Galaxies

12 pages, 528 KiB

Open AccessFeature PaperArticle

New Method to Detect and Characterize Active Be Star Candidates in Open Clusters

by Anahí Granada, Maziar R. Ghoreyshi, Carol E. Jones and Tõnis Eenmäe

Galaxies 2023, 11(1), 37; https://doi.org/10.3390/galaxies11010037 - 19 Feb 2023

Cited by 1 | Viewed by 1726

With the aim of better understanding the physical conditions under which Be stars form and evolve, it is imperative to further investigate whether poorly studied young open clusters host Be stars. In this work, we explain how data from Gaia DR2 and DR3 [...] Read more.

With the aim of better understanding the physical conditions under which Be stars form and evolve, it is imperative to further investigate whether poorly studied young open clusters host Be stars. In this work, we explain how data from Gaia DR2 and DR3 can be combined to recover and characterize active Be stars in open clusters. We test our methodology in four open clusters broadly studied in the literature, known for hosting numerous Be stars. In addition, we show that the disk formation and dissipation approach that is typically used to model long term Be star variability, can explain the observed trends for Be stars in a (

G_{D R 3}

-

G_{D R 2}

) versus

G_{D R 3}

plot. We propose that extending this methodology to other open clusters, and, in particular, those that are poorly studied, will help to increase the number of Be candidates. Eventually, Be stars may eclipse binary systems in open clusters. Full article

(This article belongs to the Special Issue Theory and Observation of Active B-type Stars)

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19 pages, 719 KiB

Open AccessReview

Recent Progress in Finding Binary Systems with the B[e] Phenomenon

by Anatoly S. Miroshnichenko, Sergei V. Zharikov, Nadine Manset, Serik A. Khokhlov, Atilkhan S. Nodyarov, Valentina G. Klochkova, Stephen Danford, Aizhan K. Kuratova, Ronald Mennickent, S. Drew Chojnowski, Ashish Raj and Devendra Bisht

Galaxies 2023, 11(1), 36; https://doi.org/10.3390/galaxies11010036 - 17 Feb 2023

Cited by 3 | Viewed by 2096

Abstract

This paper describes recent studies of the FS CMa-type objects, a group of stars showing the B[e] phenomenon defined in 2007. The objects exhibit strong emission-line spectra with both permitted and forbidden lines suggesting the presence of a B-type star as well as [...] Read more.

This paper describes recent studies of the FS CMa-type objects, a group of stars showing the B[e] phenomenon defined in 2007. The objects exhibit strong emission-line spectra with both permitted and forbidden lines suggesting the presence of a B-type star as well as strong IR excesses due to radiation of circumstellar dust. These properties are hard to explain in the framework of the evolution of single stars with luminosities between ~300 and ~30,000 L_⊙ typical of most B-type stars. We explore the hypothesis that the gaseous-and-dusty envelopes of FS CMa objects are due to either earlier or ongoing mass transfer between the binary system components. It is hard to detect the secondary components in these systems because of veiling and distortions by the circumstellar matter because of the relative faintness of the companions. Nevertheless, we detected regular radial velocity variations of the spectral lines in MWC 728, 3 Pup, and AS 386 and we found absorption lines typical of cool stars in the spectra of MWC 645, AS 174, and several other objects. The diversity of the secondary components in FS CMa objects is discussed in the context of non-conservative binary evolution. Full article

(This article belongs to the Special Issue New Insights on Binary Stars)

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34 pages, 833 KiB

Open AccessReview

Primordial Black Hole Formation in Non-Standard Post-Inflationary Epochs

by Sukannya Bhattacharya

Galaxies 2023, 11(1), 35; https://doi.org/10.3390/galaxies11010035 - 16 Feb 2023

Cited by 21 | Viewed by 2708

Abstract

When large overdensities gravitationally collapse in the early universe, they lead to primordial black holes (PBH). Depending on the exact model of inflation leading to necessary large perturbations at scales much smaller than scales probed at the Cosmic Microwave Background (CMB) surveys, PBHs [...] Read more.

When large overdensities gravitationally collapse in the early universe, they lead to primordial black holes (PBH). Depending on the exact model of inflation leading to necessary large perturbations at scales much smaller than scales probed at the Cosmic Microwave Background (CMB) surveys, PBHs of masses ≲

10^{3} M_{⊙}

are formed sometime between the end of inflation and nucleosynthesis. However, the lack of a direct probe for the exact expansion history of the universe in this duration introduces uncertainties in the PBH formation process. The presence of alternate cosmological evolution for some duration after inflation affects the relation between (i) PBH mass and the scale of the collapsing overdensity; and (ii) PBH abundance and amplitude of the overdensities. In this review, the non-standard cosmological epochs relevant for a difference in PBH production are motivated and discussed. The importance of developing the framework of PBH formation in non-standard epochs is discussed from a phenomenological point of view, with particular emphasis on the advances in gravitational wave (GW) phenomenology, since abundant PBHs are always accompanied by large induced GWs. PBH formation in general non-standard epochs is also reviewed including the mathematical formalism. Specific examples, such as PBH formation in a kinetic energy dominated epoch and an early matter dominated epoch, are discussed with figures showing higher PBH abundances as compared to the production in standard radiation domination. Full article

(This article belongs to the Special Issue Physical Processes in the Early Universe: Primordial Black Holes, Dark Matter, Baryon Asymmetry and All That)

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39 pages, 9798 KiB

Open AccessFeature PaperReview

Observational Imprints of Enhanced Scalar Power on Small Scales in Ultra Slow Roll Inflation and Associated Non-Gaussianities

by H. V. Ragavendra and L. Sriramkumar

Galaxies 2023, 11(1), 34; https://doi.org/10.3390/galaxies11010034 - 15 Feb 2023

Cited by 28 | Viewed by 1802

Abstract

The discovery of gravitational waves from merging binary black holes has generated considerable interest in examining whether these black holes could have a primordial origin. If a significant number of black holes have to be produced in the early universe, the primordial scalar [...] Read more.

The discovery of gravitational waves from merging binary black holes has generated considerable interest in examining whether these black holes could have a primordial origin. If a significant number of black holes have to be produced in the early universe, the primordial scalar power spectrum should have an enhanced amplitude on small scales, when compared to the COBE normalized values on the large scales that is strongly constrained by the anisotropies in the cosmic microwave background. In the inflationary scenario driven by a single, canonical scalar field, such power spectra can be achieved in models that permit a brief period of ultra slow roll inflation during which the first slow roll parameter decreases exponentially. In this review, we shall consider a handful of such inflationary models as well as a reconstructed scenario and examine the extent of formation of primordial black holes and the generation of secondary gravitational waves in these cases. We shall also discuss the strength and shape of the scalar bispectrum and the associated non-Gaussianity parameter that arise in such situations. We shall conclude with an outlook wherein we discuss the wider implications of the increased strengths of the non-Gaussianities on smaller scales. Full article

(This article belongs to the Special Issue Physical Processes in the Early Universe: Primordial Black Holes, Dark Matter, Baryon Asymmetry and All That)

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13 pages, 7877 KiB

Open AccessArticle

Transverse Oscillations of the M87 Jet Revealed by KaVA Observations

by Hyunwook Ro, Kunwoo Yi, Yuzhu Cui, Motoki Kino, Kazuhiro Hada, Tomohisa Kawashima, Yosuke Mizuno, Bong Won Sohn and Fumie Tazaki

Galaxies 2023, 11(1), 33; https://doi.org/10.3390/galaxies11010033 - 15 Feb 2023

Cited by 4 | Viewed by 1630

Abstract

Recent VLBI monitoring has found transverse motions of the M87 jet. However, due to the limited cadence of previous observations, details of the transverse motion have not been fully revealed yet. We have regularly monitored the M87 jet at KVN and VERA Array [...] Read more.

Recent VLBI monitoring has found transverse motions of the M87 jet. However, due to the limited cadence of previous observations, details of the transverse motion have not been fully revealed yet. We have regularly monitored the M87 jet at KVN and VERA Array (KaVA) 22 GHz from December 2013 to June 2016. The average time interval of the observation is ∼0.1 year, which is suitable for tracking short-term structural changes. From these observations, the M87 jet is well represented by double ridge lines in the region 2–12 mas from the core. We found that the ridge lines exhibit transverse oscillations in all observed regions with an average period of

0.94 \pm 0.12

years. When the sinusoidal fit is performed, we found that the amplitude of this oscillation is an order of ∼0.1 mas, and the oscillations in the northern and southern limbs are almost in phase. Considering the amplitude, it does not originate from Earth’s parallax. We propose possible scenarios of the transverse oscillation, such as the propagation of jet instabilities or magneto-hydrodynamic (MHD) waves or perturbed mass injection around magnetically dominated accretion flows. Full article

(This article belongs to the Special Issue Challenges in Understanding Black Hole Powered Jets with VLBI)

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23 pages, 365 KiB

Open AccessArticle

The Next Generation Event Horizon Telescope Collaboration: History, Philosophy, and Culture

by Peter Galison, Juliusz Doboszewski, Jamee Elder, Niels C. M. Martens, Abhay Ashtekar, Jonas Enander, Marie Gueguen, Elizabeth A. Kessler, Roberto Lalli, Martin Lesourd, Alexandru Marcoci, Sebastián Murgueitio Ramírez, Priyamvada Natarajan, James Nguyen, Luis Reyes-Galindo, Sophie Ritson, Mike D. Schneider, Emilie Skulberg, Helene Sorgner, Matthew Stanley, Ann C. Thresher, Jeroen Van Dongen, James Owen Weatherall, Jingyi Wu and Adrian Wüthrich Show full author list Hide full author list

Galaxies 2023, 11(1), 32; https://doi.org/10.3390/galaxies11010032 - 15 Feb 2023

Cited by 5 | Viewed by 7230

Abstract

This white paper outlines the plans of the History Philosophy Culture Working Group of the Next Generation Event Horizon Telescope Collaboration. Full article

(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)

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22 pages, 830 KiB

Open AccessArticle

Reddening-Free Q Parameters to Classify B-Type Stars with Emission Lines

by Yael Aidelman and Lydia Sonia Cidale

Galaxies 2023, 11(1), 31; https://doi.org/10.3390/galaxies11010031 - 15 Feb 2023

Cited by 2 | Viewed by 1975

Abstract

The emission-line B-type stars constitute a heterogeneous group. Many of these stars show similar optical spectroscopic features and color indices, making it difficult to classify them adequately by means of photometric and spectroscopic techniques. Thus, it is relevant to deal with appropriate classification [...] Read more.

The emission-line B-type stars constitute a heterogeneous group. Many of these stars show similar optical spectroscopic features and color indices, making it difficult to classify them adequately by means of photometric and spectroscopic techniques. Thus, it is relevant to deal with appropriate classification criteria to avoid as many selection effects as possible. For this purpose, we analyzed different reddening-free Q parameters, taking advantage of the Gaia and 2MASS photometric surveys, for both main sequence and emission-line B-type stars. Along with this work, we provided various criteria to search for normal and emission-line B-type stars, using different color–color, Q–color, and Q–Q diagrams. It was also possible to identify stars in different transition phases (i.e.,

(R p - J)

vs.

(J - K s)

diagrams) and to classify them according to their NIR radiation excesses (i.e., the

(B p - R p)

vs.

(H - K s)

diagram). Other diagrams, such as the

Q_{J K H K}

vs.

(H - K s)

or

Q_{B p J H K}

vs.

(B p - K s)

, were very useful to search for and classify different classes of B-type stars with emission lines. These diagrams highlighted the presence of several stars, classified as CBe, with large color excesses that seemed to be caused by the presence of dust in their envelopes. Therefore, these stars would be misclassified. Three groups of HAeBe stars with different intrinsic dust properties were also distinguished. The amount of intrinsic dust emission in the diverse groups of emission-line stars was well-recognized via the

Q_{J H K}

vs.

Q_{B p R p H K}

diagram. The different selection criteria are very important tools for automated designs of machine learning and optimal search algorithms. Full article

(This article belongs to the Special Issue Theory and Observation of Active B-type Stars)

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16 pages, 3421 KiB

Open AccessArticle

HINOTORI and Its Perspectives in the Black-Hole Jet Study

by Toshihisa Tsutsumi, Kotaro Niinuma, Hiroshi Imai, Ryoko Amari, Yusuke Shimizu, Hideo Ogawa, Atsushi Nishimura, Chieko Miyazawa, Tomoaki Oyama, Hiroyuki Kaneko, Keisuke Nakashima, Satoko Sawada-Satoh and Takahiro Aoki

Galaxies 2023, 11(1), 30; https://doi.org/10.3390/galaxies11010030 - 13 Feb 2023

Cited by 2 | Viewed by 1609

Abstract

Simultaneous multi-band very long baseline interferometry (VLBI) observations at millimeter wavelengths have huge potential for various science cases. However, there exist difficulties in expanding the scientific targets, as the sensitivity of radio telescopes at millimeter wavelengths is typically lower compared to that at [...] Read more.

Simultaneous multi-band very long baseline interferometry (VLBI) observations at millimeter wavelengths have huge potential for various science cases. However, there exist difficulties in expanding the scientific targets, as the sensitivity of radio telescopes at millimeter wavelengths is typically lower compared to that at centimeter wavelengths. In order to realize high-sensitivity mm-VLBI observations in the East Asia region, we are promoting the HINOTORI (Hybrid Installation project in NObeyama, Triple-band ORIented) project, which aims to launch the wide-band and simultaneous triple-band (22/43/86 GHz) VLBI system with the Nobeyama 45 m Radio Telescope (NRO45). The simultaneous 22/43 GHz observation mode has already been operated for the open-use program. We have recently completed the performance evaluation of the receiver and observing system at 86 GHz. In addition, a new wide-band VLBI back-end system has been installed on the NRO45 and the performance of this receiving system has been found to be sufficient to meet scientific requirements. Currently, we are performing commissioning observations to establish regular VLBI operation with simultaneous triple-band mode together with the Korean VLBI Network. The participation of the NRO45 is expected to strengthen the mm-VLBI observation network in the East Asia region and to be a very powerful addition with respect to the science of of black hole jets. Full article

(This article belongs to the Special Issue Challenges in Understanding Black Hole Powered Jets with VLBI)

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15 pages, 6010 KiB

Open AccessReview

Jet Feedback in Star-Forming Galaxies

by Martin G. H. Krause

Galaxies 2023, 11(1), 29; https://doi.org/10.3390/galaxies11010029 - 12 Feb 2023

Cited by 4 | Viewed by 2674

Abstract

In this paper, I review our understanding of how jet feedback works in star-forming galaxies. There are some interesting differences to radiative feedback from Active Galactic Nuclei (AGN). Jets act on galaxy haloes as well as on dense gas, for example in regularly [...] Read more.

In this paper, I review our understanding of how jet feedback works in star-forming galaxies. There are some interesting differences to radiative feedback from Active Galactic Nuclei (AGN). Jets act on galaxy haloes as well as on dense gas, for example in regularly rotating discs, where they can suppress star formation (particularly in the centre, negative feedback), but also enhance it (positive feedback). Jet feedback may produce turbulent, multi-phase gas structures where shocks contribute to the ionisation and is observed in connection with galactic outflows. The exact driving mechanism of these outflows is still unclear, but may be a combination of effects linked to star formation, jet-induced turbulence and radiative AGN feedback. Supermassive black holes in any galaxy can produce jets. Preferential radio detections in more massive galaxies can be explained with different conditions in the circumgalactic medium and, correspondingly, different jet–environment interactions. Full article

(This article belongs to the Special Issue The Symbiosis between Radio Source and Galaxy Evolution)

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20 pages, 8050 KiB

Open AccessArticle

Enabling Transformational ngEHT Science via the Inclusion of 86 GHz Capabilities

by Sara Issaoun, Dominic W. Pesce, Freek Roelofs, Andrew Chael, Richard Dodson, María J. Rioja, Kazunori Akiyama, Romy Aran, Lindy Blackburn, Sheperd S. Doeleman, Vincent L. Fish, Garret Fitzpatrick, Michael D. Johnson, Gopal Narayanan, Alexander W. Raymond and Remo P. J. Tilanus

Galaxies 2023, 11(1), 28; https://doi.org/10.3390/galaxies11010028 - 10 Feb 2023

Cited by 13 | Viewed by 2221

Abstract

We present a case for significantly enhancing the utility and efficiency of the ngEHT by incorporating an additional 86 GHz observing band. In contrast to 230 or 345 GHz, weather conditions at the ngEHT sites are reliably good enough for 86 GHz to [...] Read more.

We present a case for significantly enhancing the utility and efficiency of the ngEHT by incorporating an additional 86 GHz observing band. In contrast to 230 or 345 GHz, weather conditions at the ngEHT sites are reliably good enough for 86 GHz to enable year-round observations. Multi-frequency imaging that incorporates 86 GHz observations would sufficiently augment the

(u, v)

coverage at 230 and 345 GHz to permit detection of the M87 jet structure without requiring EHT stations to join the array. The general calibration and sensitivity of the ngEHT would also be enhanced by leveraging frequency phase transfer techniques, whereby simultaneous observations at 86 GHz and higher-frequency bands have the potential to increase the effective coherence times from a few seconds to tens of minutes. When observation at the higher frequencies is not possible, there are opportunities for standalone 86 GHz science, such as studies of black hole jets and spectral lines. Finally, the addition of 86 GHz capabilities to the ngEHT would enable it to integrate into a community of other VLBI facilities—such as the GMVA and ngVLA—that are expected to operate at 86 GHz but not at the higher ngEHT observing frequencies. Full article

(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)

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17 pages, 1456 KiB

Open AccessReview

Looking for Signatures of AGN Feedback in Radio-Quiet AGN

by Preeti Kharb and Sasikumar Silpa

Galaxies 2023, 11(1), 27; https://doi.org/10.3390/galaxies11010027 - 8 Feb 2023

Cited by 8 | Viewed by 2188

Abstract

In this article, we discuss the state of “AGN feedback” in radio-quiet (RQ) AGN. This study involves heterogeneous samples of nearby Seyfert and LINER galaxies as well as quasi-stellar objects (QSOs) that have been observed at low radio frequencies (few ∼100 MHz) with [...] Read more.

In this article, we discuss the state of “AGN feedback” in radio-quiet (RQ) AGN. This study involves heterogeneous samples of nearby Seyfert and LINER galaxies as well as quasi-stellar objects (QSOs) that have been observed at low radio frequencies (few ∼100 MHz) with the upgraded Giant Meterwave Radio Telescope (GMRT) and ∼GHz frequencies with the Karl G. Jansky Very Large Array (VLA) and Very Long Baseline Array (VLBA). These multi-frequency, multi-resolution observations detect a range of arcsecond-scale radio spectral indices that are consistent with the presence of multiple contributors including starburst winds and AGN jets or winds; steep spectrum “relic” emission is observed as well. Polarization-sensitive data from the VLA and GMRT suggest that the radio outflows are stratified (e.g., in IIIZw2, Mrk231); distinct polarization signatures suggest that there could either be a “spine + sheath” structure in the radio outflow, or there could be a “jet + wind” structure. Similar nested biconical outflows can also explain the VLBA and SDSS emission-line data in the KISSR sample of double-peaked emission-line Seyfert and LINER galaxies. Furthermore, the modeling of the emission-lines with plasma modeling codes such as MAPPINGS indicates that parsec-scale jets and winds in these sources can disturb or move the narrow-line region (NLR) gas clouds via the “shock + precursor” mechanism. Apart from the presence of “relic” emission, several Seyfert and LINER galaxies show clear morphological signatures of episodic jet activity. In one such source, NGC2639, at least four distinct episodes of jets are observed, the largest one of which was only detectable at 735 MHz with the GMRT. Additionally, a ∼6 kpc hole in the CO molecular gas along with a dearth of young stars in the center of its host galaxy is observed. Multiple jet episodes on the 10–100 parsec scales and a ∼10 parsec hole in the molecular gas is also observed in the Seyfert galaxy NGC4051. This suggests a link between episodic jet activity in RQ AGN and “AGN feedback” influencing the evolution of their host galaxies. However, a similar simple relationship between radio outflows and molecular gas mass is not observed in the Palomar–Green (PG) QSO sample, indicating that “AGN feedback” is a complex phenomenon in RQ AGN. “AGN feedback” must occur through the local impact of recurring multi-component outflows in RQ AGN. However, global feedback signatures on their host galaxy properties are not always readily evident. Full article

(This article belongs to the Special Issue The Symbiosis between Radio Source and Galaxy Evolution)

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15 pages, 11996 KiB

Open AccessArticle

The Influence of the Galactic Bar on the Dynamics of Globular Clusters

by Roman Tkachenko, Vladimir Korchagin, Anna Jmailova, Giovanni Carraro and Boris Jmailov

Galaxies 2023, 11(1), 26; https://doi.org/10.3390/galaxies11010026 - 6 Feb 2023

Cited by 5 | Viewed by 1973

Abstract

We make use of recent estimates for the parameters of the Milky Way’s halo globular clusters and study the influence of the galactic bar on the dynamics of these clusters by computing their orbits. We use both an axisymmetric and non-axisymmetric galactic potentials, [...] Read more.

We make use of recent estimates for the parameters of the Milky Way’s halo globular clusters and study the influence of the galactic bar on the dynamics of these clusters by computing their orbits. We use both an axisymmetric and non-axisymmetric galactic potentials, which include the rotating elongated bar/bulge structure. We account for observational errors both in the positions and in the velocities of the globular clusters and explore the influence of the bar on clusters’ evolution. This is contained in the angular momentum–total energy plane,

(L_{z}, E)

, which is widely exploited as an indicator of the groups of globular clusters that originated from the same accretion event. Particular attention is devoted to the Gaia-Sausage/Enceladus and Pontus structures identified recently as two independent accretion events. Our study shows that it is not possible to identify GSE and Pontus as different merger events. Full article

(This article belongs to the Special Issue Galactic Structure and Dynamics)

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19 pages, 1666 KiB

Open AccessArticle

The Closure Relations in High-Energy Gamma-ray Bursts Detected by Fermi-LAT

by Maria Dainotti, Delina Levine, Nissim Fraija, Donald Warren, Peter Veres and Shashwat Sourav

Galaxies 2023, 11(1), 25; https://doi.org/10.3390/galaxies11010025 - 2 Feb 2023

Cited by 9 | Viewed by 2354

Abstract

Gamma-ray bursts (GRBs) are brief, intense pulses of high-energy emission associated with extreme astrophysical phenomena, e.g. the death of massive stars or the coalescence of compact objects. They have been observed at high energies by the Fermi Large Area Telescope (LAT), which detects [...] Read more.

Gamma-ray bursts (GRBs) are brief, intense pulses of high-energy emission associated with extreme astrophysical phenomena, e.g. the death of massive stars or the coalescence of compact objects. They have been observed at high energies by the Fermi Large Area Telescope (LAT), which detects GRBs in the 20 MeV–300 GeV energy range. The Fermi-LAT Second GRB Catalog (2FLGC) presents information on 186 GRBs observed from 2008 to 2018. We consider the GRBs that have been fitted in the 2FLGC with a broken (21 GRBs) or simple power law (65 GRBs), compiling a total sample of 86 GRBs. We analyze the relationship between the spectral and temporal indices using closure relations according to the synchrotron forward-shock model evolving in stratified environments (

n \propto r^{- k}

). We find that the model without energy injection is preferred over the one with energy injection. There is a clear preference for the cooling conditions

ν >

max{

ν_{c}, ν_{m}

} and

ν_{m} < ν < ν_{c}

(where

ν_{c}

and

ν_{m}

are the cooling and characteristic frequencies, namely the frequency at the spectral break). Within these cooling conditions, density profiles

r^{- k}

with values of

k = 1.5

and 2 generally have a higher rate of occurrence when considering relations with and without energy injection. Full article

(This article belongs to the Special Issue Gamma-Ray Bursts in Multiwavelength: Theory, Observational Correlations and GRB Cosmology)

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19 pages, 2214 KiB

Open AccessArticle

Young Radio Sources Expanding in Gas-Rich ISM: Using Cold Molecular Gas to Trace Their Impact

by Raffaella Morganti, Suma Murthy, Pierre Guillard, Tom Oosterloo and Santiago Garcia-Burillo

Galaxies 2023, 11(1), 24; https://doi.org/10.3390/galaxies11010024 - 2 Feb 2023

Cited by 8 | Viewed by 2110

Abstract

We present an overview of the results obtained from the study of the resolved distribution of molecular gas around eight young (

≲ 10^{6} yr

), peaked-spectrum radio galaxies. Tracing the distribution and kinematics of the gas around these radio sources allows [...] Read more.

We present an overview of the results obtained from the study of the resolved distribution of molecular gas around eight young (

≲ 10^{6} yr

), peaked-spectrum radio galaxies. Tracing the distribution and kinematics of the gas around these radio sources allows us to trace the interplay between the jets and the surrounding medium. For three of these sources, we present new CO(1-0) observations, obtained with the Northern Extended Millimeter Array (NOEMA) with arcsecond resolution. In two of these targets, we also detected CN lines, both in emission and absorption. Combining the new observations with already published data, we discuss the main results obtained. Although we found that a large fraction of the cold molecular gas was distributed in disc-like rotating structures, in the vast majority of the sources, high turbulence and deviations from purely quiescent gas (including outflows) were observed in the region co-spatial with the radio continuum emission. This suggests the presence of an interaction between radio plasma and cold molecular gas. In particular, we found that newly born and young radio jets, even those with low power i.e., P_jet < 10⁴⁵ erg s⁻¹), are able to drive massive outflows of cold, molecular gas. The outflows are, however, limited to the sub-kpc regions and likely short lived. On larger scales (a few kpc), we observed cases where the molecular gas appears to avoid the radio lobes and, instead, wraps around them. The results suggest the presence of an evolutionary sequence, which is consistent with previous simulations, where the type of impact of the radio plasma changes as the jet expands, going from a direct jet-cloud interaction able to drive gas outflows on sub-kpc scales to a more gentle pushing aside of the gas, increasing its turbulence and likely limiting its cooling on kpc scales. This effect can be mediated by the cocoon of shocked gas inflated by the jet–cloud interactions. Building larger samples of young and evolved radio sources for observation at a similar depth and spatial resolution to test this scenario is now needed and may be possible thanks to more data becoming available in the growing public archives. Full article

(This article belongs to the Special Issue The Symbiosis between Radio Source and Galaxy Evolution)

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16 pages, 7482 KiB

Open AccessArticle

Tracing Hot Spot Motion in Sagittarius A* Using the Next-Generation Event Horizon Telescope (ngEHT)

by Razieh Emami, Paul Tiede, Sheperd S. Doeleman, Freek Roelofs , Maciek Wielgus , Lindy Blackburn , Matthew Liska , Koushik Chatterjee , Bart Ripperda, Antonio Fuentes , Avery E. Broderick, Lars Hernquist , Charles Alcock , Ramesh Narayan, Randall Smith , Grant Tremblay, Angelo Ricarte, He Sun, Richard Anantua , Yuri Y. Kovalev , Priyamvada Natarajan and Mark Vogelsberger Show full author list Hide full author list

Galaxies 2023, 11(1), 23; https://doi.org/10.3390/galaxies11010023 - 29 Jan 2023

Cited by 11 | Viewed by 2097

Abstract

We propose the tracing of the motion of a shearing hot spot near the Sgr A* source through a dynamical image reconstruction algorithm, StarWarps. Such a hot spot may form as the exhaust of magnetic reconnection in a current sheet near the black [...] Read more.

We propose the tracing of the motion of a shearing hot spot near the Sgr A* source through a dynamical image reconstruction algorithm, StarWarps. Such a hot spot may form as the exhaust of magnetic reconnection in a current sheet near the black hole horizon. A hot spot that is ejected from the current sheet into an orbit in the accretion disk may shear and diffuse due to instabilities at its boundary during its orbit, resulting in a distinct signature. We subdivide the motion into two different phases: the first phase refers to the appearance of the hot spot modeled as a bright blob, followed by a subsequent shearing phase. We employ different observational array configurations, including EHT (2017, 2022) and the next-generation Event Horizon Telescope (ngEHTp1, ngEHT) arrays, with several new sites added, and make dynamical image reconstructions for each of them. Subsequently, we infer the hot spot angular image location in the first phase, followed by the axes ratio and the ellipse area in the second phase. We focus on the direct observability of the orbiting hot spot in the sub-mm wavelength. Our analysis demonstrates that for this particular simulation, the newly added dishes are better able to trace the first phase as well as part of the second phase before the flux is reduced substantially, compared to the EHT arrays. The algorithm used in this work can be easily extended to other types of dynamics, as well as different shearing timescales. More simulations are required to prove whether the current set of newly proposed sites are sufficient to resolve any motions near variable sources, such as Sgr A*. Full article

(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)

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18 pages, 7296 KiB

Open AccessArticle

Astro-COLIBRI 2—An Advanced Platform for Real-Time Multi-Messenger Discoveries

by Patrick Reichherzer, Fabian Schüssler, Valentin Lefranc, Julia Becker Tjus, Jayson Mourier and Atilla Kaan Alkan

Galaxies 2023, 11(1), 22; https://doi.org/10.3390/galaxies11010022 - 28 Jan 2023

Cited by 6 | Viewed by 3681

Abstract

The study of flaring astrophysical events in the multi-messenger approach requires instantaneous follow-up observations to better understand the nature of these events through complementary observational data. We present Astro-COLIBRI as a platform that integrates specific tools in the real-time multi-messenger ecosystem. The Astro-COLIBRI [...] Read more.

The study of flaring astrophysical events in the multi-messenger approach requires instantaneous follow-up observations to better understand the nature of these events through complementary observational data. We present Astro-COLIBRI as a platform that integrates specific tools in the real-time multi-messenger ecosystem. The Astro-COLIBRI platform bundles and evaluates alerts about transients from various channels. It further automates the coordination of follow-up observations by providing and linking detailed information through its comprehensible graphical user interface. We present the functionalities with documented examples of Astro-COLIBRI usage through the community since its public release in August 2021. We highlight the use cases of Astro-COLIBRI for planning follow-up observations by professional and amateur astronomers, as well as checking predictions from theoretical models. Full article

(This article belongs to the Special Issue The New Era of Real-Time Multi-Messenger Astronomy)

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Graphical abstract

10 pages, 1221 KiB

Open AccessArticle

A Global Inventory of Feedback

by Timothy M. Heckman and Philip N. Best

Galaxies 2023, 11(1), 21; https://doi.org/10.3390/galaxies11010021 - 24 Jan 2023

Cited by 15 | Viewed by 1900

Abstract

Feedback from both supermassive black holes and massive stars plays a fundamental role in the evolution of galaxies and the inter-galactic medium. In this paper, we use available data to estimate the total amount of kinetic energy and momentum created per co-moving volume [...] Read more.

Feedback from both supermassive black holes and massive stars plays a fundamental role in the evolution of galaxies and the inter-galactic medium. In this paper, we use available data to estimate the total amount of kinetic energy and momentum created per co-moving volume element over the history of the universe from three sources: massive stars and supernovae, radiation pressure and winds driven by supermassive black holes, and radio jets driven by supermassive black holes. Kinetic energy and momentum injection from jets peaks at z ≈ 1, while the other two sources peak at z ≈ 2. Massive stars are the dominant global source of momentum injection. For supermassive black holes, we find that the amount of kinetic energy from jets is about an order-of-magnitude larger than that from winds. We also find that the amount of kinetic energy created by massive stars is about 2.5 ε_star times that carried by jets (where ε_star is the fraction of injected energy not lost to radiative cooling). We discuss the implications of these results for the evolution of galaxies and IGM. Because the ratio of the black hole mass to galaxy mass is a steeply increasing function of mass, we show that the relative importance of black hole feedback to stellar feedback likewise increases with mass. We show that there is a trend in the present-day universe which, in the simplest picture, is consistent with galaxies that have been dominated by black hole feedback being generally quenched, while galaxies that have been dominated by stellar feedback are star-forming. We also note that the amount of kinetic energy carried by jets and winds appears to be sufficient to explain the properties of hot gas in massive halos (>10¹³ M_ʘ). Full article

(This article belongs to the Special Issue The Symbiosis between Radio Source and Galaxy Evolution)

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3 pages, 180 KiB

Open AccessEditorial

Acknowledgment to the Reviewers of Galaxies in 2022

by Galaxies Editorial Office

Galaxies 2023, 11(1), 20; https://doi.org/10.3390/galaxies11010020 - 19 Jan 2023

Viewed by 1162

Abstract

High-quality academic publishing is built on rigorous peer review [...] Full article

35 pages, 1622 KiB

Open AccessArticle

An Overview of Compact Star Populations and Some of Its Open Problems

by Lucas M. de Sá, Antônio Bernardo, Riis R. A. Bachega, Livia S. Rocha, Pedro H. R. S. Moraes and Jorge E. Horvath

Galaxies 2023, 11(1), 19; https://doi.org/10.3390/galaxies11010019 - 18 Jan 2023

Cited by 6 | Viewed by 2991

Abstract

The study of compact object populations has come a long way since the determination of the mass of the Hulse–Taylor pulsar, and we now count on more than 150 known Galactic neutron stars and black hole masses, as well as another 180 objects [...] Read more.

The study of compact object populations has come a long way since the determination of the mass of the Hulse–Taylor pulsar, and we now count on more than 150 known Galactic neutron stars and black hole masses, as well as another 180 objects from binary mergers detected from gravitational-waves by the Ligo–Virgo–KAGRA Collaboration. With a growing understanding of the variety of systems that host these objects, their formation, evolution and frequency, we are now in a position to evaluate the statistical nature of these populations, their properties, parameter correlations and long-standing problems, such as the maximum mass of neutron stars and the black hole lower mass gap, to a reasonable level of statistical significance. Here, we give an overview of the evolution and current state of the field and point to some of its standing issues. We focus on Galactic black holes, and offer an updated catalog of 35 black hole masses and orbital parameters, as well as a standardized procedure for dealing with uncertainties. Full article

(This article belongs to the Special Issue Challenges of This Century in High-Density Compact Objects, High-Energy Astrophysics, and Multi-Messenger Observations. Quo Vadis?)

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10 pages, 1422 KiB

Open AccessArticle

A Method to Fit Phase Diagrams of Slow-Rotation Pulsars with Accretion Columns

by Rodrigo R. Silva, Rafael C. R. de Lima, Jaziel G. Coelho, Paulo E. Stecchini, Caroline M. de Liz and José C. N. de Araujo

Galaxies 2023, 11(1), 18; https://doi.org/10.3390/galaxies11010018 - 16 Jan 2023

Viewed by 1560

Abstract

We demonstrate a method to simulate a pulse profile of the emission of accretion columns in a neutron star. Given a set of parameters that characterize the star, e.g., mass and radius, and the positions and shapes of the accretion columns, the pulse [...] Read more.

We demonstrate a method to simulate a pulse profile of the emission of accretion columns in a neutron star. Given a set of parameters that characterize the star, e.g., mass and radius, and the positions and shapes of the accretion columns, the pulse profile can be calculated and compared with real data. Some characteristics of phase diagrams are shown considering an accretion column in the form of a cone trunk and also in the form of a cylinder. Furthermore, in our first approach we develop a combination between a genetic algorithm and a Bayesian sampling algorithm to constrain some variables. Finally, as an example, we apply the method to observed data of source 1A 0535+262. Full article

(This article belongs to the Special Issue Challenges of This Century in High-Density Compact Objects, High-Energy Astrophysics, and Multi-Messenger Observations. Quo Vadis?)

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9 pages, 4522 KiB

Open AccessFeature PaperArticle

Multi-Wavelength and Multi-Messenger Studies Using the Next-Generation Event Horizon Telescope

by Rocco Lico, Svetlana G. Jorstad, Alan P. Marscher, Jose L. Gómez, Ioannis Liodakis, Rohan Dahale, Antxon Alberdi, Roman Gold, Efthalia Traianou, Teresa Toscano and Marianna Foschi

Galaxies 2023, 11(1), 17; https://doi.org/10.3390/galaxies11010017 - 14 Jan 2023

Cited by 6 | Viewed by 1810

Abstract

The next-generation Event Horizon Telescope (ngEHT) will provide us with the best opportunity to investigate supermassive black holes (SMBHs) at the highest possible resolution and sensitivity. With respect to the existing Event Horizon Telescope (EHT) array, the ngEHT will provide increased sensitivity and [...] Read more.

The next-generation Event Horizon Telescope (ngEHT) will provide us with the best opportunity to investigate supermassive black holes (SMBHs) at the highest possible resolution and sensitivity. With respect to the existing Event Horizon Telescope (EHT) array, the ngEHT will provide increased sensitivity and uv-coverage (with the addition of new stations), wider frequency coverage (from 86 GHz to 345 GHz and higher), finer resolution (<15 micro-arcseconds), and better monitoring capabilities. The ngEHT will offer a unique opportunity to deeply investigate the physics around SMBHs, such as the disk-jet connection, the mechanisms responsible for high-energy photon and neutrino events, and the role of magnetic fields in shaping relativistic jets, as well as the nature of binary SMBH systems. In this white paper we describe some ngEHT science cases in the context of multi-wavelength studies and synergies. Full article

(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)

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15 pages, 2290 KiB

Open AccessArticle

The Transformational Power of Frequency Phase Transfer Methods for ngEHT

by María J. Rioja, Richard Dodson and Yoshiharu Asaki

Galaxies 2023, 11(1), 16; https://doi.org/10.3390/galaxies11010016 - 12 Jan 2023

Cited by 20 | Viewed by 1926

Abstract

(Sub) mm VLBI observations are strongly hindered by limited sensitivity, with the fast tropospheric fluctuations being the dominant culprit. We predict great benefits from applying next-generation frequency phase transfer calibration techniques for the next generation Event Horizon Telescope (ngEHT), using simultaneous multi-frequency observations. [...] Read more.

(Sub) mm VLBI observations are strongly hindered by limited sensitivity, with the fast tropospheric fluctuations being the dominant culprit. We predict great benefits from applying next-generation frequency phase transfer calibration techniques for the next generation Event Horizon Telescope (ngEHT), using simultaneous multi-frequency observations. We present comparative simulation studies to characterise its performance, the optimum configurations, and highlight the benefits of including observations at 85 GHz along with the 230 and 340 GHz bands. The results show a transformational impact on the ngEHT array capabilities, with orders of magnitude improved sensitivity, observations routinely possible over the whole year, and ability to carry out micro-arcsecond astrometry measurements at the highest frequencies, amongst others. This will enable the addressing of a host of innovative open scientific questions in astrophysics. We present a solution for highly scatter-broadened sources such as SgrA*, a prime ngEHT target. We conclude that adding the 85 GHz band provides a pathway to an optimum and robust performance for ngEHT in sub-millimeter VLBI, and strongly recommmend its inclusion in the simultaneous multi-frequency receiver design. Full article

(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)

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18 pages, 2866 KiB

Open AccessArticle

Event Horizon and Environs (ETHER): A Curated Database for EHT and ngEHT Targets and Science

by Venkatessh Ramakrishnan, Neil Nagar, Vicente Arratia, Joaquín Hernández-Yévenes, Dominic W. Pesce, Dhanya G. Nair, Bidisha Bandyopadhyay, Catalina Medina-Porcile, Thomas P. Krichbaum, Sheperd Doeleman, Angelo Ricarte, Vincent L. Fish, Lindy Blackburn, Heino Falcke, Geoffrey Bower and Priyamvada Natarajan

Galaxies 2023, 11(1), 15; https://doi.org/10.3390/galaxies11010015 - 12 Jan 2023

Cited by 11 | Viewed by 2917

Abstract

The next generation Event Horizon Telescope (ngEHT) will observe multiple supermassive black hole (SMBH) candidates down to a few tens of mJy, and profoundly transform our understanding of the local SMBH population. Given the impossibility of large-area high-resolution millimeter surveys, multi-frequency spectral energy [...] Read more.

The next generation Event Horizon Telescope (ngEHT) will observe multiple supermassive black hole (SMBH) candidates down to a few tens of mJy, and profoundly transform our understanding of the local SMBH population. Given the impossibility of large-area high-resolution millimeter surveys, multi-frequency spectral energy densities (SEDs), and models are required to both identify source samples tailored to specific science goals, and to predict the feasibility of detection of individual interesting sources. Here, we present the Event Horizon and Environs (ETHER) source and SED model database whose primary use is to enable the selection and optimization of targets for EHT and ngEHT science. The living ETHER database currently consolidates 1.6 million black hole mass estimates, ∼15,500 milliarcsec-scale radio fluxes, ∼14,000 hard X-ray fluxes (expected to grow by factor ≳40 with the eROSITA data release) and SED information as obtained from catalogs and database queries, the literature, and our own new observations. Jet and accretion flow models are fit to individual SEDs in an automated way in order to predict the ngEHT observable fluxes from the jet base and accretion inflow. The database can be filtered by parameters or cross matched to a user source list, with the automated SED fitting models optionally fine tuned by the user. We have identified an initial ngEHT ‘gold sample’ for jet base studies and potentially black hole shadows; this sample will grow significantly in the coming years. While the ngEHT requires and will best exploit the ETHER database, six (eleven) ETHER sources have already been observed (scheduled) with the EHT in 2022 (2023), and the database has wide ranging applications in galaxy and black hole mass evolution studies. Full article

(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)

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23 pages, 3035 KiB

Open AccessArticle

Spun-Up Rotation-Powered Magnetized White Dwarfs in Close Binaries as Possible Gamma-ray Sources: Signatures of Pulsed Modulation from AE Aquarii and AR Scorpii in Fermi-LAT Data

by Pieter J. Meintjes, Spencer T. Madzime, Quinton Kaplan and Hendrik J. van Heerden

Galaxies 2023, 11(1), 14; https://doi.org/10.3390/galaxies11010014 - 11 Jan 2023

Cited by 6 | Viewed by 1819

Abstract

In this paper, the possibility of periodic pulsar-like gamma-ray emission from the white dwarfs in AE Aquarii and AR Scorpii is investigated. We show that the white dwarf magnetospheres in AE Aquarii and AR Scorpii can possibly induce potentials to accelerate charged particles [...] Read more.

In this paper, the possibility of periodic pulsar-like gamma-ray emission from the white dwarfs in AE Aquarii and AR Scorpii is investigated. We show that the white dwarf magnetospheres in AE Aquarii and AR Scorpii can possibly induce potentials to accelerate charged particles to energies in excess of one tera electronvolt (TeV) with associated gamma-ray emission through processes such as curvature radiation, inverse Compton, and hadronic processes such as neutral pion decay. We report here pulsed gamma-ray signatures at or close to the spin period of white dwarfs in both AE Aquarii and AR Scorpii in the Fermi-LAT dataset. This may indicate that both these white dwarfs possibly contain a particle accelerator that can produce relativistic electrons and ions and associated high energy radiation. The possibility of pair production is also investigated, which could provide a source for relativistic

e^{\pm}

pairs in the magnetosphere. This could possibly be a driver for other forms of lepton-induced multi-wavelength pulsar-like emission from these two systems as well, for example, to explain the recently detected pulsed radio emission from AE Aquarii and R Scorpii in MeerKAT observations at the spin period of the white dwarf. The possibility of future detection of AE Aquarii and AR Scorpii with the Cherenkov Telescope Array (CTA) is also discussed. The future Vera Rubin Observatory will make a revolutionary contribution to time-domain astrophysics, which may lead to the discovery of thousands of new transient sources, possibly also many more close binaries with highly spun-up magnetized white dwarfs such as AE Aquarii and AR Scorpii for future investigation. Full article

(This article belongs to the Special Issue Challenges of This Century in High-Density Compact Objects, High-Energy Astrophysics, and Multi-Messenger Observations. Quo Vadis?)

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14 pages, 2447 KiB

Open AccessArticle

Prospects of GPU Tensor Core Correlation for the SMA and the ngEHT

by Wei Yu, John W. Romein, L. Jonathan Dursi, Ru-Sen Lu, Adrian Pope, Gareth Callanan, Dominic W. Pesce, Lindy Blackburn, Bruce Merry, Ranjani Srinivasan, Jongsoo Kim and Jonathan Weintroub

Galaxies 2023, 11(1), 13; https://doi.org/10.3390/galaxies11010013 - 11 Jan 2023

Cited by 3 | Viewed by 2352

Abstract

Building on the base of the existing telescopes of the Event Horizon Telescope (EHT) and ALMA, the next-generation EHT (ngEHT) aspires to deploy ∼10 more stations. The ngEHT targets an angular resolution of ∼15 microarcseconds. This resolution is achieved using Very Long Baseline [...] Read more.

Building on the base of the existing telescopes of the Event Horizon Telescope (EHT) and ALMA, the next-generation EHT (ngEHT) aspires to deploy ∼10 more stations. The ngEHT targets an angular resolution of ∼15 microarcseconds. This resolution is achieved using Very Long Baseline Interferometry (VLBI) at the shortest radio wavelengths ∼1 mm. The Submillimeter Array (SMA) is both a standalone radio interferometer and a station of the EHT and will conduct observations together with the new ngEHT stations. The future EHT + ngEHT array requires a dedicated correlator to process massive amounts of data. The current correlator-beamformer (CBF) of the SMA would also benefit from an upgrade, to expand the SMA’s bandwidth and also match the EHT + ngEHT observations. The two correlators share the same basic architecture, so that the development time can be reduced using common technology for both applications. This paper explores the prospects of using Tensor Core Graphics Processing Units (TC GPU) as the primary digital signal processing (DSP) engine. This paper describes the architecture, aspects of the detailed design, and approaches to performance optimization of a CBF using the “FX” approach. We describe some of the benefits and challenges of the TC GPU approach. Full article

(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)

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30 pages, 13921 KiB

Open AccessArticle

The ngEHT Analysis Challenges

by Freek Roelofs, Lindy Blackburn, Greg Lindahl, Sheperd S. Doeleman, Michael D. Johnson, Philipp Arras, Koushik Chatterjee, Razieh Emami, Christian Fromm, Antonio Fuentes, Jakob Knollmüller, Nikita Kosogorov, Hendrik Müller, Nimesh Patel, Alexander Raymond, Paul Tiede, Efthalia Traianou and Justin Vega

Galaxies 2023, 11(1), 12; https://doi.org/10.3390/galaxies11010012 - 10 Jan 2023

Cited by 23 | Viewed by 2668

Abstract

The next-generation Event Horizon Telescope (ngEHT) will be a significant enhancement of the Event Horizon Telescope (EHT) array, with ∼10 new antennas and instrumental upgrades of existing antennas. The increased

u v

-coverage, sensitivity, and frequency coverage allow a wide range of new [...] Read more.

The next-generation Event Horizon Telescope (ngEHT) will be a significant enhancement of the Event Horizon Telescope (EHT) array, with ∼10 new antennas and instrumental upgrades of existing antennas. The increased

u v

-coverage, sensitivity, and frequency coverage allow a wide range of new science opportunities to be explored. The ngEHT Analysis Challenges have been launched to inform the development of the ngEHT array design, science objectives, and analysis pathways. For each challenge, synthetic EHT and ngEHT datasets are generated from theoretical source models and released to the challenge participants, who analyze the datasets using image reconstruction and other methods. The submitted analysis results are evaluated with quantitative metrics. In this work, we report on the first two ngEHT Analysis Challenges. These have focused on static and dynamical models of M87* and Sgr A* and shown that high-quality movies of the extended jet structure of M87* and near-horizon hourly timescale variability of Sgr A* can be reconstructed by the reference ngEHT array in realistic observing conditions using current analysis algorithms. We identify areas where there is still room for improvement of these algorithms and analysis strategies. Other science cases and arrays will be explored in future challenges. Full article

(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)

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14 pages, 7565 KiB

Open AccessArticle

Probing Plasma Composition with the Next Generation Event Horizon Telescope (ngEHT)

by Razieh Emami, Richard Anantua, Angelo Ricarte, Sheperd S. Doeleman, Avery Broderick, George Wong, Lindy Blackburn, Maciek Wielgus, Ramesh Narayan, Grant Tremblay, Charles Alcock, Lars Hernquist, Randall Smith, Matthew Liska , Priyamvada Natarajan, Mark Vogelsberger, Brandon Curd and Joana A. Kramer

Galaxies 2023, 11(1), 11; https://doi.org/10.3390/galaxies11010011 - 10 Jan 2023

Cited by 8 | Viewed by 1758

Abstract

We explore the plasma matter content in the innermost accretion disk/jet in M87* as relevant for an enthusiastic search for the signatures of anti-matter in the next generation of the Event Horizon Telescope (ngEHT). We model the impact of non-zero positron-to-electron ratio using [...] Read more.

We explore the plasma matter content in the innermost accretion disk/jet in M87* as relevant for an enthusiastic search for the signatures of anti-matter in the next generation of the Event Horizon Telescope (ngEHT). We model the impact of non-zero positron-to-electron ratio using different emission models, including a constant electron to magnetic pressure (constant

β_{e}

model) with a population of non-thermal electrons as well as an R-beta model populated with thermal electrons. In the former case, we pick a semi-analytic fit to the force-free region of a general relativistic magnetohydrodynamic (GRMHD) simulation, while in the latter case, we analyze the GRMHD simulations directly. In both cases, positrons are being added at the post-processing level. We generate polarized images and spectra for some of these models and find out that at the radio frequencies, both of the linear and the circular polarizations are enhanced with every pair added. On the contrary, we show that, at higher frequencies, a substantial positron fraction washes out the circular polarization. We report strong degeneracies between different emission models and the positron fraction, though our non-thermal models show more sensitivities to the pair fraction than the thermal models. We conclude that a large theoretical image library is indeed required to fully understand the trends probed in this study, and to place them in the context of a large set of parameters which also affect polarimetric images, such as magnetic field strength, black hole spin, and detailed aspects of the electron temperature and the distribution function. Full article

(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)

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12 pages, 441 KiB

Open AccessFeature PaperArticle

Spectral Line VLBI Studies Using the ngEHT

by Dong-Jin Kim and Vincent Fish

Galaxies 2023, 11(1), 10; https://doi.org/10.3390/galaxies11010010 - 6 Jan 2023

Cited by 3 | Viewed by 1863

Abstract

Spectroscopy in the mm/sub-mm wavelength range is a powerful tool to study the gaseous medium in various astrophysical environments. The next generation Event Horizon Telescope (ngEHT) equipped with a wide-bandwidth backend system has great potential for science using high angular resolution spectroscopy. Spectral [...] Read more.

Spectroscopy in the mm/sub-mm wavelength range is a powerful tool to study the gaseous medium in various astrophysical environments. The next generation Event Horizon Telescope (ngEHT) equipped with a wide-bandwidth backend system has great potential for science using high angular resolution spectroscopy. Spectral line VLBI studies using the ngEHT will enable us to scrutinize compact astrophysical objects obscured by an optically thick medium on unprecedented angular scales. However, the capabilities of ngEHT for spectroscopy and specific scientific applications have not been properly envisioned. In this white paper, we briefly address science cases newly achievable via spectral line VLBI observations in the mm/sub-mm wavelength ranges, and suggest technical requirements to facilitate spectral line VLBI studies in the ngEHT era. Full article

(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)

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9 pages, 5954 KiB

Open AccessArticle

The Haystack Telescope as an Astronomical Instrument

by Jens Kauffmann, Ganesh Rajagopalan, Kazunori Akiyama, Vincent Fish, Colin Lonsdale, Lynn D. Matthews and Thushara G.S. Pillai

Galaxies 2023, 11(1), 9; https://doi.org/10.3390/galaxies11010009 - 4 Jan 2023

Cited by 7 | Viewed by 2618

Abstract

The Haystack Telescope is an antenna with a diameter of 37 m and an elevation-dependent surface accuracy of ≤

100 μ m

that is capable of millimeter-wave observations. The radome-enclosed instrument serves as a radar sensor for space situational awareness, with about one-third [...] Read more.

The Haystack Telescope is an antenna with a diameter of 37 m and an elevation-dependent surface accuracy of ≤

100 μ m

that is capable of millimeter-wave observations. The radome-enclosed instrument serves as a radar sensor for space situational awareness, with about one-third of the time available for research by MIT Haystack Observatory. Ongoing testing with the K-band (18–26 GHz) and W-band receivers (currently 85–93 GHz) is preparing the inclusion of the telescope into the Event Horizon Telescope (EHT) array and the use as a single-dish research telescope. Given its geographic location, the addition of the Haystack Telescope to current and future versions of the EHT array would substantially improve the image quality. Full article

(This article belongs to the Special Issue From Vision to Instrument: Creating a Next-Generation Event Horizon Telescope for a New Era of Black Hole Science)

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12 pages, 2741 KiB

Open AccessArticle

Refining Orbits of Bright Binary Systems

by Anatoly S. Miroshnichenko, Stephen Danford, Ivan L. Andronov, Alicia N. Aarnio, Duncan Lauer and Holly Buroughs

Galaxies 2023, 11(1), 8; https://doi.org/10.3390/galaxies11010008 - 31 Dec 2022

Cited by 3 | Viewed by 2043

Abstract

We obtained spectra of several bright binary systems (

ζ

02 UMa, 2 Lac, and

ϕ

Aql), which were mostly observed with photographic plates and whose orbits were not determined very accurately. Each system was monitored for a few years with the 81-cm [...] Read more.

We obtained spectra of several bright binary systems (

ζ

02 UMa, 2 Lac, and

ϕ

Aql), which were mostly observed with photographic plates and whose orbits were not determined very accurately. Each system was monitored for a few years with the 81-cm telescope equipped with an échelle spectrograph at the Three College Observatory in North Carolina. The spectra were taken in a wavelength range between 4000 and 7900 Å with a spectral resolution of

R \sim

12,000. Radial velocity measurements were done using cross-correlation in selected spectral regions or by measuring positions of individual spectral lines. Refined orbits and stellar parameters are presented. Full article

(This article belongs to the Special Issue New Insights on Binary Stars)

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