Galaxies

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

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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 [...] 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

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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

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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

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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

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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

Viewed by 643

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

Viewed by 589

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

Viewed by 626

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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Galaxies, Volume 12, Issue 3 (June 2024) – 8 articles

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