127 research outputs found
Properties of galaxy dark matter halos from weak lensing
We present the results of a study of weak lensing by galaxies based on 45.5
deg of band imaging data from the Red-Sequence Cluster Survey (RCS).
We present the first weak lensing detection of the flattening of galaxy dark
matter halos. We use a simple model in which the ellipticity of the halo is
times the observed ellipticity of the lens. We find a best fit value of
, suggesting that the dark matter halos are somewhat
rounder than the light distribution. The fact that we detect a significant
flattening implies that the halos are well aligned with the light distribution.
Given the average ellipticity of the lenses, this implies a halo ellipticity of
, in fair agreement with results from
numerical simulations of CDM. This result provides strong support for the
existence of dark matter, as an isotropic lensing signal is excluded with 99.5%
confidence. We also study the average mass profile around the lenses, using a
maximum likelihood analysis. We consider two models for the halo mass profile:
a truncated isothermal sphere (TIS) and an NFW profile. We adopt
observationally motivated scaling relations between the lens luminosity and the
velocity dispersion and the extent of the halo. The best fit NFW model yields a
mass and a scale
radius kpc. This value for the scale radius is
in excellent agreement with predictions from numerical simulations for a halo
of this mass.Comment: Significantly revised version, accepted for publication in ApJ 11
pages, 6 figure
Substructure lensing in galaxy clusters as a constraint on low-mass sterile neutrinos in tensor-vector-scalar theory: The straight arc of Abell 2390
Certain covariant theories of the modified Newtonian dynamics paradigm seem
to require an additional hot dark matter (HDM) component - in the form of
either heavy ordinary neutrinos or more recently light sterile neutrinos (SNs)
with a mass around 11eV - to be relieved of problems ranging from cosmological
scales down to intermediate ones relevant for galaxy clusters. Here we suggest
using gravitational lensing by galaxy clusters to test such a marriage of
neutrino HDM and modified gravity, adopting the framework of
tensor-vector-scalar theory (TeVeS). Unlike conventional cold dark matter
(CDM), such HDM is subject to strong phase-space constraints, which allows one
to check cluster lens models inferred within the modified framework for
consistency. Since the considered HDM particles cannot collapse into
arbitrarily dense clumps and only form structures well above the galactic
scale, systems which indicate the need for dark substructure are of particular
interest. As a first example, we study the cluster lens Abell 2390 and its
impressive straight arc with the help of numerical simulations. Based on our
results, we outline a general and systematic approach to model cluster lenses
in TeVeS which significantly reduces the calculation complexity. We further
consider a simple bimodal lens configuration, capable of producing the straight
arc, to demonstrate our approach. We find that such a model is marginally
consistent with the hypothesis of 11eV SNs. Future work including more detailed
and realistic lens models may further constrain the necessary SN distribution
and help to conclusively assess this point. Cluster lenses could therefore
provide an interesting discriminator between CDM and such modified gravity
scenarios supplemented by SNs or other choices of HDM.Comment: 22 pages, 14 figures, 2 tables; minor changes to match accepted
versio
The relation between stellar mass and weak lensing signal around galaxies: Implications for MOND
We study the amplitude of the weak gravitational lensing signal as a function
of stellar mass around a sample of relatively isolated galaxies. This selection
of lenses simplifies the interpretation of the observations, which consist of
data from the Red- sequence Cluster Survey and the Sloan Digital Sky Survey. We
find that the amplitude of the lensing signal as a function of stellar mass is
well described by a power law with a best fit slope \alpha= 0.74 \pm 0.08. This
result is inconsistent with Modified Newtonian Dynamics, which predicts \alpha
= 0.5 (we find \alpha > 0.5 with 99.7% confidence). As a related test, we
determine the MOND mass-to-light ratio as a function of luminosity. Our results
require dark matter for the most luminous galaxies (L >=10^11 L_sun). We rule
out an extended halo of gas or active neutrinos as a way of reconciling our
findings with MOND. Although we focus on a single alternative gravity model, we
note that our results provide an important test for any alternative theory of
gravity.Comment: 10 pages, 6 figs, accepted by MNRA
A Giant Metrewave Radio Telescope/Chandra view of IRAS 09104+4109: A type 2 QSO in a cooling flow
IRAS 09104+4109 is a rare example of a dust enshrouded type 2 QSO in the
centre of a cool-core galaxy cluster. Previous observations of this z=0.44
system showed that as well as powering the hyper-luminous infrared emission of
the cluster-central galaxy, the QSO is associated with a double-lobed radio
source. However, the steep radio spectral index and misalignment between the
jets and ionised optical emission suggested that the orientation of the QSO had
recently changed. We use a combination of new, multi-band Giant Metrewave Radio
Telescope observations and archival radio data to confirm that the jets are no
longer powered by the QSO, and estimate their age to be 120-160 Myr. This is in
agreement with the ~70-200 Myr age previously estimated for star-formation in
the galaxy. Previously unpublished Very Long Baseline Array data reveal a 200
pc scale double radio source in the galaxy core which is more closely aligned
with the current QSO axis and may represent a more recent period of jet
activity. These results suggest that the realignment of the QSO, the cessation
of jet activity, and the onset of rapid star-formation may have been caused by
a gas-rich galaxy merger. A Chandra X-ray observation confirms the presence of
cavities associated with the radio jets, and we estimate the energy required to
inflate them to be ~7.7x10^60 erg. The mechanical power of the jets is
sufficient to balance radiative cooling in the cluster, provided they are
efficiently coupled to the intra-cluster medium (ICM). We find no evidence of
direct radiative heating and conclude that the QSO either lacks the radiative
luminosity to heat the ICM, or that it requires longer than 100-200 Myr to
significantly impact its environment. [Abridged]Comment: 23 pages, 18 figures and 7 tables. Accepted for publication in MNRA
Assessment of technological options and economical feasibility for cyanophycin biopolymer and high-value amino acid production
Major transitions can be expected within the next few decades aiming at the reduction of pollution and global warming and at energy saving measures. For these purposes, new sustainable biorefinery concepts will be needed that will replace the traditional mineral oil-based synthesis of specialty and bulk chemicals. An important group of these chemicals are those that comprise N-functionalities. Many plant components contained in biomass rest or waste stream fractions contain these N-functionalities in proteins and free amino acids that can be used as starting materials for the synthesis of biopolymers and chemicals. This paper describes the economic and technological feasibility for cyanophycin production by fermentation of the potato waste stream Protamylasseâ„¢ or directly in plants and its subsequent conversion to a number of N-containing bulk chemicals
Perspectieven voor interventies in de bijstand:Experimenten Participatiewet
Item does not contain fulltextWelke handelings- en interventiestrategieën van gemeenten dragen bij aan perspectief op werk en een verbetering van het welbevinden en vertrouwen van mensen in de bijstand? Zes gemeenten - Groningen, Utrecht, Tilburg, Wageningen, Deventer en Nijmegen - hebben de afgelopen jaren (van 1 oktober 2017 tot 31 december 2019) unieke randomised controlled trials uitgevoerd in de bijstand. De volgende (combinatie van) interventies zijn onderzocht: ontheffing van re-integratieverplichtingen, intensivering van begeleiding en vrijlating van bijverdiensten. Er is zowel gekeken naar uitstroom naar werk als naar baanzoekintensiteit, welbevinden, zelfredzaamheid en sociaal vertrouwen. De uitstroom naar werk is bij alle interventies niet lager dan de huidige aanpak, terwijl de uitstroom naar deeltijdwerk in sommige gemeenten hoger is. Vooral intensivering op maat en vrijlating kan uitstroom naar werk (minimaal in deeltijd) vergroten. Voor wat betreft de effecten op baanzoekintensiteit, zelfredzaamheid, welbevinden en vertrouwen, is het beeld diffuus. We vinden kleine en soms ook positieve effecten, vooral voor zelfredzaamheid en vertrouwen, maar het beeld is niet eenduidig. De kleine aantallen deelnemers in de experimenten maken het lastig statistisch significante effecten te vinden.30 p
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