1,207 research outputs found
Central Mass Concentration and Bar Dissolution in Nearby Spiral Galaxies
We use data from the BIMA Survey of Nearby Galaxies (SONG) to investigate the
relationship between ellipticity and central mass concentration in barred
spirals. Existing simulations predict that bar ellipticity decreases as
inflowing mass driven by the bar accumulates in the central regions, ultimately
destroying the bar. Using the ratio of the bulge mass to the mass within the
bar radius as an estimate of the central mass concentration, we obtain
dynamical mass estimates from SONG CO 1-0 rotation curve data. We find an
inverse correlation between bar ellipticity and central mass concentration,
consistent with simulations of bar dissolution.Comment: 10 pages, 2 figures and 2 tables, accepted for publication in the
Astrophysical Journa
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
Towards the Secondary Bar: Gas Morphology and Dynamics in NGC 4303
The bulk of the molecular line emission in the double barred galaxy NGC4303
as observed in its CO(1-0) line with the OVRO mm-interferometer comes from two
straight gas lanes which run north-south along the leading sides of the
large-scale primary bar. Inside a radius of ~ 400 pc the molecular gas forms a
spiral pattern which, for the northern arm, can be traced to the nucleus.
Comparison of the OVRO and archival HST data with dynamical models of gas flow
in the inner kiloparsec of single- and double-barred galaxies shows that the
observed global properties of the molecular gas are in agreement with models
for the gas flow in a strong, large-scale bar, and the two-arm spiral structure
seen in CO in the inner kiloparsec can already be explained by a density wave
initiated by the potential of that bar. Only a weak correlation between the
molecular gas distribution and the extinction seen in the HST V-H map is found
in the inner 400 pc of NGC4303: The innermost part of one arm of the nuclear CO
spiral correlates with a weak dust filament in the color map, while the overall
dust distribution follows a ring or single-arm spiral pattern well correlated
with the UV continuum. This complicated nuclear geometry of the stellar and
gaseous components allows for two scenarios: (A) A self-gravitating m=1 mode is
present forming the spiral structure seen in the UV continuum. In this case the
gas kinematics would be unaffected by the small (~ 4'') inner bar. (B) The UV
continuum traces a complete ring which is heavily extincted north of the
nucleus. Such a ring forms in hydrodynamic models of double bars, but the
models cannot account for the UV emission observed on the leading side of the
inner bar. (abridged)Comment: 47 pages, 14 figures, accepted for publication in Ap
A Dust-Penetrated Classification Scheme for Bars as Inferred from their Gravitational Force Fields
The division of galaxies into ``barred'' (SB) and ``normal'' (S) spirals is a
fundamental aspect of the Hubble galaxy classification system. This ``tuning
fork'' view was revised by de Vaucouleurs, whose classification volume
recognized apparent ``bar strength'' (SA, SAB, SB) as a continuous property of
galaxies called the ``family''. However, the SA, SAB, and SB families are
purely visual judgments that can have little bearing on the actual bar strength
in a given galaxy. Until very recently, published bar judgments were based
exclusively on blue light images, where internal extinction or star formation
can either mask a bar completely or give the false impression of a bar in a
nonbarred galaxy. Near-infrared camera arrays, which principally trace the old
stellar populations in both normal and barred galaxies, now facilitate a
quantification of bar strength in terms of their gravitational potentials and
force fields. In this paper, we show that the maximum value, Qb, of the ratio
of the tangential force to the mean radial force is a quantitative measure of
the strength of a bar. Qb does not measure bar ellipticity or bar shape, but
rather depends on the actual forcing due to the bar embedded in its disk. We
show that a wide range of true bar strengths characterizes the category ``SB'',
while de Vaucouleurs category ``SAB'' corresponds to a much narrower range of
bar strengths. We present Qb values for 36 galaxies, and we incorporate our bar
classes into a dust-penetrated classification system for spiral galaxies.Comment: Accepted for publication in the Astrophysical Journal (LaTex, 30
pages + 3 figures); Figs. 1 and 3 are in color and are also available at
http://bama.ua.edu/~rbuta/bars
Globular cluster systems in elliptical galaxies of Coma
Globular cluster systems of 17 elliptical galaxies have been studied in the
Coma cluster of galaxies. Surface-brightness fluctuations have been used to
determine total populations of globular clusters and specific frequency (S_N)
has been evaluated for each individual galaxy. Enormous differences in S_N
between similar galaxies are found. In particular, S_N results vary by an order
of magnitude from galaxy to galaxy. Extreme cases are the following: a) at the
lower end of the range, NGC 4673 has S_N = 1.0 +/- 0.4, a surprising value for
an elliptical galaxy, but typical for spiral and irregular galaxies; b) at the
upper extreme, MCG +5 -31 -063 has S_N = 13.0 +/- 4.2 and IC 4051 S_N = 12.7
+/- 3.2, and are more likely to belong to supergiant cD galaxies than to
"normal" elliptical galaxies. Furthermore, NGC 4874, the central supergiant cD
galaxy of the Coma cluster, also exhibits a relatively high specific frequency
(S_N = 9.0 +/- 2.2). The other galaxies studied have S_N in the range [2, 7],
the mean value being S_N = 5.1. No single scenario seems to account for the
observed specific frequencies, so the history of each galaxy must be deduced
individually by suitably combining the different models (in situ, mergers, and
accretions). The possibility that Coma is formed by several subgroups is also
considered. If only the galaxies of the main subgroup defined by Gurzadyan &
Mazure (2001) are used, a trend in S_N arises in the sense of S_N being bigger
in higher density regions. This result needs further confirmation.Comment: 43 pages including 12 .ps figures, accepted for publication in Ap
Body silhouette, menstrual function at adolescence and breast cancer risk in the E3N cohort study
We analysed the relation between adult breast cancer risk and adiposity in ages 8â25, and among 90â509 women included in the E3N cohort study, and investigated the potential modification effect of certain factors. Participants completed a questionnaire that included a set of eight silhouettes corresponding to body shape at different ages. During the follow-up (mean=11.4 years), 3491 breast cancer cases were identified. Negative trends in risk of breast cancer with increasing body silhouettes at age 8 and at menarche were observed, irrespective of menopausal status, with relative risks of 0.73 (0.53â0.99) and 0.82 (0.66â1.02) for women who reported a silhouette equal or greater than the fifth silhouette at age 8 and at menarche, respectively. We observed no clear effect modification by age at menarche, delay between age at menarche, regular cycling, regularity of cycles in adult life or body mass index at baseline
The Remarkable Central Structure of the Barred Galaxy NGC 1415
A remarkable structure is observed in the innermost regions of the barred
galaxy NGC 1415 : a small stellar bar, bright circumnuclear ionized gas seen in
Halpha, two bright ionized gas sources, seen in Halpha, just beyond the ends of
the small bar and a boxy distribution of optical continuum. We have developed a
mass distribution model consisting in disk, a bulge, and a bar to approximate t
he observed central morphology and its surface brightness. In order to
reproduce the observed optical brightness distribution a two-component bar was
used, with one component to model the elongated isophotes of the bar and the
second component to model the boxy-shaped isophotes. We interpret the
circumnuclear ionized gas as forming a circumnuclear ring and the two bright
sources as a nuclear and/or circumnuclear outflow slightly out of the plane of
the disk.Comment: 19 pages, 29 figures. To be published in February 2000, ApJ, 52
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