scholarly journals Second-epoch ALMA Observations of 321 GHz Water Maser Emission in NGC 4945 and the Circinus Galaxy

2021 ◽  
Vol 923 (2) ◽  
pp. 251
Author(s):  
Yoshiaki Hagiwara ◽  
Shinji Horiuchi ◽  
Masatoshi Imanishi ◽  
Philip G. Edwards
Keyword(s):  
Velocity Gradient ◽  
Galactic Nuclei ◽  
Dynamical Mass ◽  
Disk Radius ◽  
Maser Emission ◽  
Molecular Outflows ◽  
Disk Rotation ◽  
Central Engine ◽  
The Galaxy ◽  
Circumnuclear Disk

Abstract We present the results of second-epoch ALMA observations of 321 GHz H2O emission toward two nearby active galactic nuclei, NGC 4945 and the Circinus galaxy, together with Tidbinbilla 70 m monitoring of their 22 GHz H2O masers. The two-epoch ALMA observations show that the strengths of the 321 GHz emission are variable by a factor of at least a few, confirming a maser origin. In the second epoch, 321 GHz maser emission from NGC 4945 was not detected, while for the Circinus galaxy the flux density significantly increased and the velocity gradient and dispersion have been measured. With the velocity gradient spanning ∼110 km s−1, we calculate the disk radius to be ∼28 pc, assuming disk rotation around the nucleus. We also estimate the dynamical mass within the central 28 pc to be 4.3 × 108 M ☉, which is significantly larger than the larger-scale dynamical mass, suggesting the velocity gradient does not trace circular motions on that scale. The overall direction of the velocity gradient and velocity range of the blueshifted features are largely consistent with those of the 22 GHz maser emission in a thin disk with smaller radii of 0.1–0.4 pc and molecular outflows within ∼1 pc from the central engine of the galaxy, implying that the 321 GHz masers could trace part of the circumnuclear disk or the nuclear outflows.

scholarly journals 7.14. Gaseous accretion flows in the inner parsec of the Galaxy

1998 ◽  
Vol 184 ◽  
pp. 319-320 ◽  
Author(s):  
Robert Coker ◽  
Fulvio Melia
Keyword(s):  
Galactic Nuclei ◽  
Accretion Flows ◽  
Set Constraints ◽  
Central Engine ◽  
Accretion Rates ◽  
The Galaxy ◽  
Gaseous Flows ◽  
Uniform Medium ◽  
Sgr A ◽  
Central Concentration

Many characteristics of galactic nuclei may be associated with the accretion of ambient gas by a central concentration of mass. Using a 3D hydrodynamical code, we have been simulating this accretion process for Sgr A∗, the compact nonthermal source at the center of the Milky Way, in order to realistically model the gaseous flows in the inner parsec of our Galaxy. In the most recent simulations, we have taken into account the multi-point-like distribution of wind sources and we find that the structure of the flow can be significantly different from that due to a uniform medium. We here present our results concerning the mass and angular momentum accretion rates and discuss how these may be used to set constraints on our Galaxy's central engine.

scholarly journals Powerful Water Masers in Active Galactic Nuclei

2002 ◽  
Vol 19 (4) ◽  
pp. 401-421 ◽  
Author(s):  
Philip R. Maloney
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Rotating Disk ◽  
Future Prospects ◽  
Maser Emission ◽  
X Ray ◽  
Central Engine ◽  
Water Masers ◽  
Water Maser

AbstractLuminous water maser emission in the 616–523 line at 22GHz has been detected from two dozen galaxies. In all cases the emission is confined to the nucleus and has been found only in AGN, in particular, in Type 2 Seyferts and LINERs. I argue that most of the observed megamaser sources are powered by X-ray irradiation of dense gas by the central engine. After briefly reviewing the physics of these X-Ray Dissociation Regions, I discuss in detail the observations of the maser disk in NGC 4258, its implications, and compare alternative models for the maser emission. I then discuss the observations of the other sources that have been imaged with VLBI to date, and how they do or do not fit into the framework of a thin, rotating disk, as in NGC 4258. Finally, I briefly discuss future prospects, especially the possibility of detecting other water maser transitions.

scholarly journals High-Velocity Maser Emission From Shocks Along Spiral Waves In The Circumnuclear Disk Of NGC 4258

1997 ◽  
Vol 163 ◽  
pp. 630-633
Author(s):  
Eyal Maoz
Keyword(s):  
High Velocity ◽  
Line Emission ◽  
Spiral Waves ◽  
Maser Emission ◽  
Vlbi Observations ◽  
The Galaxy ◽  
Maser Line ◽  
Circumnuclear Disk ◽  
Maser Sources

AbstractVLBI observations of H2O maser line emission from the central sub-parsec region of the galaxy NGC 4258 have recently revealed a remarkably well-defined, rapidly rotating molecular disk which is viewed nearly edge–on. We show that the peculiar clustering of the maser sources into several distinct clumps which are almost equally spaced apart from one another, and the striking asymmetry in the high-velocity maser spectrum can be naturally explained by spiral activity in the disk.

scholarly journals VLBI observations of the H2O gigamaser in TXS 2226-184

2020 ◽  
Vol 637 ◽  
pp. A57
Author(s):  
G. Surcis ◽  
A. Tarchi ◽  
P. Castangia
Keyword(s):  
Galactic Nuclei ◽  
Radio Continuum ◽  
Integration Time ◽  
Absolute Position ◽  
Maser Emission ◽  
Long Baseline ◽  
Systemic Velocity ◽  
The Galaxy ◽  
Very Long Baseline Array ◽  
First Time

Context. Outside the Milky Way the most luminous H2O masers at 22 GHz, called megamasers because of their extreme luminosity with respect to the Galactic and extragalactic H2O masers associated with star formation, are mainly detected in active galactic nuclei. In the case of the H2O maser detected in the nuclear region of the galaxy TXS 2226-184, the term gigamaser was used for the first time. However, the origin of this very luminous H2O maser emission has never been investigated in detail. Aims. We study the nature of the 22 GHz H2O gigamaser in TXS 2226-184 by measuring its absolute position for the first time at milliarcsecond resolution, by comparing the morphology and characteristics of the maser emission on very long baseline interferometry (VLBI) scales after about 20 years, and by trying to detect its polarized emission. Methods. We observed the 22 GHz H2O maser emission toward TXS 2226-184 three times: the very first time with the NRAO Very Long Baseline Array (VLBA, epoch 2017.45) and the next two times with the European VLBI Network (EVN, epochs 2017.83 and 2018.44). The first two epochs (2017.45 and 2017.83) were observed in phase-reference mode, while the last epoch (2018.44) was observed in full-polarization mode, but not in phase-reference mode to increase the on-source integration time. We also retrieved and analyzed the VLBA archival data at 22 GHz of TXS 2226-184 observed in epoch 1998.40. Results. We detected six H2O maser features in epoch 2017.45 (VLBA), one in epoch 2017.83 (EVN), and two in epoch 2018.44 (EVN). All but one are red-shifted with respect to the systemic velocity of TXS 2226-184; we detected only one blue-shifted maser feature and it is the weakest one. All the H2O maser features but the blue-shifted one are composed of two components with very different linewidths. For the first time we were able to measure the absolute position of the H2O maser features with errors below 1 milliarcsec. No linear and circular polarization was detected. Conclusions. We were able to associate the H2O maser features in TXS 2226-184 with the most luminous radio continuum clump reported in the literature. The comparison between epochs 1998.40 and 2017.45 reveals a difference in the morphology and velocity of the maser features that can be justified accounting for maser variability.

The GLEAM 4-Jy Sample: The brightest radio-sources in the southern sky

2019 ◽  
Vol 15 (S356) ◽  
pp. 375-375
Author(s):  
Sarah White
Keyword(s):  
Radio Emission ◽  
Active Galactic Nuclei ◽  
Visual Inspection ◽  
Low Frequency ◽  
Galactic Nuclei ◽  
Radio Sources ◽  
Relativistic Jets ◽  
The Galaxy ◽  
Murchison Widefield Array ◽  
Past Activity

AbstractLow-frequency radio emission allows powerful active galactic nuclei (AGN) to be selected in a way that is unaffected by dust obscuration and orientation of the jet axis. It also reveals past activity (e.g. radio lobes) that may not be evident at higher frequencies. Currently, there are too few “radio-loud” galaxies for robust studies in terms of redshift-evolution and/or environment. Hence our use of new observations from the Murchison Widefield Array (the SKA-Low precursor), over the southern sky, to construct the GLEAM 4-Jy Sample (1,860 sources at S151MHz > 4 Jy). This sample is dominated by AGN and is 10 times larger than the heavily relied-upon 3CRR sample (173 sources at S178MHz > 10 Jy) of the northern hemisphere. In order to understand how AGN influence their surroundings and the way galaxies evolve, we first need to correctly identify the galaxy hosting the radio emission. This has now been completed for the GLEAM 4-Jy Sample – through repeated visual inspection and extensive checks against the literature – forming a valuable, legacy dataset for investigating relativistic jets and their interplay with the environment.

scholarly journals Megamasers as probes of galaxy mass spectrum evolution

1991 ◽  
Vol 147 ◽  
pp. 440-440
Author(s):  
V.K. Khersonskii ◽  
N.V. Voshchinnikov
Keyword(s):  
Mass Spectrum ◽  
Spectral Line ◽  
Emission Line ◽  
Frequency Shift ◽  
Empirical Relation ◽  
Far Infrared ◽  
Merging Galaxies ◽  
Maser Emission ◽  
The Galaxy ◽  
Very High

OH megamasers having very high luminosities in the spectral line can be effectively used for the probing of the evolutionary properties of the galaxies in the earliest cosmological epochs. The frequency shift of the emission line uniqually determines the redshift z, which tells about the epoch of emission. One of the important cosmological problems is the investigation of the galaxy mass spectrum in the expanding Universe. There is the empirical relation between the OH and far-infrared luminosities of galaxies. Therefore, if in the earliest cosmological epochs, there were galaxies with sufficient powerful infrared excesses and containing molecular material, they can be detected using the observations of their OH maser emission. The interacting and merging galaxies can be considered as the best candidates for such objects.

scholarly journals Probing the cool ISM in galaxies via 21 cm H i absorption

2012 ◽  
Vol 8 (S292) ◽  
pp. 188-188
Author(s):  
J. R. Allison ◽  
E. M. Sadler ◽  
S. J. Curran ◽  
S. N. Reeves
Keyword(s):  
Spectral Line ◽  
Active Galactic Nuclei ◽  
Large Scale ◽  
Galactic Nuclei ◽  
Host Galaxies ◽  
The Galaxy ◽  
Early Type Galaxy ◽  
Finding Method ◽  
Compact Array ◽  
Cold Gas

AbstractRecent targeted studies of associated H i absorption in radio galaxies are starting to map out the location, and potential cosmological evolution, of the cold gas in the host galaxies of Active Galactic Nuclei (AGN). The observed 21 cm absorption profiles often show two distinct spectral-line components: narrow, deep lines arising from cold gas in the extended disc of the galaxy, and broad, shallow lines from cold gas close to the AGN (e.g. Morganti et al. 2011). Here, we present results from a targeted search for associated H i absorption in the youngest and most recently-triggered radio AGN in the local universe (Allison et al. 2012b). So far, by using the recently commissioned Australia Telescope Compact Array Broadband Backend (CABB; Wilson et al. 2011), we have detected two new absorbers and one previously-known system. While two of these show both a broad, shallow component and a narrow, deep component (see Fig. 1), one of the new detections has only a single broad, shallow component. Interestingly, the host galaxies of the first two detections are classified as gas-rich spirals, while the latter is an early-type galaxy. These detections were obtained using a spectral-line finding method, based on Bayesian inference, developed for future large-scale absorption surveys (Allison et al. 2012a).

scholarly journals Past, Present, and Future of the Scaling Relations of Galaxies and Active Galactic Nuclei

2021 ◽  
Vol 8 ◽  
Author(s):  
Mauro D’Onofrio ◽  
Paola Marziani ◽  
Cesare Chiosi
Keyword(s):  
Active Galactic Nuclei ◽  
Galaxy Formation ◽  
Galactic Nuclei ◽  
Scaling Relations ◽  
Short History ◽  
Physical Mechanisms ◽  
Galaxy Formation And Evolution ◽  
The Galaxy ◽  
History Of ◽  
Formation And Evolution

We review the properties of the established Scaling Relations (SRs) of galaxies and active galactic nuclei (AGN), focusing on their origin and expected evolution back in time, providing a short history of the most important progresses obtained up to now and discussing the possible future studies. We also try to connect the observed SRs with the physical mechanisms behind them, examining to what extent current models reproduce the observational data. The emerging picture clarifies the complexity intrinsic to the galaxy formation and evolution process as well as the basic uncertainties still affecting our knowledge of the AGN phenomenon. At the same time, however, it suggests that the detailed analysis of the SRs can profitably contribute to our understanding of galaxies and AGN.

scholarly journals The impact of AGN feedback on galaxy intrinsic alignments in the Horizon simulations

2020 ◽  
Vol 492 (3) ◽  
pp. 4268-4282 ◽  
Author(s):  
Adam Soussana ◽  
Nora Elisa Chisari ◽  
Sandrine Codis ◽  
Ricarda S Beckmann ◽  
Yohan Dubois ◽  
...  
Keyword(s):  
Galaxy Evolution ◽  
Gravitational Lensing ◽  
Large Scale ◽  
Galactic Nuclei ◽  
Three Dimensions ◽  
High Mass ◽  
Angular Momenta ◽  
The Galaxy ◽  
The Impact ◽  
The Universe

ABSTRACT The intrinsic correlations of galaxy shapes and orientations across the large-scale structure of the Universe are a known contaminant to weak gravitational lensing. They are known to be dependent on galaxy properties, such as their mass and morphologies. The complex interplay between alignments and the physical processes that drive galaxy evolution remains vastly unexplored. We assess the sensitivity of intrinsic alignments (shapes and angular momenta) to active galactic nuclei (AGN) feedback by comparing galaxy alignment in twin runs of the cosmological hydrodynamical Horizon simulation, which do and do not include AGN feedback, respectively. We measure intrinsic alignments in three dimensions and in projection at $z$ = 0 and $z$ = 1. We find that the projected alignment signal of all galaxies with resolved shapes with respect to the density field in the simulation is robust to AGN feedback, thus giving similar predictions for contamination to weak lensing. The relative alignment of galaxy shapes around galaxy positions is however significantly impacted, especially when considering high-mass ellipsoids. Using a sample of galaxy ‘twins’ across simulations, we determine that AGN changes both the galaxy selection and their actual alignments. Finally, we measure the alignments of angular momenta of galaxies with their nearest filament. Overall, these are more significant in the presence of AGN as a result of the higher abundance of massive pressure-supported galaxies.

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