scholarly journals Dynamics of the Galactic Bulge from gas motions

1993 ◽  
Vol 153 ◽  
pp. 275-282
Author(s):  
Ortwin E. Gerhard ◽  
James Binney
Keyword(s):  
Angular Momentum ◽  
Star Formation ◽  
Galactic Center ◽  
Galactic Disk ◽  
Line Of Sight ◽  
Asymmetric Distribution ◽  
Kinematical Model ◽  
Lindblad Resonance ◽  
Inner Lindblad Resonance ◽  
Significant Mass

Observations of cold gas in the inner galactic disk show a clumpy, highly asymmetric distribution, with large non-circular velocities. Recent work has shown that the flow of gas in the inner few kpc is dominated by a rapidly rotating bar, with corotation at R ≃ 2.4 kpc and oriented at an angle of θincl = 16 ± 2° with the line-of-sight to the Galactic Center. From the kinematical model the gravitational potential in the inner Galaxy can be determined. Gas falls inwards through the bar's inner Lindblad resonance at a rate of ∼ 0.1M⊙/ yr; this suggests that in episodic star formation significant mass and angular momentum may be added to the inner bulge.

scholarly journals 11.15. The effect of a central massive black hole on the gas fueling

1998 ◽  
Vol 184 ◽  
pp. 485-486
Author(s):  
H. Fukuda ◽  
A. Habe ◽  
K. Wada
Keyword(s):  
Black Hole ◽  
Numerical Simulations ◽  
Gravitational Potential ◽  
Galactic Center ◽  
The Self ◽  
Massive Black Hole ◽  
Nuclear Regions ◽  
Self Gravity ◽  
Lindblad Resonance ◽  
Inner Lindblad Resonance

Nuclear activities in galaxies, such as nuclear starbursts or AGNs, are supposed to be induced by gas fueling into nuclear regions of galaxies. Non-axisymmetric gravitational potential caused by a stellar bar is a convincing mechanism for triggering gas fueling (Phinney 1994). However, numerical simulations have shown that the bar can not force the gas to accrete toward the galactic center beyond the inner Lindblad resonance (ILR). As a mechanism to overcome the ILR barrier, the double barred structure (Friedli & Martinet 1993), or the self-gravity of gas (Wada & Habe 1992, 1995; Elmegreen 1994) are proposed.

scholarly journals Stellar bars in counter-rotating dark matter haloes: the role of halo orbit reversals

2019 ◽  
Vol 489 (3) ◽  
pp. 3102-3115 ◽  
Author(s):  
Angela Collier ◽  
Isaac Shlosman ◽  
Clayton Heller
Keyword(s):  
Dark Matter ◽  
Angular Momentum ◽  
Galaxy Evolution ◽  
Secular Evolution ◽  
Resonant Interactions ◽  
Disc Galaxies ◽  
Simulation Time ◽  
Lindblad Resonance ◽  
Inner Lindblad Resonance

Abstract Disc galaxies can exchange angular momentum and baryons with their host dark matter (DM) haloes. These haloes possess internal spin, λ, which is insignificant rotationally but does affect interactions between the baryonic and DM components. While statistics of prograde and retrograde spinning haloes in galaxies is not available at present, the existence of such haloes is important for galaxy evolution. In the previous works, we analysed dynamical and secular evolution of stellar bars in prograde spinning haloes and the DM response to the bar perturbation, and found that it is modified by the resonant interactions between the bar and the DM halo orbits. In this work, we follow the evolution of stellar bars in retrograde haloes. We find that this evolution differs substantially from evolution in rigid unresponsive haloes, discussed in the literature. First, we confirm that the bar instability is delayed progressively along the retrograde λ sequence. Secondly, the bar evolution in the retrograde haloes differs also from that in the prograde haloes, in that the bars continue to grow substantially over the simulation time of 10 Gyr. The DM response is also substantially weaker compared to this response in the prograde haloes. Thirdly, using orbital spectral analysis of the DM orbital structure, we find a phenomenon we call the orbit reversal – when retrograde DM orbits interact with the stellar bar, reverse their streaming and precession, and become prograde. This process dominates the inner halo region adjacent to the bar and allows these orbits to be trapped by the bar, thus increasing efficiency of angular momentum transfer by the inner Lindblad resonance. We demonstrate this reversal process explicitly in a number of examples.

scholarly journals Cloud–cloud collisions in the common foot point of molecular loops 1 and 2 in the Galactic Center

2019 ◽  
Author(s):  
Rei Enokiya ◽  
Kazufumi Torii ◽  
Yasuo Fukui
Keyword(s):  
Star Formation ◽  
Galactic Center ◽  
Galactic Disk ◽  
Volume Density ◽  
High Mass ◽  
Molecular Gas ◽  
Large Area ◽  
Elapsed Time ◽  
The Common ◽  
First Time

Abstract Recent large-area, deep CO surveys in the Galactic disk have revealed the formation of ~50 high-mass stars or clusters triggered by cloud–cloud collisions (CCCs). Although the Galactic Center (GC)—which contains the highest volume density of molecular gas—is the most favorable place for cloud collisions, systematic studies of CCCs in that region are still untouched. Here we report for the first time evidence of CCCs in the common foot point of molecular loops 1 and 2 in the GC. We have investigated the distribution of molecular gas toward the foot point by using a methodology for identifying CCCs, and we have discovered clear signatures of CCCs. Using the estimated displacements and relative velocities of the clouds, we find the elapsed time since the beginnings of the collisions to be 105–106yr. We consider possible origins for previously reported peculiar velocity features in the foot point and discuss star formation triggered by CCCs in the GC.

scholarly journals OH/IR stars as tracers of Galactic populations

1993 ◽  
Vol 153 ◽  
pp. 57-72 ◽  
Author(s):  
H.J. Habing
Keyword(s):  
Angular Momentum ◽  
Galactic Center ◽  
Galactic Disk ◽  
Galactic Bulge ◽  
High Luminosity ◽  
Rotating System ◽  
Circular Orbits ◽  
Long Period ◽  
Ir Stars ◽  
Different Populations

I discuss observable quantities of OH/IR stars and their interpretation. The strong 1612 MHz maser is found in about 1/2 of all the stars that reach the AGB and then have the following properties: they are oxygen–rich, of high–luminosity (3,000 → 30,000L⊙), vary in luminosity with a long period (P>500 d), lose mass rapidly and have a metallicity high enough to form sufficient amounts of dust (the metallicity of the LMC is probably the lowest value sufficient to produce OH/IR stars). OH/IR stars can be several Gyr old. There are at least three different populations each characterized by different galactic orbits. (1) OH/IR stars in the galactic disk on almost circular orbits; (2) OH/IR stars in the galactic bulge on orbits of lower angular momentum; (3) OH/IR stars within 150 pc from the galactic center forming a rapidly rotating system.

Molecular Gas in the Centers of Barred and Starburst Galaxies

1994 ◽  
Vol 140 ◽  
pp. 282-292
Author(s):  
Jeffrey D. P. Kenney
Keyword(s):  
Star Formation ◽  
Large Scale ◽  
Starburst Galaxy ◽  
Molecular Gas ◽  
Barred Galaxies ◽  
Twin Peaks ◽  
Ngc 1068 ◽  
Lindblad Resonance ◽  
Inner Lindblad Resonance ◽  
Co Emission

AbstractHigh resolution interferometric CO maps of the circumnuclear regions of several barred galaxies show intense CO emission arising from twin peaks, which are oriented perpendicular to the large-scale stellar bars and located where dust lanes intersect nuclear rings of HII regions. These twin gas concentrations can be explained by the crowding of gas streamlines near stellar inner Lindblad resonances. In the barred nuclear starburst galaxy NGC 3504, a large concentration of molecular gas is centered on the nucleus, apparently inside an inner Lindblad resonance. Star formation is consuming the gas most rapidly where the rotation curve is nearly solid body, suggesting that tidal shear helps control the rate of star formation. A comparison with M82 and NGC 1068 suggests that the starburst in NGC 3504 is in an early phase of its evolution, and that starburst evolution is strongly influenced by shear.

scholarly journals The Herschel view of the Galactic center

2013 ◽  
Vol 9 (S303) ◽  
pp. 1-14
Author(s):  
John Bally ◽  
Keyword(s):  
Star Formation ◽  
Massive Star ◽  
Galactic Center ◽  
Galactic Plane ◽  
Formation Rate ◽  
Asymmetric Distribution ◽  
The Galaxy ◽  
Sgr A ◽  
Almost All

AbstractThe 3.5 meter diameter Herschel Space Observatory conducted a ∼720 square-degree survey of the Galactic plane, the Herschel Galactic plane survey (Hi-GAL). These data provide the most sensitive and highest resolution observations of the far-IR to sub-mm continuum from the central molecular zone (CMZ) at λ = 70, 160, 250, 350, and 500 μm obtained to date. Hi-GAL can be used to map the distributions of temperature and column density of dust in CMZ clouds, warm dust in Hii regions, and identify highly embedded massive protostars and clusters and the dusty shells ejected by supergiant stars. These data enable classification of sources and re-evaluation of the current and recent star-formation rate in the CMZ. The outer CMZ beyond |l| = 0.9 degrees (Rgal > 130 pc) contains most of the dense (n > 104 cm−3 gas in the Galaxy but supports very little star formation. The Hi-GAL and Spitzer data show that almost all star formation occurs in clouds moving on x2 orbits at Rgal < 100 pc. While the 106 M⊙ Sgr B2 complex, the 50 km s−1 cloud near Sgr A, and the Sgr C region are forming clusters of massive stars, other clouds are relatively inactive star formers, despite their high densities, large masses, and compact sizes. The asymmetric distribution of dense gas about Sgr A* on degree scales (most dense CMZ gas and dust is at positive Galactic longitudes and positive VLSR) and compact 24 μm sources (most are at negative longitudes) may indicate that eposidic mini-starbursts occasionally ‘blow-out’ a portion of the gas on these x2 orbits. The resulting massive-star feedback may fuel the compact 30 pc scale Galactic center bubble associated with the Arches and Quintuplet clusters, the several hundred pc scale Sofue-Handa lobe, and the kpc-scale Fermi/LAT bubble, making it the largest ‘superbubble’ in the Galaxy. A consequence of this model is that in our Galaxy, instead of the supermassive black hole (SMBH) limiting star formation, star formation may limit the growth of the SMBH.

scholarly journals Large scale magnetic fields of our Galaxy

2009 ◽  
Vol 5 (H15) ◽  
pp. 450-451
Author(s):  
JinLin Han
Keyword(s):  
Star Formation ◽  
Magnetic Fields ◽  
Large Scale ◽  
Galactic Halo ◽  
Galactic Center ◽  
Galactic Plane ◽  
Galactic Disk ◽  
Zeeman Splitting ◽  
Radio Sources ◽  
Star Formation Regions

AbstractLarge-scale magnetic fields in the Galactic disk have been revealed by distributions of pulsar rotation measures (RMs) and Zeeman splitting data of masers in star formation regions, which have several reversals in arm and interarm regions. Magnetic fields in the Galactic halo are reflected by the antisymmetric sky distribution of RMs of extragalactic radio sources, which have azimuthal structure with reversed directions below and above the Galactic plane. Large-scale magnetic fields in the Galactic center probably have a poloidal and toroidal structure.

scholarly journals Herschel/HIFI Discoveryof a Far-Infrared DIB Analog

2013 ◽  
Vol 9 (S297) ◽  
pp. 197-202
Author(s):  
H. S. P. Müller ◽  
P. Schilke ◽  
M. Gerin ◽  
D. C. Lis ◽  
E. A. Bergin ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Molecular Clouds ◽  
Galactic Center ◽  
Galactic Disk ◽  
Far Infrared ◽  
Line Of Sight ◽  
Absorption Feature ◽  
Substantial Part ◽  
Star Forming ◽  
Star Forming Regions

AbstractThe Herschel Space Observatory carried out observations at far-infrared wavelengths, which significantly increased our knowledge of the interstellar medium and the star-formation process in the Milky Way and external galaxies, as well as our understanding of astrochemistry.Absorption features, known, e.g., from observations at millimeter wavelengths, are more commonly observed in the far-infrared, in particular toward strong dust continuum sources. The lowest energy transitions are not only observed at LSR-velocities related to the source, but often also at velocities associated with diffuse molecular clouds along the line of sight toward the background source.Unbiased spectral line surveys of the massive and very luminous Galactic Center sources Sagittarius B2(M) and (N) were carried out across the entire frequency range of the high-resolution Heterodyne Instrument for Far-Infrared Astronomy (HIFI). An absorption feature was detected toward both sources at about 617.531 GHz, corresponding to 20.599 cm−1, 485.47 μm, or 2.5539 meV. This feature is unique in its appearance at all velocity components associated with diffuse foreground molecular clouds, together with its conspicuous absence at velocities related to the sources themselves. The carriers of at least a substantial part of the DIBs are thought to reside in the diffuse interstellar medium. Therefore, we consider this absorption feature to be a far-infrared DIB analog.Subsequent dedicated observations confirmed that the line is present only in the foreground clouds on the line of sight toward other massive star-forming regions in the Galactic disk. There is indication that the feature has substructure, possibly of fine or hyperfine nature. Attempts to assign the feature to atomic or molecular species have been unsuccessful so far.

scholarly journals The molecular chemistry of diffuse and translucent clouds in the line-of-sight to Sgr B2: Absorption by simple organic and inorganic molecules in the GBT PRIMOS survey

2018 ◽  
Vol 610 ◽  
pp. A10 ◽  
Author(s):  
J. F. Corby ◽  
B. A. McGuire ◽  
E. Herbst ◽  
A. J. Remijan
Keyword(s):  
Molecular Hydrogen ◽  
Galactic Center ◽  
Galactic Disk ◽  
Outer Edge ◽  
Line Of Sight ◽  
Galactocentric Distance ◽  
Molecular Chemistry ◽  
Inorganic Molecules ◽  
Diffuse Clouds ◽  
First Time

The 1–50 GHz PRebiotic Interstellar MOlecular Survey (PRIMOS) contains ~50 molecular absorption lines observed in clouds located in the line-of-sight to Sgr B2(N). The line-of-sight material is associated with diffuse and translucent clouds located in the Galactic center, bar, and spiral arms in the disk. We measured the column densities and estimate abundances, relative to H2, of 11 molecules and additional isotopologues observed in this material. We used absorption by optically thin transitions of c-C3H2 to estimate the molecular hydrogen columns, and argue that this method is preferable to more commonly used methods. We discuss the kinematic structure and abundance patterns of small molecules including the sulfur-bearing species CS, SO, CCS, H2CS, and HCS+; oxygen-bearing molecules OH, SiO, and H2CO; and simple hydrocarbon molecules c-C3H2, l-C3H, and l-C3H+. Finally, we discuss the implications of the observed chemistry for the structure of the gas and dust in the ISM. Highlighted results include the following. First, whereas gas in the disk has a molecular hydrogen fraction of 0.65, clouds on the outer edge of the Galactic bar and in or near the Galactic center have molecular fractions of 0.85 and >0.9, respectively. Second, we observe trends in isotope ratios with Galactocentric distance; while carbon and silicon show enhancement of the rare isotopes at low Galactocentric distances, sulfur exhibits no trend with Galactocentric distance. We also determine that the ratio of c-C3H2/c-H13CCCH provides a good estimate of the 12C/13C ratio, whereas H2CO/H213CO exhibits fractionation. Third, we report the presence of l-C3H+ in diffuse clouds for the first time. Finally, we suggest that CS has an enhanced abundance within higher density clumps of material in the disk, and therefore may be diagnostic of cloud conditions. If this holds, the diffuse clouds in the Galactic disk contain multiple embedded hyperdensities in a clumpy structure, and the density profile is not a simple function of AV.

scholarly journals A Large-Scale CO Imaging of the Galactic Center

1998 ◽  
Vol 179 ◽  
pp. 189-190
Author(s):  
T. Oka ◽  
T. Hasegawa ◽  
F. Sato ◽  
H. Yamasaki ◽  
M. Tsuboi ◽  
...  
Keyword(s):  
Star Formation ◽  
Large Scale ◽  
Galactic Center ◽  
Galactic Disk ◽  
Molecular Gas ◽  
Physical Conditions ◽  
Relative Paucity ◽  
Center Region ◽  
Star Formation Activity

Molecular gas in the Galactic center region is spatially and kinematically complex, and its physical conditions are distinctively different from those of molecular gas in the Galactic disk (e.g., Morris 1996). Relative paucity of current star formation activity, despite the abundance of dense molecular gas in this region, is one of the problem at issue.

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