass distribution of galaxies and the nature of dark matter. However, its modeling is computationally demanding due to the large volume of strong lensing observations. In this work, we explore the application of Convolutional Neural [...] Read more.

Strong gravitational lensing provides valuable insights into the mass distribution of galaxies and the nature of dark matter. However, its modeling is computationally demanding due to the large volume of strong lensing observations. In this work, we explore the application of Convolutional Neural Networks to infer physical parameters from simulated galaxy–galaxy lens systems, described by the Singular Isothermal Ellipsoid (SIE) profile for the galaxy lens. We construct a dataset of 76,396 synthetic lensing images derived from the China Space Station Telescope catalog and employ it to train a modified CNN model, based on the AlexNet architecture, to predict four key SIE parameters, the Einstein radius, the axis ratio and ellipticity components. We analyze the network performance under three distinct dropout configurations to quantify their influence on generalization and parameter inference accuracy. The results indicate that the incorporation of dropout is critical for enhancing the precision and robustness of the estimated parameters as demonstrated using a 4-fold cross-validation procedure. When dropout tools are included, we obtain coefficients of determination up to

R^{2} \sim 0.96

for most SIE parameters and mean peak signal-to-noise ratios of up to ∼37 dB. Relative to the configuration without dropout, the use of dropout reduces the relative errors in the inferred SIE parameters by approximately 60–76%, resulting in errors of at most ∼9% at the 90% confidence level for the majority of parameters. These findings highlight the potential of deep learning approaches to enable scalable, computationally efficient, and high-precision modeling of strong gravitational lensing systems. Full article

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7 pages, 420 KB

Open AccessCommunication

Molybdenum Abundances in MINCE Stars

by Linda Lombardo and Francesca Lucertini

Galaxies 2026, 14(2), 17; https://doi.org/10.3390/galaxies14020017 - 28 Feb 2026

Abstract

Molybdenum (Mo, Z = 42) is a neutron-capture element with seven stable isotopes that can be produced by different processes. Previous studies have shown a large scatter in molybdenum abundances for metal-poor ([Fe/H] <

- 1

) stars, indicating that multiple nucleosynthetic channels [...] Read more.

Molybdenum (Mo, Z = 42) is a neutron-capture element with seven stable isotopes that can be produced by different processes. Previous studies have shown a large scatter in molybdenum abundances for metal-poor ([Fe/H] <

- 1

) stars, indicating that multiple nucleosynthetic channels are responsible for molybdenum production even at very low metallicity. To understand which different nucleosynthesis processes are involved in the chemical enrichment of this element in the Galaxy, a large sample of precise molybdenum abundance is required. In this study, we present molybdenum abundances of 27 metal-poor stars from the Measuring at Intermediate Metallicity Neutron-Capture Elements project sample. We derived molybdenum abundances using three Mo i lines at 550.6 nm, 557.0 nm, and 603.0 nm, which proved to be reliable for measuring Mo abundances in giant stars with [Fe/H]

> - 2

. Our derived [Mo/Fe] abundance ratios show on average slightly higher values (∼0.2 dex) compared to the literature samples. This may be due to an observational bias or to non-local thermodynamic equilibrium effects. We also found that Gaia-Sausage-Enceladus candidate stars have lower [Mo/Fe] than the sample average, while the only Sequoia candidate star has a higher [Mo/Fe] than most sample stars. Full article

(This article belongs to the Special Issue Neutron Capture Processes in the Universe)

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36 pages, 1103 KB

Open AccessArticle

A Common Origin of the H₀ and S₈ Cosmological Tensions and a Resolution Within a Modified ΛCDM Framework

by Dimitris M. Christodoulou, Demosthenes Kazanas and Silas G. T. Laycock

Galaxies 2026, 14(2), 16; https://doi.org/10.3390/galaxies14020016 - 27 Feb 2026

Abstract

The two most severe cosmological tensions in the Hubble constant

H_{0}

and the matter clustering amplitude

S_{8}

have the same relative discrepancy of 8.3%, which suggests that they may have a common origin. Modifications of gravity and exotic dark fields with [...] Read more.

The two most severe cosmological tensions in the Hubble constant

H_{0}

and the matter clustering amplitude

S_{8}

have the same relative discrepancy of 8.3%, which suggests that they may have a common origin. Modifications of gravity and exotic dark fields with numerous free parameters introduced in the Einstein field equations often struggle to simultaneously alleviate both tensions; thus, we need to look for a common cause within the standard

Λ

CDM framework. At the same time, linear perturbation analyses of matter in the expanding

Λ

CDM universe have always neglected the impact of comoving peculiar velocities

v

(generally thought to be a second-order effect), the same velocities that, in physical space, cannot be fully accounted for in the observed late-time universe when the cosmic distance ladder is used to determine the local value of

H_{0}

. We have reworked the linear density perturbation equations in the conformal Newtonian gauge (sub-horizon limit) by introducing an additional drag force per unit mass

- Γ (t) v

in the Euler equation with

Γ \equiv γ (2 H)

, where

γ ≪ 1

is a positive dimensionless constant and

2 H (t)

is the time-dependent Hubble friction. We find that a damping parameter of

γ = 0.083

is sufficient to resolve the

S_{8}

tension by suppressing the growth of structure at low redshifts, starting at

z_{★} ≃ 3.5 - 6.5

to achieve

S_{8} ≃ 0.78 - 0.76

, respectively. Furthermore, we argue that the physical source causing this additional friction (a tidal field generated by nonlinear structures in the late-time universe) is also responsible for a systematic error in the local determinations of

H_{0}

—the inability to subtract peculiar tidal velocities along the lines of sight when determining the Hubble flow via the cosmic distance ladder. Finally, the dual action of the tidal field on the expanding background—reducing both the matter and the dark energy sources of the squared Hubble rate

H^{2}

, thereby holding back the cosmic acceleration

\ddot{a}

—is of fundamental importance in resolving cosmological tensions and can also substantially alleviate the density coincidence problem. Full article

(This article belongs to the Special Issue Theoretical and Observational Approaches to the Hubble Tension in Cosmology)

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27 pages, 29463 KB

Open AccessArticle

Revealing the Morpho-Kinematics of NGC 2371—A Planetary Nebula with a [WR] Central Star

by Roberto Vázquez, Jesús A. Toalá, Luis F. Miranda, Sandra Ayala, María E. Contreras, Marco A. Gómez-Muñoz, Pedro F. Guillen, Lorenzo Olguín, Gerardo Ramos-Larios, Laurence Sabin and Federico Soto-Badilla

Galaxies 2026, 14(2), 15; https://doi.org/10.3390/galaxies14020015 - 27 Feb 2026

Abstract

We present new high-dispersion optical spectra of the planetary nebula NGC 2371 obtained with the Manchester Echelle Spectrometer at the OAN-SPM 2.1 m telescope, complemented with 3D morpho-kinematic modelling using ShapeX. The data reveal that the present-day morphology of NGC 2371 is [...] Read more.

We present new high-dispersion optical spectra of the planetary nebula NGC 2371 obtained with the Manchester Echelle Spectrometer at the OAN-SPM 2.1 m telescope, complemented with 3D morpho-kinematic modelling using ShapeX. The data reveal that the present-day morphology of NGC 2371 is the outcome of multiple episodic mass-loss events rather than a single outflow. Our best-fitting model simultaneously reproduces the direct images and the Position–Velocity (PV) diagrams, and consists of a barrel-shaped shell with younger polar caps, extended bipolar lobes, and a pair of misaligned low-excitation [N ii] knots interpreted as jet-like ejections. The derived kinematical ages of the main structures, spanning ≃1600 to ≃4400 yr, indicate successive episodes of mass loss with different geometries and timescales. The nearly perpendicular bipolar lobes, the absence of a pronounced waist, and the surface distortions of the large-scale structures cannot be explained solely by standard axisymmetric wind interactions. Instead, our results point to a combination of shaping agents, including a late thermal pulse (born-again scenario) possibly related to the H-deficient [WR]-type nature of the central star, binary-driven interactions, and episodic jet activity. NGC 2371 thus provides a particularly instructive case where multiple shaping agents may operate, and where some of the relevant physical processes remain only marginally explored in current models of PN formation and evolution. Full article

(This article belongs to the Special Issue Origins and Models of Planetary Nebulae, 2nd Edition)

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38 pages, 106096 KB

Open AccessArticle

Validating the CROCODILE Model Within the AGORA Galaxy Simulation Framework

by Pablo Granizo, Yuri Oku and Kentaro Nagamine

Galaxies 2026, 14(2), 14; https://doi.org/10.3390/galaxies14020014 - 27 Feb 2026

Abstract

Numerical galaxy formation simulations are sensitive to numerical methods and sub-grid physics models, making code comparison projects essential for quantifying uncertainties. Here, we evaluate gadget4-osaka within the AGORA project framework by conducting a systematic comparison with its predecessor. We perform an [...] Read more.

Numerical galaxy formation simulations are sensitive to numerical methods and sub-grid physics models, making code comparison projects essential for quantifying uncertainties. Here, we evaluate gadget4-osaka within the AGORA project framework by conducting a systematic comparison with its predecessor. We perform an isolated disk galaxy and a cosmological zoom-in run of a Milky Way-mass halo, following the multi-step AGORA calibration procedure. By systematically deconstructing the updated stellar feedback model, we demonstrate that mechanical momentum injection is necessary to suppress unphysical gas fragmentation and regulate star formation, yielding agreement with the Kennicutt–Schmidt relation. Meanwhile, stochastic thermal heating is essential for driving a hot metal-enriched gaseous halo, thereby creating a multiphase circumgalactic medium that is absent in the predecessor code. In the cosmological context, we calibrate the simulation to match the stellar mass growth history targeted by the AGORA collaboration. The validated gadget4-osaka simulation has been contributed to the AGORA CosmoRun suite, providing a new data point for understanding the impact of numerical and physical modeling choices on galaxy evolution. Full article

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21 pages, 5684 KB

Open AccessArticle

The Optical Properties of Host Galaxies of Radio Sources in the Coma Cluster

by Xiaolan Hou, Heng Yu, Tong Pan, Hu Zou, Haoran Dou, Emily Moravec and Chengkui Li

Galaxies 2026, 14(1), 13; https://doi.org/10.3390/galaxies14010013 - 19 Feb 2026

Abstract

We present a comprehensive study of host galaxies of radio sources within the 1.35

R_{200}

of the Coma cluster by combining deep

144 MHz

observations from the LOFAR Two-Metre Sky Survey (LoTSS-DR2) with optical spectroscopy and photometry from DESI and SDSS. We [...] Read more.

We present a comprehensive study of host galaxies of radio sources within the 1.35

R_{200}

of the Coma cluster by combining deep

144 MHz

observations from the LOFAR Two-Metre Sky Survey (LoTSS-DR2) with optical spectroscopy and photometry from DESI and SDSS. We identify 79 spectroscopically confirmed cluster members with reliable radio emission and classify them into compact, extended, and tailed subsamples according to their radio morphologies. By combining their radio and optical properties, we find compact radio sources are predominantly associated with massive, quiescent galaxies driven by

AGN

activity, while tailed sources are largely hosted by star-forming galaxies, tracing ongoing ram pressure stripping (

RPS

). Using phase-space analysis and a projected infall time proxy (

d_{R}

), we find that extended sources are preferentially located in the cluster outskirts (

d_{R} > 1

), while tailed sources are concentrated in the intermediate infall region (

0.4 < d_{R} < 1.0

), highlighting the influence of the dense intracluster medium. Full article

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26 pages, 1718 KB

Open AccessArticle

Single Parameter Model for Galaxy Rotation Curves

by Sophia N. Cisneros, Rich Ott, Meagan Crowley, Amy Roberts and Marcus Paz

Galaxies 2026, 14(1), 12; https://doi.org/10.3390/galaxies14010012 - 15 Feb 2026

Abstract

One key piece of evidence for dark matter is the rotation-curve problem: the disagreement between measured galactic rotation curves and their luminous mass. A novel solution to this problem is presented here, in a model that predicts observed Doppler-shifted spectra based only on [...] Read more.

One key piece of evidence for dark matter is the rotation-curve problem: the disagreement between measured galactic rotation curves and their luminous mass. A novel solution to this problem is presented here, in a model that predicts observed Doppler-shifted spectra based only on the luminous matter estimates and one free model parameter

α

. This model is applied to fit the rotation curves of the SPARC sample of 175 galaxies, yielding mass-to-light ratios, goodness of fit measurements, and

α

. The measured average

χ_{r}^{2} = 2.24

compares favorably with the Navarro-Frenk-White dark matter model’s average of

χ_{r}^{2} = 4.19

for the same data, and more galaxies are successfully fit by this model. The model provides a useful formulation linking luminous matter to the observed rotation curves, with the dark matter contribution to galaxies encoded in two transformation terms of the luminous mass. It also offers a lower-parameter characterization of the rotation curve problem, and a power law relationship between

α

and galactic photometric quantities is observed, potentially removing the need for the free parameter. Full article

(This article belongs to the Special Issue Alternative Interpretations of Observed Galactic Behaviors)

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19 pages, 2294 KB

Open AccessArticle

IFU Spectroscopic Study of the Planetary Nebula Abell 30: Mapping the Ionisation and Kinematic Structure of the Inner Complex

by Kam Ling Chan, Andreas Ritter, Quentin Andrew Parker and Katrina Exter

Galaxies 2026, 14(1), 11; https://doi.org/10.3390/galaxies14010011 - 5 Feb 2026

Abstract

This work presents integrated flux and velocity channel maps of the planetary nebula Abell 30 (A30) inner knot system. The observations were taken with the INTEGRAL spectrograph at the William Herschel Telescope (WHT), La Palma, Spain. Our IFU data cube has a field [...] Read more.

This work presents integrated flux and velocity channel maps of the planetary nebula Abell 30 (A30) inner knot system. The observations were taken with the INTEGRAL spectrograph at the William Herschel Telescope (WHT), La Palma, Spain. Our IFU data cube has a field of view (FoV) of 12.3″× 16″ that partially covers knots J1 and J2, and completely covers knots J3 and J4 in the system. Optical Recombination Lines (ORLs) of C II, He I, He II, N III, O II and Collisionally Excited Lines (CELs) of [Ar IV], [Ar V], [N II], [Ne III], [Ne IV], and [O III] were detected. Our integrated flux maps visualise the ionisation structure and the chemical inhomogeneity in the system previously reported by other groups. We find that ORLs are concentrated in the polar region (J1, J3), whereas the equatorial knots (J2, J4) are dominated by CELs. The flux ratio map of the diagnostic [O III

λ

5007/4363 Å] lines reveals the electron temperature distribution, which shows cold cores of 15,000 K in knots J3 and J4 surrounded by a hot outer layer of above 20,000 K. Our channel maps show positive and negative velocity excursions from the systemic value among the ions. Several ions show variation in their velocity structures from their lower-energy-level counterparts, including [Ar IV] and [Ar V], [Ne III] and [Ne IV], and He I and He II. New recurrent velocity structures are identified in the low-density regions where the ions move much faster compared to their surrounding environments. The velocity dispersion measurements highlight extreme turbulence in some of the ions (

σ_{v_{rad}} \approx 140

km/s), consistent with supersonic/hypersonic motion driven by shocks. The forbidden line species [N II] exhibits lower turbulence (

σ_{v_{rad}} \approx

50–60 km/s), tracing denser, less-turbulent gases. Based on our data, we conclude that both the ionisation and kinematic studies hint at shock heating and multiple ejection history in the evolutionary pathway of A30. Full article

(This article belongs to the Special Issue Origins and Models of Planetary Nebulae)

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23 pages, 8113 KB

Open AccessArticle

Estimating H I Mass Fraction in Galaxies with Bayesian Neural Networks

by Joelson Sartori, Cristian G. Bernal and Carlos Frajuca

Galaxies 2026, 14(1), 10; https://doi.org/10.3390/galaxies14010010 - 2 Feb 2026

Abstract

Neutral atomic hydrogen (H I) regulates galaxy growth and quenching, but direct 21 cm measurements remain observationally expensive and affected by selection biases. We develop Bayesian neural networks (BNNs)—a type of neural model that returns both a prediction and an associated uncertainty—to infer [...] Read more.

Neutral atomic hydrogen (H I) regulates galaxy growth and quenching, but direct 21 cm measurements remain observationally expensive and affected by selection biases. We develop Bayesian neural networks (BNNs)—a type of neural model that returns both a prediction and an associated uncertainty—to infer the H I mass,

{log}_{10} (M_{HI})

, from widely available optical properties (e.g., stellar mass, apparent magnitudes, and diagnostic colors) and simple structural parameters. For continuity with the photometric gas fraction (PGF) literature, we also report the gas-to-stellar-mass ratio,

{log}_{10} (G / S)

, where explicitly noted. Our dataset is a reproducible cross-match of SDSS DR12, the MPA–JHU value-added catalogs, and the 100% ALFALFA release, resulting in 31,501 galaxies after quality controls. To ensure fair evaluation, we adopt fixed train/validation/test partitions and an additional sky-holdout region to probe domain shift, i.e., how well the model extrapolates to sky regions that were not used for training. We also audit features to avoid information leakage and benchmark the BNNs against deterministic models, including a feed-forward neural network baseline and gradient-boosted trees (GBTs, a standard tree-based ensemble method in machine learning). Performance is assessed using mean absolute error (MAE), root-mean-square error (RMSE), and probabilistic diagnostics such as the negative log-likelihood (NLL, a loss that rewards models that assign high probability to the observed H I masses), reliability diagrams (plots comparing predicted probabilities to observed frequencies), and empirical 68%/95% coverage. The Bayesian models achieve point accuracy comparable to the deterministic baselines while additionally providing calibrated prediction intervals that adapt to stellar mass, surface density, and color. This enables galaxy-by-galaxy uncertainty estimation and prioritization for 21 cm follow-up that explicitly accounts for predicted uncertainties (“risk-aware” target selection). Overall, the results demonstrate that uncertainty-aware machine-learning methods offer a scalable and reproducible route to inferring galactic H I content from widely available optical data. Full article

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13 pages, 1484 KB

Open AccessArticle

TV UMi: A Shallowly Eclipsing Marginal-Contact Binary

by Atila Čeki and Olivera Latković

Galaxies 2026, 14(1), 9; https://doi.org/10.3390/galaxies14010009 - 31 Jan 2026

Abstract

Using twenty sectors of TESS observations and the hitherto unutilized radial velocities from the David Dunlap Observatory survey, we fully characterize the close binary TV UMi. Its nearly sinusoidal light curves are well explained by a low-inclination, shallowly-eclipsing model in marginal contact, with [...] Read more.

Using twenty sectors of TESS observations and the hitherto unutilized radial velocities from the David Dunlap Observatory survey, we fully characterize the close binary TV UMi. Its nearly sinusoidal light curves are well explained by a low-inclination, shallowly-eclipsing model in marginal contact, with a dark spot whose longitudinal migration is strongly correlated with the eclipse time variations. We derive the orbital parameters of the binary and determine the masses and radii of the components with a precision of a few percent. The estimated age and the position of TV UMi on the theoretical HR diagram indicate it’s a relatively young late-type contact binary of the W subtype. Full article

(This article belongs to the Special Issue Study on Contact Binary Stars)

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27 pages, 5529 KB

Open AccessEssay

The Meaning of “Big Bang”

by Emilio Elizalde

Galaxies 2026, 14(1), 8; https://doi.org/10.3390/galaxies14010008 - 30 Jan 2026

Abstract

What does “Big Bang” mean? What was the actual origin of these two words? There are many aspects hidden under this name, which are seldom explained. They are discussed here. To frame the analysis, help will be sought from the highly authoritative voices [...] Read more.

What does “Big Bang” mean? What was the actual origin of these two words? There are many aspects hidden under this name, which are seldom explained. They are discussed here. To frame the analysis, help will be sought from the highly authoritative voices of two exceptional writers: William Shakespeare and Umberto Eco. Both have explored the tension existing between words and the realities they name. And this includes names given to outstanding theorems and spectacular discoveries, too. Stigler’s law of eponymy is recalled in this context. These points will be at the heart of the quest here, concerning the concept of “Big Bang”, which only a few people know what it means, actually. Fred Hoyle was the first to pronounce these words, in a BBC radio program, with a meaning that was later called inflation. But listeners were left with the image he was trying to destroy: the explosion of Lemaître’s primeval atom (an absolutely wrong concept). Hoyle’s Steady State will be carefully compared with inflation cosmology. They are quite different, and yet, in both cases, the possibility of creating matter/energy out of expanding space is rooted in the same fundamental principles: those of General Relativity. As is also, the possibility of having a universe with zero total energy, anticipated by R.C. Tolman, in 1934 already. It will be shown, how to obtain accelerated expansion from negative pressure; how to reconcile energy conservation with matter creation in an expanding universe; and a curious relation between de Sitter spacetime and Steady State cosmology. Concerning the naming issue, it will be remarked that, today, the same label “Big Bang” is used in very different contexts: (a) the Big Bang Singularity; (b) as the equivalent of cosmic inflation; (c) speaking of the Big Bang cosmological model; (d) to name a very popular TV program; and more. Full article

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15 pages, 1881 KB

Open AccessArticle

Finite-Range Scalar–Tensor Gravity: Constraints from Cosmology and Galaxy Dynamics

by Elie Almurr and Jean Claude Assaf

Galaxies 2026, 14(1), 7; https://doi.org/10.3390/galaxies14010007 - 27 Jan 2026

Abstract

Objective: We examine whether a finite-range scalar–tensor modification of gravity can be simultaneously compatible with cosmological background data, galaxy rotation curves, and local/astrophysical consistency tests, while satisfying the luminal gravitational-wave propagation constraint (

c_{T} = 1

) implied by GW170817 at low [...] Read more.

Objective: We examine whether a finite-range scalar–tensor modification of gravity can be simultaneously compatible with cosmological background data, galaxy rotation curves, and local/astrophysical consistency tests, while satisfying the luminal gravitational-wave propagation constraint (

c_{T} = 1

) implied by GW170817 at low redshifts. Methods: We formulate the model at the level of an explicit covariant action and derive the corresponding field equations; for cosmological inferences, we adopt an effective background closure in which the late-time dark-energy density is modulated by a smooth activation function characterized by a length scale

λ

and amplitude

ϵ

. We constrain this background model using Pantheon+, DESI Gaussian Baryon Acoustic Oscillations (BAOs), and a Planck acoustic-scale prior, including an explicit

Λ

CDM comparison. We then propagate the inferred characteristic length by fixing

λ

in the weak-field Yukawa kernel used to model 175 SPARC galaxy rotation curves with standard baryonic components and a controlled spherical approximation for the scalar response. Results: The joint background fit yields

Ω_{m} = 0.293 \pm 0.007

,

λ = 7 . 69_{- 1.71}^{+ 1.85}

Mpc

, and

H_{0} = 72.33 \pm 0.50

km s^{- 1} {Mpc}^{- 1}

. With

λ

fixed, the baryons + scalar model describes the SPARC sample with a median reduced chi-square of

χ_{ν}^{2} = 1.07

; for a 14-galaxy subset, this model is moderately preferred over the standard baryons + NFW halo description in the finite-sample information criteria, with a mean

Δ

AICc outcome in favor of the baryons + scalar model (≈2.8). A Vainshtein-type screening completion with

Λ = 1.3 \times 10^{- 8}

eV satisfies Cassini, Lunar Laser Ranging, and binary pulsar bounds while keeping the kpc scales effectively unscreened. For linear growth observables, we adopt a conservative General Relativity-like baseline (

μ_{0} = 0

) and show that current

f σ_{8}

data are consistent with

μ_{0} ≃ 0

for our best-fit background; the model predicts

S_{8} = 0.791

, consistent with representative cosmic-shear constraints. Conclusions: Within the present scope (action-level weak-field dynamics for galaxy modeling plus an explicitly stated effective closure for background inference), the results support a mutually compatible characteristic length at the Mpc scale; however, a full perturbation-level implementation of the covariant theory remains an issue for future work, and the role of cold dark matter beyond galaxy scales is not ruled out. Full article

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28 pages, 4913 KB

Open AccessArticle

The miniJPAS and J-NEP Surveys: Machine Learning for Star-Galaxy Separation

by Ana Paula Jeakel, Gabriel Vieira dos Santos, Valerio Marra, Rodrigo von Marttens, Siddhartha Gurung-López, Raul Abramo, Jailson Alcaniz, Narciso Benitez, Silvia Bonoli, Javier Cenarro, David Cristóbal-Hornillos, Simone Daflon, Renato Dupke, Alessandro Ederoclite, Rosa M. González Delgado, Antonio Hernán-Caballero, Carlos Hernández-Monteagudo, Jifeng Liu, Carlos López-Sanjuan, Antonio Marín-Franch, Claudia Mendes de Oliveira, Mariano Moles, Fernando Roig, Laerte Sodré, Jr., Keith Taylor, Jesús Varela, Héctor Vázquez Ramió, José M. Vilchez, Christopher Willmer and Javier Zaragoza-Cardiel Show full author list Hide full author list

Galaxies 2026, 14(1), 6; https://doi.org/10.3390/galaxies14010006 - 27 Jan 2026

Abstract

We present a supervised machine learning classification of sources from the Javalambre Physics of the Accelerating Universe Astrophysical Survey (J-PAS) Pathfinder datasets: miniJPAS and J-NEP. Leveraging crossmatches with spectroscopic and photometric catalogs, we construct a robust labeled dataset comprising 14,594 sources classified into [...] Read more.

We present a supervised machine learning classification of sources from the Javalambre Physics of the Accelerating Universe Astrophysical Survey (J-PAS) Pathfinder datasets: miniJPAS and J-NEP. Leveraging crossmatches with spectroscopic and photometric catalogs, we construct a robust labeled dataset comprising 14,594 sources classified into extended (galaxies) and point-like (stars and quasars) objects. We assess dataset representativeness using UMAP analysis, confirming broad and consistent coverage of feature space. An XGBoost classifier, with hyperparameters tuned using automated optimization, is trained using purely photometric data (60-band J-PAS magnitudes) and combined photometric and morphological features, with performance thoroughly evaluated via ROC and purity–completeness metrics. Incorporating morphology significantly improves classification, outperforming the baseline classifications available in the catalogs. Permutation importance analysis reveals morphological parameters, particularly concentration, normalized peak surface brightness, and PSF, alongside photometric features around 4000 and 6900 Å, as crucial for accurate classifications. We release a value-added catalog with our models for star-galaxy classification, enhancing the utility of miniJPAS and J-NEP for subsequent cosmological and astrophysical analyses. Full article

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18 pages, 1868 KB

Open AccessReview

Stray Light Analysis and Mitigation Perspectives for Next Generation Gravitational-Wave Detectors

by Eleonora Polini and Antonino Chiummo

Galaxies 2026, 14(1), 5; https://doi.org/10.3390/galaxies14010005 - 21 Jan 2026

Abstract

The low-frequency sensitivity of gravitational-wave detectors can be degraded by noise arising from the re-coupling of stray light with the main interferometer beam. This review describes the re-coupling mechanism and shows how the experience gained with current detectors can be used to anticipate [...] Read more.

The low-frequency sensitivity of gravitational-wave detectors can be degraded by noise arising from the re-coupling of stray light with the main interferometer beam. This review describes the re-coupling mechanism and shows how the experience gained with current detectors can be used to anticipate and mitigate stray-light issues in third-generation instruments. We summarize the work carried out on numerical simulations and on the extensive characterization of stray light originating from both core and auxiliary optics. We also discuss possible improvements to the interferometric readout system aimed at reducing stray-light-induced noise, as well as diagnostic approaches for identifying potentially harmful scattering elements. Overall, this review summarizes best practices for the effective control of stray light in future gravitational-wave detectors, supporting design approaches aimed at preventing unforeseen noise issues. Full article

(This article belongs to the Special Issue Challenges for Third-Generation Gravitational Wave Detectors and Beyond)

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27 pages, 7773 KB

Open AccessArticle

Boxy/Peanut Bulges: Comparative Analysis of EGIPS Galaxies and TNG50 Models

by Anton Smirnov, Alexander Marchuk, Viktor Zozulia, Natalia Sotnikova and Sergey Savchenko

Galaxies 2026, 14(1), 4; https://doi.org/10.3390/galaxies14010004 - 13 Jan 2026

Abstract

We investigated the properties of boxy/peanut-shaped (B/PS) bulges in a sample of 71 galaxies from the Edge-on Galaxies in the Pan-STARRS Survey (EGIPS) and 20 simulated galaxies from Illustris TNG50 using multicomponent photometric decomposition. For each real and simulated galaxy, we obtained a [...] Read more.

We investigated the properties of boxy/peanut-shaped (B/PS) bulges in a sample of 71 galaxies from the Edge-on Galaxies in the Pan-STARRS Survey (EGIPS) and 20 simulated galaxies from Illustris TNG50 using multicomponent photometric decomposition. For each real and simulated galaxy, we obtained a suitable photometric model in which the B/PS bulge was represented by a dedicated 2D photometric function. For real galaxies, we found that more flattened X-structures are generally residing in larger B/PS bulges. When tested against the galaxy masses, we verified that both larger bulges and more flattened X-structures are typically found in more massive galaxies. Since large bars are also known to reside in more massive galaxies, we conclude that the flatness of X-structures in larger B/PS bulges has a physical origin, rather than being solely a result of projection effects due to differences in observed bar viewing angles. When comparing the properties of B/PS bulges between EGIPS galaxies and TNG50 galaxies, with bars rotated for different viewing angles, we found that B/PS bulges in TNG50 are considerably smaller and less luminous in terms of total intensity. This is consistent with previous studies of bar properties in TNG50, indicating the B/PS bulges in TNG50 differ from those in real galaxies, as do their parent bars. Full article

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18 pages, 1390 KB

Open AccessArticle

Probing the Dusty Torus of Seyfert Galaxy NGC 4151: A Multi-Band Study

by Arya Sudhakaran, Debbijoy Bhattacharya, Puthiyaveettil Shalima, Gulab Chand Dewangan and Parameshwaran Sreekumar

Galaxies 2026, 14(1), 3; https://doi.org/10.3390/galaxies14010003 - 6 Jan 2026

Abstract

Despite several efforts to investigate the accretion disk and torus, near-simultaneous broadband studies of the nuclear regions of radio-quiet AGNs remain lacking. NGC 4151, one of the closest and brightest Seyfert galaxies, provides an excellent laboratory for probing the circum-nuclear regions of AGNs. [...] Read more.

Despite several efforts to investigate the accretion disk and torus, near-simultaneous broadband studies of the nuclear regions of radio-quiet AGNs remain lacking. NGC 4151, one of the closest and brightest Seyfert galaxies, provides an excellent laboratory for probing the circum-nuclear regions of AGNs. A detailed, near-simultaneous broadband spectral study of NGC 4151 is carried out during one of its historic minimum activity states, using archival data from the Ultraviolet (UV) to the Infrared (IR) regions. We used the radiative transfer code SKIRT to model the source and to constrain the properties of the torus. We found that the observed broadband spectral energy distribution is best explained by a two-torus geometry with a polar conical shell structure. Full article

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12 pages, 1203 KB

Open AccessArticle

On the Origin and Nature of Double-Double Radio Galaxies

by David Garofalo, Zhiyuan Liu and Atticus V. Magerko

Galaxies 2026, 14(1), 2; https://doi.org/10.3390/galaxies14010002 - 3 Jan 2026

Abstract

Double-double radio galaxies (DDRGs) display inner and outer jets or lobes thought to result from intermittent accretion. Due to randomly triggered accretion events, the lifetime of the retriggered jet is not expected to have any connection to the time of quiescence between jets, [...] Read more.

Double-double radio galaxies (DDRGs) display inner and outer jets or lobes thought to result from intermittent accretion. Due to randomly triggered accretion events, the lifetime of the retriggered jet is not expected to have any connection to the time of quiescence between jets, yet we show that a correlation between the two quantities may exist, which we interpret as resulting from continued accretion through the quiescent jet phase. Despite continuous accretion, a jet is absent because its presence depends on a non-zero value of black hole spin, but accretion transitions the system from counter-rotation to corotation, and therefore through zero black hole spin where a jet cannot form. The time of jet quiescence depends on how long it takes to spin the black hole up again in corotation, which is longer for lower accretion rates. Once the black hole spin is large enough for a renewed jet, this inner jet will last longer the lower the accretion rate is. Hence, in a continuous accretion scenario, longer quiescent times tend to associate to longer inner jet times. In addition, DDRG jets are of FRII morphology which we show to result from the absence of a tilt in the accretion disk in the transition through zero black hole spin, ensuring the absence of an FRI jet in a way that connects with our understanding of X-shaped radio galaxies. Both correlated timescales as well as sameness in jet morphology offers evidence in favor of our picture. Full article

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24 pages, 14381 KB

Open AccessArticle

Effects of the Intraday Variability of the Radio Galaxy Perseus A (3C 84) at a Frequency of 6.5 GHz and Evidence for a Possible FRB Event

by Vladislavs Bezrukovs, Oleg Ulyanov, Artem Sukharev, Vyacheslav Zakharenko, Mikhail Ryabov, Viktor Ozhinskyi, Volodymyr Vlasenko, Anatolyi Poikhalo, Oleksandr Konovalenko, Eugene Alekseev, Mykhailo Palamar, Viktor Voityuk, Vladyslav Chmil, Dmytro Bakun, Daniil Zabora, Ivar Shmeld and Marina Konuhova

Galaxies 2026, 14(1), 1; https://doi.org/10.3390/galaxies14010001 - 23 Dec 2025

Abstract

Perseus A (3C 84), a powerful radio source located at the centre of the giant elliptical galaxy NGC 1275—classified as a Seyfert type II AGN and the dominant member of the X-ray bright Abell 426 cluster–exhibits radio emission variability over a wide range [...] Read more.

Perseus A (3C 84), a powerful radio source located at the centre of the giant elliptical galaxy NGC 1275—classified as a Seyfert type II AGN and the dominant member of the X-ray bright Abell 426 cluster–exhibits radio emission variability over a wide range of timescales, from decades to hours. This study investigates intraday variability (IDV) in the 6.5 GHz radio emission of 3C 84 using the RT-32 radio telescope in Zolochiv, Ukraine. A novel low-amplitude azimuthal scanning method enabled quasi-simultaneous measurements of antenna and system temperatures, allowing for separation of intrinsic source variations from propagation effects. During an observation session in August 2021, a burst with a peak intensity of 13.5 Jy above the background was detected, likely corresponding to a Fast Radio Burst (FRB). Additionally, quasi-periodic low-amplitude variations with timescales from 0.3 to 6 h were observed. These fluctuations correlate strongly with local atmospheric changes, such as dew formation on the telescope structure, and, to a lesser extent, with ionospheric acoustic–gravity waves. The findings highlight the importance of accounting for propagation conditions when interpreting short-timescale radio variability in AGNs and suggest the need for multi-station, multi-frequency monitoring campaigns to distinguish between intrinsic and environmental modulation of AGN flux densities. Full article

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