148 research outputs found
Delayed Photoionization Feedback in a Super Star Cluster in SBS0335-052E
SBS0335-052 is a well studied Blue Compact Dwarf galaxy with one of the
lowest metallicities of any known galaxy. It also contains 6 previously
identified Super Star Clusters. We combine archival HST NICMOS images in the Pa
alpha line and the 1.6 micron continuum of the eastern component, SBS0335-052E,
with other space and ground based data to perform a multi-wavelength analysis
of the super star clusters. We concentrate on the southern most clusters,
designated S1 and S2, which appear to be the youngest clusters and are the
strongest emitters of Pa alpha, radio, and x-ray flux. Our analysis leads to a
possible model for S1 and perhaps S2 as a cluster of very young, massive stars
with strong stellar winds. The wind density can be high enough to absorb the
majority of ionizing photons within less than 1000 AU of the stars, creating
very compact HII regions that emit optically thick radiation at radio
wavelengths. These winds would then effectively quench the photoionizing flux
very close to the stars. This can delay the onset of negative feedback by
photoionization and photodissociation on star formation in the clusters. This
is significant since SBS0335-052E resembles the conditions that were probably
common for high redshift star formation in galaxies near the epoch of
reionization.Comment: Accepted for publication in the Astrophysical Journa
The Second Byurakan Survey Galaxies. I. The Optical Database
A database for the entire catalog of the Second Byurakan Survey (SBS)
galaxies is presented. It contains new measurements of their optical parameters
and additional information taken from the literature and other databases. The
measurements were made using Ipg(near-infrared), Fpg(red) and Jpg(blue) band
images from photographic sky survey plates obtained by the Palomar Schmidt
telescope and extracted from the STScI Digital Sky Survey (DSS). The database
provides accurate coordinates, morphological type, spectral and activity
classes, apparent magnitudes and diameters, axial ratios, and position angles,
as well as number counts of neighboring objects in a circle of radius 50 kpc.
The total number of individual SBS objects in the database is now 1676. The 188
Markarian galaxies which were re-discovered by SBS are not included in this
database. We also include redshifts that are now available for 1576 SBS
objects, as well as 2MASS infrared magnitudes for 1117 SBS galaxies.Comment: 13 pages, 1 figure, 1 tabl
Chaos and stability in a two-parameter family of convex billiard tables
We study, by numerical simulations and semi-rigorous arguments, a
two-parameter family of convex, two-dimensional billiard tables, generalizing
the one-parameter class of oval billiards of Benettin--Strelcyn [Phys. Rev. A
17, 773 (1978)]. We observe interesting dynamical phenomena when the billiard
tables are continuously deformed from the integrable circular billiard to
different versions of completely-chaotic stadia. In particular, we conjecture
that a new class of ergodic billiard tables is obtained in certain regions of
the two-dimensional parameter space, when the billiards are close to skewed
stadia. We provide heuristic arguments supporting this conjecture, and give
numerical confirmation using the powerful method of Lyapunov-weighted dynamics.Comment: 19 pages, 13 figures. Submitted for publication. Supplementary video
available at http://sistemas.fciencias.unam.mx/~dsanders
Photometric Properties of Kiso Ultraviolet-Excess Galaxies in the Lynx-Ursa Major Region
We have performed a systematic study of several regions in the sky where the
number of galaxies exhibiting star formation (SF) activity is greater than
average. We used Kiso ultraviolet-excess galaxies (KUGs) as our SF-enhanced
sample. By statistically comparing the KUG and non-KUG distributions, we
discovered four KUG-rich regions with a size of . One of these regions corresponds spatially to a filament of length
Mpc in the Lynx-Ursa Major region (). We call this ``the Lynx-Ursa
Major (LUM) filament''. We obtained surface photometry of 11 of
the KUGs in the LUM filament and used these to investigate the integrated
colors, distribution of SF regions, morphologies, and local environments. We
found that these KUGs consist of distorted spiral galaxies and compact galaxies
with blue colors. Their star formation occurs in the entire disk, and is not
confined to just the central regions. The colors of the SF regions imply that
active star formation in the spiral galaxies occurred yr ago,
while that of the compact objects occurred yr ago. Though the
photometric characteristics of these KUGs are similar to those of interacting
galaxies or mergers, most of these KUGs do not show direct evidence of merger
processes.Comment: 39 pages LaTeX, using aasms4.sty, 20 figures, ApJS accepted. The
Title of the previous one was truncated by the author's mistake, and is
corrected. Main body of the paper is unchange
Spectral Statistics in the Quantized Cardioid Billiard
The spectral statistics in the strongly chaotic cardioid billiard are
studied. The analysis is based on the first 11000 quantal energy levels for odd
and even symmetry respectively. It is found that the level-spacing distribution
is in good agreement with the GOE distribution of random-matrix theory. In case
of the number variance and rigidity we observe agreement with the random-matrix
model for short-range correlations only, whereas for long-range correlations
both statistics saturate in agreement with semiclassical expectations.
Furthermore the conjecture that for classically chaotic systems the normalized
mode fluctuations have a universal Gaussian distribution with unit variance is
tested and found to be in very good agreement for both symmetry classes. By
means of the Gutzwiller trace formula the trace of the cosine-modulated heat
kernel is studied. Since the billiard boundary is focusing there are conjugate
points giving rise to zeros at the locations of the periodic orbits instead of
exclusively Gaussian peaks.Comment: 20 pages, uu-encoded ps.Z-fil
The lensing system towards the doubly imaged quasar SBS 1520+530
The gravitational potential responsible for the lensing effect in SBS
1520+530 is studied over length scales from a few arc-seconds to a few
arc-minutes. For this purpose, we use sharply deconvolved Hubble Space
Telescope images in the optical and near-IR, in combination with ground based
optical data obtained over a wider field-of-view. In particular, we have
carried out a multi-color analysis in order to identify groups or clusters of
galaxies along the line of sight. Photometric redshifts are measured for 139
galaxies unveiling significant excesses of galaxies 1.0 arcmin, NW and 1.7
arcmin, SW of the main lensing galaxy. The photometric redshift inferred both
for the main lensing galaxy and for the galaxy concentrations is
z=0.9^{+0.10}_{-0.25}. This is in rough agreement with the measured
spectroscopic redshift of the main lensing galaxy, z=0.71 (Burud et al. 2002),
suggesting that it is part of a larger group or cluster. We investigate the
impact of including the galaxy cluster, first on the modelling of the lensing
system, and second on the expected time--delay between the two quasar images.Comment: Accepted in A&A. 10 pages. Includes 3 jpg figure
Separating the regular and irregular energy levels and their statistics in Hamiltonian system with mixed classical dynamics
We look at the high-lying eigenstates (from the 10,001st to the 13,000th) in
the Robnik billiard (defined as a quadratic conformal map of the unit disk)
with the shape parameter . All the 3,000 eigenstates have been
numerically calculated and examined in the configuration space and in the phase
space which - in comparison with the classical phase space - enabled a clear
cut classification of energy levels into regular and irregular. This is the
first successful separation of energy levels based on purely dynamical rather
than special geometrical symmetry properties. We calculate the fractional
measure of regular levels as which is in remarkable
agreement with the classical estimate . This finding
confirms the Percival's (1973) classification scheme, the assumption in
Berry-Robnik (1984) theory and the rigorous result by Lazutkin (1981,1991). The
regular levels obey the Poissonian statistics quite well whereas the irregular
sequence exhibits the fractional power law level repulsion and globally
Brody-like statistics with . This is due to the strong
localization of irregular eigenstates in the classically chaotic regions.
Therefore in the entire spectrum we see that the Berry-Robnik regime is not yet
fully established so that the level spacing distribution is correctly captured
by the Berry-Robnik-Brody distribution (Prosen and Robnik 1994).Comment: 20 pages, file in plain LaTeX, 7 figures upon request submitted to J.
Phys. A. Math. Gen. in December 199
SBS 1150+599A: an extremely oxygen-poor planetary nebula in the Galactic halo?
We report results of a spectrophotometric study of SBS 1150+599A and discuss
the nature of this object based upon our data. Our study shows that SBS
1150+599A is most probably a planetary nebula located in the Galactic halo and
not a cataclysmic variable as originally proposed by the authors of the Second
Byurakan Survey from low resolution spectroscopy. We have further elaborated on
the properties of SBS 1150+599A (now becoming PN G135.9+55.9) with tools used
for planetary nebula analysis. Our photoionization models show that, in order
to match the observational constraints, the oxygen abundance in the nebula is
probably extremely low, around 1/500 solar, which is one order of magnitude
lower than the most oxygen-poor planetary nebulae known so far. This finding
has strong implications on our understanding of the formation of planetary
nebulae and of the evolution of the Galactic halo.Comment: 13 pages, 5 figures, accepted for publication in Astronomy and
Astrophysic
Edge Diffraction, Trace Formulae and the Cardioid Billiard
We study the effect of edge diffraction on the semiclassical analysis of two
dimensional quantum systems by deriving a trace formula which incorporates
paths hitting any number of vertices embedded in an arbitrary potential. This
formula is used to study the cardioid billiard, which has a single vertex. The
formula works well for most of the short orbits we analyzed but fails for a few
diffractive orbits due to a breakdown in the formalism for certain geometries.
We extend the symbolic dynamics to account for diffractive orbits and use it to
show that in the presence of parity symmetry the trace formula decomposes in an
elegant manner such that for the cardioid billiard the diffractive orbits have
no effect on the odd spectrum. Including diffractive orbits helps resolve peaks
in the density of even states but does not appear to affect their positions. An
analysis of the level statistics shows no significant difference between
spectra with and without diffraction.Comment: 25 pages, 12 Postscript figures. Published versio
3D Spectroscopy of Local Luminous Compact Blue Galaxies: Kinematics of NGC 7673
The kinematic properties of the ionized gas of local Luminous Compact Blue
Galaxy (LCBG) NGC 7673 are presented using three dimensional data taken with
the PPAK integral field unit at the 3.5-m telescope in the Centro Astron\'omico
Hispano Alem\'an. Our data reveal an asymmetric rotating velocity field with a
peak to peak difference of 60 km s. The kinematic centre is found to be
at the position of a central velocity width maximum ( km
s), which is consistent with the position of the luminosity-weighted
centroid of the entire galaxy. The position angle of the minor rotation axis is
168 as measured from the orientation of the velocity field contours.
At least two decoupled kinematic components are found. The first one is compact
and coincides with the position of the second most active star formation region
(clump B). The second one is extended and does not have a clear optical
counterpart. No evidence of active galactic nuclei activity or supernovae
galactic winds powering any of these two components has been found. Our data,
however, show evidence in support of a previously proposed minor merger
scenario in which a dwarf galaxy, tentatively identified with clump B, is
falling into NGC 7673. and triggers the starburst. Finally, it is shown that
the dynamical mass of this galaxy may be severely underestimated when using the
derived rotation curve or the integrated velocity width, under the assumption
of virialization.Comment: Accepted for publication by MNRAS. The paper contains 10 figures and
2 table
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