Session CM1 - Mini-conference on Astrophysical Jets I.
ORAL session, Monday afternoon, November 15
Room 100/101, SCC

[CM1.001] The HH 46/47 mid-IR cavity. New Spitzer Observations and models.

We present the early release observations of the HH 46/47 system and HH 46 IRS1 source, taken with the three instruments aboard the Spitzer Space Telescope. The optically invisible SW lobe, driven by the HH 47C bow shock is revealed in full detail by the IRAC images, and displays a ``loop'' like morphology. Both of the mid-infrared outflow lobes are narrower than those of CO flow. We believe that the combination of emission by H_2 rotational lines (S(11)-S(4)) and some atomic lines, which fall within the IRAC passbands, are responsible for the bulk of the observed emission, although contributions from the 3.3, 6.2 and 7.7 \mu~PAH emission bands can not be ruled out.

We have modeled the limb-brightened cavity seen in the new Spitzer IR images of the SW lobe of HH 46/47 as the bow shock driven by an outflow from a young, low mass star. We present models in which the outflow is a perfectly collimated, straight jet, in which we have a precessing jet, and finally a model in which the outflow takes the form of a latitude-dependent wind. We study cases in which the outflow moves into a constant density cloud and into a stratified cloud. We find that the best agreement with the observed cavity is obtained for the precessing jet in a stratified cloud. However, the ``straight jet'' (travelling in a stratified cloud) also gives cavity shapes close to the observed one. The ``latitude-dependent wind'' model that we have computed gives cavity shapes which are substantially wider than the observed cavity.

[CM1.002] What Role Do Magnetic Fields Play in Jets from Young Stars?

The birth of stars involves not only the formation of accretion disks but also the generation of highly collimated jets/outflows. These outflows can stretch for several parsecs, transporting energy and momentum to the surrounding cloud and even, in some cases, producing turbulent cloud support against gravity. While it is very obvious that magnetic fields play a significant role in the generation and collimation of AGN jets, what function they have in jets from young stellar objects (YSOs) remains uncertain. This is primarily because we lack a good diagnostic tool of field strength in YSO jets although, ironically, we have excellent probes for their other basic parameters, e.g. velocity, density, temperature, etc. In this talk, I will review what we can infer about the importance of magnetic fields from a variety of sources, such as angular momentum transport, line ratios in the post-shock cooling zone and even, in some cases, gyro-synchrotron radiation.

[CM1.003] Relativistic Plasma Jets from Black Hole Accretion

Jets are a ubiquitous product of accretion of matter onto compact astrophysical objects. Here we concentrate on those associated with black holes. A number of basic properties of jets have been derived in the recent past from observations with radio, optical, X-ray and gamma-ray telescopes. Jets are broad-band emitters that can radiate photons from the radio to TeV energy. Continuous particle acceleration takes place along the entire plasma flow. Jets traverse many orders of magnitude in spatial scales and remain self-similar over a long range. They are found in stellar as well as supermassive black holes showing remarkably scale-invariant properties. Magnetic fields are likely the dominating driving mechanism at the jet footpoint, coupled to some form of an accretion flow. The origin of jets is very close to the central object, possibly being as small as a few Schwarzschild radii. In a few cases this region is even observed with radio interferometers -- in the future this can be used to image the event horizon. Interestingly, jet-formation seems to be almost always possible, irrespective of the accretion rate or spin of the black hole and one can present a unified view of jets across many orders of magnitude of accretion rate and mass of the central object.

[CM1.004] Theory and Simulations of the Origin of Astrophysical Jets

Powerful radio, and in some cases optical and gamma ray, emitting jets are observed to emanate from many compact accreting objects, from stellar mass black holes to super massive black holes in galactic nuclei. The jets are widely thought to arise from the twisting of an ordered magnetic field threading a differentially rotating accretion disk which acts to magnetically extract angular momentum and energy from the disk. Two main regimes have been discussed, hydromagnetic jets, which have a significant mass flux and have energy and angular momentum carried by both matter and electromagnetic field and, Poynting jets, where the mass flux is small and energy and angular momentum are carried predominantly by the electromagnetic field. Here, we describe recent theoretical work on the formation of Poynting jets from magnetized accretion disks. Further, we describe new relativistic, fully-electromagnetic, particle-in-cell simulations of the formation of jets from accretion disks. Laboratory Z-pinch experiments promise to further our understanding of the origin and nature of astrophysical jets.

[CM1.005] Accretion power and the origin of astrophysical jets

Astrophysical jets are observed in a wide variety of systems ranging from stars in the act of formation to quasars. In most if not all of these systems, a central object such as a massive black hole or a young star accretes gas from a surrounding, Keplerian, gaseous disk. One of the most popular and best tested models for jet formation posits that jets are highly collimated, hydromagnetic winds that are flung out from the surfaces of accretion disks along open field lines that thread them. Basic theoretical calculations predict that these jets are powered by the gravitational potential energy that must be released as gas in the underlying disk slowly spirals in towards the central object. In addition, the magnetic torque exerted by such a wind can efficiently extract the angular momentum of gas within the disk, enabling the accretion process. Recent observations of jets from young stellar objects reveal that these flows rotate and can be traced back to an extended region of the underlying disk, and these provide stringent tests for the model. I shall review the basic elements of this picture and show that it provides a very promising universal model for jets. This is supported by sophisticated 3D numerical simulations.

[CM1.006] Hydromagnetic Driving of Astrophysical Jets

Magnetic fields are believed to play a key role in the powering of astrophysical jets (through extraction of rotational kinetic energy from a compact central mass or its surrounding accretion disk) and in the acceleration and collimation of these outflows. Using semianalytic MHD models, I address the following issues: (1) How are jets launched from accretion disks? Can one construct equilibrium configurations of magnetic disk/jet systems, and are they stable? (2) How do magnetic stresses accelerate and collimate the flow? What are the distinguishing features of hydromagnetic acceleration and how do they manifest themselves when other driving forces are also present? What are the similarities and differences between nonrelativistic outflows (as in young stellar objects) and relativistic jets (as in gamma-ray burst sources and the blazar class of active galactic nuclei)? (3) How does the magnetic field advected by the flow influence the equilibrium structure of the jet beyond the acceleration region?

Part C of program listing