Galaxies

12 pages, 588 KiB

Open AccessArticle

Necessary Conditions for Earthly Life Floating in the Venusian Atmosphere

by Jennifer J. Abreu, Alyxander R. Anchordoqui, Nyamekye J. Fosu, Michael G. Kwakye, Danijela Kyriakakis, Krystal Reynoso and Luis A. Anchordoqui

Galaxies 2025, 13(3), 48; https://doi.org/10.3390/galaxies13030048 - 22 Apr 2025

Abstract

Millimeter-waveband spectra of Venus from both the James Clerk Maxwell Telescope (JCMT) and the Atacama Large Millimeter/submillimeter Array (ALMA) seem to indicate there may be evidence (signal-to-noise ratio of about \(15\sigma\)) of a phosphine absorption-line profile against the thermal background from deeper, hotter [...] Read more.

Millimeter-waveband spectra of Venus from both the James Clerk Maxwell Telescope (JCMT) and the Atacama Large Millimeter/submillimeter Array (ALMA) seem to indicate there may be evidence (signal-to-noise ratio of about \(15\sigma\)) of a phosphine absorption-line profile against the thermal background from deeper, hotter layers of the atmosphere. Phosphine is an important biomarker; e.g., the trace of phosphine in the Earth’s atmosphere is unequivocally associated with anthropogenic activity and microbial life (which produces this highly reducing gas even in an overall oxidizing environment). Motivated by the JCMT and ALMA tantalizing observations, we reexamine whether Venus could accommodate Earthly life. More concretely, we hypothesize that the microorganisms populating the Venusian atmosphere are not free floating but confined to the liquid environment inside cloud aerosols or droplets. Armed with this hypothesis, we generalize a study of airborne germ transmission to constrain the maximum size of droplets that could be floating in the Venusian atmosphere by demanding that their Stokes fallout times to reach moderately high temperatures are pronouncedly larger than the microbe’s replication time. We also comment on the effect of cosmic ray showers on the evolution of aerial microbial life. Full article

10 pages, 539 KiB

Open AccessArticle

Fundamental Parameters and Evolutionary Scenario of HD 327083

by Nadezhda L. Vaidman, Anatoly S. Miroshnichenko, Sergey V. Zharikov, Serik A. Khokhlov, Aldiyar T. Agishev and Berik S. Yermekbayev

Galaxies 2025, 13(3), 47; https://doi.org/10.3390/galaxies13030047 - 22 Apr 2025

Abstract

In this study, we present refined orbital and fundamental parameters of the Galactic B[e] supergiant binary system HD 327083 using the Bayesian Markov Chain Monte Carlo (MCMC) method applied to the radial velocities data of HD 327083. We found that the system is [...] Read more.

In this study, we present refined orbital and fundamental parameters of the Galactic B[e] supergiant binary system HD 327083 using the Bayesian Markov Chain Monte Carlo (MCMC) method applied to the radial velocities data of HD 327083. We found that the system is well described by a circular orbital model with the mass ratio of the components of

q = 1.15 \pm 0.07

. We modeled the evolutionary history of the system using MESA code. Initially, the system was formed by a binary with the orbital period of

P o r b = 108

day, which contained stars with 13.00

\pm 0.05

M_{⊙}

and

11.50 \pm 0.05

M_{⊙}

masses. They had a relatively slow rotation

υ_{r o t} = 0.40 \pm 0.13 υ_{c r i t}

and provided a strong stellar wind. The current system age is

13.6 \pm 0.1

Myr, and the state of the system corresponds to a close filling of the high massive component’s Roche lobe and a beginning of the mass transfer. The mass-transfer event will occur in a short interval of ≲0.1 Myr only. After that, the mass of the post-primary drops to ≈5

M_{⊙}

, the post-secondary mass grows until ≈20

M_{⊙}

, and the binary will convert to a detached system with a long orbital period of ≈700 days. Full article

(This article belongs to the Special Issue Circumstellar Matter in Hot Star Systems)

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14 pages, 3588 KiB

Open AccessReview

Intermediate-Mass Mergers: A New Scenario for Several FS CMa Stars

by Daniela Korčáková, Nela Dvořáková, Iris Bermejo Lozano, Gregg A. Wade, Alicia Moranchel Basurto, Pavel Kroupa, Raul Ortega Chametla, Colin Peter Folsom and Ondrej Juhás

Galaxies 2025, 13(3), 46; https://doi.org/10.3390/galaxies13030046 - 22 Apr 2025

Abstract

We summarise the properties and nature of a peculiar group of B-type stars called FS CMa stars. These stars show the B[e] phenomenon, i.e., their spectra exhibit both forbidden emission lines and infrared excess. Such properties point to an extended circumstellar gas and [...] Read more.

We summarise the properties and nature of a peculiar group of B-type stars called FS CMa stars. These stars show the B[e] phenomenon, i.e., their spectra exhibit both forbidden emission lines and infrared excess. Such properties point to an extended circumstellar gas and dust component. Although the phenomenon has been explained in most B[e] stars, the origin and nature of FS CMa stars is disputed. Here, we focus on the merger hypothesis, for which evidence has recently been discovered. Full article

(This article belongs to the Special Issue Circumstellar Matter in Hot Star Systems)

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34 pages, 2012 KiB

Open AccessArticle

Numerical Study of Bar Suppression in Galaxy Models Due to Disc Heating

by Alejandro López Gómez, Ruslan Gabbasov and Isaura Luisa Fuentes-Carrera

Galaxies 2025, 13(2), 45; https://doi.org/10.3390/galaxies13020045 - 21 Apr 2025

Abstract

The process of bar formation, evolution and destruction is still a controversial topic regarding galaxy dynamics. Numerical simulations show that these phenomena strongly depend on physical and numerical parameters. In this work, we study the combined influence of the softening parameter,

ϵ

and [...] Read more.

The process of bar formation, evolution and destruction is still a controversial topic regarding galaxy dynamics. Numerical simulations show that these phenomena strongly depend on physical and numerical parameters. In this work, we study the combined influence of the softening parameter,

ϵ

and disc mass fraction,

m_{d}

, on the formation and evolution of bars in isolated disc-halo models via N-body simulations with different particle resolutions. Previous studies indicate that the bar strength depends on

m_{d}

as

\propto m_{d}^{- 1}

, which is seen as a delay in bar formation. However, the distorsion parameter,

η

, which measures the bar’s momentum through time, shows that an increase in

m_{d}

does not always induce a delay in bar formation. This suggests that

ϵ

interact to either enhance or weaken the bar. Moreover, numerical heating dominates in models with small softening values, creating highly accelerated particles at the centre of discs, regardless of

m_{d}

or resolution. These enhanced particle accelerations produce chaotic orbits for

ϵ \leq 5

pc, resulting in bar suppression due to collisional dynamics in the centre. In our high-resolution models (

N \approx 10^{7}

), small softening values are incapable of reproducing the bar instability. The role of disc mass is as follows: increasing

m_{d}

for moderate

ϵ

(≥10 pc) reduces the amount of drift in the acceleration profile, without affecting the bar’s behaviour. Models with lower

m_{d}

values, coupled with small softening values, have an excess of highly accelerated particles, introducing unwanted effects into otherwise reliable simulations. Finally, we show that the evolution of the disc’s vertical acceleration profile is a reliable indicator of numerical heating introduced by

ϵ

and the bar. Full article

(This article belongs to the Special Issue From Tides to Waves: Understanding the Formation Mechanisms of Galactic Spirals)

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35 pages, 6349 KiB

Open AccessArticle

Examination of the Functional Form of the Light and Mass Distribution in Spiral Arms

by Ilia V. Chugunov, Alexander A. Marchuk and Sergey S. Savchenko

Galaxies 2025, 13(2), 44; https://doi.org/10.3390/galaxies13020044 - 19 Apr 2025

Abstract

Spiral arms are a common feature of local galaxies, but the exact form of the distribution of mass and light in them is not well known. In this work, we aim to measure this distribution as accurately as possible, focusing on individual spiral [...] Read more.

Spiral arms are a common feature of local galaxies, but the exact form of the distribution of mass and light in them is not well known. In this work, we aim to measure this distribution as accurately as possible, focusing on individual spiral arms and using the so-called slicing method. The sample consists of 19 well-resolved, viewed face-on spiral galaxies from the S⁴G survey. We work primarily with infrared images at 3.6 μm from the same survey and, secondarily, with ultraviolet data from the GALEX telescope. We derive the properties of the spiral arms step by step, starting from their overall shape, then measuring their brightness profile and width variation along the arm and then examining the fine structure of the profile across the arm, namely, its skewness and Sérsic index. We construct a 2D photometric function of the spiral arm that can be used in further decomposition studies, validate it and identify the most and least important parameters. Finally, we show how our results can be used to unravel the nature of the spiral arms, supporting the evidence that NGC 4535 has a density wave in its disc. Full article

(This article belongs to the Special Issue From Tides to Waves: Understanding the Formation Mechanisms of Galactic Spirals)

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16 pages, 1546 KiB

Open AccessReview

Red and Yellow Hypergiants

by Terry Jones

Galaxies 2025, 13(2), 43; https://doi.org/10.3390/galaxies13020043 - 18 Apr 2025

Abstract

The red and yellow hypergiants are a rare and important phase in the evolution of the most massive stars that can reach the cool part of the HR Diagram. The hypergiant phase is commonly characterized by high, often episodic mass-loss rates and significant [...] Read more.

The red and yellow hypergiants are a rare and important phase in the evolution of the most massive stars that can reach the cool part of the HR Diagram. The hypergiant phase is commonly characterized by high, often episodic mass-loss rates and significant changes in spectral type, probably due to the formation of a pseudo photopsphere during a high mass-loss episode. Many of the yellow hypergiants are the immediate successors to the most luminous red supergiants, and often show evidence in their dusty, circumstellar envelopes from past red supergiant activity. In this paper we review the yellow and red hypergiants with an emphasis on how they differ from more normal red supergiants. Full article

(This article belongs to the Special Issue The Red Supergiants: Crucial Signposts for the Fate of Massive Stars)

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15 pages, 477 KiB

Open AccessArticle

Global Mean-Motion Resonances: Part I—An Exceptional Multiplanetary Resonant Chain in TOI-270 and an Exact Laplace-like Resonance in HD 110067

by Dimitris M. Christodoulou, Nicholas M. Sorabella, Sayantan Bhattacharya, Silas G. T. Laycock and Demosthenes Kazanas

Galaxies 2025, 13(2), 42; https://doi.org/10.3390/galaxies13020042 - 15 Apr 2025

Abstract

Super-Earth b and sub-Neptunes c and d are orbiting about the M3.0V dwarf TOI-270 in that order from the star. Their global resonant chain (3:5, 1:1, 2:1) is extremely surprising because planet d appears to be the only known planet occupying the 2:1 [...] Read more.

Super-Earth b and sub-Neptunes c and d are orbiting about the M3.0V dwarf TOI-270 in that order from the star. Their global resonant chain (3:5, 1:1, 2:1) is extremely surprising because planet d appears to be the only known planet occupying the 2:1 resonant orbit without participating in a Laplace resonance (LR) or another planet intervening between the 1:1 and 2:1 orbits as in HD 110067. We do not believe that TOI-270 d is an exception to the empirical rule calling for 2:1 vacancy except in 1:2:4 LRs and Laplace-like 2:3:4 chains. Instead, a LR might exist in this system, and we searched (to no avail) the TESS light curves of TOI-270 for hints of an outer planet that would complete the LR chain. Alternative explanations would be an unknown planet more massive than planet c (

M_{c} = 6.20 M_{\oplus}

) establishing the actual 1:1 orbit, or planet b residing in the 1:2 Laplace orbit with a period shorter by 0.53 days. However, these possibilities are ruled out by current data. This leaves only one other option to explore: the observed orbits could be in a stable

\frac{3}{5}

:1:2 resonant chain. Preliminary calculations do not preclude this possibility that should be investigated further by numerical orbit integrations. To this end, we determine two potentially resonant angles,

φ

and

\hat{φ}

, related via the Laplace phase

φ_{L}

by

\hat{φ} = φ_{L} + 2 φ

. In contrast, HD 110067 is shown to have planets d-e-f in a Laplace-like 1:

\frac{3}{2}

:2 resonance with phase

φ = 2 φ_{L}

precisely. Full article

(This article belongs to the Collection A Trip across the Universe: Our Present Knowledge and Future Perspectives)

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18 pages, 531 KiB

Open AccessArticle

Global Mean-Motion Resonances: Part II—Laplace-like Phase Angles to Facilitate Libration Searches in Multiplanetary N-body Simulations

by Dimitris M. Christodoulou, Nicholas M. Sorabella, Sayantan Bhattacharya, Silas G. T. Laycock and Demosthenes Kazanas

Galaxies 2025, 13(2), 41; https://doi.org/10.3390/galaxies13020041 - 14 Apr 2025

Abstract

We describe a method of determining three-body and four-body Laplace-like phase angles with the potential to librate about a mean value in multiplanet extrasolar systems. Unlike in past searches of N-body results, this method relies on global mean-motion resonances (MMRs) and takes into [...] Read more.

We describe a method of determining three-body and four-body Laplace-like phase angles with the potential to librate about a mean value in multiplanet extrasolar systems. Unlike in past searches of N-body results, this method relies on global mean-motion resonances (MMRs) and takes into consideration the location of the most massive planet that defines the 1:1 global MMR in each (sub)system. We compiled lists of potentially librating phase angles and prevalent MMRs in 35 real multibody systems, and we discuss their properties in conjunction with recent investigations of librations discovered in sophisticated N-body simulations. We hope that our results will facilitate systematic libration searches in dynamical models of compact systems with three or more orbiting bodies. Full article

(This article belongs to the Collection A Trip across the Universe: Our Present Knowledge and Future Perspectives)

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15 pages, 507 KiB

Open AccessReview

Spectropolarimetry for Discerning Geometry and Structure in Circumstellar Media of Hot Massive Stars

by Richard Ignace, Kenneth G. Gayley, Roberto Casini, Paul Scowen, Christiana Erba and Jeremy Drake

Galaxies 2025, 13(2), 40; https://doi.org/10.3390/galaxies13020040 - 11 Apr 2025

Abstract

Spectropolarimetric techniques are a mainstay of astrophysical inquiry, ranging from Solar System objects to the Cosmic Background Radiation. This review highlights applications of stellar polarimetry for massive hot stars, particularly in the context of ultraviolet (UV) spaceborne missions. The prevalence of binarity in [...] Read more.

Spectropolarimetric techniques are a mainstay of astrophysical inquiry, ranging from Solar System objects to the Cosmic Background Radiation. This review highlights applications of stellar polarimetry for massive hot stars, particularly in the context of ultraviolet (UV) spaceborne missions. The prevalence of binarity in the massive star population and uncertainties regarding the degree of rotational criticality among hot stars raises important questions about stellar interactions, interior structure, and even the lifetimes of evolutionary phases. These uncertainties have consequences for stellar population synthesis calculations. Spectropolarimetry is a key tool for extracting information about stellar and binary geometries. We review methodologies involving electron scattering in circumstellar envelopes; gravity darkening from rapid rotation; spectral line effects, including the (a) “line effect”, (b) Öhman effect, and (c) Hanle effect; and the imprint of interstellar polarization on measurements. Finally, we describe the Polstar UV spectropolarimetric SMEX mission concept as one means for employing these diagnostics to clarify the state of high rotation and its impacts for massive stars. Full article

(This article belongs to the Special Issue Circumstellar Matter in Hot Star Systems)

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31 pages, 4553 KiB

Open AccessArticle

Accurate Decomposition of Galaxies with Spiral Arms: Dust Properties and Distribution

by Alexander A. Marchuk, Ilia V. Chugunov, Frédéric Galliano, Aleksandr V. Mosenkov, Polina V. Strekalova, Sergey S. Savchenko, Valeria S. Kostiuk, George A. Gontcharov, Vladimir B. Il’in, Anton A. Smirnov and Denis M. Poliakov

Galaxies 2025, 13(2), 39; https://doi.org/10.3390/galaxies13020039 - 9 Apr 2025

Abstract

We analyze three nearby spiral galaxies—NGC 1097, NGC 1566, and NGC 3627—using images from the DustPedia database in seven infrared bands (3.6, 8, 24, 70, 100, 160, and 250 μm). For each image, we perform photometric decomposition and construct a multi-component model, including [...] Read more.

We analyze three nearby spiral galaxies—NGC 1097, NGC 1566, and NGC 3627—using images from the DustPedia database in seven infrared bands (3.6, 8, 24, 70, 100, 160, and 250 μm). For each image, we perform photometric decomposition and construct a multi-component model, including a detailed representation of the spiral arms. Our results show that the light distribution is well described by an exponential disk and a Sérsic bulge when non-axisymmetric components are properly taken into account. We test the predictions of the stationary density wave theory using the derived models in bands, tracing both old stars and recent star formation. Our findings suggest that the spiral arms in all three galaxies are unlikely to originate from stationary density waves. Additionally, we perform spectral energy distribution (SED) modeling using the hierarchical Bayesian code HerBIE, fitting individual components to derive dust properties. We find that spiral arms contain a significant (>10%) fraction of cold dust, with an average temperature of approximately 18–20 K. The estimated fraction of polycyclic aromatic hydrocarbons (PAHs) declines significantly toward the galactic center but remains similar between the arm and interarm regions. Full article

(This article belongs to the Special Issue From Tides to Waves: Understanding the Formation Mechanisms of Galactic Spirals)

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16 pages, 310 KiB

Open AccessArticle

Non-Zero Coriolis Field in Ehlers’ Frame Theory

by Federico Re and Oliver F. Piattella

Galaxies 2025, 13(2), 38; https://doi.org/10.3390/galaxies13020038 - 5 Apr 2025

Abstract

Ehlers’ Frame Theory is a class of geometric theories parameterized by

λ : = 1 / c^{2}

and identical to the General Theory of Relativity for

λ \neq 0

. The limit

λ \to 0

does not recover Newtonian gravity, as one [...] Read more.

Ehlers’ Frame Theory is a class of geometric theories parameterized by

λ : = 1 / c^{2}

and identical to the General Theory of Relativity for

λ \neq 0

. The limit

λ \to 0

does not recover Newtonian gravity, as one might expect, but yields the so-called Newton–Cartan theory of gravity, which is characterized by a second gravitational field

ω

, called the Coriolis field. Such a field encodes at a non-relativistic level the dragging feature of general spacetimes, as we show explicitly for the case of the

(η, H)

geometries. Taking advantage of the Coriolis field, we apply Ehlers’ theory to an axially symmetric distribution of matter, mimicking, for example, a disc galaxy, and show how its dynamics might reproduce a flattish rotation curve. In the same setting, we further exploit the formal simplicity of Ehlers’ formalism in addressing non-stationary cases, which are remarkably difficult to treat with the General Theory of Relativity. We show that the time derivative of the Coriolis field gives rise to a tangential acceleration which allows for studying a possible formation in time of the rotation curve’s flattish feature. Full article

(This article belongs to the Special Issue From Tides to Waves: Understanding the Formation Mechanisms of Galactic Spirals)

6 pages, 228 KiB

Open AccessArticle

Stellar Wind Parameters of Massive Stars in Accretion-Powered High-Mass X-Ray Binary Pulsars

by Nina Beskrovnaya, Nazar Ikhsanov and Vitaliy Kim

Galaxies 2025, 13(2), 37; https://doi.org/10.3390/galaxies13020037 - 5 Apr 2025

Abstract

The process of mass exchange between the components of High-Mass X-ray Binary (HMXB) systems with neutron stars undergoing wind-fed accretion is discussed. The X-ray luminosity of these systems allows us to evaluate the mass capture rate by the neutron star from the stellar [...] Read more.

The process of mass exchange between the components of High-Mass X-ray Binary (HMXB) systems with neutron stars undergoing wind-fed accretion is discussed. The X-ray luminosity of these systems allows us to evaluate the mass capture rate by the neutron star from the stellar wind of its massive companion and set limits on the relative velocity between the neutron star and the wind. We found that the upper limit to the wind velocity in the orbital plane during the high state of the X-ray source is in the range of 120–1000

km s^{- 1}

, which is by a factor of 2–4 lower than both the terminal wind velocity and the speed of the wind flowing out from the polar regions of massive stars for all the objects under investigation. This finding is valid not only for the systems with Be stars, but also for the systems in which the optical components do not exhibit the Be phenomenon. We also show that the lower limit to the radial wind velocity in these systems can unlikely be smaller than a few percent of the orbital velocity of the neutron star. This provides us with a new constraint on the mass transfer process in the outflowing disks of Be-type stars. Full article

(This article belongs to the Special Issue Circumstellar Matter in Hot Star Systems)

8 pages, 1341 KiB

Open AccessReview

Chemical Synthesis in the Circumstellar Environment

by Sun Kwok

Galaxies 2025, 13(2), 36; https://doi.org/10.3390/galaxies13020036 - 3 Apr 2025

Abstract

We discuss the spectral distinctions between B[e] stars and compact planetary nebulae. The differentiation between proto-planetary nebulae, transition objects between the asymptotic giant branch and planetary nebulae, and reflection nebulae in binary systems is also discussed. Infrared and millimeter-wave observations have identified many [...] Read more.

We discuss the spectral distinctions between B[e] stars and compact planetary nebulae. The differentiation between proto-planetary nebulae, transition objects between the asymptotic giant branch and planetary nebulae, and reflection nebulae in binary systems is also discussed. Infrared and millimeter-wave observations have identified many inorganic and organic molecules, as well as solid-state minerals, in the circumstellar environment. There is evidence that complex organics in the form of mixed aromatic/aliphatic nanoparticles (MAONs) are synthesized during the proto-planetary nebulae phase of evolution. Their ejection into the interstellar medium may have enriched the primordial Solar System, and the complex organics found in comets, asteroids, and planetary satellites could be stellar in origin. Full article

(This article belongs to the Special Issue Circumstellar Matter in Hot Star Systems)

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10 pages, 1540 KiB

Open AccessArticle

Why Jet Power and Star Formation Are Uncorrelated in Active Galaxies

by David Garofalo, Brent McDaniel and Max North

Galaxies 2025, 13(2), 35; https://doi.org/10.3390/galaxies13020035 - 3 Apr 2025

Abstract

Jet luminosity from active galaxies and the rate of star formation have recently been found to be uncorrelated observationally. We show how to understand this in the context of a model in which powerful AGN jets enhance star formation for up to hundreds [...] Read more.

Jet luminosity from active galaxies and the rate of star formation have recently been found to be uncorrelated observationally. We show how to understand this in the context of a model in which powerful AGN jets enhance star formation for up to hundreds of millions of years while jet power decreases in time, followed by a longer phase in which star formation is suppressed but coupled to jet power increasing with time. We also highlight characteristic differences, depending on environment richness in a way that is compatible with the observed SEDs of high redshift radio galaxies. While the absence of a direct correlation between jet power and star formation rate emerges naturally, our framework allows us to also predict the environment richness, range of excitation, and redshift values of radio AGN in the jet power-star formation rate plane. Full article

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15 pages, 685 KiB

Open AccessReview

An Updated Repository of Sub-mJy Extragalactic Source-Count Measurements in the Radio Domain

by Vincenzo Galluzzi, Meriem Behiri, Marika Giulietti and Andrea Lapi

Galaxies 2025, 13(2), 34; https://doi.org/10.3390/galaxies13020034 - 2 Apr 2025

Abstract

We present an updated repository of sub-mJy extragalactic radio source counts between 150 MHz and 10 GHz, incorporating recent advances in radio surveys and observational techniques. By compiling and refining previous datasets, we provide a comprehensive catalog that enhances the understanding of faint [...] Read more.

We present an updated repository of sub-mJy extragalactic radio source counts between 150 MHz and 10 GHz, incorporating recent advances in radio surveys and observational techniques. By compiling and refining previous datasets, we provide a comprehensive catalog that enhances the understanding of faint radio-source populations, including Dusty Star-Forming Galaxies (DSFGs) and Radio-Quiet Active Galactic Nuclei (RQAGNs), from intermediate to high redshifts. Our analysis accounts for observational biases, such as resolution effects and Eddington bias, ensuring improved accuracy in flux-density estimations. We also discuss the implications of new-generation radio telescopes, such as the Square-Kilometer Array Observatory (SKAO) and its precursors and pathfinders, to further resolve these populations. Our collection contributes to constraining evolutionary models of radio sources, highlighting the increasing role of polarization studies in distinguishing different classes. This work serves as a key reference for future deep radio surveys targeting the faintest end of the extragalactic radio sky. Full article

(This article belongs to the Special Issue The Observation and Detection of Dusty Star-Forming Galaxies)

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24 pages, 1031 KiB

Open AccessReview

Red Supergiants as Supernova Progenitors

by Schuyler D. Van Dyk

Galaxies 2025, 13(2), 33; https://doi.org/10.3390/galaxies13020033 - 2 Apr 2025

Abstract

The inevitable fate of massive stars in the initial mass range of ≈8–

30 M_{⊙}

in the red supergiant (RSG) phase is a core-collapse supernova (SN) explosion, although some stars may collapse directly to a black hole. We know that this is [...] Read more.

The inevitable fate of massive stars in the initial mass range of ≈8–

30 M_{⊙}

in the red supergiant (RSG) phase is a core-collapse supernova (SN) explosion, although some stars may collapse directly to a black hole. We know that this is the case, since RSGs have been directly identified and characterized for a number of supernovae (SNe) in pre-explosion archival optical and infrared images. RSGs likely all have some amount of circumstellar matter (CSM), through nominal mass loss, although evidence exists that some RSGs must experience enhanced mass loss during their lifetimes. The SNe from RSGs are hydrogen-rich Type II-Plateau (II-P), and SNe II-P at the low end of the luminosity range tend to arise from low-luminosity RSGs. The typical spectral energy distribution (SED) for such RSGs can generally be fit with a cool photospheric model, whereas the more luminous RSG progenitors of more luminous SNe II-P tend to require a greater quantity of dust in their CSM to account for their SEDs. The SN II-P progenitor luminosity range is

log (L_{bol} / L_{⊙}) \sim 4.0

–5.2. The fact RSGs are known up to

log (L_{bol} / L_{⊙}) \sim 5.7

leads to the so-called “RSG problem”, which may, in the end, be a result of small number of available statistics to date. Full article

(This article belongs to the Special Issue The Red Supergiants: Crucial Signposts for the Fate of Massive Stars)

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11 pages, 2062 KiB

Open AccessArticle

IRAS 17449+2320: A Possible Binary System with the B[e] Phenomenon and a Strong Magnetic Field

by Sergey Zharikov, Anatoly Miroshnichenko, Inna Reva, Raushan Kokumbaeva, Chingis Omarov, Steve Danford, Alicia Aarnio, Nadine Manset, Ashish Raj, S. Drew Chojnowski and Joseph Daglen

Galaxies 2025, 13(2), 32; https://doi.org/10.3390/galaxies13020032 - 31 Mar 2025

Abstract

We report the recent results of a long-term spectroscopic and photometric monitoring of IRAS 17449+2320, a member of the least studied group of objects with the B[e] phenomenon called FS CMa-type objects. The main hypothesis for explaining the strong emission-line spectra and infrared [...] Read more.

We report the recent results of a long-term spectroscopic and photometric monitoring of IRAS 17449+2320, a member of the least studied group of objects with the B[e] phenomenon called FS CMa-type objects. The main hypothesis for explaining the strong emission-line spectra and infrared excesses of these objects assumes an ongoing or past mass transfer between the components in binary systems. The object is the only star with a gaseous and dusty envelope, where a strong and variable magnetic field (5.5–7.2 kG) was found through the splitting of some spectral lines. Additionally, we discovered the regular appearance of a red-shifted absorption component in spectral lines of neutral hydrogen, helium, and oxygen as well as one of ionized silicon with a period of 36.13 ± 0.20 days. We show that the magnetic field strength also followed this period. The process was accompanied by increasing emission component strengths for the hydrogen lines as well as the helium and metallic absorption lines. We refined the fundamental parameters of the optical counterpart of IRAS 17449+2320 (

T_{eff} = 9800 \pm 300

K, log L/

L_{⊙} = 1.86 \pm 0.06

,

v sin i = 9 \pm 2

km s⁻¹) and concluded that the star was slightly metal-deficient and viewed nearly pole-on. No signs of a secondary component were found. Possible interpretations of the observed phenomena are suggested, and some earlier findings about the object’s nature are revised. Full article

(This article belongs to the Special Issue Circumstellar Matter in Hot Star Systems)

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11 pages, 520 KiB

Open AccessArticle

The Photometric Variability and Spectrum of the Hot Post-AGB Star IRAS 21546+4721

by Natalia Ikonnikova, Marina Burlak and Alexander Dodin

Galaxies 2025, 13(2), 31; https://doi.org/10.3390/galaxies13020031 - 31 Mar 2025

Abstract

We present the results of photometric and spectroscopic observations of a poorly studied B-type supergiant with infrared excess, the hot post-AGB star IRAS 21546+4721. Based on our photometric observations in the

U B V R_{C} I_{C}

bands, we detected rapid, night-to-night, [...] Read more.

We present the results of photometric and spectroscopic observations of a poorly studied B-type supergiant with infrared excess, the hot post-AGB star IRAS 21546+4721. Based on our photometric observations in the

U B V R_{C} I_{C}

bands, we detected rapid, night-to-night, non-periodic brightness variations in the star with peak-to-peak amplitudes up to

0 .^{m} 3

in the V band, as well as color–color and color–brightness correlations. Based on its variability characteristics, IRAS 21546+4721 appears similar to other hot post-AGB stars. Possible causes of the photometric variability are discussed. Additionally, we acquired low-resolution spectra in a wavelength range from 3500 to 7500 Å. The spectrum contains absorption lines typical of an early B-type star, along with a set of emission lines of H I, He I, [O I], [O II], [N II], [S II], and C II originating from an ionized circumstellar envelope. An analysis of the emission spectrum allowed us to estimate the parameters of the gas envelope (

N_{e}

∼ 10⁴ cm⁻³,

T_{e}

∼ 10,000 K) and the star’s temperature (∼26,500 K). The radial velocity measured from the emission lines was

V_{r} = - 141 \pm 7

km s⁻¹. Full article

(This article belongs to the Special Issue Circumstellar Matter in Hot Star Systems)

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13 pages, 2295 KiB

Open AccessArticle

Nonlinear Stability of the Bardeen–De Sitter Wormhole in f(R) Gravity

by A. Eid

Galaxies 2025, 13(2), 30; https://doi.org/10.3390/galaxies13020030 - 28 Mar 2025

Abstract

This paper discusses the nonlinear stability of a thin-shell wormhole from a regular black hole in Bardeen–de Sitter spacetime in the

f (R)

gravity framework. The stability is examined under the linear perturbation about static solution and a nonlinear variable equation [...] Read more.

This paper discusses the nonlinear stability of a thin-shell wormhole from a regular black hole in Bardeen–de Sitter spacetime in the

f (R)

gravity framework. The stability is examined under the linear perturbation about static solution and a nonlinear variable equation of state, such as the modified generalized Chaplygin gas. The stability solutions for a suitable choice of different parameters included in the variable equation of state and

f (R)

gravity models, as well as the metric space–time, are illustrated. Full article

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