787 research outputs found
Photometric structure of the peculiar galaxy ESO 235-G58
We present the near-infrared and optical properties of the peculiar galaxy
ESO 235-G58, which resembles a late-type ringed barred spiral seen close to
face-on. However, the apparent bar of ESO 235-G58 is in reality an edge-on disk
galaxy of relatively low luminosity. We have analyzed the light and color
distributions of ESO 235-G58 in the NIR and optical bands and compared them
with the typical properties observed for other morphological galaxy types,
including polar ring galaxies. Similar properties are observed for ESO 235-G58,
polar ring galaxies, and spiral galaxies, which leads us to conclude that this
peculiar system is a polar-ring-related galaxy, characterized by a low inclined
ring/disk structure, as pointed out by Buta & Crocker in an earlier study,
rather than a barred galaxy.Comment: 16 pages, 15 figures, accepted for publication in Astronomy &
Astrophysic
Comparison of bar strengths in active and non-active galaxies
Bar strengths are compared between active and non-active galaxies for a
sample of 43 barred galaxies. The relative bar torques are determined using a
new technique (Buta and Block 2001), where maximum tangential forces are
calculated in the bar region, normalized to the axisymmetric radial force
field. We use JHK images of the 2 Micron All Sky Survey. We show a first clear
empirical indication that the ellipticies of bars are correlated with the
non-axisymmetric forces in the bar regions. We found that nuclear activity
appears preferentially in those early type galaxies in which the maximum bar
torques are weak and appear at quite large distances from the galactic center.
Most suprisingly the galaxies with the strongest bars are non-active. Our
results imply that the bulges may be important for the onset of nuclear
activity, but that the correlation between the nuclear activity and the early
type galaxies is not straightforward.Comment: MNRAS macro in tex format, 9 pages, 10 figure
Galaxy transmutations: The double ringed galaxy ESO 474-G26
Surface photometry and a 21cm HI line spectrum of the giant double-ringed
galaxy ESO 474-G26 are presented. The morphology of this system is unique among
the 30,000 galaxies with >B15. Two almost orthogonal optical rings with
diameters of 60 and 40 kpc surround the central body (assuming H0=70 km/s/Mpc).
The outer one is an equatorial ring, while the inner ring lies in a nearly
polar plane. The rings have blue optical colors typical of late-type spirals.
Both appear to be rotating around the central galaxy, so that this system can
be considered as a kinematically confirmed polar ring galaxy. Its observational
characteristics are typical of galaxy merger remnants. Although the central
object has a surface brightness distribution typical of elliptical galaxies, it
has a higher surface brightness for its effective radius than ordinary
ellipticals. Possible origins of this galaxy are discussed and numerical
simulations are presented that illustrate the formation of the two rings in the
merging process of two spiral galaxies, in which the observed appearance of ESO
474-G26 appears to be a transient stage.Comment: Accepted for publication in A&
The Kinematically Measured Pattern Speeds of NGC 2523 and NGC 4245
We have applied the Tremaine-Weinberg continuity equation method to derive
the bar pattern speed in the SB(r)b galaxy NGC 2523 and the SB(r)0/a galaxy NGC
4245 using the Calcium Triplet absorption lines. These galaxies were selected
because they have strong inner rings which can be used as independent tracers
of the pattern speed. The pattern speed of NGC 2523 is 26.4 6.1 km
s kpc, assuming an inclination of 49.7 and a distance
of 51.0 Mpc. The pattern speed of NGC 4245 is 75.5 31.3 km s
kpc, assuming an inclination of 35.4 and a distance of 12.6
Mpc. The ratio of the corotation radius to the bar radius of NGC 2523 and NGC
4245 is 1.4 0.3 and 1.1 0.5, respectively. These values place the
bright inner rings near and slightly inside the corotation radius, as predicted
by barred galaxy theory. Within the uncertainties, both galaxies are found to
have fast bars that likely indicate dark halos of low central concentration.
The photometric properties, bar strengths, and disk stabilities of both
galaxies are also discussed.Comment: Accepted for publication in The Astronomical Journal, 11 figures, 2
table
N-body simulations in reconstruction of the kinematics of young stars in the Galaxy
We try to determine the Galactic structure by comparing the observed and
modeled velocities of OB-associations in the 3 kpc solar neighborhood. We made
N-body simulations with a rotating stellar bar. The galactic disk in our model
includes gas and stellar subsystems. The velocities of gas particles averaged
over large time intervals ( bar rotation periods) are compared with the
observed velocities of the OB-associations. Our models reproduce the directions
of the radial and azimuthal components of the observed residual velocities in
the Perseus and Sagittarius regions and in the Local system. The mean
difference between the model and observed velocities is km
s. The optimal value of the solar position angle providing
the best agreement between the model and observed velocities is
, in good accordance with several recent estimates. The
self-gravitating stellar subsystem forms a bar, an outer ring of subclass
, and slower spiral modes. Their combined gravitational perturbation leads
to time-dependent morphology in the gas subsystem, which forms outer rings with
elements of the - and -morphology. The success of N-body simulations
in the Local System is likely due to the gravity of the stellar -ring,
which is omitted in models with analytical bars.Comment: 13 pages, 13 figures, accepted to Astronomy and Astrophysic
The Distribution of Maximum Relative Torques in Disk Galaxies
The maximum ratio of the tangential force to the mean background radial force
is a useful quantitative measure of the strength of nonaxisymmetric
perturbations in disk galaxies. Here we consider the distribution of this
ratio, called Qg, for a statistically well-defined sample of 180 spiral
galaxies from the Ohio State University Bright Galaxy Survey and the Two Micron
All-Sky Survey. Qg is derived from gravitational potentials inferred from
near-infrared images under the assumptions of a constant mass-to-light ratio
and an exponential vertical density law. In order to derive the most reliable
maximum relative torques, orientation parameters based on blue-light isophotes
are used to deproject the galaxies, and the more spherical shapes of bulges are
taken into account using two-dimensional decompositions which allow for
analytical fits to bulges, disks, and bars. Also, vertical scaleheights hz are
derived by scaling the radial scalelengths hR from the two-dimensional
decompositions allowing for the type dependence of hR/hz indicated by optical
and near-infrared studies of edge-on spiral galaxies. The impact of dark matter
is assessed using a "universal rotation curve" parametrization, and is found to
be relatively insignificant for our sample. In agreement with a previous study
by Block et al. (2002), the distribution of maximum relative gravitational
torques is asymmetric towards large values and shows a deficiency of low Qg
galaxies. However, due to the above refinements, our distribution shows more
low Qg galaxies than Block et al. We also find a significant type-dependence in
maximum relative gravitational torques, in the sense that Qg is lower on
average in early-type spirals compared to late-type spirals.Comment: Accepted for publication in the Astronomical Journal, January 2004
issue (Latex, 39 pages + 17 figures, uses aastex.cls
A Mixed-Methods Investigation of Community Attachment in Rural Romania
This article explores the intricacies of community attachment using a multidimensional construct; attachment to the social and natural environment. A central focus is to assess whether attachment to the social and natural environment are distinctively predicted by length of residence, social interaction, and sociodemographic characteristics. Furthermore, this work elaborates on current understandings of community attachment by qualitatively exploring feelings of attachment toward the place of residence. All are explored in the context of rural Romania and communities managing the natural resources available to them. The results show the effect of several independent variables on attachment to social and natural environments. Residency was a stronger predictor of attachment to the social environment, while social interaction was a stronger predictor of attachment to the natural environment. Residentsâ narratives underscored the importance, and interconnection, of the social and natural environment in defining feelings of local attachment. We conclude that community attachment is grounded in different facets of the locale that each play unique roles in shaping citizen perceptions
Inner Molecular Rings in Barred Galaxies: BIMA SONG CO Observations
Although inner star-forming rings are common in optical images of barred
spiral galaxies, observational evidence for the accompanying molecular gas has
been scarce. In this paper we present images of molecular inner rings, traced
using the CO (1-0) emission line, from the
Berkeley-Illinois-Maryland-Association Survey of Nearby Galaxies (BIMA SONG).
We detect inner ring CO emission from all five SONG barred galaxies classified
as inner ring (type (r)). We also examine the seven SONG barred galaxies
classified as inner spiral (type (s)); in one of these, NGC 3627, we find
morphological and kinematic evidence for a molecular inner ring. Inner ring
galaxies have been classified as such based on optical images, which emphasize
recent star formation. We consider the possibility that there may exist inner
rings in which star formation efficiency is not enhanced. However, we find that
in NGC 3627 the inner ring star formation efficiency is enhanced relative to
most other regions in that galaxy. We note that the SONG (r) galaxies have a
paucity of CO and H alpha emission interior to the inner ring (except near the
nucleus), while NGC 3627 has relatively bright bar CO and H alpha emission; we
suggest that galaxies with inner rings such as NGC 3627 may be misclassified if
there are significant amounts of gas and star formation in the bar.Comment: To be published in the Astrophysical Journal, July 2002 A version of
the paper with full resolution figures is available at:
http://www.astro.umd.edu/~mregan/ms.ps.g
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