1,078 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
The ultraviolet visibility and quantitative morphology of galactic disks at low and high redshift
We used ultraviolet (200 nm) images of the local spiral galaxies M33, M51,
M81, M100, M101 to compute morphological parameters of galactic disks at this
wavelength : half-light radius , surface brightness distributions,
asymmetries () and concentrations (). The visibility and the evolution
of the morphological parameters are studied as a function of the redshift. The
main results are : local spiral galaxies would be hardly observed and
classified if projected at high redshifts (z 1) unless a strong
luminosity evolution is assumed. Consequently, the non-detection of large
galactic disks cannot be used without caution as a constraint on the evolution
of galatic disks. Spiral galaxies observed in ultraviolet appear more irregular
since the contribution from the young stellar population becomes predominent.
When these galaxies are put in a (log vs. log ) diagram, they move to
the irregul ar sector defined at visible wavelengths. Moreover, the log
parameter is degenerate and cannot be used for an efficient classification of
morphological ultraviolet types. The analysis of high redshift galaxies cannot
be carried out in a reliable way so far and a multi-wavelength approach is
required if one does not want to misinterpret the data.Comment: 12 pages, accepted for publication in A&A on 15 January 200
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
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
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