68 research outputs found
Radial density profiles of time-delay lensing galaxies
We present non-parametric radial mass profiles for ten QSO strong lensing
galaxies. Five of the galaxies have profiles close to ,
while the rest are closer to r^{-1}, consistent with an NFW profile. The former
are all relatively isolated early-types and dominated by their stellar light.
The latter --though the modeling code did not know this-- are either in
clusters, or have very high mass-to-light, suggesting dark-matter dominant
lenses (one is a actually pair of merging galaxies). The same models give
H_0^{-1} = 15.2_{-1.7}^{+2.5}\Gyr (H_0 = 64_{-9}^{+8} \legacy), consistent
with a previous determination. When tested on simulated lenses taken from a
cosmological hydrodynamical simulation, our modeling pipeline recovers both H_0
and within estimated uncertainties. Our result is contrary to some
recent claims that lensing time delays imply either a low H_0 or galaxy
profiles much steeper than r^{-2}. We diagnose these claims as resulting from
an invalid modeling approximation: that small deviations from a power-law
profile have a small effect on lensing time-delays. In fact, as we show using
using both perturbation theory and numerical computation from a
galaxy-formation simulation, a first-order perturbation of an isothermal lens
can produce a zeroth-order change in the time delays.Comment: Replaced with final version accepted for publication in ApJ; very
minor changes to text; high resolution figures may be obtained at
justinread.ne
The Hubble flow around the Local Group
We use updated data on distances and velocities of galaxies in the proximity
of the Local Group (LG) in order to establish properties of the local Hubble
flow. For 30 neighbouring galaxies with distances 0.7 < D_LG < 3.0 Mpc, the
Local flow is characterized by the Hubble parameter H_loc = (78+/-2)
km/(s*Mpc), the mean-square peculiar velocity sigma_v = 25 km/s, corrected for
errors of radial velocity measurements (~4 km/s) and distance measurements (~10
km/s), as well as the radius of the zero-velocity surface R_0 = (0.96+/-0.03)
Mpc. The minimum value for sigma_v is achieved when the barycenter of the LG is
located at the distance D_c = (0.55+/-0.05) D_M31 towards M31 corresponding to
the Milky Way-to-M31 mass ratio M_MW / M_M31 ~ 4/5. In the reference frame of
the 30 galaxies at 0.7 - 3.0 Mpc, the LG barycenter has a small peculiar
velocity ~(24+/-4) km/s towards the Sculptor constellation. The derived value
of R_0 corresponds to the total mass M_T(LG) = (1.9+/-0.2) 10^12 M_sun with
Omega_m = 0.24 and a topologically flat universe, a value in good agreement
with the sum of virial mass estimates for the Milky Way and M31.Comment: 14 pages, 6 figures, 1 table. Accepted for publication in MNRA
Non-minimally coupled dark matter: effective pressure and structure formation
We propose a phenomenological model in which a non-minimal coupling between
gravity and dark matter is present in order to address some of the apparent
small scales issues of \lcdm model. When described in a frame in which gravity
dynamics is given by the standard Einstein-Hilbert action, the non-minimal
coupling translates into an effective pressure for the dark matter component.
We consider some phenomenological examples and describe both background and
linear perturbations. We show that the presence of an effective pressure may
lead these scenarios to differ from \lcdm at the scales where the non-minimal
coupling (and therefore the pressure) is active. In particular two effects are
present: a pressure term for the dark matter component that is able to reduce
the growth of structures at galactic scales, possibly reconciling simulations
and observations; an effective interaction term between dark matter and baryons
that could explain observed correlations between the two components of the
cosmic fluid within Tully-Fisher analysis.Comment: 18 pages, 6 figures, references added. Published in JCA
Determining orbits for the Milky Way's dwarfs
We calculate orbits for the Milky Way dwarf galaxies with proper motions, and
compare these to subhalo orbits in a high resolution cosmological simulation.
We use this same simulation to assess how well are able to recover orbits in
the face of measurement errors, a time varying triaxial gravitational
potential, and satellite-satellite interactions. We find that, for present
measurement uncertainties, we are able to recover the apocentre r_a and
pericentre r_p to ~ 40%. However, even with better data the non-sphericity of
the potential and satellite interactions during group infall make the orbital
recovery more challenging. Dynamical friction, satellite mass loss and the mass
evolution of the main halo play a more minor role.
We apply our technique to nine Milky Way dwarfs with observed proper motions.
We show that their mean apocentre is consistent with the most massive subhalos
that form before z=10, lending support to the idea that the Milky Way dwarfs
formed before reionisation.Comment: 2 pages, 1 figure, conference proceeding in "Hunting for the Dark:
The Hidden Side of Galaxy Formation", Malta, 19-23 Oct. 2009, eds. V.P.
Debattista & C.C. Popesc
Cluster Lenses
Clusters of galaxies are the most recently assembled, massive, bound
structures in the Universe. As predicted by General Relativity, given their
masses, clusters strongly deform space-time in their vicinity. Clusters act as
some of the most powerful gravitational lenses in the Universe. Light rays
traversing through clusters from distant sources are hence deflected, and the
resulting images of these distant objects therefore appear distorted and
magnified. Lensing by clusters occurs in two regimes, each with unique
observational signatures. The strong lensing regime is characterized by effects
readily seen by eye, namely, the production of giant arcs, multiple-images, and
arclets. The weak lensing regime is characterized by small deformations in the
shapes of background galaxies only detectable statistically. Cluster lenses
have been exploited successfully to address several important current questions
in cosmology: (i) the study of the lens(es) - understanding cluster mass
distributions and issues pertaining to cluster formation and evolution, as well
as constraining the nature of dark matter; (ii) the study of the lensed objects
- probing the properties of the background lensed galaxy population - which is
statistically at higher redshifts and of lower intrinsic luminosity thus
enabling the probing of galaxy formation at the earliest times right up to the
Dark Ages; and (iii) the study of the geometry of the Universe - as the
strength of lensing depends on the ratios of angular diameter distances between
the lens, source and observer, lens deflections are sensitive to the value of
cosmological parameters and offer a powerful geometric tool to probe Dark
Energy. In this review, we present the basics of cluster lensing and provide a
current status report of the field.Comment: About 120 pages - Published in Open Access at:
http://www.springerlink.com/content/j183018170485723/ . arXiv admin note:
text overlap with arXiv:astro-ph/0504478 and arXiv:1003.3674 by other author
Phase II biomarker trial of a multimarker diagnostic for ovarian cancer
The primary hypothesis to be tested in this study was that the diagnostic performance (as assessed by the area under the receiver operator characteristic curve, AUC) of a multianalyte panel to correctly identify women with ovarian cancer was significantly greater than that for CA-125 alone
CCL18 from ascites promotes ovarian cancer cell migration through proline-rich tyrosine kinase 2 signaling
Cosmology: small scale issues
The abundance of dark matter satellites and subhalos, the existence of
density cusps at the centers of dark matter halos, and problems producing
realistic disk galaxies in simulations are issues that have raised concerns
about the viability of the standard cold dark matter (LambdaCDM) scenario for
galaxy formation. This talk reviews these issues, and considers the
implications for cold vs. various varieties of warm dark matter (WDM). The
current evidence appears to be consistent with standard LambdaCDM, although
improving data may point toward a rather tepid version of LambdaWDM - tepid
since the dark matter cannot be very warm without violating observational
constraints.Comment: 7 pages, 1 figure, to appear in the proceedings of the 8th UCLA Dark
Matter Symposium, Marina del Rey, USA, 20-22 February 200
Leptin receptor signaling is required for high-fat diet-induced atrophic gastritis in mice
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