4 research outputs found
Three-Dimensional Simulations of a Starburst-Driven Galactic Wind
We have performed a series of three-dimensional simulations of a
starburst-driven wind in an inhomogeneous interstellar medium. The introduction
of an inhomogeneous disk leads to differences in the formation of a wind, most
noticeably the absence of the ``blow-out'' effect seen in homogeneous models. A
wind forms from a series of small bubbles that propagate into the tenuous gas
between dense clouds in the disk. These bubbles merge and follow the path of
least resistance out of the disk, before flowing freely into the halo.
Filaments are formed from disk gas that is broken up and accelerated into the
outflow. These filaments are distributed throughout a biconical structure
within a more spherically distributed hot wind. The distribution of the
inhomogeneous interstellar medium in the disk is important in determining the
morphology of this wind, as well as the distribution of the filaments. While
higher resolution simulations are required in order to ascertain the importance
of mixing processes, we find that soft X-ray emission arises from gas that has
been mass-loaded from clouds in the disk, as well as from bow shocks upstream
of clouds, driven into the flow by the ram pressure of the wind, and the
interaction between these shocks.Comment: 37 pages, 16 figures, mpg movie can be obtained at
http://www.mso.anu.edu.au/~jcooper/movie/video16.mpg, accepted for
publication in Ap
Hubble Space Telescope Imaging of the Circinus Galaxy
We present an HST imaging study of the nearby (4 Mpc distant) Circinus
galaxy, which contains the nearest type 2 Seyfert nucleus and prominent
circumnuclear star formation. Images have been obtained in the
[OIII]5007, H and H v=1--0 S(1) emission lines, and in the
green (5470 \AA), red (8140 \AA) and near infrared (2.04 and 2.15 m)
continua. An image in the [Fe II] 1.644 m line has been taken
with a ground-based telescope. The [OIII] and H images reveal the
detailed structure of the complex of streamers and knots of high-excitation
gas, which extends out of the galaxy disk. The morphology some 250 pc from the
nucleus strongly suggests that the high-excitation gas is concentrated on the
surface of a hollow cone with apex close to the nucleus. Such a structure may
result through entrainment of dense gas from a circumnuclear torus in the
galaxy disk by a low density, outflowing wind or jet. Within 40 pc of the
nucleus, the high-excitation gas takes the form of a striking, filled V-shaped
structure extending in the same direction as the larger scale high-excitation
emission. This `V' can be described as an ionization cone, though a
matter-bounded structure is also possible. The implied collimation of the
ionizing photons or gaseous outflow must occur within 2 pc of the apex of the
cone, presumed to be the location of the nucleus. The H image shows a
complex structure of HII regions, including the well known starburst ring of
radius 150 - 270 pc. In addition, there is a more compact (40 pc radius),
elliptical ring of HII regions around the `ionization cone'. We argue that this
latter ring, which we call the nuclear ring, is intrinsically circular and
located in the plane of the galaxy disk. Abstract truncated.Comment: With 12 figures, to be published in the Astronomical Journal,
September 2000 issu
Evolution of galaxies and their environments at z = 0.1-3 in COSMOS
Large-scale structures (LSSs) out to z 0.8, the SFR density is uniformly distributed over all environmental density percentiles, while at lower redshifts the dominant contribution is shifted to galaxies in lower density environments
COSMOS: Hubble Space Telescope Observations
The Cosmic Evolution Survey (COSMOS) was initiated with an extensive allocation (590 orbits in Cycles 12-13) using the Hubble Space Telescope (HST) for high-resolution imaging. Here we review the characteristics of the HST imaging with the Advanced Camera for Surveys (ACS) and parallel observations with NICMOS and WFPC2. A square field (1.8 deg2) has been imaged with single-orbit ACS I-band F814W exposures with 50% completeness for sources 0.5'' in diameter at IAB = 26.0 mag. The ACS is a key part of the COSMOS survey, providing very high sensitivity and high-resolution (0.09'' FWHM and 0.05'' pixels) imaging and detecting a million objects. These images yield resolved morphologies for several hundred thousand galaxies. The small HST PSF also provides greatly enhanced sensitivity for weak-lensing investigations of the dark matter distribution