Counter-rotating Component Research Articles

Constraining photon trajectories in black hole shadows

We examine the shadow cast by a Kerr black hole, focusing on constraints on photons corresponding to different shadow boundaries. The photons are related to different orbital ranges and impact parameter values, creating a map of the shadow boundaries. Our analysis fixes also the conditions under which it is possible to observe an “imprint” of the black hole (outer) ergosurface and (outer) ergoregion on the Kerr black hole shadow boundary. The counter-rotating case resulted strongly constrained with respect to the co-rotating case, constituting a remarkable and significant difference where the counter-rotating component associated with the shadow boundary is strongly distinct from the co-rotating one. However, in this framework, even the co-rotating photons imply restrictions on conditions on the spins and planes, which are bounded by limiting values. We believe the results found here, being a tracer for the central black hole, can constitute new templates for the ongoing observations.

Gas and stellar kinematic misalignment in MaNGA galaxies: What is the origin of counter-rotating gas?

Context. Kinematic misalignment between gas and stellar components is observed in a certain fraction of galaxies. It believed to be caused by the acquisition of gas from the external reservoir by, for example, major or minor mergers, accretion from cosmological filaments, or the circumgalactic medium. Aims. We aim to constrain the possible sources of the gas that forms the counter-rotating component. Methods. We derived the gas-phase oxygen abundances of 69 galaxies with a kinematic misalignment between gas and stellar components from the MaNGA DR17 survey and compared them with the metallicity expected according to the mass–metallicity relation. Results. We find that the oxygen abundance of the counter-rotating gas in our sample is higher than 8.2 dex, which rules out a significant role for the inflow of pristine gas. Meanwhile, there is a significant difference in the oxygen abundance of the counter-rotating gas between red and blue galaxies. In general, the oxygen abundance is lower than expected for the stellar mass in red galaxies but is compatible with or even higher than typical values for the stellar mass in blue galaxies. Conclusions. We show that the exchange of enriched gas between galaxies is the most plausible mechanism for explaining the metallicity of counter-rotating gas components in galaxies of all masses and colors. Meanwhile, minor mergers may play a significant role in the formation of counter-rotating gas components in red and quenched galaxies.

Deciphering the origin of ionized gas in IC 1459 with VLT/MUSE

ABSTRACT IC 1459 is an early-type galaxy (ETG) with a rapidly counter-rotating stellar core, and is the central galaxy in a gas-rich group of spirals. In this work, we investigate the abundant ionized gas in IC 1459 and present new stellar orbital models to connect its complex array of observed properties and build a more complete picture of its evolution. Using the Multi-Unit Spectroscopic Explorer (MUSE), the optical integral field unit (IFU) on the Very Large Telescope (VLT), we examine the gas and stellar properties of IC 1459 to decipher the origin and powering mechanism of the galaxy’s ionized gas. We detect ionized gas in a non-disc-like structure rotating in the opposite sense to the central stars. Using emission-line flux ratios and velocity dispersion from full-spectral fitting, we find two kinematically distinct regions of shocked emission-line gas in IC 1459, which we distinguished using narrow (σ ≤ 155 km s−1) and broad (σ > 155 km s−1) profiles. Our results imply that the emission-line gas in IC 1459 has a different origin than that of its counter-rotating stellar component. We propose that the ionized gas is from late-stage accretion of gas from the group environment, which occurred long after the formation of the central stellar component. We find that shock heating and AGN activity are both ionizing mechanisms in IC 1459 but that the dominant excitation mechanism is by post-asymptotic giant branch stars from its old stellar population.

Investigation of electron vortices in time-delayed circularly polarized laser pulses with a semiclassical perspective.

We theoretically investigate strong-filed electron vortices in time-delayed circularly polarized laser pulses by a generalized quantum-trajectory Monte Carlo (GQTMC) model. Vortex interference patterns in photoelectron momentum distributions (PMDs) with various laser parameters can be well reproduced by the semiclassical simulation. The phase difference responsible for the interference structures is analytically identified through trajectory-based analysis and simple-man theory, which reveal the underlying mechanism of electron vortex phenomena for both co-rotating and counter-rotating component. This semiclassical analysis can also demonstrate the influences of laser intensity and wavelength on the number of arms of vortices. Furthermore, we show the influence of the Coulomb effect on the PMDs. Finally, the controlling of the ionization time intervals in the tens to hundreds of attosecond magnitude is qualitatively discussed.

Numerical simulation of wave mode transition in rotating detonation engine with OpenFOAM

Two-dimensional numerical simulations of rotating detonation engine are carried out with detailed chemical kinetic mechanism using detoFoam, a custom solver based on OpenFOAM 7. The results show the transition process from single wave with counter-rotating components mode to two counter-rotating waves at equal speed mode. Counter-rotating components are weak waves propagating in the opposite direction against the primary detonation wave. The mechanism behind the transition process is that the counter-rotating components gain energy from collisions with detonation waves and the fresh gas region. When counter-rotating components gain more energy than they lose in one cycle, they become stronger until the peak pressure reaches a threshold value. When a counter-rotating component is strong enough, its collision with fresh gas region will ignite a detonation wave, breaking the steady state. The new detonation wave propagates in the opposite direction against the original detonation wave, leading to the formation of two counter-rotating detonation waves.

Possibility of Direct Observation of the Bloch—Siegert Shift in Coherent Dynamics of Multiphoton Raman Transitions

We study Rabi oscillations of the second-order Raman transition realized on dressed states of a qubit excited by an amplitude-modulated microwave field. The co-rotating component of the ultrastrong low-frequency modulation field excites virtual multiple photon processes between the dressed states and forms the Rabi frequency in the so-called rotating wave approximation (RWA). The counter-rotating modulation component also gives a significant contribution to the Rabi frequency owing to the Bloch--Siegert effect. It is shown that for properly chosen parameters of the modulation field and qubit, the Rabi oscillations in the RWA vanish due to destructive interference of multiple photon processes. In this case the Rabi oscillation results exclusively from the Bloch--Siegert effect and is directly observed in the time-resolved coherent dynamics as the Bloch--Siegert oscillation. Correspondingly, in Fourier spectra of the coherent response, triplets are transformed into doublets with the splitting between the lines equal to twice the Bloch--Siegert shift. We demonstrate these features by calculations of the qubit's evolution in the conditions of experiments with a NV center in diamond, where Raman transitions were observed. The direct observation of the Bloch--Siegert oscillation offers new possibilities for studying driven quantum systems in the ultastrong regime.

Spotting a counter-rotating galaxy

AbstractThe presence of counter-rotating (CR) components in galaxies is not that rare but their origin is still unclear. Important clues to the formation and evolution of CR galaxies are provided by galaxy kinematics, such as the mass distribution and the shape of the gravitational potential. In order to better understand the origin and incidence of CR galaxies, we aim at modeling CR stellar disks, as they would be observed with Integral Field Units (IFU) instruments, and measuring the kinematics of these peculiar astrophysical objects to reveal the CR signatures. In the bi-dimensional maps of analysed models, the double sigma signature is the best diagnostic to spot the presence of a CR disk component.

Strong coupling of a two-dimensional electron ensemble to a single-mode cavity resonator

We investigate the regime of strong coupling of an ensemble of two-dimensional electrons to a single-mode cavity resonator. In particular, we realized such a regime of light-matter interaction by coupling the cyclotron motion of a collection of electrons on the surface of liquid helium to the microwave field in a semi-confocal Fabry-Perot resonator. For the co-rotating component of the microwave field, the strong coupling is pronouncedly manifested by the normal-mode splitting in the spectrum of coupled field-particle motion. We present a complete description of this phenomenon based on classical electrodynamics, as well as show that the full quantum treatment of this problem results in mean-value equations of motion that are equivalent to our classical result. For the counter-rotating component of the microwave field, we observe a strong resonance when the microwave frequency is close to both the cyclotron and cavity frequencies. We show that this surprising effect, which is not expected to occur under the rotating-wave approximation, results from the mixing between two polarization components of the microwave field in our cavity.

Vacuum Bloch–Siegert shift in Landau polaritons with ultra-high cooperativity

A two-level system resonantly interacting with an a.c. magnetic or electric field constitutes the physical basis of diverse phenomena and technologies. However, Schrodinger’s equation for this seemingly simple system can be solved exactly only under the rotating-wave approximation, which neglects the counter-rotating field component. When the a.c. field is sufficiently strong, this approximation fails, leading to a resonance-frequency shift known as the Bloch–Siegert shift. Here, we report the vacuum Bloch–Siegert shift, which is induced by the ultra-strong coupling of matter with the counter-rotating component of the vacuum fluctuation field in a cavity. Specifically, an ultra-high-mobility two-dimensional electron gas inside a high-Q terahertz cavity in a quantizing magnetic field revealed ultra-narrow Landau polaritons, which exhibited a vacuum Bloch–Siegert shift up to 40 GHz. This shift, clearly distinguishable from the photon-field self-interaction effect, represents a unique manifestation of a strong-field phenomenon without a strong field. The Bloch–Siegert shift—a strong-field phenomenon that implies a failure of the rotating-wave approximation—is observed in the polariton dispersion diagram of a two-dimensional electron gas system inside a high-Q terahertz photonic crystal cavity.

Kinematic and stellar population properties of the counter-rotating components in the S0 galaxy NGC 1366

Context. Many disk galaxies host two extended stellar components that rotate in opposite directions. The analysis of the stellar populations of the counter-rotating components provides constraints on the environmental and internal processes that drive their formation. Aims. The S0 NGC 1366 in the Fornax cluster is known to host a stellar component that is kinematically decoupled from the main body of the galaxy. Here we successfully separated the two counter-rotating stellar components to independently measure the kinematics and properties of their stellar populations. Methods. We performed a spectroscopic decomposition of the spectrum obtained along the galaxy major axis and separated the relative contribution of the two counter-rotating stellar components and of the ionized-gas component. We measured the line-strength indices of the two counter-rotating stellar components and modeled each of them with single stellar population models that account for the {\alpha}/Fe overabundance. Results. We found that the counter-rotating stellar component is younger, has nearly the same metallicity, and is less {\alpha}/Fe enhanced than the corotating component. Unlike most of the counter-rotating galaxies, the ionized gas detected in NGC 1366 is neither associated with the counter-rotating stellar component nor with the main galaxy body. On the contrary, it has a disordered distribution and a disturbed kinematics with multiple velocity components observed along the minor axis of the galaxy. Conclusions. The different properties of the counter-rotating stellar components and the kinematic peculiarities of the ionized gas suggest that NGC 1366 is at an intermediate stage of the acquisition process, building the counter-rotating components with some gas clouds still falling onto the galaxy.

Disk heating and bending instability in galaxies with counterrotation

With the help of high-resolution long-slit and integral-field spectroscopy observations, the number of confirmed cases of galaxies with counterrotation is increasing rapidly. The evolution of such counterrotating galaxies remains far from being well understood. In this paper we study the dynamics of counterrotating collisionless stellar disks by means ofN-body simulations. We show that, in the presence of counterrotation, an otherwise gravitationally stable disk can naturally generate bending waves accompanied by strong disk heating across the disk plane, that is in the vertical direction. Such a conclusion is found to hold even for dynamically warm systems with typical values of the initial vertical-to-radial velocity dispersion ratioσz/σR≈ 0.5, for which the role of pressure anisotropy should be unimportant. We note that, during evolution, theσz/σRratio tends to rise up to values close to unity in the case of locally Jeans-stable disks, whereas in disks that are initially Jeans-unstable it may reach even higher values, especially in the innermost regions. This unusual behavior of theσz/σRratio in galaxies with counterrotation appears not to have been noticed earlier. Our investigations of systems made of two counterrotating components with different mass-ratios suggest that even apparently normal disk galaxies (i.e., with a minor counterrotating component so as to escape detection in current observations) might be subject to significant disk heating especially in the vertical direction.

Stellar counter-rotation in lenticular galaxy NGC 448

The counter-rotation phenomenon in disc galaxies directly indicates a complex galaxy assembly history which is crucial for our understanding of galaxy physics. Here we present the complex data analysis for a lenticular galaxy NGC 448, which has been recently suspected to host a counter-rotating stellar component. We collected deep long-slit spectroscopic observations using the Russian 6-m telescope and performed the photometric decomposition of Sloan Digital Sky Survey (SDSS) archival images. We exploited (i) a non-parametric approach in order to recover stellar line-of-sight velocity distributions and (ii) a parametric spectral decomposition technique in order to disentangle stellar population properties of both main and counter-rotating stellar discs. Our spectral decomposition stays in perfect agreement with the photometric analysis. The counter-rotating component contributes $\approx$30 per cent to the total galaxy light. We estimated its stellar mass to be $9.0^{+2.7}_{-1.8}\cdot10^{9}M_\odot$. The radial scale length of counter-rotating disc is $\approx$3 times smaller than that of the main disc. Both discs harbour old stars but the counter-rotating components reveals a detectable negative age gradient that might suggest an extended inside-out formation during $3\dots4$ Gyrs. The counter-rotating disc hosts more metal-rich stars and possesses a shallower metallicity gradient with respect to the main disc. Our findings rule out cosmological filaments as a source of external accretion which is considered as a potential mechanism of the counter-rotating component formation in NGC 448, and favour the satellite merger event with the consequent slow gas accretion.

The low dark matter content of the lenticular galaxy NGC 3998

We observed the lenticular galaxy NGC 3998 with the Mitchell Integral-Field Spectrograph and extracted line-of-sight velocity distributions out to 3 half-light radii. We constructed collisionless orbit models in order to constrain NGC 3998's dark and visible structure, using kinematics from both the Mitchell and SAURON instruments. We find NGC 3998 to be almost axisymmetric, seen nearly face on with a flattened intrinsic shape - i.e., a face-on fast-rotator. We find an I-band mass-to-light ratio of $4.7_{-0.45}^{+0.32}$ in good agreement with previous spectral fitting results for this galaxy. Our best-fit orbit model shows a both a bulge and a disc component, with a non-negligible counter-rotating component also evident. We find that relatively little dark matter is needed to model this galaxy, with an inferred dark mass fraction of just $(7.1^{+8.1}_{-7.1})\%$ within one half-light radius.

Hubble Space Telescope scale 3D simulations of MHD disc winds: a rotating two-component jet structure

We present the results of large scale, three-dimensional magnetohydrodynamics simulations of disc winds for different initial magnetic field configurations. The jets are followed from the source to 90 au scale, which covers several pixels of Hubble Space Telescope images of nearby protostellar jets. Our simulations show that jets are heated along their length by many shocks. We compute the emission lines that are produced, and find excellent agreement with observations. The jet width is found to be between 20 and 30 au while the maximum velocities perpendicular to the jet are found to be up to above 100 km s−1. The initially less open magnetic field configuration simulations result in a wider, two-component jet; a cylindrically shaped outer jet surrounding a narrow and much faster, inner jet. These simulations preserve the underlying Keplerian rotation profile of the inner jet to large distances from the source. However, for the initially most open magnetic field configuration the kink mode creates a narrow corkscrew-like jet without a clear Keplerian rotation profile and even regions where we observe rotation opposite to the disc (counter-rotating). The RW Aur jet is narrow, indicating that the disc field in that case is very open meaning the jet can contain a counter-rotating component that we suggest explains why observations of rotation in this jet have given confusing results. Thus magnetized disc winds from underlying Keplerian discs can develop rotation profiles far down the jet that is not Keplerian.

The difference in age of the two counter-rotating stellar disks of the spiral galaxy NGC 4138

The Sa spiral NGC 4138 is known to host two counter-rotating stellar disks, with the ionized gas co-rotating with one of them. We measured the kinematics and properties of the two counter-rotating stellar populations to constrain their formation scenario. A spectroscopic decomposition of the observed major-axis spectrum was performed to disentangle the relative contribution of the two counter-rotating stellar and one ionized-gas components. The line-strength indices of the two counter-rotating stellar components were measured and modeled with single stellar population models that account for the alpha/Fe overabundance. The counter-rotating stellar population is younger, marginally more metal poor, and more alpha-enhanced than the main stellar component. The younger stellar component is also associated with a star-forming ring. The different properties of the counter-rotating stellar components of NGC~4138 rule out the idea that they formed due to bar dissolution. Our findings support the results of numerical simulations in which the counter-rotating component assembled from gas accreted on retrograde orbits from the environment or from the retrograde merging with a gas-rich dwarf galaxy.

Unstable m= 1 modes of counter-rotating Keplerian discs

We study the linear $m=1$ counter-rotating instability in a two-component, nearly Keplerian disc. Our goal is to understand these \emph{slow} modes in discs orbiting massive black holes in galactic nuclei. They are of interest not only because they are of large spatial scale--and can hence dominate observations--but also because they can be growing modes that are readily excited by accretion events. Self-gravity being nonlocal, the eigenvalue problem results in a pair of coupled integral equations, which we derive for a two-component softened gravity disc. We solve this integral eigenvalue problem numerically for various values of mass fraction in the counter-rotating component. The eigenvalues are in general complex, being real only in the absence of the counter-rotating component, or imaginary when both components have identical surface density profiles. Our main results are as follows: (i) the pattern speed appears to be non negative, with the growth (or damping) rate being larger for larger values of the pattern speed; (ii) for a given value of the pattern speed, the growth (or damping) rate increases as the mass in the counter-rotating component increases; (iii) the number of nodes of the eigenfunctions decreases with increasing pattern speed and growth rate. Observations of lopsided brightness distributions would then be dominated by modes with the least number of nodes, which also possess the largest pattern speeds and growth rates.

On the alleged duality of the Galactic halo

We examine the kinematics of the Galactic halo based on SDSS/SEGUE data by Carollo et al. We find that their claims of a counter-rotating halo are the result of substantial biases in distance estimates (of the order of 50 per cent): the claimed retrograde component, which makes up only a tiny fraction of the entire sample, prone to contaminations, is identified as the tail of distance overestimates. The strong overestimates also result in a lift in the vertical velocity component, which explains the large altitudes those objects were claimed to reach. Errors are worst for the lowest metallicity stars, which explains the metal-poor nature of the artificial component. We also argue that measurement errors were not properly accounted for and that the use of Gaussian fitting on intrinsically non-Gaussian Galactic components invokes the identification of components that are distorted or even artificial. Our evaluation of the data leads to a revision of the estimated velocity ellipsoids and does not yield any reliable evidence for a counter-rotating halo component. If a distinct counter-rotating halo component exists, then it must be far weaker than claimed by Carollo et al. Finally, we note that their revised analysis presented in Beers et al. does not alleviate our main concerns.

Multiplication of qubits in a doubly resonant bichromatic field

Multiplication of spin qubits arises at double resonance in a bichromatic field when the frequency of the radio-frequency (rf) field is close to that of the Rabi oscillation in the microwave field, provided its frequency equals the Larmor frequency of the initial qubit. We show that the operational multiphoton transitions of dressed qubits can be selected by the choice of both the rotating frame and the rf phase. In order to enhance the precision of dressed qubit operations in the strong-field regime, the counter-rotating component of the rf field is taken into account.

SEYFERT'S SEXTET: A SLOWLY DISSOLVING STEPHAN'S QUINTET?

We present a multiwavelength study of the highly evolved compact galaxy group known as Seyfert's Sextet (HCG79: SS). We interpret SS as a 2-3 Gyr more evolved analog of Stephan's Quintet (HCG92: SQ). We postulate that SS formed by sequential acquisition of 4-5 primarily late-type field galaxies. Four of the five galaxies show an early-type morphology which is likely the result of secular evolution driven by gas stripping. Stellar stripping has produced a massive/luminous halo and embedded galaxies that are overluminous for their size. These are interpreted as remnant bulges of the accreted spirals. H79d could be interpreted as the most recent intruder, being the only galaxy with an intact interstellar medium (ISM) and uncertain evidence for tidal perturbation. In addition to stripping activity we find evidence for past accretion events. H79b (NGC6027) shows a strong counter-rotating emission line component interpreted as an accreted dwarf spiral. H79a shows evidence for an infalling component of gas representing feedback or possible cross-fueling by H79d. The biggest challenge to this scenario involves the low gas fraction in the group. If SS formed from normal field spirals then much of the gas is missing. Finally, despite its advanced stage of evolution, we find no evidence for major mergers and infer that SS (and SQ) are telling us that such groups coalesce via slow dissolution.

A Counterrotating Central Component in the Barred Galaxy NGC 5728

We present a detailed study of the stellar kinematics in the barred galaxy NGC 5728 based on I-band photometry and long-slit spectroscopic observations in the region of the near-IR Ca II triplet. The analysis of the stellar line-of-sight velocity distribution (LOSVD) has revealed, in the central regions of the bar, the presence of a cold (v/sigma~2.5) prograde $S$-shaped velocity component that coexists in the central 4 kpc with a fainter and hotter (v/sigma~0.5) counterrotating component. Beyond 4 kpc from the nucleus the LOSVD shows the stellar bar kinematics. The comparison of the radial surface brightness profile of the velocity components with that obtained from an I-band image shows that the counterrotating core follows a r^(1/4) profile, while the S-shaped component does not follows the flat bar surface brightness profile. Several possible scenarios accounting for such kinematic signatures found in the center of the bar in NGC 5728 are discussed.