338 research outputs found
Porciones 69, 70, 71, 72
From John Closner and Family Collection, contains two typed documents: 1) Affidavit of Francisco Tagle, Sr. as to possession of Porciones No. 71 and 72 (12 March 1906); 2) affidavit describing property purchase options among John Closner, J. P. Withers, James B. Wells (2 May 1902).
Porcion 69, 70, 71, 72, 1902-1906, Container: 39, Box: 1, Folder: 8. University of Texas Rio Grande Valley Special Collections and Archives, Edinburg Campus. https://archives.lib.utrgv.edu/repositories/2/archival_objects/80722https://scholarworks.utrgv.edu/hidalgohist/1011/thumbnail.jp
Simple Models for Turbulent Self-Regulation in Galaxy Disks
We propose that turbulent heating, wave pressure and gas exchanges between
different regions of disks play a dominant role in determining the preferred,
quasi-equilibrium, self-similar states of gas disks on large-scales. We present
simple families of analytic, thermohydrodynamic models for these global states,
which include terms for turbulent pressure and Reynolds stresses. Star
formation rates, phase balances, and hydrodynamic forces are all tightly
coupled and balanced. The models have stratified radial flows, with the cold
gas slowly flowing inward in the midplane of the disk, and with the warm/hot
phases that surround the midplane flowing outward.
The models suggest a number of results that are in accord with observation,
as well as some novel predictions, including the following. 1) The large-scale
gas density and thermal phase distributions in galaxy disks can be explained as
the result of turbulent heating and spatial couplings. 2) The turbulent
pressures and stresses that drive radial outflows in the warm gas also allow a
reduced circular velocity there. This effect was observed by Swaters, Sancisi
and van der Hulst in NGC 891, a particularly turbulent edge-on disk. The models
predict that the effect should be universal in such disks. 3) They suggest that
a star formation rate like the phenomenological Schmidt Law is the natural
result of global thermohydrodynamical balance, and may not obtain in disks far
from equilibrium. (Abridged)Comment: 37 pages, 1 gif figure, accepted for publication in the Astrophysical
Journa
Superbubble evolution including the star-forming clouds: Is it possible to reconcile LMC observations with model predictions?
Here we present a possible solution to the apparent discrepancy between the
observed properties of LMC bubbles and the standard, constant density bubble
model. A two-dimensional model of a wind-driven bubble expanding from a
flattened giant molecular cloud is examined. We conclude that the expansion
velocities derived from spherically symmetric models are not always applicable
to elongated young bubbles seen almost face-on due to the LMC orientation. In
addition, an observational test to differentiate between spherical and
elongated bubbles seen face-on is discussed.Comment: 25 pages, 7 figures, accepted to ApJ (September, 1999 issue
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
On the Spatial Distribution of Stellar Populations in the Large Magellanic Cloud
We measure the angular correlation function of stars in a region of the Large
Magellanic Cloud (LMC) that spans 2 degrees by 1.5 degrees. We find that the
correlation functions of stellar populations are represented well by
exponential functions of the angular separation for separations between 2 and
40 arcmin (corresponding to ~ 30 pc and 550 pc for an LMC distance of 50 kpc).
The inner boundary is set by the presence of distinct, highly correlated
structures, which are the more familiar stellar clusters, and the outer
boundary is set by the observed region's size and the presence of two principal
centers of star formation within the region. We also find that the
normalization and scale length of the correlation function changes
systematically with the mean age of the stellar population. The existence of
positive correlation at large separations (~300 pc), even in the youngest
population, argues for large-scale hierarchical structure in current star
formation. The evolution of the angular correlation toward lower normalizations
and longer scale lengths with stellar age argues for the dispersion of stars
with time. We show that a simple, stochastic, self-propagating star formation
model is qualitatively consistent with this behavior of the correlation
function.Comment: 30 pages, 13 Figures. Scheduled for publication in AJ in June 199
Is the Cygnus Loop two supernova remnants?
The Cygnus Loop is classified as a middle-aged supernova remnant (SNR)
located below the Galactic equator (l=74, b=-8.6) and 770 pc away from us. Its
large size and little confusion with Galactic emission makes it an ideal test
ground for evolutionary and structural theories of SNRs. New radio continuum
mapping of the Cygnus Loop at 2695 MHz with the Effelsberg 100-m telescope
provides indications that the Cygnus Loop consists of two separate SNRs.
Combining this result with data from the literature we argue that a secondary
SNR exists in the south with a recently detected neutron star close to its
center. Two interacting SNRs seem to be the best explanation to account for the
Cygnus Loop observations at all wavelengths.Comment: 4 pages, 2 figures, Astron. Astrophys., accepte
Two Large HI Shells in the Outer Galaxy near l=279 degrees
As part of a survey of HI 21-cm emission in the Southern Milky Way, we have
detected two large shells in the interstellar neutral hydrogen near l=279 deg.
The center velocities are +36 and +59 km/s, which puts the shells at kinematic
distances of 7 and 10 kpc. The larger shell is about 610 pc in diameter and
very empty, with density contrast of at least 15 between the middle and the
shell walls. It has expansion velocity of about 20 km/s and swept up mass of
several million solar masses. The energy indicated by the expansion may be as
high as 2.4 X 10^53 ergs. We estimate its age to be 15 to 20 million years. The
smaller shell has diameter of about 400 pc, expansion velocity about 10 km/s
and swept up mass of about 10^6 solar masses.
Morphologically both regions appear to be shells, with high density regions
mostly surrounding the voids, although the first appears to have channels of
low density which connect with the halo above and below the HI layer. They lie
on the edge of the Carina arm, which suggests that they may be expanding
horizontally into the interarm region as well as vertically out of the disk. If
this interpretation is correct, this is the first detection of an HI chimney
which has blown out of both sides of the disk.Comment: 21 pages, 14 jpeg figures, accepted for publication in A
On the Hydrodynamic Interaction of Shock Waves with Interstellar Clouds. II. The Effect of Smooth Cloud Boundaries on Cloud Destruction and Cloud Turbulence
The effect of smooth cloud boundaries on the interaction of steady planar
shock waves with interstellar clouds is studied using a high-resolution local
AMR technique with a second-order accurate axisymmetric Godunov hydrodynamic
scheme. A 3D calculation is also done to confirm the results of the 2D ones. We
consider an initially spherical cloud whose density distribution is flat near
the cloud center and has a power-law profile in the cloud envelope. When an
incident shock is transmitted into a smooth cloud, velocity gradients in the
cloud envelope steepen the smooth density profile at the upstream side,
resulting in a sharp density jump having an arc-like shape. Such a ``slip
surface'' forms immediately when a shock strikes a cloud with a sharp boundary.
For smoother boundaries, the formation of slip surface and therefore the onset
of hydrodynamic instabilities are delayed. Since the slip surface is subject to
the Kelvin-Helmholtz and Rayleigh-Taylor instabilities, the shocked cloud is
eventually destroyed in cloud crushing times. After complete cloud
destruction, small blobs formed by fragmentation due to hydrodynamic
instabilities have significant velocity dispersions of the order of 0.1 ,
where is the shock velocity in the ambient medium. This suggests that
turbulent motions generated by shock-cloud interaction are directly associated
with cloud destruction. The interaction of a shock with a cold HI cloud should
lead to the production of a spray of small HI shreds, which could be related to
the small cold clouds recently observed by Stanimirovic & Heiles (2005). The
linewidth-size relation obtained from our 3D simulation is found to be
time-dependent. A possibility for gravitational instability triggered by shock
compression is also discussed.Comment: 62 pages, 16 figures, submitted to Ap
Supernova Enrichment of Dwarf Spheroidal Galaxies
(Abridged) Many dwarf galaxies exhibit sub-Solar metallicities, with some
star-to-star variation, despite often containing multiple generations of stars.
The total metal content in these systems is much less than expected from the
heavy element production of massive stars in each episode of star formation.
Such a deficiency implies that a substantial fraction of the enriched material
has been lost from these small galaxies. Mass ejection from dwarf galaxies may
have important consequences for the evolution of the intergalactic medium and
for the evolution of massive galaxies, which themselves may have formed via the
merger of smaller systems. We report here the results of three-dimensional
simulations of the evolution of supernova-enriched gas within dwarf spheroidal
galaxies (dSph's), with the aim of determining the retention efficiency of
supernova ejecta. We consider two galaxy models, selected to represent opposite
ends of the dSph sequence. For each model galaxy we investigate a number of
scenarios, ranging from a single supernova in smooth gas distributions to more
complex multiple supernovae in highly disturbed gas distributions. The results
of these investigations suggest that, for low star-formation efficiencies, it
is difficult to completely expel the enriched material from the galaxy. Most of
the enriched gas is, however, lost from the core of the galaxy following
multiple supernovae, especially if the interstellar medium is already highly
disturbed by processes such as photo-ionization and stellar winds. If
subsequent star formation occurs predominantly within the core where most of
the residual gas is concentrated, then these results could explain the poor
self-enrichment efficiency observed in dwarf galaxies.Comment: 29 pages, 10 figures, to appear in Astrophysical Journa
Expansion of W 3(OH)
A direct measurement of the expansion of W 3(OH) is made by comparing Very
Large Array images taken about 10 yr apart. The expansion is anisotropic with a
typical speed of 3 to 5 km/s, indicating a dynamical age of only 2300 yr. These
observations are inconsistent with either the freely expanding shell model or a
simple bow shock model. The most favored model is a slowly expanding shell-like
HII region, with either a fast rarefied flow or another less massive diffuse
ionized region moving towards the observer. There is also a rapidly evolving
source near the projected center of emission, perhaps related to the central
star.Comment: LaTeX file, 28 pages, includes 8 figures. To appear in ApJ in
December 10 (1998) issue. Also available at
http://www.submm.caltech.edu/~kawamura/w3oh_pp.p
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