Journal Description
Galaxies
Galaxies
is an international, peer-reviewed, open access journal on astronomy, astrophysics, and cosmology published bimonthly online by MDPI.
- Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
- High Visibility: indexed within Scopus, ESCI (Web of Science), Astrophysics Data System, INSPIRE, Inspec, and other databases.
- Journal Rank: CiteScore - Q2 (Astronomy and Astrophysics)
- Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 21 days after submission; acceptance to publication is undertaken in 4.9 days (median values for papers published in this journal in the second half of 2023).
- Recognition of Reviewers: reviewers who provide timely, thorough peer-review reports receive vouchers entitling them to a discount on the APC of their next publication in any MDPI journal, in appreciation of the work done.
Impact Factor:
2.5 (2022);
5-Year Impact Factor:
1.9 (2022)
Latest Articles
The Response of the Inner Dark Matter Halo to Stellar Bars
Galaxies 2024, 12(3), 27; https://doi.org/10.3390/galaxies12030027 - 28 May 2024
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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
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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.
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ALMA Band 3 Source Counts: A Machine Learning Approach to Contamination Mitigation below 5 Sigma
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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
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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
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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.
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High-Redshift Quasars at z ≥ 3: Radio Variability and MPS/GPS Candidates
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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
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We present a study of the radio variability of bright, mJy, high-redshift quasars at 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
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We present a study of the radio variability of bright, mJy, high-redshift quasars at 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, , 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 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 distribution peaks around 0.4) compared to the lower frequencies (the 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 ( ) 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.
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Galaxy Groups as the Ultimate Probe of AGN Feedback
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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
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.
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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 .
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(This article belongs to the Special Issue Multi-Phase Fueling and Feedback Processes in Jetted AGN)
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Doppler Tomography of the Circumstellar Disk of the Be Star κ Draconis
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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
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 line with peak intensity ratio (V/R) variations phase-locked with the orbital period P = 61.55 days. Among
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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 line with peak intensity ratio (V/R) variations phase-locked with the orbital period P = 61.55 days. Among binaries demonstrating the Be phenomenon, 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 line using the Doppler tomography method. The results show that the disk has a non-uniform density distribution with a prominent enhancement at ≈ 99 km and km that corresponds to a cloud-like source of the double-peaked H line profile. We argue that this enhancement’s motion is responsible for the periodic variations in the H V/R ratio, which is synchronised in orbital phase with the radial velocity (RV) of absorption lines from the atmosphere of the primary component.
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(This article belongs to the Collection A Trip across the Universe: Our Present Knowledge and Future Perspectives)
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CHANG-ES XXXI—A Decade of CHANG-ES: What We Have Learned from Radio Observations of Edge-on Galaxies
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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 Yangadd
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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
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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.
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(This article belongs to the Special Issue The 10th Anniversary of Galaxies: New Perspectives on Radio Surveys)
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Flattened Galaxy Rotation Curves in the Exochronous Metric
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Robin Booth
Galaxies 2024, 12(3), 21; https://doi.org/10.3390/galaxies12030021 - 24 Apr 2024
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We examine some of the consequences of the Exochronous (timeless) metric and the associated 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
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We examine some of the consequences of the Exochronous (timeless) metric and the associated 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 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.
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Investigating the Properties of the Relativistic Jet and Hot Corona in AGN with X-ray Polarimetry
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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
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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.
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(This article belongs to the Special Issue Multi-Phase Fueling and Feedback Processes in Jetted AGN)
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The Seeding of Cosmic Ray Electrons by Cluster Radio Galaxies: A Review
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Franco Vazza and Andrea Botteon
Galaxies 2024, 12(2), 19; https://doi.org/10.3390/galaxies12020019 - 22 Apr 2024
Cited by 2
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
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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.
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(This article belongs to the Special Issue Multi-Phase Fueling and Feedback Processes in Jetted AGN)
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Astrochemistry of the Molecular Gas in Dusty Star-Forming Galaxies at the Cosmic Noon
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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
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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 ∼ 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.
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(This article belongs to the Special Issue The Observation and Detection of Dusty Star-Forming Galaxies)
Open AccessReview
Observational Tests of Active Galactic Nuclei Feedback: An Overview of Approaches and Interpretation
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Chris M. Harrison and Cristina Ramos Almeida
Galaxies 2024, 12(2), 17; https://doi.org/10.3390/galaxies12020017 - 10 Apr 2024
Cited by 3
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
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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.
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(This article belongs to the Special Issue Multi-Phase Fueling and Feedback Processes in Jetted AGN)
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Impact of Active Galactic Nuclei Feedback on the Dynamics of Gas: A Review across Diverse Environments
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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
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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.
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(This article belongs to the Special Issue Multi-Phase Fueling and Feedback Processes in Jetted AGN)
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AGN Feedback Signatures in UV Emission
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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
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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.
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(This article belongs to the Special Issue Multi-Phase Fueling and Feedback Processes in Jetted AGN)
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Teaming up Radio and Sub-mm/FIR Observations to Probe Dusty Star-Forming Galaxies
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Meriem Behiri, Marika Giulietti, Vincenzo Galluzzi, Andrea Lapi, Elisabetta Liuzzo and Marcella Massardi
Galaxies 2024, 12(2), 14; https://doi.org/10.3390/galaxies12020014 - 29 Mar 2024
Abstract
In this paper, we investigate the benefits of teaming up data from the radio to the far-infrared (FIR) regime for the characterization of dusty star-forming galaxies (DSFGs). These galaxies are thought to be the star-forming progenitors of local massive quiescent galaxies and to
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In this paper, we investigate the benefits of teaming up data from the radio to the far-infrared (FIR) regime for the characterization of dusty star-forming galaxies (DSFGs). These galaxies are thought to be the star-forming progenitors of local massive quiescent galaxies and to play a pivotal role in the reconstruction of the cosmic star formation rate density up to high redshift. Due to their dust-enshrouded nature, DSFGs are often invisible in the near-infrared/optical/UV bands. Therefore, they necessitate observations at longer wavelengths, primarily the FIR band, where dust emission occurs, and the radio band, which is not affected by dust absorption. Combining data from these two spectral windows makes it possible to characterize even the dustiest objects, enabling the retrieval of information about their age, dust temperature, and star-formation status, and facilitates the differentiation between various galaxy populations that evolve throughout cosmic history. Despite the detection of faint radio sources being a challenging task, this study demonstrates that an effective strategy to build statistically relevant samples of DSFGs would be reaching deep sensitivities in the radio band, even restricted to smaller areas, and then combining these radio observations with FIR/submm data. Additionally, this paper quantifies the improvement in the spectral energy distribution (SED) reconstruction of DSFGs by incorporating ALMA band measurements, in particular, in its upgraded status thanks to the anticipated Wideband Sensitivity Upgrade.
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(This article belongs to the Special Issue The Observation and Detection of Dusty Star-Forming Galaxies)
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Significance of Fabry-Perot Cavities for Space Gravitational Wave Antenna DECIGO
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Kenji Tsuji, Tomohiro Ishikawa, Kurumi Umemura, Yuki Kawasaki, Shoki Iwaguchi, Ryuma Shimizu, Masaki Ando and Seiji Kawamura
Galaxies 2024, 12(2), 13; https://doi.org/10.3390/galaxies12020013 - 15 Mar 2024
Cited by 1
Abstract
DECIGO is a future Japanese project for the detection of gravitational waves in space. To conduct various scientific missions, including the verification of cosmic inflation through the detection of primordial gravitational waves as the main objective, DECIGO is designed to have high sensitivity
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DECIGO is a future Japanese project for the detection of gravitational waves in space. To conduct various scientific missions, including the verification of cosmic inflation through the detection of primordial gravitational waves as the main objective, DECIGO is designed to have high sensitivity in the frequency band from to 10 Hz, with arms of length 1000 km. Furthermore, the use of the Fabry-Perotcavity in these arms has been established for the DECIGO project. In this paper, we scrutinize the significance of the Fabry-Perot cavity for promoting this project, with a focus on the possibility of observing gravitational waves from cosmic inflation and binary compact star systems as indicators. The results show that using the Fabry-Perot cavity is extremely beneficial for detecting them, and it is anticipated to enable the opening of a new window in gravitational wave astronomy.
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(This article belongs to the Special Issue Third-Generation Gravitational Wave Detectors and Beyond)
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Enhancing Gamma-Ray Burst Detection: Evaluation of Neural Network Background Estimator and Explainable AI Insights
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Riccardo Crupi, Giuseppe Dilillo, Giovanni Della Casa, Fabrizio Fiore and Andrea Vacchi
Galaxies 2024, 12(2), 12; https://doi.org/10.3390/galaxies12020012 - 14 Mar 2024
Abstract
The detection of Gamma-Ray Bursts (GRBs) using spaceborne X/gamma-ray photon detectors depends on a reliable background count rate estimate. This study focuses on evaluating a data-driven background estimator based on a neural network designed to adapt to various X/gamma-ray space telescopes. Three trials
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The detection of Gamma-Ray Bursts (GRBs) using spaceborne X/gamma-ray photon detectors depends on a reliable background count rate estimate. This study focuses on evaluating a data-driven background estimator based on a neural network designed to adapt to various X/gamma-ray space telescopes. Three trials were conducted to assess the effectiveness and limitations of the proposed estimator. Firstly, quantile regression was employed to obtain an estimation with a confidence range prediction. Secondly, we assessed the performance of the neural network, emphasizing that a dataset of four months is sufficient for training. We tested its adaptability across various temporal contexts, identified its limitations and recommended re-training for each specific period. Thirdly, utilizing Explainable Artificial Intelligence (XAI) techniques, we delved into the neural network output, determining distinctions between a network trained during solar maxima and one trained during solar minima. This entails conducting a thorough analysis of the neural network behavior under varying solar conditions.
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(This article belongs to the Special Issue Gamma-Ray Bursts in Multiwavelength: Theory, Observational Correlations and GRB Cosmology)
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What Have We Learned about the Life Cycle of Radio Galaxies from New Radio Surveys
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Raffaella Morganti
Galaxies 2024, 12(2), 11; https://doi.org/10.3390/galaxies12020011 - 13 Mar 2024
Abstract
The recurrent activity of radio AGN, with phases of activity alternating with periods of quiescence, has been known since the early studies of these objects. The full relevance of this cycle is emphasised by the requirement, from the AGN feedback scenario, of a
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The recurrent activity of radio AGN, with phases of activity alternating with periods of quiescence, has been known since the early studies of these objects. The full relevance of this cycle is emphasised by the requirement, from the AGN feedback scenario, of a recurrent impact of the energy released by the SMBH during the lifetime of the host galaxy: only in this way can AGN feedback influence galaxy evolution. Radio AGN in different evolutionary phases can be identified by their properties, like morphology and spectral indices. Dying/remnant and restarted sources have been the most elusive to select and characterise, but they are crucial to quantify the full life cycle. Thanks to the availability of new, large radio surveys (particularly at low frequencies), it is finally possible to make a more complete census of these rare sources and start building larger samples. This paper gives an overview of the recent work conducted using a variety of radio telescopes and surveys, highlighting some of the new results characterising the properties of dying/remnant and restarted radio sources and what has been learned about the life cycle of radio AGN. The comparison with the predictions from numerical simulations is also discussed. The results so far show that remnant and restarted radio AGN have a variety of properties which make these objects more complex than previously thought.
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(This article belongs to the Special Issue Multi-Phase Fueling and Feedback Processes in Jetted AGN)
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Central Engine and Spectral Energy Distribution Properties of High Redshift Gamma Ray Blazars
by
Anilkumar Tolamatti, Krishna Kumar Singh and Kuldeep Kumar Yadav
Galaxies 2024, 12(2), 10; https://doi.org/10.3390/galaxies12020010 - 11 Mar 2024
Abstract
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We report on the properties of central engines in the -ray blazars located at high redshifts beyond z > 0.4, where the extra-galactic background light (EBL) starts affecting their -ray spectra. The physical engine that provides power to the blazars of
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We report on the properties of central engines in the -ray blazars located at high redshifts beyond z > 0.4, where the extra-galactic background light (EBL) starts affecting their -ray spectra. The physical engine that provides power to the blazars of very high bolometric luminosity is assumed to be a highly collimated jet of matter moving relativistically away from the supermassive black hole (SMBH), located in the central region of the host galaxy, in a direction aligned toward the Earth. Due to their peculiar geometry and special physical conditions, blazars at redshifts beyond z > 0.4 are bright enough to be detected in the -ray energy band. In this work, we investigate the physical properties of high-z -ray blazars detected by the Large Area Telescope (LAT) on board the Fermi satellite. We also study the properties of their emission regions and the central engines and discuss cosmological and astrophysical implications.
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Open AccessReview
Observing Dusty Star-Forming Galaxies at the Cosmic Noon through Gravitational Lensing: Perspectives from New-Generation Telescopes
by
Marika Giulietti, Giovanni Gandolfi, Marcella Massardi, Meriem Behiri and Andrea Lapi
Galaxies 2024, 12(2), 9; https://doi.org/10.3390/galaxies12020009 - 8 Mar 2024
Abstract
Gravitational lensing, a compelling physical phenomenon, offers a unique avenue to investigate the morphology and physical properties of distant and faint celestial objects. This paper seeks to provide a comprehensive overview of the current state of observations concerning strongly lensed Dusty Star-Forming Galaxies.
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Gravitational lensing, a compelling physical phenomenon, offers a unique avenue to investigate the morphology and physical properties of distant and faint celestial objects. This paper seeks to provide a comprehensive overview of the current state of observations concerning strongly lensed Dusty Star-Forming Galaxies. Emphasis is placed on the pivotal role played by cutting-edge facilities like the James Webb Space Telescope and the Square Kilometer Array Observatory. These advanced instruments operating at the two opposite ends of the electromagnetic spectrum, in conjunction with the amplifying effect of gravitational lensing, promise significant steps in our understanding of these sources. The synergy between these observatories is poised to unlock crucial insights into the evolutionary path of high-redshift, dust-obscured systems and unravel the intricate interplay between Active Galactic Nuclei and their host galaxies.
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(This article belongs to the Special Issue The Observation and Detection of Dusty Star-Forming Galaxies)
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Open AccessArticle
Superluminal Motion and Jet Parameters in the Gamma-ray-Emitting Narrow-Line Seyfert 1 Galaxy TXS 1206+549
by
Bettina Kozák, Sándor Frey and Krisztina Éva Gabányi
Galaxies 2024, 12(1), 8; https://doi.org/10.3390/galaxies12010008 - 17 Feb 2024
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Narrow-line Seyfert 1 (NLS1) galaxies are a peculiar subclass of active galactic nuclei (AGN). Among them, TXS 1206+549 belongs to a small group of radio-loud and -ray-emitting NLS1 galaxies. We focus on the radio properties of this galaxy by analysing archival, high-resolution,
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Narrow-line Seyfert 1 (NLS1) galaxies are a peculiar subclass of active galactic nuclei (AGN). Among them, TXS 1206+549 belongs to a small group of radio-loud and -ray-emitting NLS1 galaxies. We focus on the radio properties of this galaxy by analysing archival, high-resolution, very long baseline interferometry (VLBI) imaging observations taken at 8 GHz frequency in six epochs between 1994 and 2018. Using the milliarcsecond-scale radio structure, we can resolve a core and a jet component whose angular separation increases by mas yr−1. This corresponds to an apparent superluminal jet component motion of . From the core brightness temperature and the jet component proper motion, we determine the characteristic Doppler-boosting factor, the bulk Lorentz factor, and the jet viewing angle. We find no compelling evidence for a very closely aligned blazar-type jet. The parameters for TXS 1206+549 resemble those of radio-loud quasar jets with a moderate Lorentz factor ( ) and inclination to the line of sight.
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