Group items matching

in title, tags, annotations or url

Valkenburg et al look at the way inhomogeneities in the universe introduce apparent uncertainty in dark energy measurements, if one assumes a homogeneous world model when interpreting distance measurements. They also point out that cosmic variance will lead to bias in w(a). Modeling the structure in the universe is important! My question: is weak lensing immune from these worries, since it involves treatment of all the inhomogeneities?

From N-body simulation, the authors find that concentration-mass relation displays a turnover for group scale dark matter haloes, for the case of WDM particles with masses of the order ~0.25 keV. This may be interpreted as a hint for top-down structure formation on small scales. Is there any reionization mechanism in this scenario?

1)Because the size of the simulated boxes were ten times smaller in previous studies. 2)Weak lensing at scale below ~1arcsec could work. Their results might be helpful for estimating non-linear power spectrum based on a certain halo model.

Cooool. Was Malin there this morning? This could be right up her street, with her flexion stuff! Also, weak lensing at < 1" sounds a bit like strong lensing to me - I'll read the paper in detail and see if there's anything we can already say from our (admittedly modest) SDSS samples. Thanks!

"An expanding fluid leaves its equilibrium state; the energy density decreases and the pressure also decreases. In the absence of bulk viscosity, the fluid relaxes instantaneously and pressure and density are related by the equation of state. Bulk viscosity dampens this behavior by introducing a finite relaxation timescale, hence producing a shift between the equation of state pressure and the true pressure. We note that for a large enough ζ, the effective pressure becomes negative and could mimic a dark energy behavior." In particular, authors Gagnon & Lesgourges predict effective neutrino number around 3.04, w0 around -0.9, and wa around 0.1. Something to shoot for!

Hezaveh et al simulate ALMA cycle 1 (ie 0.16" resolution) observations of Herschel/SPT sub mm lensed galaxies, and claim that the magnification is high enough, and the sources likely to be complex enough, to enable the detection of at least one DM subhalo of mass 10^8 or greater *in every system*

"We extrapolate a dark matter (DM) density in the solar neighborhood of 0+-1 mM_sun pc^-3, and all the current models of a spherical DM halo are excluded at a confidence level higher than 4sigma."

An explanation of the anomalously low measurement of the local dark matter density that we discussed a few weeks ago?

The authors claim a detection of a missing dark satellite in a galaxy-galaxy strong lens system B1938+666. The claimed perturber is located at the brightest region in the lensed image.

Using N-body simulation, the authors showed that velocity-dependent self-interacting dark matter gives the inner circular velocity profiles of the most massive subhalos that are compatible with the data of the brightest Milky Way dSphs.

Axions are ultra-light particles that arise in string theory, and could make up some part of the dark matter in the universe. If so, what are the prospects for detecting their effects with galaxy surveys/CMB/weak lensing with future experiments? Come and ask the authors.

Pontzen and I were sitting there reckoning axions look a lot like hot dark matter - but I guess there must be some key difference at large angular scales to enable Dodi et al to distinguish between massive neutrinos and axions in a Planck+Euclid combo. Pretty cool :-)

Suyu et al combine strong gravitational lensing and stellar kinematics data for a spiral galaxy to measure the mass of both the disk and the dark matter halo. The constraints are very strong - they find an oblate, flattened halo, and get a disk stellar mass with small uncertainty (0.1dex); when they compare this with the stellar mass from the disk colours and K-band magnitude they find that stellar population models with Chabrier IMF work, and Salpeter does not - the opposite to the case of massive elliptical galaxies.

BAO detected at z > 2 using BOSS quasars

"Observations of lensing of the 21-cm background from the dark ages will be capable of detecting M>~10^12 Msun/h mass halos, but will require futuristic experiments to overcome the contaminating sources."

More dipoles!