Group items tagged

First kSZ detection! From ACT and BOSS together.

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

The first detection of a filament.

Very nice. I'm a little surprised that it's the first detection - I swear some people working on this a few years ago. But maybe their detection wasn't significant enough. At least, they didn't get a Nature paper out of it!

Purcell and Zentner on why the "Too Big To Fail" problem might be a storm in a teacup: "We propose that the large variation in subhalo populations among different host halos can explain the dearth of large, dense subhalos orbiting the Milky Way without any making any adjustments to the host halo mass or accounting for baryonic feedback processes."

Rather than being split up into two components of different aged stellar populations with distinct scale heights, a thin and thick disc, the Milky Way seems to have "a continuous and monotonic distribution of disk thicknesses".

That's not what Lucio Meyer said!

The authors find a dipole in the variance of the Hubble flow, which they attribute to the effects of local structure. They find that local structure induces a ~0.5% variation in the distance to last scattering over the sky.

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.

Another analysis of the kSZ signal in the WMAP data finds no evidence for Kashlinsky's claimed anomalous bulk flow.

This set of three papers (the link is to the first one, by Nikhil Padmanabhan) describes a factor of two improvement in the SDSS DR7 BAO distance estimate, just by improving the data analysis. Basically, non-linear gravitational collapse causes the usual BAO feature in the galaxy correlation function to appear smoothed out: it can be partially sharpened back up by using the Zel'dovich approximation to reconstruct the density field given the redshift and position data. The result is an increase in cosmological parameter accuracy roughly equivalent to surveying 3-4 times more sky. Software is vital!

It is interesting to see, in the third paper, how the constraints on H_0 \Omega_m space are robust to different scenarios of curvature and dark energy, and compatible with direct measurements of H_0. But also, as expected, this is effected by what one assumes about the neutrinos.

WMAP confirmation of Planck's SZ-mass relation

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 :-)

There's been quite a bit of discussion about this issue this summer, it came up at the Bologna dark matter meeting as well as the Aosta strong lensing workshop. Basically, in strong lens systems we infer *more* subhalos/satellites than CDM predicts for massive lens galaxies (the satellites cause "millilensing", where the quasar/radio source image fluxes are affected by the small amounts of additional magnification and demagnification). One suggested resolution to this problem is to include all the subhalos along the line of sight - Metcalf (2008) claimed this was the answer, and now Dan Dan Xu has tested this claim using the Millenium Simulation, and various assumptions for the satellite subhalo density profile.

One of the interesting things about this paper, is that they have a modular code, StringFast which they release here: http://www.astro.ubc.ca/people/scott/stringfast.html

Nice to see our (Morganson et al, ref 17) lensing limit on the string tension (from not finding any sets of split pairs of faint blue galaxy images in the HST archive) is still competitive - its equal to the CMB limit they take as their best case scenario :-) Mind you, we could only rule out long straight strings.We could probably put some limit on their wiggliness parametr too I suppose - but its nice that the CMB power doesn't care about wiggliness or anything.

There are a number of `screening' mechanisms that are designed to suppress the effects of modified gravity below cluster scales. What are the characteristic radii at which this switch-off occurs in the different mechanisms?