2,264 research outputs found
Inference of the Cold Dark Matter substructure mass function at z=0.2 using strong gravitational lenses
We present the results of a search for galaxy substructures in a sample of 11
gravitational lens galaxies from the Sloan Lens ACS Survey. We find no
significant detection of mass clumps, except for a luminous satellite in the
system SDSS J0956+5110. We use these non-detections, in combination with a
previous detection in the system SDSS J0946+1006, to derive constraints on the
substructure mass function in massive early-type host galaxies with an average
redshift z ~ 0.2 and an average velocity dispersion of 270 km/s. We perform a
Bayesian inference on the substructure mass function, within a median region of
about 32 kpc squared around the Einstein radius (~4.2 kpc). We infer a mean
projected substructure mass fraction at the 68
percent confidence level and a substructure mass function slope < 2.93
at the 95 percent confidence level for a uniform prior probability density on
alpha. For a Gaussian prior based on Cold Dark Matter (CDM) simulations, we
infer and a slope of =
1.90 at the 68 percent confidence level. Since only one
substructure was detected in the full sample, we have little information on the
mass function slope, which is therefore poorly constrained (i.e. the Bayes
factor shows no positive preference for any of the two models).The inferred
fraction is consistent with the expectations from CDM simulations and with
inference from flux ratio anomalies at the 68 percent confidence level.Comment: Accepted for publication on MNRAS, some typos corrected and some
important references adde
Growth dynamics of reactive-sputtering-deposited AlN films
8 pages, 7 figures.-- PACS nrs.: 81.05.Ea, 68.47.Fg, 81.15.Cd, 68.55.Ac, 68.55.Jk, 68.35.Bs.-- Issue title: "Structural, mechanical, thermodynamical and optical properties of condensed matter".We have studied the surface kinetic roughening of AlN films grown on Si(100) substrates by dc reactive sputtering within the framework of the dynamic scaling theory. Films deposited under the same experimental conditions for different growth times were analyzed by atomic force microscopy and x-ray diffraction. The AlN films display a (002) preferred orientation. We have found two growth regimes with a crossover time of 36 min. In the first regime, the growth dynamics is unstable and the films present two types of textured domains, well textured and randomly oriented, respectively. In contrast, in the second regime the films are homogeneous and well textured, leading to a relative stabilization of the surface roughness characterized by a growth exponent β=0.37±0.03. In this regime a superrough scaling behavior is found with the following exponents: (i) Global exponents: roughness exponent α=1.2±0.2 and β=0.37±0.03 and coarsening exponent 1/z=0.32±0.05; (ii) local exponents: α(loc)=1, β(loc)=0.32±0.01. The differences between the growth modes are found to be related to the different main growth mechanisms dominating their growth dynamics: sticking anisotropy and shadowing, respectively.Financial support from Spanish MCyT: Projects No. MAT 2002-04037-C03-03 and BFM 2003-07749-C05-01, BFM 2003-07749-C05-02, and BFM 2003-07749-C05-05, European Community: Project No. G5RD-CT-2000-00333, Slovak governmental Project No. 2003-SO 51/03R0600/01, and Slovak Grant Agency for Science VEGA, Project No. 2/3149/23, are acknowledged.Publicad
Global Production Increased by Spatial Heterogeneity in a Population Dynamics Model
Spatial and temporal heterogeneity are often described as important factors having a strong impact on biodiversity. The effect of heterogeneity is in most cases analyzed by the response of biotic interactions such as competition of predation. It may also modify intrinsic population properties such as growth rate. Most of the studies are theoretic since it is often difficult to manipulate spatial heterogeneity in practice. Despite the large number of studies dealing with this topics, it is still difficult to understand how the heterogeneity affects populations dynamics. On the basis of a very simple model, this paper aims to explicitly provide a simple mechanism which can explain why spatial heterogeneity may be a favorable factor for production.We consider a two patch model and a logistic growth is assumed on each patch. A general condition on the migration rates and the local subpopulation growth rates is provided under which the total carrying capacity is higher than the sum of the local carrying capacities, which is not intuitive. As we illustrate, this result is robust under stochastic perturbations
Disentangling Baryons and Dark Matter in the Spiral Gravitational Lens B1933+503
Measuring the relative mass contributions of luminous and dark matter in
spiral galaxies is important for understanding their formation and evolution.
The combination of a galaxy rotation curve and strong lensing is a powerful way
to break the disk-halo degeneracy that is inherent in each of the methods
individually. We present an analysis of the 10-image radio spiral lens
B1933+503 at z_l=0.755, incorporating (1) new global VLBI observations, (2) new
adaptive-optics assisted K-band imaging, (3) new spectroscopic observations for
the lens galaxy rotation curve and the source redshift. We construct a
three-dimensionally axisymmetric mass distribution with 3 components: an
exponential profile for the disk, a point mass for the bulge, and an NFW
profile for the halo. The mass model is simultaneously fitted to the kinematics
and the lensing data. The NFW halo needs to be oblate with a flattening of
a/c=0.33^{+0.07}_{-0.05} to be consistent with the radio data. This suggests
that baryons are effective at making the halos oblate near the center. The
lensing and kinematics analysis probe the inner ~10 kpc of the galaxy, and we
obtain a lower limit on the halo scale radius of 16 kpc (95% CI). The dark
matter mass fraction inside a sphere with a radius of 2.2 disk scale lengths is
f_{DM,2.2}=0.43^{+0.10}_{-0.09}. The contribution of the disk to the total
circular velocity at 2.2 disk scale lengths is 0.76^{+0.05}_{-0.06}, suggesting
that the disk is marginally submaximal. The stellar mass of the disk from our
modeling is log_{10}(M_{*}/M_{sun}) = 11.06^{+0.09}_{-0.11} assuming that the
cold gas contributes ~20% to the total disk mass. In comparison to the stellar
masses estimated from stellar population synthesis models, the stellar initial
mass function of Chabrier is preferred to that of Salpeter by a probability
factor of 7.2.Comment: 16 pages, 13 figures, minor revisions based on referee's comments,
accepted for publication in Ap
The Sloan Lens ACS Survey. IX. Colors, Lensing and Stellar Masses of Early-type Galaxies
We present the current photometric dataset for the Sloan Lens ACS (SLACS)
Survey, including HST photometry from ACS, WFPC2, and NICMOS. These data have
enabled the confirmation of an additional 15 grade `A' (certain) lens systems,
bringing the number of SLACS grade `A' lenses to 85; including 13 grade `B'
(likely) systems, SLACS has identified nearly 100 lenses and lens candidates.
Approximately 80% of the grade `A' systems have elliptical morphologies while
~10% show spiral structure; the remaining lenses have lenticular morphologies.
Spectroscopic redshifts for the lens and source are available for every system,
making SLACS the largest homogeneous dataset of galaxy-scale lenses to date. We
have developed a novel Bayesian stellar population analysis code to determine
robust stellar masses with accurate error estimates. We apply this code to
deep, high-resolution HST imaging and determine stellar masses with typical
statistical errors of 0.1 dex; we find that these stellar masses are unbiased
compared to estimates obtained using SDSS photometry, provided that informative
priors are used. The stellar masses range from 10^10.5 to 10^11.8 M and
the typical stellar mass fraction within the Einstein radius is 0.4, assuming a
Chabrier IMF. The ensemble properties of the SLACS lens galaxies, e.g. stellar
masses and projected ellipticities, appear to be indistinguishable from other
SDSS galaxies with similar stellar velocity dispersions. This further supports
that SLACS lenses are representative of the overall population of massive
early-type galaxies with M* >~ 10^11 M, and are therefore an ideal
dataset to investigate the kpc-scale distribution of luminous and dark matter
in galaxies out to z ~ 0.5.Comment: 20 pages, 18 figures, 5 tables, published in Ap
Real-time inversion of VLP source functions at Stromboli Volcano, Italy.
We present a comprehensive processing tool for the real-time analysis of the source mechanism of Very-Long-Period (VLP) seismic data based on waveform inversions performed in the frequency domain for a point source.
A search for the source providing the best-fitting solution is conducted over a three-dimensional grid of assumed source locations, in which the Green’s functions associated with each point source are calculated by finite differences using the reciprocal relation between source and receiver. Tests performed on 62 nodes of a Linux cluster indicate that the waveform
inversion and search for the best-fitting signal over 100,000 point sources require roughly 30 s of processing time for a 2-min-long record. The procedure is applied to post-processing of a data archive and to continuous automatic inversion of real-time data at Stromboli, providing insights into
different modes of degassing at this volcano
The Structure & Dynamics of Massive Early-type Galaxies: On Homology, Isothermality and Isotropy inside one Effective Radius
Based on 58 SLACS strong-lens early-type galaxies with direct total-mass and
stellar-velocity dispersion measurements, we find that inside one effective
radius massive elliptical galaxies with M_eff >= 3x10^10 M_sun are
well-approximated by a power-law ellipsoid with an average logaritmic density
slope of = -dlog(rho_tot)/dlog(r)=2.085^{+0.025}_{-0.018} (random
error on mean) for isotropic orbits with beta_r=0, +-0.1 (syst.) and
sigma_gamma' <= 0.20^{+0.04}_{-0.02} intrinsic scatter (all errors indicate the
68 percent CL). We find no correlation of gamma'_LD with galaxy mass (M_eff),
rescaled radius (i.e. R_einst/R_eff) or redshift, despite intrinsic differences
in density-slope between galaxies. Based on scaling relations, the average
logarithmic density slope can be derived in an alternative manner, fully
independent from dynamics, yielding =1.959 +- 0.077. Agreement
between the two values is reached for =0.45 +- 0.25, consistent with
mild radial anisotropy. This agreement supports the robustness of our results,
despite the increase in mass-to-light ratio with total galaxy mass: M_eff ~
L_{V,eff}^(1.363+-0.056). We conclude that massive early-type galaxies are
structurally close-to homologous with close-to isothermal total density
profiles (<=10 percent intrinsic scatter) and have at most some mild radial
anisotropy. Our results provide new observational limits on galaxy formation
and evolution scenarios, covering four Gyr look-back time.Comment: Accepted for publication by ApJL; 4 pages, 2 figure
Testing metallicity indicators at z~1.4 with the gravitationally lensed galaxy CASSOWARY 20
We present X-shooter observations of CASSOWARY 20 (CSWA 20), a star-forming
(SFR ~6 Msol/yr) galaxy at z=1.433, magnified by a factor of 11.5 by the
gravitational lensing produced by a massive foreground galaxy at z=0.741. We
analysed the integrated physical properties of the HII regions of CSWA 20 using
temperature- and density-sensitive emission lines. We find the abundance of
oxygen to be ~1/7 of solar, while carbon is ~50 times less abundant than in the
Sun. The unusually low C/O ratio may be an indication of a particularly rapid
timescale of chemical enrichment. The wide wavelength coverage of X-shooter
gives us access to five different methods for determining the metallicity of
CSWA 20, three based on emission lines from HII regions and two on absorption
features formed in the atmospheres of massive stars. All five estimates are in
agreement, within the factor of ~2 uncertainty of each method. The interstellar
medium of CSWA 20 only partially covers the star-forming region as viewed from
our direction; in particular, absorption lines from neutrals and first ions are
exceptionally weak. We find evidence for large-scale outflows of the
interstellar medium (ISM) with speeds of up 750 km/s, similar to the values
measured in other high-z galaxies sustaining much higher rates of star
formation.Comment: 18 pages, 11 figures, accepted for publication in MNRA
SHARP - I. A high-resolution multi-band view of the infra-red Einstein ring of JVAS B1938+666
We present new mass models for the gravitational lens system B1938+666, using
multi-wavelength data acquired from Keck adaptive optics (AO) and Hubble Space
Telescope (HST) observations. These models are the first results from the
Strong-lensing at High Angular Resolution Program (SHARP), a project designed
to study known quadruple-image and Einstein ring lenses using high-resolution
imaging, in order to probe their mass distributions in unprecedented detail.
Here, we specifically highlight differences between AO- and HST-derived lens
models, finding that -- at least when the lens and source galaxies are both
bright and red, and the system has a high degree of circular symmetry --
AO-derived models place significantly tighter constraints on model parameters.
Using this improved precision, we infer important physical properties about the
B1938+666 system, including the mass density slope of the lensing galaxy (gamma
= 2.045), the projected dark matter mass fraction within the Einstein radius
(M_dark/M_lens = 0.55), and the total magnification factor of the source galaxy
(~ 13). Additionally, we measure an upper-limit constraint on luminous
substructure (M_V > 16.2), based on the non-detection of bright satellite
galaxies in all data sets. Finally, we utilize the improved image resolution of
the AO data to reveal the presence of faint arcs outside of the primary
Einstein ring. The positions and orientations of these arcs raise the
intriguing possibility that B1938+666 has a second source galaxy, located at a
more distant redshift. However, future work is needed to verify this
hypothesis.Comment: 12 pages, 7 figures; Accepted for publication in MNRA
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