Galaxies

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

Cited by 1 | Viewed by 645

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

Cited by 3 | Viewed by 623

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

Viewed by 466

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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Figure 1
(Lower panel) Trajectory of the Mariner 5 spacecraft projected in cylindrical coordinates in its flyby past Venus. Labels 1 to 5 along the trajectory mark important events in the plasma properties (a bow shock is identified at features 1 and 5), and the intermediate plasma transition occurs at features 2 and 4). (Upper panel) Magnetic field intensity and its latitudinal and azimuthal orientation, together with the plasma properties (thermal speed, density, and bulk speed) measured around Venus [<a href="#B1-galaxies-12-00028" class="html-bibr">1</a>]. Full article ">Figure 2
Ion speed and temperature measured along the orbit of Venera 10 on 19 April 1976. The Venera orbit in cylindrical coordinates is shown at the top. The temperature burst at position 1 was recorded during a flank crossing of a bow shock. A boundary layer is apparent by the increase in temperature and decrease in speed, and is initiated by the intermediate transition at the position labeled 2. A latter discontinuity in the boundary layer temperature profile corresponds to the boundary of the magneto-tail (from [<a href="#B6-galaxies-12-00028" class="html-bibr">6</a>]). Full article ">Figure 3
Vector velocity speeds of the trans-terminator flow in the Venus upper ionosphere measured with instruments onboard the Pioneer Venus Orbiter spacecraft [<a href="#B9-galaxies-12-00028" class="html-bibr">9</a>]. Full article ">Figure 4
Measured flow velocities versus VEX altitude for solar wind H+ ions, and ionospheric H+ and O+ ions. The curve marked vesc illustrates escape velocity versus altitude above Venus. The data points represent average values in 50 km altitude intervals sampled within Y = +0.5 of the dawn-dusk Meridian (left panel) and of the noon–midnight Meridian (right panel). Regions and boundaries are marked on the right-hand side as the I-sphere (the ionopause (IP), and the ionosheath (IMB) (from Lundin et al., (2011) [<a href="#B17-galaxies-12-00028" class="html-bibr">17</a>]). Full article ">Figure 5
Mean free path values λH of the solar wind obtained in wave-particle interactions and also in magnetic field fluctuations using the solar wind thermal speed VT and its kinematic viscosity coefficient ﬠ during the Mariner 5 trajectory in <a href="#galaxies-12-00028-f001" class="html-fig">Figure 1</a>. The connecting line labeled “W” refers to a value in the Venus inner and in the outer ionosheath that is implied by wave-particle interactions. The connecting line labeled “F” is implied by the magnetic field fluctuations. Full article ">Figure 6
(Upper panel) Trajectory of the PVO in orbit 87 projected on one quadrant in cylindrical coordinates. The bow shock, the intermediate transition, and the ionopause are indicated. (Lower panel) Ion flux values measured as a function of energy in cycles I, II, III, and IV state their start time (their position is noted in the upper panel along the PVO trajectory). Positions A, B, and C in spectrum III mark the time when the ion fluxes were obtained ([<a href="#B24-galaxies-12-00028" class="html-bibr">24</a>]). Full article ">Figure 7
View of a corkscrew vortex flow in fluid dynamics. Its geometry is equivalent to that of a vortex flow in the Venus wake, with its width and position varying during the solar cycle. Near the solar cycle minimum, the vortex is located closer to Venus (located by the right side) and there are also indications that its width becomes smaller with increasing distance downstream from the planet [<a href="#B13-galaxies-12-00028" class="html-bibr">13</a>]. Full article ">

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

Cited by 2 | Viewed by 559

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

Viewed by 632

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 | Viewed by 784

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 3 | Viewed by 887

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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Figure 1
Impact of AGN feedback on galaxy group atmospheres. The left-panel shows an SDSS i-band image of the brightest group galaxy IC 2476 with X-ray observations of the IGrM superimposed in red. The white contours shows radio emission from the associated radio galaxy B2 0924+30 from LoTSS DR2 data [<a href="#B20-galaxies-12-00024" class="html-bibr">20</a>]. The right-hand panel shows the relation between the binding energy of IGrM gas particles and the energy injection from the central BH (figure reproduced from [<a href="#B17-galaxies-12-00024" class="html-bibr">17</a>]). The dashed line indicates equality between BH and binding energy. Full article ">Figure 2
Impact of AGN feedback on the thermodynamic profiles of galaxy groups. The figure shows the profiles of IGrM gas density (a) and entropy (b) in four state-of-the-art simulations (EAGLE, Illustris-TNG100, SIMBA, and ROMULUS; [<a href="#B40-galaxies-12-00024" class="html-bibr">40</a>]). Increasing the feedback energy leads to lower gas densities (left) and higher gas entropies (right), highlighting the sensitivity of the IGrM to the feedback scheme. For comparison, the dashed curves show observed galaxy group thermodynamic profiles from Chandra [<a href="#B45-galaxies-12-00024" class="html-bibr">45</a>] and XMM-Newton [<a href="#B46-galaxies-12-00024" class="html-bibr">46</a>]. Full article ">Figure 3
X-GAP group selection cross-matching extended sources detected in RASS with SDSS spectroscopic galaxy groups [<a href="#B56-galaxies-12-00024" class="html-bibr">56</a>]. The plot shows the RASS X-ray luminosity and the corresponding mass estimated through a luminosity–mass relation as a function of the source redshift. The points are color-coded by the apparent size <math display="inline"><semantics> <msub> <mi>θ</mi> <mn>500</mn> </msub> </semantics></math> of <math display="inline"><semantics> <msub> <mi>R</mi> <mrow> <mn>500</mn> <mi>c</mi> </mrow> </msub> </semantics></math>. The selected sample is highlighted by the red stars. Full article ">Figure 4
Analysis results for four groups matching the X-GAP selection criteria with available observations in the XMM-Newton archive. The selected groups exhibit a flat brightness distribution, as highlighted in the (a), where we show the combined XMM-Newton/EPIC image of one of the systems (SDSSTG 8050 = A1213) with RASS contours overlaid in green. The low surface brightness implies a strong entropy excess (b) extending all the way out to <math display="inline"><semantics> <msub> <mi>R</mi> <mrow> <mn>500</mn> <mi>c</mi> </mrow> </msub> </semantics></math>. The gas is evacuated towards the outskirts, where the gas fraction rises sharply (c). Given our selection process, we are able to determine the gas fraction at <math display="inline"><semantics> <msub> <mi>R</mi> <mrow> <mn>500</mn> <mi>c</mi> </mrow> </msub> </semantics></math> without requiring any extrapolation. Full article ">Figure A1
Background subtracted, vignetting corrected, and adaptively smoothed XMM-Newton/EPIC maps of X-GAP groups in the [0.7–1.2] keV band. Shown are SDSSTG 828, SDSSTG 885, SDSSTG 1011 (top row), SDSSTG 1162, SDSSTG 1398, SDSSTG 1601 (second row), SDSSTG 1695, SDSSTG 2424, SDSSTG 2620 (third row), SDSSTG 3128, SDSSTG 3460, SDSSTG 3513 (bottom row). The magenta squares show the position of SDSS member galaxies selected using the FoF algorithm [<a href="#B19-galaxies-12-00024" class="html-bibr">19</a>]. In all cases, the axes are right ascension and declination in unit of degrees. Full article ">Figure A2
Same as <a href="#galaxies-12-00024-f0A1" class="html-fig">Figure A1</a> for SDSSTG 3669, SDSSTG 4047, SDSSTG 4436 (top row), SDSSTG 4654, SDSSTG 4936, SDSSTG 5742 (second row), SDSSTG 6058, SDSSTG 6159, SDSSTG 8050 (third row), SDSSTG 8102, SDSSTG 9178, SDSSTG 9370 (bottom row). Full article ">Figure A3
Same as <a href="#galaxies-12-00024-f0A1" class="html-fig">Figure A1</a> for SDSSTG 9399, SDSSTG 9647, SDSSTG 9695 (top row), SDSSTG 9771, SDSSTG 10094, SDSSTG 10159 (second row), SDSSTG 10842, SDSSTG 11320, SDSSTG 11631 (third row), SDSSTG 11844, SDSSTG 12349, SDSSTG 15354 (bottom row). Full article ">Figure A4
Same as <a href="#galaxies-12-00024-f0A1" class="html-fig">Figure A1</a> for SDSSTG 15641, SDSSTG 15776, SDSSTG 16150 (top row), SDSSTG 16393, SDSSTG 21128, SDSSTG 22635 (second row), SDSSTG 24595, SDSSTG 28674, SDSSTG 35976 (third row), SDSSTG 39344, SDSSTG 40241, SDSSTG 46701 (bottom row). Full article ">

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

Viewed by 781

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 1211

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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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 968

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 1016

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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