scholarly journals Multiple bars and secular evolution

2012 ◽  
Vol 10 (H16) ◽  
pp. 327-327
Author(s):  
Juntai Shen
Keyword(s):  
Near Infrared ◽  
Initial Conditions ◽  
Galactic Nuclei ◽  
Building Blocks ◽  
Barred Galaxies ◽  
Secular Evolution ◽  
Stellar Velocity ◽  
Pattern Speed ◽  
Pattern Speeds ◽  
Short Time

AbstractBars are the most important driver of secular evolution. A significant fraction of barred galaxies also harbor small secondary bars. Secondary bars are visible even in near-infrared images, so they are not just dusty and blue, but stellar features (Erwin & Sparke 2002). Since they are quite common, secondary bars are probably long-lived stellar features. The random relative orientation of the two bars indicates that they are dynamically decoupled with different pattern speeds (Buta & Crocker 1993). Corsini et al. (2003) presented conclusive direct kinematic evidence for a decoupled secondary bar in NGC 2950. Dynamically decoupled secondary bars have long been hypothesized to be a mechanism to drive gas past the ILR of primary bars to feed active galactic nuclei (Shlosman et al. 1989). However, the dynamics of secondary bars are still not well understood, and it is still unclear what role secondary bars play in the AGN fueling process.Numerical simulations offer the best approach to understanding double-barred systems. Decoupled secondary bar in the earlier gaseous simulations only last a short time (< 1 Gyr, e.g. Friedli & Martinet 1993). Orbital studies of double-barred systems discovered a family of loop orbits that may be building blocks of long-lived nuclear stellar bars (Maciejewski & Sparke 1997, 2000). To complement orbital studies, which are not fully self-consistent, N-body simulations are preferred to further our understanding of double-barred systems. Debattista & Shen (2007) and Shen & Debattista (2009) managed to form long-lived double-barred systems with purely collisionless simulations, where a pre-existing rotating pseudo-bulge is introduced initially. The shape and size of secondary bars in the models are comparable to observed ones. They found that the rotation of the two bars is not rigid. The amplitude and pattern speed of the secondary bars oscillate as they rotate through their primary counterparts. Although the secondary bar rotates faster than the primary bar in this model, the stellar velocity field in the central region only shows a weakly twisted kinematic minor axis.Recently more simulations of double-barred galaxies with simpler initial conditions are explored (Du, Shen & Debattista 2014). We expect that the new models can be used to cross-check with the kinematic properties of double-barred galaxies from IFU observations such as SAURON and Atlas3D.

scholarly journals A New Method for Corotation Determination in Spiral and Barred Galaxies

2006 ◽  
Vol 2 (S235) ◽  
pp. 149-149
Author(s):  
Xiaolei Zhang ◽  
Ronald J. Buta
Keyword(s):  
Near Infrared ◽  
Density Wave ◽  
Disk Galaxies ◽  
State University ◽  
Dynamical Mechanism ◽  
Barred Galaxies ◽  
Secular Evolution ◽  
The Ohio State University ◽  
Pattern Speeds ◽  
Wave Modes

AbstractThe approaches proposed in the past for determining the pattern speeds and corotation radii of the density waves in spiral and barred galaxies are mostly limited in their scope and accuracy. In this work, we have developed a general approach for the determination of corotation radii, which is applicable to any galaxy whose density wave modes have reached quasi-steady state – a condition empirically found to be the case for most nearby disk galaxies. The method utilizes an azimuthal phase shift between the potential and the density distributions for the density wave modes, the existence and the radial variations of which are closely related to the dynamical mechanism leading to the secular evolution of the basic state of the same disk galaxies (Zhang 1996, ApJ, 457, 125). We have used this method to derive corotation radii of over 100 galaxies using the near-infrared images of the Ohio State University Bright Galaxy Survey (OSUBGS, Eskridge et al. 2002, ApJS, 143, 73).

scholarly journals Manifold spirals in barred galaxies with multiple pattern speeds

2020 ◽  
Vol 636 ◽  
pp. A44
Author(s):  
C. Efthymiopoulos ◽  
M. Harsoula ◽  
G. Contopoulos
Keyword(s):  
Invariant Manifolds ◽  
Relative Phase ◽  
Spiral Structure ◽  
Galactic Disk ◽  
Time Varying ◽  
Barred Galaxies ◽  
Single Pattern ◽  
Pattern Speed ◽  
Pattern Speeds ◽  
Manifold Theory

In the manifold theory of spiral structure in barred galaxies, the usual assumption is that the spirals rotate with the same pattern speed as the bar. Here, we generalize the manifold theory under the assumption that the spirals rotate with a different pattern speed than the bar. More generally, we consider the case in which one or more modes, represented by the potentials V2, V3, etc., coexist in the galactic disk in addition to the bar’s mode Vbar, but the modes rotate with pattern speeds, Ω2, Ω3, etc., which are incommensurable between themselves and with Ωbar. Through a perturbative treatment (assuming that V2, V3, etc. are small with respect to Vbar), we then show that the unstable Lagrangian points L1 and L2 of the pure bar model (Vbar, Ωbar) are continued in the full model as periodic orbits, in the case of one extra pattern speed, or as epicyclic “Lissajous-like” unstable orbits, in the case of more than one extra pattern speeds. We use GL1 and GL2 to denote the continued orbits around the points L1 and L2. Furthermore, we show that the orbits GL1 and GL2 are simply unstable. As a result, these orbits admit invariant manifolds, which can be regarded as the generalization of the manifolds of the L1 and L2 points in the single pattern speed case. As an example, we computed the generalized orbits GL1, GL2, and their manifolds in a Milky-Way-like model in which bar and spiral pattern speeds were assumed to be different. We find that the manifolds produce a time-varying morphology consisting of segments of spirals or “pseudorings”. These structures are repeated after a period equal to half the relative period of the imposed spirals with respect to the bar. Along one period, the manifold-induced time-varying structures are found to continuously support at least some part of the imposed spirals, except at short intervals around specific times at which the relative phase of the imposed spirals with respect to the bar is equal to ±π/2. The connection of these effects to the phenomenon of recurrent spirals is discussed.

scholarly journals Coronal-line forest active galactic nuclei – I. Physical properties of the emission-line regions

2020 ◽  
Vol 500 (2) ◽  
pp. 2666-2684
Author(s):  
F C Cerqueira-Campos ◽  
A Rodríguez-Ardila ◽  
R Riffel ◽  
M Marinello ◽  
A Prieto ◽  
...  
Keyword(s):  
Emission Line ◽  
Active Galactic Nuclei ◽  
Near Infrared ◽  
Galactic Nuclei ◽  
Infrared Emission ◽  
Ionization Mechanism ◽  
Coronal Line ◽  
Coronal Emission ◽  
High Ionization ◽  
Stellar Velocity

ABSTRACT Coronal-line forest (CLiF) active galactic nuclei (AGNs) are characterized by strong high-ionization lines, which contrasts with what is found in most AGNs. Here, we carry out a multiwavelength analysis aimed at understanding the physical processes in the narrow-line region (NLR) of these objects, and at discovering whether they are indeed a special class of AGNs. By comparing coronal emission-line ratios we conclude that there are no differences between CLiF and non-CLiF AGNs. We derive physical conditions of the NLR gas and we find electron densities in the range of 3.6 × 102 to 1.7 × 104 cm−3 and temperatures of 3.7 × 103 to 6.3 × 104 K, suggesting that the ionization mechanism is associated primarily with photoionization by the AGN. We suggest an NLR dominated by matter-bounded clouds to explain the high-ionization line spectrum observed. The mass of the central black hole, derived from the stellar velocity dispersion, shows that most of the objects have values in the interval 107–108 M⊙. Our results imply that CLiF AGNs are not in a separate category of AGNs. In all optical/near-infrared emission-line properties analysed, they represent an extension to the low/high ends of the distribution within the AGN class.

scholarly journals Bar pattern speeds in CALIFA galaxies

2019 ◽  
Vol 632 ◽  
pp. A51 ◽  
Author(s):  
Virginia Cuomo ◽  
J. Alfonso Lopez Aguerri ◽  
Enrico Maria Corsini ◽  
Victor P. Debattista ◽  
Jairo Méndez-Abreu ◽  
...  
Keyword(s):  
Formation Process ◽  
Systematic Investigation ◽  
Sloan Digital Sky Survey ◽  
Stellar Kinematics ◽  
Barred Galaxies ◽  
Tidal Interaction ◽  
Wide Range ◽  
Area Survey ◽  
Pattern Speed ◽  
Pattern Speeds

Context. About 35% of the nearby disc galaxies host a weak bar for which different formation scenarios, including the weakening of a strong bar and tidal interaction with a companion, have been suggested. Measuring the bar pattern speeds of a sample of weakly barred galaxies is a key step in constraining their formation process, but such a systematic investigation is still missing. Aims. We investigated the formation process of weak bars by measuring their properties in a sample of 29 nearby weakly barred galaxies, spanning a wide range of morphological types and luminosities. The sample galaxies were selected to have an intermediate inclination, a bar at an intermediate angle between the disc minor and major axes, and an undisturbed morphology and kinematics to allow the direct measurement of the bar pattern speed. Combining our analysis with previous studies, we compared the properties of weak and strong bars. Methods. We measured the bar radius and strength from the r band images available in the Sloan Digital Sky Survey and bar pattern speed and corotation radius from the stellar kinematics obtained by the Calar Alto Legacy Integral Field Area Survey. We derived the bar rotation rate as the ratio between the corotation and bar radii. Results. Thirteen out of 29 galaxies (45%), which were morphologically classified as weakly barred from a visual inspection, do not actually host a bar component or their central elongated component is not in rigid rotation. We successfully derived the bar pattern speed in 16 objects. Two of them host an ultrafast bar. Using the bar strength to differentiate between weak and strong bars, we found that the weakly barred galaxies host shorter bars with smaller corotation radii than their strongly barred counterparts. Weak and strong bars have similar bar pattern speeds and rotation rates, which are all consistent with being fast. We did not observe any difference between the bulge prominence in weakly and strongly barred galaxies, whereas nearly all the weak bars reside in the disc inner parts, contrary to strong bars. Conclusions. We ruled out that the bar weakening is only related to the bulge prominence and that the formation of weak bars is triggered by the tidal interaction with a companion. Our observational results suggest that weak bars may be evolved systems exchanging less angular momentum with other galactic components than strong bars.

scholarly journals Bar-driven evolution of fast rotators: the role and fate of bars in early and late-type galaxies

2012 ◽  
Vol 10 (H16) ◽  
pp. 363-363
Author(s):  
Eric Emsellem ◽  
Renaud Florent
Keyword(s):  
Stellar Population ◽  
State Of The Art ◽  
Initial Conditions ◽  
Early Type ◽  
Barred Galaxies ◽  
Secular Evolution ◽  
Population Distributions ◽  
Type Object ◽  
Multi Phase ◽  
Metallicity Distribution

AbstractWe have performed state-of-the-art high resolution simulations of early-type galaxies with bars, including (multi-phase) gas, star formation and feedback. The aim of this programme is to better understand the observed morphology, kinematical structures, (2D) metallicity distribution, observed in fast rotators with bars. Our simulations were designed via a newly developed code allowing us to build a library of initial conditions closely mimicking barred galaxies in the Atlas3D sample. We will present the role and importance of bars on the gas fueling, redistribution of angular momentum, and overall secular evolution of fast rotators. These results are compared with actual observations (IFU, CO maps, stellar population distributions) obtained in the course of the Atlas3D project. The results from these “early-type“ simulations will also be compared in the context of recently conducted simulations of later-type barred galaxies, including one of a Milky-Way type object with a resolution down to 0.05 parsec.

scholarly journals The origin of hotspots around Sgr A*: orbital or pattern motion?

2020 ◽  
Vol 497 (2) ◽  
pp. 2385-2392
Author(s):  
Tatsuya Matsumoto ◽  
Chi-Ho Chan ◽  
Tsvi Piran
Keyword(s):  
Near Infrared ◽  
Good Alternative ◽  
Keplerian Orbit ◽  
Gravitational Radius ◽  
Circular Pattern ◽  
Pattern Motion ◽  
Best Fitting ◽  
Pattern Speed ◽  
Sgr A ◽  
Short Time

ABSTRACT The Gravity Collaboration detected a near-infrared hotspot moving around Sgr A* during the 2018 July 22 flare. They fitted the partial loop the hotspot made on the sky with a circular Keplerian orbit of radius $\simeq 7.5\, r_{\rm g}$ around the supermassive black hole (BH), where rg is the gravitational radius. However, because the hotspot traversed the loop in a short time, models in which the hotspot tracks the motion of some fluid element tend to produce a best-fitting trajectory smaller than the observed loop. This is true for a circular Keplerian orbit, even when BH spin is accounted for, and for motion along a radiatively inefficient accretion flow (RIAF) streamline. A marginally bound geodesic suffers from the same problem; in addition, it is not clear what the origin of an object following the geodesic would be. The observed hotspot motion is more likely a pattern motion. Circular motion with $r\simeq 12.5\, r_\mathrm{g}$ and a super-Keplerian speed $\simeq 0.8\, c$ is a good fit. Such motion must be pattern motion because it cannot be explained by physical forces. The pattern speed is compatible with magnetohydrodynamic perturbations, provided that the magnetic field is sufficiently strong. Circular pattern motion of radius $\sim 20\, r_{\rm g}$ on a plane above the BH is an equally good alternative; in this case, the hotspot may be caused by a precessing outflow interacting with a surrounding disc. As all our fits have relatively large radii, we cannot constrain the BH spin using these observations.

scholarly journals Relations among structural parameters in barred galaxies with a direct measurement of bar pattern speed

2020 ◽  
Vol 641 ◽  
pp. A111
Author(s):  
V. Cuomo ◽  
J. A. L. Aguerri ◽  
E. M. Corsini ◽  
V. P. Debattista
Keyword(s):  
Direct Measurement ◽  
Structural Parameters ◽  
Host Galaxies ◽  
Massive Galaxies ◽  
Barred Galaxies ◽  
Stellar Spectroscopy ◽  
Corotation Radius ◽  
Wide Range ◽  
Pattern Speed ◽  
Pattern Speeds

We investigate the relations between the properties of bars and their host galaxies in a sample of 77 nearby barred galaxies, spanning a wide range of morphological types and luminosities, with 34 SB0-SBa and 43 SBab-SBc galaxies. The sample includes all the galaxies with reliable direct measurement of their bar pattern speed based on long-slit or integral-field stellar spectroscopy using the Tremaine-Weinberg method. We limited our analysis to the galaxies with a relatively small relative error on the bar pattern speed (≤50%) and that do not host an ultrafast bar. For each galaxy, we collected the radius, strength, pattern speed, corotation radius, and rotation rate for the bar and we also collected the Hubble type and absolute SDSS r-band magnitude. We also used literature bulge-to-total luminosity ratios for a subsample of 53 galaxies with an available photometric decomposition. We confirmed earlier observational findings that longer bars rotate at lower bar pattern speeds, shorter bars are weaker, and bars with a low rate of bar rotation rotate at faster bar pattern speeds and have smaller corotation radii. In addition, we found that stronger bars rotate at lower bar pattern speeds, as predicted from the interchange of angular momentum during bar evolution, which in turn may depend on different galaxy properties. Moreover, we report that brighter galaxies host longer bars, which rotate at lower bar pattern speeds and have larger corotation radii. This result is in agreement with a scenario of downsizing in bar formation, if more massive galaxies formed earlier and had sufficient time to slow down, grow in length, and push corotation outwards.

scholarly journals Integrated Optical Phased Arrays for Beam Forming and Steering

2021 ◽  
Vol 11 (9) ◽  
pp. 4017
Author(s):  
Yongjun Guo ◽  
Yuhao Guo ◽  
Chunshu Li ◽  
Hao Zhang ◽  
Xiaoyan Zhou ◽  
...  
Keyword(s):  
Near Infrared ◽  
Phased Arrays ◽  
Mechanical Stability ◽  
Building Blocks ◽  
High Yield ◽  
Beam Forming ◽  
Integrated Optical ◽  
Optical Phased Arrays ◽  
Infrared Spectral ◽  
Spectral Ranges

Integrated optical phased arrays can be used for beam shaping and steering with a small footprint, lightweight, high mechanical stability, low price, and high-yield, benefiting from the mature CMOS-compatible fabrication. This paper reviews the development of integrated optical phased arrays in recent years. The principles, building blocks, and configurations of integrated optical phased arrays for beam forming and steering are presented. Various material platforms can be used to build integrated optical phased arrays, e.g., silicon photonics platforms, III/V platforms, and III–V/silicon hybrid platforms. Integrated optical phased arrays can be implemented in the visible, near-infrared, and mid-infrared spectral ranges. The main performance parameters, such as field of view, beamwidth, sidelobe suppression, modulation speed, power consumption, scalability, and so on, are discussed in detail. Some of the typical applications of integrated optical phased arrays, such as free-space communication, light detection and ranging, imaging, and biological sensing, are shown, with future perspectives provided at the end.

scholarly journals Double X/Peanut Structures in Barred Galaxies – Insights from an N–body Simulation

2020 ◽  
Author(s):  
Bogdan C Ciambur ◽  
Francesca Fragkoudi ◽  
Sergey Khoperskov ◽  
Paola Di Matteo ◽  
Françoise Combes
Keyword(s):  
Dark Matter ◽  
Milky Way ◽  
Large Fraction ◽  
Formation Time ◽  
Dark Matter Halo ◽  
Barred Galaxies ◽  
Pattern Speed ◽  
Nearby Galaxies ◽  
Dynamical Instabilities ◽  
Bow Tie

Abstract Boxy, peanut– or X–shaped “bulges” are observed in a large fraction of barred galaxies viewed in, or close to, edge-on projection, as well as in the Milky Way. They are the product of dynamical instabilities occurring in stellar bars, which cause the latter to buckle and thicken vertically. Recent studies have found nearby galaxies that harbour two such features arising at different radial scales, in a nested configuration. In this paper we explore the formation of such double peanuts, using a collisionless N–body simulation of a pure disc evolving in isolation within a live dark matter halo, which we analyse in a completely analogous way to observations of real galaxies. In the simulation we find a stable double configuration consisting of two X/peanut structures associated to the same galactic bar – rotating with the same pattern speed – but with different morphology, formation time, and evolution. The inner, conventional peanut-shaped structure forms early via the buckling of the bar, and experiences little evolution once it stabilises. This feature is consistent in terms of size, strength and morphology, with peanut structures observed in nearby galaxies. The outer structure, however, displays a strong X, or “bow-tie”, morphology. It forms just after the inner peanut, and gradually extends in time (within 1 to 1.5 Gyr) to almost the end of the bar, a radial scale where ansae occur. We conclude that, although both structures form, and are dynamically coupled to, the same bar, they are supported by inherently different mechanisms.

scholarly journals Exploring the inner parsecs of active galactic nuclei using near-infrared high resolution polarimetric simulations with MontAGN

2018 ◽  
Vol 612 ◽  
pp. A69 ◽  
Author(s):  
L. Grosset ◽  
D. Rouan ◽  
D. Gratadour ◽  
D. Pelat ◽  
J. Orkisz ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Optical Depth ◽  
Near Infrared ◽  
Galactic Nuclei ◽  
Constant Density ◽  
Characteristic Model ◽  
Infrared Observations ◽  
Current Estimation ◽  
Direct Light ◽  
Ngc 1068

Aims. In this paper we aim to constrain the properties of dust structures in the central first parsecs of active galactic nuclei (AGN). Our goal is to study the required optical depth and composition of different dusty and ionised structures. Methods. We developed a radiative transfer code called Monte Carlo for Active Galactic Nuclei (MontAGN), which is optimised for polarimetric observations in the infrared. With both this code and STOKES, designed to be relevant from the hard X-ray band to near-infrared wavelengths, we investigate the polarisation emerging from a characteristic model of the AGN environment. For this purpose, we compare predictions of our models with previous infrared observations of NGC 1068, and try to reproduce several key polarisation patterns revealed by polarisation mapping. Results. We constrain the required dust structures and their densities. More precisely, we find that the electron density inside the ionisation cone is about 2.0 × 109 m−3. With structures constituted of spherical grains of constant density, we also highlight that the torus should be thicker than 20 in term of K-band optical depth to block direct light from the centre. It should also have a stratification in density: a less dense outer rim with an optical depth at 2.2 μm typically between 0.8 and 4 for observing the double scattering effect previously proposed. Conclusions. We bring constraints on the dust structures in the inner parsecs of an AGN model supposed to describe NGC 1068. When compared to observations, this leads to an optical depth of at least 20 in the Ks band for the torus of NGC 1068, corresponding to τV ≈ 170, which is within the range of current estimation based on observations. In the future, we will improve our study by including non-uniform dust structures and aligned elongated grains to constrain other possible interpretations of the observations.

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