929 research outputs found
Dark matter in low mass surface density galaxies
Low mass surface density spiral and irregular galaxies like low surface
brightness (LSB) and dwarf galaxies are unique laboratories to study the
dynamical properties of Dark Matter halos because their mass is generally
dominated by dark matter at all galactocentric radii. We present results from
the largest sample ever assembled of high resolution Halpha velocity fields of
LSB and dwarf galaxies in order to study their mass distributions.Comment: 2 pages, 1 figure, proceedings of the conference "Pathways Through an
Eclectic Universe", Johan Knapen, Terry Mahoney, and Alexandre Vazdekis ed
Harmonic analysis of the Ha velocity field of NGC 4254
The ionized gas kinematics of the Virgo Cluster galaxy NGC 4254 (Messier 99)
is analyzed by an harmonic decomposition of the velocity field into Fourier
coefficients. The aims of this study are to measure the kinematical asymmetries
of Virgo cluster galaxies and to connect them to the environment. The analysis
reveals significant terms which origins are discussed.Comment: 3 pages, 2 figures, to appear in "Science Perspectives for 3D
Spectroscopy", ESO Astrophysics Symposia, M. Kissler-Patig, M.M. Roth & J.R.
Walsh ed
Kinematics and Mass Modeling of Messier 33: Halpha observations
As part of a long-term project to revisit the kinematics and dynamics of the
large disc galaxies of the Local Group, we present the first deep, wide-field
(42' x 56') 3D-spectroscopic survey of the ionized gas disc of Messier 33.
Fabry-Perot interferometry has been used to map its Ha distribution and
kinematics at unprecedented angular resolution (<3'') and resolving power
(12600), with the 1.6m telescope at the Observatoire du Mont Megantic. The
ionized gas distribution follows a complex, large-scale spiral structure,
unsurprisingly coincident with the already-known spiral structures of the
neutral and molecular gas discs. The kinematical analysis of the velocity field
shows that the rotation center of the Ha disc is distant from the photometric
center by 170 pc (sky projected distance) and that the kinematical major-axis
position angle and disc inclination are in excellent agreement with photometric
values. The Ha rotation curve agrees very well with the HI rotation curves for
0 6.5 kpc.
The reason for this discrepancy is not well understood. The velocity dispersion
profile is relatively flat around 16 km/s, which is at the low end of velocity
dispersions of nearby star-forming galactic discs. A strong relation is also
found between the Ha velocity dispersion and the Ha intensity. Mass models were
obtained using the Ha rotation curve but, as expected, the dark matter halo's
parameters are not very well constrained since the optical rotation curve only
extends out to 8 kpc.Comment: 26 pages, 18 figures, accepted for publication in MNRA
Kinematics and dynamics of the M51-type galaxy pair NGC 3893/96 (KPG 302)
We study the kinematics and dynamics of the M51-type interacting galaxy pair
KPG 302 (NGC 3893/96). We analyse the distribution of the dark matter (DM) halo
of the main galaxy in order to explore possible differences between DM halos of
"isolated" galaxies and those of galaxies belonging to a pair. The velocity
field of each galaxy was obtained using scanning Fabry-Perot interferometry. A
two-dimensional kinematic and dynamical analysis of each galaxy and the pair as
a whole is done emphasizing the contribution of circular and non-circular
velocities. Non-circular motions can be traced on the rotation curves of each
galaxy allowing us to differentiate between motions associated to particular
features and motions that reflect the global mass distribution of the galaxy.
For the main galaxy of the pair, NGC 3893, optical kinematic information is
complemented with HI observations from the literature to build a
multi-wavelength rotation curve. We try to fit this curve with a
mass-distribution model using different DM halos. We find that the
multi-wavelength rotation curve of NGC 3893, "cleaned" from the effect of
non-circular motions, cannot be fitted neither by a pseudo-isothermal nor by a
NFW DM halo.Comment: Accepted for publication in A&A. 11 pages, 9 figures and 2 table
Accurate Determination of the Mass Distribution in Spiral Galaxies: II. Testing the Shape of Dark Halos
New high resolution CFHT Fabry-Perot data, combined with published VLA 21 cm
observations are used to determine the mass distribution of NGC 3109 and IC
2574. The multi-wavelength rotation curves allow to test with confidence
different dark halo functional forms from the pseudo-isothermal sphere to some
popular halo distributions motivated by N-body simulations. It appears that
density distribution with an inner logarithmic slope <= -1 are very hard to
reconcile with rotation curves of late type spirals. Modified Newtonian
Dynamics (MOND) is also considered as a potential solution to missing mass and
tested the same way. The new higher resolution data show that MOND can
reproduce in details the rotation curve of IC 2574 but confirm its difficulty
to fit the kinematics of NGC 3109.Comment: 28 pages, accepted by AJ. New HI profile increases the compatibility
of NGC 3109 rotation curve with MON
A galactic weigh-in: mass models of SINGS galaxies using chemospectrophotometric galactic evolution models
The baryonic mass-to-light ratio used to perform the photometry-to-mass
conversion has a tremendous influence on the measurement of the baryonic
content and distribution, as well as on the determination of the dark halo
parameters. Since numerous clues hint at an inside-out formation process for
galaxies, a radius-dependant mass-to-light ratio is needed to physically
represent the radially varying stellar population. In this article, we use
chemo-spectrophotometric galactic evolution (CSPE) models to determine the
mass-to-light ratio for a wide range of masses and sizes in the scenario of an
inside-out formation process by gas accretion. We apply our method on a SINGS
subsample of ten spiral and dwarf galaxies for stellar bands covering from the
UV to the MIR. The CSPE models prove to be a good tool to weight the different
photometric bands in order to obtain consistent stellar discs' masses
regardless of the spectral band used. On the other hand, we show that colour
index vs. the mass-to-light ratio relation is an imperfect tool to assign
masses to young stellar populations because of the degeneracy affecting
mass-to-light ratio in all bands at low colour index. Resulting discs from our
analysis are compatible with the maximum disc hypothesis provided that adequate
bulge/disc decomposition is performed and correction for the presence of a bar
is not neglected since it disturbs the internal disc kinematics. Disc-mass
models including mass-to-light ratio-as a free parameter as well as models
using our physically motivated radial variation of mass-to-light ratio are
presented and discussed for each galaxy.Comment: 27 pages, 15 figures, accepted for publication in the Astrophysical
Journa
The ratio of pattern speeds in double-barred galaxies
We have obtained two-dimensional velocity fields in the ionized gas of a set
of 8 double-barred galaxies, at high spatial and spectral resolution, using
their H emission fields measured with a scanning Fabry-Perot
spectrometer. Using the technique by which phase reversals in the non-circular
motion indicate a radius of corotation, taking advantage of the high angular
and velocity resolution we have obtained the corotation radii and the pattern
speeds of both the major bar and the small central bar in each of the galaxies;
there are few such measurements in the literature. Our results show that the
inner bar rotates more rapidly than the outer bar by a factor between 3.3 and
3.6.Comment: 5 pages, 1 figure, 1 tabl
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