scholarly journals Do nuclear rings in barred galaxies form at the shear minimum of the rotation curve?

2020 ◽  
Vol 494 (4) ◽  
pp. 6030-6035 ◽  
Author(s):  
Mattia C Sormani ◽  
Zhi Li
Keyword(s):  
Rotation Curve ◽  
Turbulent Viscosity ◽  
Necessary Condition ◽  
Scale Free ◽  
Barred Galaxies ◽  
Acoustic Instability ◽  
Central Regions ◽  
Hydrodynamical Simulations ◽  
Spurious Result ◽  
Self Gravity

ABSTRACT It has been recently suggested that (i) nuclear rings in barred galaxies (including our own Milky Way) form at the radius where the shear parameter of the rotation curve reaches a minimum; and (ii) the acoustic instability of Montenegro et al. is responsible for driving the turbulence and angular momentum transport in the central regions of barred galaxies. Here, we test these suggestions by running simple hydrodynamical simulations in a logarithmic barred potential. Since the rotation curve of this potential is scale free, the shear minimum theory predicts that no ring should form. We find that in contrast to this prediction, a ring does form in the simulation, with morphology consistent with that of nuclear rings in real barred galaxies. This proves that the presence of a shear-minimum is not a necessary condition for the formation of a ring. We also find that perturbations that are predicted to be acoustically unstable wind up and eventually propagate off to infinity, so that the system is actually stable. We conclude that (i) the shear-minimum theory is an unlikely mechanism for the formation of nuclear rings in barred galaxies; and (ii) the acoustic instability is a spurious result and may not be able to drive turbulence in the interstellar medium, at least for the case without self-gravity. The question of the role of turbulent viscosity remains open.

scholarly journals Hydrodynamical Simulations of the Barred Spiral Galaxy NGC 1365

1996 ◽  
Vol 157 ◽  
pp. 413-415
Author(s):  
P. A. B. Lindblad ◽  
P. O. Lindblad ◽  
E. Athanassoula
Keyword(s):  
Gravitational Field ◽  
Gas Dynamics ◽  
Rotation Curve ◽  
Barred Galaxies ◽  
Mosaic Image ◽  
Dynamical Parameters ◽  
Pattern Speed ◽  
Barred Spiral Galaxy ◽  
Hydrodynamical Simulations ◽  
Ngc 1365

Several authors have explored the field of gas dynamics in barred systems. One of the aims of these investigations was to compare the model gaseous response, due to some assumed underlying stellar gravitational field, with observed gas density distribution and kinematics of barred galaxies. The gas is known to respond in a highly non-linear way, and therefore should give clues to dynamical parameters like the mass distribution, positions and existence of principal resonances and thereby the pattern speed.High resolution HI data now exist for NGC 1365 (Jörsäter & van Moorsel 1995), and the kinematical HI data have been combined with optical long slit measurements to obtain the velocity field (Lindblad et al. 1995) used for extracting the rotation curve, representing the axisymmetric forces in NGC 1365, and for comparisons with models. A mosaic image of NGC 1365 in the J-band was used to compute the perturbing potential used in the models.

scholarly journals How much does turbulence change the pebble isolation mass for planet formation?

2018 ◽  
Vol 615 ◽  
pp. A110 ◽  
Author(s):  
S. Ataiee ◽  
C. Baruteau ◽  
Y. Alibert ◽  
W. Benz
Keyword(s):  
Aspect Ratio ◽  
Planet Formation ◽  
Turbulent Viscosity ◽  
Analytical Calculation ◽  
Radial Pressure ◽  
Stokes Number ◽  
High Viscosity ◽  
Necessary Condition ◽  
Pressure Maximum ◽  
Hydrodynamical Simulations

Context. When a planet becomes massive enough, it gradually carves a partial gap around its orbit in the protoplanetary disk. A pressure maximum can be formed outside the gap where solids that are loosely coupled to the gas, typically in the pebble size range, can be trapped. The minimum planet mass for building such a trap, which is called the pebble isolation mass (PIM), is important for two reasons: it marks the end of planetary growth by pebble accretion, and the trapped dust forms a ring that may be observed with millimetre observations. Aims. We study the effect of disk turbulence on the PIM and find its dependence on the gas turbulent viscosity, aspect ratio, and particles Stokes number. Methods. By means of 2D gas hydrodynamical simulations, we found the minimum planet mass to form a radial pressure maximum beyond the orbit of the planet, which is the necessary condition to trap pebbles. We then carried out 2D gas plus dust hydrodynamical simulations to examine how dust turbulent diffusion impacts particles trapping at the pressure maximum. We finally provide a semi-analytical calculation of the PIM based on comparing the radial drift velocity of solids and the root mean square turbulent velocity fluctuations around the pressure maximum. Results. From our results of gas simulations, we provide an expression for the PIM vs. disk aspect ratio and turbulent viscosity. Our gas plus dust simulations show that the effective PIM can be nearly an order of magnitude larger in high-viscosity disks because turbulence diffuse particles out of the pressure maximum. This is quantified by our semi-analytical calculation, which gives an explicit dependence of the PIM with Stokes number of particles. Conclusions. Disk turbulence can significantly alter the PIM, depending on the level of turbulence in regions of planet formation.

scholarly journals Molecular Gas in the Central Regions of Barred Galaxies

1996 ◽  
Vol 157 ◽  
pp. 150-156 ◽  
Author(s):  
Jeffrey Kenney
Keyword(s):  
Star Formation ◽  
Solid Body ◽  
Rotation Curve ◽  
Molecular Gas ◽  
Star Forming ◽  
Barred Galaxies ◽  
Central Regions ◽  
Early Phases ◽  
Intense Star Formation

AbstractThe morphology and kinematics of molecular gas in the central regions of barred galaxies are described. The largest gas concentrations are often located near ILRs, although there is a range of morphologies. The gas motions associated with star-forming rings are predominantly circular, while motions just beyond the rings are often non-circular and in some cases show clear radial inflow. In barred galaxies with circumnuclear starbursts in early phases of evolution, the CO is centrally peaked, perhaps inside IILRs. The most intense star formation occurs where the gas motions are circular, and where the rotation curve rises steeply and is nearly solid body.

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.

scholarly journals Composite bulges – II. Classical bulges and nuclear discs in barred galaxies: the contrasting cases of NGC 4608 and NGC 4643

2021 ◽  
Vol 502 (2) ◽  
pp. 2446-2473
Author(s):  
Peter Erwin ◽  
Anil Seth ◽  
Victor P Debattista ◽  
Marja Seidel ◽  
Kianusch Mehrgan ◽  
...  
Keyword(s):  
Large Scale ◽  
Stellar Kinematics ◽  
Barred Galaxies ◽  
Circular Structure ◽  
Model Predictions ◽  
The Galaxy ◽  
Central Regions ◽  
Total Light ◽  
Kinematic Analyses ◽  
Stellar Kinematic

ABSTRACT We present detailed morphological, photometric, and stellar-kinematic analyses of the central regions of two massive, early-type barred galaxies with nearly identical large-scale morphologies. Both have large, strong bars with prominent inner photometric excesses that we associate with boxy/peanut-shaped (B/P) bulges; the latter constitute ∼30 per cent of the galaxy light. Inside its B/P bulge, NGC 4608 has a compact, almost circular structure (half-light radius Re ≈ 310 pc, Sérsic n = 2.2) we identify as a classical bulge, amounting to 12.1 per cent of the total light, along with a nuclear star cluster (Re ∼ 4 pc). NGC 4643, in contrast, has a nuclear disc with an unusual broken-exponential surface-brightness profile (13.2 per cent of the light), and a very small spheroidal component (Re ≈ 35 pc, n = 1.6; 0.5 per cent of the light). IFU stellar kinematics support this picture, with NGC 4608’s classical bulge slowly rotating and dominated by high velocity dispersion, while NGC 4643’s nuclear disc shows a drop to lower dispersion, rapid rotation, V–h3 anticorrelation, and elevated h4. Both galaxies show at least some evidence for V–h3correlation in the bar (outside the respective classical bulge and nuclear disc), in agreement with model predictions. Standard two-component (bulge/disc) decompositions yield B/T ∼ 0.5–0.7 (and bulge n > 2) for both galaxies. This overestimates the true ‘spheroid’ components by factors of 4 (NGC 4608) and over 100 (NGC 4643), illustrating the perils of naive bulge-disc decompositions applied to massive barred galaxies.

scholarly journals Dark Matter in Dwarf Galaxies: High Resolution Observations

2004 ◽  
Vol 220 ◽  
pp. 353-358 ◽  
Author(s):  
Alberto D. Bolatto ◽  
Joshua D. Simon ◽  
Adam Leroy ◽  
Leo Blitz
Keyword(s):  
Dark Matter ◽  
High Resolution ◽  
Rotation Curve ◽  
Dwarf Galaxies ◽  
Full Range ◽  
Dark Matter Halo ◽  
Central Density ◽  
Constant Density ◽  
Density Profiles ◽  
Central Regions

We present observations and analysis of rotation curves and dark matter halo density profiles in the central regions of four nearby dwarf galaxies. This observing program has been designed to overcome some of the limitations of other rotation curve studies that rely mostly on longslit spectra. We find that these objects exhibit the full range of central density profiles between ρ ∝ r0 (constant density) and ρ ∝ r–1 (NFW halo). This result suggests that there is a distribution of central density slopes rather than a unique halo density profile.

scholarly journals 3.3. Circumnuclear regions of active and non-active barred galaxies

1998 ◽  
Vol 184 ◽  
pp. 93-94
Author(s):  
J.H. Knapen
Keyword(s):  
High Resolution ◽  
Near Infrared ◽  
Infrared Imaging ◽  
Seyfert Galaxy ◽  
Active Galaxies ◽  
Necessary Condition ◽  
Nuclear Activity ◽  
Barred Galaxies ◽  
Galaxy Cores

I discuss the role of galactic bars in the fuelling of (circum)nuclear activity. Since the majority of all galaxies are barred, the presence of a bar in a Seyfert galaxy cannot be the sole reason for their activity, although it appears to be a necessary condition for activity. Two options for further work are being explored, high-resolution near-infrared imaging of samples of active and non-active galaxies, and detailed case studies of selected galaxy cores.

scholarly journals Kinematical signatures of disc instabilities and secular evolution in the MUSE TIMER Survey

2019 ◽  
Vol 14 (S353) ◽  
pp. 135-139
Author(s):  
Dimitri A. Gadotti ◽  
Adrian Bittner ◽  
Jesus Falcón-Barroso ◽  
Jairo Méndez-Abreu ◽  
Keyword(s):  
Spatial Resolution ◽  
High Signal ◽  
Stellar Kinematics ◽  
Secular Evolution ◽  
Integral Field Spectroscopy ◽  
Central Regions ◽  
Hydrodynamical Simulations ◽  
Cosmic History ◽  
Disc Galaxies ◽  
Integral Field

AbstractThe MUSE TIMER Survey has obtained high signal and high spatial resolution integral-field spectroscopy data of the inner ~ 6×6 kpc of 21 nearby massive disc galaxies. This allows studies of the stellar kinematics of the central regions of massive disc galaxies that are unprecedented in spatial resolution. We confirm previous predictions from numerical and hydrodynamical simulations of the effects of bars and inner bars on stellar and gaseous kinematics, and also identify box/peanuts via kinematical signatures in mildly and moderately inclined galaxies, including a box/peanut in a face-on inner bar. In 20/21 galaxies we find inner discs and show that their properties are fully consistent with the bar-driven secular evolution picture for their formation. In addition, we show that these inner discs have, in the region where they dominate, larger rotational support than the main galaxy disc, and discuss how their stellar population properties can be used to estimate when in cosmic history the main bar formed. Our results are compared with photometric studies in the context of the nature of galaxy bulges and we show that inner discs are identified in image decompositions as photometric bulges with exponential profiles (i.e., Sérsic indices near unity).

scholarly journals Filament Formation in Molecular Clouds as a Scale-Free Process

2015 ◽  
Vol 11 (A29B) ◽  
pp. 709-710
Author(s):  
Enrique Vázquez-Semadeni ◽  
Gilberto Gómez
Keyword(s):  
Hierarchical Structure ◽  
Molecular Clouds ◽  
Large Scale ◽  
Filament Formation ◽  
Molecular Line ◽  
Scale Free ◽  
The Core ◽  
Free Process ◽  
Self Gravity

AbstractWe discuss the formation of filaments in molecular clouds (MCs) as the result of large-scale collapse in the clouds. We first give arguments suggesting that self-gravity dominates the nonthermal motions, and then briefly describe the resulting structure, similar to that found in molecular-line and dust observations of the filaments in the clouds. The filaments exhibit a hierarchical structure in both density and velocity, suggesting a scale-free nature, similar to that of the cosmic web, resulting from the domination of self-gravity from the MC down to the core scale.

scholarly journals Thawing the frozen-in approximation: implications for self-gravity in deeply plunging tidal disruption events

2019 ◽  
Vol 485 (1) ◽  
pp. L146-L150 ◽  
Author(s):  
Elad Steinberg ◽  
Eric R Coughlin ◽  
Nicholas C Stone ◽  
Brian D Metzger
Keyword(s):  
Free Fall ◽  
Tidal Disruption ◽  
Massive Black Hole ◽  
High Penetration ◽  
Order Of Magnitude ◽  
Sphere Radius ◽  
Hydrodynamical Simulations ◽  
Self Gravity ◽  
Hydrostatic Balance ◽  
Mesh Technique

ABSTRACT The tidal destruction of a star by a massive black hole, known as a tidal disruption event (TDE), is commonly modelled using the ‘frozen-in’ approximation. Under this approximation, the star maintains exact hydrostatic balance prior to entering the tidal sphere (radius rt), after which point its internal pressure and self-gravity become instantaneously negligible and the debris undergoes ballistic free fall. We present a suite of hydrodynamical simulations of TDEs with high penetration factors β ≡ rt/rp = 5−7, where rp is the pericentre of the stellar centre of mass, calculated using a Voronoi-based moving-mesh technique. We show that basic assumptions of the frozen-in model, such as the neglect of self-gravity inside rt, are violated. Indeed, roughly equal fractions of the final energy spread accumulate exiting and entering the tidal sphere, though the frozen-in prediction is correct at the order-of-magnitude level. We also show that an $\mathcal {O}(1)$ fraction of the debris mass remains transversely confined by self-gravity even for large β which has implications for the radio emission from the unbound debris and, potentially, for the circularization efficiency of the bound streams.

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