1,295 research outputs found
Disc galaxies with multiple triaxial structures. II. JHK surface photometry and numerical simulations
We present detailed JHK surface photometry with ellipse fits of 13 galaxies
selected from previous optical observations as likely candidates for having a
secondary bar or a triaxial bulge within the primary bar. We have found 7
double-barred galaxies, 3 double-barred galaxies with an additional
intermediate structure with twisted isophotes, and 3 galaxies with a bar and
central twisted isophotes. A global analysis of the structural parameter
characteristics in the I- and K-bands is presented. Various numerical models of
galaxies with bars within bars are also analysed using the ellipse fitting
technique and compared to the observations. A thorough review of the possible
hypotheses able to explain this phenomenon is given with emphasis on the most
likely ones.Comment: 12 pages, AATEX. Accepted for publication in A&A. Large color
postscript figures omitted (Figs. 1), figures 2-9 included; gzip'ed
postscript files of the paper and Figs. 1 available via anonymous ftp at
ftp://obsftp.unige.ch/pub/fri/aasjhk/ , files fri_aasjhk.ps.gz and ngc*.ps.g
The -Class Tower of
The seminal papers in the field of root-discriminant bounds are those of
Odlyzko and Martinet. Both papers include the question of whether the field
has finite or infinite -class tower. This is a
critical case that will either substantially lower the best known upper bound
for lim inf of root-discriminants (if infinite) or else give a counter-example
to what is often termed Martinet's conjecture or question (if finite). Using
extensive computation and introducing some new techniques, we give strong
evidence that the tower is in fact finite, establishing other properties of its
Galois group en route
Tight contact structures and taut foliations
We show the equivalence of several notions in the theory of taut foliations
and the theory of tight contact structures. We prove equivalence, in certain
cases, of existence of tight contact structures and taut foliations.Comment: Published in Geometry and Topology at
http://www.maths.warwick.ac.uk/gt/GTVol4/paper7.abs.htm
Near-infrared probing of embedded structures in starburst and Seyfert galaxies
Surface photometry in the J and K' bands of 15 southern Seyfert or starburst
galaxies is presented. The detailed central morphology and structural
properties of these objects were analyzed by fitting ellipses to isophotes. New
central peculiar structures have been identified like, for instance, three
double-barred systems (ESO 215-G031; ESO 320-G030; ESO 443-G017), one object
with a nested nuclear spiral structure at the center of a primary bar (NGC
5135), one object with a nuclear bar without evidence of a large-scale bar (NGC
4941), and one galaxy with a likely dissolved secondary bar within a primary
one (ESO 508-G005). The J-K' radial profile proved to be reasonably well linked
with the presence of a starburst, but not with the Seyfert activity. For
significant starbursts, the central J-K' value is 0.3-1.5 magnitude larger than
the disc one.Comment: 19 pages, 10 figures, accepted for publication in A&A
Density hardening plasticity and mechanical aging of silica glass under pressure: A Raman spectroscopic study
In addition of a flow, plastic deformation of structural glasses (in
particular amorphous silica) is characterized by a permanent densification.
Raman spectroscopic estimators are shown to give a full account of the plastic
behavior of silica under pressure. While the permanent densification of silica
has been widely discussed in terms of amorphous-amorphous transition, from a
plasticity point of view, the evolution of the residual densification with the
maximum pressure of a pressure cycle can be discussed as a density hardening
phenomenon. In the framework of such a mechanical aging effect, we propose that
the glass structure could be labelled by the maximum pressure experienced by
the glass and that the saturation of densification could be associated with the
densest packing of tetrahedra only linked by their vertices
The Distribution of Bar and Spiral Strengths in Disk Galaxies
The distribution of bar strengths in disk galaxies is a fundamental property
of the galaxy population that has only begun to be explored. We have applied
the bar/spiral separation method of Buta, Block, and Knapen to derive the
distribution of maximum relative gravitational bar torques, Q_b, for 147 spiral
galaxies in the statistically well-defined Ohio State University Bright Galaxy
Survey (OSUBGS) sample. Our goal is to examine the properties of bars as
independently as possible of their associated spirals. We find that the
distribution of bar strength declines smoothly with increasing Q_b, with more
than 40% of the sample having Q_b <= 0.1. In the context of recurrent bar
formation, this suggests that strongly-barred states are relatively short-lived
compared to weakly-barred or non-barred states. We do not find compelling
evidence for a bimodal distribution of bar strengths. Instead, the distribution
is fairly smooth in the range 0.0 <= Q_b < 0.8. Our analysis also provides a
first look at spiral strengths Q_s in the OSU sample, based on the same torque
indicator. We are able to verify a possible weak correlation between Q_s and
Q_b, in the sense that galaxies with the strongest bars tend also to have
strong spirals.Comment: Accepted for publication in the Astronomical Journal, August 2005
issue (LaTex, 23 pages + 11 figures, uses aastex.cls
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