Strange attractors in periodically-kicked degenerate Hopf bifurcations

We prove that spiral sinks (stable foci of vector fields) can be transformed into strange attractors exhibiting sustained, observable chaos if subjected to periodic pulsatile forcing. We show that this phenomenon occurs in the context of periodically-kicked degenerate supercritical Hopf bifurcations. The results and their proofs make use of a new multi-parameter version of the theory of rank one maps developed by Wang and Young.Comment: 16 page

Chandra Observations of the Galactic Center and Nearby Edge-on Galaxies

I review our recent Chandra surveys of the center region of the Milky Way and other nearby edge-on galaxies. Our Galactic center survey provides an unprecedented high-resolution, broad-band X-ray panorama of a 0.8x2 square degree swath along the Galactic plane. Our preliminary analysis has led a detection of about 1000 discrete sources. We find that the diffuse X-ray emission dominates over the contribution from faint discrete sources and is globally associated with distinct interstellar structures observed at radio and mid-infrared wavelengths. We study how high-energy activities in the center region affect the immediate vicinity and may influence other aspects of the Galaxy. We have further observed nearby edge-on late-type disk galaxies in fields of low foreground Galactic extinction to gain external perspectives of the global disk/halo interaction. We have detected a giant diffuse X-ray-emitting corona around the galactic disk of NGC 4631. Extraplanar diffuse X-ray emission is also detected around NGC 3556. These X-ray-emitting coronae morphologically resemble the radio halos of these galaxies, indicating a close connection between outflows of hot gas, cosmic rays, and magnetic field from the galactic disks. There is only marginal evidence for extraplanar diffuse X-ray emission in NGC 4244 -- a galaxy with an extremely low star formation rate. In general, the extraplanar diffuse X-ray emission is evidently related to recent massive star forming activities in the galactic disks, especially in their central regions.Comment: 7 pages plus figures, based on an invited talk presented at Proc. Symposium "New Vision of the X-ray Universe in the XMM-Newton and Chandra Era", a complete and high-resolution version can be found at http://xray.astro.umass.edu/wqd/papers/gcs/qwang_E3.p

A General Signal of a Phase Transition from Single-Particle Momentum Distributions

A two-particle space correlation function is derived from the single-particle momentum distribution of the emission source. A signal of a first order phase transition is obtained from this correlation function if density fluctuations are large.Comment: 5 pages, 2 Postscript figure

Confronting feedback simulations with observations of hot gas in elliptical galaxies

Elliptical galaxies comprise primarily old stars, which collectively generate a long-lasting feedback via stellar mass-loss and Type Ia SNe. This feedback can be traced by X-ray-emitting hot gas in and around such galaxies, in which little cool gas is typically present. However, the X-ray-inferred mass, energy, and metal abundance of the hot gas are often found to be far less than what are expected from the feedback, particularly in so-called low L_X/L_B ellipticals. This "missing" stellar feedback is presumably lost in galaxy-wide outflows, which can play an essential role in galaxy evolution (e.g., explaining the observed color bi-modality of galaxies). We are developing a model that can be used to properly interpret the X-ray data and to extract key information about the dynamics of the feedback and its interplay with galactic environment.Comment: To be published in Highlights of Astronomy, Vol 15, XXVIIth IAU General Assembly, JD