15,286 research outputs found
Model-Free Multi-Probe Lensing Reconstruction of Cluster Mass Profiles
Lens magnification by galaxy clusters induces characteristic spatial
variations in the number counts of background sources, amplifying their
observed fluxes and expanding the area of sky, the net effect of which, known
as magnification bias, depends on the intrinsic faint-end slope of the source
luminosity function. The bias is strongly negative for red galaxies, dominated
by the geometric area distortion, whereas it is mildly positive for blue
galaxies, enhancing the blue counts toward the cluster center. We generalize
the Bayesian approach of Umetsu et al. for reconstructing projected cluster
mass profiles, by incorporating multiple populations of background sources for
magnification bias measurements and combining them with complementary lens
distortion measurements, effectively breaking the mass-sheet degeneracy and
improving the statistical precision of cluster mass measurements. The approach
can be further extended to include strong-lensing projected mass estimates,
thus allowing for non-parametric absolute mass determinations in both the weak
and strong regimes. We apply this method to our recent CLASH lensing
measurements of MACS J1206.2-0847, and demonstrate how combining multi-probe
lensing constraints can improve the reconstruction of cluster mass profiles.
This method will also be useful for a stacked lensing analysis, combining all
lensing-related effects in the cluster regime, for a definitive determination
of the averaged mass profile.Comment: 13 pages, 2 figures; Typo corrections (Appendix A.2.) to match the
published version in Ap
Poisson structures on the homology of the space of knots
In this article we study the Poisson algebra structure on the homology of the
totalization of a fibrant cosimplicial space associated with an operad with
multiplication. This structure is given as the Browder operation induced by the
action of little disks operad, which was found by McClure and Smith. We show
that the Browder operation coincides with the Gerstenhaber bracket on the
Hochschild homology, which appears as the E2-term of the homology spectral
sequence constructed by Bousfield. In particular we consider a variant of the
space of long knots in higher dimensional Euclidean space, and show that
Sinha's homology spectral sequence computes the Poisson algebra structure of
the homology of the space. The Browder operation produces a homology class
which does not directly correspond to chord diagrams.Comment: This is the version published by Geometry & Topology Monographs on 19
March 200
Supernovae in Three-Dimension: A Link to Gamma-Ray Bursts
Observational consequences of a jet-driven supernova (SN) explosion model are
presented. The results are compared in detail with optical observations of SN
1998bw associated with a Gamma-Ray Burst. It is shown that the jet model is
able to reproduce virtually all the optical observations available for this SN,
although a spherical model fails to explain some of observed features. Because
of the viewing angle effect, the required kinetic energy of the SN ejecta is
reduced to ~ 2 x 10^{52} erg as compared to that obtained by the previous
spherical model (~ 5 x 10^{52} erg), but this is still much larger than that of
a canonical SN (~10^{51} erg).Comment: 6 pages, 3 figures. Invited talk at "Frascati Workshop 2007:
Multifrequency Behaviour of High Energy Cosmic Sources", 28 May - 2 June,
2007, Vulcano, Italy. To apper in the Chinese Journal of Astronomy and
Astrophysics (ChJAA
Imaging the outward motions of clumpy dust clouds around the red supergiant Antares with VLT/VISIR
We present a 0.5"-resolution diffraction-limited 17.7 micron image of the red
supergiant Antares obtained with the VLT mid-infrared instrument VISIR. The
VISIR image shows six clumpy dust clouds located at 0.8"--1.8" (43--96 stellar
radii = 136--306 AU) away from the star. We also detected compact emission
within a radius of 0.5" from the star. Comparison of our VISIR image taken in
2010 and the 20.8 micron image taken in 1998 with the Keck telescope reveals
the outward motions of four dust clumps. The proper motions of these dust
clumps amount to 0.2"--0.6" in 12 years. This translates into expansion
velocities (projected onto the plane of the sky) of 13--40 km/s with an
uncertainty of +/-7 km/s. The velocities of the dust clumps cannot be explained
by a simple accelerating outflow, implying the possible random nature of the
dust cloud ejection mechanism. The inner compact emission seen in the 2010
VISIR image is presumably newly formed dust, because it is not detected in the
image taken in 1998. The mass of the dust clouds is estimated to be
(3-6)x10^{-9} Msun. These values are lower by a factor of 3--7 than the amount
of dust ejected in one year estimated from the (gas+dust) mass-loss rate of
2x10^{-6} Msun/yr, suggesting that the continuous mass loss is superimposed on
the clumpy dust cloud ejection.Comment: 10 pages, 8 figures, accepted for publication in Astronomy and
Astrophysic
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