641 research outputs found
Tidal decay and orbital circularization in close-in two-planet systems
The motion of two planets around a Sun-like star under the combined effects
of mutual interaction and tidal dissipation is investigated. The secular
behaviour of the system is analyzed using two different approaches. First, we
solve the exact equations of motion through the numerical simulation of the
system evolution. In addition to the orbital decay and circularization, we show
that the final configuration of the system is affected by the shrink of the
inner orbit. Our second approach consist in the analysis of the stationary
solutions of mean equations of motion based on a Hamiltonian formalism. We
consider the case of a hot super-Earth planet with a more massive outer
companion. As a real example, the CoRoT-7 system is analyzed solving the exact
and mean equations of motion. The star-planet tidal interaction produces
orbital decay and circularization of the orbit of CoRoT-7b. In addition, the
long-term tidal evolution is such that the eccentricity of CoRoT-7c is also
circularized and a pair of final circular orbits is obtained. A curve in the
space of eccentricities can be constructed through the computation of
stationary solutions of mean equations including dissipation. The application
to CoRoT-7 system shows that the stationary curve agrees with the result of
numerical simulations of exact equations. A similar investigation performed in
a super-Earth-Jupiter two-planet system shows that the doubly circular state is
accelerated when there is a significant orbital migration of the inner planet,
in comparison with previous results were migration is neglected.Comment: Accepted for publication in MNRAS; 10 pages, 13 figure
The Sloan Lens ACS Survey. X. Stellar, Dynamical, and Total Mass Correlations of Massive Early-type Galaxies
We use stellar masses, photometry, lensing, and velocity dispersions to
investigate empirical correlations for the final sample of 73 early-type lens
galaxies (ETGs) from the SLACS survey. The traditional correlations
(Fundamental Plane [FP] and its projections) are consistent with those found
for non-lens galaxies, supporting the thesis that SLACS lens galaxies are
representative of massive ETGs. The addition of strong lensing estimates of the
total mass allows us to gain further insights into their internal structure: i)
the mean slope of the total mass density profile is = 2.078+/-0.027
with an intrinsic scatter of 0.16+/-0.02; ii) gamma' correlates with effective
radius and central mass density, in the sense that denser galaxies have steeper
profiles; iii) the dark matter fraction within reff/2 is a monotonically
increasing function of galaxy mass and size; iv) the dimensional mass M_dim is
proportional to the total mass, and both increase more rapidly than stellar
mass M*; v) the Mass Plane (MP), obtained by replacing surface brightness with
surface mass density in the FP, is found to be tighter and closer to the virial
relation than the FP and the M*P, indicating that the scatter of those
relations is dominated by stellar population effects; vi) we construct the
Fundamental Hyper-Plane by adding stellar masses to the MP and find the M*
coefficient to be consistent with zero and no residual intrinsic scatter. Our
results demonstrate that the dynamical structure of ETGs is not scale invariant
and that it is fully specified by the total mass, r_eff, and sigma. Although
the basic trends can be explained qualitatively in terms of varying star
formation efficiency as a function of halo mass and as the result of dry and
wet mergers, reproducing quantitatively the observed correlations and their
tightness may be a significant challenge for galaxy formation models.Comment: 16 pages, 9 figures; submitted to ApJ after responding to the referee
comment
Post-Newtonian SPH calculations of binary neutron star coalescence. II. Binary mass ratio, equation of state, and spin dependence
Using our new Post-Newtonian SPH (smoothed particle hydrodynamics) code, we
study the final coalescence and merging of neutron star (NS) binaries. We vary
the stiffness of the equation of state (EOS) as well as the initial binary mass
ratio and stellar spins. Results are compared to those of Newtonian
calculations, with and without the inclusion of the gravitational radiation
reaction. We find a much steeper decrease in the gravity wave peak strain and
luminosity with decreasing mass ratio than would be predicted by simple
point-mass formulae. For NS with softer EOS (which we model as simple
polytropes) we find a stronger gravity wave emission, with a
different morphology than for stiffer EOS (modeled as polytropes as
in our previous work). We also calculate the coalescence of NS binaries with an
irrotational initial condition, and find that the gravity wave signal is
relatively suppressed compared to the synchronized case, but shows a very
significant second peak of emission. Mass shedding is also greatly reduced, and
occurs via a different mechanism than in the synchronized case. We discuss the
implications of our results for gravity wave astronomy with laser
interferometers such as LIGO, and for theoretical models of gamma-ray bursts
(GRBs) based on NS mergers.Comment: RevTeX, 38 pages, 24 figures, Minor Corrections, to appear in Phys.
Rev.
Spectroscopy of the near-nuclear regions of Cygnus A: estimating the mass of the supermassive black hole
We use a combination of high spatial resolution optical and near-IR
spectroscopic data to make a detailed study of the kinematics of the NLR gas in
the near-nuclear regions of the powerful, FRII radio galaxy Cygnus A
(z=0.0560), with the overall goal of placing limits on the mass of any
supermassive black hole in the core. Our K-band infrared observations (0.75
arcsec seeing) -- taken with NIRSPEC on the Keck II telescope -- show a smooth
rotation pattern across the nucleus in the Paschen alpha and H_2 emission lines
along a slit position (PA180) close to perpendicular to the radio axis,
however, there is no evidence for such rotation along the radio axis (PA105).
Higher spatial resolution observations of the [OIII]5007 emission line -- taken
with STIS on the Hubble Space Telescope (HST) -- confirm the general rotation
pattern of the gas in the direction perpendicular to the radio axis, and
provide evidence for steep velocity gradients within a radius of 0.1 arcsec of
the core. The circular velocities measured from both the Keck and HST data lead
to an estimate of the mass of the supermassive black hole of 2.5+/-0.7x10^9
solar masses. For the host galaxy properties of Cygnus A, this mass is
consistent with the global correlations between black hole mass and host galaxy
properties deduced for non-active galaxies. Therefore, despite the extreme
power of its radio source and the quasar-like luminosity of its AGN, the black
hole in Cygnus A is not unusually massive considering theluminosity of its host
galaxy. Indeed, the estimated mass of the black hole in Cygnus A is similar to
that inferred for the supermassive black hole in the FRI radio galaxy M87,
despite the fact that the AGN and radio jets of Cygnus A are 2 -- 3 orders of
magnitude more powerful.Comment: 17 pages, 12 figure
Accuracy and Stability of Computing High-Order Derivatives of Analytic Functions by Cauchy Integrals
High-order derivatives of analytic functions are expressible as Cauchy
integrals over circular contours, which can very effectively be approximated,
e.g., by trapezoidal sums. Whereas analytically each radius r up to the radius
of convergence is equal, numerical stability strongly depends on r. We give a
comprehensive study of this effect; in particular we show that there is a
unique radius that minimizes the loss of accuracy caused by round-off errors.
For large classes of functions, though not for all, this radius actually gives
about full accuracy; a remarkable fact that we explain by the theory of Hardy
spaces, by the Wiman-Valiron and Levin-Pfluger theory of entire functions, and
by the saddle-point method of asymptotic analysis. Many examples and
non-trivial applications are discussed in detail.Comment: Version 4 has some references and a discussion of other quadrature
rules added; 57 pages, 7 figures, 6 tables; to appear in Found. Comput. Mat
The Size Evolution of Passive Galaxies: Observations from the Wide Field Camera 3 Early Release Science Program
We present results on the size evolution of passively evolving galaxies at
1<z<2 drawn from the Wide Field Camera 3 Early Release Science program. Our
sample was constructed using an analog to the passive BzK selection criterion,
which isolates galaxies with little or no on-going star formation at z>1.5. We
identify 30 galaxies in ~40 square arcmin to H<25 mag. We supplement
spectroscopic redshifts from the literature with photometric redshifts
determined from the 15-band photometry from 0.22-8 micron. We determine
effective radii from Sersic profile fits to the H-band image using an empirical
PSF. We find that size evolution is a strong function of stellar mass, with the
most massive (M* ~ 10^11 Msol) galaxies undergoing the most rapid evolution
from z~2 to the present. Parameterizing the size evolution as (1+z)^{-alpha},
we find a tentative scaling between alpha and stellar mass of alpha ~ -1.8+1.4
log(M*/10^9 Msol). We briefly discuss the implications of this result for our
understanding of the dynamical evolution of the red galaxies.Comment: 11 pages, 7 figures, 4 tables. Submitted to Ap
Extragalactic Background Light Inferred from AEGIS Galaxy SED-type Fractions
The extragalactic background light (EBL) is of fundamental importance both
for understanding the entire process of galaxy evolution and for gamma-ray
astronomy, but the overall spectrum of the EBL between 0.1-1000 microns has
never been determined directly from galaxy spectral energy distribution (SED)
observations over a wide redshift range. The evolving, overall spectrum of the
EBL is derived here utilizing a novel method based on observations only. This
is achieved from the observed evolution of the rest-frame K-band galaxy
luminosity function up to redshift 4 (Cirasuolo et al. 2010), combined with a
determination of galaxy SED-type fractions. These are based on fitting SWIRE
templates to a multiwavelength sample of about 6000 galaxies in the redshift
range from 0.2 to 1 from the All-wavelength Extended Groth Strip International
Survey (AEGIS). The changing fractions of quiescent galaxies, star-forming
galaxies, starburst galaxies and AGN galaxies in that redshift range are
estimated, and two alternative extrapolations of SED-types to higher redshifts
are considered. This allows calculation of the evolution of the luminosity
densities from the UV to the IR, the evolving star formation rate density of
the universe, the evolving contribution to the bolometric EBL from the
different galaxy populations including AGN galaxies and the buildup of the EBL.
Our EBL calculations are compared with those from a semi-analytic model, from
another observationally-based model and observational data. The EBL
uncertainties in our modeling based directly on the data are quantified, and
their consequences for attenuation of very high energy gamma-rays due to pair
production on the EBL are discussed. It is concluded that the EBL is well
constrained from the UV to the mid-IR, but independent efforts from infrared
and gamma-ray astronomy are needed in order to reduce the uncertainties in the
far-IR.Comment: 25 pages, 18 figures, 4 tables; accepted for publication in MNRAS on
September 3, 2010. Online material available at http://side.iaa.es/EB
The Galaxy Population of Abell 1367: The Stellar Mass-Metallicity Relation
Using wide baseline broad-band photometry, we analyse the stellar population
properties of a sample of 72 galaxies, spanning a wide range of stellar masses
and morphological types, in the nearby spiral-rich and dynamically young galaxy
cluster Abell 1367. The sample galaxies are distributed from the cluster centre
out to approximately half the cluster Abell radius. The optical/near-infrared
colours are compared with simple stellar population synthesis models from which
the luminosity-weighted stellar population ages and metallicities are
determined. The locus of the colours of elliptical galaxies traces a sequence
of varying metallicity at a narrow range of luminosity-weighted stellar ages.
Lenticular galaxies in the red sequence, however, exhibit a substantial spread
of luminosity-weighted stellar metallicities and ages. For red sequence
lenticular galaxies and blue cloud galaxies, low mass galaxies tend to be on
average dominated by stellar populations of younger luminosity-weighted ages.
Sample galaxies exhibit a strong correlation between integrated stellar mass
and luminosity-weighted stellar metallicity. Galaxies with signs of
morphological disturbance and ongoing star formation activity, tend to be
underabundant with respect to passive galaxies in the red sequence of
comparable stellar masses. We argue that this could be due to tidally-driven
gas flows toward the star-forming regions, carrying less enriched gas and
diluting the pre-existing gas to produce younger stellar populations with lower
metallicities than would be obtained prior to the interaction. Finally, we find
no statistically significant evidence for changes in the luminosity-weighted
ages and metallicities for either red sequence or blue cloud galaxies, at fixed
stellar mass, with location within the cluster.Comment: 15 pages, 10 figures, MNRAS in pres
Searches for Gravitational Waves from Binary Neutron Stars: A Review
A new generation of observatories is looking for gravitational waves. These
waves, emitted by highly relativistic systems, will open a new window for ob-
servation of the cosmos when they are detected. Among the most promising
sources of gravitational waves for these observatories are compact binaries in
the final min- utes before coalescence. In this article, we review in brief
interferometric searches for gravitational waves emitted by neutron star
binaries, including the theory, instru- mentation and methods. No detections
have been made to date. However, the best direct observational limits on
coalescence rates have been set, and instrumentation and analysis methods
continue to be refined toward the ultimate goal of defining the new field of
gravitational wave astronomy.Comment: 30 pages, 5 Figures, to appear in "Short-Period Binary Stars:
Observations, Analyses, and Results", Ed.s Eugene F. Milone, Denis A. Leahy,
David W. Hobil
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