335 research outputs found
Probing the Slope of Cluster Mass Profile with Gravitational Einstein Rings: Application to Abell 1689
The strong lensing modelling of gravitational ``rings'' formed around massive
galaxies is sensitive to the amplitude of the external shear and convergence
produced by nearby mass condensations. In current wide field surveys, it is now
possible to find out a large number of rings, typically 10 gravitational rings
per square degree. We propose here, to systematically study gravitational rings
around galaxy clusters to probe the cluster mass profile beyond the cluster
strong lensing regions. For cluster of galaxies with multiple arc systems, we
show that rings found at various distances from the cluster centre can improve
the modelling by constraining the slope of the cluster mass profile. We outline
the principle of the method with simple numerical simulations and we apply it
to 3 rings discovered recently in Abell~1689. In particular, the lens modelling
of the 3 rings confirms that the cluster is bimodal, and favours a slope of the
mass profile steeper than isothermal at a cluster radius \sim 300 \kpc. These
results are compared with previous lens modelling of Abell~1689 including weak
lensing analysis. Because of the difficulty arising from the complex mass
distribution in Abell~1689, we argue that the ring method will be better
implemented on simpler and relaxed clusters.Comment: Accepted for publication in MNRAS. Substantial modification after
referee's repor
Radial Dependence of the Pattern Speed of M51
The grand-design spiral galaxy M51 has long been a crucial target for
theories of spiral structure. Studies of this iconic spiral can address the
question of whether strong spiral structure is transient (e.g.
interaction-driven) or long-lasting. As a clue to the origin of the structure
in M51, we investigate evidence for radial variation in the spiral pattern
speed using the radial Tremaine-Weinberg (TWR) method. We implement the method
on CO observations tracing the ISM-dominant molecular component. Results from
the method's numerical implementation--combined with regularization, which
smooths intrinsically noisy solutions--indicate two distinct patterns speeds
inside 4 kpc at our derived major axis PA=170 deg., both ending at corotation
and both significantly higher than the conventionally adopted global value.
Inspection of the rotation curve suggests that the pattern speed interior to 2
kpc lacks an ILR, consistent with the leading structure seen in HST near-IR
observations. We also find tentative evidence for a lower pattern speed between
4 and 5.3 kpc measured by extending the regularized zone. As with the original
TW method, uncertainty in major axis position angle (PA) is the largest source
of error in the calculation; in this study, where \delta PA=+/-5 deg. a ~20%
error is introduced to the parameters of the speeds at PA=170 deg. Accessory to
this standard uncertainty, solutions with PA=175 deg. (also admitted by the
data) exhibit only one pattern speed inside 4 kpc, and we consider this
circumstance under the semblance of a radially varying PA.Comment: 14 pages in emulateapj format, 12 figures, accepted for publication
in Ap
A New Mechanism for Radial Migration in Galactic Disks: Spiral-Bar Resonance Overlap
While it has long been known that a large number of short-lived transient
spirals can cause stellar migration, here we report that another mechanism is
also effective at mixing disks of barred galaxies. The resonance overlap of the
bar and spiral structure induces a nonlinear response leading to a strong
redistribution of angular momentum in the disk. We find that, depending on the
amplitudes of the perturbers, the changes in angular momentum, dL, could occur
up to an order of magnitude faster than in the case of recurrent spirals. The
signature of this mechanism is a bimodality in dL with maxima near the bar's
corotation and its outer Lindblad resonance; this is independent of the
properties of the spiral structure. For parameters consistent with the Milky
Way the disk mixes in about 3 Gyr and the stellar velocity dispersion increases
with time in a manner roughly consistent with observations. This new mechanism
could account for both the observed age-velocity relation and the absence of
age-metallicity relation in the solar neighborhood. Spiral-bar interaction
could also explain observations showing that strongly barred galaxies have
weaker metallicity gradients than weakly barred or non-barred galaxies.Comment: 10 pages, 7 figures. Substantially expanded. Main results remain the
same. Accepted for publication in Ap
On the clustering phase transition in self-gravitating N-body systems
The thermodynamic behaviour of self-gravitating -body systems has been
worked out by borrowing a standard method from Molecular Dynamics: the time
averages of suitable quantities are numerically computed along the dynamical
trajectories to yield thermodynamic observables. The link between dynamics and
thermodynamics is made in the microcanonical ensemble of statistical mechanics.
The dynamics of self-gravitating -body systems has been computed using two
different kinds of regularization of the newtonian interaction: the usual
softening and a truncation of the Fourier expansion series of the two-body
potential. particles of equal masses are constrained in a finite three
dimensional volume. Through the computation of basic thermodynamic observables
and of the equation of state in the plane, new evidence is given of the
existence of a second order phase transition from a homogeneous phase to a
clustered phase. This corresponds to a crossover from a polytrope of index
, i.e. , to a perfect gas law , as is shown by
the isoenergetic curves on the plane. The dynamical-microcanonical
averages are compared to their corresponding canonical ensemble averages,
obtained through standard Monte Carlo computations. A major disagreement is
found, because the canonical ensemble seems to have completely lost any
information about the phase transition. The microcanonical ensemble appears as
the only reliable statistical framework to tackle self-gravitating systems.
Finally, our results -- obtained in a ``microscopic'' framework -- are compared
with some existing theoretical predictions -- obtained in a ``macroscopic''
(thermodynamic) framework: qualitative and quantitative agreement is found,
with an interesting exception.Comment: 19 pages, 20 figure
A non-variational approach to nonlinear stability in stellar dynamics applied to the King model
In previous work by Y. Guo and G. Rein, nonlinear stability of equilibria in
stellar dynamics, i.e., of steady states of the Vlasov-Poisson system, was
accessed by variational techniques. Here we propose a different,
non-variational technique and use it to prove nonlinear stability of the King
model against a class of spherically symmetric, dynamically accessible
perturbations. This model is very important in astrophysics and was out of
reach of the previous techniques
The regeneration of stellar bars by tidal interactions. Numerical simulations of fly-by encounters
We study the regeneration of stellar bars triggered by a tidal interaction,
using numerical simulations of either purely stellar or stellar+gas disc
galaxies. We find that interactions which are sufficiently strong to regenerate
the bar in the purely stellar models do not lead to a regeneration in the
dissipative models, owing to the induced gas inflow in those models. In models
in which the bar can be regenerated, we find a tight correlation between the
strength and the pattern speed of the induced bar. This relation can be
explained by a significant radial redistribution of angular momentum in the
disc due to the interaction, similar to the processes and correlations found
for isolated barred spirals. We furthermore show that the regenerated bars show
the same dynamical properties as their isolated counterparts.Comment: 18 pages, 26 figures, accepted for publication in MNRA
A search for edge-on galaxy lenses in the CFHT Legacy Survey
[ABRIDGED] The new generation of wide field optical imaging like the Canada
France Hawaii Telescope Legacy Survey (CFHTLS) enables discoveries of all types
of gravitational lenses present in the sky. The Strong Lensing Legacy Survey
(SL2S) project has started an inventory, respectively for clusters or groups of
galaxies lenses, and for Einstein rings around distant massive ellipticals.
Here we attempt to extend this inventory by finding lensing events produced by
massive edge-on disk galaxies which remains a poorly documented class of
lenses. We implement and test an automated search procedure of edge-on galaxy
lenses in the CFHTLS Wide fields with magnitude 18Comment: several major edits, 8 pages, A&A accepte
Uncovering the Origins of Spiral Structure by Measuring Radial Variation in Pattern Speeds
Current theories of spiral and bar structure predict a variety of pattern
speed behaviors, calling for detailed, direct measurement of the radial
variation of pattern speeds. Our recently developed Radial Tremaine-Weinberg
(TWR) method allows this goal to be achieved for the first time. Here we
present TWR spiral pattern speed estimates for M101, IC 342, NGC 3938 and NGC
3344 in order to investigate whether spiral structure is steady or winding,
whether spirals are described by multiple pattern speeds, and the relation
between bar and spiral speeds. Where possible, we interpret our pattern speeds
estimates according to the resonance radii associated with each (established
with the disk angular rotation), and compare these to previous determinations.
By analyzing the high-quality HI and CO data cubes available for these
galaxies, we show that it is possible to determine directly multiple pattern
speeds within these systems, and hence identify the characteristic signatures
of the processes that drive the spiral structure. Even this small sample of
galaxies reveals a surprisingly complex taxonomy, with the first direct
evidence for the presence of resonant coupling of multiple patterns found in
some systems, and the measurement of a simple single pattern speed in others.
Overall, this study demonstrates that we are now in a position to uncover more
of the apparently complex physics that lies behind spiral structure.Comment: 15 pages in emulateapj format, 12 figures, accepted for publication
in Ap
The CFHTLS Strong Lensing Legacy Survey: I. Survey overview and T0002 release sample
AIMS: We present data from the CFHTLS Strong Lensing Legacy Survey (SL2S).
Due to the unsurpassed combined depth, area and image quality of the
Canada-France-Hawaii Legacy Survey it is becoming possible to uncover a large,
statistically well-defined sample of strong gravitational lenses which spans
the dark halo mass spectrum predicted by the concordance model from galaxy to
cluster haloes. METHODS: We describe the development of several automated
procedures to find strong lenses of various mass regimes in CFHTLS images.
RESULTS: The preliminary sample of about 40 strong lensing candidates
discovered in the CFHTLS T0002 release, covering an effective field of view of
28 deg is presented. These strong lensing systems were discovered using an
automated search and consist mainly of gravitational arc systems with splitting
angles between 2 and 15 arcsec. This sample shows for the first time that it is
possible to uncover a large population of strong lenses from galaxy groups with
typical halo masses of about . We discuss the future
evolution of the SL2S project and its main scientific aims for the next 3
years, in particular our observational strategy to extract the hundreds of
gravitational rings also present in these fields.Comment: 11 pages, 5 figures, A&A in pres
The SWELLS Survey. I. A large spectroscopically selected sample of edge-on late-type lens galaxies
The relative contribution of baryons and dark matter to the inner regions of
spiral galaxies provides critical clues to their formation and evolution, but
it is generally difficult to determine. For spiral galaxies that are strong
gravitational lenses, however, the combination of lensing and kinematic
observations can be used to break the disk-halo degeneracy. In turn, such data
constrain fundamental parameters such as i) the mass density profile slope and
axis ratio of the dark matter halo, and by comparison with dark matter-only
numerical simulations the modifications imposed by baryons; ii) the mass in
stars and therefore the overall star formation efficiency, and the amount of
feedback; iii) by comparison with stellar population synthesis models, the
normalization of the stellar initial mass function. In this first paper of a
series, we present a sample of 16 secure, 1 probable, and 6 possible strong
lensing spiral galaxies, for which multi-band high-resolution images and
rotation curves were obtained using the Hubble Space Telescope and Keck-II
Telescope as part of the Sloan WFC Edge-on Late-type Lens Survey (SWELLS). The
sample includes 8 newly discovered secure systems. [abridged] We find that the
SWELLS sample of secure lenses spans a broad range of morphologies (from
lenticular to late-type spiral), spectral types (quantified by Halpha
emission), and bulge to total stellar mass ratio (0.22-0.85), while being
limited to M_*>10^{10.5} M_sun. The SWELLS sample is thus well-suited for
exploring the relationship between dark and luminous matter in a broad range of
galaxies. We find that the deflector galaxies obey the same size-mass relation
as that of a comparison sample of elongated non-lens galaxies selected from the
SDSS survey. We conclude that the SWELLS sample is consistent with being
representative of the overall population of high-mass high-inclination disky
galaxies.Comment: 21 pages, 6 figures, MNRAS, in pres
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