116 research outputs found
Supercomputer Simulations of Disk Galaxies
The time evolution of models for an isolated disk of highly flattened
galaxies of stars is investigated by direct integration of the Newtonian
equations of motion of N=30,000 identical stars over a time span of many
galactic rotations. Certain astronomical implications of the simulations to
actual disk-shaped (i.e. rapidly rotating) galaxies are explored as well.Comment: 3 pages, 2 figure Aat.sty, Aattable.sty, presented by E. Griv at the
JENAM 2000, S02, Moscow, Russia, 200
Flows along cometary tails in the Helix planetary nebula NGC 7293
Previous velocity images which reveal flows of ionized gas along the most
prominent cometary tail (from Knot 38) in the Helix planetary nebula are
compared with that taken at optical wavelengths with the Hubble Space Telescope
and with an image in the emission from molecular hydrogen. The flows from the
second most prominent tail from Knot 14 are also considered. The kinematics of
the tail from the more complex Knot 32, shown here for the first time, also
reveals an acceleration away from the central star. All of the tails are
explained as accelerating ionized flows of ablated material driven by the
previous, mildly supersonic, AGB wind from the central star. The longest tail
of ionized gas, even though formed by this mechanism in a very clumpy medium,
as revealed by the emission from molecular hydrogen, appears to be a coherent
outflowing feature.Comment: 8 pages, 4 figures, accepted for publication in MNRA
A Catalogue of M51 type Galaxy Associations
A catalog of 232 apparently interacting galaxy pairs of the M51 class is
presented. Catalog members were identified from visual inspection of mult-band
images in the IRSA archive. The major findings in the compilation of this
catalog are (1) A surprisingly low number of the main galaxies in M51 systems
are early type spirals and barred spirals. (2) Over 70% of the main galaxies in
M51 systems are 2-armed spirals. (3) Some systems that were classified as M51
types in previous studies are not M51 types as defined in this catalog. There
were a number of systems previously classified as M51 systems for which the
companion is identified as an HII region within the main galaxy or a foreground
star within the Milky Way. (4) It was found that only 18% of the M51 type
companions have redshift measurements in the literature. There is a significant
need for spectroscopic study of the companions in order to improve the value of
the catalog as a sample for studying the effects of M51 type interaction on
galaxy dynamics, morphology, and star formation. Further spectroscopy will also
help constrain the statistics of possible chance projections between foreground
and background galaxies in this catalog. The catalog also contains over 430
additional systems which are classified as "possible M51" systems. The reasons
for classifying certain systems as possible M51 systems are discussed.Comment: 19 pages including 6 figures and tables 3-8, Tables 1 and 2 are found
at http://www.jorcat.com, Accepted for publication in Astrophysics and Space
Scienc
3D Spectroscopy of Blue Compact Galaxies. Diagnostic Diagrams
Here we present the analysis of 3D spectroscopic data of three Blue Compact
Galaxies (Mrk324, Mrk370, and IIIZw102). Each of the more than 22500 spectra
obtained for each galaxy has been fitted by a single gaussian from which we
have inferred the velocity dispersion (sigma), the peak intensity (Ipeak), and
the central wavelength (lambda_c). The analysis shows that the sigma vs Ipeak
diagrams look remarkably similar to those obtained for giant extragalactic HII
regions. They all present a supersonic narrow horizontal band that extends
across all the range of intensities and that result from the massive nuclear
star-forming regions of every galaxy. The sigma vs Ipeak diagrams present also
several inclined bands of lower intensity and an even larger sigma, arising
from the large galactic volumes that surround the main central emitting knots.
Here we also show that the sigma vs lambda_c and lambda_c vs Ipeak diagrams,
are powerful tools able to unveil the presence of high and low mass stellar
clusters, and thus allow for the possibility of inferring the star formation
activity of distant galaxies, even if these are not spatially resolved.Comment: 15 pages, 3 figures, accepted for publication in The Astronomical
Journa
A Radio Spectral Line Study of the 2-Jy IRAS-NVSS Sample: Part I
We present results from an on-going survey for the HI 21 cm line and the OH
18 cm lines in IR galaxies with the Arecibo 305 m Radio Telescope. The
observations of 85 galaxies extracted from the 2 Jy IRAS-NVSS sample in the
R.A. (B1950) range 20 h-00 h are reported in this paper. We detected the HI 21
cm line in 82 of these galaxies, with 18 being new detections, and the OH 18 cm
lines in 7 galaxies, with 4 being new detections. In some cases, the HI spectra
show the classic double-horned or single-peaked emission profiles. However, the
majority exhibit distorted HI spectral features indicating that the galaxies
are in interacting and/or merging systems. From these HI and OH observations,
various properties of the sample are derived and reported.Comment: 38 pages, 7 figures, 9 tables. Accepted for publication in A
Chain Galaxies in the Tadpole ACS Field
Colors and magnitudes were determined for 69 chain galaxies, 58 other linear
structures, 32 normal edge-on galaxies, and all of their large star formation
clumps in the HST ACS field of the Tadpole galaxy. Redshifts of 0.5 to 2 are
inferred from comparisons with published color-evolution models. The linear
galaxies have no red nuclear bulges like the normal disk galaxies in our field,
but the star formation clumps in each have about the same colors and
magnitudes. Light profiles along the linear galaxies tend to be flat, unlike
the exponential profiles of normal galaxies. Although the most extreme of the
linear objects look like beaded filaments, they are all probably edge-on disks
that will evolve to late Hubble type galaxies. The lack of an exponential
profile is either the result of a dust scale height that is comparable to the
stellar scale height, or an intrinsically irregular structure. Examples of
galaxies that could be face-on versions of linear galaxies are shown. They have
an irregular clumpy structure with no central bulge and with clump colors and
magnitudes that are comparable to those in the linears. Radiative transfer
solutions to the magnitudes and surface brightnesses of inclined dusty galaxies
suggest that edge-on disks should become more prominent near the detection
limit for surface brightness. The surface brightness distribution of the
edge-on galaxies in this field confirm this selection effect. The star
formation regions are much more massive than in modern galaxies, averaging up
to 10^9 Msun for kpc scales.Comment: 15 pages, 9 figures, accepted for ApJ, 603, March 1, 200
Mapping the Hidden Universe: The Galaxy Distribution in the Zone of Avoidance
Due to the foreground extinction of the Milky Way, galaxies become
increasingly faint as they approach the Galactic Equator creating a ``zone of
avoidance'' (ZOA) in the distribution of optically visible galaxies of about
25%. A ``whole-sky'' map of galaxies is essential, however, for understanding
the dynamics in our local Universe, in particular the peculiar velocity of the
Local Group with respect to the Cosmic Microwave Background and velocity flow
fields such as in the Great Attractor (GA) region. The current status of deep
optical galaxy searches behind the Milky Way and their completeness as a
function of foreground extinction will be reviewed. It has been shown that
these surveys - which in the mean time cover the whole ZOA (Fig. 2) - result in
a considerable reduction of the ZOA from extinction levels of A_B = 1.0 mag
(Fig. 1) to A_B = 3.0 mag (Fig. 2). In the remaining, optically opaque ZOA,
systematic HI surveys are powerful in uncovering galaxies, as is demonstrated
for the GA region with data from the full sensitivity Parkes Multibeam HI
survey (300 < l < 332 deg, |b| < 5.5 deg, Fig. 4).Comment: Accepted for publication in PASA (Volume 17, 1, to appear April
2000); LaTex, 4 encapsulated (reduced) ps-figures, requires psfig.
Full-resolution color figures 1, 3, and 4 are available upon request at
e-mail: [email protected] or at http://www.atnf.csiro.au/pasa/17_1
The Compact Group of Galaxies HCG 31 is in an early phase of merging
We have obtained high spectral resolution (R = 45900) Fabry-Perot velocity
maps of the Hickson Compact Group HCG 31 in order to revisit the important
problem of the merger nature of the central object A+C and to derive the
internal kinematics of the candidate tidal dwarf galaxies in this group. Our
main findings are: (1) double kinematic components are present throughout the
main body of A+C, which strongly suggests that this complex is an ongoing
merger (2) regions and E, to the east and south of complex A+C, present
rotation patterns with velocity amplitudes of and they
counterrotate with respect to A+C, (3) region F, which was previously thought
to be the best example of a tidal dwarf galaxy in HCG 31, presents no rotation
and negligible internal velocity dispersion, as is also the case for region
. HCG 31 presents an undergoing merger in its center (A+C) and it is likely
that it has suffered additional perturbations due to interactions with the
nearby galaxies B, G and Q.Comment: 5 pages + figures - Accepted to ApJ Lette
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