328 research outputs found
Simulation of disk-disk encounters with co-moving polar grids
The two-grid simulation method combining advantages of both polar and Cartesian mesh-codes is described. In addition to the stellar component reacting solely to gravitational forces, the gas component is included with dissipatively colliding particles. This allows fairly realistic simulation of planar encounters where both systems contain star plus gas disks
The opposition and tilt effects of Saturn's rings from HST observations
The two major factors contributing to the opposition brightening of Saturn's
rings are i) the intrinsic brightening of particles due to coherent
backscattering and/or shadow-hiding on their surfaces, and ii) the reduced
interparticle shadowing. We utilize the Hubble Space Telescope observations for
different elevation angles B to disentangle these contributions. We assume that
the intrinsic contribution is independent of B, so that any B dependence of the
phase curves is due to interparticle shadowing, which must also act similarly
for all colors. We construct a grid of dynamical/photometric simulation models
to fit the elevation-dependent part of opposition brightening. Eliminating the
modeled interparticle component yields the intrinsic contribution to the
opposition effect: for the B and A rings it is almost entirely due to coherent
backscattering; for the C ring, an intraparticle shadow hiding contribution may
also be present.
Based on our simulations, the width of the interparticle shadowing effect is
roughly proportional to B. This follows from the observation that as B
decreases, the scattering is primarily from the rarefied low filling factor
upper ring layers, whereas at larger 's the dense inner parts are visible.
The elevation angle dependence of interparticle shadowing also explains most of
the B ring tilt effect (the increase of brightness with elevation). From
comparison of the magnitude of the tilt effect at different filters, we show
that multiple scattering can account for at most a 10% brightness increase as B
-> 26^o, whereas the remaining 20% brightening is due to a variable degree of
interparticle shadowing. The negative tilt effect of the middle A ring is well
explained by the the same self-gravity wake models that account for the
observed A ring azimuthal brightness asymmetry.Comment: Accepted to icaru
Influence of galaxy stellar mass and observed wavelength on disc breaks in SG, NIRS0S, and SDSS data
Breaks in the surface brightness profiles in the outer regions of galactic
discs are thought to have formed by various internal and external processes,
and by studying the breaks we aim to better understand what processes are
responsible for the evolution of the outer discs. We use a large well-defined
sample to study how common the breaks are, and whether their properties depend
on galaxy stellar mass or observed wavelength. We study radial surface
brightness profiles of 753 galaxies, obtained from the images of
the Spitzer Survey of Stellar Structure in Galaxies (SG), and the
-band data from the Near InfraRed S0-Sa galaxy Survey (NIRS0S), covering a
wide range of galaxy morphologies and stellar masses. Optical SDSS or Liverpool
telescope data was used for 480 of these galaxies. We find that in low-mass
galaxies the single exponential discs (Type I) are most common, and that their
fraction decreases with increasing galaxy stellar mass. The fraction of
down-bending (Type II) discs increases with stellar mass, possibly due to more
common occurrence of bar resonance structures. The up-bending (Type III) discs
are also more common in massive galaxies. The observed wavelength affects the
scalelength of the disc of every profile type. Especially the scalelength of
the inner disc of Type II profiles increases from infrared to u-band on average
by a factor of . Consistent with the previous studies, we find that
Type II outer disc scalelengths () in late-type and low-mass galaxies are
shorter in bluer wavelengths, possibly due to stellar radial migration
populating the outer discs with old stars. In Type III discs are larger
in the u-band, hinting to the presence of young stellar population in the outer
disc. While the observed wavelength affects the disc parameters, it does not
significantly affect the profile type in our sample. (Abridged)Comment: 22 pages, 16 figures. Accepted for publication in Astronomy &
Astrophysic
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
Evidence for the concurrent growth of thick discs and central mass concentrations from SG imaging
We have produced vertically integrated radial
luminosity profiles of 69 edge-on galaxies from the Spitzer Survey of Stellar
Structure in Galaxies (SG). We decomposed the luminosity profiles into a
disc and a central mass concentration (CMC). These fits, combined with
thin/thick disc decompositions from our previous studies, allow us to estimate
the masses of the CMCs, the thick discs, and the thin discs (, , and ). We obtained atomic
disc masses () from the literature. We then consider the
CMC and the thick disc to be dynamically hot components and the thin disc and
the gas disc to be dynamically cold components. We find that the ratio between
the mass of the hot components and that of the cold components,
, does not depend on the total galaxy mass as described
by circular velocities (). We also find that the higher the , the more concentrated the hot component of a galaxy. We suggest that our
results are compatible with having CMCs and thick discs built in a short and
early high star forming intensity phase. These components were born thick
because of the large scale height of the turbulent gas disc in which they
originated. Our results indicate that the ratio between the star forming rate
in the former phase and that of the formation of the thin disc is of the order
of 10, but the value depends on the duration of the high star forming intensity
phase.Comment: Accepted for publication in A&
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