Non-axisymmetric Potentials Research Articles

Fueling Processes on (Sub-)kpc Scales

Since the 1970s, astronomers have struggled with the issue of how matter can be accreted to promote black-hole growth. While low-angular-momentum stars may be devoured by a black hole, they are not a sustainable source of fuel. Gas, which could potentially provide an abundant fuel source, presents another challenge due to its enormous angular momentum. While viscous torques are not significant, gas is subject to gravity torques from non-axisymmetric potentials such as bars and spirals. Primary bars can exchange angular momentum with the gas within corotation, causing it to spiral inwards until reaching the inner Lindblad resonance. An embedded nuclear bar can then take over. As the gas reaches the black hole’s sphere of influence, the torque becomes negative, fueling the center. Dynamical friction also accelerates the infall of gas clouds closer to the nucleus. However, because of the Eddington limit, growing a black hole from a stellar-mass seed is a slow process. The existence of very massive black holes in the early universe remains a puzzle that could potentially be solved through direct collapse of massive clouds into black holes or super-Eddington accretion.

The spatially resolved gas and dust connection in neutral inflows and outflows in nearby AGN

ABSTRACT Dusty, neutral outflows and inflows are a common feature of nearby star-forming galaxies. We characterize these flows in eight galaxies – mostly active galactic nuclei (AGN) – selected for their widespread Na i D signatures from the Siding Spring Southern Seyfert Spectroscopic Snapshot Survey (S7). This survey employs deep, wide field-of-view (FOV) integral field spectroscopy at moderate spectral resolution (R = 7000 at Na i D). We significantly expand the sample of sightlines in external galaxies in which the spatially resolved relationship has been studied between cool, neutral gas properties – N(Na i), Weq(Na i D) – and dust – E(B − V) from both stars and gas. Our sample shows strong, significant correlations of total Weq with E(B − V)⋆ and g − i colour within individual galaxies; correlations with E(B − V)gas are present but weaker. Regressions yield slope variations from galaxy to galaxy and intrinsic scatter ∼1 Å. The sample occupies regions in the space of N(Na i) and $W_\mathrm{eq}^\mathrm{abs}$ versus E(B − V)gas that are consistent with extrapolations from other studies to higher colour excess [E(B − V)gas ∼ 1]. For perhaps the first time in external galaxies, we detect inverse P Cygni profiles in the Na i D line, presumably due to inflowing gas. Via Doppler-shifted Na i D absorption and emission lines, we find ubiquitous flows that differ from stellar rotation by $\gtrsim$100 km s−1 or have $|v_{\mathrm{ abs}} - v_{\mathrm{ em}}|\gtrsim 100$ km s−1. Inflows and outflows extend towards the edge of the detected stellar disc/FOV, together subtend 10–40 per cent of the projected disc, and have similar mean N(Na i) and Weq(Na i D). Outflows are consistent with minor axis or jet-driven flows, while inflows tend towards the projected major axis. The inflows may result from non-axisymmetric potentials, tidal motions, or halo infall.

Tracing Stellar Close Encounters with Our Sun from GAIA DR2, LAMOST DR4, and RAVE DR5 Catalogues

Our Sun is surrounded by the Oort Cloud (in radius 0.5 pc) which can be perturbed by various external factors. One of those is the stellar close encounter with our Sun. This kind of perturbation can induce the cometary showers in our Solar System. In this work, we attempt to make numerical simulations to trace the orbit of stars which close encounter with our Sun in the cases of Milky Way’s axisymmetric only and with non-axisymmetric potentials. We have 306 selected solar neighborhood stars from GAIA DR2, LAMOST DR4, and RAVE DR5 which have highly precise kinematics.In this work, we find a few stars that have counter parameter (dm) less than or equal to 2 pc in both of past and future close encounters with the Sun. We also find a few stars (ID 283, 290, 297, 298) even with dm ≤ 0.5 pc within their errors, for past close encounters at time tm ≥ 0.5 Myr ago. These stars should have perturbed the Oort Cloud’s stability long time ago. Furthermore, we find a few stars (ID 293, 299, 300) with dm ≤ 1 pc within their errors, at tm > 0.6 Myr for future close encounters. Besides that,cadding non-axisymmetric component of Milky Way does not change the results. This suggests that the non-axisymmetric component of Milky Way potential has small effect in perturbing the orbital motion of stars for short timescale. That’s why the values of dm are relatively similar within their errors, for both cases of the Milky Way potential.

Integrals of motion for non-axisymmetric potentials

Context. The modelling of stationary galactic stellar populations can be performed using distribution functions. Aims. This paper aims to write explicit integrals of motion and distribution functions. Methods. We propose an analytic formulation of the integrals of motion with an explicit dependence on potential. This formulation applies to potentials with rotational symmetry or triaxial symmetry. It is exact for Stäckel potentials and approximate for other potentials. Results. Modelling a stationary stellar population using these integrals of motion allows the force field to be found with satisfactory accuracy. On the other hand, the mass density distribution that generates the force field and the gravitational potential is recovered with less accuracy due to lower precision in modelling box-type orbits.

IFU spectroscopy of 10 early-type galactic nuclei – III. Properties of the circumnuclear gas emission

Many Early-type galaxies (ETG) have ionized gas emission in their centres that extends to scales of ~ 1kpc. The majority of such objects are classified as LINERs, but the nature of their ionizing source is still not clear. The kinematics associated with these gaseous structures usually shows deviations from a pure rotational motion due to non-gravitational effects or to non-axisymmetric potentials. This is the third of a series of papers that describes a sample of 10 nearby and massive ETG observed with the Gemini Multi-Object Spectrograph in Integral Field mode installed on the Gemini-South telescope. In paper II, we performed spectral synthesis to subtract the stellar components from the data cubes of the sample galaxies in order to study their nuclear spectra. Here, we analyse the circumnuclear gas emission (scales of ~ 100 pc) of the sample galaxies. Circumnuclear gas emission was detected in seven galaxies, all of them classified as LINERs. Pure gaseous discs are found in three galaxies. In two objects, gaseous discs are probably present, but their kinematics are affected by non-Keplerian motions. In IC 5181, we detected a spiral structure of gas that may be caused either by a non-axisymmetric potential or by an outflow together with a gaseous disc. In NGC 3136, an ionization bicone is present in addition to five compact structures with LINER-like emission. In galaxies with a gaseous disc, we found that ionizing photons emitted by an AGN are not enough to explain the observed Ha flux along this structure. On the other hand, the Ha flux distribution and equivalent width along the direction perpendicular the gaseous disc suggest the presence of low-velocity ionized gas emission which seem to be related to the nuclear activity. We propose a scenario for LINER-like circumnuclear regions where a low-velocity ionization cone is formed by a collimating agent aligned with the gaseous disc.

Simulations of Recoiling Massive Black Holes

AbstractThe coalescence of black hole binaries is a significant source of gravitational wave radiation. The typically asymmetric nature of this emission, which carries linear momentum, can result in the recoil of the black hole remnant with velocities in the range 100 < Vrecoil < 3750 km s−1. The detectability of recoiling massive black holes (MBH) as off-nuclear QSOs is tightly connected with the properties of the host galaxy, which determine the MBH's orbit and fuel reservoir. We present the results of N-body simulations of recoiling MBHs in high-resolution, non-axisymmetric potentials. We find that if the recoil velocities are high enough to reach regions of the galaxy dominated by the generally triaxial dark matter distribution, the return time is significantly extended when compared to a spherical distribution. We also perform simulations of recoiling MBHs traveling in gas merger remnants, where large amounts of gas have been funneled to the central regions, In this case, the MBHs remain within R<1 kpc from the center of the host even for high recoil velocities (Vrecoil = 1200 km s−1) due to the compactness of the remnant galaxy's nuclear disk. We discuss the implications of both scenarios for detectability.

CONSTRAINING THE NFW POTENTIAL WITH OBSERVATIONS AND MODELING OF LOW SURFACE BRIGHTNESS GALAXY VELOCITY FIELDS

We model the NFW potential to determine if, and under what conditions, the NFW halo appears consistent with the observed velocity fields of low surface brightness (LSB) galaxies. We present mock DensePak IFU velocity fields and rotation curves of axisymmetric and non-axisymmetric potentials that are well-matched to the spatial resolution and velocity range of our sample galaxies. We find that the DensePak IFU can accurately reconstruct the velocity field produced by an axisymmetric NFW potential and that a tilted-ring fitting program can successfully recover the corresponding NFW rotation curve. We also find that non-axisymmetric potentials with fixed axis ratios change only the normalization of the mock velocity fields and rotation curves and not their shape. The shape of the modeled NFW rotation curves does not reproduce the data: these potentials are unable to simultaneously bring the mock data at both small and large radii into agreement with observations. Indeed, to match the slow rise of LSB galaxy rotation curves, a specific viewing angle of the non-axisymmetric potential is required. For each of the simulated LSB galaxies, the observer's line-of-sight must be along the minor axis of the potential, an arrangement which is inconsistent with a random distribution of halo orientations on the sky.

Hiding cusps in cores: kinematics of disc galaxies in triaxial dark matter haloes

We study the kinematics of gaseous discs in triaxial dark matter haloes using the closed-loop orbit solutions in non-axisymmetric potentials. The orbits are in general non-circular and, for a given triaxiality, their ellipticity depends on the ratio of escape to circular velocities, V2esc/V2c. This ratio increases steeply towards the centre for cold dark matter (CDM) halo density profiles, implying that even minor deviations from spherical symmetry may induce large deviations from circular orbits in the velocity field of a gaseous disc, especially near the centre. This result suggests that caution should be exercised when interpreting constraints on the presence of density cusps in the dark halo derived from the innermost velocity profile. Simulated long-slit rotation curves vary greatly in shape, depending primarily on the viewing angle of the disc and on its orientation relative to the principal axes of the potential. ‘Solid-body’ rotation curves – typically interpreted as a signature of a constant density core in the dark matter distribution – are often obtained when the slit samples velocities near the major axis of the closed-loop orbits. Triaxial potentials imprint specific symmetries in 2D velocity fields, generally inducing ‘twists’ in the isovelocity contours and antisymmetric patterns in opposite quadrants. We suggest that triaxial haloes may be responsible for the variety of shapes of long-slit rotation curves of low surface brightness (LSB) galaxies, as well as for the complex central kinematics of LSBs, which are sometimes ascribed to the presence of ‘radial motions’ in the gas. We argue that LSB rotation curves might be reconciled with the structure of CDM haloes once the effects of halo triaxiality on the dynamics of gaseous discs are properly taken into account.

Formation of Nuclear Spirals in Barred Galaxies

We have performed smoothed particle hydrodynamics (SPH) simulations for the response of the gaseous disk to the imposed moderately strong non-axisymmetric potentials. The model galaxies are composed of the three stellar components (disk, bulge and bar) and two dark ones (supermassive black hole and halo) whose gravitational potentials are assumed to be invariant in time in the frame corotating with the bar. We found that the torques alone generated by the moderately strong bar that gives the maximum of tangential-to-radial force ratio as $(F_{Tan}/F_{Rad})_{max}= 0.3$ are not sufficient to drive the gas particles close to the center due to the barrier imposed by the inner Lindblad resonances (ILRs). In order to transport the gas particles towards the nucleus ($r<100$ pc), a central supermassive black hole (SMBH) and high sound speed of the gas are required to be present. The former is required to remove the inner inner Lindblad resonance (IILR) that prevents gas inflow close to the nucleus, while the latter provides favourable conditions for the gas particles to lose their angular momentum and to spiral in. Our models that have no IILR show the trailing nuclear spirals whose innermost parts reach close to the center in a curling way when the gas sound speed is $ c_{s} \gtrsim 15$ km s$^{-1}$. They resemble the symmetric two-armed nuclear spirals observed in the central kiloparsec of spiral galaxies. We found that the symmetric two-armed nuclear spirals are formed by the hydrodynamic spiral shocks caused by the gravitational torque of the bar in the presence of a central SMBH that can remove IILR when the sound speed of gas is high enough to drive a large amount of gas inflow deep inside the ILR. However, the detailed morphology of nuclear spirals depends on the sound speed of gas.

On Bars, Bulges, and the Fueling of Active Galactic Nuclei

Both the fueling of a central black hole and the buildup of bulges are—at least theoretically—facilitated by nonaxisymmetric potentials. It is argued here that the recently established surface brightness division between bulge-dominated galaxies that dominate the local type 2 active galactic nucleus (AGN) luminosity function and disk-dominated galaxies that host (at best) weak AGNs can be understood in terms of a simple bar-instability criterion.

SECULAR EVOLUTION OF BARRED GALAXIES

Owing to several observational evidences and theoretical predictions for morphological evolution of galaxies, it is now widely accepted that galaxies do evolve from late types to early ones along the Hubble sequence. It is also well established that non-axisymmetric potentials of bar-like or oval mass distributions can change the morphology of galaxies significantly during the Hubble time. Here, we review the observational and theoretical grounds of the secular evolution driven by bar-like potentials, and present the results of SPH simulations for the response of the gaseous disks to the imposed potentials to explore the secular evolution in the central regions of barred galaxies.

Dissipative motion in galaxies with non-axisymmetric potentials

In contrast to the case of most other topics treated in this volume, it is not clear whether galactic gas dynamics can be discussed in terms of standard hydrodynamics. Nevertheless, it is clear that certain generic properties related to orbital structure in a given potential and the effect of dissipation can be used to understand qualitatively gas motion in galaxies. The effect of dissipation is examined in triaxial galaxy potentials with and without rotating time-dependent components. In the former case, dissipative trajectories settle around closed-loop orbits when these exist. When they do not, e.g., inside a constant density core, then the only attractor is the centre and this leads to mass inflow. This provides a self-regulating mechanism for accession of material towards the centre – since the formation of a central masses destroys the central density core and eventually stops the accession. In the case when a rotating bar is present, there are usually several types of attractors, including those on which long-lived chaotic motion can occur (strange attractors). Motion on these is erratic with large radial and vertical oscillations.

A map for eccentric orbits in non-axisymmetric potentials

We construct a simple symplectic map to study the dynamics of eccentric orbits in non-spherical potentials. The map offers a dramatic improvement in speed over traditional integration methods, while accurately representing the qualitative details of the dynamics. We focus attention on planar, non-axisymmetric power-law potentials, in particular the logarithmic potential. We confirm the presence of resonant orbit families (``boxlets'') in this potential and uncover new dynamics such as the emergence of a stochastic web in nearly axisymmetric logarithmic potentials. The map can also be applied to triaxial, lopsided, non-power-law and rotating potentials.

Obscuration in the Host Galaxies of Soft X‐Ray–selected Seyfert Nuclei

We define a new sample of 96 low-redshift (z < 0.1), soft X-ray-selected Seyfert galaxies from the catalog of the Einstein Slew Survey. We probe the geometry and column depth of obscuring material in the host-galaxy disks using galactic axial ratios determined mainly from the Digitized Sky Survey. The distribution of host-galaxy axial ratios clearly shows a bias against edge-on spirals, which confirms the existence of a geometrically thick layer of obscuring material in the host-galaxy planes. Soft X-ray selection recovers some of the edge-on objects missed in UV and visible surveys but still results in 30% incompleteness for type 1 nuclei. We speculate that thick rings of obscuring material such as the ones we infer for these Seyfert galaxies might be commonly present in early-type spirals, sitting at the inner Lindblad resonances of the nonaxisymmetric potentials of the host galaxies.

Rapidly Rotating Circumnuclear Gas Disks in Virgo Disk Galaxies

From a set of 80 Virgo cluster galaxies for which we have obtained high-resolution, long-slit spectra near H , we have identified 14 with interesting circumnuclear (CN) properties. These 14 galaxies exhibit rapidly rotating, discrete gas disks extending of order 500 pc from the nucleus. Peak CN disk velocities match well the outer disk maximum velocity. Masses interior to the outer edge of the CN disk range from some to a few 10<SUP>10</SUP> M<SUB>sun</SUB>, about 3% or 4% of the mass interior to R<SUB>25</SUB>. Clear counterrotation is observed in only one galaxy, the previously discussed NGC 4550. While discrete circumnuclear disks are well studied in early-type galaxies, few are known in types Sb or later. Our sample includes types E7/S0 to Sc; half are Sb or later. The frequency of discrete CN components is higher for early-type galaxies. For eight of these galaxies, morphological and kinematic evidence clearly identifies the discrete components as disks. For a few, we have evidence that a stellar disk is corotating with the gas. Many of these galaxies are barred, some weakly; the CN disks exist within the more extended bars. We suggest that gravitational interactions and/or nonaxisymmetric potentials have caused gas to be funneled to the nucleus where it forms the kinematically distinct CN disk. It is likely that we have detected only a fraction of the discrete CN features. Hence, the true frequency may approach 50% for bright galaxies in the Virgo cluster.

Radial ion transport measurements in a nonaxisymmetric magnetic mirror

Experimental radial ion transport rates and diffusion coefficients are presented for the Constance-B magnetic mirror [Phys. Rev. Lett. 58, 1853 (1987)]. The transport experiments are performed by measuring steady state equilibrium radial profiles of plasma density, ionization source, end loss current, electric field, electron temperature, and ion temperature. A charge coupled device (CCD) camera system [Rev. Sci. Instrum. 60, 2835 (1989)] is used to measure the two-dimensional radial density, source, and electron temperature profiles. End loss diagnostics including movable Faraday cups, electrostatic end loss analyzers, and an ion time-of-flight analyzer [Rev. Sci. Instrum. 59, 601 (1988)] are used to measure radial profiles of potential and ion temperature. The ion confinement time perpendicular to the magnetic field is found to be an order of magnitude shorter than predicted by classical and neoclassical transport theories. The radial profiles of the perpendicular diffusion coefficient (D⊥) are presented for hydrogen, helium, and argon plasmas. The coefficients are a factor of 10 larger than the maximum classical and neoclassical coefficients in all three plasmas. Plasma fluctuations resulting from whistler mode microinstability [Phys. Rev. Lett. 59, 1821 (1987)] as well as nonaxisymmetric potentials are suggested as possible explanations for the experimentally measured radial transport rate.

Fueling Activity in Galactic Nucleia

Theoretical models developed to explain the high luminosity of AGN are discussed, reviewing the results of recent investigations. It is pointed out that, whereas most models involve a central supermassive black hole accreting matter from the surrounding medium, various hypotheses as to the nature of the accreted material have been proposed. Consideration is given to nuclear sources (dense central star clusters or the tidal disruption of stars), galactic sources (stellar mass loss or torques in nonaxisymmetric potentials), and extragalactic sources (the infall of intergalactic gas or the accretion of gas-rich dwarfs). A hierarchical framework linking these mechanisms is outlined, and results obtained with the gasdynamic simulation code TREESPH (Hernquist and Katz, 1989) are presented in graphs and briefly characterized. 72 refs.

Internal kinematics of spiral galaxies - Gas and stellar rotation curves and dispersion profiles

view Abstract Citations (77) References (40) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Internal Kinematics of Spiral Galaxies: Gas and Stellar Rotation Curves and Dispersion Profiles Fillmore, J. A. ; Boroson, T. A. ; Dressler, A. Abstract Emission- and absorption-line observations of six moderately inclined spiral galaxies are presented. The mean rotation and velocity dispersion for the gas and the stars have been measured. Two component mass models are fitted to surface brightness measurements are used to fit kinematic models to the velocity data. Models with constant mass-to-light ratios and isotropic velocity dispersions roughly fit the inner regions of spiral galaxies with three caveats: (1) several galaxies show significant kinematic differences between the two sides of the galaxy. While the differences might be caused by nonaxisymmetric potentials, variations in the line-of-sight extinction are a more likely cause; (2) the inner portion (R less than of equal to 1 kpc) of the emission-line (gas) rotation curve falls below the predicted circular velocity. Because the model circular velocities are computed from the observed stellar velocities, variations in the total mass-to-light ratio will not change the model values. It is noted that gas lost from bulge giants (planetary nebulae) will have a significant noncircular velocity component. It is shown that these emitted clouds live a sufficient time to explain the lower-than-circular velocity of the emission-line rotation curves; Some of the bulges are flatter than one would expect from their rotation rate, assuming isotropic random motions, but this additional flattening could be caused by the disk potential. Publication: The Astrophysical Journal Pub Date: March 1986 DOI: 10.1086/163984 Bibcode: 1986ApJ...302..208F Keywords: Galactic Structure; Spiral Galaxies; Stellar Rotation; Absorption Spectra; Emission Spectra; Kinematics; Line Spectra; Mass To Light Ratios; Radial Velocity; Tables (Data); Astrophysics; GALAXIES: INTERNAL MOTIONS; GALAXIES: STRUCTURE full text sources ADS | data products SIMBAD (6) NED (6)

Value distribution of potentials in three real variables

The object of this paper is to study the value distribution of potentials in three real variables by means of the Bergman integral operator with methods drawn from the analytic theory of polynomials. In this paper we obtain results on the value distribution of nonaxisymmetric potentials which generalize recent papers of the author [3] and of Morris Marden [2] which treat the value distribution of axisymmetric potentials, generalized axisymmetric potentials, and in Marden's paper, some special classes of harmonic polynomials in three real variables. Let (x, y, z) be a point in E3. A function 1i=T(x, y, z) with continuous second partial derivatives in a domain G shall be referred to as a potential if it satisfies (1) Tcx +Tyy + Tzz = O in G. Bergman has shown [1, p. 43] that potentials are generated by the integral operator (2) T(x, y, z) = t f f(, ()4` dt where the functionf(r, 4) which is the associate of T is an analytic function of T for all T over some region Q in the complex plane and continuous in ;, for 4 over the contour Y with (3) z = x + 1(iy + Z) + (iy-Z) The Bergman operator (2) shall be designated by (4) 'F(x, y, z) = B(f, Y, X), X = (x, y, z). Presented to the Society, June 17, 1972; received by the editors February 7, 1972 and, in revised form, May 8, 1972. AMS (MOS) subject classifications (1970). Primary 31B05, 44A15; Secondary 30A08, 30A70. 1 This paper is based on a part of the author's Ph.D. dissertation which was directed by Professor Morris Marden at the University of Wisconsin-Milwaukee. ? American Mathematical Society 1973