scholarly journals Ionized gas dynamics in the inner 2 pc of Sgr A West

2013 ◽  
Vol 9 (S303) ◽  
pp. 69-72
Author(s):  
John H. Lacy ◽  
Wesley T. Irons ◽  
Matthew J. Richter
Keyword(s):  
Density Wave ◽  
Spiral Wave ◽  
Wave Model ◽  
Wave Pattern ◽  
Data Cube ◽  
Ionized Gas ◽  
Wave Compression ◽  
Sgr A ◽  
Set Up ◽  
Self Gravity

AbstractWe present a data cube of the [NeII] (12.8 μm) emission from the inner 2 pc of Sgr A West with 1″ and 4 km s−1 resolution, and with substantially better SNR and velocity resolution than previous observations of the ionized gas. We compare the observations to two proposed models of the gas motions and distribution: flows along tidally stretched streamers, and more nearly circular motions with density wave compression. The density wave model provides a considerably better fit to the kinematics of the northern arm and western arc. Neither model fits the eastern arm and bar kinematics well.To help understand the origin of the spiral pattern we calculated orbits in the potential of a black hole in a star cluster and find that the orbits naturally evolve to set up a one-armed spiral wave very similar to that observed, both spatially and kinematically. Magnetic or other perturbing forces may influence the formation of the spiral wave, but self gravity is not required. Because a density wave evolves on the orbit precession timescale, rather than the orbital timescale, a wave pattern should persist for several 105 yr. No net inward motion of the gas is required by the model. If there is inflow, it is much smaller than is suggested by the infalling streamer model.

scholarly journals Mini-Spiral at the Galactic Center: A Link between its Structure and the Value of a Central Point Mass

1996 ◽  
Vol 169 ◽  
pp. 241-246
Author(s):  
A.M. Fridman ◽  
O.V. Khoruzhii ◽  
V.V. Lyakhovich ◽  
L. Ozernoy ◽  
L. Blitz
Keyword(s):  
Galactic Center ◽  
Density Wave ◽  
Neutral Hydrogen ◽  
Wave Model ◽  
Molecular Gas ◽  
Stellar Cluster ◽  
Nonthermal Radio ◽  
H Ii Region ◽  
Circumnuclear Disk ◽  
Sgr A

The innermost 2 pc contain a rotating ring (“circumnuclear disk”) of molecular gas, neutral hydrogen, and dust with an embedded H II region called Sgr A West; a dense stellar cluster; and a compact nonthermal radio source Sgr A∗ (for a recent review, see Blitz et al. 1993). The clumped, spiral-shaped morphology of Sgr A West, sometimes called lthe mini-spiral”, has been a subject of numerous speculations concerning its origin (for a review, see Genzel & Townes 1987). Lacy et al. (1991) demonstrated that both the kinematics and shape of a part of Sgr A West can be fairly well approximated using an one-armed density-wave model.

scholarly journals Fragmentation of ring galaxies and transformation to clumpy galaxies

2021 ◽  
Author(s):  
Shigeki Inoue ◽  
Naoki Yoshida ◽  
Lars Hernquist
Keyword(s):  
Gravitational Instability ◽  
High Redshift ◽  
Density Wave ◽  
Wave Model ◽  
Linear Perturbation ◽  
Physical Conditions ◽  
Disc Rotation ◽  
Ring Galaxies ◽  
The Stability ◽  
Self Gravity

Abstract We study the fragmentation of collisional ring galaxies (CRGs) using a linear perturbation analysis that computes the physical conditions of gravitational instability, as determined by the balance of self-gravity of the ring against pressure and Coriolis forces. We adopt our formalism to simulations of CRGs and show that the analysis can accurately characterise the stability and onset of fragmentation, although the linear theory appears to under-predict the number of fragments of an unstable CRG by a factor of 2. In addition, since the orthodox ‘density-wave’ model is inapplicable to such self-gravitating rings, we devise a simple approach that describes the rings propagating as material waves. We find that the toy model can predict whether the simulated CRGs fragment or not using information from their pre-collision states. We also apply our instability analysis to a CRG discovered at a high redshift, z = 2.19. We find that a quite high velocity dispersion is required for the stability of the ring, and therefore the CRG should be unstable to ring fragmentation. CRGs are rarely observed at high redshifts, and this may be because CRGs are usually too faint. Since the fragmentation can induce active star formation and make the ring bright enough to observe, the instability could explain this rarity. An unstable CRG fragments into massive clumps retaining the initial disc rotation, and thus it would evolve into a clumpy galaxy with a low surface density in an inter-clump region.

scholarly journals Insights into the physics when modelling cold gas clouds in a hot plasma

2019 ◽  
Vol 490 (1) ◽  
pp. L52-L56
Author(s):  
Bastian Sander ◽  
Gerhard Hensler
Keyword(s):  
Adaptive Mesh Refinement ◽  
Adaptive Mesh ◽  
Careful Consideration ◽  
Necessary Condition ◽  
Interstellar Clouds ◽  
Hot Plasma ◽  
Magnetic Dipole Field ◽  
Set Up ◽  
Self Gravity ◽  
Cold Gas

ABSTRACT This paper aims at studying the reliability of a few frequently raised, but not proven, arguments for the modelling of cold gas clouds embedded in or moving through a hot plasma and at sensitizing modellers to a more careful consideration of unavoidable acting physical processes and their relevance. At first, by numerical simulations we demonstrate the growing effect of self-gravity on interstellar clouds and, by this, moreover argue against their initial set-up as homogeneous. We apply the adaptive-mesh refinement code flash with extensions to metal-dependent radiative cooling and external heating of the gas, self-gravity, mass diffusion, and semi-analytic dissociation of molecules, and ionization of atoms. We show that the criterion of Jeans mass or Bonnor–Ebert mass, respectively, provides only a sufficient but not a necessary condition for self-gravity to be effective, because even low-mass clouds are affected on reasonable dynamical time-scales. The second part of this paper is dedicated to analytically study the reduction of heat conduction by a magnetic dipole field. We demonstrate that in this configuration, the effective heat flow, i.e. integrated over the cloud surface, is suppressed by only 32 per cent by magnetic fields in energy equipartition and still insignificantly for even higher field strengths.

On the path toward a universal outflow mechanism in light of NGC 4151 and NGC 1068

2020 ◽  
Vol 15 (S359) ◽  
pp. 283-284
Author(s):  
D. May ◽  
J. E. Steiner ◽  
R. B. Menezes
Keyword(s):  
Near Infrared ◽  
Feedback Mechanism ◽  
Data Cube ◽  
Low Velocity ◽  
Ionized Gas ◽  
Ngc 4151 ◽  
Molecular Outflow ◽  
Ngc 1068 ◽  
Field Unit ◽  
First Time

AbstractWe use near-infrared Integral Field Unit (IFU) data to analyze the galaxies NGC 4151 and NGC 1068, which have very different Eddington ratios - ˜50 times lower for NGC 4151. Together with a detailed data cube treatment methodology, we reveal remarkable similarities between both AGN, such as the detection of the walls of an “hourglass” structure for the low-velocity [Fe ii] emission with the high-velocity emission within this hourglass; a molecular outflow - detected for the first time in NGC 4151; and the fragmentation of an expanding molecular bubble into bullets of ionized gas. Such observations suggest that NGC 4151 could represent a less powerful and more compact version of the outflow seen in NGC 1068, suggesting a universal feedback mechanism acting in quite different AGN.

scholarly journals Precision geoinformatical system of the pear gene-collection orchard

2012 ◽  
Vol 18 (1) ◽  
Author(s):  
J. Tamás ◽  
A. Nagy ◽  
T. Fórián ◽  
J. Nyéki ◽  
T. Szabó ◽  
...  
Keyword(s):  
Data Base ◽  
Spatial Data ◽  
Single Species ◽  
Field Work ◽  
Stress Sensitivity ◽  
Hyperspectral Data ◽  
Data Cube ◽  
The Sustainable Development ◽  
Fruit Species ◽  
Set Up

The principle task of the sustainable development is the preservation of the genetic variety, which is similar challenge in the horticulture regarding the sublimation of fruit species. The breeders of the traditional fruit strains give stock to the sustenance diversity of the agro-environment on the species and landscape level. In 2009, hyperspectral images have been taken by AISA Dual sensors from the pear gene pool in Újfehértó, Hungary. The hyperspectral data cube (in the wavelength range of 400-2500 nm, with 1.5 m ground resolution) ensured possibility to make the spectral library of pear species. In the course of the simultaneously field work the spatial position and individual extent of all pear trees was defined to set up a detailed GIS data base. The water stress sensitivity of single species and the descriptive spectral curves were determined with common evaluation of the spectral and spatial data. Based on the unique methodology processing and the hyperspectral data base suitable strains can be chosen for agro-environment and let take adaptive stocks regarding climate change into the genetic grafting work. Furthermore we could determine and map the sparsely species in the region with the help of the hyperspectral data.

Dynamics of a Traveling Density Wave Model for Earthquakes

1996 ◽  
Vol 76 (22) ◽  
pp. 4285-4288 ◽  
Author(s):  
John B. Rundle ◽  
W. Klein ◽  
Susanna Gross
Keyword(s):  
Density Wave ◽  
Wave Model

scholarly journals How far actually is the Galactic Center IRS 13E3 from Sagittarius A*?

2020 ◽  
Vol 72 (3) ◽  
Author(s):  
Masato Tsuboi ◽  
Yoshimi Kitamura ◽  
Takahiro Tsutsumi ◽  
Ryosuke Miyawaki ◽  
Makoto Miyoshi ◽  
...  
Keyword(s):  
Galactic Center ◽  
Three Dimensional ◽  
Line Of Sight ◽  
Recombination Line ◽  
Intermediate Mass ◽  
Ionized Gas ◽  
Sagittarius A ◽  
Projection Distance ◽  
Spectroscopic Information ◽  
Sgr A

Abstract The Galactic Center IRS 13E cluster is a very intriguing infrared object located at ${\sim } 0.13$ pc from Sagittarius A$^\ast$ (Sgr A$^\ast$) in projection distance. There are arguments both for and against the hypothesis that a dark mass like an intermediate mass black hole (IMBH) exists in the cluster. We recently detected the rotating ionized gas ring around IRS 13E3, which belongs to the cluster, in the H30$\alpha$ recombination line using ALMA. The enclosed mass is derived to be $M_{\mathrm{encl.}}\simeq 2\times 10^{4}\, M_\odot$, which agrees with an IMBH and is barely less than the astrometric upper limit mass of an IMBH around Sgr A$^\ast$. Because the limit mass depends on the true three-dimensional (3D) distance from Sgr A$^\ast$, it is very important to determine it observationally. However, the 3D distance is indefinite because it is hard to determine the line-of-sight (LOS) distance by usual methods. We attempt here to estimate the LOS distance from spectroscopic information. The CH$_3$OH molecule is easily destroyed by the cosmic rays around Sgr A$^{\ast }$. However, we detected a highly excited CH$_3$OH emission line in the ionized gas stream associated with IRS 13E3. This indicates that IRS 13E3 is located at $r\gtrsim 0.4$ pc from Sgr A$^{\ast }$.

scholarly journals 7.15. The Fourier analysis of the observed velocity field of gas in the inner 1.5 pc of the Galaxy

1998 ◽  
Vol 184 ◽  
pp. 321-324
Author(s):  
A.M. Fridman ◽  
V.V. Lyakhovich ◽  
O.V. Khoruzhii ◽  
O.K. Silchenko
Keyword(s):  
Velocity Field ◽  
Fourier Analysis ◽  
Galactic Center ◽  
Second Harmonic ◽  
Density Wave ◽  
Ionized Gas ◽  
Density Maximum ◽  
Fourier Harmonic ◽  
Wave Nature ◽  
The Galaxy

The Fourier analysis of the observed velocity field of ionized gas in the inner 1.5 pc of the Galactic Center (obtained by Roberts and Goss, 1993) is made. As follows from the analysis, the observed field of residual velocities is dominated by the second Fourier harmonic. This fact can be treated as a consequence of the presence of an one-armed density wave with the density maximum along the Northern Arm plus the Western Arc structure. The wave nature of this structure is proved on the base of the behaviour of the phase of the second harmonic of line-of-sight velocity field in the whole region. The Fourier analysis shows also the presence of systematic radial velocity. We consider this flow as a quasi-stationary radial drift caused by one-armed nonlinear density wave (‘mini-spiral’).

scholarly journals Ionized gas in the NGC 5253 supernebula: high spatial and spectral resolution observations with the JVLA and TEXES

2020 ◽  
Vol 497 (2) ◽  
pp. 1675-1683
Author(s):  
Sara C Beck ◽  
John Lacy ◽  
Jean Turner ◽  
Hauyu Baobab Liu ◽  
Thomas Greathouse ◽  
...  
Keyword(s):  
Spectral Resolution ◽  
Large Scale ◽  
Massive Star ◽  
Dwarf Galaxy ◽  
Data Cube ◽  
Test Case ◽  
Echelle Spectrograph ◽  
Full Data ◽  
Ionized Gas ◽  
Very Large Array

ABSTRACT The youngest, closest, and most compact embedded massive star cluster known excites the supernebula in the nearby dwarf galaxy NGC 5253. It is a crucial target and test case for studying the birth and evolution of the most massive star clusters. We present observations of the ionized gas in this source with high spatial and spectral resolution. The data include continuum images of free–free emission with ≈0.15 arcsec resolution made with the Karl G. Jansky Very Large Array (JVLA) at 15, 22, and 33 GHz, and a full data cube of the [S iv] 10.5 μm  fine-structure emission line with ≈4.5 km s−1 velocity resolution and 0.3 arcsec beam, obtained with the Texas Echelon Cross Echelle Spectrograph (TEXES) on Gemini North. We find that (1) the ionized gas extends out from the cluster in arms or jets, and (2) the ionized gas comprises two components offset both spatially and in velocity. We discuss mechanisms that may have created the observed velocity field; possibilities include large-scale jets or a subcluster falling on to the main source.

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