Galaxies

14 pages, 893 KiB

Open AccessArticle

More Luminous Red Novae That Require Jets

by Noam Soker

Galaxies 2024, 12(4), 33; https://doi.org/10.3390/galaxies12040033 - 26 Jun 2024

In this paper, I study two intermediate luminosity optical transients (ILOTs), classified as luminous red novae (LRNe), and argue that their modeling with a common envelope evolution (CEE) without jets encounters challenges. LRNe are ILOTs powered by violent binary interaction. Although in the [...] Read more.

In this paper, I study two intermediate luminosity optical transients (ILOTs), classified as luminous red novae (LRNe), and argue that their modeling with a common envelope evolution (CEE) without jets encounters challenges. LRNe are ILOTs powered by violent binary interaction. Although in the literature it is popular to assume a CEE is the cause of LRNe, I here repeat an old claim that many LRNe are powered by grazing envelope evolution (GEE) events; the GEE might end in a CEE or a detached binary system. I find that the LRN AT 2021biy might have continued to experience mass ejection episodes after its eruption and, therefore, might not have suffered a full CEE during the outburst. This adds to an earlier finding that a jetless model does not account for some of its properties. I find that a suggested jetless CEE model for the LRN AT 2019zhd does not reproduce its photosphere radius evolution. These results that challenge jetless models of two LRNe strengthen a previous claim that jets play major roles in powering ILOTs and sha** their ejecta and that, in many LRNe, the more compact companion launches the jets during a GEE. Full article

16 pages, 608 KiB

Open AccessArticle

A 3 mm Spectral Line Study of the Central Molecular Zone Infrared Dark Cloud G1.75-0.08

by Oskari Miettinen and Miguel Santander-García

Galaxies 2024, 12(4), 32; https://doi.org/10.3390/galaxies12040032 - 25 Jun 2024

Abstract

Infrared dark clouds (IRDCs) are fruitful objects to study the fragmentation of interstellar filaments and initial conditions and early stages of high-mass (

M > 8

M_⊙) star formation. We used the Yebes 40 m and Institut de Radioastronomie Millimétrique (IRAM) [...] Read more.

Infrared dark clouds (IRDCs) are fruitful objects to study the fragmentation of interstellar filaments and initial conditions and early stages of high-mass (

M > 8

M_⊙) star formation. We used the Yebes 40 m and Institut de Radioastronomie Millimétrique (IRAM) 30 m radio telescopes to carry out the first single-pointing spectral line observations towards the IRDC G1.75-0.08, which is a filamentary Central Molecular Zone (CMZ) cloud. Our aim is to reach an improved understanding of the gas kinematics and dynamical state of the cloud and its two clumps that we call clumps A and B. We also aim to determine the fractional abundances of the molecules detected at 3 mm towards G1.75-0.08. We detected HNCO

(J_{K_{a}, K_{c}} = 4_{0, 4} - 3_{0, 3})

, HCN

(J = 1 - 0)

, and HCO⁺

(J = 1 - 0)

towards both clumps. The N₂H⁺

(J = 1 - 0)

line was detected only in clump B, while N₂D⁺

(J = 1 - 0)

was not detected at all. The HCN and HNCO spectra exhibit two velocity components. The abundances of the detected species are comparable to those in other IRDCs. An upper limit to the [N₂D⁺]/[N₂H⁺] deuterium fraction of <0.05 derived towards clump B is consistent with values observed in many high-mass clumps. The line mass analysis suggests that the G1.75-0.08 filament is subcritical by a factor of

11 \pm 6

, and the clumps were found to be gravitationally unbound (

α_{vir} > 2

). Our finding that G1.75-0.08 is strongly subcritical is atypical compared to the general population of Galactic filamentary clouds. The cloud’s location in the CMZ might affect the cloud kinematics similar to what has been found for the Brick IRDC, and the cloud’s dynamical state might also be the result of the turbulent motions or shear and tidal forces in the CMZ. Because the target clumps are dark at 70

μ

m and massive (several

10^{3}

M_⊙), they can be considered candidates for being high-mass starless clumps but not prestellar because they are not gravitationally bound. Full article

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18 pages, 2170 KiB

Open AccessArticle

Constraints on Prospective Deviations from the Cold Dark Matter Model Using a Gaussian Process

by Martiros Khurshudyan and Emilio Elizalde

Galaxies 2024, 12(4), 31; https://doi.org/10.3390/galaxies12040031 - 24 Jun 2024

Abstract

Recently, using Bayesian Machine Learning, a deviation from the cold dark matter model on cosmological scales has been put forward. Such a model might replace the proposed non-gravitational interaction between dark energy and dark matter, and help solve the

H_{0}

tension problem. [...] Read more.

Recently, using Bayesian Machine Learning, a deviation from the cold dark matter model on cosmological scales has been put forward. Such a model might replace the proposed non-gravitational interaction between dark energy and dark matter, and help solve the

H_{0}

tension problem. The idea behind the learning procedure relies on a generated expansion rate, while the real expansion rate is just used to validate the learned results. In the present work, however, the emphasis is put on a Gaussian Process (GP), with the available

H (z)

data confirming the possible existence of the already learned deviation. Three cosmological scenarios are considered: a simple one, with an equation-of-state parameter for dark matter

ω_{d m} = ω_{0} \neq 0

, and two other models, with corresponding parameters

ω_{d m} = ω_{0} + ω_{1} z

and

ω_{d m} = ω_{0} + ω_{1} z / (1 + z)

. The constraints obtained on the free parameters

ω_{0}

and

ω_{1}

hint towards a dynamical nature of the deviation. The dark energy dynamics is also reconstructed, revealing interesting aspects connected with the

H_{0}

tension problem. It is concluded, however, that improved tools and more data are needed, to reach a better understanding of the reported deviation. Full article

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18 pages, 3160 KiB

Open AccessArticle

A Supermassive Binary Black Hole Candidate in Mrk 501

by Gustavo Magallanes-Guijón and Sergio Mendoza

Galaxies 2024, 12(3), 30; https://doi.org/10.3390/galaxies12030030 - 18 Jun 2024

Abstract

Using multifrequency observations, from radio to

γ

-rays of the blazar Mrk 501, we constructed their corresponding light curves and built periodograms using RobPer and Lomb–Scargle algorithms. Long-term variability was also studied using the power density spectrum and the detrended function analysis. Using [...] Read more.

Using multifrequency observations, from radio to

γ

-rays of the blazar Mrk 501, we constructed their corresponding light curves and built periodograms using RobPer and Lomb–Scargle algorithms. Long-term variability was also studied using the power density spectrum and the detrended function analysis. Using the software VARTOOLS Version 1.40, we also computed the analysis of variance, box-least squares and discrete fourier transform. The result of these techniques showed an achromatic periodicity ≲

229 d

. This, combined with the result of pink-color noise in the spectra, led us to propose that the periodicity was produced via a secondary eclipsing supermassive binary black hole orbiting the primary one locked inside the central engine of Mrk 501. We built a relativistic eclipsing model of this phenomenon using Jacobi elliptical functions, finding a periodic relativistic eclipse occurring every ∼

224 d

in all the studied wavebands. This implies that the frequency of the emitted gravitational waves falls slightly above

0.1

mHz, well within the operational range of the upcoming LISA space-based interferometer, and as such, these gravitational waves must be considered as a prime science target for future LISA observations. Full article

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14 pages, 7277 KiB

Open AccessArticle

Planetary Nebula Morphologies Indicate a Jet-Driven Explosion of SN 1987A and Other Core-Collapse Supernovae

by Noam Soker

Galaxies 2024, 12(3), 29; https://doi.org/10.3390/galaxies12030029 - 6 Jun 2024

Abstract

I demonstrate the usage of planetary nebulae (PNe) to infer that a pair of jets shaped the ejecta of the core-collapse supernova (CCSN) SN 1987A. The main structure of the SN 1987A inner ejecta, the ‘keyhole’, comprises two low-intensity zones. The northern one [...] Read more.

I demonstrate the usage of planetary nebulae (PNe) to infer that a pair of jets shaped the ejecta of the core-collapse supernova (CCSN) SN 1987A. The main structure of the SN 1987A inner ejecta, the ‘keyhole’, comprises two low-intensity zones. The northern one has a bright rim on its front, while the southern one has an elongated nozzle. An earlier comparison of the SN 1987A ‘keyhole’ with bubbles in the galaxy group NGC 5813 led to its identification as a jet-shaped rim–nozzle structure. Here, I present rim–nozzle asymmetry in planetary nebulae (PNe), thought to be shaped by jets, which solidifies the claim that jets powered the ejecta of SN 1987A and other CCSNe. This finding for the iconic SN 1987A with its unique properties strengthens the jittering-jets explosion mechanism (JJEM) of CCSNe. In a few hundred years, the CCSN 1987A will have a complicated structure with two main symmetry axes, one along the axis of the three circumstellar rings that was shaped by two opposite 20,000-year pre-explosion jets, and the other along the long axis of the ‘keyhole’ that was shaped by the main (but not the only) jet pair of the exploding jets of SN 1987A in the frame of the JJEM. Full article

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

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11 pages, 3803 KiB

Open AccessArticle

Wave-Particle Interactions in Astrophysical Plasmas

by Héctor Pérez-De-Tejada

Galaxies 2024, 12(3), 28; https://doi.org/10.3390/galaxies12030028 - 6 Jun 2024

Abstract

Dissipation processes derived from the kinetic theory of gases (shear viscosity and heat conduction) are employed to examine the solar wind that interacts with planetary ionospheres. The purpose of this study is to estimate the mean free path of wave-particle interactions that produce [...] Read more.

Dissipation processes derived from the kinetic theory of gases (shear viscosity and heat conduction) are employed to examine the solar wind that interacts with planetary ionospheres. The purpose of this study is to estimate the mean free path of wave-particle interactions that produce a continuum response in the plasma behavior. Wave-particle interactions are necessary to support the fluid dynamic interpretation that accounts for the interpretation of various features measured in a solar wind–planet ionosphere region; namely, (i) the transport of solar wind momentum to an upper ionosphere in the presence of a velocity shear, and (ii) plasma heating produced by momentum transport. From measurements conducted in the solar wind interaction with the Venus ionosphere, it is possible to estimate that in general terms, the mean free path of wave-particle interactions reaches λ_H ≥ 1000 km values that are comparable to the gyration radius of the solar wind particles in their Larmor motion within the local solar wind magnetic field. Similar values are also applicable to conditions measured by the Mars ionosphere and in cometary plasma wakes. Considerations are made in regard to the stochastic trajectories of the plasma particles that have been implied from the measurements made in planetary environments. At the same time, it is as possible that the same phenomenon is applicable to the interaction of stellar winds with the ionosphere of exoplanets, and also in regions where streaming ionized gases reach objects that are subject to rotational motion in other astrophysical problems (galactic flow–plasma interactions, black holes, etc.). Full article

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

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17 pages, 1175 KiB

Open AccessArticle

The Response of the Inner Dark Matter Halo to Stellar Bars

by Daniel A. Marostica, Rubens E. G. Machado, E. Athanassoula and T. Manos

Galaxies 2024, 12(3), 27; https://doi.org/10.3390/galaxies12030027 - 28 May 2024

Abstract

Barred galaxies constitute about two-thirds of observed disc galaxies. Bars affect not only the mass distribution of gas and stars but also that of the dark matter. An elongation of the inner dark matter halo is known as the halo bar. We aim [...] Read more.

Barred galaxies constitute about two-thirds of observed disc galaxies. Bars affect not only the mass distribution of gas and stars but also that of the dark matter. An elongation of the inner dark matter halo is known as the halo bar. We aim to characterize the structure of the halo bars, with the goal of correlating them with the properties of the stellar bars. We use a suite of simulated galaxies with various bar strengths, including gas and star formation. We quantify the strengths, shapes, and densities of these simulated stellar bars. We carry out numerical experiments with frozen and analytic potentials in order to understand the role played by a live responsive stellar bar. We find that the halo bar generally follows the trends of the disc bar. The strengths of the halo and stellar bars are tightly correlated. Stronger bars induce a slight increase in dark matter density within the inner halo. Numerical experiments show that a non-responsive frozen stellar bar would be capable of inducing a dark matter bar, but it would be weaker than the live case by a factor of roughly two. Full article

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22 pages, 2559 KiB

Open AccessArticle

ALMA Band 3 Source Counts: A Machine Learning Approach to Contamination Mitigation below 5 Sigma

by Ivano Baronchelli, Matteo Bonato, Gianfranco De Zotti, Viviana Casasola, Michele Delli Veneri, Fabrizia Guglielmetti, Elisabetta Liuzzo, Rosita Paladino, Leonardo Trobbiani and Martin Zwaan

Galaxies 2024, 12(3), 26; https://doi.org/10.3390/galaxies12030026 - 20 May 2024

Abstract

We performed differential number counts down to 4.25 sigma using ALMA Band 3 calibrator images, which are known for their high dynamic range and susceptibility to various types of contamination. Estimating the fraction of contaminants is an intricate process due to correlated non-Gaussian [...] Read more.

We performed differential number counts down to 4.25 sigma using ALMA Band 3 calibrator images, which are known for their high dynamic range and susceptibility to various types of contamination. Estimating the fraction of contaminants is an intricate process due to correlated non-Gaussian noise, and it is often compounded by the presence of false positives generated during the cleaning phase. In addition, calibrator extensions further complicate the counting of background sources. In order to address these challenges, our strategy employs a machine learning-based approach utilizing the UMLAUT algorithm. UMLAUT assigns a value to each detection, and it considers how likely it is for there to be a genuine background source or a contaminant. With respect to this goal, we provide UMLAUT with eight observational input parameters, each automatically weighted using a gradient descent method. Our methodology significantly improves the precision of differential number counts, thus surpassing conventional techniques, including visual inspection. This study contributes to a better understanding of radio sources, particularly in the challenging sub-5 sigma regime, within the complex context of a high dynamic range of ALMA calibrator images. Full article

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49 pages, 1670 KiB

Open AccessArticle

High-Redshift Quasars at z ≥ 3: Radio Variability and MPS/GPS Candidates

by Yulia Sotnikova, Alexander Mikhailov, Timur Mufakharov, Tao An, Dmitry Kudryavtsev, Marat Mingaliev, Roman Udovitskiy, Anastasia Kudryashova, Vlad Stolyarov and Tamara Semenova

Galaxies 2024, 12(3), 25; https://doi.org/10.3390/galaxies12030025 - 15 May 2024

Cited by 1

Abstract

We present a study of the radio variability of bright,

S_{1.4} \geq 100

mJy, high-redshift quasars at

z \geq 3

on timescales of up to 30–40 yrs. The study involved simultaneous RATAN-600 measurements at the frequencies of 2.3, 4.7, 8.2, 11.2, and [...] Read more.

We present a study of the radio variability of bright,

S_{1.4} \geq 100

mJy, high-redshift quasars at

z \geq 3

on timescales of up to 30–40 yrs. The study involved simultaneous RATAN-600 measurements at the frequencies of 2.3, 4.7, 8.2, 11.2, and 22.3 GHz in 2017–2020. In addition, data from the literature were used. We have found that the variability index,

V_{S}

, which quantifies the normalized difference between the maximum and minimum flux density while accounting for measurement uncertainties, ranges from 0.02 to 0.96 for the quasars. Approximately half of the objects in the sample exhibit a variability index within the range from 0.25 to 0.50, which is comparable to that observed in blazars at lower redshifts. The distribution of

V_{S}

at 22.3 GHz is significantly different from that at 2.3–11.2 GHz, which may be attributed to the fact that a compact AGN core dominates at the source’s rest frame frequencies greater than 45 GHz, leading to higher variability indices obtained at 22.3 GHz (the

V_{S}

distribution peaks around 0.4) compared to the lower frequencies (the

V_{S}

distribution at 2.3 and 4.7 GHz peaks around 0.1–0.2). Several source groups with distinctive variability characteristics were found using the cluster analysis of quasars. We propose seven new candidates for gigahertz-peaked spectrum (GPS) sources and five new megahertz-peaked spectrum (MPS) sources based on their spectrum shape and variability features. Only 6 out of the 23 sources previously reported as GPS demonstrate a low variability level typical of classical GPS sources (

V_{S} < 0.25

) at 4.7–22.3 GHz. When excluding the highly variable peaked-spectrum blazars, we expect no more than 20% of the sources in the sample to be GPS candidates and no more than 10% to be MPS candidates. Full article

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16 pages, 14681 KiB

Open AccessFeature PaperArticle

Galaxy Groups as the Ultimate Probe of AGN Feedback

by Dominique Eckert, Fabio Gastaldello, Ewan O’Sullivan, Alexis Finoguenov, Marisa Brienza and the X-GAP Collaboration

Galaxies 2024, 12(3), 24; https://doi.org/10.3390/galaxies12030024 - 13 May 2024

Cited by 2

Abstract

The co-evolution between supermassive black holes and their environment is most directly traced by the hot atmospheres of dark matter halos. The cooling of the hot atmosphere supplies the central regions with fresh gas, igniting active galactic nuclei (AGN) with long duty cycles. [...] Read more.

The co-evolution between supermassive black holes and their environment is most directly traced by the hot atmospheres of dark matter halos. The cooling of the hot atmosphere supplies the central regions with fresh gas, igniting active galactic nuclei (AGN) with long duty cycles. The outflows from the central engine tightly couple with the surrounding gaseous medium and provide the dominant heating source, preventing runaway cooling. Every major modern hydrodynamical simulation suite now includes a prescription for AGN feedback to reproduce the realistic populations of galaxies. However, the mechanisms governing the feeding/feedback cycle between the central black holes and their surrounding galaxies and halos are still poorly understood. Galaxy groups are uniquely suited to constrain the mechanisms governing the cooling–heating balance, as the energy supplied by the central AGN can exceed the gravitational binding energy of halo gas particles. Here, we provide a brief overview of our knowledge of the impact of AGN on the hot atmospheres of galaxy groups, with a specific focus on the thermodynamic profiles of the groups. We then present our on-going efforts to improve on the implementation of AGN feedback in galaxy evolution models by providing precise measurements of the properties of galaxy groups. We introduce the XMM-Newton Group AGN Project (X-GAP), a large program on XMM-Newton targeting a sample of 49 galaxy groups out to

R_{500 c}

. Full article

(This article belongs to the Special Issue Multi-Phase Fueling and Feedback Processes in Jetted AGN)

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9 pages, 10540 KiB

Open AccessArticle

Doppler Tomography of the Circumstellar Disk of the Be Star κ Draconis

by Ilfa A. Gabitova, Anatoly S. Miroshnichenko, Sergey V. Zharikov, Ainash Amantayeva and Serik A. Khokhlov

Galaxies 2024, 12(3), 23; https://doi.org/10.3390/galaxies12030023 - 7 May 2024

Abstract

κ

Draconis is a binary system with a classical Be star as the primary component. Its emission-line spectrum consists of hydrogen lines, notably the H

α

line with peak intensity ratio (V/R) variations phase-locked with the orbital period P = 61.55 days. Among [...] Read more.

κ

Draconis is a binary system with a classical Be star as the primary component. Its emission-line spectrum consists of hydrogen lines, notably the H

α

line with peak intensity ratio (V/R) variations phase-locked with the orbital period P = 61.55 days. Among binaries demonstrating the Be phenomenon,

κ

Dra stands out as one of a few systems with a discernible mass of its secondary component. Based on more than 200 spectra obtained in 2014–2023, we verified the physical parameters and constructed the mass function. We used part of these data obtained in 2014–2021 to investigate regions in the circumstellar disk of the primary component that emit the H

α

line using the Doppler tomography method. The results show that the disk has a non-uniform density distribution with a prominent enhancement at

V_{y}

≈ 99 km

s^{- 1}

and

V_{x}

\approx - 6

km

s^{- 1}

that corresponds to a cloud-like source of the double-peaked H

α

line profile. We argue that this enhancement’s motion is responsible for the periodic variations in the H

α

V/R ratio, which is synchronised in orbital phase with the radial velocity (RV) of absorption lines from the atmosphere of the primary component. Full article

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

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27 pages, 21113 KiB

Open AccessArticle

CHANG-ES XXXI—A Decade of CHANG-ES: What We Have Learned from Radio Observations of Edge-on Galaxies

by Judith Irwin, Rainer Beck, Tanden Cook, Ralf-Jürgen Dettmar, Jayanne English, Volker Heesen, Richard Henriksen, Yan Jiang, Jiang-Tao Li, Li-Yuan Lu, Crystal Mele, Ancla Müller, Eric Murphy, Troy Porter, Richard Rand, Nathan Skeggs, Michael Stein, Yelena Stein, Jeroen Stil, Andrew Strong, Rene Walterbos, Q. Daniel Wang, Theresa Wiegert and Yang Yang Show full author list Hide full author list

Galaxies 2024, 12(3), 22; https://doi.org/10.3390/galaxies12030022 - 6 May 2024

Abstract

CHANG-ES (Continuum Halos in Nearby Galaxies—an EVLA Survey) is an ambitious project to target 35 nearby disk galaxies that are edge-on to the line of sight. The orientation permits both the disk and halo regions to be studied. The observations were initially at [...] Read more.

CHANG-ES (Continuum Halos in Nearby Galaxies—an EVLA Survey) is an ambitious project to target 35 nearby disk galaxies that are edge-on to the line of sight. The orientation permits both the disk and halo regions to be studied. The observations were initially at 1.5 GHz (L-band) and 6.0 GHz (C-band) in a variety of VLA array configurations, and in all four Stokes parameters, which allowed for spatially resolved images in total intensity plus polarization. The inclusion of polarization is unique to an edge-on galaxy survey and reveals the galaxies’ halo magnetic fields. This paper will summarize the results to date, some of which are new phenomena, never seen prior to CHANG-ES. For example, we see that ‘X-type’ fields, as well as rotation measure reversals, are common features of spiral galaxies. Further observations at 3.0 GHz (S-band) as well as future scientific opportunities will also be described. Full article

(This article belongs to the Special Issue The 10th Anniversary of Galaxies: New Perspectives on Radio Surveys)

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Graphical abstract

18 pages, 2825 KiB

Open AccessArticle

Flattened Galaxy Rotation Curves in the Exochronous Metric

by Robin Booth

Galaxies 2024, 12(3), 21; https://doi.org/10.3390/galaxies12030021 - 24 Apr 2024

Abstract

We examine some of the consequences of the Exochronous (timeless) metric and the associated

Σ

GR cosmological model for the formation of galaxies, and, in particular, their characteristic rotation curves. We show how the cumulative curvature from the multiple spatial hypersurfaces in this [...] Read more.

We examine some of the consequences of the Exochronous (timeless) metric and the associated

Σ

GR cosmological model for the formation of galaxies, and, in particular, their characteristic rotation curves. We show how the cumulative curvature from the multiple spatial hypersurfaces in this model leads to a modified version of the Poisson equation, in which the gravitational potential is computed over 4D space. Using this new form of the Poisson equation, we derive an analytic expression for gravitational potential as a function of radial distance for a uniform gas cloud undergoing gravitational collapse. We show that this results in a radial velocity profile that provides an excellent fit with commonly observed galaxy rotation curves, and hence fully accounts for the effects previously ascribed to dark matter. An expression can be derived for the equivalent matter density profile corresponding to the

Σ

GR gravitational potential, from which it is evident that this is very similar in form to the well-known Navarro–Frenk–White profile. As a further illustration of the consequences of adopting the Exochronous metric, we show how the principle can readily be incorporated into particle-mesh N-body simulations of large-scale structure evolution, using a relaxation solver for the solution to the Poisson equation and the evolution of the gravitational potential. Examples of the use of this simulation model are shown for the following cases: (a) the initial evolution of a large-scale structure, and (b) galaxy formation from a gravitationally collapsing gas cloud. In both cases, it is possible to directly visualise the build-up of the gravitational potential in 3D space as the simulation evolves and note how this corresponds to what is currently assumed to be dark matter. Full article

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16 pages, 1306 KiB

Open AccessReview

Investigating the Properties of the Relativistic Jet and Hot Corona in AGN with X-ray Polarimetry

by Dawoon E. Kim, Laura Di Gesu, Frédéric Marin, Alan P. Marscher, Giorgio Matt, Paolo Soffitta, Francesco Tombesi, Enrico Costa and Immacolata Donnarumma

Galaxies 2024, 12(3), 20; https://doi.org/10.3390/galaxies12030020 - 23 Apr 2024

Abstract

X-ray polarimetry has been suggested as a prominent tool for investigating the geometrical and physical properties of the emissions from active galactic nuclei (AGN). The successful launch of the Imaging X-ray Polarimetry Explorer (IXPE) on 9 December 2021 has expanded the previously restricted [...] Read more.

X-ray polarimetry has been suggested as a prominent tool for investigating the geometrical and physical properties of the emissions from active galactic nuclei (AGN). The successful launch of the Imaging X-ray Polarimetry Explorer (IXPE) on 9 December 2021 has expanded the previously restricted scope of polarimetry into the X-ray domain, enabling X-ray polarimetric studies of AGN. Over a span of two years, IXPE has observed various AGN populations, including blazars and radio-quiet AGN. In this paper, we summarize the remarkable discoveries achieved thanks to the opening of the new window of X-ray polarimetry of AGN through IXPE observations. We will delve into two primary areas of interest: first, the magnetic field geometry and particle acceleration mechanisms in the jets of radio-loud AGN, such as blazars, where the relativistic acceleration process dominates the spectral energy distribution; and second, the geometry of the hot corona in radio-quiet AGN. Thus far, the IXPE results from blazars favor the energy-stratified shock acceleration model, and they provide evidence of helical magnetic fields inside the jet. Concerning the corona geometry, the IXPE results are consistent with a disk-originated slab-like or wedge-like shape, as could result from Comptonization around the accretion disk. Full article

(This article belongs to the Special Issue Multi-Phase Fueling and Feedback Processes in Jetted AGN)

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16 pages, 6667 KiB

Open AccessFeature PaperReview

The Seeding of Cosmic Ray Electrons by Cluster Radio Galaxies: A Review

by Franco Vazza and Andrea Botteon

Galaxies 2024, 12(2), 19; https://doi.org/10.3390/galaxies12020019 - 22 Apr 2024

Cited by 3

Abstract

Radio galaxies in clusters of galaxies are a prominent reservoir of magnetic fields and of non-thermal particles, which become mixed with the intracluster medium. We review the observational and theoretical knowledge of the role of these crucial ingredients for the formation of diffuse [...] Read more.

Radio galaxies in clusters of galaxies are a prominent reservoir of magnetic fields and of non-thermal particles, which become mixed with the intracluster medium. We review the observational and theoretical knowledge of the role of these crucial ingredients for the formation of diffuse radio emission in clusters (radio halos, relics, mini halos) and outline the open questions in this field. Full article

(This article belongs to the Special Issue Multi-Phase Fueling and Feedback Processes in Jetted AGN)

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33 pages, 549 KiB

Open AccessReview

Astrochemistry of the Molecular Gas in Dusty Star-Forming Galaxies at the Cosmic Noon

by Francesca Perrotta, Martina Torsello, Marika Giulietti and Andrea Lapi

Galaxies 2024, 12(2), 18; https://doi.org/10.3390/galaxies12020018 - 22 Apr 2024

Abstract

Far-infrared and submillimeter observations have established the fundamental role of dust-obscured star formation in the assembly of stellar mass over the past ∼12 billion years. At z = 2–4, the so-called “cosmic noon”, the bulk of star formation is enshrouded in dust, and [...] Read more.

Far-infrared and submillimeter observations have established the fundamental role of dust-obscured star formation in the assembly of stellar mass over the past ∼12 billion years. At z = 2–4, the so-called “cosmic noon”, the bulk of star formation is enshrouded in dust, and dusty star-forming galaxies (DSFGs) contain ∼

50 %

of the total stellar mass density. Star formation occurs in dense molecular clouds, and is regulated by a complex interplay between all the ISM components that contribute to the energy budget of a galaxy: gas, dust, cosmic rays, interstellar electromagnetic fields, gravitational field, and dark matter. Molecular gas is the actual link between star-forming gas and its complex environment: much of what we know about star formation comes from observations of molecular line emissions. They provide by far the richest information about the star formation process. However, their interpretation requires complex modeling of the astrochemical networks which regulate molecular formation and establish molecular abundances in a cloud, and a modeling of the physical conditions of the gas in which molecular energy levels become populated. This paper critically reviews the main astrochemical parameters needed to obtain predictions about molecular signals in DSFGs. Molecular lines can be very bright compared to the continuum emission, but radiative transfer models are required to properly interpret the observed brightness. We review the current knowledge and the open questions about the interstellar medium of DSFGs, outlining the key role of molecular gas as a tracer and shaper of the star formation process. Full article

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

30 pages, 1896 KiB

Open AccessReview

Observational Tests of Active Galactic Nuclei Feedback: An Overview of Approaches and Interpretation

by Chris M. Harrison and Cristina Ramos Almeida

Galaxies 2024, 12(2), 17; https://doi.org/10.3390/galaxies12020017 - 10 Apr 2024

Cited by 5

Abstract

Growing supermassive black holes (Active Galactic Nuclei; AGN) release energy with the potential to alter their host galaxies and larger-scale environment; a process named “AGN feedback”. Feedback is a required component of galaxy formation models and simulations to explain the observed properties of [...] Read more.

Growing supermassive black holes (Active Galactic Nuclei; AGN) release energy with the potential to alter their host galaxies and larger-scale environment; a process named “AGN feedback”. Feedback is a required component of galaxy formation models and simulations to explain the observed properties of galaxy populations. We provide a broad overview of observational approaches that are designed to establish the physical processes that couple AGN energy to the multi-phase gas, or to find evidence that AGN impact upon galaxy evolution. The orders-of-magnitude range in spatial, temporal, and temperature scales, requires a diverse set of observational studies. For example, studying individual targets in detail sheds light on coupling mechanisms; however, evidence for the long-term impact of AGN is better established within galaxy populations that are not necessarily currently active. We emphasise how modern surveys have revealed the importance of radio emission for identifying and characterising feedback mechanisms. At the achieved sensitivities, the detected radio emission can trace a range of processes, including a shocked interstellar medium caused by AGN outflows (driven by various mechanisms including radiation pressure, accretion disc winds, and jets). We also describe how interpreting observations in the context of theoretical work can be challenging, in part, due to some of the adopted terminology. Full article

(This article belongs to the Special Issue Multi-Phase Fueling and Feedback Processes in Jetted AGN)

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13 pages, 1202 KiB

Open AccessReview

Impact of Active Galactic Nuclei Feedback on the Dynamics of Gas: A Review across Diverse Environments

by Mojtaba Raouf, Mohammad Hossein Purabbas and Fatemeh Fazel Hesar

Galaxies 2024, 12(2), 16; https://doi.org/10.3390/galaxies12020016 - 8 Apr 2024

Abstract

This review examines the relationship between black hole activity and kinematic gas–star misalignment in brightest group galaxies (BGGs) with different merger rates. The formation history of galaxy groups is assessed through “age-dating” as an indicator of distinct major mergers involving the BGGs. BGGs [...] Read more.

This review examines the relationship between black hole activity and kinematic gas–star misalignment in brightest group galaxies (BGGs) with different merger rates. The formation history of galaxy groups is assessed through “age-dating” as an indicator of distinct major mergers involving the BGGs. BGGs within groups characterized by a higher frequency of major mergers are more likely to host active SMBHs. A consistent correlation is identified between the level of black hole activity, as indicated by the 1.4 GHz and 325 MHz radio emissions, and the degree of kinematic misalignment between the gas and stellar components in BGGs. In dynamically fossil groups, where black hole accretion rate is relatively (∼1 dex) lower due to the lack of recent (≤1 Gyr) major mergers, there is reduced (∼30%) misalignment between the gas and stellar components of BGGs compared to non-fossil groups. Additionally, this study reveals that BGGs in non-fossil groups show higher levels of star formation rate and increased occurrence of mergers, contributing to observed color differences. Exploring the properties and dynamics of the gas disk influenced by mechanical AGN feedback through hydrodynamic simulations suggests that AGN wind-induced effects further lead to the persistent gas misalignment in the disk around the supermassive black hole. Full article

(This article belongs to the Special Issue Multi-Phase Fueling and Feedback Processes in Jetted AGN)

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16 pages, 2560 KiB

Open AccessReview

AGN Feedback Signatures in UV Emission

by K. Rubinur

Galaxies 2024, 12(2), 15; https://doi.org/10.3390/galaxies12020015 - 4 Apr 2024

Abstract

Supermassive black holes (SMBH) are believed to influence galaxy evolution through AGN (active galactic nuclei) feedback. Galaxy mergers are key processes of galaxy formation that lead to AGN activity and star formation. The relative contribution of AGN feedback and mergers to star formation [...] Read more.

Supermassive black holes (SMBH) are believed to influence galaxy evolution through AGN (active galactic nuclei) feedback. Galaxy mergers are key processes of galaxy formation that lead to AGN activity and star formation. The relative contribution of AGN feedback and mergers to star formation is not yet well understood. In radio-loud objects, AGN outflows are dominated by large jets. However, in radio-quiet objects, outflows are more complex and involve jet, wind, and radiation. In this review, we discuss the signatures of AGN feedback through the alignment of radio and UV emissions. Current research on AGN feedback is discussed, along with a few examples of studies such as the galaxy merger system MRK 212, the radio-quiet AGN NGC 2639, and the radio-loud system Centaurus A. Multi-frequency observations of MRK 212 indicate the presence of dual AGN, as well as feedback-induced star-forming UV clumps. The fourth episode of AGN activity was detected in radio observations of the Seyfert galaxy NGC 2639, which also showed a central cavity of 6 kpc radius in CO and UV maps. This indicates that multi-epoch jets of radio-quiet AGN can blow out cold molecular gas, which can further reduce star formation in the center of the galaxies. Recent UV observations of Cen A have revealed two sets of stellar population in the northern star-forming region, which may have two different origins. Recent studies have shown that there is evidence that both positive and negative feedback can be present in galaxies at different scales and times. High-resolution, multi-band observations of large samples of different types of AGN and their host galaxies are important for understanding the two types of AGN feedback and their effect on the host galaxies. Future instruments like INSIST and UVEX will be able to help achieve some of these goals. Full article

(This article belongs to the Special Issue Multi-Phase Fueling and Feedback Processes in Jetted AGN)

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