In radio galaxies such as M84 dust features tend to be nearly perpendicular to radio jets yet are not aligned with the galaxy isophotes. The timescale for precession in the galaxy is short (~ 107 yr at 100 pc), suggesting that an alternative mechanism causes the gas disk to be misaligned with the galaxy. In M84 we estimate the pressure on the disk required to overcome the torque from the galaxy and find that it is small compared with the thermal pressure in the hot ambient interstellar medium estimated from the X-ray emission. We therefore propose that pressure gradients in a jet-associated hot interstellar medium exert a torque on the gas disk in M84 causing it to be misaligned with the galaxy isophotal major axis. We propose that active galactic nuclei-associated outflows or associated hot low-density media in nearby radio galaxies could strongly affect the orientation of their gas disks on 100 pc scales. This mechanism could explain the connection between gas disk angular momentum and jet axes in nearby radio galaxies. By integrating the light of the galaxy through a warped gas and dust disk we find that the geometry of a gas disk in M84 is likely to differ from that predicted from a simple precession model. We find that the morphology of the gas disk in M84 is consistent with a warped geometry where precession is caused by a combination of a galactic torque and a larger torque due to pressure gradients in the ambient X-ray-emitting gas. Precession occurs at an axis between the jet and galaxy major axis, but nearer to the jet axis, implying that the pressure torque is 2-4 times larger than the galactic torque. We estimate that precession has occurred about this particular axis for about 107 yr. A better model for the morphology of the disk is achieved when precession takes place about an elliptical rather than circular path. This suggests that the isobars in the hot medium are strongly dependent on the angle from the jet axis.
view Abstract Citations (94) References (48) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS An Estimate of the Gas Inflow Rate along the Bar in NGC 7479 Quillen, A. C. ; Frogel, Jay A. ; Kenney, Jeffrey D. P. ; Pogge, R. W. ; Depoy, D. L. Abstract We present images of the barred galaxy NGC 7479 in the optical and near-infrared broad bands B, V, R, J, H, K, and images in Hα + [N II] and CO (J = 1 - 0) emission. The Hα and CO emission in the bar are coincident and confined to narrow linear features that are offset from the center of the bar as observed in the near-infrared. We estimate the gravitational potential from the K image, which provides an estimate of the torque on the gas at the position of the CO emission in the bar. We find that the implied gas inflow velocity derived from the torque is 10-20 km s^-1^, Our inflow velocity is independent of the large streaming motions which can be observed in CO and H I. Publication: The Astrophysical Journal Pub Date: March 1995 DOI: 10.1086/175381 arXiv: arXiv:astro-ph/9409033 Bibcode: 1995ApJ...441..549Q Keywords: Barred Galaxies; Flow Velocity; Gas Streams; Infrared Imagery; Carbon Monoxide; Gravitational Fields; H Alpha Line; Image Analysis; Morphology; Nitrogen; Torque; Astrophysics; GALAXIES: KINEMATICS AND DYNAMICS; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 7479; GALAXIES: PHOTOMETRY; INFRARED: GALAXIES; Astrophysics E-Print: 16pages, postscript, ~accepted to ApJ, Paper is available with compressed postscript figures via anonymous ftp from payne.mps.ohio-state.edu in the directory pub/quillen/n7479, AYOSU-9-94-002 full text sources arXiv | ADS | data products SIMBAD (5) NED (1)
Spitzer observations of the young star CoKu Tau/4 reveal a disk with a 10 AU hole that is most likely caused by a newly formed planet. Assuming that the planet opened a gap in the viscous disk, we estimate that the planet mass is greater than 0.1 Jupiter masses. This estimate depends on a lower limit to the disk viscosity derived from the timescale needed to accrete the inner disk, creating the now detectable hole. The planet migration timescale must at least modestly exceed the time for the spectrally inferred hole to clear. The proximity of the planet to the disk edge implied by our limits suggests that the latter is perturbed by the nearby planet and may exhibit a spiral pattern rotating with the planet. This pattern might be resolved with current ground-based mid-infrared cameras and optical cameras on the Hubble Space Telescope. The required submegayear planet formation may challenge core accretion formation models. However, we find that only if the planet mass is larger than about 10 Jupiter masses, allowing for a high enough surface density without inducing migration, would formation by direct gravitational instability be possible.
The authors explore the possibility that near-earth, rubble pile asteroids might be used as habitats for human settlement by increasing their rotation to produce spin gravity. Using previously published scaling by Maindl et al. and studies of asteroid populations, it is shown that there is no class of hollowed body that would survive the spin-up process on its own without additional reinforcement. Large solid-rock asteroids (diameter D > 10 km) would not have the tensile strength to withstand the required rotation rates and would fracture and break apart. Smaller asteroids, being ‘rubble piles’, have little tensile strength and would quickly disperse. The possibility of containing the asteroid mass using higher-strength materials like carbon nanofiber is instead considered. It is found that a moderate tensile strength container can maintain the integrity of a large spinning cylinder composed of dispersed asteroid regolith. The research extends the range of possible asteroid habitat candidates, since it may become feasible to construct habitats from the more numerous smaller bodies, including NEAs (Near Earth Asteroids). The required tensile strength of the container material scales with habitat radius and thickness and is ∼ 200 MPa for a starting asteroid body of radius 300 m that is spun up to provide 0.3 g ⊕ while increasing its radius to 3 km and maintaining a rubble and regolith shield thickness of 2 m to protect against cosmic rays. Ambient solar power can be harvested to aid in spin-up and material processing.
We propose that the eccentricity and sharpness of the edge of Fomalhaut’s disk are due to a planet just interior to the ring edge. The collision timescale consistent with the disk opacity is long enough that spiral density waves cannot be driven near the planet. The ring edge is likely to be located at the boundary of a chaotic zone in the corotation region of the planet. We find that this zone can open a gap in a particle disk as long as the collision timescale exceeds the removal or ejection timescale in the zone. We use the slope measured from the ring edge surface brightness profile to place an upper limit on the planet mass. The removal timescale in the chaotic zone is used to estimate a lower limit. The ring edge has eccentricity caused by secular perturbations from the planet. These arguments imply that the planet has a mass between that of Neptune and that of Saturn, a semi-major axis of approximately 119 AU and longitude of periastron and eccentricity, 0.1, the same as that of the ring edge.
We consider the nature of orbits near the solar neighborhood that are perturbed by local spiral arms and the Milky Way bar. We present a simplified Hamiltonian model that includes resonant terms from both types of perturbations and is similar to the forced pendulum. Via numerical integration of this model, we construct Poincaré maps to illustrate the nature and stability of the phase space. We find that resonance overlap is most likely to cause widespread chaos when the pattern of the spiral structure puts the solar neighborhood near the 2 : 1 inner Lindblad resonance (ILR) in the case of a two-armed pattern, or near the 4 : 1 ILR in the case of a four-armed pattern. When this happens, both the quasi-periodic orbits that support the spiral structure and those that oscillate with the bar are disrupted near the bar's 2 : 1 outer Lindblad resonance (OLR). Consequently, the pattern speed of spiral structure that passes through the bar's OLR must be faster than ∼0.45 times the solar neighborhood angular rotation rate if it is two-armed, or faster than 0.75 times this value if it is four-armed. Alternatively, the bar's OLR may form a boundary between spiral modes at different pattern speeds. In all cases, we find that spiral structure is disrupted by the bar's OLR over a narrow range of radius, and that the extent of the orbits aligned perpendicular to the bar at the bar's OLR is limited by the spiral perturbations. We find that the boundary, at an azimuthal velocity component of 30 km s-1 below that of the Sun, of the u-anomaly in the velocity distribution in the solar neighborhood is due to the abrupt bifurcation of the orbit families associated with the OLR. The upper boundary at 60 km s-1 is truncated by the spiral structure. The radial velocity width of the anomaly is probably bounded by chaotic regions that surround the family of quasi-periodic orbits oriented perpendicular to the bar.
We explore scenarios for the origin of two different density planets in the Kepler 36 system in adjacent orbits near the 7:6 mean motion resonance.We find that fine tuning is required in the stochastic forcing amplitude, the migration rate and planet eccentricities to allow two convergently migrating planets to bypass mean motion resonances such as the 4:3, 5:4 and 6:5, and yet allow capture into the 7:6 resonance.Stochastic forcing can eject the system from resonance causing a collision between the planets, unless the disk causing migration and the stochastic forcing is depleted soon after resonance capture.We explore a scenario with approximately Mars mass embryos originating exterior to the two planets and migrating inwards toward two planets.We find that gravitational interactions with embryos can nudge the system out of resonances.Numerical integrations with about a half dozen embryos can leave the two planets in the 7:6 resonance.Collisions between planets and embryos have a wide distribution of impact angles and velocities ranging from accretionary to disruptive.We find that impacts can occur at sufficiently high impact angle and velocity that the envelope of a planet could have been stripped, leaving behind a dense core.Some of our integrations show the two planets exchanging locations, allowing the outer planet that had experienced multiple collisions with embryos to become the innermost planet.A scenario involving gravitational interactions and collisions with embryos may account for both the proximity of the Kepler 36 planets and their large density contrast..
We compute the strengths of zero-th order (in eccentricity) three-body resonances for a co-planar and low eccentricity multiple planet system. In a numerical integration we illustrate that slowly moving Laplace angles are matched by variations in semi-major axes among three bodies with the outer two bodies moving in the same direction and the inner one moving in the opposite direction, as would be expected from the two quantities that are conserved in the three-body resonance. A resonance overlap criterion is derived for the closely and equally spaced, equal mass system with three-body resonances overlapping when interplanetary separation is less than an order unity factor times the planet mass to the one quarter power. We find that three-body resonances are sufficiently dense to account for wander in semi-major axis seen in numerical integrations of closely spaced systems and they are likely the cause of instability of these systems. For interplanetary separations outside the overlap region, stability timescales significantly increase. Crudely estimated diffusion coefficients in eccentricity and semi-major axis depend on a high power of planet mass and interplanetary spacing. An exponential dependence previously fit to stability or crossing timescales is likely due to the limited range of parameters and times possible in integration and the strong power law dependence of the diffusion rates on these quantities.
We compare the soft diffuse X-ray emission from Chandra images of 12 nearby intermediate-inclination spiral galaxies to the morphology seen in Hα, molecular gas, and mid-infrared emission. We find that diffuse X-ray emission is often located along spiral arms in the outer parts of spiral galaxies but tends to be distributed in a more nearly radially symmetric morphology in the center. The X-ray morphology in the spiral arms matches that seen in the mid-infrared or Hα and thus implies that the X-ray emission is associated with recent active star formation. In the spiral arms there is a good correlation between the level of diffuse X-ray emission and that in the mid-infrared in different regions. The correlation between X-ray and mid-IR flux in the galaxy centers is less strong. We also find that the central X-ray emission tends to be more luminous in galaxies with brighter bulges, suggesting that more than one process is contributing to the level of central diffuse X-ray emission. We see no strong evidence for X-ray emission trailing the location of high-mass star formation in spiral arms. However, population synthesis models predict a high mechanical energy output rate from supernovae for a time period that is about 10 times longer than the lifetime of massive ionizing stars, conflicting with the narrow appearance of the arms in X-rays. The fraction of supernova energy that goes into heating the interstellar medium must depend on environment and is probably higher near sites of active star formation. The X-ray estimated emission measures suggest that the volume filling factors and scale heights are low in the outer parts of these galaxies but higher in the galaxy centers. The differences between the X-ray properties and morphology in the centers and outer parts of these galaxies suggest that galactic fountains operate in outer galaxy disks but that winds are primarily driven from galaxy centers.
The question of how much gas cools in the cores of clusters of galaxies has been the focus of many, multiwavelength studies in the past 30 years. In this letter we present the first detections of the strongest atomic cooling lines, [C II], [O I] and [N I] in two strong cooling flow clusters, A1068 and A2597, using Herschel PACS. These spectra indicate that the substantial mass of cold molecular gas (>10^9 Mo) known to be present in these systems is being irradiated by intense UV radiation, most probably from young stars. The line widths of these FIR lines indicate that they share dynamics similar but not identical to other ionised and molecular gas traced by optical, near-infrared and CO lines. The relative brightness of the FIR lines compared to CO and FIR luminosity is consistent with other star-forming galaxies indicating that the properties of the molecular gas clouds in cluster cores and the stars they form are not unusual. These results provide additional evidence for a reservoir of cold gas that is fed by the cooling of gas in the cores of the most compact clusters and provide important diagnostics of the temperature and density of the dense clouds this gas resides in.
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