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We present a pilot study of the stellar populations of 8 AGN hosts at z~1 and compare to (1) lower redshift samples and (2) a sample of nonactive galaxies of similar redshift. We utilize K' images in the GOODS South field obtained with the laser guide star adaptive optics (LGSAO) system at Keck Observatory. We combine this K' data with B, V, i, and z imaging from the ACS on HST to give multi-color photometry at a matched spatial resolution better than 100 mas in all bands. The hosts harbor AGN as inferred from their high X-ray luminosities (L_X > 10^42 ergs/s) or mid-IR colors. We find a correlation between the presence of younger stellar populations and the strength of the AGN, as measured with [OIII] line luminosity or X-ray (2-10 keV) luminosity. This finding is consistent with similar studies at lower redshift. Of the three Type II galaxies, two are disk galaxies and one is of irregular type, while in the Type I sample there only one disk-like source and four sources with smooth, elliptical/spheroidal morphologies. In addition, the mid-IR SEDs of the strong Type II AGN indicate that they are excited to LIRG (Luminous InfraRed Galaxy) status via galactic starbursting, while the strong Type I AGN are excited to LIRG status via hot dust surrounding the central AGN. This supports the notion that the obscured nature of Type II AGN at z~1 is connected with global starbursting and that they may be extincted by kpc-scale dusty features that are byproducts of this starbursting., Comment: 56 pages, 39 figures, accepted to AJ

The NSF Science and Technology Center for Adaptive Optics (CfAO) is supporting a major scientific legacy project called the CfAO Treasury Survey (CATS). CATS is obtaining near-infrared AO data in deep HST survey fields, such as GEMS, GOODS-N, & EGS. Besides summarizing the main objectives of CATS, we highlight some recent imaging work on the study of distant field galaxies, AGNs, and a redshift z = 1.32 supernova. CATS plans the first data release to the community in early 2007 (check http://www.astro.ucla.edu/~irlab/cats/index.shtml for more details on CATS and latest updates)., Comment: 2 pages. Proceedings of the IAU Symposium 235, "Galaxy Evolution across the Hubble Time", F. Combes & J. Palous (eds.)

We present preliminary results from high resolution (~ 0.05") adaptive optics observations of Cygnus A. The images show a bi-conic structure strongly suggestive of an obscuring torus around a quasar nucleus. A bright (K'=18.5) point source is found near the expected position of the nucleus. We interpret this source as the hot inner rim of the torus seen through the opening of the torus. Using high angular resolution K-band spectroscopy, we measure the ratio of molecular to recombination hydrogen lines as a function of distance to the center of the putative torus. These measurements place constraints on the properties of the torus and indicate a projected diameter of ~600 pc., Comment: To appear in proceeding from "Penetrating Bars through Masks of Cosmic Dust" conference in South Africa. 5 pages

We have used laser guide star adaptive optics and a near-infrared dual-channel imaging polarimeter to observe light scattered in the circumstellar environment of Herbig Ae/Be stars on scales of 100-300 AU. We discover a strongly polarized, biconical nebula 10 arcseconds in diameter (6000 AU) around the star LkHa 198, and also observe a polarized jet-like feature associated with the deeply embedded source LkHa 198-IR. The star LkHa 233 presents a narrow, unpolarized dark lane consistent with an optically thick circumstellar disk blocking our direct view of the star. These data show that the lower-mass T Tauri and intermediate mass Herbig Ae/Be stars share a common evolutionary sequence., Comment: To appear in Science, 27 February 2004 (4 pages, 2 figures + refs)

We have obtained adaptive optics, high spatial resolution (0.15 arcsecond) K-band spectra and images of the region around the two active nuclei in NGC 6240 which show the presence of circumnuclear shocks. The data are consistent with the thermal excitation mechanism being the dominant one in the nuclear region. UV fluorescence and associative detachment may also contribute to the fraction of the energy emitted through molecular hydrogen transitions. The near-IR continuum emission appears closely associated with the two active nuclei. The morphological similarities between the near-IR images and the Chandra X-ray images indicate the same mechanisms may be responsible for the emission in near-IR and X-ray band., Comment: 22 pages, 4 figures, to appear in AJ

We present Keck II adaptive optics near infrared imaging and spectroscopic observations of the central regions of the powerful radio galaxy Cygnus A. The 0.05" resolution images clearly show an unresolved nucleus between two spectacular ionization/scattering cones. We report the discovery of a relatively bright (K'~19) secondary point source 0.4" or 400 pc in projection southwest of the radio nucleus. The object is also visible in archival Hubble Space Telescope optical images, although it is easily confused with the underlying structure of the host. Although the near infrared colors of this secondary point source are roughly consistent with those of an L-dwarf, its spectrum and optical-to-infrared spectral energy distribution (SED) virtually rule out the possibility that it may be any foreground projected object. We conclude that the secondary point source is likely to be an extragalactic object associated with Cygnus A. We consider several interpretations of the nature of this object, including: a young star cluster peering through the dust at the edge of one of the ionization cones; an older, large globular cluster; a compact cloud of dust or electrons that is acting as a mirror of the hidden active nucleus; and the dense core of a gas stripped satellite galaxy that is merging with the giant elliptical host. The data presented here are most consistent with the minor merger scenario. The spectra and SED of the object suggest that it may be a densely packed conglomeration of older stars heavily extincted by dust, and its high luminosity and compact nature are consistent with those of a satellite that has been stripped to its tidal radius. Further spectroscopic observations are nevertheless necessary to confirm this possibility., Comment: To appear in November 10 issue of ApJ. 22 pages, 5 figures (2 color)

Using adaptive optics on the W.M. Keck II telescope we imaged Titan several times during 1999 to 2001 in narrowband near-infrared filters selected to probe Titan's stratosphere and upper troposphere. We observed a bright feature around the south pole, possibly a collar of haze or clouds. Further, we find that solar phase angle explains most of the observed east-west brightness asymmetry of Titan's atmosphere, although the data do not preclude the presence of a `morning fog' effect at small solar phase angle., Comment: Icarus, accepted 6 January 2002

Adaptive optics (AO) on 8-10 m telescopes is an enormously powerful tool for studying young nearby stars. It is especially useful for searching for companions. Using AO on the 10-m W.M. Keck II telescope we have measured the position of the brown dwarf companion to TWA5 and resolved the primary into an 0.055 arcsecond double. Over the next several years follow-up astrometry should permit an accurate determination of the masses of these young stars. We have also re-observed the candidate extrasolar planet TWA6B, but measurements of its motion relative to TWA6A are inconclusive. We are carrying out a search for new planetary or brown dwarf companions to TWA stars and, if current giant planet models are correct, are currently capable of detecting a 1 Jupiter-mass companion at ~1 arcsecond and a 5 Jupiter-mass companion at ~0.5 arcsecon around a typical TWA member., Comment: 6 pages, 4 inline eps figues. To appear in "Young Stars Near Earth: Progress and Prospects", ASP conference series, R. Jayawardhana and T. Green eds. uses pasp style file "newpasp.sty" (included)

One-dimensional particle-in-cell plasma simulations are used to examine the mechanical structure and thermalization properties of collisionless relativistic shock waves in electron-positron plasmas. Shocks propagating perpendicularly to the magnetic field direction are considered. It is shown that these shock waves exist, and that they are completely parameterized by the ratio of the upstream Poynting flux to the upstream kinetic energy flux. The way in which the Rankine-Hugoniot shock jump conditions are modified by the presence of wave fluctuations is shown, and they are used to provide a macroscopic description of these collisionless shock flows. The results of a 2D simulation that demonstrates the generality of these results beyond the assumption of the 1D case are discussed. It is suggested that the thermalization mechanism is the formation of a synchrotron maser by the coherently reflected particles in the shock front. Because the downstream medium is thermalized, it is argued that perpendicular shocks in pure electron-positron plasmas are not candidates as nonthermal particle accelerators.

The role of sophisticated numerical models and simulations in the field of plasma astrophysics is discussed. The need for an iteration between microphysics and macrophysics in order for astrophysical plasma physics to produce quantitative results that can be related to astronomical data is stressed. A discussion on computational requirements for simulations of astrophysical plasmas contrasts microscopic plasma simulations with macroscopic system models. An overview of particle-in-cell simulations (PICS) is given and two examples of PICS of astrophysical plasma are discussed including particle acceleration by collisionless shocks in relativistic plasmas and magnetic field reconnection in astrophysical plasmas.