1,797 research outputs found
Bulge properties and dark matter content of early-type barred galaxies
The dynamics of a barred galaxy depends on the pattern speed of its bar. The
only direct method for measuring the pattern speed of a bar is the
Tremaine-Weinberg technique. This method is best suited to the analysis of the
distribution and dynamics of the stellar component. Therefore it has been
mostly used for early-type barred galaxies. Most of them host a classical
bulge. On the other hand, a variety of indirect methods, which are based on the
analysis of the distribution and dynamics of the gaseous component, has been
used to measure the bar pattern speed in late-type barred galaxies. Nearly all
the measured bars are as rapidly rotating as they can be. By comparing this
result with high-resolution numerical simulations of bars in dark matter halos,
it is possible to conclude that these bars reside in maximal disks.Comment: 4 pages. To appear in the proceedings of IAU Symposium 245 "Formation
and Evolution of Galaxy Bulges", M. Bureau, E. Athanassoula, and B. Barbuy,
ed
Counter-Rotation in Disk Galaxies
Counter-rotating galaxies host two components rotating in opposite directions
with respect to each other. The kinematic and morphological properties of
lenticulars and spirals hosting counter-rotating components are reviewed.
Statistics of the counter-rotating galaxies and analysis of their stellar
populations provide constraints on the formation scenarios which include both
environmental and internal processes.Comment: 10 pages, 2 figures. To appear in ASP Conf. Ser., Multi-Spin
Galaxies, E. Iodice and E. M. Corsini (eds.
Direct measurements of bar pattern speeds
The dynamics of a barred galaxy depends on the angular velocity or pattern
speed of its bar. Indeed, it is related to the location of corotation where
gravitational and centrifugal forces cancel out in the rest frame of the bar.
The only direct method for measuring the bar pattern speed is the
Tremaine-Weinberg technique. This method is best suited to the analysis of the
distribution and kinematics of the stellar component in absence of significant
star formation and patchy dust obscuration. Therefore, it has been mostly used
for early-type barred galaxies. The main sources of uncertainties on the
directly-measured bar pattern speeds are discussed. There are attempts to
overcome the selection bias of the current sample of direct measurements by
extending the application of the Tremaine-Weinberg method to the gaseous
component. Furthermore, there is a variety of indirect methods which are based
on the analysis of the gas distribution and kinematics. They have been largely
used to measure the bar pattern speed in late-type barred galaxies. Nearly all
the bars measured with direct and indirect methods end close to their
corotation radius, i.e., they are as rapidly rotating as they can be.Comment: 8 pages, 1 figure. To appear in "Tumbling, twisting, and winding
galaxies: Pattern speeds along the Hubble sequence", E. M. Corsini and V. P.
Debattista (eds.), Memorie della Societa` Astronomica Italian
The dark matter content of early-type barred galaxies
The dynamics of a barred galaxy depends on the pattern speed of its bar. The
only direct method for measuring the pattern speed of a bar is the
Tremaine-Weinberg technique. This method relies on the analysis of the
distribution and dynamics of the stellar component. It is best suited to
gas-poor galaxies and therefore it has been restricted to early-type barred
galaxies. On the other hand, a variety of indirect methods, which are based on
the analysis of the distribution and dynamics of the gaseous component, has
been used to measure the bar pattern speed in late-type barred galaxies. The
complete sample of galaxies for which the bar pattern speed has been directly
measured with the Tremaine-Weinberg method is given. Nearly all the measured
bars are as rapidly rotating as they can be. By comparing this result with
recent high-resolution N-body simulations of bars in cosmologically-motivated
dark matter halos, it is possible to conclude that these bars are not located
inside centrally-concentrated halos.Comment: 5 pages. Proceedings of "Baryons in Dark Matter Halos". Novigrad,
Croatia, 5-9 Oct 2004. Editors: R. Dettmar, U. Klein, P. Salucci. Published
by SISS
Properties of bars in the local universe
We studied the fraction and properties of bars in a sample of about 3000
galaxies extracted from SDSS-DR5. This represents a volume limited sample with
galaxies located between redshift 0.01-20, and
inclination i < 60. Interacting galaxies were excluded from the sample. The
fraction of barred galaxies in our sample is 45%. We found that 32% of S0s, 55%
of early-type spirals, and 52% of late-type spirals are barred galaxies. The
bars in S0s galaxies are weaker than those in later-type galaxies. The bar
length and galaxy size are correlated, being larger bars located in larger
galaxies. Neither the bar strength nor bar length correlate with the local
galaxy density. On the contrary, the bar properties correlate with the
properties of their host galaxies. Galaxies with higher central light
concentration host less and weaker bars.Comment: 2 pages, 1 figure to appear in the proceedings of "Formation and
Evolution of Galaxy Disks", Rome, October 2007, Eds. J. Funes and E. M.
Corsin
The V_c-sigma_c relation in high and low surface brightness galaxies
We investigate the relation between the asymptotic circular velocity, V_c,
and the central stellar velocity dispersion, sigma_c, in galaxies. We consider
a new sample of high surface brightness spiral galaxies (HSB), low surface
brightness spiral galaxies (LSB), and elliptical galaxies with HI-based V_c
measurements. We find that: 1) elliptical galaxies with HI measurements fit
well within the relation; 2) a linear law can reproduce the data as well as a
power law (used in previous works) even for galaxies with sigma_c < 70 km/s; 3)
LSB galaxies, considered for the first time with this respect, seem to behave
differently, showing either larger V_c values or smaller sigma_c values.Comment: 2 pages, 2 figures, to appear in Proc. IAU Symp. 222, "The Interplay
among Black Holes, Stars and ISM in Galactic Nuclei" eds. Th. Storchi
Bergmann, L.C. Ho & H.R. Schmitt (Cambridge University Press
Structural properties of disk galaxies I. The intrinsic ellipticity of bulges
(Abridged) A variety of formation scenarios was proposed to explain the
diversity of properties observed in bulges. Studying their intrinsic shape can
help in constraining the dominant mechanism at the epochs of their assembly.
The structural parameters of a magnitude-limited sample of 148 unbarred S0--Sb
galaxies were derived in order to study the correlations between bulges and
disks as well as the probability distribution function (PDF) of the intrinsic
equatorial ellipticity of bulges. It is presented a new fitting algorithm
(GASP2D) to perform the two-dimensional photometric decomposition of galaxy
surface-brightness distribution. This was assumed to be the sum of the
contribution of a bulge and disk component characterized by elliptical and
concentric isophotes with constant (but possibly different) ellipticity and
position angles. Bulge and disk parameters of the sample galaxies were derived
from the J-band images which were available in the Two Micron All Sky Survey.
The PDF of the equatorial ellipticity of the bulges was derived from the
distribution of the observed ellipticities of bulges and misalignments between
bulges and disks. Strong correlations between the bulge and disk parameters
were found. About 80% of bulges in unbarred lenticular and
early-to-intermediate spiral galaxies are not oblate but triaxial ellipsoids.
Their mean axial ratio in the equatorial plane is = 0.85. There is not
significant dependence of their PDF on morphology, light concentration, and
luminosity. The interplay between bulge and disk parameters favors scenarios in
which bulges assembled from mergers and/or grew over long times through disk
secular evolution. But all these mechanisms have to be tested against the
derived distribution of bulge intrinsic ellipticities.Comment: 24 pages, 13 figures, accepted for publication in A&A, corrected
proof
Dissecting Kinematics and Stellar Populations of Counter-Rotating Galaxies with 2-Dimensional Spectroscopy
We present a spectral decomposition technique and its applications to a
sample of galaxies hosting large-scale counter-rotating stellar disks. Our
spectral decomposition technique allows to separate and measure the kinematics
and the properties of the stellar populations of both the two counter-rotating
disks in the observed galaxies at the same time. Our results provide new
insights on the epoch and mechanism of formation of these galaxies.Comment: 4 pages, 3 figures. Contributed talk presented at the Conference
"Multi-Spin galaxies", September 30 - October 3, 2013, INAF-Astronomical
Observatory of Capodimonte, Naples, Italy. To be published in ASP Conf. Ser.,
Multi-Spin Galaxies, ed. E. Iodice & E. M. Corsini (San Francisco: ASP
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